Friday, July 24, 2015

Discovery Proposals to Explore the Solar System’s Smallest Worlds

Minor corrections were made to the previous version of this post. Launch for the selected mission will need to happen by the end of 2021, not 2020.  Also, one previous space telescope, the Kepler mission to search for planets around other stars was also selected under the Discovery program although it was later moved to NASA's astrophysics program.

This summer, NASA’s managers are in the delightful position of having a tough choice to make. 

For the space agency’s lowest cost planetary missions, known as Discovery missions, NASA’s managers ask the planetary science community to propose the missions they’d like to see fly.  Any solar system body except the sun and Earth (both covered under other programs) can be targeted.  (Missions to study planets around other stars are also funded through other programs.) There’s a strict cost cap of $450M for the spacecraft and instruments, with the agency separately picking up other costs such as the launch and mission operations. 

The competitions are extremely competitive, with a single mission selected every few years from what’s typically a field of 25 to 30 proposals.  Because it’s common to resubmit proposals in the next competition, in the past, proposers often have been reluctant to even give the names of their missions and only a few released any details of the concepts.  Why give your competitors ideas for their next proposal?

For the Discovery competition in progress, the thirteenth, that near silence has been broken and most teams have published or presented summaries (and in at least one case, nearly a full description) of their proposed missions.  We now know at least the names and destinations for 24 of the 28 proposals.  I am delighted with the creativity and quality of the ideas.  I suspect that NASA’s managers are equally impressed and find themselves having to make a tough choice this summer among a number of top-notch proposals.

Images of all the comets and asteroids imaged by spacecraft except the much larger Vesta and Ceres.  The moons of Mars also are not shown.  Credit: Montage by Emily Lakdawalla. Data from NASA / JPL / JHUAPL / UMD / JAXA / ESA / OSIRIS team / Russian Academy of Sciences / China National Space Agency. Processed by Emily Lakdawalla, Daniel Machacek, Ted Stryk, Gordan Ugarkovic.
  
My understanding of the selection process is that each proposal is evaluated twice for the initial round of selection.  First, teams of scientists review the scientific merits of the proposals and rank them.  Second, teams of engineers review the proposals for technical feasibility and likelihood of be able to be built within the cost cap.  The very few proposals that receive top scores in both evaluations become eligible to be selected as finalists that receive funding for a year to more fully develop their concepts (typically three proposals in recent competitions).  Approximately a year later, NASA’s associate administrator for science makes the ultimate selection from among the finalists.  Launch of the selected mission is expected by 2020.

The openness of the proposing teams for the current competition allowed James Callahan to publish brief summaries of most of the proposals.  I’ve published fuller descriptions for the four proposals for missions to study the outer planets, as well as more detailed descriptions of a proposed mission to a metallic asteroid and a mission to remap Venus with modern instruments.  (While the latter focused on a European proposal for their own mission competition, at least two teams reportedly have submitted similar proposals for the current Discovery competition.)

At a meeting of the Small Bodies Assessment Group at the end of June, scientists proposing missions to the solar system’s comets and asteroids gave 10 minute summaries of their proposals.  In this post, I’ll report on the concepts presented.  

The key to thinking about the small body Discovery proposals is to understand how diverse these worlds are.  They lay scattered from the inner solar system to the edge of interstellar space.  Some are rich in volatiles and are commonly called comets.  Some are almost all rock and are called asteroids.  Some (like Ceres where the Dawn spacecraft now orbits) are mixtures of both and we don’t yet have a good name for them.  Within these broad classes of objects, they show tremendous diversity in size, shape, and composition. 

To understand the clues these bodies provide on the solar system and its formation, we need to explore a few of them in depth to tease out their subtle details.  We also need to observe many more with less detail to build up a statistical understanding of their diversity.  Each of the small body Discovery mission proposals plays to one or the other of these strategies.

Comet missions

Depending on how you define a comet, either three or four teams propose missions to rendezvous with a comet and explore their target in depth.  Several spacecraft have made quick observations of comets during the minutes surrounding closest approach during high speed flybys.  The Rosetta spacecraft and its lander Philae are currently conducting a lengthy in-depth exploration of comet 67P/Churyumov–Gerasimenko.

All four of the Discovery comet missions would rendezvous and then orbit their comet for long-term studies.  Unlike the Rosetta spacecraft, these missions would carry just a few selected instruments for focused studies.  The Rosetta mission has cost approximately 1.4 billion Euros (~$1.5B) and carries 11 instruments on the orbiter and another ten on its Philae lander.  To fit within the $450M cost cap of a Discovery mission, these missions have to carefully target just one or two questions with as few as two instruments.

Comet Hartley 2 imaged during a brief flyby by the EPOXI/Deep Impact spacecraft.   Credit: NASA/JPL-CALECH

Interestingly, two missions propose to study the same comet, the 2.3 kilometer long Hartley 2 that was previously visited by the Deep Impact EPOXI spacecraft during a brief flyby in 2010.  The choice of the target may owe partially to the chance alignment of its orbit with Earth around 2020 allowing an easy flight.  However, the comet itself is interesting with highly active jets emitting water vapor from one part of the surface and carbon dioxide and ice from another.  Both the CHagall mission and the Primitive Material Explorer would orbit the comet and study the structure and composition of its surface with cameras and an infrared spectrometer.  A mass spectrometer would taste the gases jetting from the surface to analyze their composition including measuring the fractions of key isotopes that provide compositional clues to the formation of the solar system.  The CHagall spacecraft would place small explosive charges on the surface to expose fresh subsurface material.  The PriME spacecraft would carry an additional ion and electron spectrometer to further analyze the material emitted from the comet.  While the primary science questions for the Chagall are to understand the formation and heterogeneity of comets, the primary question for the PriME mission is to determine whether comets such as Hartely 2 could have delivered water to the Earth. 

In the last Discovery competition, a mission proposal similar to CHagall, CHOPPER, was the one of the three finalists (but not chosen).  PriME, too, competed last time, and while the mission was not a finalist, its MASPEX mass spectrometer was funded for further development.  MASPEX was selected for NASA’s mid-2020’s Europa mission and is proposed to be included by several of this Discovery competition’s proposed missions.

The Proteus mission would visit 238P/Read, a small body within the asteroid belt that behaves like a comet and are known as main belt comets.  The spacecraft would make slow flybys past this 0.4 km radius world before entering orbit.  This mission would carry just two instruments, a copy of the Dawn spacecraft's camera and the MASPEX mass spectrometer.  Like the PriME mission, this mission would focus on determining whether comets like this could be the source of Earth’s water as well as seek clues in its composition as to where it formed in the solar system.

