Monday, March 23, 2015

Four Ideas to Bust the Floor on Outer Planet Mission Costs

In 1972 and 1973, NASA launched two simple spacecraft, Pioneer 10 and 11, to Jupiter.  They were charged with scouting the way for the more sophisticated spacecraft that would follow.  Since then, the outer solar system has been the realm of large, expensive missions: the Voyagers, Galileo, and Cassini.

Large missions costing well over $1B have proven very successful, but they are launched at the rate of approximately one per decade and outer solar system destinations have had to vie with Mars for these rare slots.

At last month’s Outer Planet Analysis Group, scientists and engineers presented three proposals in competition for selection in NASA’s cheapest category of planetary missions, the Discovery program.  One other proposal may eventually vie for a slot in NASA’s mid-range New Frontiers program. 

The road to lower costs outer planet missions has been paved by NASA’s first two New Frontiers missions, the $700M New Horizons mission en route to Pluto and the $1.1B Juno mission en route to Jupiter.  But can the cost of a mission to the outer solar system be cut to $450M, the limit for a Discovery mission?

The three Discovery proposals take very different approaches.

The Enceladus Life Finder (ELF) team proposes to take the tightly focused, minimalistic path. 

We now suspect that many of the icy worlds in the outer solar system harbor oceans beneath their icy crusts.  Among those bodies, Europa and Enceladus are special because their oceans appear to rest atop their rocky cores, providing access to elements and minerals believed essential to life.  These rocky surfaces are also are believed to have hot hydrothermal springs that could provide the energy needed for the complex chemistry needed to support life.  For other icy worlds, the oceans are sandwiched between layers of ice and not in contact with their rocky cores, making Europa and Enceladus priorities for exploring potentially habitable worlds.

Enceladus so far is unique in having plumes of water that steadily jet from its surface, spilling the contents of its ocean into space where they can be easily sampled by a passing spacecraft.  (Hubble Telescope observations suggest that Europa may also have plumes, but repeat observations have failed to confirm the initial sighting.  Any plumes may be episodic, repeating only every few years.) 

The Cassini spacecraft currently at Saturn has already sampled the plumes, but its instruments were designed in the 1990s, and weren't designed to study the highly complex molecules that could indicate life.  The ELF spacecraft would narrowly focus on sampling these plumes with modern, highly sensitive instruments. 

The mission would enter orbit around Saturn and then make ten flights through Enceladus’ plumes. ELF’s instrument payload would consist of two mass spectrometers that “weigh” atoms and molecules to measure composition.  The spectrometers would analyze particles in the plume that are a mixture of frozen ocean water and particles from the seafloor. One of the mass spectrometers would be optimized to study the liquids that originate from the ocean and the other the solid particles that likely originate from the rocky core.  A third instrument might be included that would test whether any amino acids found have predominately left- or right-handed structures.  (Life on Earth predominately creates left-handed forms, and it’s suspected that life that originates elsewhere will similarly favor one form over the other instead of a random mixture likely from abiotic chemistry.)  The spacecraft’s navigation camera also would image the plumes to judge their activity at the time of each flyby.

To appreciate the simplicity of the ELF proposal, you need to consider previous concepts for exploring Enceladus following Cassini’s last flyby late this year.  When Decadal Survey considered this decade’s priorities for exploring the solar system, several Enceladus options were considered.  The simplest would have been a multi-flyby spacecraft like ELF, but that would also have included two cameras and an ice penetrating radar in addition to the mass spectrometers.  The preferred mission would have studied Enceladus both during flybys and from orbit about the moon with a somewhat different, but equally rich instrument compliment.  These concepts would have generated volumes of data that would have investigated the structure of Enceladus, its ocean, and ice shell along with the chemistry of its internal ocean.  Unfortunately, the estimated costs of these missions were over $1.5B. 

(Quoted mission costs often vary based on the specifics of what’s included; in this post, I’ve tried to quote the costs for the items included the widely-quoted $450M cap for Discovery missions.  NASA’s final cost for a full mission including launch and operations would be higher than the costs I’m including here.)

