Mars Versus Europa

Spaceflightnow.com had a recent article on the competition between Mars sample return and the Jupiter System mission for the next large NASA and ESA missions.  (The article primarily focuses on the Mars mission, but I'd like to explore the competition.)  Both missions are large: The sample return is likely to cost $6-7B while the combined costs to NASA and ESA of the Jupiter Europa and Jupiter Ganymede missions will be ~$4.5B.  The backers of a Mars sample return would like to see the three elements of the sample return fly in 2018 (the ExoMars rover and the sample cache rover, MAX-C), 2022 (an orbiter to carry the samples brought up from the surface back to Earth), and 2024 (a lander and ascent vehicle to deliver the sample to Mars orbit).  (I believe that the 2022 mission would have to enter development around 2018 in this scenario.)  The backers of the Jupiter system mission would like to see that mission fly in 2020.

The Spaceflightnow.com article and others (see Decadal Survey Showdown) have suggested that the two space agencies cannot afford both sets of missions.  The U.S Decadal Survey is seen as the body that will decide between the missions.  In this blog post, I consider whether it might be possible for both to fly without consuming the budget.

The ESA elements for the 2018 ExoMars rover are already budgeted, while ESA's Jupiter Ganymede orbiter (if chosen over two other missions) would be funded out of its large science mission budget.  Funding for subsequent ESA contributions to the sample return, would according to the Spaceflightnow.com article, require more money than is currently being budgeted for Mars exploration.

On the NASA side, there is room in a ~$12-13B (in current dollars) decade budget to fly both missions.  Doing so would consume most of that budget, probably crowding out all but a handful of low cost missions to other targets.  (And if these two large missions experience significant cost overruns, even those small missions may have to go.)

However, I wonder if there might be a sequence of missions that allows both to fly.  The currently discussed sample return mission series assumes that missions fly as quickly as budgets could allow.  Another option would be fly the 2018 sample mission and wait for its results to commit to the subsequent orbiter and lander/ascent vehicle.  The 2018 rover might crash on landing, become stuck in the mother of all dust pits for eternity, or simply fail to find compelling samples.  Committing to flying the subsequent sample return elements before the results of the 2018 mission are known would seem to commit NASA's resources to a single large program predicated on success in 2018.

An alternative might be to fly the sample cache mission in 2018 and the Jupiter Europa mission in 2020 (hopefully with their ESA counterparts).  The results of the 2018 mission should be known by 2020 or 2021, and then if compelling samples are safely cached, development of the subsequent missions could begin with flights in the later half of the 2020s.  (I don't know whether a decade or more waiting on the Martian surface would cause the cached samples to degrade.)  In this scenario, the NASA would need to commit $6-7B between the two missions, leaving room for a couple of New Frontiers and Discovery missions.  The majority of the remaining funds needed for the subsequent sample return elements would come from the following decade's budget.

It's easy to be an armchair mission planner.  There may be many reasons why this possiblity may be infeasible or unwise and there may be better alternatives.  The Decadal Survey may also conclude that it wants to recommend just one (or no) multi-billion dollar missions in the coming decade, eliminating the competition.  However, I have not seen a discussion of the question of whether or not results from the 2018 caching mission should be known before committing to the next sample return element.  I hope that the Decadal Survey will consider that question as it reportedly is considering whether to recommend either or both of these two large missions.

Why I Favor EJSM and Focused Exploration

As with all my editorials, I am not trying to convince anyone to my point of view.  No one on the Decadal Survey has ever heard of me, and my opinion counts for no more than any of the readers of this blog.  Rather, I find that reading a good editorial (and I hope my efforts are 'good') helps me focus my own thinking and reach my own conclusions.  So, with that in mind, here is one of the rare editorials on this blog.

In the next few months, the Decadal Survey will have to select missions to recommend for flight in the coming decade (2013-2022).  We have already been warned that sticker shock is coming and that fewer missions can be flown than advocates and scientists would hope.  At $3.2B and perhaps $4B with inflation and cost increases, the Jupiter Europa Orbiter would consume a substantial chunk of that ~$12-13B budget.  (ESA's Jupiter Ganymede Orbiter, if selected, would be paid for out of Europe's budget for its next large science mission.)  Perhaps most damning, funding EJSM would preclude funding for a flagship mission to Titan and Enceladus. 

