Europe Plans Its Next Large Missions

Last spring, the European Space Agency (ESA) put out a call for concepts for its next two €1 billion science missions.  If history proves to be a guide, there’s a good chance that one of the selected concepts will be a solar system mission.  ESA’s managers will announce their selection this coming November.

These large European missions are particularly important because they have the resources both to reach targets throughout the solar system and to carry enough instruments to conduct wide ranging studies once there.  If one of the solar system concepts is selected, we may get our first orbiter for Uranus, a return to Titan, or an orbiter and balloon for Venus.   The range of concepts proposed shows that planetary exploration continues to have a wealth of possible missions.

However, don’t hold your breath.  ESA believes in long term planning and the launches of the selected missions are planned for 2028 and 2034.  Add in ten to sixteen years for, say, a flight to Uranus, and you may be looking at first science return in the 2040s or 2050s.  (Actuarial tables suggest I won’t be around then, so for purely selfish reasons, I like the concepts with much shorter flight times, like those to Venus.)

ESA breaks its science missions into three classes: Large (~€1B or $1.2B), medium (~€400M or $480M), and small (for which I couldn’t find a price target).  For comparison, NASA also has three classes of missions: Discovery ($425M likely to become $500M), New Frontiers ($750M likely to become $1B), and Flagship (>$2B for the last three Flagship missions). 

ESA and NASA account for mission costs differently, making direct currency conversion comparisons difficult.  For example, ESA includes the launch but not the instruments or much of the data analysis (which are paid for by its member states separately).  NASA does the opposite.  As a rough guide, I assume a Large ESA mission buys somewhere between the equivalents of up to $1.5B in terms of how NASA implements missions.  That mission cost target nicely fits between NASA’s New Frontiers and Flagship mission classes.  (ESA also conducts some planetary missions out of different accounts, such as the two ExoMars missions planned for 2016 and 2018.) 

Previously selected ESA Large missions (at one time called Cornerstone missions) show what can be done within the ESA budget.  The Rosetta mission will conduct humanity’s first rendezvous and landing on a comet.  The BepiColombo mission will be the equivalent of the Cassini mission to Mercury with a far more capable instrument suite than the Discovery-program MESSANGER currently at that planet.  The JUICE mission will carry out extensive studies of Jupiter, flybys of Europa and Callisto, and will orbit Ganymede.

ESA’s budget allows it to fly three Large missions every 20 years.  In the past, ESA has balanced its large missions between astronomy/astrophysics and planetary missions.  The first mission selection for the upcoming 20 year period, JUICE, is a solar system mission to launch in 2020.   A second solar system mission in a row for the 2028 slot seems to me unlikely.  A solar system mission for the 2034 mission seems likely, but ESA could pick a second astronomy mission in a row and restore the balance in the following 20 year period.  I’ve looked through the astronomy/astrophysics concepts, and they are stiff competition for the solar system concepts.

So no guarantees, but the list of solar system mission concepts is exciting, and I’m hopeful for one of the two slots going one of them.  I’ve listed the mission concepts in order from the sun.  None of the proposed concepts returns to the target of a previous ESA large mission.  One though, returns to Mars where ESA will send its two ExoMars missions and two would return to Titan where the joint NASA/ESA Cassini/Huygens mission is conducted a descent and landing and continues to make frequent flybys.

How may ESA decide among what are a number of exciting proposals?  My guess is that three criteria will be used.  First, would the mission fundamentally enrich our understanding of an important world or class of objects?  Second, would a broad spectrum of the European planetary science community be involved?  Third, would the mission be feasible within the budget target and with technology likely to be available?

A mission to Uranus, for example, would greatly deepen our understanding the ice giant worlds.  By studying the atmosphere, magnetosphere, and moons, it would involve a wide range of planetary science disciplines.  However, a Uranus mission would need a radioactive power supply to produce electric power for the spacecraft.  U.S. law prevents supplying plutonium 238 to other nations (and the supply is already critically low).   ESA has proposed developing power supplies based on another radioactive element, americium, but that would represent a bet on an unproven technology.

