Tuesday, January 31, 2012

A Programming Note

For the last several weeks, my days have been consumed writing a paper describing my current research, and my energy for writing for the blog has been limited.  With the paper done (at least until the reviewers get their say!), I want to return the blog for a couple of lengthy mission descriptions for the Insight Mars Discovery proposal (see the last post before this one) and the Bepi-Colombo mission.  If I can find sufficient material, I'll also describe the Comet Hopper Discovery proposal to round out the current Discovery missions in competition (I've covered the third mission in the Discovery competition, the TiME Titan lake probe, previously).

You’ll also see that the blog has a new look (and my apologies to the three readers who were on the blog when I tried out several different color schemes in rapid succession).  A couple of readers said that the previous colors made the blog difficult to read.  If you have any problems with the new colors, please let me know in the comments.

Mars Insight Mission Proposal: Part 1

The one-slide justification for a geophysical pathfinder mission to Mars.  While a sequence of missions have given us detailed information on the Martian surface ("What y'all got"), geophysicists have a much poorer understanding of the interior of Mars ("What we got").  From a presentation by the Insight proposal PI Bruce Banerdt at JPL to the Mars Exploration Analysis Group (MEPAG). Dr. Banerdt has spent twenty years working to get a seismometer on Mars (with some interesting detours along the way, such as being the 
Mars Exploration Rover (MER) project scientist).

At its core, the Mars Insight mission (previously called the Geophysical Monitoring Station (GEMS) mission) is pretty simple: Duplicate the Phoenix lander, deploy a seismometer and heat flow instrument, maintain a radio link with Earth, and then passively record data for the next two (one Martian) years,   With this post and the next, I’ll explore the justification for this mission and place it within the context of the long line of proposed Mars geophysical missions.  In today’s post, I’ll address two questions:

1)            Why a geophysical mission?

2)            How does the Insight proposal compare to previous proposals?

and then in the next post I’ll address two additional questions:

3)            What can be done with a single station?

4)            How would the Insight mission conduct its studies?

Why a geophysical mission?

Because we live on the surface of our planet, it's often easy to forget that the vast bulk of our planet lies beneath our feet.  The interior of our world is the product of the processes that formed and evolved the Earth and the other terrestrial planets.  In turn, the processes that operate inside the Earth have shaped the surface of our planet and contributed gases to our atmosphere.   The decades of research into the Earth's interior have been essential to understanding our planet's history and current state.

All the reasons for studying the Earth's interior also apply to Mars -- we cannot understand that planet without understanding its interior.  However a geophysical mission to Mars may give us more than just a deeper understanding of that world.   We continue to explore the Martian surface because it retains records of conditions from the earliest history of the terrestrial planets (including perhaps the conditions that led to life).

The Earth's interior retains considerable heat that causes vigorous mantle convection that has erased the record of Earth's earliest interior structure and composition.  Mars is much smaller than the Earth and appears to have lost much of its internal heat early in its history.  As a result, Mars may preserve the internal structure and composition from its early history.  Understanding the interior of Mars may help us understand what the interior of the early Earth was like and serve to constrain our models of how our world evolved.

The 2011 Decadal Survey reports listed the key questions for a geophysics mission:
  • "What is the interior structure of Mars?  How are core separation and differentiation processes related to the initiation and/or failure of plate tectonic processes on Mars?
  • "When did these major interior events occur, and how did they affect the magnetic field and internal structure? What is the history of the Martian dynamo? What were the major heat flow mechanisms that operated on Early Mars?
  • "What is Mars’s tectonic, seismic, and volcanic activity today? How, when, and why did the crustal dichotomy form? What is the present lithospheric structure? What are the Martian bulk, mantle and core compositions? How has Mars’s internal structure affected its magmatism, atmosphere, and habitability?"

The 2002 Decadal Survey listed three recommended Mars missions -- the Mars Science Laboratory (on its way to Mars), an upper atmospheric mission (the MAVEN mission in development), and a network of geophysical stations.  Subsequent reviews of Mars priorities continued to rank a geophysical mission highly, but none has gotten beyond the proposal stage.  The 2011 Decadal Survey did not prioritize a geophysical mission because of, "its lower scientific priority relative to the initiation of the Mars sample return campaign," but noted that, "potential Discovery missions to Mars include a 1-node geophysical pathfinder station."  Conducting the first flagship scale mission in a series to return samples from Mars would consume enough of NASA’s planetary science budget that the members of the Decadal Survey could not justify prioritizing a second Mars mission.  They left open the possibility of a limited geophysical mission that might fit within the budget of a Discovery mission.  Insight is a proposal for such a 1-node geophysical station. 