My first reason for favoring EJSM is that it would explore three classes of important objects: (1) icy moons that may be habitats of life either in our solar system or others, (2) a large gas giant that is our best analogue for the many gas giants found around other stars, and (3) an intense magnetospheres that serves as a surrogate for other such structures in the universe.  The last two points speak for themselves, but I will expand a bit on the first point.  I believe that the ultimate exploration of an icy moon environment will be at Titan, but that world has such active surface processes that untangling its geologic history will prove difficult.  At Jupiter, we have four moons that provide case studies a range of tidally influenced moons (with Io and Callisto at the extremes) without the confusion of active surface processes.  Finally, Europa may be a habitat for life, and we should explore that potential with a highly capable spacecraft.

My second reason for favoring EJSM is that the JEO mission is ready to fly.  A decade of technology development and mission design has brought the mission to a point where risks are low.  We learned last year in the shoot out between EJSM and the Saturn Titan System Mission (TSSM) that the same was not true for concepts to explore the Saturn system (click here for the orbiter and here for the in situ elements). 

My final reason for favoring EJSM is the lesson learned from Mars exploration in the last decade.  At the Red Planet, we have learned that a series of highly capable missions can together bring a deep insight into a world or, in the case of Jupiter, a system of worlds.  NASA's JEO could be just the most capable of a fleet of craft that could also include ESA's Jupiter Ganymede Orbiter, Japan's magnetosphere orbiter, Russia's Europa lander, and possibly penetrators for Ganymede and/or Europa from another space agency.  Together, this flotilla would do for the Jovian system what a decade of missions have done for Mars.  What we learn from the Galilean moons will build towards our understanding of ice-ocean-rock moons including Titan and Enceladus.

Of these three arguments, I personally find the final most compelling.  We have done most of the easy missions for the solar system.  Significantly deepening our understanding of key worlds and systems will require focused exploration.  (Even if JEO turns out to be the only mission to fly to Jupiter, it is capable enough that it would count in my opinion as focused exploration.)  In the coming decade, I favor focused exploration on three and a half targets.  First, there will continue to be Mars which is likely to receive several orbiters from Russia, China, and ESA/NASA, 2-3 rovers, and possibly a network of science stations.  Second, could be the Jovian system.  And third, there could be Venus which could be the recipient of Russian and American landers, a European balloon platform, and several orbiters.  All in all, the next decade, thanks to the combined contributions of a number of space agencies, could see the in-depth exploration of the solar system expand from one target (Mars) to several.

The half target in my scenario would be the Saturn system.  Eventually, we need to return there with flagship class spacecraft.  I found the case laid out for a flagship class orbiter to take the global study of Titan to the next level in the TSSM study compelling.  Not only will a battery of instruments be required, but a high power communications system (which drives the need for a flagship class spacecraft) is essential to return the data stream.  However, there are, I think, a couple of low hanging fruits available for the Saturn system.  The first is Enceladus, for which a New Frontiers-class mission with with advanced instruments should provide a significant advancement in our understanding.  The second is in situ probes for Titan, which is about the easiest place in the solar system to land on or fly or float above.  The proposals in progress for a Discovery-class lake lander and a Discovery-class airplane suggest that in situ Titan probes could be within the budgets and technical capabilites of several space agencies in the coming decade.  The key problem for most in situ probes is the data communications challenge -- there simply isn't room within these probes to house the power systems and antennas to return large amounts of data.  So, I favor a New Frontiers class orbiter that would switch between focused Enceladus studies and relay duties for Titan in situ probes over the course of perhaps a decade or more in orbit around Saturn.

For the past year, I have closely followed the Decadal Survey process as well as the planning processes of other space agencies.  In this blog entry, I lay out the conclusions I've reached.  I hope that the readers of this blog will lay out their own or challenge mine in their comments.

