Monday, December 27, 2010

News from AGU and Elsewhere

From the web traffic reports it seems that many people are still on holiday.  That makes this a good time to catch up on a number of topics that haven't quite fit in anywhere else.

Hayabusa 2 Approved

John Freeman at the Ancient Solar System blog reports the the Hayabusa 2 mission to sample a near Earth asteroid has been approved for funding by the Japanese government.  He reports, that provisional plans for "the next Hayabusa will return samples from a body that has had organic chemistry, interacting with liquid water., in a rocky environment.... those are conditions close to the ones life is thought to have started in, but preserved and uncontaminated by actual life for over 4 billion years. To a guy like me, fascinated by the idea of how chemical systems evolve towards life, that's a mouth watering prospect!"  See Breaking news.....Hayabusa 2 lives!  (I just recently found Freeman's blog, but have been enjoying reading it.  You can see the latest posting on the list of blogs in the right column of this page.)

Tidbits from AGU

My time to pursue future planetary exploration topics at the AGU conference was limited by my real job.  For example, I missed NASA night to discuss a possible project in my research field.  I did pick up some tidbits in addition to the discussion with the proposing PI for the Journey to Enceladus and Titan (JET).  First, I got an explanation of why an Enceladus multiple encounter mission could carry six instruments while a minimal orbiter mission would have to drop both a radar sounder and a narrow angle camera (although it would pick up a magnetometer, which would cost much less than either of the dropped instruments) and still cost almost $200M more.  The orbiter would require both a large flight team be funded for several additional years to manage a large number of encounters with moons as the orbit is pumped down and would require a substantial retropropulsion system.  Seemingly simple mission options -- a longer flight and a larger propulsion system -- can raise costs substantially.

I also learned that most of the 28 Discovery missions proposed for the current competition would not require ASRGs.  Here is the list of missions that I've heard that were proposed that would use ASRGs:  Titan Mare Explorer (TIME lake lander), AVIATR Titan plane, Journey to Enceladus and Titan (JET), Io Volcano Observer (IVO), and a lunar lander (that presumably would explore the permanently shadowed polar craters).  In addition, the RAVEN Venus radar mapper mission has been proposed, but would be solar powered.  NASA has said that the mission with the best science within the cost cap will be the one chosen.  (That leaves just 22 mission proposals that I haven't heard about.)

Ryan Anderson is blogging on the planetary science news from AGU at the Martian Chronicles.  He's a bit behind, with only two days' reports (of five) so far, but I know what it's like to run a blog and try to complete your PhD at the same time.  Check back for his excellent summaries as they appear.

Budget Pressures

A Space News report on NASA night reports that the budget pressures on NASA's planetary science program are creating a difficult financial environment.  The major immediate challenges are additional funds required by the Mars Science Laboratory and rising launcher costs.  On the latter concern, Jim Green, head of the Planetary Division is quoted as saying, “We are surprised at how extensive those cost increases are,” he said. “You start to wonder where we go from here. How do we get out of low-Earth orbit on a regular basis?” See Rising Costs Cloud Future of NASA Planetary Program for the complete article.

One piece of good news from that article was the proposed FY2011 budget (still unapproved) would fund the first steps to renew production of plutonium essential to power missions to the outer solar system.  The article states, “This is really tremendous news,” Green said. “This is very, very, very important to us.”  Unfortunately, NASA's FY11 budget is caught up in politics and NASA, like much of the federal government, is being funded through a continuing resolution.  That resolution does not allow, or fund NASA to begin any new programs including restarting plutonium production.  (The news on the manned spaceflight side is worse, where NASA must continue funding programs that both the President and Congress have decided to cancel.)  See Congress freezes NASA's budget until March.  It's unclear what budget will eventually appear next spring for the remainder of FY2011 (which ends September 30).

Updates on the Akatsuki Venus Mission

It's now been some time since the Akatsuki spacecraft failed to enter orbit around Venus.  For anyone interested in following the investigation, a discussion at the board has been discussing the news as it comes out. See  Akatuki's problems follows problems with Japan's Nozomi Mars (failed) and Haybusa asteroid missions (ultimately successful after near death experiences).  The Japanese space agency JAXA apparently is rethinking its low cost approach to planetary missions and is considering spending more on future missions (possibly with the tradeoff of doing fewer missions).  See: Venus Probe's Problems May Cause Japan to Scale Back.

Other Interesting Articles

NASA's Next Mars Rover to Zap Rocks With Laser provides an overview of the ChemCam instrument for the Mars Science Laboratory.  The proposed SAGE Venus lander would study the chemistry of that world using similar techniques.

Team extends Stardust's fuel mileage for comet mission gives an update on the Stardust mission to re-encounter the Temple 1 comet.

Sunday, December 19, 2010

JET: Journey to Enceladus and Titan

At the just completed AGU conference, I had a chance to talk with the PI, Christophe Sotin from JPL, for a Discovery proposal to continue the exploration of Enceladus and Titan.  The JET proposal would send a small Saturn orbiter to explore those two moons within a constrained ($425M FY10 PI cost), which is substantially less than the estimated costs of the Enceladus missions under consideration by the Decadal Survey (equivalent PI costs of ~>$1.1B FY15 and up depending on option selected).  As you may guess, the JET proposal makes some tough choices to fit within the Discovery program -- there's no magic wand.

The biggest compromise is that JET would fly just two instruments: a mid-infrared camera/thermal imager and a mass spectrometer.  The most minimal of the proposed Enceladus payloads considered by the Decadal Survey would add a medium angle camera, a magnetometer, and a dust instrument.  Other versions of the the Decadal Survey concepts would add up to another nine instruments beyond that minimal list.

Even flying two instruments on JET requires using an already built Rosetta mission mass spectrometer plus other hardware contributed by other nations that wouldn't be counted towards the NASA cost cap.  Without those contributions, and with the mission cost estimates shared by the PI, JET would be unable to fit within a Discovery budget.  Even adding a simple instrument like a magnetometer would push the JET proposal close to the cost cap, and the PI held firm against what he described as many requests to add an instrument.

Even within these limitations, the JET mission would considerably extend the measurements that the Cassini mission has been able to make in key areas.  The JET camera would take advantage of spectral windows in Titan's atmosphere to image the surface at up to 25 m per pixel, 40 times better resolution than the equivalent imager on Cassini and up to 12 times higher resolution than the Cassini radar.  The camera would image 15% of Titan in the nominal one year mission at resolutions of 50 m or better  The cameras would take images in mid-infrared bands, possibly enabling some compositional studies if the surface materials differ in their mid-IR spectrum.  At Enceladus, two of the bands would allow imaging of the distribution of heat sources associated with the tiger stripes and vents at up to 5 m resolution.  The higher resolution at both moons would reveal details not seen by Cassini and allow a better understanding of the processes that may have created those structures.

The mass spectrometer would both extend the range of compounds that could be measured by sampling larger molecules and provide greater resolution within ranges of atomic weights.  Combined, this mass spectrometer would allow detection of a wider range of organic molecules in the upper atmosphere of Titan and (if present) in the jets of Enceladus.