How does the Insight proposal compare to previous proposals?
There has been a long history of proposed Mars geophysical missions extending back into the late 1970s at least.  Perhaps only the Mars sample return mission has had as many serious proposals and near-starts without actual approval as a geophysical mission.

Proposals for geophysical missions often are called network missions because the measurements ideally would be done from a network of stations across the surface.  In these posts, I will focus on geophysical goals, however, meteorologists also would like to place a network of stations on Mars.  While meteorologists and geophysicists would propose different types of networks (meteorologists would like many relatively simple stations distributed across the globe while geophysicists would be delighted with regional cluster of three stations and a fourth on the opposite side of the globe), most network mission proposals have included sets of instruments for both disciplines.  (However, the Pascal Discovery proposal in the early 2000's would have landed 18-24 simple meteorological stations on Mars.).

Two geophysical proposals proceeded almost to approval before budgetary issues forced their cancellation.  The French Netlander mission would have landed four stations.  The Humboldtstation, on the other hand would have landed with the European ExoMars rover and made measurements from a single location. 

The following table compares the proposed instruments of Insight with those proposed for the Netlander and Humboldt stations:

Two observations stand out from this table.  First, there are a wide range of measurements that geophysicists would like to conduct from a geophysical station (and none of these proposals included some additional priority instruments such as electromagnetic sounders that, like the ground penetrating radars, would probe the local subsurface to considerable depths).  Second, the Insight mission has far fewer instruments than either of its predecessor proposals.  To fit within a Discovery budget, this mission would carry the barebones instrument compliment.  There's not even a panoramic camera, although there would be a camera on the arm that deploys the instruments to pick out locations to deploy them.  (I suspect that after instrument deployment, the camera arm might be used to look around at the surrounding scenery.)

Thursday, January 19, 2012

ExoMars and Budgets Update

Space News today had an article on the evolving politics of the ExoMars mission from the European side.  According the the article, "CNES [the French space agency] President Yannick d’Escatha said both the ExoMars program and the space station budget will be on the table for European ministers when they meet in November to set multiyear space budget and program priorities."  The article reports that European nations have committed only 850M euros of the 1B euros required for the European portion of this joint mission with NASA.  One idea to lower the European costs, dropping the demonstration lander, was proposed by France but rejected by Italy.  The article suggests that France as well as other nations may be wavering in their support for the ExoMars mission.

There has been no news on NASA's commitment to the ExoMars mission, pending the release of the President's FY13 budget proposal next month.  That budget will also determine how funding for the Webb Space Telescope will impact NASA's planetary program.  

Several recent articles have discussed how difficult it will be to fund new flagship missions.  While the emphasis is on astronomy missions, the same issues likely  will apply to flagship planetary missions.  I recommend Big science in an era of tight budgets.

Editorial Thoughts: The impacts of the continuing financial downturn are still being felt.  NASA's budget proposal to be released next month will be the first to follow the release of the Decadal Survey and the commitment to the higher funding needed to complete the James Webb Space Telescope.  If the Decadal Survey laid out a vision, then the next budget will be the administration's response to that vision and the other competing priorities for NASA in an era of budget cutting.  The administration has promised to include its decision on NASA's participation in the ExoMars as part of that budget release.  I plan to release an analysis of the budget proposal the day it is released.

From the Space News article, it appears that the next opportunity to revisit ESA's commitments will come at the ministerial meeting next November.

Friday, January 13, 2012

Cassini - An Example Extended Mission

"You didn't say things about existing missions. Rumor says that Cassini's going to have a 50% cut to science. At some point it's below the threshold of viability and it will destroy science... Planetary science is on the verge here, and it's not just future missions, it's present missions too."
Statement by a planetary scientist at EPSC/DPS conference last fall as reported by Emily Lakdawalla in her Planetary Society Blog 

In my last blog post, I talked about the Senior Reviews that NASA will be holding early this year to decide funding for continuing science missions.  Continued operation of missions past their initially funded prime mission incurs considerable costs.  I've seen quotes of $5M per year to $60M per year depending on the complexity of the spacecraft, the mission activity, and the size of the science team.  To ensure that sufficient funding remains to fly new missions, NASA sets a budget for continuing missions and then periodically appoints a Senior Review panel to recommend the mix of continuing missions to maximize the science return from that budget.  Rumors, as noted in the opening quote, suggest that the budget for continuing missions is likely to be tight and good missions may suffer significant cuts.  We don't yet know what the budget will be for the Senior Review, and may not know until the release of the FY13 budget in approximately a month.  So these are rumors, possibly correct, possibly not.  However, the community is worried.