Europa/Ganymede Penetrator

A conference on the  Europa Jupiter System Mission (EJSM) has just completed, and the presentations are a treasure trove of information on the proposed missions from three space agencies.  (The presentation from the fourth, the Russian space agency, has not been posted.)  The conference focused on the science questions and goals for these missions, and I recommend reading them (http://jakal.sp.ph.ic.ac.uk/EJSM/#Presentations)

This is the next to last post in a series that looks at the science of the EJSM missions (see Satellites, Jupiter, and Magnetosphere), with a focus on science other than that which would be done in orbit around Ganymede and Europa.  In this post, I’ll summarize the proposal for penetrators for Ganymede and Europa.  These are not the only lander concepts that are being investigated.  A conference was held last year to discuss lander missions that range from a very large Russian lander to small hard impact landers and penetrators.  I summarized these concepts in two blog posts (Russian Lander and Small Landers) or your can read the presentions at http://www.iki.rssi.ru/conf/2009elw/

At the more recent EJSM conference, presentations were given on the large Russian lander (not posted at the time I write this) and for a small penetrator that would be carried by the Jupiter Ganymede Orbiter and the Jupiter Europa Orbiter (see Europa Surface Element presentation).  The penetrator would weigh just 15 kg with 1 kg for science instruments.  The deorbit module for Ganymede would weigh 70 kg.  After achieving orbit around its target moon, the orbiter would release the penetrator, the deorbit module would perform the deorbit maneuver and orient the penetrator for impact.  Penetration into the surface would be a half to a full meter.  Polar landing locations would provide optimum data relay opportunities since the orbiter would pass over the poles each orbit but over each equatorial location just twice twice for every revolution of the moon around Jupiter. Surface lifetime for the penetrator would be just two orbits of the moon around Jupiter (~7 days for Europa and ~14 days for Ganymede).  [No explanation is given for why the Europa lander would not also operate for 14 days.  It seems unlikely to be due to radiation; the penetrator will have already been subjected to intense radiation while still attached to the orbiter.]

The scientific goals for the penetrator would focus on the internal structure of the moons, surface composition, and surface strength and mechanical characteristics.  The core payload would be a seismometer to study the internal structure of the moon, which would consume a third of the payload mass.  A number of other instruments could also be added.  One slide lists a possible instrument compliment that adds a mass spectrometer, accelerometer, thermal sensor, descent imager, and a magnetometer.  The slide notes that including the descent imager could pose problems for the other instruments sampling the surface.

Not discussed in this presentation is a possible enhancement that would essentially be a mini-probe carried within the penetrator that has received some publicity lately (see thermal drill article).  This would be a thermal drill that would melt and drill its way to depths as great as 10 m below the surface where the material should be free of chemical changes caused by radiation.  The unit would be a small, self contained package that would leave the body of the penetrator but remain connected by wires for power and communications.  A paper in Advances in Space Research is vague about what kinds of useful instruments could fit within the small body of the unit: “A melting system could sample waters which are transported into the instrument by the use of a micro-pump. A series of filters retains biogenic material, if present, for further analysis by an optical microscope, a chemical micro-laboratory or spectrometry.  Gases, as indicators of biological activity, could be acquired by this combination of heating and drilling... Current GCMSs are not suited to be integrated into the thermal drill itself (due to size), but could eventually be mounted inside the penetrator... A wet experiment was developed for the Deep-Space-2 penetrators and tested in impact trials.”

Editorial Thoughts: Penetrators would significantly enhance the science return from these missions, and I hope they will be flown.  As I understand it, neither ESA nor NASA are planning to pay for their development.  Their inclusion into the mission would require another national space agency to fund the development.  The presentation on penetrators was made by the Penetrator Consortium, a group of researchers located primarily in Britain.  (The site has several interesting presentations on penetrator concepts for various solar system targets.)

The presentation at the EJSM conference and those at the consortium website suggest that the primary focus for now is on a penetrator for Ganymede.  Analysis of for a Europa penetrator has several "to be determined" entries, with the key one probably being whether the penetrator's electronics could withstand the radiation dose as the orbiter maneuvers into Europa orbiter and then in Europa's orbit.  It's hard enough to design electronics that can withstand slamming into an icy surface.  Designing electronics that could also withstand the radiation may be too difficult.  However, the metal body of the penetrator would provide some shielding and perhaps additional shielding could be carried by the orbiter (think of the penetrator and deorbit module inside a box or tube mounted on the orbiter). 

Europa is a significantly smaller moon than Ganymede, and the deorbit module would be correspondingly smaller.  The JEO orbiter is reserving 100 kg of mass for a possible penetrator.  I wonder if the deorbit module might be enough smaller that JEO could carry two penetrators (assuming that the space can be found on the orbiter to house two penetrators).