The final comet mission would also orbit a comet, this time 10P/Tempel 2 (which should not be confused with the more famous Tempel 1 comet that has had two spacecraft flybys).  This mission, though, carries no instruments to measure composition.  Its focus is on the structure of the comet from its surface to its center.  A camera (another copy of the DAWN instrument) would map the surface morphology, and an infrared imager will study how the surface heats and cools to determine its properties (for example, a hard solid or a fluffy dust pile).  The main instrument, as the mission’s name – the Comet Radar Explorer (CORE) – suggests would be an ice-penetrating radar that would see into the depths of the comet to give it the equivalent of a CAT scan.  The data would allow scientists to determine how the comet came together (large chunks or small snow balls) and would map the distribution of ices, rocky material, and voids.  (Similar ice penetrating radars are operating on two spacecraft at Mars, and the JUICE and Europa missions will use them to study Ganymede and Europa next decade.)

Asteroid orbiters

Scientists are proposing four missions that would orbit asteroids ranging from those in near Earth orbits to asteroids that share an orbit with Jupiter.  The Binary Asteroid in-situ Explorer (BASiX) shares similar goals with CORE – understand the structure of a tiny asteroid (1.7 km 1996 FG3) at its tinier (0.5 km) moon.  Both bodies are likely aggregates (a nice way to say rubble pile), but scientists are unclear as to how they form, how they are structured, and how they have changed through time.  While larger bodies have substantial gravity to hold them together, these are worlds of microgravity.  The BASiX spacecraft would image these worlds, measure the surface properties with thermal imaging, and study the interior through gravity studies.  Small explosive pods along with geophones would be placed on the surface to study the interior from the seismic waves created by the explosions.

Credit: Peter Rubin/JPL-CALTECH.

If tiny worlds are rubble piles, the Psyche mission could explore the opposite end of the spectrum – a metal asteroid that may be the solid remnant core of a shattered proto world.  The deep core of our world, the other terrestrial worlds, and the larger asteroids remains hidden beneath layers of rock.  One or more ancient impacts may have blasted these layers off the surface of the asteroid 16 Psyche.  This mission’s spacecraft would image the surface, map its composition, and study the interior through gravity studies.  Its scientists may find the intact core of a young world, a core broken into a rubble pile, or a metal world that formed directly through accretion without a rocky surface.  One of the primary goals of this mission will be to determine what this world is and what it can say about the formation of the interior of larger rocky worlds.

The Advanced Jovian Asteroid Explorer (AJAX) spacecraft would journey beyond the asteroid belt to the Trojan asteroids that share Lagrangian orbits with Jupiter.  Scientists have two theories about how these asteroids formed, which based on their colors are different than other asteroid populations.  The Trojan asteroids may have formed from the same cloud of dust and gas as Jupiter.  Or, thanks to the planetary migration in the early solar system, they may have formed from beyond the orbit of Neptune and later been captured into their present orbits.  Either way, they could tell us much about conditions in the outer solar system early in its history.  AJAX would orbit a 32 km diameter D-type Trojan asteroid (I didn’t catch the name) and map its surface morphology and composition.  It would also place a lander with mobility (a hopper? a wheeled rover?) on the surface for more precise composition measurements.  The mission also has an option to flyby a second Trojan asteroid.

The mission proposal for which I have the least information is the Dark Asteroid Rendezvous (DARe).  No slides were presented at the SBAG meeting.  It would orbit multiple asteroids – it’s not clear if these are near-Earth or in the main belt or both – that are the rarer and likely more primitive D- and P-Types.  The spacecraft would carry copies of the DAWN cameras (this design is popular), instruments to map composition of the surface, and a radar.

Martian Moons

Phobos as viewed by NASA’s Reconnaissance Orbiter.  Credit: NASA-JPL/CALTECH

Mars’ two tiny moons, Phobos and Deimos, are favorites for Discovery competitions (and their European counterpart) for several reasons.  First, there is the mystery of their origin.  Are they captured asteroids (in which case their color suggests they may be rare primitive bodies)?  Are they material left from the formation of Mars?  Or are they material blasted into orbit from asteroid strikes on Mars’ surface?  Any of these choices makes them interesting scientific targets.  A second reason for the interest is that these moons may serve as initial targets for human exploration as we build the skills and technologies to enable missions to the surface of Mars.  And third, transits to Mars and therefore its moons are relatively easy.

For this competition, three teams are proposing missions to these moons using three distinct strategies.  The Phobos and Deimos and Mars Environment (PADME) would be a small spacecraft that would orbit Mars and make 16 flybys of Phobos and 9 of Deimos.  The craft would carry a suite of cameras that would take images with resolutions as small at 2.8 centimeters to study fine scale features and the processes that formed them.  During the flybys, a neutron spectrometer would remotely measure surface composition while a mass spectrometer would directly measure the composition of surrounding dust particles ejected from the surface.  Tracking the radio signal during flybys would provide information on the gravity field and therefore the interior structure of the moons.

The Pandora mission, in contrast, would use a solar electric propulsion system (similar to that used on the DAWN spacecraft currently at the asteroid Ceres) to enable it to orbit each of the moons for extended studies.  The Pandora mission would use cameras, a near infrared spectrometer, and a gamma ray neutron spectrometer to remotely study the surface as well as radio tracking.  Unlike PADME, Pandora wouldn’t carry a mass spectrometer to directly measure the composition of dust ejected from the surface.  That type of measurement requires high relative speeds so that the dust vaporizes on impact with the instrument to enable the composition to be determined.  PADME’s flybys would provide the relative speed necessary while Pandora’s slower relative motion in orbit likely would not.  This is an example of the types of tradeoffs that mission proposers must make – PADME’s simpler mission design enables a valuable measurement while Pandora’s mission design enables longer and more detailed measurements with other instruments.  (This mission proposal is in many ways similar to NASA’s possible 2020s Mars orbiter that also would use solar electric propulsion.  On its way to its close in orbit around the Red Planet, NASA has discussed that its future Mars orbiter could visit and orbit Deimos and Phobos.  The Pandora team would transfer their spacecraft to the Mars program at the end of their mission.  However, the Pandora spacecraft would lack the ultra-high resolution camera and atmospheric instruments that the Mars program would want for a dedicated mission.)

Deimos as viewed by NASA’s Reconnaissance Orbiter.  Credit: NASA-JPL/CALTECH

The final mission proposed for these moons, the Mars-moons Exploration, Reconnaissance, and Landed Investigation (MERLIN) makes a different set of tradeoffs.  Remote composition measurements are less precise than those that a landed spacecraft can make.  The MERLIN team proposes to carry just a camera, a simple dust counter, and its radio tracking system for remote studies done during flybys past Deimos and in orbit around Phobos.  However, the spacecraft would land twice on Phobos in areas that appear to have different compositions (the so called blue and red materials).  There it would use a small arm, much like the rovers on Mars have, to put two additional instruments directly in contact with the surface for detailed study of its texture and elemental composition.  With this proposal, richer global studies from flybys and orbits are traded off for more detailed studies at two locations on the surface.