As you read through the list of proposals below, you might ask yourself how you would rank each according to these three criteria.  If you decide to read the original mission concept proposals (130MB download), be prepared for a lack of detail in some of them.  While NASA typically selects missions after detailed design studies and then launches in four to five years, ESA selects concepts far in advance of launch and fills in the details after selection.  In addition, based on cost estimates from previous mission studies, some of the concepts as presented may well bust the €1B price cap.  So it is possible that a selected concept would be scaled back as definition progresses.

With this background, here are the solar system concepts.  Where the concept title itself doesn’t summarize the goals, I’ve quoted a sentence or two from the proposal that captures the essence the concept’s goals.

Sun

SOLARIS: SOLAR sail Investigation of the Sun  “SOLARIS from its highly inclined orbit around the Sun, aims to combine helioseismic and magnetic observations, solar irradiance measurements and EUV images at various latitudes.”  A solar sail would be used to place a spacecraft into an orbit close to the sun and eventually over the solar poles.

Venus

Possible future missions to Venus have been extensively studied, and so it’s no surprise that the three Venus concepts propose addressing similar goals and similar approaches.  The main difference appears to be in the ambition of the concepts.  The following summary of goals is quoted from the first of the three concepts and summarizes the overall goals for all three (although the focus for each is somewhat different): “A common thread for Venus and Mars is that the atmospheres on both planets appear to have undergone catastrophic change change—Mars may have lost almost all of its atmosphere, while Venus may have driven off much of the water in a runaway greenhouse and perhaps increased its atmosphere… A major part of understanding how Venus evolved as a terrestrial planet is its  [internal] thermal evolution.”

Venus: A Natural Planetary Laboratory.    Implementation: Two orbiters for atmospheric, surface, and interior measurements, balloon or unmanned aerial vehicle, short lifespan landers.

Venus: Key to understanding the evolution of terrestrial planets.  Single orbiter to study the atmosphere and surface, a balloon, and an optional atmospheric descent probe to measure the atmosphere and image the surface.

Europe returns to Venus.  Implementation: Single orbiter to study the atmosphere and surface and a balloon or unmanned aerial vehicle.

Lunar

Lunar Science as a Window into the Early History of the Solar System.  Implementation: multiple penetrators to sample volatiles at the poles and a return of lunar samples.

Science from the Farside of the Moon. Implementation: Multiple landers to conduct radio astronomy measurements and to measure the composition of the surface and surface impact rates.

Mars

Master: A Mission to Return a Sample from Mars to Earth.  Implementation: A single unified mission to land, grab a 150 g surface and atmospheric sample, and return it to Earth

Asteroids

INSIDER - Interior of Primordial Asteroids and the Origins of Earths Water. “The scientific objectives of the proposed INSIDER mission require the exploration of diverse primordial asteroids - possibly the smallest surviving protoplanets of our Solar System - in order to constrain the earliest stages of planetesimal formation.”  Implementation: Spacecraft to orbit several >100 km diameter main belt asteroids and a lander/rover to explore the surface of a volatile-rich asteroid.

The Case for an ESA L-Class Mission to Volatile-Rich Asteroids.  Explore one of the class of asteroids known as a main belt comet, which are in the asteroid belt but which have been observed to emit volatile gases like a comet.  Determine if bodies like these could have been the source for Earth’s water.  Implementation: Spacecraft to orbit one or more bodies.  Possibly carry a lander or return a sample to Earth.

Saturn, Uranus, and/or Neptune

In situ exploration of the giant planets and an entry probe concept for Saturn.  “Comparative studies of the elemental enrichments and isotopic abundances measured on the four giant planets would provide unique insights into the processes at work within our planetary system at the time of giant planet formation.”  Implementation: Put a probe into the atmosphere of Saturn, Uranus, or Neptune, with Saturn suggested as the highest priority.