While this blog has primarily focused on new missions, today I'd like to examine what continued funding for missions can enable using the Cassini mission as an example.  First, though, I'd like to make it clear that I'm not stating a preference for which missions should be continued.  A good case can be made for all the missions up for review (see the list in my previous post), and I certainly don't have the information to make an informed recommendation.  Rather, the Cassini mission nicely illustrates the wide range of what continuing missions as a group can achieve because it is exploring an entire system rather than a single world.  (Well, okay, I'll admit to really liking the Cassini mission, but I have other favorites, too.)

The Cassini mission currently is in its second extended mission scheduled to last -- pending funding decisions based on the Senior Review recommendations -- until 2017.  From a news article, it appears that each year of continued operation costs around $60M a year.  That funding level, if continued, would pay for about three-quarters of a Discovery mission or about a fifth of a small Flagship mission to Europa.  Emily Lakdawalla reports in the same post quoted above that three-quarters of the Cassini budget (~$45M/year) is required to continue operations of the spacecraft at the minimum safe level, and the remainder pays for scientific analysis of the returned data.

So, what is the Cassini spacecraft doing in its extended mission?  The spacecraft is in its second extended mission, frequently called the Solstice mission.  When Cassini arrived at Saturn in 2004, it was winter in the northern hemispheres of Saturn and Titan, equivalent to January on Earth.  In the first extended mission, spring arrived.  When the mission is currently scheduled to end, summer will have begun, equivalent to June on Earth.  Saturn orbits the sun much more slowly than Earth, so the total mission from arrival to end will have been 17 Earth years long.

The many planned encounters of the Cassini prime and two extended missions.  In addition to encounter science, the spacecraft will conduct on-going studies of the rings, Saturn's atmosphere, and the magnetosphere.

The science being conducted can be broken down into three types of investigations.  In the first, the spacecraft is examining the Saturn system for changes in time, particularly those brought on by the changing seasons.  In the past year, these observations saw the birth of the Great Northern Storm on Saturn and the spring deluge on Titan that created extensive changes on the surface over an area equal to the states of Arizona and Utah. 

A second set of observations extend measurements previously made.  For example, new observations with the cosmic dust analyzer and ultraviolet spectrometer found that the larger grains of ice deep within the plumes of Enceladus are salt-rich, strengthening the case for a subterranean ocean inside that world.  This discovery was made from the close flybys of Enceladus done in the first extended mission.  Similarly, the Cassini spacecraft continues to image new areas of Titan in higher resolutions, explore the composition of the rings, and conduct additional flybys of the other moons.

A third set of observations come under the heading of entirely new exploration.  In all the orbits of Saturn so far, the Cassini spacecraft has been kept well away from the major rings.  At the end of the Solstice mission, Cassini will dip its closest approach to just outside the F ring for 20 orbits.  Then the periapsis will be lowered to fly through the ~3,000 km clear region between the inner edge of the D ring and the top of Saturn's atmosphere for another 22 orbits before finally plunging into Saturn to terminate the mission.  With these orbits, the Cassini spacecraft will conduct science at Saturn similar to that the Juno spacecraft will do with its close-hugging orbits of Jupiter. 

Cassini's proximal orbits from this presentation.

In this final mission phase, new higher resolution studies of the gravity field and magnetic field will allow scientists to better model the deep interior and rotation rate of Saturn.  The close orbits will enable better estimates of the mass of the rings to estimate the age of the rings.  New portions of the magnetosphere and its trapped plasmas will be directly sampled.   (Alas, no one in the 1990s when the mission was planned thought to put a microwave instrument on Cassini like the one on Juno to enable deep probing of Saturn's atmospheric structure and composition.  :>   On the other hand, Juno won't have an extensive ring system to explore up close.)

Cassini provides in a single extended mission examples of the science that extended missions can produce: long term observations of variability and change, continuation of measurements to fill in gaps, and entirely new studies.  Each of the missions in contention for continued funding through the Senior Review would extend our knowledge of the solar system.  The members of the Senior Review will have to choose among an embarrassment of riches.

