Balance

One key to understanding the recommended program is that the Survey's members sought balance.  While Mars has dominated NASA's program for over 15 years, the goal going forward was to have a balanced program.  There are a couple of ways to look at balance.  One is by type of target -- inner planet other than Mars, outer planets, primitive bodies, etc.  Another way is by the method of study: remote sensing of surfaces or atmosphere, measurements within an atmosphere, measurements on the surface, measurements within a magnetosphere, sample return.  The latter approach is often more telling than the destination.  An atmospheric chemist, for example, can switch between Venus, Titan, or Uranus, but is left out on a lunar mission.

With that in mind, how do the recommended missions compare by target and type of study?

Among the Flagship missions, the Giant Planets were a clear favored destination.  This isn't surprising.  Mounting missions to these distant worlds in inherently expensive and once that initial cost is assumed, the inclination is to fly more capable missions that require Flagship (>~$2B) funding.  Among the New Frontiers candidates, however, there are no clear winners.  Candidate missions are well distributed by type of destination and by type of study.  I believe that the goal of achieving this balance explains why a near Earth asteroid sample return mission was dropped from the list (although it remains a candidate for the selection in progress).  Including it would have meant too many primitive body missions and too many sample return missions.

(I want to emphasize that the chart above has been simplified to focus on major types of study.  The Venus Climate Mission, for example, would include a camera on the orbiter for context images, but this would not a major focus of the mission.  On the other hand, the Comet Sample Return mission has to have capable remote sensing instruments to select landing sites and would make a major contribution to our understanding of the surface of these bodies even though the focus of the mission would be on the sample return.  I also chose to count the Enceladus orbiter as making an "atmospheric" measurement within that moon's plumes, but counted measurements of the near-vacuum atmospheres of Europa and Io as magnetosphere studies.  Please forgive any oversights.)

It's also interesting to look at the program in terms of financial balance.  The Survey members stated that they did not want a single mission to dominate the program.  Here is a list of the estimated mission costs in the Survey report with acceptable costs in parentheses if the full cost was unacceptable:

Flagship missions not recommended
Titan Saturn System Mission $6.7B
Jupiter Europa Orbiter $4.7B
Mars MAX-C and ESA ExoMars rovers $3.5B

Flagship missions with high priority
Descoped Mars rover mission $2.5B
Descoped Europa mission (cost target not given)
Uranus Orbiter and Probe $2.7B

Flagship missions with lower priority
Enceladus Orbiter $1.9B
Venus Climate Mission $2.4B

New Frontiers mission candidates
Lunar Geophysical Network $1.3B
Io Observer $1.4B
Trojan Tour $1.3B
Saturn Probe $1.3B
Comet Surface Sample Return $1.5B

(Cost estimates were not given for the Venus lander and lunar sample return missions; since both have proposals in competition for the next selection, it was assumed their costs would fall within the present New Frontiers cost cap.)

From this list, it appears that Flagship missions around ~$2.5B were acceptable because they would each represent less than a quarter of the then presumed funding for new missions.  (Under the new funding outlook, none can be afforded except for a possible even more descoped joint rover mission with ESA.)

Interestingly, the additional New Frontiers candidate missions all exceed the recommended budget of $1B per mission for candidates selected mid decade and beyond.  The Survey chair, Steve Squyres, has said that they believed that clever proposing teams will find ways to fit several of these missions within that budget cap.   These missions at these prices may represent a new class of mission.  Previously, the principal investigator's budget for the craft, instruments, and operations was capped at ~$650M; the new proposed cap at $1B represents a significant increase in funding per mission.

Articles on Juno Jupiter Mission

The Juno mission to Jupiter is scheduled to launch this coming summer.  Aviation Week and Space Technology just published two articles on the mission, one focused on design and implementation and the other on the science.  Normally, AWST requires a subscription to read, but both articles are posted on public websites.

The science article is posted on AWST's website.  The other, longer article, appears to be available on the Zinio website, which provides an electronic subscription service to magazines and other media.  I subscribe to AWST through Zinio, so it is possible that the link to this article may not work for those without the subscription.

JET - Cost Capped Titan-Enceladus Proposal

JET Titan and Enceladus orbital tour

Following the release of the planetary Decadal Survey, I’ve discussed the need for missions in the coming decade to be highly focused to fit with fixed cost caps.  Nowhere will that need be greater than for outer planet missions to explore the icy-ocean moons.