Asteroid Surveys

All of the mission discussed above would study just one or two (it’s not clear how many asteroids DARe would orbit) comets or asteroids.  Surveying larger populations of asteroids through close flybys would give us a look at a greater variety of these bodies.

The Main-belt Asteroid and NEO Tour with Imaging and Spectroscopy (MANTIS) spacecraft would fly by nine asteroids (two of which are binary systems so two extra bodies are thrown in for free) that orbit near Earth and in the main asteroid belt.  The targets were chosen (subject to the laws of astrodynamics and fuel constraints) to sample a range of asteroid sizes and compositions.  The spacecraft would carry a narrow angle camera, a near-infrared imaging spectrometer, a mid-infrared multispectral imager, and a dust instrument.   (It’s not clear if the last simply counts dust particles thrown off the surface of the asteroids by micro-meteorite strikes or would measure their composition.)  The proposers emphasize that the capabilities of modern instruments will give us resolutions from flybys today that exceed the resolutions available from asteroid orbiters in the 1990s.

The Lucy mission would flyby a number of the Trojan asteroids that follow Jupiter’s orbit about the sun.  The leading group of asteroids are sometimes referred to as the “Greeks” and the trailing as the “Trojans.”  Source: Wikipedia

The Lucy mission would explore the “fossils of planet formation” among the Trojan asteroids (with a flyby of one main belt asteroid thrown in).  The goal of this mission is to sample all the composition types within the Trojans (C-, D-, and P-Types) and sample both those asteroids that lead and follow Jupiter in their shared orbit.  This mission looks to the New Horizon Pluto mission for its instruments with copies of that mission’s LORRI high resolution camera and the RALPH color camera and imaging spectrometer.  Another infrared spectrometer would draw on instrument heritage from Mars orbiters and the upcoming OSIRIX-REx asteroid sample return.  Tracking of the spacecraft’s radio signal would provide information on each asteroids mass and therefore density which provides clues to their composition and to whether they are solid objects or rubble piles.

Telescopes

Eleven of the Discovery missions selected to date have sent spacecraft to a disperse set of solar system bodies.  NASA, however, allows teams to propose space telescopes that study planetary bodies, and previously selected the Kepler mission to search for planets around other stars.  (Today, missions to study exoplanets are funded by the astrophysics program instead of the planetary program.)  

Three proposed space telescopes would gather limited information about each small body – color or spectra, size, and orbit.  However, these measurements would be made for thousands or even millions of bodies.  These are the ultimate in survey missions.

The Near-Earth Object Camera (NEOCAM) would follow the Earth from inside Earth’s orbit from the stable Lagrange 1 point between the Earth and the sun.  From this location, it would look to either side of the Earth for asteroids and comets whose orbits approach the Earth.  The proposers expect to find and determine the orbits and physical characteristics of up to millions of objects.  The goal is to catalog bodies that might someday hit the Earth, characterize the origins and evolution of these populations, and find new destinations for future exploration.  This mission was originally proposed in the previous Discovery competition and awarded funding to further its critical technology development.  It has returned, as a more mature concept, for the current competition.



 What the NEOCAM mission would do for small bodies in the inner solar system, the Kuiper space telescope would do for small bodies in the outer solar system.   In addition to the small bodies, this mission would also study the planets of the outer solar system along with their active moons.   This mission would survey the Trojan asteroids, the Centaur asteroid-comets that orbit between the outer planets, and bodies in the Kuiper belt of which Pluto is just the largest and best known.  The goal will be to use the statistics gathered on these worlds to trace the formation and evolution of the outer solar system.  (For information on Kuiper’s goals for studying the outer planets and their moons, see this earlier post.)

Both the NEOCAM and Kuiper telescopes would study bodies close enough to the sun and large enough to be detected through the reflection of the sun’s light.  At the fringes of the solar system lies a large population of small worlds in the Kuiper and Oort belts too small to detect by their reflected sun light.  The Whipple telescope would instead stare at the more distant stars to watch as these small bodies randomly pass in front of the stars.  From the way the starlight is defracted, scientists will learn the size and the distance of these distant small bodies.  The statistics built up from these observations will provide us with our first observations of the hypothesized Oort bodies and clues to the formation and evolution of these fossil populations.  Like NEOCAM, the Whipple team received funds in the last Discovery competition to mature their technology.


Saturday, July 4, 2015

MarCO: Planetary CubeSats Become Real

We have moved closer to having a new tool set to explore the planets.  For several years, scientists and engineers have talked about using tiny spacecraft, known as CubeSats, for interplanetary missions.  However, a number of daunting engineering challenges have stood between these ideas and reality.  A pioneering mission was needed that would take on those challenges and prove the technologies.

Recently, NASA announced the Mars Cube One (MarCO) mission that will fly two CubeSat spacecraft past Mars as part of its larger InSight Mars mission.  While the MarCO spacecraft will fulfill a specific role in the InSight mission, their real importance likely will be to prove that these tiny spacecraft can be used for deep space missions.

Artist’s illustration of the design for the MarCO spacecraft.  Credit: NASA, JPL/CALTECH

CubeSats were originally conceived to use the revolution in miniaturized electronics to allow university students to design, build, test, and fly their own tiny, complete satellites.  A basic CubeSat is 10 x 10 x 10 cm (1 liter) and weighs no more than 1.3 kilograms   Within that tiny space the satellite has to perform all the essential functions of a spacecraft: power, command and control, communications, and operate a payload that makes some kind of measurement. 

The specification of a standard form factor for these nano spacecraft has allowed companies to offer pre-built subsystems designed to fit within the volume.  (This reminds me, on a much smaller scale, of the industry created by the release of the original IBM PC to supply subsystems for clones and add-ins.)  If one liter of volume proves to be too small for a mission, the specification allows for cubes to be combined to create spacecraft of 2, 3, 6, and 12 liters, or units (U) as they are called, to be built. 

So far, well over a hundred CubeSats (and probably several hundred) have been delivered to Earth orbit.  Sending them into deep space, however, requires simultaneously addressing a number of new technical challenges including:
  • An interplanetary CubeSat must be able to function reliably for months to years, while the lifetime of many CubeSats so far has been measured in days or weeks. 
  • The Earth’s magnetosphere shields Earth-orbiting craft from the potentially electronics-damaging radiation present outside this cocoon.  An interplanetary spacecraft would need to be built with hardier electronics. 
  • Almost all Earth orbiting CubeSats are like bottles tossed into the sea and are carried passively in the orbit in which they were delivered.  A CubeSat traveling to another body in the solar system would need its own propulsion system to make course corrections.
  • For all CubeSats to date, the Earth is never far away and communication is fairly straightforward.  An interplanetary CubeSat must be able to communicate from tens to hundreds of millions of kilometers away.