I'll close with this link to the top 10 discoveries from the Cassini mission in the past year enabled by its continuing missions.  You can also look through this presentation to learn more about the science goals of the Solstice mission (also called the XXM mission.)  This post describes how the Solstice mission was designed.

I'll also reproduce the statement from the Outer Planets Analysis Group on why it believes that the final close flybys of the rings and Saturn deserve continued funding:

OPAG Statement On The Cassini Mission’s Proximal Orbits: Critical Data for Giant Planet & Solar System Origins

Completion of the Cassini mission’s Proximal Orbits is critical to multiple high-priority planetary science objectives. Cassini is poised to perform these orbits near the end of its Solstice Mission, making measurements not possible from previous orbits. These measurements will be a key component of a broad multi-mission data set needed to reveal giant planet and solar system formation and evolution processes from comparisons of the gas giants Jupiter and Saturn, followed by future comparisons of the gas giants to the ice giants Uranus and Neptune. This knowledge is critical to understanding the veritable zoo of different planetary systems now being found around other stars.

Comparative planetology of gas giants is a high priority objective for research into giant planet and solar system formation and evolution [1,2]. Fundamental aspects of these areas are currently unknown, including processes and materials that deliver volatiles such as water and organics to giant planets and terrestrial planets, and time scales for planetary formation and protoplanetary disk evolution. Comparisons among giant planets, beginning with comparisons of Jupiter and Saturn, are a tool for examining the results of these processes and thus the processes themselves. A meaningful comparison of Jupiter and Saturn requires knowledge of elemental and isotope composition in the well--‐mixed atmospheres of both planets, and knowledge of gross interior structure to provide context for the compositional information [3,4].

The data set needed to provide this knowledge is being assembled using data from multiple past, present, and future NASA Flagship and New Frontiers missions. The Galileo Probe provided the elemental and isotope composition measurements at Jupiter, except for oxygen. NASA’s Juno mission, part of the New Frontiers Program, is en route to Jupiter to make the interior structure measurements needed there. This objective, together with composition measurements (ammonia, and the water the Galileo Probe missed), comprises a significant part of the Juno mission’s science and the mission budget, and completes the comparison data set for Jupiter. The recently completed Planetary Science Decadal Survey recommends a NASA New Frontiers Program mission, a Saturn atmospheric entry probe mission, to make the elemental and isotope composition measurements needed at Saturn [1]. Interior structure measurements at Saturn, equivalent in science value to that of Juno’s interior structure measurements at Jupiter, would round out the data set. Without these, the comparisons would be inadequate for unambiguous models of planet formation.

It is precisely these Saturn interior structure measurements the Cassini Proximal Orbits would provide. The cost of acquiring the data with Cassini is a relatively small fraction of the Solstice Mission budget. If Cassini does not acquire that data set, the task of acquiring it would fall to a new, future Saturn orbiter mission. Such a future mission is not within NASA’s planning horizon, so it would be decades in the future. This would delay understanding fundamental giant planet and planetary system formation processes in our own solar system, and notably in other planetary systems now coming to light as a result of NASA--‐funded exoplanet search programs.  

 [1] Prepublication release of “Vision & Voyages for Planetary Science in the Decade 2013--‐2022,” National Academies Press, Mar. 7, 2011; Available at http://www.nap.edu/catalog.php?record_id=13117 .
 [2] Entry Probe Missions to the Giant Planets, D.H. Atkinson, T.R. Spilker, S.K. Atreya, & 53 others; white paper submitted to the NRC 2012 Planetary Science Decadal Survey, available at http://www.archive.org/details/EntryProbeMissionstotheGiantPlanets .
 [3] Saturn Exploration Beyond Cassini--‐Huygens, T. Guillot, S. K. Atreya, S. Charnoz, M. Dougherty, & P. Read, in Saturn From Cassini-­Huygens (M. K. Dougherty et al., eds.), Chapter 23, pp 745--‐761, 2009, DOI 10.1007/978--‐1--‐4020--‐9217--‐6_23, Springer Dordrecht, Heidelberg--‐London--‐New York.
 [4] Coupled Chemistry and Clouds of the Giant Planets, S.K. Atreya, A.S. Wong, A chapter in The Outer Planets and their Moons (T. Encrenaz, R. Kallenbach, T. C. Owen, C. Sotin, eds.), pp 121--‐136, Springer, Berlin--‐New York--‐Heidelberg, 2005. Also in Space Sci. Rev., 116, Nos. 1--‐2, pp 121--‐136, 2005.