Friday, July 18, 2014

Mars and Europa: Contrasts in Mission Planning

The big news for future planetary exploration this month is likely to be the announcement of the instrument selection for NASA’s 2020 Mars rover that will define how it will fulfill its scientific goals.  In the meantime, there have been several announcements for proposed missions to Mars and on the planning for a NASA return to Europa that highlight the contrasts in planning missions for these two high priority destinations. 

China’s chief scientist for its lunar program has stated that China is planning a rover mission to Mars for 2020 and a sample return from that planet by 2030.  The Chinese space program tends to be tight lipped about its plans (especially those still several years out), and I’ve been unable to find any more information.  Is this mission a placeholder on the space agency’s roadmap – much like an eventual Martian sample return for NASA – or an approved and funded program?  Would the rover be delivered by a small lander and therefore be small itself, perhaps like NASA’s 1996 Sojourner rover?  Or perhaps it would be a medium sized rover like China’s Yutu lunar rover and NASA’s Opportunity rover.  Given China’s string of successes and careful build up to more complex missions, if a Martian rover is firmly in their plans, they seem likely to succeed. 

A Chinese rover would find itself part of a crowd on the Martian surface in 2020.  As mentioned above, NASA plans its own Curiosity-class rover for that year.  Europe’s ExoMars rover is likely to still be operating along with its Russian stationary lander.  I’m willing to bet that NASA’s 2016 InSight lander and Curiosity rover will still be functioning, and I have some hope that the Energizer bunny-Opportunity rover will still be alive (although perhaps as a stationary platform by then).

Mars exploration has reached the point where private organizations can promote credible plans for complex Mars missions on the web.  Credit: BodlyGo Institute and Mars One

If two private organizations have their way, the party at Mars will be more raucous still.  The BoldlyGo Institute would like to raise funds for its SCIM spacecraft that would dip briefly into the upper atmosphere during a high speed flyby to snag dust and atmosphere samples to return to Earth.  While we have some 130 rocks delivered as meteorites that are believed to be from Mars, this mission would return samples of the dust that ubiquitously blankets the planet.  If this idea seems familiar, it was proposed twice before in NASA’s Mars Scout and Discovery mission competitions.  Now its backers hope that this mission will have better success at securing private funders.

Another organization, Mars One has been planning to land humans on Mars in about a decade’s time.  Recently, it announced plans for a Martian lander for 2018 built on the same platform as NASA’s Phoenix and InSight landers.  Mars One is seeking proposals for instruments that would be useful to eventually colonization of Mars.  For example, the organization is requesting proposals to demonstrate water extraction from the soil.  It would also deliver one instrument developed by a university to the surface of Mars.

Both of these missions depend on finding funding from some combination of rich donors, corporate sponsors, and crowd sourcing from small donors. I’m never quite certain how much hope to hold out for missions that depend on private donations.  Given their scope, these two missions would likely costs of several hundred million dollars; each mission would either need a fantastic number of small contributors or one or more wealthy contributors.  While rich space enthusiasts exist (I’m thinking of  Elon Musk of SpaceX as an example), if you are very, very rich and have the slightest inkling towards philanthropy, then fund raisers from many worthy causes from universities to global health to saving species are already in touch with you. 

Rather than dividing potential support, having multiple organizations trying to raise funds may benefit private planetary exploration.  We can’t know beforehand which, if any, approaches will open check books and competition may help us learn what will work.  (The B612 Foundation is another player looking to finance a challenging mission, in their case a space telescope to search for near Earth asteroids.)

Jeff Foust at The Space Review had a story recently on the potential for private funding of space missions.   While raising hundreds of millions of dollars my prove too daunting, technology is on the cusp of enabling small planetary spacecraft based on CubeSat and SmallSat technologies that would cost just a few tens of millions of dollars.  The Planetary Society’s LightSail project is an example of such a mission (although it will test critical hardware in Earth orbit rather than fly to another world).

If planning for Mars missions is becoming commonplace, NASA is still trying to find a plan to for a dedicated mission to Europa.  In a step forward, the agency has released a request for proposals to the scientific community for instruments for a Europa mission.  It did so, however, in a rather odd fashion.

Reddish features in this colorized image of Europa's surface likely contain  water ice mixed with hydrated salts, potentially magnesium sulfate or sulfuric acid that may represent material from the interior ocean.  Full caption available at Credit: NASA/JPL-Caltech/SETI Institute

Usually when NASA requests instrument proposals, it has a solid mission concept in mind.   For this call, NASA said that the Europa mission might be an orbiter or might be a multi-flyby spacecraft.  The request document was vague as to the budget for instruments and just said that past studies assumed it would likely be around 15% of the total mission cost.  While many instruments by their nature have modest costs, some could be quite costly and it might help proposers to know whether the total instrument budget is closer to $150M (for the $1B total mission cost NASA would like) or to $300M (for the ~$2B that past studies have said is needed to achieve all the high priority scientific goals).

For some instruments, proposers will have to bet that NASA either selects a multi-flyby spacecraft or an orbiter.  For example, measuring Europan tides would help pin down the depth of the ice covering the ocean.  A laser altimeter could accurately measure the tides, but it requires an orbiting platform to pin down the size of the tides.  If NASA goes with a flyby spacecraft, any group that proposed an altimeter is likely to be out of luck.