Solutions to all these problems have been developed and proven for large conventional spacecraft.  CubeSats present the problem of meeting these challenges in a volume about the size of a loaf of bread (a 3U design) or two (a 6U design). 

Many teams are working on these problems (there’s even an annual conference).  The MarCO spacecraft will be the first to make the attempt.

This initial interplanetary flight will focus on an engineering goal instead of a scientific investigation.  The InSight mission will place a lander on the Martian surface that will study Mars’ interior.  During its descent, the lander will relay engineering data that will signal its status and its expected successful touchdown.  Unfortunately, geometry between Earth and the lander’s descent path means it can’t send its data directly back to Earth.  The Mars Reconnaissance Orbiter (MRO, already at Mars) will listen to InSight’s data stream, but its design prevents it from simultaneously listening to the lander and relaying that data back to Earth.  The orbiter then disappears behind Mars as seen from Earth before it can relay its data.  We will not know whether InSight survived its seven minutes of terror for another hour or so until MRO reappears from behind Mars.

The MarCO spacecraft will be positioned so that they can receive and transmit the data from the InSight lander in real time.  Credit: NASA, JPL/CALTECH

The twin MarCO CubeSats will fill this gap with real time relay of the InSight lander’s descent data.  They will flyby Mars at an altitude of 3500 kilometers (just inside the orbit of the Martian moon Phobos) where one antenna will listen to the InSight lander’s UHF broadcast while another antenna relays the data in real time to Earth (using X-band frequencies). 

While the MarCO spacecraft will not conduct scientific investigations, their mission does impose some engineering challenges in addition to those faced by all planetary CubeSats.  First, the spacecraft must operate from the distance of Mars, where the sun is fainter and generating power from the solar cells a greater challenge.  For the crucial data relay, the solar cells must be turned away from the sun to point the antennas to Mars and Earth.  As a result, a capable battery system must be shoehorned into the spacecraft’s internal volume.

A full size mockup of the MarCO spacecraft, with its solar panels and antenna deployed, shows its small size.  Credit: NASA, JPL/CALTECH.

The MarCO spacecraft will be carried into space on the same upper stage that will send the InSight lander to Mars.  Following its release from the booster stage, each CubeSat becomes an independent spacecraft.  It must successfully deploy its solar panels and antennas.  It must survive and operate in deep space without any critical hardware or software failures for six and a half months.  It must keep itself steadily oriented with its solar panels pointed to the sun and later its antennas pointed to Mars and the Earth.  It must keep in contact with its operators on Earth.  It must correctly perform up to five trajectory correction maneuvers to align its trajectory to correctly pass over the InSight landing zone.  It must be able to relay up to eight thousand kilobytes of data per second from distant Mars.  And all this capability must be packaged inside a volume of space that’s about twice the size of the shredded wheat box in my pantry.

Design for the MarCO spacecraft.  Credit: NASA, JPL/CALTECH

The spacecraft designers also have a stretch goal to include a camera.  If they find the time, then we should get postcards of Mars as the spacecraft swing by.

Time to design, build, and test the spacecraft is tight.  Launch comes next March, and the spacecraft will need to be delivered earlier than that to be integrated into the upper stage.


An artist’s illustration of the InSight lander on Mars following its landing and deployment of its instruments.  The MarCO spacecraft will relay data from the lander as it descends to the surface.  Credit: NASA, JPL/CALTECH.

CubeSat spacecraft have been built for as little as several tens of thousands of dollars (plus free student time).  Those figures, though, are only for the tiniest and simplest of CubeSats that operate in Earth orbit.  The MarCO budget reflects the difficultly of building larger, robust, and more capable spacecraft and is $13 million.  This investment, though, will be repaid as the engineering solutions developed for this mission are applied to future planetary CubeSats.  

Following MarCO, planetary CubeSat missions will continue to cost more than their education-oriented Earth orbiting brethren.  A few months ago, NASA solicited proposals for a planetary CubeSat mission that would launch after MarCO and listed a total budget of $5.6 million.  These kinds of prices are similar to those for small instruments on planetary spacecraft.  And that may be the best way to think of planetary CubeSats: small, independently flying instruments.

Fortunately, there seems to be no shortage of ideas for science missions using small, independently flying instruments.  You can read about several of these here, and I plan to have a post later this summer with a number of new ideas.


CubeSats won’t replace traditional, much more expensive planetary spacecraft.  Instead, they promise to give scientists new flexibility to have missions disperse instruments for distributed measurements or to send an instrument or two to carry out a job where the expense of a traditional mission doesn’t make sense.  The MarCO mission will be the first step toward interplanetary CubeSats being used to explore the solar system.

Saturday, June 6, 2015

NASA Goes First Class for Europa

There’s an old saying that the clothes make the man.  In planetary exploration, the instrument suite makes the mission.  Fewer and simpler instruments can enable a lower cost mission but at the cost of restricting the richness of the scientific investigations.   

Jupiter’s moon Europa has been a priority to explore because there’s good evidence that its vast ocean, hidden beneath an icy crust, may have the conditions needed to enable life.  However, NASA’s managers have struggled to define a mission that is both compelling and affordable.  Over the last several years, engineers at the Jet Propulsion Laboratory and Applied Physics Laboratory have rethought the entire approach to exploring Europa.  They started with a bare bones list of just three must have instruments (with a longer list of optional desired instruments).  Their breakthrough was to plan a mission that would orbit Jupiter and make many brief swoops past Europa before swinging back out of the high radiation zone.  NASA now has a concept that's affordable.

Current concept for the Europa Clipper spacecraft.  Credit: NASA-JPL/Caltech.  You can read a summary of the mission concept here, although current plans would replace the radioisotope power supplies discussed in the article with the solar panels shown above.

What would ultimately define the mission, though, would be the suite of instruments NASA’s managers would chose.  Designing instruments that can withstand the radiation has proven difficult.  NASA's managers could have decided on a minimal instrument suite to reduce mission costs and risks, in effect to fly an economy class mission to Europa.

As we learned last week (see here), however, they announced that the selection of a rich instrument suite that will make this a first class voyage.  Not only is the list long – and includes everything on that original desired list – the instruments individually look to be highly capable.  The resulting mission promises to be incredible. 