Titan/Enceladus

These two proposals would continue the exploration of these two moons following the Cassini mission.  Fairly little detail is provided on implementation.

The Exploration of Titan with an Orbiter and a Lake-Probe.  Implementation: Saturn/Titan orbiter and a probe to land one of the polar lakes.

The science goals and mission concept for a future exploration of Titan and Enceladus.  Spacecraft delivers balloon to Titan and then performs multiple flybys of Enceladus before entering orbit around Titan.

Uranus and/or Neptune

The Science Case for an Orbital Mission to Uranus: Exploring the Origins and Evolution of Ice Giant Planets.  “The Ice Giants (Uranus and Neptune) are fundamentally different from the Gas

Giants (Jupiter and Saturn) in a number of ways and Uranus in particular is the most challenging to our understanding of planetary formation and evolution.”  Implementation: Orbiter to observe Uranus remotely, explore its magnetosphere, and flyby all major moons.  An atmospheric probe would study the structure and composition of the atmosphere.

The ODINUS Mission Concept – The Scientific Case for a Mission to the Ice Giant Planets with Twin spacecraft to Unveil the History of our Solar System.  Implementation: Two relatively modest spacecraft that would orbit Uranus and Neptune to allow comparative studies of these two ice giants and their systems of moons.

Neptune and Triton: Essential Pieces of the Solar System Puzzle.  “Neptune and Triton hold the keys to paradigm-changing advances in multiple fields of planetary science: Solar System and planetary formation, exoplanetary systems, geology and geophysics, atmospheric science, magnetospheric physics, and astrobiology.”  Implementation: Neptune orbiter to observe that planet and perform multiple flybys of Neptune.

General Solar System

Solar System Debris Disk.  “The dynamical and compositional interrelations between dust, interplanetary meteoroids and their parent objects are still largely unknown… [This mission] will shed light on all these questions by mapping our solar system in dust, using the unique combination of in-situ dust measurements, analyses of returned samples, and a bird’s eye view for infrared observations of our outer “home” debris disk and beyond.”  Implementation: Infrared telescope and a spacecraft that will analyze dust in-situ and return samples to Earth.

Exploring Planetary Origins and Environments in the Infrared.  “We propose an observatory--‐class ESA mission to provide spatially resolved infrared spectroscopy of solar system and planetary objects in all their guises, from their origins (remaining debris in our solar system and planet--‐forming discs around other stars) to their present--‐day appearance (atmospheres, surfaces and interactions with their host stars for planets in our solar system and beyond).  Implementation: Space-based thermal infrared telescope.

ExoPlanets

Several concepts propose telescopes that could observe exoplanets in addition to other targets.  Only the concept below addresses exoplanet studies as its focus.

Exploring Habitable Worlds beyond our Solar System.  “Among the remarkable feats of the exoplanet community has been the ingenuity with which new observing techniques have been invented and put into successful use over the past twenty years. We now have a diverse set of tools at our disposal, with which we can explore different aspects of exoplanetary systems. A number of complementary approaches have been identified that can address habitability from different angles. Coronographs and infrared interferometers have been studied at some level of detail, and other more recent concepts (external occulters and integratedlight telescopes) also show considerable promise. While none of these is ready yet for flight, the rapid progress over the past few years in the development of the key enabling technologies gives confidence that an exoplanet exploration mission will become viable technically and financially in time for implementation in the middle of the next decade.”  Implementation: Several possible approaches are given.

Finally, an FY13 NASA Planetary Budget, Just 11 Months Late

Just a month before the end of Fiscal Year 2013 (September 30), Space Policy Online has released the final resolution of NASA’s FY13 budget.  The final budget figures were not released by the government but were supplied following a request by Space Policy Online.  The final figures for the Planetary Science program still reflect a substantial cut from the previous year but are much better than the proposed budget for FY13.