Here are some examples of the specific studies enabled by JET's instruments from Sotin's poster:

  • Search for sedimentary layering in Titan valleys resulting from erosion of plateaus and mountains
  • Map the distribution of solid organics and organics in Titan's small lakes
  • Measure the energy output and lifetime of Enceladus' jets by high resolution mapping
  • Inventory organic and heavy molecules (mass >100 Daltons) in Enceladus' plumes (if present) and Titan's upper atmosphere
  • Determine what molecules (CO, N2, hydrocarbons) make up the mass 28 in Enceladus' plume that has been identified by Cassini

In the nominal one year mission at Saturn, JET would encounter Enceladus several times and encounter both the pro- and anti-Saturn facing sides of Titan on opposite sides of Saturn.  This will allow mapping of both hemispheres of Titan while they are illuminated by the sun.  For comparison, the Jupiter Europa Orbiter would encounter the Galilean moons on just a single hemisphere of each in its flybys, limiting studies to that hemisphere.

Two extended mission options (which would require additional funding as the prime mission nears its end) would be particularly exciting.  JET would be powered by ASRG plutonium power sources, and NASA would like to have a full 14 year test of those power sources.  To fulfill that desire, JET would need to continue for approximately seven years after entering Saturn orbit (although further science observations aren't required for the engineering life test).  During that time, JET could act as a data relay for any in-situ craft that might land or fly above Titan.  This could enhance the data return of a mission such as the Titan Aerial Explorer or AVIATR plane by many times what they could return direct to Earth using their own antennas.  Complimentary to this first option (but not required for it), JET could spend three years pumping down its Saturn orbit using Titan flybys and eventually enter orbit around Titan.  The orbit could be high, 2500 km, well above the atmosphere and would allow continued observations of Titan's surface for years.

Editorial Thoughts:  JET is a good example of the trade offs necessary to conduct Discovery missions in the further reaches of the solar system.  Assuming that the Discovery review panel agrees with the PI's cost estimates, Discovery missions to the Saturn system are possible if you can get friends to contribute some hardware and instruments and stick to minimal payloads.  JET's two instruments would provide valuable science in key areas of study, though.  I would prefer to see one of the more capable Enceladus missions described in the Decadal Survey studies fly over JET -- more instruments are better.  (The mass spectrometer and thermal imagers of those missions should fulfill JET's Titan goals.)  However, if the Survey doesn't recommend one of those missions, then I believe that JET would be an exciting mission to fly.  Better a simple mission than no flight to these worlds in the coming decade.

Thursday, December 16, 2010

Two Articles

Two articles you may want to read:

Rising Costs Cloud Future of NASA Planetary Program from Space News discusses new pressures on NASA's planetary budget from dramatic increases in the costs of launch vehicles and shorter term pressures from a rise in the costs to complete the Mars Science Laboratory and the lack of a new budget for FY11.

Lunar Eclipse, the Moon’s Interior, and the Holy GRAIL provides back ground information on the science goals and methods of the GRAIL mission to map the distribution of mass across and within the moon.

Monday, December 13, 2010

Another Take at Decadal Survey Priorities

Another blogger has started his own prioritization of missions under consideration by the Decadal Survey.  Ray states that he will make his selections based "in the context of our overall exploration and development of space.  A mission that helps NASA's human spaceflight program (whether Vision for Space Exploration, Flexible Path to Mars, or other approach) and/or traditional and new commercial space efforts will have an edge in my evaluation."

As I've said in my posts, the goal in presenting my priority list is to use the exercise to provide a way of examining the choices in the hope that a well reasoned argument helps you decide on your own priorities.  This other blog starts from a different set of priorities and reaches different conclusions than I have.  I encourage you to read his selections.

You can find the blog at Vision Restoration, which appears to primarily focus on manned spaceflight.

Choices Three and Four

This blog entry continues the series to pick the 5 missions that I personally find most compelling for the next decade.  I'm under no illusion that I will persuade anyone (especially anyone who influences government spending).  However, I find a well argued (and I hope these will be) argument to help me form my own opinions.  Please provide your opinions, too, in the comments.

My first choice went to a series of missions to lead to sample return from Mars (Mars Trace Gas Orbiter, the 2018 NASA and ESA rovers, and technology development for eventual sample return) and the second choice to a Venus mission to study the other major terrestrial planet.  My third and fourth missions would go to explore the ice-ocean moons of Jupiter and Saturn.

The last several posts have looked at options for exploring those ice-ocean moons.  The options range from the Flagship Jupiter Europa orbiter, to a Ganymede orbiter from NASA or ESA, to an Enceladus orbiter (with Titan and other moon flybys), to a Titan lake lander, airplane, or balloon.  Writing about these options has been an education for me (and I hope interesting to my readers).  In this final entry in this series on ice-ocean moons, I'll look at one way to prioritize these missions.

My ranking of missions is influenced by a senior scientist who has reminded me in emails that you get what you pay for.  A mission done too cheaply is one that eventually you'll refly to get the information that was really needed to answer the key questions.   With this in mind, here is how I would prioritize the missions:

1) Jupiter Europa Orbiter - A Flagship mission to study Europa and the Jupiter system would return more information, I believe, for the dollar than any other mission choice.  However, this choice comes with risks and collateral costs: Assuming that Mars will be the Decadal Survey's highest priority, will there be sufficient funds to fly this mission?  Will there be sufficient plutonium to power the spacecraft and would any plutonium remain for other missions?  Is the technology mature enough that the risk of major cost overruns is low?  I don't have answers to these questions and lack the information to make informed guesses.  That's why they pay the Decadal Survey the [metaphorical] big bucks.

2) Either an Enceladus orbiter or a Titan lake lander/submersible:  Either mission seeks to explore a constrained set of questions: the cryovolcanic activity and interior of a small moon or the chemistry and properties of an exotic sea.

3) If the Jupiter Europa Orbiter mission doesn't fly, then my third choice would be a Ganymede orbiter that explores that ice-ocean moon in depth and performs several flybys of Callisto.  I also hope -- although the mission concept study did not address this possibility -- that this mission would also make several flybys of Europa to further our knowledge of its interior and surface.

4) Either an airplane or balloon to explore the atmosphere and remotely observe the surface of Titan in detail.  Placing these options last was a hard call.  From the personal arm chair explorer perspective, I would pick either the Titan airplane or balloon as my first choice.  I want to see the surface up close and personal as if I was flying above it.  However, both missions would suffer from severe limitations on the information they could return to Earth without an orbital relay spacecraft.  If either flies, I suspect that we'll eventually refly the mission when a capable orbiter is also sent to Saturn or Titan to enable high bandwidth data return and in-depth coverage of many locations rather than a few.  (However, the Galileo mission with its crippled antenna showed how much science can be done with limited bandwidth -- these would be good missions without the data relay.)

These choices assume that all missions have an equal chance of being selected.  In reality, each faces significant challenges on the path to selection.  Each must fit within an available budget and beat out tough competition to be selected.  If any of these missions surmounts these obstacles, then any would be an excellent choice.

In a perfect world, several of these missions could fly, funded from different NASA and ESA budgets.  NASA might fund a Flagship Jupiter Europa Orbiter and a small Enceladus flyby or orbiter mission  that also acts as a data relay for an ESA Titan balloon mission while a Titan lake lander is funded from NASA's Discovery program.   An ESA Ganymede orbiter would also explore that world.  In our less than perfect real world, I would be happy to see at least one and, if all gods smile, two of these missions fly.  Which one or two will be the result of hard looks at budgets and winning out over tough competition from other excellent missions.

Tuesday, December 7, 2010

This is Hard

We occasionally are reminded just how hard planetary exploration is.  I have just read the news that the Japanese Akatsuki failed to enter Venus orbit.  So many things must go right in a mission.  Many missions have had that moment where they didn't.  Most were able to recover and continue.  A few were not so fortunate.  We'll have to wait to see what can be salvaged for the Akatsuki mission.