The Io Volcano Observer would take a different tact than the ELF mission.  Like the proposed Enceladus mission, the IVO spacecraft would observe Jupiter’s volcano-rich moon during several flybys.  Unlike the Enceladus mission, the Io mission would carry four instruments – a two camera suite, a thermal imager, a magnetometer, a mass spectrometer – along with a student-built instrument to map volcanic hot spots.  The spacecraft’s radio system would do double duty by also allow precise tracking of the spacecraft’s speed during flybys to study the distribution of matter within this moon.  This would be a data rich mission, and the spacecraft would carry an experimental high data rate optical communications system in addition to the traditional radio system. 

While ELF would focus on one investigation – the chemistry of the ocean – IVO would perform an integrated series of studies to understand Io as a world and a member of the Jovian system.  The mission’s goals are divided between understanding the sources and extent of its intense volcanic activity, the effects of the injection of its volcanic plume material into the wider Jovian system, and long term monitoring of Europa for plumes and Jupiter’s atmosphere.  The nominal mission would last 22 months, but an extended mission might carry on for an additional 6 years to monitor Io through time.  If the extended mission occurred, then we might have three spacecraft simultaneously studying the Jovian system in the early 2030’s: IVO in a polar Jovian orbit with periodic flybys of Io, Europe’s JUICE mission with broad studies of the Jovian system and a focus on the icy moon Ganymede, and NASA’s Europa mission.

The third Discovery proposal takes an entirely different approach to exploring the outer solar system on a budget.  The Kuiper mission would launch a space telescope dedicated to studying the outer solar system.

The Kuiper proposal addresses two problems.  First, we cannot afford to have spacecraft at each of the major outer planets to observe their weather, their magnetospheres, and their moons.  This dedicated outer solar telescope would be able to examine each of these worlds multiple times each day to study these worlds as dynamic systems.  Scientists will be able to observe how storm systems in their atmospheres exchange energy, how variations in auroral activity provides clues to the state of their magnetospheres, and how volcanic and plume activities on the moons Io, Europa, and Enceladus vary over time. 

The second problem is that we don’t understand key questions about the formation of the outer solar system.  We suspect that the outer planets migrated during the early ages of the solar system, but there are competing theories as to whether that migration was smooth or more chaotic.  As the planets’ orbits shifted, they would have flung smaller bodies about.  The Kuiper telescope would analyze the spectra of thousands of small bodies ranging from Jupiter’s orbit to the distant Kuiper belt to analyze their compositions.  The mixture of compositions at different distances from the sun would allow astronomers to distinguish between the competing theories.

Telescopic observations have always played a crucial role in studying the outer solar system.  Earth-based telescopes, however, have key limitations – any solar system target is visible for only a few hours each day and our atmosphere blurs vision and blocks key wavelengths of light.  The science proposed for the Kuiper mission could be done by the Hubble Space Telescope, but its observing time is precious and little is allocated to solar system studies. 

The Kuiper mission would be smaller than Hubble (a 1.2 meter primary mirror versus the Hubble’s 2.4 meter mirror) but would be dedicated to observing the outer solar system.  The spacecraft would be parked in an orbit around the L2 Lagrange point beyond the moon where it could observe the sky without Earth occultations and would be beyond stray Earth light. 

In addition to the three Discovery mission proposals, a fourth mission concept was proposed, the LIFE Enceladus Sample Return.  A previous incarnation of this mission was proposed for the last Discovery competition but wasn't selected.  Like the ELF mission, the LIFE mission would make multiple flybys through Enceladus’ plumes and would use a mass spectrometer to study their chemistry.  Unlike ELF, the LIFE spacecraft would collect dust plumes in a fashion similar to that done by the Stardust spacecraft that collected comet dust samples in the mid-2000s.  The samples would later be returned to Earth where far more sensitive measurements would be made than could ever be done by instruments on a spacecraft.  The cost estimates presented by the LIFE team puts the mission outside the current scope of the Discovery program, and the team is building support to add an Enceladus sample return mission to the New Frontiers candidate mission list for the 2020s. 