For me, there were two major surprises in the Decadal Survey.  The estimated costs of missions, especially the Flagship missions, stunned me.  As I’ve had a week to think about the Survey, though, the bigger surprise has been the lack of focus on the icy-ocean worlds.  Perhaps there is no way to meaningfully explore Europa given limited budgets and its location deep in Jupiter’s radiation belts – perhaps only the surface of Venus is a more hellish location for spacecraft.  Titan and Enceladus are comparatively easy to explore, and their major drawback for further exploration is the many years needed for a spacecraft to reach them.  (I heard in a conference this week that operating a spacecraft during cruise costs $7-10M a year, and Saturn can take up to seven years to reach.)  Cassini’s discoveries at these two moons, in my opinion, however, put them on the short list of the highest priority worlds to explore.

I believe that the Survey’s members concluded that the cost of incremental missions to these moons for the science they could return would be too low to make them priorities.  They prioritized a $2.9B Uranus mission to begin the in-depth exploration of the ice giant worlds over a $1.9B Enceladus orbiter.  As budget projections stand, we are likely to get neither.

A Discovery mission to the outer planets would set a new cost-return point that might be quite attractive.  At least two Discovery-class missions have been proposed for missions to Titan or Titan and Enceladus.  The proposers are attempting to implement missions that would be approximately half the cost or less of equivalent missions briefly studied by the Decadal Survey.  However, several observers have pointed out that the Decadal Survey mission concepts tended to have rich payloads, weren't optimized to reduced costs, and were made under conservative design and cost assumptions.

I don’t know if the Discovery budget (perhaps ~$800M with launch) can enable missions to explore the outer solar system.  While the proposers of the three outer planet Discovery missions I know about (Io Volcano Obersver, Titan Mare Explorer, and Journey to Enceladas and Titan) have a great deal credibility, mission champions have also been known to be too optimistic.  I hope they succeed.  It is instructive, however, to look at the tradeoffs that might enable an outer planets Discovery mission.

The Decadal Survey examined an Enceladus orbiter that would also make a number of Titan and other moon flybys.  That mission would carry five instruments and involve a complex 4-4.5 years of moon flybys and orbital operations.  By comparison, the Journey to Enceladus and Titan (JET) Discovery proposal would have just two instruments and one year of operations.  The Principal Investigator for the proposal, Christophe Sotin, was kind enough to give me permission to reprint his team’s abstract on the mission from the just completed Lunar and Planetary Science Conference.  This abstract both shows how Discovery missions to the outer planets must have limited goals and shows how they may be able to still address interesting science.

Example of the improved imaging JET would offer for Titan.

JET: JOURNEY TO ENCELADUS AND TITAN
C. Sotin1, K. Altwegg2, R. H. Brown3, K. Hand1, J.I. Lunine3, J. Soderblom3, J. Spencer4, P. Tortora5, and the JET Team, 1Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove drive, 91109, Pasadena, CA, 2University of Bern, Switzerland, 3University of Arizona, Lunar and Planetary Laboratory, Tucson, AZ, 4Southwest Research Institute, Boulder, CO, 5Universita di Bologna, Italy.

Introduction: The Cassini-Huygens mission has demonstrated that Enceladus and Titan represent two crucial end-members in our understanding of planet/moon formation that might have habitable environments. Enceladus is a small icy world with active jets of water erupting from its surface (Fig. 1) that might be connected to a subsurface water ocean. Titan is the only moon with a dense atmosphere and the only object besides Earth with stable open bodies of liquid on its surface (Fig. 2). An organic-rich world, Titan has a methane cycle comparable in atmospheric and geological processes to Earth’s water cycle.

Fig. 1. Jets emanating from faults on Enceladus form a plume that provides access to internally processed material that can be studied in situ. 

Fig. 2. Specular reflection at 5 μm from Jingpo Lacus, Titan [1] demonstrates the lack of scattering in Titan's atmosphere at 5 μm (Credit: NASA/UA). JET exploits this unexpected “window.” 

The questions that JET would answer directly respond to the wealth of discoveries made by the Cassini- Huygens mission. High-resolution mapping of Titan surface is required to determine what processes have shaped and are shaping Titan. High-resolution mass spectroscopy would permit assessment of the astrobiological potential of Enceladus and Titan.