You can read about the mission here.

Sunday, December 5, 2010

Titan Lake Lander Concepts - Part 2

Last October, I was fortunate to receive a preview of the Decadal Survey's Titan lake lander mission concept study.  At that time, I published what proved to be one of the most popular entries in this blog, Titan Lake Probe Mission Concepts.

In this entry, I'll provide some additional background on information provided by the report that wasn't in the conference presentation that the earlier entry was based on.  To recap that earlier summary, the study looked at four variations of Titan lake landers that would approximately fit within the FY15 budget for a New Frontier's class mission.  The study looked at various combinations of probes that would float on a Titan lake surface or would descend to the lake bottom, carry out measurements, and resurface to relay the results.  Two of the options provided long-lived plutonium-based power systems on the floater to allow a long period of study from the lake surface.  Another option had a battery powered floater, and the final option had a battery-powered submersible.  (One Flagship-class option combined a long-lived floater and a battery-powered submersible.)  All options would study the atmosphere during the descent to the lake.

  • SGa: Atmospheric evolution (studied during descent through the atmosphere and by analyzing the lake)
  • SGb: Lake and atmospheric interaction to determine how the two exchange material much as the Earth's hydrosphere and atmosphere influence each other (studied by a long-lived floater on the surface of a lake)
  • SGc: Lake chemistry (studied by either a floater or a submersible)
  • SGd: Interior structure (studied by a long-lived submersible on the lake bottom to determine whether or not there is a large ocean deep beneath the surface as there is at Ganymede and Europa)

For me, the most interesting new information in the complete mission concept report was the cost estimates for the different options.  The estimates range from $1.3B (FY15 $s) to $1.5B.  (And I'll quote the verbiage on estimates from the report: "Cost estimates described or summarized in this document were generated as part of a preliminary concept study, are model-based, assume a JPL in-house build, and do not constitute a commitment on the part of JPL or Caltech."  In other words, these are preliminary estimates useful for evaluating concepts.  Cost estimates for an actual mission probably would differ.)

Instrument lists, mission cost estimates, and relative science return from the Planetary Science Decadal Survey JPL Team X Titan Lake Probe Study.  Instrument list for the proposed TiME long-lived lake floater Discovery Mission proposal shown for comparison.  Click on chart for larger version.

I was surprised at the relatively small difference -- ~14% -- in estimated costs between the short-lived floater with just three instruments and long-lived floater with ten instruments.  Or for about the same amount as the long-lived floater, a short-lived submersible could provide slightly greater relative science return.  In the initial studies of the Europa and Titan Flagship missions, costs were initially held to a predetermined figure.  Later, the concept teams were allowed to define the science sweet spot where the cost-benefit curve provided maximum return.  It appears that there may be a similar case for spending another ~15% above the minimum mission to return significantly more science.

The Flagship option is a bit of  ringer in the list of mission concepts.  To be able to provide both a long-lived floater and a very capable submersible, the concept presumes that a Flagship-class orbiter mission bears most of the costs of launch and mission operations.  A stand alone floater/submersible mission presumably would cost significantly more.  However, both the short-live submersible and the long-lived floater as stand alone missions would provide much of the science benefit of the Flagship option within the cost ranges being studied.

For comparison, I included the proposed Discovery-class long-lived floater TiME mission that is competing for launch in the current Discovery selection.  I don't know what the equivalent cost of an FY15 $ Discovery mission is, but in FY10 $s, the PI cost must be kept to $425M, not including launch vehicle and the plutonium ASRG power supply.  I attempted a back-of-the-envelope comparison of the short-lived floater mission concept and the TiME mission.  After accounting for inflation, differences in reserve allowances, and possible launch vehicle differences, I was able to get to within $100-150M of an FY10 Discovery mission.  The TiME mission is being designed to Discovery costs by a very capable team.  Getting to this small of a difference makes me hopeful that the TiME mission can be implemented within a Discovery budget.  If it can, it would implement an in-between option not considered by the concept team: a long-lived floater with a constrained instrument payload.  I believe this would be a dynamite mission, especially at the cost of a Discovery mission.


The Titan Lake Probe Concept Study can be downloaded from 

Monday, November 29, 2010

NASA's Budget Politics

Space Review has two articles on the politics of NASA's budget that you may find interesting:

Year of the Solar System (robotic missions, especially planetary)

NASA's Extended Limbo (overall budget picture in the short term)

Sunday, November 28, 2010

Titan on a Budget

The last full proposal for a mission to Titan was the Titan Saturn System Mission with a cost of ~$3.4B for the orbiter (FY15 $s) and an additional ~$1B for the balloon and lake lander elements. (Source Titan Saturn System Mission Decadal Survey concept report)   At the time of the proposal, reviewers judged that a number of mission elements required further technology development before they would be ready for flight.  NASA and ESA tentatively gave the nod to Europa and Ganymede missions subject to the recommendations of the Decadal Survey (Europa) and a competitive selection process (Ganymede).

The TSSM reviewers emphasized that the science was excellent.  Further study of Titan would yield significant new advances in planetary research.  Recently, several groups of scientists have put forward proposals to study Titan with Discovery (~$425M PI costs) to New Frontiers (~$650M PI costs) (FY10 $s) class missions.  These missions address subsets of the TSSM goals in an effort to keep costs down.  In this post, I'll continue a series that looks at the trade offs proposed to fit missions to the Saturn system within these budgets.  (See New Frontiers to Ganymede and Enceladus and Let's Add an Instrument for previous installments.)

One proposal, the Journey to Enceladus and Titan, would study those two worlds remotely.  Little has been published on this proposal.  The spacecraft presumably would make multiple flybys of those two moons and possibly orbit one or the other.

More information is available on three other proposals:

Each of these missions attempts to bite off a significant piece of Titan Exploration at less than a quarter the cost of the TSSM mission.  TiME and AVIATR been proposed as a Discovery class missions, with the TAE to be proposed as an ESA medium class mission that perhaps has an even tighter budget.  (Different budgeting approaches makes it difficult to exactly compare NASA and ESA mission budgets.  Both agencies also allow collaboration with other nations, which can add to a mission's funding.)  To fit within these budgets, the proposers have reduced mission goals to what appears to be core minimums.

The TSSM balloon platform had goals for studying the structure of Titan's atmosphere, the chemistry of the atmosphere, and remotely studying the surface and subsurface.  Both TAE and AVIATR drop the TSSM's mass spectrometer, which would have focused on detailed measurements of atmospheric chemistry.  In it's place, both have one or more instruments that would partially replace the science that a mass spectrometer could have performed.  However, the organic chemistry of Titan is one of the strongest scientific draws of Titan.  This key area of study would have to be fulfilled by other missions.

Instruments proposed for the Titan Aerial Explorer (TAE), the AVIATR plane, and the Titan Saturn System Mission (TSSM) balloon platform.  Proposed masses for the TSSM instruments shown for comparison; actual masses of instruments for the TAE and AVIATR missions likely would be different.

In the case of TAE, the proposers might have retained the mass spectrometer by dropping the subsurface radar sounder.  (In the TSSM proposal, the mass spectrometer had a mass of 6 kg compared to the radar sounder's 8 kg.)  The TAE mission, however, would focus on understanding the methane cycle (analogous  to the water cycle on Earth), and the proposers evidently decided that detecting subsurface reservoirs of liquid methane was more central to that goal than atmospheric chemistry.   In the case of the AVIATR plane, mass and space constraints would be tight, and the radar sounder would be dropped in addition the mass spectrometer.