After 2017, there are no plans to have a spacecraft operating in the outer solar system until the late 2020s at the earliest.  That decade gap will exist because outer planet missions in the past have had to be infrequent because of their costs.  The four proposals presented at last month’s meeting represent the planetary community’s attempt to find a new class of much lower cost missions that could fly more frequently.  The Kuiper telescope would be an entirely new approach to the problem that could begin providing data in the early 2020s.  The missions to Io and Enceladus face a tougher challenge because they propose to do missions for half the cost of any previous outer planet mission orbiter. 

Missions to both Enceladus and Io have been studied before, and the costs were two to four times that of the cost cap for Discovery missions ($450M).  Teams that propose missions are generally fairly open about the great science their missions would do if they are selected to fly.  These teams tend to be much more reluctant, however, to discuss the specifics of how they would accomplish their goals within the tight cost caps of a Discovery competition – that is their secret sauce.  The teams proposing ELF and IVO are seasoned veterans and their credibility gives me hope that the outer solar system may open to low cost missions.  We can assume that they have had a laser focus on finding ways to reduce costs to a fraction of what previous studies have assumed.  Estimating development cost, however, is always part art.  NASA will perform its own assessment of mission risks and costs, and its reviewers may be more risk adverse and conservative than the mission proposers in assessing likely costs and risks. 

For this Discovery competition, NASA’s managers have changed the rules in a key way that will help outer planet proposals.  In previous competitions, the costs of mission operations had to be included in the mission cap.  A mission to Mars with an operations lifetime of two to three years had an inherent advantage over an outer planets mission that might take five to seven years to reach its target and then require another year or two of operations.  Now NASA has excluded “reasonable” mission operations costs from the cost cap (which means it picks up those costs separately).  This goes a long way to leveling the playing field between inner and outer solar system Discovery proposals.

In the last Discovery competition, a mission to land on a lake in the north polar region of Saturn’s moon Titan made it to the list of finalists.  (The Mars InSight geophysical lander was the winner.)  If either ELF or IVO is selected this time, then outer solar system will have been opened to exploration by a new, low cost class of missions.  If neither mission is selected, then the experience learned from these proposals will become part of the community experience that is likely to sharpen future Discovery proposals for the outer solar system.  I believe that eventually an outer planets Discovery proposal will find the right formula for selection; I hope that this happens sooner rather than later.

You can read the original presentations for these proposals as well as the other presentations from the OPAG meeting here.

Saturday, March 7, 2015

Understanding why our most Earth-like neighbor, Venus, is so different

When I first learned about the solar system a few decades ago, the scientific consensus held that the structure of our solar system resulted from standard processes of stellar evolution.  The arrangement of planets with small rocky worlds closer to the star and gas and ice giants further out would be the normal arrangement of planetary systems.  Then we began to find planets around other stars and we learned that our solar system is – if not an oddity – by no means typical.  With just one example, it is easy to be led astray.

In our solar system, there are only two large rocky worlds, Venus and Earth.  Mercury and Mars are small enough that both lost most of their internal heat billions of years ago and they have largely ceased to further evolve.  (The ancient, preserved, surface of Mars is what makes it so attractive to explore for the types of habitable environments that were long ago erased from the Earth’s surface.)  Both Venus and the Earth, however, retain substantial heat in their cores.  That heat drives plate tectonics on our world and appears to have caused the near global resurfacing of Venus in the last few hundred millions of years (which counts for recent when compared to the age of the solar system).

While Venus and Earth have similar sizes and are solar system neighbors, they have evolved very differently.  Venus today lacks oceans, appears to lack plate tectonics, and has a massive carbon dioxide atmosphere that creates a greenhouse effect that makes the surface a hot hell.  Understanding why Venus and Earth became so different will help us understand why Earth evolved as it has and what the range of conditions for similarly sized worlds around other stars may be.  Venus provides the contrast to the Earth that can help us both better understand the origins of our world’s characteristics and the range of possibilities for similar sized planets orbiting other stars.

Cover page for the EnVision proposal.

Today, our knowledge of Venus’ surface and its interior is similar to our knowledge of Mars in the 1970s following the Viking mission.   The Soviet Union placed several probes on the surface that made simple measurements in the hour or so before the surface heat fried their electronics.  NASA’s Magellan spacecraft mapped the surface with radar in the early 1990s at about 120 m resolution globally.  We know, however, from our experiences mapping the moon and Mars’ surfaces that teasing out the details of geologic processes requires mapping surfaces with resolutions less than 50 m resolution with smaller areas mapped at a few meters resolution.