And I am disappointed that there’s no mention of a surface camera.  I understand the problems of including a deployable mast in a small penetrator.  Still, it would be wonderful to see Jupiter in the sky above these moons.

Jovian Magnetosphere Science from EJSM

Across the universe, plasmas are the dominant form of baryonic matter (that is the particles that make up the universe we can see and touch).  Many missions have been flown to investigate the (magnetic) fields and (charged or ionized) particles within them, both around our own planet and around the sun and other planets.  This blog entry continues the series that looks at contributions that the Europa Jupiter System Mission can make beyond the studies of the primary targets, Europa and Ganymede.  Although this entry will touch upon those worlds since understanding the magnetic and radiation fields at those two moons are key to exploring them.  The interaction of these moons with Jupiter's magnetosphere is a key method to explore their interior oceans, and the radiation delivered to Europa's surface may be a key source of energy to create the organic compounds that might enable life within its ocean.

Slides are from a presentation given at the last OPAG meeting in February (http://www.lpi.usra.edu/opag/feb2010/presentations/KruppEJSMSynergisticScience.pdf).

Before I get too far into the topic, I'll be the first to admit that I lack the training in physics to properly understand this field, so I apologize if I don't go into depth (and for any mistakes I make).  This is also not a topic that receives a lot of public attention.  There's no pretty pictures (beyond auroras) and little that we can compare to our everyday lives.  However, Jupiter offers an extreme laboratory to study magnetospheres and their plasmas.  To quote from Wikipedia (http://en.wikipedia.org/wiki/Jupiter#Magnetosphere and http://en.wikipedia.org/wiki/Magnetosphere_of_Jupiter):

"Jupiter's broad magnetic field is 14 times as strong as the Earth's... making it the strongest in the Solar System (except for sunspots). This field is believed to be generated by eddy currents — swirling movements of conducting materials—within the metallic hydrogen core. The field traps a sheet of ionized particles from the solar wind, generating a highly energetic magnetic field outside the planet — the magnetosphere. Electrons from this plasma sheet ionize the torus-shaped cloud of sulfur dioxide generated by the tectonic activity on the moon Io. Hydrogen particles from Jupiter's atmosphere are also trapped in the magnetosphere."

  "The action of the magnetosphere traps and accelerates particles, producing intense belts of radiation similar to Earth's Van Allen belts, but thousands of times stronger. The interaction of energetic particles with the surfaces of Jupiter's largest moons markedly affects their chemical and physical properties. Those same particles also affect and are affected by the motions of the particles within Jupiter's tenuous planetary ring system. Radiation belts present a significant hazard for spacecraft and potentially to humans."

Both NASA's Jupiter Europa Orbiter and ESA's Jupiter Ganymede Orbiter will carry advanced sets of instruments for studying magnetic fields and their plasmas such as megnetometeris, plasma/energetic particle packages, UV spectrometers, plasma wave instruments, and ion/neutral mass spectrometers.  The JGO spacecraft may also carry an energetic neutral atom (ENA) camera (http://en.wikipedia.org/wiki/Energetic_neutral_atom) to image particles within the magnetosphere similar to the instrument carried by the Cassini spacecraft at Saturn.

The true power of the mission, though, comes from having two spacecraft in orbit around Jupiter at the same time that can measure conditions at different places within the magnetosphere.  That capability may be substantially enhanced with the addition of a dedicated Jupiter Magnetospheric Orbiter supplied by the Japanese JAXA space agency.

This is the third in a series of posts that look at the science of the EJSM mission.  You may also want to check out EJSM Jupiter Science and EJSM Satellite Flyby Science.

EJSM Jupiter Science

Two previous blog entries (see Overview and Satellite Flyby Science) have looked at the science that the Europa Jupiter System Mission (EJSM) could perform prior to the two spacecraft entering orbit around Europa and Ganymede.  This blog entry looks at the science that could be performed by observing Jupiter itself.  The material for this discussion is drawn from the Jupiter Science and Capabilities on the Europa Jupiter Science Mission presentation made at the last OPAG meeting in February.  The presentation focuses on science that could be performed on the visible outer layers of Jupiter, including the weather layers with their swirling cloud decks.