NASA’s announcement was widely reported on and by now I expect that many of you have seen the instrument list.  In this blog post, I’ll discuss how these instruments will work together to reveal Europa’s secrets.  NASA did little more than announce the names of the instruments and said little about their capabilities.  (This is standard; we usually learn the details about the instruments in the next year or two as their science team discuss them at scientific conferences.)   Where possible, I’ve expanded upon the brief list of instruments with previously published information or from information published since NASA’s announcement.  I’ve also provided comparisons with the instrument suite for the European Space Agency’s JUICE mission that will briefly study Europa but focus on the neighboring moon Ganymede and Jupiter itself.

Ice and Ocean

The Europa Clipper mission will study the structure of the icy crusts, ocean, and the rocky world below.  Credit: NASA-JPL/Caltech.

Europa is an ocean world that likely hosts twice as much water as the Earth, capped by an icy crust several kilometers to several tens of kilometers thick.  Several of the instruments will focus on studying the ocean and the structure of the crust.

Europa is embedded within the powerful magnetosphere that surrounds Jupiter.  A salty ocean would interact with the magnetic fields and reveal both its depth and salinity.  NASA’s Galileo spacecraft all but proved the existence of Europa’s ocean by measuring the induced magnetic field from this interaction.  Europa Clipper will refine Galileo’s measurements with its own magnetometer (Interior Characterization of Europa using Magnetometry (ICEMAG) – principal investigator Dr. Carol Raymond of NASA’s Jet Propulsion Laboratory (JPL)).  The plasma fields carried within Jupiter’s magnetosphere locally modify the magnetic field, and the Europa Clipper will carry a basic plasma instrument to allow the modifications to be accounted for (Plasma Instrument for Magnetic Sounding (PIMS) – principal investigator Dr. Joseph Westlake of Johns Hopkins Applied Physics Laboratory (APL)).  

NASA appears to have selected a core instrument set focused on the investigation of Europa’s ocean.  ESA’s JUICE spacecraft will carry a richer set of investigations that will carry out broader investigations of Jupiter’s magnetosphere.  However, if the Europa Clipper and JUICE operate at the same time, the Clipper’s instruments could enhance JUICE’s investigations by providing a basic measurement of the magnetic field at a second location.  (JUICE will arrive at Jupiter in 2030; a date for the Clipper’s arrival has yet to be set.)

Galileo’s camera and spectrometers revealed that the icy crust is fractured and frequently covered with material that appears to have originated in the ocean below.   The Clipper’s radar instrument (Radar for Europa Assessment and Sounding: Ocean to Near-surface (REASON) – principal investigator Dr. Donald Blankenship of the University of Texas, Austin) will see below the surface to investigate the structure of the shell, potentially all the way to the interface with the ocean below.   

Ground and ice penetrating radars face a fundamental tradeoff – do they focus on the highest resolution to reveal fine structures (higher frequencies) beneath the surface at the cost of shallow penetration or do they focus on maximizing the depth of penetration (lower frequencies)?  Radar systems can focus on one or the other measurement based on the frequency they operate at.  The Clipper’s REASON instrument will use dual frequencies to enable both fine resolution in the upper layers of the icy shell and deep penetration.  (JUICE’s radar system will use a single lower frequency.)  The frequencies that allow deep measurements are subject to interference from radio wave emitted from Jupiter, and these measurements will be made only on the hemisphere of Europa that faces away from Jupiter where the bulk of the moon blocks Jupiter’s emissions.  (At Mars, two spacecraft carry subsurface radar.  NASA’s SHARAD instrument uses higher frequencies while ESA’s MARSIS instrument uses lower frequencies.)

The bulk of Europa is a rocky world covered with an ocean that may be around 100 kilometers deep covered by an icy shell that likely is kilometers thick.  Measuring variations in Europa’s gravity field can reveal this moon’s internal structure to its core.  Differences in the gravity field would arise from variations in the thickness of the icy shell, variations in the topography of the ocean floor, or deep variations in the structure of the rocky body.   The Clipper engineering team has put considerable effort into enabling sensitive measurements of the gravity field from multiple flybys by measuring slight differences in the Doppler shifts of the radio.  NASA did not announce a science team for gravity measurements when it announced the instrument suite.  However, according to NASA’s program manager for Europa instruments, Curt Niebur, “We have spent considerable effort accommodating gravity science into the mission design. At this point NASA is considering options as to how best to inject the necessary expertise to the science team.  But gravity science remains a key investigation of the Europa mission.”

Composition

The Europa Clipper’s instruments will explore the composition of Europa’s surface, which includes darker material that may be salts or organics from the ocean below.  Credit: NASA/JPL-Caltech/SETI Institute (See here for additional information about this image.)

While Europa’s potentially life-bearing ocean lies hidden beneath the icy shell, the surface of that shell is streaked and spotted with darker stains.  Scientists believe that the staining materials are likely materials such as salts or potentially organic molecules brought to the surface when the ice shell fractures and ocean material erupts to the surface.  Three of the instruments will examine the composition of these materials.

The composition of the surface will be mapped across the globe by the Mapping Imaging Spectrometer for Europa (MISE) (principal investigator Dr. Diana Blaney of JPL).  Cameras are typically optimized to provide sharp images but record only a selected few colors (or specific spectral bands).  Mapping spectrometers trade imaging resolution for the fidelity of their spectral measurements across many spectral bands.  MISE will use the spectra of light reflected from Europa to map the distribution of “organics, salts, acid hydrates, water ice phases, and other materials” across this moon’s surface. 

Various processes such as sublimation and micrometeoroid impacts expel material from the surface to form a tenuous cloud around Europa.  The Europa mission’s two mass spectrometers will directly sample this material and determine its composition by “weighing” the atoms and molecules they encounter.  By doing so, they will be able to directly taste the ices, salts, and any organic molecules present on the surface and will provide more sensitive measurements of surface composition than MISE (but without MISE’s ability to map composition across the surface).  

The MAss SPectrometer for Planetary EXploration/Europa (MASPEX) (principal investigator Dr. Jack (Hunter) Waite, of the Southwest Research Institute (SwRI)) will measure the composition of gasses, ices, and organic molecules.  (MASPEX is the current state of the art and will be more sensitive than the equivalent instruments that have been flown on the Cassini Saturn and Rosetta comet missions.  I’ve seen this instrument included in a number of current proposals for new missions.) 

The SUrface Dust Mass Analyzer (SUDA) (principal investigator Dr. Sascha Kempf of the University of Colorado, Boulder) will measure dust and salt particles ejected from the surface.  

Previous generation equivalents to these two instruments were included in the Cassini mission and in combination have provided the data from measuring the composition of the plumes of Enceladus to show that its internal ocean may provide a habitable environment.

Geology

The Europa Clipper’s moderate resolution camera will map the geology of this moon across its surface.  Credit: NASA/JPL-Caltech.  (See here for additional information about this image.)