Mapping Venus’ surface (with one exception we’ll return to later) requires using imaging radars that can penetrate its thick cloud cover.  The technology in the early 1990s when Magellan flew was relatively new and crude by today’s standards.  Now imaging radars are widely used to study the earth both from airplanes and from satellites.  The technology is mature and relatively low cost. 

As a result, something of a cottage industry has grown up proposing new missions to map Venus either through the European Space Agency’s Medium Class program or through NASA’s Discovery program.  The different accounting rules applied by the two agencies make direct cost comparisons difficult, but these missions cost in the neighborhood of $500M to $600M.  A Venus radar mapping mission has been proposed for the current ESA Medium Class competition, and I hear that up to three missions are in competition for selection through the NASA program.

The European selection process tends to be more open than the U.S. process, and the EnVision team led by Dr. Richard Ghail at Imperial College London shared a copy of their proposal to ESA with me. 

Unfortunately, the EnVision mission will not move forward for the M4 competition.  From the team’s Facebook page: “ESA announced this morning that EnVision has been evaluated as 'incompatible with the technical and/or programmatic boundary conditions for the M4 Call'.  Essentially this means that ESA believe we would over-run on cost and/or schedule. We await further feedback which will inform our proposal to the M5 Call expected later this year.”

While EnVision is out for this current M4 contest, reviewing its proposal can still let us see what type of Venus mapping missions are being proposed.  The proposals to NASA’s current Discovery program will have differences from EnVision and the cost assumptions are different.  Also, ESA is expected to begin the competition for its 5th Medium Class mission later this year and there may be a larger mission budget.  The EnVision team hopes to propose this mission, perhaps with modifications, in the next competition.

To get a mission selected for Venus requires playing the long game.  Each competition that a team doesn’t win gives them feedback on how to improve their proposal. 

So let’s look at what a Venus mapping mission might look like using the EnVision proposal as are guide.

The EnVision mission would address several key questions:

  • The average age of Venus’ surface is just a few hundred million years old, a tiny fraction of the age of the surfaces of most rocky and icy moons in the solar system.  What processes resurfaced the planet?  Did they occur in the same time period or have they been spread over time?
  • Is Venus currently geologically active and therefore continuing to remake its surface and release new gases into the atmosphere?
  • What processes modify rocks once they are delivered to the surface?  Venus’ atmosphere is so thick that its surface in many ways is similar in terms of pressure to what is found at the bottom of our oceans.  This should lead to complex weathering and erosion, which is consistent with what we saw from the pictures taken on the surface by the Soviet Union’s Venera landers.
  • What is the internal structure of Venus like?  This is the part of a planet we can never see, but scientists can study it indirectly through the combination of Venus’s gravity field and surface topography.  Both were mapped by Magellan, but at too crude of resolutions to answer key questions.

To address these questions, the EnVision spacecraft would carry four instruments. 

These images, derived from radar imaging of Hawaii, show the improvement in resolution possible with modern radar systems compared to the data returned by the Magellan mission.  This image is from a poster describing a 2012 JPL VERITAS mission that was proposed for the NASA Discovery program.  Credit: JPL

The EnVision spacecraft’s primary instrument would be its VenSAR synthetic aperture radar.  Operating in its primary mode, VenSAR would map almost the entire planet in stereo at a resolution of 27 m.  The radar would produce both images (the equivalent of images from a camera) as well as high resolution measurements of the absolute elevation of the surface to map its topography.  VenSAR would have a number of special modes that would enable other forms of mapping.  Small splotches of the surface would be mapped with resolutions as fine as 1 to 2 meters, which would allow, for example, the instrument to spot the Venera landers on the surface.  An interferometric mode would enable EnVision to spot tiny changes in relative elevation in a location that could indicate movement from a seismic event or the swelling of a volcano.  By using different polarizations of the radar beam, the spacecraft will be able to map differences in texture across the surface to distinguish, say, a plain covered with rocks too small to image directly versus a plain covered in sandy material.