Concept: The JET mission has been proposed in response to the 2010 NASA Discovery Announcement of Opportunity. In order to achieve JET’s rich science return within the Discovery cost cap, a planetary orbiter with a simple, two-instrument, but powerful payload would make a total of 16 flybys of Enceladus and Titan. The only new technology is the NASAprovided Advanced Stirling Radioisotope Generator (ASRG) that would be validated as part of the Discovery Program’s engineering goals.

Along with making new observations of Enceladus and Titan, JET would fill a critical temporal gap in our understanding of the Saturnian system. Enceladus and Titan have near-equatorial orbits around Saturn, and Saturn has an inclination of 26º relative to its orbital plane around the Sun. Consequently, Saturn and its moons have seasons. Voyager briefly observed Saturn and its moons during the Saturnian Vernal equinox. Cassini observations extend from winter solstice to the summer solstice. JET would observe Titan during autumnal equinox, an opportunity that will not arise again until 2054. Observations during the Autumnal equinox are critical to understanding the fate of lakes and seas, Titan’s complex meteorological cycle, and the fate of organic molecules.

Science: The three goals of the mission are to determine the processes that have shaped and are shaping Titan, to assess the astrobiological potential of Enceladus and Titan, and to investigate the formation and evolution of Enceladus and Titan. These three goals are then detailed in eleven science objectives and thirty-one science questions that cannot be answered by the Cassini mission. Three examples are given. First, the Cassini mission has discovered that mass 28 in Enceladus’ plume has possible CO, N2 and/or hydrocarbon components. JET would confirm what fraction is CO vs. N2 vs. hydrocarbons. Second, the Cassini-Huygens mission has discovered that rivers and valleys are carved into plateaus and mountains. JET would search for sedimentary layering in valleys to determine the history of the flows. Third, Cassini has discovered that heavy molecules (m>100 Da) are produced in Titan’s upper atmosphere. JET would determine the nature of these molecules. This list of questions includes ten of the major discoveries of the Cassini mission that await a more capable mission to unveil the geological history and astrobiological potential of these two unique moons in the solar system. JET’s payload—a camera (TIGER [Titan Imaging and Geology, Enceladus Reconnaissance]) and a mass spectrometer (STEAM [Spectrometer for Titan and Enceladus Astrobiology Mission]—would provide the capability for achieving these science goals.

Instruments: The payload is limited to two powerful instruments and the radioscience investigation. The total data volume would be on the order of 120 Gb during the one year nominal mission.

STEAM: The reflectron time of flight mass spectrometer [2] is the Rosetta flight-spare of the Rosina mass spectrometer. It would characterize elements and molecules including complex organic molecules with a 10× larger mass range, 100× higher resolution, and 1000× better sensitivity than Cassini (Fig. 3). It would resolve fundamental issues related to the chemical composition of Enceladus’ jets and their relationship to the structure and evolution of Enceladus’ interior. STEAM would also characterize Titan’s organic-rich upper atmosphere.

Fig. 3. STEAM (right) has 102 better mass resolution and 103 better sensitivity than Cassini/INMS (left). Mass 28 and 40 will be definitively characterized. 

TIGER: This high-heritage IR camera exploits four IR windows through Titan’s haze and would image the heat of Enceladus’ fractures (Fig. 4). This camera uses the 5 μm window [3] to provide 10× better imaging resolution of Titan’s surface than Cassini, yielding 50 m/pix images of 15% of Titan’s surface. At each Titan flyby, an area twice as large as France would be mapped at 50 m/pixel in addition to Titan full disk at 500 m/pixel. The 50 m/pixel resolution is achieved at 2250 km from Titan’s surface. Currently, only ~10-6 of Titan’s surface area was imaged at this resolution by the Huygens probe. JET would deliver a five order of magnitude increase in coverage of highresolution imagery of Titan’s surface. Similarly, TIGER would provide 10 m/pix images of selected Enceladus’ tiger stripe fractures, permitting detailed thermal modeling.