The instrument trade offs are less dramatic than the trade off on data rates.  The TSSM balloon platform would have returned 300Gb-1.3Tb of data using the orbiter as a relay.  The expected data return from the AVIATR mission would be ~2GB.  By analogy to previous balloon-only missions to Titan (Titan and Enceladus $1B Mission Feasibility Study), the TAE mission might return a similar amount of data.  By forgoing the cost of a data relay orbiter (perhaps an additional $200M based on costs in the Decadal Survey mission concept reports), these missions would forgo significant quantities of data.  A simple Saturn orbiter returning to Titan every few weeks likely would not have the relay capabilities of the TSSM orbiter by perhaps an order of magnitude or two, but it would dramatically increase the data return.   Since both missions have goals that focus on surface imaging, this is a major reduction in capability compared to what an eventual Flagship mission could do.

Editorial Thoughts:  I favor flying one or two Discovery to New Frontiers-class missions to Titan in the next decade (assuming that the Decadal Survey does not resurrect the TSSM mission, which I consider doubtful given its costs and technology readiness issues).  These missions would likely be incremental.  Eventually, we would need to fly a full Flagship mission, perhaps in the 2020s.

In the next installment, I'll look at the trade offs to enable lower cost Titan lake landers.

Monday, November 22, 2010

Let's Add an Instrument

I think many of readers of this blog read about a proposed mission and imagine how much the mission might be improved with just another instrument or two or another goal or two.  I certainly do.
I learned in my life in a high tech company, though, that "simple" additions often turn out not to be simple and could drive up cost rapidly.  For those of us outside of the planetary mission design world, it's hard for us to understand which additions might truly simple additions and which would be unacceptably complex and costly.

The recently published Decadal Survey mission concept studies offer a peak into some of these tradeoffs.  Several reports explicitly explore several versions of missions with a variety of goals and instrument costs.  In this blog entry, I'll look at examples of the cost tradeoffs for possible missions to Ganymede and Enceladus.  The concept studies don't cover all options I would have liked to see discussed.  For example, how much would it drive up the costs of an Enceladus orbiter to have an instrument or two to study Titan during several flybys?  Or, what would be the design and cost impacts of adding several Europa flybys for a Ganymede orbiter?  Still, these reports offer insights that often aren't available to the public.  They also were all carried out under the same ground rules and using the same FY15 dollar costs, making comparisons between them reasonable.

The following table list a number of Ganymede and Enceladus mission options.  The Ganymede missions differ both in the number of instruments and in the length of time in Ganymede orbit.  The Enceladus missions would all orbit that moon for 12 months (except for a multiple flyby mission), but differ in the number of instruments.  Several of the Enceladus options were also ranked for relative science value.

Option numbers are from the reports listed at the end of this blog entry.  Click on image for a larger version.

The Ganymede mission options range from $1.3B to $1.7B.  Looking at the charts in the table, most of the difference in costs appears to be driven by costs associated with building and operating additional instruments rather than the longer time in orbit.   This is dramatically shown by adding up the costs to build and test the instruments suites for the Ganymede orbiter.  They are $62M, $96M, and $190M for the three options (reserves do not appear to be included in these numbers, so the real costs probably could be higher by ~50%).  Additional instruments also require additional operational costs and additional teams of scientists to plan instrument usage and analyze the results.  (Instrument costs given do not have reserves included; total mission costs do.)

The Enceladus orbiter missions range from $1.6B to $2.7B.  The costs of individual items wasn't detailed in charts, but by examing the graph showing relative cost elements, it appears that this difference again is largely driven by the costs of building and operating different instrument suites.

Costs of individual instruments vary considerably.  A magnetometer is only a few million dollars.  A mass spectrometer, radio and plasma wave package, or a subsurface radar isseveral tens of millions of dollars.

Even for a specific instrument type, costs can vary considerably.  The simpler Ganymede mass spectrometer apparently would cost ~$25M to build while the more sophisticated Enceladus mass spectrometer would cost ~$57M.  (Note: For some items, I'm making educated guesses to determine which instrument costs in the reports go with which instruments.)

Neither the Ganymede nor Enceladus mission reports spell out the cost of a narrow angle camera (NAC), which would be useful for exploring their target worlds and really useful for observing the rest of the Jupiter or Saturn systems.  However, it appears that instrument #10 in the Ganymede report at ~$13M is the NAC and the Io observer NAC is listed at ~$17M.  These are simple cameras compared to those proposed for the Titan and Europa flagship missions that proposed NACs costing ~$54M and ~$43M respectively.  A lot of capability is given up to keep the costs of these Decadal Survey concept missions below the Flagship mission costs.

Editorial Thoughts: My favorite instrument to add to an Enceladus mission would be a 2-micron imager that would use a spectral window in the atmosphere for high resolution imaging of Titan.  The specific costs of that instrument wasn't spelled out in the reports.  However, assuming that its cost might be similar to that of a NAC (similar optical and mechanical design but a different sensor, I think), then the final cost to the mission might be $35-40M with design, fabrication, testing, operation, analysis.

I would hate to see a mission go to Enceladus and not carry this instrument.  However, it might be that adding this instrument would  bust the budget and jeopardize approval of the mission.  In my experience, engineers are very creative at exploring all the options.  Then they become hard nosed about what has to be left out to fit within the financial, manpower, expertise, and weight restrictions.  If this instrument can be flown within those restrictions, I expect that it will be.  In the meantime, I can imagine what such a mission might do.

Source reports:

Reports can be downloaded from:

Ganymede Orbiter Concept Study
Enceladus Flyby & Sample Return Concept Studies*
Enceladus Orbiter Concept Study

*Despite its title, this study examined a range of missions from multiple flybies to several flavors of orbiters to samples return and landers.

Friday, November 19, 2010

Change to comments

Lately, spam comments have out numbered real comments.  To try to control this, I have enabled moderation on comments.  All legitimate comments will be posted.  But if you want to sell something (especially viagra) or want a link to a blog with no relevance to space exploration or science, your comment won't be posted.

Sorry for the change.

Titan Aerial Explorer Proposal

Jonathan Lunine at the University of Arizona has just posted his intent to develop a proposal for a Titan Aerial Explorer.  From his announcement, "The mission to be proposed includes a balloon with the capability for ground-penetrating radar, radio science and multi-spectral imaging and spectroscopy, aerosol analyses, and possibly other instruments. The goal is to explore the processes that are at work on the surface on and near-surface of Titan with sufficient resolution and wavelength capability to quantify Titan’s methane hydrologic cycle."  The proposal would be submitted for the European Space Agency's next Medium class science mission for launch around 2022.

Editorial Thoughts: I would like to see one or more Titan in-situ missions fly in the 2020's.  Titan's thick atmosphere and low gravity makes it an easy world (once you spend many years flying there) to land on, float above, or fly around.  Lunine's mission potentially would face several challenges such as power (ESA currently does not have plutonium power sources, which as I understand it would be necessary both for power and to heat the gases for the balloon) and bringing the balloon technology up to flight readiness (the Titan Flagship mission's balloon reportedly was judged to require further technology development before flight).  However, Dr. Lunine has a solid resume, so he must have ideas on how to address these problems.

Wednesday, November 17, 2010

New Frontiers to Ganymede and Enceladus

In my previous post, I listed missions to explore the diversity of icy ocean moons such as Europa, Ganymede, Titan, and Enceladus as my third and fourth picks for my most compelling missions.  This post begins a series that looks at approximately New Frontiers-class missions to these worlds based on mission concepts examined by the Decadal Survey.