To provide new science, the EJSM mission must build on results provided by past and planned missions.  Four spacecraft with instruments suitable for observing this world's weather have conducted studies: the two Voyager spacecraft, Cassini, and New Horizons.  All were limited by short observation times and except for Cassini possessed either 1970s technology instruments or instruments not optimized for gas giant observations.  The Galileo craft orbited Jupiter for a number of years, but it suffered from both 1970s vintage instruments and a malfunctioning antenna that severely crippled planned observations of Jupiter.  The Galileo probe did successfully enter Jupiter's atmosphere and provided irreplaceable composition measurements that, unfortunately, were not fully typical of the planet since the the probe entered a hot spot, which is the equivalent of a Jovian desert.  Key measurements of water and clouds could not be made.  In addition to these past missions, by the time EJSM arrives in the mid 2020s, the Juno orbiter will have completed its studies of the bulk composition of Jupiter and structure of the planet below the cloud tops.

The EJSM mission would bring several new capabilities to the study of Jupiter:

• Modern instruments that span the spectral range from 70 nanometers (ultraviolet) to 2 micron (mid-infrared)
• Multi-year observations with large data storage systems and high bandwidth communications systems
• Two spacecraft that can study the clouds decks at different times and at other times observe the same features to produce 3D images
• Two spacecraft that can probe the atmospheric structure by tracking each other's radio signals as they pass behind Jupiter as viewed from each other

A science working group identified three key science objectives: atmospheric dynamics and circulation, atmospheric composition and chemistry, and atmospheric vertical structure.  Some of the more detailed questions that struck me as particularly interesting (and you can read the entire list on pages 19-21 of the presentation) included:

• Investigating the dynamical of the weather layer to understand the redistribution of energy and momentum (particularly interesting on a world where a solid surface doesn't steal energy from wind systems)
• Coupling of the weather layer patterns with the deep interior
• Study localized variations in atmospheric composition
• Determine the 3D structure of Jupiter's atmosphere from deep within the clouds to the upper troposphere

The strawman payload of the NASA Jupiter Europa orbiter (JEO) would provide a range of resolutions (quoted resolutions are from 9.5 Jupiter radii):

• 7km/pixel from the narrow-angle camera
• 70km/pixel from the medium-angle camera
• 170km/pixel from the near-IR spectrometer
• 700km/pixel from the wide angle camera and UV spectrometer
• 1700km/pixel from the thermal

The planned orbits for the two craft would place perijove on the sunlit side of the planet.  These means that for the majority of each orbit, the instruments would view the night side of planet.  As a result, most of the atmospheric observations would take place in the three days centered on each perijove when the sunlit Jupiter would be visible (which represents approximately 10% of the time).  During this time, both contextual images and hundreds of narrow angle camera images would be taken to produce nearly 25GB of data per orbit.  A key strategy would be to repeatedly image the same locations on the cloud deck in multiple wavelengths to track evolution of cloud structure across the daytime and between days.

The current strawman instrument list and mission orbits are optimized for studying the Galilean moons, not the atmosphere of Jupiter.  The science working group identified a number of areas in which the mission could be enhanced:

• Optimize the spectral coverage of the instruments to observed key wavelengths to probe structure and composition
• Improve spatial resolution of the near-IR and UV spectrometers
• Add instruments specifically designed for probing Jupiter's atmosphere including a mid-to-far IR (5-500 microns) spectrometer and a sub-mm (500-1000 micron) spectrometer on the NASA spacecraft and a thermal imager on the European spacecraft
• Consider lengthening the orbital tour so that the apoapses of later orbits could lie on the daylight side of Jupiter for more observing time

Even without these enhancements, the EJSM mission would provide a major advance in our understanding of Jupiter and by extension the gas giants that have been found orbiting other stars.  Where Juno will focus on the interior of Jupiter, EJSM will focus on the top-most levels of the atmosphere.  In the words of the presentation, "Together, EJSM and Juno would provide the tools to significantly enhance our understanding of the fundamental physical processes in gas giant atmospheres... A long baseline of high resolution observations would allow us to construct a Jupiter 'climate database' to inform detailed physiochemical models of the atmosphere and the coupling processes between layers."

EJSM Satellite Flyby Science

Mercury as imaged from the MESSENGER spacecraft in January 2008.  2.8 km/pixel resolution at the equator.

This week's blog entry continues looking at the science the Europa Jupiter Science Mission (EJSM), which could consist of at least NASA's Jupiter Europa Orbiter and possibly ESA's Jupiter Ganymede Orbiter. (See this blog entry for the introduction to this series.)  Both missions still face a selection hurdle.  JEO must be prioritized by the Decadal Survey and JGO must win out in a selection against two astronomy missions.