Fig. 4. Cassini/VIMS spectra of Titan revealed a major surprise: the surface is visible in several atmospheric windows. High resolution surface imaging requires a careful balance between spectral regions of high transparency and low absorption, matched appropriately with detector sensitivity. The red curve shows the transparency of Titan’s atmosphere. The black curve is a typical reflected spectrum of Titan where high values show low absorption. The four TIGER channels (C1 to C4) shown in grey are optimized for these critical parameters. C3 and C4 provide thermal emission maps of EnceladusJets emanating from faults on Enceladus form a plume that provides access to internally processed material that can be studied in situ. 

Mission: The mission would be launched in February 2016 and would be inserted into Saturn’s system in May 2023. The nominal one-year mission would start with 12 Titan flybys with the closest ones at 900 km from Titan’ surface. This distance would vary from one flyby to the other in order to sample different layers of the upper atmosphere. Both Saturn and anti- Saturn hemispheres would be mapped. The Titan phase would be followed by 4 Enceladus flybys to sample the different jets of the South pole. The nominal end of mission would be a Dione disposal. A 6- year science enhancement option would permit to get into Titan orbit, offering the opportunity to further test the ASRG and to relay data from any element present on Titan’s surface or in its low atmosphere at that time.

References: [1] Stephan K. et al. (2010) GRL, 37, L07104. [2] Scherer S. et al. (2006) Int. J. Mass Spectrometry, 251, 73–81. [3] LeMouelic S. et al. (2011) LPS XLII.

More on Partnership Challenges

It turns out that I wrote my previous post about the process to plan for possible planetary partnerships between NASA and ESA a few hours too early.  Since I wrote that, two articles have appeared that give additional information, especially from the European perspective.

Amy Svitak (whose stories I have come to look forward to) at Space News writes a good summary of the issues focusing on joint Mars and Jupiter system missions.  She reports that industry bids for building ESA's ExoMars rover have come back higher than expected, giving ESA a possible additional incentive to continue a partnership with NASA to share costs.  (ESA originally sought a partnership because its previous cost estimates for the entire mission exceeded its budget.)

On the journal Science's website is a story that focuses on a new redefinition of ESA's three candidate missions for its next large science mission, one of which is the Jupiter Ganymede Orbiter (JGO).  All three candidate proposals depended on a partnership with NASA (and one on a partnership with Japan).  However, none of these missions were top-ranked candidates in the U.S. astronomy or planetary Decadal Surveys.  Given budget issues in both these programs at NASA, ESA has concluded that NASA partnerships are unlikely as previously envisioned.  (For JGO, the previous plan had been for NASA to fly its own complimentary Jupiter Europa Orbiter and contribute instruments to JGO.  NASA can no longer do the former, but still plans to offer to do the latter if JGO is eventually selected as ESA's next large mission.)  ESA has asked the three proposing teams to reexamine their proposals and rescope them as ESA-only missions.  The new mission proposals are due in a year.

NASA Joint Missions With ESA

NASA has begun to explore its options in light of both the Decadal Survey's recommendations and its new reduced budget outlook.  One way to stretch dollars is to share a ride with a partner, in this case the European Space Agency.  NASA already had arrangements in place with ESA to cooperate on two missions, the Europa Jupiter System Mission and the 2018 joint Mars rover mission.  NASA's new budget outlook makes the scale of previously planned the U.S. contribution to those missions impossible.  As a fall back, NASA will honor its agreement to supply up to five instruments to ESA potential Jupiter Ganymede Orbiter.  The U.S. agency will also seek to redefine the Mars mission in conjunction with ESA to enable the mission to fly with a U.S contribution of up to $1B (which is approximately the planned European contribution).  

Editorial Thoughts:  If current plans hold, the next decade will see several moderate sized planetary missions fly: ESA's BepiColombo Mercury orbiter (with a Japanese sub-satellite), a Russian Venus mission, three NASA New Frontiers missions, ESA's Jupiter Ganymede Orbiter if selected as the next large science mission, and potentially a 2018 ESA-NASA Mars rover.  It's difficult to compare costs between  missions because of different accounting rules.  Including spacecraft, instruments, operations, and launch, however, these missions would range from approximately $1B (the next NASA New Frontiers mission) to perhaps $2B (ESA and NASA's contribution to a 2018 Mars rover mission).  These costs are a big step back from past flagship missions like Galileo and Cassini that might in today's inflated dollars cost $4B+.  