The surface of Europa’s icy shell records a history of fracturing and interaction with the ocean below.  Globally mapping the surface will provide scientists with clues to what processes shaped the surface and how material is exchanged between the ocean and surface. 

The wide angle camera in the Europa Imaging System (EIS) (principal investigator Dr. Elizabeth Turtle of APL) will map the surface of Europa at 50 meter resolution in color to document the surface structure.  While 50 meter resolution may seem to be coarse compared to the high resolution images we have come to expect from Mars and the moon, for a first dedicated mission to a world this will be detailed global coverage.  The best global maps of Venus from the Magellan mission are approximately 300 m resolution.  (Mars has better coverage, but it has been the focus of many missions. At Mars, 75% of the surface has been mapped at 6 meter resolution (as of April 2012) in black and white by the Mars Context Camera on the Mars Reconnaissance Orbiter while 61% has been mapped in color at 20 meters by the camera on the Mars Express orbiter (as of February 2013).)

During each of the planned 45 flybys, the spacecraft will travel close to the surface of Europa.  At each encounter, the wide and narrow angle EIS cameras will record the surface geology in high resolution recording details as small as one meter.   The MISE spectrometer likely will provide high resolution composition maps across the narrow strips of terrain that the spacecraft will traverse during its close encounters.

Reconnaissance

The very highest resolution images of Europa taken by the Galileo spacecraft in the 1990s show rough terrain.  (This image has a nine meter resolution.)  NASA’s Europa Clipper mission will scout for safe landing zones using its suite of instruments.  Credit: NASA/JPL.  (See here for additional information about this image.)

The ultimate goal for Europa exploration will be to directly sample material from the ocean to determine whether it has the conditions likely to be habitable and whether complex organic molecules indicative of life are present.  There are two ways to achieve this goal.  The first will be to find a location where a future lander could sample material recently delivered from Europa’s ocean to the surface.  The second would be to find plumes erupting from the surface that would be spewing the contents of Europa’s subsurface water into space.

Two instruments are dedicated to scouting out landing sites for future landers.  The high resolution EIS camera will image sites at resolutions as fine as 1 meter to search for landing zones smooth enough for a safe landing.  The Europa Thermal Emission Imaging System (E-THEMIS) (principal investigator Dr. Philip Christensen of Arizona State University) will map the surface in the thermal infrared to look for locations warmer than the surrounding ice that may indicate the presence of warmer water close to the surface.  Locations with water near the surface may be sites where a future lander could drill beneath the to reach liquid water. 

E-THEMIS appears to be based on the THEMIS instrument on the Mars Odyssey orbiter, which provides thermal imaging in multiple spectral to map the composition of the Red Planet.  There’s no mention that I have found for E-THEMIS being used for composition mapping for Europa (the expected surface materials may not have characteristic spectra in these bands at the frigid temperatures of Europa’s surface).

Researchers using the Hubble spacecraft appear to have observed a large plume erupting from the surface.  Repeat observations so far have failed to observe subsequent plumes, which may mean that these large plumes rarely erupt.  However, plumes that would be too small to be seen by the Hubble’s telescope may be more common.

The Ultraviolet Spectrograph/Europa (UVS) (principal investigator Dr. Kurt Retherford of SwRI) will study the space above Europa’s surface to look for plumes and to more generally study the composition and structure of the rarified atmosphere surrounding Europa.  (That near-vacuum atmosphere will be the material that the MASPEX mass spectrometer will sample.)  The location of any plumes also may be revealed by the E-THEMIS instrument by mapping very warm surface locations that could be the vent sources for plumes (as has been done for the plume sources for Saturn’s moon Enceladus).

If any plumes are discovered, the Clipper almost certainly would be retargeted to fly through them.  The MASPEX and SUDA mass spectrometers would then be able to directly sample and analyze the composition of Europa’s subsurface water.  (The source of any plumes could either be the ocean itself in the case of a deep fracture or a lake trapped in the ice below the surface but above the ocean.)

More to Come?

This instrument suite could be made even richer by future announcements.  NASA has requested and received proposals for possible CubeSat spacecraft that the Europa Clipper spacecraft would carry to Europa and release.  (See here.)  These spacecraft, each likely the size of a loaf of bread, might enhance the mission by providing, for example, additional magnetometer measurements to study the ocean’s depth and salinity or by providing high resolution imaging as they fly into the surface.

NASA has also asked the European Space Agency if it would like to provide a daughter craft that might be a small lander or a probe that might fly through and analyze and plumes.  (See here.)  ESA’s managers have said that any contribution to NASA’s mission would have to come from a competition that would pit it against a number of excellent proposals for other science missions.

Also, one US Congressman (who chairs the House subcommittee that funds NASA) has said that he thinks NASA’s mission should be enhanced with a capable lander.  (See here.)  While I appreciate his enthusiasm (which has led to hundreds of millions of dollars being added to NASA’s planning for its Europa mission), I’m skeptical that this will happen.  Capable landers are expensive, and the interesting places on Europa’s surface look to be exceeding rugged.  I doubt that a credible design could be put into place in time to launch with the Europa Clipper by the mid-2020’s even if the funding were provided.

NASA’s Europa spacecraft will also be joined by Europe’s JUICE spacecraft.  The focus of the latter will be Europa’s neighboring icy-ocean world, Ganymede.  Because Ganymede lies outside the intense Jovian radiation fields, the JUICE spacecraft will be able to orbit Ganymede for an extended period of close up studies.  JUICE also will add to the Clipper’s studies of Europa by making two Europa flybys of its own.

In many ways, the instrument list for NASA’s Europa spacecraft and JUICE’s are similar.  They both have cameras, imaging spectrometers, mass spectrometers, a magnetometer, ice penetrating radar, and a UV spectrometer.  JUICE, however, also will carry a laser altimeter to map the elevations of Ganymede’s surface that won’t be in NASA’s suite.  The European mission has a goal to study Jupiter itself and therefore has a richer set of plasma instruments and a radio and plasma wave instrument to study Jupiter’s magnetosphere along with a submillimetre wave Instrument to study Jupiter’s atmosphere.

(It’s interesting to compare the estimated costs for NASA’s Clipper mission (~$2B) with those for JUICE, which is a similarly complex mission.  NASA’s mission will be approximately twice as expensive, indicating how hard it is to design a spacecraft and instruments to survive the radiation fields at Europa.)

When to Fly?