Examples of instruments that the scientific community may propose to study Europa.  From the Europa instrument Announcement of Opportunity available here.

The request for proposals gives two roadmaps for how NASA will select the winning proposals.  Its managers expect that they will select up to 20 proposals in April 2015 for which they will fund further development towards a final selection of approximately eight instruments a year later.  NASA also reserves the right to simply select the final instrument suite in April 2015.  The document implies that the longer timeline assumes a launch no earlier than 2021, while the shorter timeline could either reflect a possible earlier launch date or the possibility that the proposals seem ready for selection without an additional year of maturation. 

With this request, NASA appears to be showing its commitment to an eventual Europa mission, but it still hopes to find a cheaper alternative that will win the allegiance of the scientific community.  The large cost overruns on the Curiosity Mars rover and James Webb Space Telescope have made the White House’s budget managers and NASA’s senior managers wary of multi-billion dollar missions. reports that NASA has received a number of concepts for Europa missions that might cost no more than $1B.  The agency is currently assessing these ideas for their cost, technical, and scientific feasibility.  Comments by NASA’s chief scientist suggest that these missions likely would perform only a fraction of the science considered high priority by the scientific community (and that would be accomplished by the current ~$2B mission concept).

In the request for instrument proposals, NASA specifically asked for instruments that could study possible plumes of water erupting from Europa.  The recent possible discovery of plumes at Europa has raised the question of whether and how planning to explore this world should be changed.  If the plumes are verified, then they represent a chance to directly study material being ejected into space from beneath Europa’s surface as Cassini has been able to do for Saturn’s moon Enceladus. 

The request comes despite the recommendations a few weeks earlier of NASA’s Europa Science Definition Team.  They reviewed both the evidence for Europan plumes and the experience studying plumes erupting from Saturn’s moon Enceladus with the Cassini spacecraft.  Their recommendation was that a mission to Europa should be capable of exploring plumes if they exist, but that a dedicated focus on the plumes would not be appropriate. 

First of all, the team noted, only one observation made by the Hubble Space Telescope saw possible plumes.  Other searches for plumes by telescopes and by the Galileo spacecraft when it orbited Jupiter have not found unambiguous evidence for plumes.  (Some Galileo data is consistent with plumes but also have other possible explanations.)  Even if the Hubble did observe one or more plumes, they may occur at sporadic intervals separated by years or decades.  If so, they would be more like the sporadic eruptions of each volcano on Io than the so-far continuous eruptions seen at Saturn’s Enceladus.  A mission to Europa lasting a few years might entirely miss plumes if they sporadically erupt.

Second, Cassini’s observations of Enceladus’ plumes have shown the power of a diverse instrument set to characterize plumes.  Instruments already recommended for the ~$2B Europa mission concept could be used to search for and study any plumes.  A mass spectrometer, for example, could determine the composition of the gases expelled from the surface, while the thermal imager could look for warm spots that would be the source of the plumes.  A couple of instruments such as a UV spectrometer and a dust spectrometer that haven’t made the straw man list of instruments used for mission studies to date would enhance plume studies, but these instruments also would be useful for studying the rest of Europa.

The instrument request document acknowledges the science team’s assessment, but states that, “the scientific potential presented by the plumes is sufficiently high that NASA will continue to emphasize the importance of plume investigations and encourages instrument investigations focused on this area.”

Draft summary of findings by the Europa Science Definition Team regarding possible Europa plumes and planning for a mission to that moon.  Entire presentation available here.

While NASA’s management decides the scope of a Europa mission, engineers at JPL continue to refine the design of the current leading concept, the Europa Clipper that comes with an estimated cost of $2.1B.  The current concept would have the Clipper spacecraft make 45 dashes through the radiation fields surrounding Europa for close up looks at the surface and interior.  Building a spacecraft and instruments that can survive that radiation exposure is one of the factors that has driven the cost well above the $1B NASA’s senior managers would like to see.

A presentation made to the science team also provides more insight as to why a large number of encounters are required to study Europa.  The science team has carefully justified what measurements are needed at Europa to understand this world and to enable planning for a lander that would follow the Europa Clipper. 

As an example, the science team has stated a requirement that the composition of 70% of the surface be mapped at resolutions of  less than 10 kilometers by an instrument known as a short-wave infrared spectrometer.  With 45 encounters, this goal would be just missed with 68% of the surface mapped.  (Thirty flybys would map 50% at this resolution or better.)  Similarly, mapping 70% of the surface with an imaging camera at resolutions of 1 kilometer or better would require 38 flybys.  A global distribution of flybys to study the structure of the ice and ocean beneath the surface with an ice penetrating radar would not be met until 43 flybys. 

If the radiation belt did not exist, the next stage to exploring Europa would be to orbit it instead of frantically gathering data during numerous brief flybys.  (Europe, for example, will send the JUICE spacecraft to orbit Europa’s sister moon Ganymede, but that moon lies outside the harshest portions of the radiation belt.)  JPL’s studies suggest that a Europa orbiter would cost about the same as the Europa Clipper, but its lifetime would be so short that the Clipper with its many flybys would better study this moon.

We are left with contrasting opportunities for studying these two worlds.  Mars is close enough and benign enough that both China and private organizations can seriously consider challenging missions.  Europa’s location within harsh radiation belts leaves it as both a technical and a budget challenge.