From my examination of the mission concept studies from the Decadal Survey, it appears that there were two classes of missions examined.  The first were flagship class missions costing over ~$2B.  These were the three missions composing a Mars sample return, the Europa Jupiter System Mission, and the Titan Saturn System Mission. (There were also some Flagship-scale options in other reports.)  In addition, the Survey commissioned a number of concept studies for missions that might fit within the New Frontiers class of missions (~$650M for principle investigator costs; ~$1.2B for NASA's fully burdened costs).  All costs in the studies were for FY15 costs, when the burdened costs of a New Frontiers mission (assuming 3% inflation per year) would be ~$750M for the PI costs and ~$1.4B for the fully burdened costs*.  (The Survey reportedly will recommend specific Flagship and New Frontiers-class missions; it will not recommend specific missions for the lower cost Discovery missions.)

Several New Frontiers class missions were studied for the icy moons of Jupiter and Saturn:
  • Several incremental flavors of a Ganymede orbiter that would also conduct several flybys of Callisto
  • A number of variations of Enceladus missions that included flybys, orbiters, landers, and flyby sample returns along with flybys of other moons of Saturn
  • Four variations of probes to float on or descend into one of the polar lakes of Titan

Option numbers are taken from the reports listed below.  Missions in the Enceladus Flyby & Sample Return Concept Studies report were ranked by the relative value of the science they would be expected to return.  Click on table for a larger image.

In this post, I'll begin looking at the orbiters of Ganymede and Enceladus.  Unfortunately, the concepts studies for Enceladus landers and flyby sample returns determined that these missions are premature.  For landers, we don't understand the nature of the surface (fluffy snow or rock hard ice? gentle plains or steep slopes?) and for sample returns there are uncertainties associated with the design of the sampling mechanism (a derivative of the Stardust aerogel collector) requiring "a significant technology development" as would issues of ensuring sterilization of the return probe for planetary protection.  The studies concluded that for Enceladus, an orbiter represents the most attractive target for the next mission (after Cassini) to this moon.

In several ways, a mission to Ganymede and Enceladus have similar requirements.  Both must travel to and operate in the outer solar system.  Both would study icy ocean worlds, and hence their list of desired instruments are similar.  However, there are also important differences.  A Ganymede orbiter is close enough to the sun that solar panels could be used.  An Enceladus orbiter is far enough from the sun that the safe bet is on plutonium-powered spacecraft (ASRG's).  An Enceladus orbiter would study a tiny moon so close to its dominant planet that a polar orbit would be unstable.  Instead, the southern polar geysers and terrain would have to be studied during a series of flybys prior to orbit insertion.  The final orbit could not exceed 60 degrees latitude to ensure a stable orbit.

While missions with costs in the $1.3-1.6B range are possible for both moons, the capabilities of the instruments suites would differ considerably.  For $1.6B, the Ganymede orbiter would carry the full suite of desired instruments.  For the same cost, the Enceladus orbiter would have to forgo desirable instruments such as a narrow angle camera, an imaging spectrometer to study the composition of surface materials, and an ice penetrating radar to directly detect the presence of a subsurface ocean.  These instruments could be added to an Enceladus orbiter, but only by increasing costs to almost twice that of a New Frontiers-class mission.

Either mission, however, would substantially expand on the knowledge of their target moons.  A Ganymede orbiter has been a priority mission for NASA for several years and is currently in contention as an ESA mission.  The discovery of active geysers at Enceladus have made it a priority since it provides our only near term option to directly sample the composition of an icy moon's ocean in the next two decades.  In lieu of a Flagship mission to study the moons of either Jupiter or Saturn, these seem to be worthy missions.

In my next post, I'll look at the impact of instrument costs on options for exploring these two moons.
*Note: The budgets for New Frontiers missions are something of a mystery to me.  The PI budget is stated in the Announcements of Opportunity, and the fully burdened cost can be derived from NASA's New Frontiers budget line and include some obvious big ticket items like launchers.  The Decadal Survey studies seem to be giving cost estimates somewhere in between these two numbers.  As near as I can determine, the budget for a New Frontiers mission using the items included for FY15 would be between $1.0B and $1.1B.
Source reports:

Reports can be downloaded from:

Ganymede Orbiter Concept Study
Enceladus Flyby & Sample Return Concept Studies*
Enceladus Orbiter Concept Study

*Despite its title, this study examined a range of missions from multiple flybies to several flavors of orbiters to samples return and landers.

Friday, November 12, 2010

Compelling Missions 3 & 4: Icy Ocean Worlds

This blog entry continues the series to pick the 5 missions that I personally find most compelling for the next decade.  I'm under no illusion that I will persuade anyone (especially anyone who influences government spending).  However, I find a well argued (and I hope these will be) argument to help me form my own opinions.  Please provide your opinions, too, in the comments.  You can find the earlier installments of this series at these links:  Mars Caching Rover and Venus Climate Flagship.

Concept for a Ganymede Orbiter

Over the last fifteen years, we've come to learn that icy worlds with internal oceans appear to be common in the solar system.  At scientific conferences, sessions are devoted both to individual worlds such as Enceladus and Titan where we have newly arriving data and to comparing these worlds with the moons of Jupiter, Triton, and Pluto .  The AGU conference this December will have sessions on "The Potential for Water-Organics Interactions on Titan," "Eyes on Enceladus," "The Amazing Nature, Origin, and Evolution of Outer Planet Satellites", and "Icy Ocean Worlds" to name just a few.  (As a side note, I appreciate the AGU scheduling these sessions this year so that they largely don't overlap with the sessions on my field of study.)  For the first two picks in my list of compelling missions, I chose missions that would advance the comparison of terrestrial worlds with atmospheres.  For my third and fourth picks, I my choice is for two missions to advance the comparison of icy ocean moons.

The Decadal Survey's list of missions it considered (it's made its selections, but we won't learn of them until next March) is rich with missions to pick from.  There are the Flagship missions to Europa and the Jovian system and to Titan and Enceladus at the high end with price tags of $2.7B and $3.2B, respectively.  (All costs are from the just released mission studies and were stated in the reports in FY15 dollars.  The two Flagship missions have been studied in depth, and their costs probably have greater fidelity than the other costs listed, which represent early assessment costs developed as part of the mission concept studies.)  At the low end, there is an option for an Enceladus multiple flyby mission for $1.4B.  In between are Enceladus orbiters ($1.6B - $2.4B), a Ganymede orbiter ($1.35B - $1.7B), and Titan lake landers ($1.3B - $1.5B).  My choices for the third and fourth missions on my list would be one to explore the icy moons of Jupiter and one to explore Titan and Enceladus.

Ideally, NASA would fly the Europa Jupiter System Flagship mission along with a capable Enceladus orbiter (that would also do multiple Titan flybys) and a Titan lake lander.  However, this combination would cost almost $6B.  Combine that with a $3-4B investment in Mars missions (which I predict will be the Decadal Survey's top priority) and a couple of Discovery missions, and that's pretty much the entire budget for missions next decade.  I also think that the Flagship missions may face have a couple of programmatic challenges.  First, NASA's last two choices for Flagship-scale missions, the Mars Science Laboratory and the James Webb Space Telescope, both experienced large cost overruns.  The latter mission is facing another large cost overrun, and that may make the Survey and NASA skittish about recommending another large mission.  The second challenge is that NASA apparently does not have the plutonium 238 on hand to fly a Flagship mission.  They apparently will receive sufficient Pu-238 if Russia resumes sales or if Congress funds new production.  Will NASA want to bet a large chunk of its planetary mission budget on these two ifs?