The next key question for NASA’s Europa mission will be when it will launch.  JPL’s design team are working towards a 2022 launch, provided the money can be found.  The funding is the rub, though.  While Congress has pushed for an early flight and backed that with generous funding, only this year has the President’s Office of Management and Budget, which sets the administration’s budget policy, agreed to make a trip to Europa an official NASA program and proposed a tiny down payment towards the mission’s cost.  However, they and NASA’s managers, who ultimately work for the President and must publicly support the administration’s position, only speak vaguely of a launch in the mid-2020s or possibly later.  (This reminds me of the father who tells his children that, yes, absolutely we will go to Disneyland someday (and means it), to get them to stop pestering him about the trip now.)  The issue is that an earlier flight means either increasing NASA’s budget to pay for the mission or trading it for other work that is on NASA’s plate.  (See these good background pieces by Casey Drier at the Planetary Society and Jeff Foust at the Space Review.  I’ve also written about this.)

Over the last twenty years, I’ve watched NASA struggle to find a Europa mission that is both affordable and compelling.  The Europa Clipper mission design achieves the affordable and the instrument suite NASA just announced provides the compelling.    The instruments that NASA selected will enable a suite of complimentary studies that will allow us to understand Europa as an ocean world, judge whether it is likely to have conditions that would make it habitable, and scout for locations for the next logical mission, a lander.  This is possible because NASA’s managers took the gutsy move and decided against an economy class mission that might have had just three or four instruments and selected the full set of instruments needed to do the job right.


Saturday, May 2, 2015

Mars Plans Advance (and occasionally fade)



Mars has the twin attributes of being close by (at least by solar system standards) and retaining a record of its earliest epoch (lost on Earth) when life might have formed.   These have made it a popular destination with five orbiters currently operating around it and two rovers driving across its sands.  At least as many new missions are in various stages of development or are proposal, ranging from hardware headed for the launch pad in a few months to some that eventually may prove to be no more than vaporware.

In the last two months, there have been significant news about the European-Russian 2018 mission and about NASA’s 2020 rover.  NASA also has announced that it would like to send a new orbiter to the Red Planet in the early 2020’s.  These announcements will be the meat of this blog post, but first I’ll quickly run through the status of other planned and proposed missions.

Assembly of the 2016 Trace Gas Orbiter and Schiaparelli demonstration lander.  Credit:ESA
Six craft to launch as four missions are firmly in development and have fully funded budgets.  Europe’s Trace Gas Orbiter and its Schiaparelli technology demonstration lander are in assembly and on track to launch next January.  NASA’s InSight geophysical lander also is in assembly for its launch next March, although the mission’s principal investigator reports that the schedule is tight.  Design of the 2018 ExoMars European rover and Russian lander are on track as is NASA’s 2020 rover

Icebreaker concept.  Credit: McKay/NASA

It’s likely that another mission to return to the Martian northern polar plains has been proposed for the NASA Discovery program.  The Phoenix lander explored these regions, but was frustrated by clumpy soils that made it difficult to deliver samples to its instruments.  What the Phoenix spacecraft did find was a layer of ice just below the surface dust that could provide a habitat for life.  The proposed Icebreaker mission would follow up on the Phoenix mission with a sampling system that would drill well into the ice and is designed to work with the clumpy soil.  The lander, which would be a near copy of the Phoenix and InSight landers, would carry new instruments that would search for signs of life.  While this proposal has received considerable publicity, I haven’t heard whether it was actually proposed.  Sometimes, proposers learn as they develop their plans that their missions would not fit within the tight budgets of Discovery missions.  (I’ve heard of one proposal that I was excited about that wasn’t submitted for the current Discovery selection for this reason.)  If the Icebreaker mission was proposed and is selected (beating out 27 other proposals), it would launch in 2021.

China announced plans a few months ago for its own Martian rover mission to launch in 2020.  More recently, a Chinese official stated that the budget for this mission was unlikely to be approved in time for a 2020 launch.

There have also been press accounts that India is considering a second Mars mission that might be an orbiter and/or a lander.  I haven’t heard whether the budget for a follow on mission has been approved or not.

And now on to the major announcements of the last couple of months.

The 2018 ExoMars mission will use a Russian landing system and platform to deliver a European rover to the surface.  Russia has planned to use the landing platform as a scientific station after the rover rolls off it.  Until recently, I’ve been unable to find any details about the planned experiments.  Now an announcement of opportunity has been issued for European scientists to contribute to Russian-led instruments and to propose their own additions (see here). 

The Russian landing stage and long term science station with the European rover on top prior to its deployment.  Credit: Russian Academy of Science Space Research Institute.

The documents state that the priorities for the stations are:

“Priority 1:
• Context imaging;
• Long-term climate monitoring and atmospheric investigations.
Priority 2:
• Studies of subsurface water distribution at the landing site;
• Atmosphere/surface exchange;
• Monitoring of the radiation environment
• Geophysical investigations of Mars’ internal structure.”

The documents lists the names only for an ambitious suite of instruments, although it’s not always clear what instruments are already firmly planned versus those that might be added by European scientists.  The instruments break down into several groups:

Camera

Meteorology and atmospheric science: Meteorological package, multi-channel Laser Spectrometer, IR Fourier spectrometer, atmospheric dust particle instrument, and a gas chromatograph-mass spectrometer to study composition.

Ground and shallow below ground: Active neutron spectrometer and dosimeter, radio thermometer for soil temperatures

Geophysics: Magnetometer and seismometer

This suite would be a highly capable science station.  For example, the station will monitor both the physical state of the atmosphere (temperature, pressure, dust load, etc.) as well has changes in its composition (presumably with a focus on changes in trace gases to provide ground truth measurements for the 2016 Trace Gas Orbiter).  The listed target weight for the seismometer suggests a simpler instrument than the InSight lander will carry.  Having a second seismometer would help geophysicists narrow down the source locations of Mars quakes.  The sensitivity of this new seismometer may be limited if there isn’t a way to lower it to the ground to isolate it from the vibrations within the station.

What I am surprised by is that the call for instruments includes requests for significant pieces of hardware to be supplied by European scientists for Russian-led instruments.  In terms of instrument and spacecraft development, 2018 is practically around the corner.  I will be interested to see how the Russians and Europeans manage the selection, development, testing, and integration of these instruments in this short time frame.  Perhaps considerable work has already been done or there are flight-ready designs already available.

Two years after the ExoMars station and rover arrive, NASA will land its 2020 rover.  The rover itself will be a near copy of the Curiosity rover currently on Mars, but with a next generation instrument suite.  A major new goal will be to select and cache a suite of samples that a later mission might collect and return to Earth. 

2020 NASA Mars rover concept drawing.  Credit: JPL/NASA

Each sample will be about the size of a stubby pencil.  Previously, NASA had planned to put each sample into a canister as it was collected.  This canister would then be placed on the surface for later collection after it was full.  NASA has announced a major change in how these samples will be cached (see here).