Prior to entering orbit around their namesake moons, both craft would perform a number of flybys of the Galilean moons.  Messenger's flybys of Mercury and Cassini's flybys of Saturn's moons have shown what modern spacecraft with modern instruments can do from quick encounters.

JEO and JGO would bring three key assets to a tour of the Galilean moons:

• They would have working antennas to return torrents of data compared to the trickle of data from the Galileo orbiter with its crippled antenna
• They would carry instruments new to studying icy moons including laser altimeters and ice penetrating radars
• They would have modern instruments that would be three decades more advanced than the instruments carried by Galileo

Perhaps the single greatest accomplishment these craft could perform would be to extend our high resolution coverage of these moons.  This map shows the resolution of the current coverage for Ganymede following the Voyager and Galileo missions:

The next map shows the resolution of coverage that would be possible from the current, nominal JEO mission, which may well be improved as mission design progresses:

The strips of high resolution coverage would be the ground tracks beneath JEO as it makes its closest approach.  The JEO instruments would be designed to capture data as the craft orbits Europa, and this ability to acquire data rapidly apparently would be employed to provide very high resolution images beneath the ground tracks during flybys.  The cameras would also be able to acquire images at greater ranges (and lower resolutions), much as the Cassini cameras have for Saturn's moons.  Certain instruments, such as the laser altimeter and ice penetrating radar, however, would operate only during closest approach.

The following chart shows the coverage the nominal JEO mission would provide for each moon from the flybys.  IPR is the ice penetrating radar and LA is the laser altimeter.

Of the two craft, JEO would have the more capable instruments (part of what the ~$3B JEO price buys compared to the ~$1.2B JGO price).  The following two maps show image coverage of Callisto following JEO's nine and JGO's fifteen flybys of Callisto:

The flyby science campaign would provide incredible advances in our understanding of these moons.  However, it is important to place the return in perspective.  The orbital geometry of the missions mean that the high resolution coverage occurs over only a single hemisphere for each moon.  It is my understanding that with time, the orbital geometries could be changed to view the opposite hemisphere and the science analysis group as asked if this could be reasonably done.  I expect that it is a tradeoff between more science from flybys versus the risk of the craft not surviving for their prime missions in orbit about their respective moons.

Multiple flybys also aren't a substitute for studies from orbit to understand the processes that have formed moons.  An orbiter can image the entire surface in high resolution and selected portions in very high resolution.  Certain instruments crucial to understanding the structure of the surface and interior such as the laser altimeter, ice penetrating radar would gain relatively little from flybys (see how limited the ground tracks would be in the chart above), but could provide global coverage from orbit.  Should NASA and ESA decide not to fund Galilean satellite orbiters, a Cassini-like spacecraft could substantially enhance our knowledge of these moons, but future orbiters would still be needed in the future.  For comparison, imagine if instead of orbiters around Mars, we had only a dozen flybys of that world by Cassini.  We would have global maps of what was there, but likely only a limited understanding of the processes that created the surface.

It's also reasonable to speculate how the missions might change if only one of the craft eventually flies.  JGO would not be designed to handle the radiation fields inside the oribit of Ganymede, so it would be difficult for it to add significantly to our knowledge of Europa and Io.  The JEO mission, however, could be lengthened to provide additional flybys of Callisto and Ganymede to extend high resolution coverage.  In theory, additional Io flybys could also be done, but the tradeoff there would be the additional radiation exposure that each of those flybys would cause.

References:

All images except the opening Mercury image are from these two presentations made at the last OPAG meeting:

NASA-ESA Outer Planet Flagship SDT
Ron Greeley, Arizona State University
Olivier Grasset, Université de Nantes


EJSM Satellite Science
David Senske, Jet Propulsion Laboratory

Note: Jason Perry has excellent summaries of what JEO could do during its flybys of Io at 

Io Science with EJSM

Io Science with EJSM Part Deux

Io Science with the Jupiter Ganymede Orbiter

Animation of the Jupiter Europa Orbiter's Four Io Flybys

JEO & JGO Jupiter Science - Overview

The two spacecraft planned for the Europa Jupiter System Mission -- NASA's Jupiter Europa Orbiter (JEO) and ESA's Jupiter Ganymede Orbiter (JGO) -- will focus on in-depth studies of those two moons with intensive studies conducted from orbit around their respective targets.  Both craft will spend 2-3 years in orbit around Jupiter before settling into their final orbits around their destination moons.  During that time, they can replicate science that Cassini has been performing for the Saturn system.  Jupiter has already had one orbiting spacecraft, Galileo, but it had mid-1970's technology instruments and a crippled antenna that reduced the data return to a bare trickle.  These two planned missions will have 2010's technology instruments and high data rate X-band and Ka-band communications.