I hope that these issues can be overcome.  If they can't, my next three posts will look at the lower cost mission alternatives presented in the Decadal Survey's studies for studying Jupiter and Saturn's icy ocean worlds.

Tuesday, November 9, 2010

Decadal Survey: The Candy Store Posted

As part of its analysis, the Decadal Survey commissioned 25 mission studies to define potential missions it would select its final list from.  The full list of mission studies, plus three technology studies to enable missions in the 2020s and beyond, have been posted (  As one poster at Unmanned Spaceflight put it, this is a candy store for those interested in future planetary missions.

In future entries, I'll be summarizing the reports (a typical length is around 30 pages) and where appropriate comparing them to each other and to past missions and other mission concepts.  Generally, each report will get its own entry, but in the case of similar mission types, I'll compare the mission concepts in a single entry.  I'll also combine the summaries with my continued list of the five missions that I find most compelling for the coming decade.

To kick off the process, I'll post a table comparing the missions for cost and mission flight times (be sure to read the notes on the table for important caveats).  In going through this list, I was happy to see that a large number of missions are reasonably close to the fully burdened New Frontiers mission cost of ~$1,350M inflated at 3% per year for Fiscal Year 2015 costs.  Another group of missions could probably fly at a New Frontiers mission and a half budget.  Assuming that the Max-C rover, the Mars Trace Gas Orbiter, and three Discovery missions fly in the next decade, this would allow two to four of the sub-$2B missions on this list to fly.

Click on the list for a larger version.

Notes on the table:

  • A number of the reports analyze several options for a mission target.  In this case, I picked either the lowest cost or a typical cost and did the same with the mission timeline.
  • The mission dates can be somewhat arbitrary.  For many missions, launch windows occur every year to every few years.  For the purposes of the studies, a given time frame was chosen.  Use the dates to get a feeling for how long the flight to the target would take and how long science would be gathered at the target.  For missions that would involve multiple targets or that require entry into orbit around Jupiter or Saturn, the arrival date is the date at the first target or orbit insertion around the major planet.
  • The cost estimates were prepared by the mission assessment teams.  These are not the rigorous cost estimates that will be prepared by an independent team for a subset of  these missions that the Survey considered most likely to be recommended.  The costs, therefore, should be considered approximations.  A difference of a couple of hundred million dollars may not be significant, while a difference of a billion dollars almost certainly is.  In addition, early cost estimates are often low, and many of these estimates may also be low.  Where the various mission options came with widely different costs, I showed the range of estimates.
The next blog entry will describe the two mission concepts that together would be for me be the third most compelling mission for the coming decade.

Wednesday, November 3, 2010

Budget Cuts and Future Planetary Exploration

Anyone not living in a cave has heard that the elections in the United States have resulted in a more conservative Congress promising to reduce the federal deficit.  Budget tightening in the United States is hardly unique.  As the Wall Street Journal reported last summer, ESA may be facing its own budget problems, or at the least not growing its programs as fast as some would hope.  (Subsequent news from Europe seems to suggest no ESA budget cuts in the short term.)

This blog is purposefully not political. If you want to argue politics, there are many good blogs and discussion boards for that.  I will not discuss whether or not I think the federal budget should be cut.  Rather, I want to explore the implications of some ideas that have been put out by newly ascendant Republican leadership.

One idea is to return the level of federal spending in 2011 to the level in 2008.  The other is impose a freeze on discretionary spending (essentially anything other than interest on the federal debt and entitlements; military and security might or might not be included; without the military and security spending, discretionary spending is roughly 15% of the budget) for an unspecified number of years.

As I have done for previous analyses of budgets for future planetary missions, I have added up the budget amounts for future mission development and current mission operations.  (This leaves out funds for scientific research and R&D.)  I have then multiplied the current year budget by ten as an estimate of funding available for the next decade.  This assumes that future budget increases match the inflation rate, and that funding for operation of missions that have yet to launch will be similar to funding for missions currently in flight.  So, this is a fairly simplistic analysis that makes use of easily obtained public budget documents.

Here are some key budget figures:

FY08 ~$949M (approved) or ~$9.5 over a decade
FY10 ~$1.1B (approved) or ~$11.0B over a decade
FY11 ~1.16 (proposed) or ~$11.6B over a decade

The proposed FY11 budget has not been approved.  The politics get murky at this point, but based on precedence, NASA's planetary program is likely to be funded in FY11 (Oct. 2010 to Sept. 2011) at about the FY10 rate.  The difference over a decade would almost fund an additional Discovery mission at the fully burdened rate (or ~$800M which includes costs above the $450M available to the principle investigator).

If the budget is reduced to FY08 levels, then NASA's looses ~$1.5B over a decade compared to the FY10 budget level, or a bit more than the burdened cost of a New Frontiers mission.

If NASA's budget for future missions was frozen for a decade, NASA would lose about the equivalent funding of a New Frontiers program whether the initial level is at FY08 or FY10 budget levels.  If the starting budget was the FY08 level and then frozen, then the result would be the loss of funding equivalent to approximately two New Frontiers missions compared to the FY10 budget level increased for inflation.

Editorial thoughts: In one important sense, this analysis is extremely simplistic.  NASA has two major programs, the manned program and the unmanned science program of which planetary exploration is a part.  (And even this is simplistic since it leaves out aeronautical research.)  NASA's manned spaceflight program is at a crossroads.  Meeting either the ambitious return to the moon goals of President Bush or the go to Mars via near Earth asteroids goals of President Obama requires high levels of funding.  It is my observation that the manned side of NASA gets more political attention than the science side.  It is quite possible that any budget cuts would not be applied equally to the two sides, and the net impact on future planetary missions may be greater than the quick analysis above suggests.

Planetary exploration is discretionary spending.  Nations budget for it after they fund what they see as the core needs of their people.  If the political process in the United States or elsewhere determines that spending levels must be reduced, I would not argue for special dispensation for planetary exploration.  Rather, I hope that the program that will be recommended by the Decadal Survey will be flexible enough to remain viable if spending cuts do occur.

Friday, October 29, 2010

Compelling Missions - Part 2

At the moment, news for future planetary missions is scarce as the U.S. waits for the results of the Decadal Survey.  (Other nations continue their own planning cycles, but news is scarce there, too.)  The Decadal Survey has published a list of 25 missions it is considering for the next decade.  I thought that I would take the next few blog entries to pick the five missions from that list that I find most compelling.  I'm under no illusion that I will persuade anyone (especially anyone who influences government spending).  However, I find a well argued (and I hope these will be) argument to help me form my own opinions.  Please provide your opinions, too, in the comments.  You can find the first installment in this series at Thoughts on the Most Compelling Proposed Planetary Mission.


We live on a terrestrial planet, and one on which we are undertaking a grand experiment to see what happens when we dramatically increase the proportion of greenhouse gases in the atmosphere.  As a result, I think that furthering our understanding of Venus as a terrestrial planet and a greenhouse atmosphere carried to extremes is a compelling target for exploration in the next decade, and is for me, the target for the second most compelling mission for the coming decade.

The complete presentation by VEXAG on goals and objectives for exploring Venus can be found at

Venus has been essentially ignored by NASA spacecraft for over 15 years (brief studies by spacecraft en route to other worlds have been the only exceptions).  The Europeans and Japanese, however, have sent orbiters to this world, and the Russians are planning a mission in the coming decade that may include a lander, orbiter, and balloon.  I believe that the U.S. should join the party in the coming decade.