The original plan had two key limitations.  First, as the canister acquired more and more samples, it would become an increasingly precious resource.  This would lead the mission’s operators to become increasingly conservative in their operation of the rover.  Should they, for example, explore an interesting looking ridge, but one where if the rover fails the rock face would prevent a future mission from being able to reach the canister?  Second, there was no good way to remove samples once they were in the canister.  What if the canister was full and then scientists find the one sample they absolutely want to collect for return to Earth?

In the new plan, dubbed the Adaptable Cache, the rover would still drill out samples and put them into sample tubes.  Then instead of putting the tubes into a canister, the rover would place them on the surface and then move on.  A future sample return mission would carry a rover that would pick up the samples and place them into a canister it carries.  This way the 2020 rover can cache more samples than could be returned and scientists would send the subsequent rover to pick up only the most important ones.  Even with the old scheme where the 2020 rover carried the canister, the follow on mission would still need a rover to fetch the canister.  Now that follow on rover would need a more capable arm to pick up tubes lying on the surface and place them into its own canister.

The new rover will also have an upgrade to its engineering cameras.  On Curiosity, the navcam/hazcam cameras used to operate the rover take black and white images.  The 2020 rover will carry color cameras that will take higher resolution images.  Curiosity carried just one camera to record its descent and landing, placed on the bottom of the rover to look down.  The 2020 rover will carry additional cameras that will look up at the descent stage that carries the descent rockets, a camera on the descent stage looking down at the rover, and a final camera on the backshell to image the parachute opening. 

With these new cameras, being an armchair explorer of Mars will get, as they say, a whole lot better.

In one other item of Mars 2020 rover news, the current cost estimates for the mission appear to be in the $2.14 – $2.35 billion range instead of the previously quoted $1.5 billion.  A reasonable portion of this increase likely comes from the new figures representing inflation through launch and operations, while the original cost estimates were, I’m told, were in 2015 dollars.  At the new figures, the 2020 mission, given inflation, still will be considerably cheaper than the Curiosity mission on which much of the design will be based.

The final major news for Mars exploration was NASA’s announcement that it would like to fly a new orbiter to Mars in the early 2020s (see here).  NASA will need a new orbiter to act as a communications relay for future lander missions (such as a sample return fetch mission).  The agency could fly a fairly simple orbiter to do just this task.  Instead the agency is considering flying a highly capable orbiter that would use solar electric propulsion (SEP).

NASA is considering a range of options for an early 2020s orbiter to replace the Mars Reconnaissance Orbiter (MRO) currently at Mars.  At a minimum, the new orbiter would act as a communications relay for future landed missions.  In the most expansive scenario, the new orbiter would carry a much larger payload than any spacecraft has done in the past to Mars.  Credit: NASA.

All previous Mars missions have used rockets to enter Mars orbit.  Solar electric engines, such as those used by the Dawn and Hayabusa-2 missions, provide a great deal more cumulative thrust.  By using SEP, the new orbiter could spiral into Martian orbit.  At it lowers its orbit, it could rendezvous with each of Mars’ tiny moons for in-depth studies.  Then the orbiter could switch from a near equatorial orbit (where the moons are) to a polar orbit to allow it to study the entire Martian surface. 

NASA’s Mars program manager stated that the agency would like to have the orbiter carry a substantial scientific payload (one chart lists a capability to host up to 300 kg of instruments, which would be a very substantial payload).  The agency has not stated a preference for what types of instruments – a future scientific definition team would make those recommendations.  However, we can do some informed speculation.

In the 2000s, two scientific definition teams looked at science that then future orbiters could make.   The highest priority measurements would be to study the upper atmosphere and trace gases in the atmosphere.  Time has moved on, and the MAVEN orbiter is at Mars studying the upper atmosphere and the 2016 European-Russian orbiter will study trace gases.

The panels in the 2000s did recommend that future orbiters carry high resolution cameras to image possible landing sites and carry out scientific imaging.  Since the mid-2000s, the HiRise camera on the Mars Reconnaissance orbiter has been imaging the planet at 25 to 32 cm pixel resolution.  The HiRise team described a possible future instrument that would use the same optics, but would provide color imaging across the entire image.  (See here.) (The current HiRise camera has color only for the center fifth of each image.)  A future camera also could add imaging in spectral bands in the near infrared that would allow studies of surface composition at high resolution.  This future camera could also acquire stereo images to allow 3D analysis of each scene.

Another concept for a future high resolution camera comes from Malin Space Science Systems that has built cameras for several Mars missions.  (See here.) This camera would carry a bigger telescope than HiRise camera, and the orbiter would fly closer to the planet -- skimming just above the top of the atmosphere at perihelion --  to acquire images at 5 to 10 cm pixel resolution.  This finer resolution would allow more detailed scientific studies of surface features, such as the fine sedimentary bands that are often almost  visible in current HiRise images.  (The published abstract for this proposal doesn’t discuss whether the camera would image in multiple color bands.  It also doesn’t say how narrow the image strips would be.  HiRise’s lower resolution likely would provide wider image strips.)

Another proposal suggested that a future mission might carry a suite of radar instruments and laser to map the surface and subsurface in detail.  (See here.) Ground penetrating radar instruments are already at Mars mapping the subsurface stratigraphy.  However, their capabilities are limited by the power and mass available to them within the overall suite of instruments the orbiters carried.  The proposal suggests that a future orbiter carry one radar optimized for subsurface stratigraphy and a second for surface mapping that would be able to penetrate the sand and dust that covers much of the planet to image the rock structures below. The proposal also recommended flying a new generation Laser Ranging and Detection (LiDAR) instrument that would remap the altimetry of the surface at much higher resolution.  A new orbiter such as the one NASA is discussing would have the power and payload mass to optimize instruments such as these along with a high resolution camera.

Another key capability of the proposed orbiter is that it would use laser optical communication to return data to Earth as well as newer generation radio systems (Ka band).  The limit on how much data past and current orbiters have been able to return has not been the instruments, but instead the bottleneck of the communications system.  High resolution cameras and radar instruments want to be data hogs, and a new generation orbiter with advanced communication could be an enabling technology to map much larger areas of the planet at high resolution.

This orbiter has just been discussed publicly as a concept for the first time in the last couple of months.  None of NASA’s scientific panels have looked into missions past 2020.  They may recommend another mission instead.  It’s also not clear where the money for the mission would come from.  NASA’s planetary program will be funding the development of the $2 billion-ish Europa mission in the early 2020s.  If the agency also wants to continue developing a mixture of the smaller Discovery and New Frontiers missions in the same time frame, a major new Mars orbiter may stretch the budget.  A next generation Mars orbiter would provide new instrument eyes to study the fourth planet.  We will need to wait and see whether the programmatic priorities and budgets line up to enable it to fly.