These figures show the improvement in topographic resolution possible with a modern radar instrument using data from Iceland.  The top image shows the equivalent Magellan resolution and the bottom image shows simulated resolution possible from a new Venus radar mission.  Credit: Decadal Survey White Paper, NASA

Example of the ability to detect geologic changes in vertical heights as small as a few centimeters.  This example is from an Earth-orbiting radar mission for changes following a terrestrial earthquake in 1992.  Credit: EnVision proposal, Fialko 2004; Peltzer et al. 1998.

Mapping mode
Prime mission
Extended mission
Stereo imaging
27 m
High resolution imaging
7.3 m
Spotlight imaging
1.15 m
Selected locations
Selected locations
27 m
63 m

Expected mapping coverage of Venus by the VenSAR instrument for the proposed prime and possible extended missions.  The Spotlight mode would be used for only selected areas such as the locations of the Venera landers.

The VenSAR instrument cannot see below the very top of the surface of Venus.  EnVision would carry a low frequency radar sounder whose beams would penetrate several hundred meters below the surface.  The result is a radargram that looks a bit like a sonogram or x-ray of the stratigraphy of the upper surface.  Two similar instruments are at Mars now, where they have examined the distribution of soils and ice at that world.  At Venus, this instrument would study the depths of lava flows and sedimentary rock layers and search for faults and folds that indicate past tectonic activity.

Example of subsurface stratigraphy revealed by a low frequency radar sounder for the Martian northern polar cap.  Credit:  NASA/ESA/JPL-Caltech/ASI/University of Rome/University of Washington St. Louis

The third instrument, the Venus Emission Mapper (VEM) would study Venus in an entirely different way than the radar instruments.  The Galileo and Venus Express spacecraft’s instruments discovered narrow spectral windows where thermal emissions can be transmitted through the otherwise opaque clouds.  These few windows would give the VEM instrument the ability to map thermal hotspots that would indicate areas of current volcanic activity, map differences in the composition of the surface, and detect changes in key atmospheric gases that could indicate the eruption of a gas-spewing volcano.  Because Venus’ thick atmosphere would scatter the light, the surface resolution of VEM would be low, around 50 km.  It could make, however, ground breaking measurements of the surface variation.  The recently completed Venus Express mission carried out some measurements using this technique, but its instrument wasn’t optimized for measurements using these spectral bands.  The VEM instrument would provide much more sensitive measurements.

The Venus Express mission carried out the first mapping of Venus’ surface using thermal emissions. Red-orange colors in this Venus Express image of Venus’ Idunn Mons volcanic peak indicate warmer areas suggesting different surface compositions and younger ages than surrounding material.  Credit: ESA

The EnVision radio system would be its fourth instrument.  By tracking minute differences in radio frequency caused by the spacecraft speeding up or slowing down as the mass of the planet below it varies, the spacecraft can study variations structure deep below the surface.

EnVision has been proposed for ESA’s fourth Medium-class scientific mission.  The ESA competitions pit proposals from across space science against each other, so the EnVision proposal will be judged against both other solar system missions as well as those that would study astrophysics and the Earth’s magnetosphere.  The next key milestone will come in the next month or two when ESA’s managers select several finalists for more detailed analysis.  If the EnVision mission is the final selection, it would launch in December 2024 and would arrive at Venus a few months later.  The prime science mission would take approximately two and a half years, although the team hopes that the mission would be extended for a second 18 month observing campaign. 

The Envision team expects to hear the result of the technical review of their proposal in a week or two (it’s a straight pass or fail). If they pass on the technical review, the proposal then goes through a science review stage with ESA expected to make the final selection of M4 candidates in May/June.  You can find more information on the proposal at their website:

When I read about proposals for most small-scale planetary missions (ESA’s Medium class, NASA’s Discovery class) their goals are often narrowly focused so that they can be met within a constrained budget.  In the last Discovery mission selection, several Venus mapping missions were proposed.  I’ve heard that each focused its science questions in different somewhat narrow ways that lead review panels to be confused about what the actual priority would be.  For me, the true value of a mission like EnVision is the breadth of its data.  Scientists could mine the data from a mission like this for many years and use the data to develop and then answer questions that we don’t yet know enough to ask.