The VEXAG analysis group chartered by NASA has put together an ambitious plan for a highly sophisticated Venus Flagship mission.  This mission would include a very capable orbiter, two balloon platforms, and two atmospheric probes/landers that would survive for many hours on the surface for detailed soil analysis.  Unfortunately, this mission would cost over $3B and requires technology development in several areas.  As a result, it is proposed as a mission for the 2020s and not the coming decade.

However, VEXAG members have also proposed a less capable mission, the Venus Climate Flagship, as a possible mission for this coming decade.  In the types of mission elements -- an orbiter, a single balloon, and a single lander -- it seems much like the full Venus Flagship proposal with the duplicate platforms removed.  However, the Climate Flagship would focus on using existing technology, resulting in less capable measurements but doing them as much as a decade sooner.  For example, the full Flagship mission would have brought samples into the landers for analyses that would take several hours to complete.  This would result in expensive sample handling mechanisms, an air lock, and the requirement to survive on the surface for almost a full Earth day.  The Climate Flagship proposal, on the other hand, would  use lasers to illuminate or melt the surface materials with the results analyzed via spectrometry through a porthole in less than an hour.  Similarly, the full Flagship proposal would have carried a radar on the orbiter that would have mapped the surface with resolutions as fine 5 m.  The Climate Flagship would map the surface at "10X" better resolution than the Magellan mission.  This would result in mapping resolutions of several 10s of meters.  (The exact figure depends on whether average or best Magellan resolution would be the baseline, and it's likely that the Climate Flagship proposal hasn't been studied in sufficient detail that the final resolution is known.)

There isn't a firm public estimate for the cost of the Climate Flagship.  A swag in the presentation describing the mission suggests a figure of ~$1.6B, but notes that your "mileage may vary."   However, with international cooperation, the NASA contribution might be substantially less.  Several nations are interested in missions to Venus.  Russia, for example, wants to fly its Venera-D lander this decade.  The Europeans have expressed interest in flying a balloon platform.  NASA might contribute an orbiter for data relay from landers and balloons, to remap portions of the surface with radar at higher resolutions, and carry cameras and imaging spectrometers to extend the atmospheric and surface studies of the European Venus Express and Japanese Akatsuki orbiters.  The RAVEN radar mission has been proposed for the current Discovery mission selection.  NASA also might contribute a lander if the SAGE mission is selected as the next New Frontiers mission.

The Decadal Survey has three flavors of landers and a "climate mission" (no details on what that might include) on its list of candidate missions it is considering.  If any of these missions are recommended, or if the SAGE lander is selected, NASA could participate a series of missions that would perform the science of the Climate Flagship.  (I think it is unlikely that the Decadal Survey would recommend the entire Climate Flagship mission, which as its cost become better understood, might be substantially more expensive than the swag quoted above.)  The Survey could recommend a single element -- the orbiter or a lander -- or a combination such as an orbiter and atmospheric probe.  It could also recommend no NASA-led mission, and instead recommend participation in the missions of others.  The Russians, Europeans, and Japanese could supply missions that meet the goals of the Climate Flagship.  China and India are also on the verge of being able to send probes to other planets and might also participate.

Except for the recent European and Japanese orbiters, our knowledge of Venus is based on missions with decades old technology.  The science questions motivating a return to Venus seem compelling to me.  I believe that NASA should make continued exploration -- preferably as part of an international effort -- a priority for the coming decade.

Thursday, October 28, 2010

Interesting Articles

Here are links to several interesting articles:

India Plans Moon Mission Sequel, Like China ( - India's plans for a joint mission with Russia for an lunar orbiter, lander, and rover to launch in 2013.

Meteorite-Based Debate Over Martian Life Is Far from Over ( - The debate over whether meteorite ALJ84001 from Mars has signs of past Martian life continues.  This suggests how hard it will be to detect signs of life even in returned samples.  (While I've come to favor a Martian sample return mission, it's not because I think it will settle the question of past life on Mars, but for what it will tell us about the earliest history of processes on terrestrial worlds.)

Two articles focus on how the James Webb Space Telescope came to dominate NASA's astronomy program and what the effects will be.  This is a cautionary tale about what happens when Decadal Surveys prioritize a mission the ends up costing far more than expected.  The lesson was learned -- both the recently completed Astronomy and the in-progress Planetary Decadal Surveys put a strong focus on attempting to cost out missions in more detail than was done for the previous round of Surveys.

The golden age (is ending) (
Space science: The telescope that ate astronomy (

The following essay discusses one of the casualties resulting from the JWST's cost growth

SIM and the “ready, aim, aim” syndrome (

Tomorrow I'll post my personal choice for the second most compelling planetary mission under consideration.

Wednesday, October 20, 2010

Thoughts on the Most Compelling Proposed Planetary Mission

At the moment, news for future planetary missions is scarce as the U.S. waits for the results of the Decadal Survey.  (Other nations continue their own planning cycles, but news is scarce there, too.)  The Decadal Survey has published a list of 25 missions it is considering for the next decade.  I thought that I would take the next few blog entries to pick the five missions from that list that I find most compelling.  I'm under no illusion that I will persuade anyone (especially anyone who influences government spending).  However, I find a well argued (and I hope these will be) argument to help me form my own opinions.  Please provide your opinions, too, in the comments.

There are many ways to decide on what would be a compelling mission.  One would be on the vicarious thrill of exploration.  On this basis, I would favor missions such as the Venus SAGE lander, the AVIATR Titan plane, and the Argo Neptune-Triton-KBO mission.  (All would also provide great science.)  However, nations chose to fund these expensive mission primarily on their scientific return.  So I have taken that as my criteria.  Which set of missions would most fundamentally advance our understanding of the solar system?

A recent paper in the scientific journal Astrobiology, New Priorities in the Robotic Exploration of Mars: The Case for In Situ Search for Extant Life (subscription or purchase required), has got me rethinking the priority for a Mars sample return.  Mars has been the major focus of NASA's planetary program for the last 15 years.  With the recent cooperative agreement, it has also become a major focus for ESA.  Review board after review board for the last 30 years have concluded that the highest priority for Mars exploration is to return samples to Earth (see, for example, the 2003 Decadal Survey report).  The mission has been recommended for flight at the earliest opportunity, but NASA's budgets have never permitted the mission to begin development.

There have been scientists who recommend a slower approach.  Mars is highly diverse and we have explored its surface in only six places, and landing safety concerns limited our choice of places to explore.  Samples of past or present life are likely to be hard to find.  Instead of rushing to a sample return, these scientists argue, fly a number of landed missions, probably most of them rovers, to find the best place to return a sample.  This, in a nutshell, is the argument the authors make in the New Priorities in the Robotic Exploration of Mars paper.

At least based on presentations at meetings and the roadmap adopted by the Mars science community (principally through MEPAG), this appears to be a minority view.  Most of the community apparently has decided that we know enough about Mars to pick a very interesting site.  The samples returned from that site when analyzed with Earth-based instruments (most of which would be larger than the rover collecting the sample and some of which would be larger than the launch vehicle -- size and power counts for sophisticated study at the scale of individual rock grains) would greatly deepen our understanding of the early history of terrestrial planets.  Only Mars preserves that early history on a body that had both a significant atmosphere and liquid water.