This is the first of several blogs that will look at the science these two missions can perform prior to their ultimate investigations in orbit around their respective moons.  The missions studies that previously have been carried out focused on the studies from orbit, with only minimal attention to studies of the moons from flybys and of Jupiter from orbit.  That is beginning to change as the missions undergo further definition.

I believe that looking at what these missions can do prior to their Europa and Ganymede orbit science campaigns is instructive for three reasons.  First, both missions can carry out synoptic studies of the weather of Jupiter.  The Juno mission will study the interior of Jupiter and the weather in slices that will be tiny both in spatial and temporal coverage.  These two follow on missions can study the entire planet's weather for years.  Second, Io and Callisto will be studied only from flybys and distant observations.  The MESSENGER flybys of Mercury has shown what kinds of science can be performed by a modern suite of instruments.  And third, the present mission concepts are not guaranteed to fly.  NASA's mission is subject to prioritization by the Decadal Survey.  ESA's mission is in competition with two attractive astronomy missions for funding.  Supply problems for NASA with plutonium-238 to power their craft may force a radical restructuring of the mission with the result that more focus goes to remote studies.

The February OPAG meeting had several presentations on planning for the current mission concepts, with greater focus on NASA's mission (OPAG is a NASA-chartered group).  The presentations state that the current mission designs are preliminary and have had limited attention.  They suggest that the oribital tours are likely to be considerably refined as mission definition continues.

Click on any image for a larger version.

Currently envisions mission timelines. (From http://www.lpi.usra.edu/opag/feb2010/presentations/GreeleyEtal.pdf)

Example JEO tour showing satellite encounters and distance and phase angles from Jupiter.  This tour design includes an Io science campaign (four science flybys) and a system science campaign that includes numerous remote observations of Jupiter and Io as well as flybys of the other Galilean moons.  JEO will also conduct magnetospheric studies (not shown). (From http://www.lpi.usra.edu/opag/feb2010/presentations/GreeleyEtal.pdf)

Example JGO tour with Ganymede and Callisto flybys and extensive monitoring of Jupiter and the magnetosphere. (From http://www.lpi.usra.edu/opag/feb2010/presentations/GreeleyEtal.pdf)

Example activities for one JEO orbit that includes a flyby of Ganymede and remote monitoring of Jupiter and Io.  The JEO and JGO spacecraft will be able to probe the atmosphere of Jupiter by tracking each other's radio waves as they pass behind Jupiter as seen by the other craft.  (From http://www.lpi.usra.edu/opag/feb2010/presentations/LockScienceScenarioModeling.pdf)

A science definition team (SDT) has been looking into issues relating to the current mission design.  Some items they suggest for further consideration include:

• Could the orbital tours be modified so that the apoapsis of some orbits occur on the day side of Jupiter?  This would allow exploration of additional portions of the magnetosphere and allow longer observations of the daylit side of Jupiter. 
• Can the orbital inclination be increased to allow observation of Jupiter's poles, the rings, and better coverage of the magnetosphere?

Editorial Thoughts: Either of these missions has the potential to do considerable Jupiter system science.  That science could be considerably enhanced if the Jupiter tour prior to beginning the orbit of the their target moons was extended.  This has been propsosed for JEO if the JGO mission were to launch later than expected.  The synergistic science opportunities with two orbiters is great enough that NASA is willing to consider lingering longer in orbit around Jupiter to wait for JGO rather than rushing to orbit Europa.  Should the JGO mission not be selected, extending the JEO Jupiter tour would make good science sense.  An extra year or two could enable a number of additional flybys of Ganymede and Callisto to partially make up the loss of the science from the JGO mission.  However, NASA has to balance this against the increased risk of a malfunction on the JEO craft if it delays its final science campaign at Europa.