ESA and NASA are now planning missions of comparable scale.  Cooperation can allow more capable missions than either could do alone.  NASA's contribution of up to five instruments to JGO might represent half the instrument compliment and 10-20% of the mission costs. 

Cooperation can also be made difficult by differing goals.  For the 2018 mission, ESA has as core goal developing and demonstrating rover technology.  It also has a kick-ass instrument compliment for analyzing samples drilled from up to two meters below the surface.  The design of ESA's rover is almost complete.  NASA has the goal to collect and cache samples for future return to Earth.  The requirements include sampling a variety of rocks and soils, which is likely to require a sophisticated robotic arm along with the sample handling hardware.  Conceptually, the arm and sampling handling system could be "bolted" on to the ESA rover.  In reality, merging high tech systems that must survive launch, cruise, and operation on Mars means that this could be a complicated redesign.

One basis for a cooperative mission might be a redesigned rover that hosts the subsurface drill, the instrument compliment, a sampling arm (probably with some instruments of its own), and the caching system.  NASA could provide the entry, descent, and landing system derived from the Mars Science Laboratory mission that would allow precision landing into the most scientifically interesting sites.  NASA could also provide the launch.  Such a mission might have approximately equal financial contributions by both nations.  The devil, however, will be in the details of design, financing, and meshing goals.

To provide additional background on the issues from NASA's perspective, I'm reprinting a portion of the notes from this week's meeting of the Planetary Society Subcommittee meeting.  The quotes come from the meeting notes and NASA's director of Planetary Science presentation.  You can download both at http://www.lpi.usra.edu/pss/.

From the Notes:

A back of the envelope calculation suggests that after accounting for the higher priority elements (R&A, technology development, Discovery, and New Frontiers), we will have about $1B between now and 2018 to discuss a Flagship. This is nowhere near what even the recommended descoped MAX‐C will cost. Sanjay Limaye asked if that $1B includes launch costs, to which Jim responded that it does if we launch it (as opposed to ESA or another partner).

In response to a question from Mini Wadhwa on how MAX‐C [NASA's proposed rover for the 2018 mission] might be descoped, Jim replied that our first step will be to go back and talk with ESA, starting with a clean sheet of paper to see if we can build a joint Mars mission that meets both our needs and theirs within a budget both sides can afford. John Grant asked whose requirements would be used to develop the new mission, Jim noted that ESA has certain technology development needs and we have requirements on our side, sample caching in particular, that will all need to be addressed. Discussions on this front already began at LPSC and they will continue in earnest at the NASA/ESA bilateral on March 30th ‐ 31st.

Mark Sykes asked what would happen if there is no viable flagship option. Jim responded that the decision‐making rules for Flagships are clearly laid out in the decadal. The emphasis is placed on a balanced program. Flagships provide an enormous science per $ value. There are opportunities to move forward by partnering in the international arena, we need to carefully explore those options, then, and only then can we say no flagship. 

Jim noted that at the NASA/ESA bilateral, we will reconfirm our commitment to support ESA’s Laplace mission (Jupiter Ganymede Orbiter), should it be chosen. The PSS also confirmed their support for Laplace and for working with ESA in general. Jim Slavin asked when ESA might make a decision about the Laplace mission. Jim Green noted that ESA will not make a down‐select for their L‐class mission anytime

soon, they are putting together Science Definition Teams to explore what ESA‐only missions might look like, and it will take about a year for those studies to complete.

In response to a question from Bill McKinnon, Jim noted that for the time being, PSD is not undertaking a cost exercise to look at a descoped Jupiter Europa Orbiter. There has been no discussion of how to get a useful Europa mission for ~$1B. In response to a question from Julie Castillo about the future of the JEO community, Jim stated that from a US perspective, the JEO SDT [Science Definition Team] has been thanked and disbanded; any new discussions will be in concert with ESA.

From James Green's presentation:

• Determine if Mars 2018 can be accomplished starting with the minimum set of requirements and “a clean sheet of paper” as Planetary’s top priority flagship mission
• Reaffirm NASA’s commitment to support ESA’s Laplace mission if it is chosen as the CV‐Large class mission
• Up to 5 (as budget allows) of the scientific instruments on JGO as a Mission of Opportunity and support for their PI‐led teams
• Support for Interdisciplinary Scientists
• A NASA Project Scientist to co‐chair the international Project Science Group (PSG) with ESA Project Scientist