Long term readers of this blog know that I am a skeptic on Mars sample return.  Not because I don't think the science is absolutely compelling -- it is -- but rather because I doubt that Congress will fund a $6B+ program for robotic exploration.  I've come to reevaluate that position, though.  Congress has funded the James Webb Space Telescope to the tune of over $5B  (but at the cost of the astronomy program foregoing many other missions).  Also, events seem to make this the time to move forward:

  • Fifteen years of missions by NASA and ESA to Mars have revolutionized our understanding of the Red Planet.  We may not be able to pick THE most compelling site on Mars, but we can pick A (and actually several) very compelling sites.
  • JPL has developed for the Mars Science Laboratory the entry, landing, and roving technology essential to carry out this type of mission.  (Of course, it also hasn't been flight tested...)  If NASA does not continue a program to use this technology, the key engineers will move on to other projects.  As it is, waiting seven years between the launch of MSL and the proposed Max-C sample caching rover is stretching the period over which teams can be kept together.
  • The opportunity to fly the caching rover with the ExoMars in 2018 rover is unique.  ExoMars can allow samples to be collected from up to two meters below the surface while Max-C collects samples at the surface.  This could greatly enhance the value of the returned samples.
  • ESA has agreed to partner with NASA on a sample return (exact roles and funding levels to be determined).  This offers an opportunity to share costs that may not come again.

So, I have come to decide that moving towards a Mars sample return with the 2018 Max-C rover/ExoMars mission is the most compelling mission to me on the list of missions under consideration by the Decadal Survey.  This mission depends on an orbiter being launched by 2016 to act as a communications relay; the Mars Trace Gas Orbiter is currently slotted for this role.  Together, the two missions would cost NASA probably $3B, perhaps as much as $4B with inflation and cost overruns (ESA would also make a substantial contribution for the orbiter and the ExoMars rover).  This would represent a quarter to a third the expected NASA planetary mission funding for the next decade.

There is the risk that the current estimates for cost will turn out to be wildly optimistic and the true costs will eat up a large portion of the planetary science budget.  After approval, politicians could cancel the mission to save money.  It happened with the Venus Orbiting Imaging Radar mission in 1981 (the eventual Magellan mission was less capable), the Comet Rendezvous and Asteroid Flyby mission (ESA's Rosetta eventually filled this slot), and almost happened to the Galileo mission.

Given these risks, I favor a go slow approach.  Fly the Max-C and ExoMars rover in 2018.  Wait until we know there is a compelling set of samples waiting on the surface for pickup before committing to the next mission in the sequence (see this blog entry for a description of the three missions needed to return a sample to Earth).  If the 2018 mission fails or is skunked, launch another rover to find and cache a compelling set of samples.  Under this approach, the earliest a sample could be returned would probably be 2028 (instead of the current strawman for 2026).

Going with a sample return mission isn't without its risks, both technically and politically.  However, the return seems to me to be greater than any other mission on the list.

I hope to hear your opinion whether or not you agree or disagree.

Monday, October 11, 2010

Titan Lake Probe Mission Concepts

Note: We appear to be in a quiet time for planning future planetary missions.  In the U.S., we are awaiting the recommendations of the Decadal Survey to be released next March.  In Europe, we are waiting for the decision for the next large mission selection between a Jupiter Ganymede orbiter and two astronomy missions.  I will post as information and ideas become available, but I expect that posts may occur every week or so for awhile.

One of the most exciting concepts for a future planetary mission has been a mission to land on and sample one of the large lakes of Titan.  The lakes are likely to be chemical repositories that contained important clues to Titan's "are repositories, through dissolution of airborne solids, of organics scattered globally on Titan, as well as noble gases, which are a key clue to Titan’s origin and evolution." Sampling the lakes will help answer important questions about Titan:

Cassini-Huygens leaves us with many questions that require a future mission to answer.  These include whether methane is out-gassing from the interior or ice crust today, whether the lakes are fed primarily by rain or underground methane-ethane aquifers (more properly, “alkanofers”), how often heavy methane rains come to the equatorial region, whether Titan’s surface supported vaster seas of methane in the past, and whether complex self organizing chemical systems have come and gone in the water volcanism, or even exist in exotic form today in the high latitude lakes." [NASA/ESA JOINT SUMMARY TITAN SATURN SYSTEM MISSION, January 2009]

As part of its analysis of missions to recommend in the coming decade, the Decadal Survey commissioned a study of possible Titan lake probe missions.  The results of the analysis was presented at a recent conference, and the studies' lead, John Elliott of JPL was kind enough to send me a copy of the presentation and answer some questions.

The study looked at addressing four key scientific questions using variations of two variations of probes that would sample one of Titan's large northern lakes.  The scientific questions were:

  • SGa: Atmospheric evolution (studied during descent through the atmosphere and by analyzing the lake)
  • SGb: Lake and atmospheric interaction to determine how the two exchange material much as the Earth's hydrosphere and atmsphere influence each other (studied by a long-lived floater on the surface of a lake)
  • SGc: Lake chemistry (studied by either a floater or a submersible)
  • SGd: Interior structure (studied by a long-lived submersible on the lake bottom to determine whether or not there is a large ocean deep beneath the surface as there is at Ganymede and Europa)

The study looked at a Flagship class (multiple billions of dollars) and three New Frontiers class (~$650M) missions.  Only the Flagship class mission would be able to address all questions.  It would place a long lived, plutonium-powered (via ASRGs) floater on the lake surface to study long term interactions and would deploy a submersible to the lake bottom for a thirty day stay before popping to the surface for data relay.  The presence of an interior ocean would be explored by measuring the depth of the lake from the lake bottom using an echo sounder.  The amplitude and phases of the lake tides would be used to infer the presence of an interior ocean.

The three New Frontiers missions would conduct subsets of the Flagship mission:

  • Long lived floater (ASRG powered) to study atmospheric evolution, lake/atmospheric interaction, and lake chemistry.  Communications would be direct to Earth and the carrier craft would be a simple stage attached to the entry shell, much like the carrier craft for NASA's Martian landers. 
  • A battery-powered submersible to study atmospheric evolution and lake chemistry.  The submersible would remain on the lake bottom for only six hours before returning to the surface to relay its data back to the carrier stage for retransmission to Earth.  (The presentation notes that this option would provide the most science for the dollar.)
  • A battery-powered floater that would survive on the lake surface for twelve hours to study atmospheric evolution and lake chemistry.  (The presentation notes that this would be the cheapest option.)

In addition to options for the lake probe, the mission also had multiple options for arriving at Titan and for relaying data.  One option would be to arrive at Titan by 2026 to enable direct transmission of data to Earth.   This option requires launch by 2020, and to achieve this short (for a Saturn mission) transit, the carrier would require substantial fuel to enable two deep space maneuvers.  A second option would be two launch by 2023 and arrive by 2032.  In this latter case, data relay would have to be through the carrier, which the study assumes would be ASRG powered.  (Elliot told me that solar powered carriers might be an option, but, "but there are a lot of unknowns (e.g. required technology developments) and uncertainties in how much array area we’d need and how well cells would perform at Saturn distances, etc., so we chose for the study to assume ASRGs as the simpler implementation given our current understanding.  This is something that could benefit from a more detailed trade if further studies are performed.")

The TIME Discovery proposal that is been discussed in this blog would most resemble the long-lived floater concept with direct communication to Earth and a dumb carrier.  The TIME mission assumes a launch by the mid portion of this decade, possibly eliminating the need for powered deep space maneuvers.  The Discovery proposal also would benefit from NASA providing the ASRG's outside the mission's PI budget of ~$450M, enabling the mission to potentially fit within that lower budget instead of a New Frontier budget (~$650M).

See Titan Mare Explorer (TiME) and Dive, Dive! Titan Submersible for additional background information.