The FY13 budget approval was especially messy this year because Congress failed to pass a final budget until last spring (around six months late).  The budget was then automatically cut through a process known as the Sequester.  The Administration then reportedly proposed larger cuts to the planetary program to spare other parts of the NASA budget the effects of the Sequester.  Congress reportedly rejected that division of cuts, resulting in negotiations and the final budget supplied to Space Policy Online.

News reports have also discussed other impacts – some potentially serious – that may eventually result from the continuing cuts to NASA’s Planetary Science budget.  I summarize these following the table of numbers.

Planetary Science Budgets

$1501.4M – FY12 approved

       $1,192.3M – FY13 Administration proposed budget

       $1,415.0M – FY13 Congressionally approved budget, pre Sequester

       $1196.0M – FY13 reported proposed Administration budget following Sequester

 $1271.5M – FY13 final budget per Space Policy Online post Sequester

In a nutshell, the final budget represents a substantial cut compared to the previous year (FY12) and compared to what was approved by Congress.  The final budget approximately splits the difference between the Administration’s proposed budget and Congress’ approved budgets.

The disagreement over the level of the Planetary Science budget looks to continue for the next year, too.  The Administration requested $1,217.5M for FY14, while the House and Senate have approved $1,315.0M and $1,317.6M, respectively for next year.

Space Policy Online does not provide any detail on spending within the Planetary Science program.  Important details would be the level of funding for the Discovery and New Frontiers programs, which would indicate when the selection of the next missions in the programs could begin.  We also don’t know at what level studies of a future Europa mission are funded.

In the meantime, Space News has provided a steady trickle of the effects of the declining Planetary Science budget over the last couple of months:

The declining budgets may not support continued funding for both the Cassini and Curiosity rover missions.  Science News July 18  (I was afraid of this possibility when the FY14 budget proposal showed a dramatic decline in outer planet funding following the completion of the current phase of the Cassini mission.  If the Cassini mission were terminated early, we would lose the close in orbits – just outside and then inside the rings – that essentially constitutes an entirely new mission similar to the Juno mission at Jupiter.  The key as to whether or not this tradeoff must be made may lie with whether the future on-going budgets are closer to the Administration’s ~$1,200M mark or Congress’ ~$1,300M mark.)

The start dates for the competitions to select the next Discovery and New Frontiers missions are uncertain and won’t be known until the Administration releases its FY15 budget around February 2014.  Space News July 16  (NASA cannot begin the competitions until it knows whether or not it can plan on adequate funding to implement the selected missions.  It has to base those projections on the projected budgets supplied with the Administration’s annual budgets.  If the Administration continues to propose low budget numbers, the start of the competitions may continue to be pushed out even if Congress increases the final budget numbers for the current year.)

While the Administration’s budget proposals state that there is no plan or funding for a future mission to Europa, Congressionally approved funds in the FY13 budget allow early design and technology development efforts to continue.  Space News July 22.

The grass roots lobbying by the Planetary Society is one of the reasons that Congress continues to provide more money to the Planetary Science program than is requested by the Administration.  Space News August 26  (See this post by Casey Drier on the inside story about how the lobbying is done.)

MAVEN

The MAVEN Mars orbiter is set to launch in November or early December.  Once it reaches Mars, it will return data that scientists will use to explore the composition and dynamics of the upper atmosphere where air meets space.  A key goal will be to better understand the processes that likely lead to the loss of the Red Planet's likely much thicker early atmosphere.

Aviation Week and Space Technology has an excellent article describing the mission and its science here.

Small Could be Beautiful - Planetary SmallSats

The concept is new enough that there’s not even a consensus on what to call the spacecraft – SmallSats, micro-satellites, tiny spacecraft. 

Traditional spacecraft – let’s call them LargeSats – weigh hundreds of kilograms and cost hundreds of millions of dollars.  At the other end of the spectrum, CubeSats are based on the electronics that have enabled phones to be respectable computers, entertainment centers, and cameras.  The smallest form factor for CubeSats is just 10 × 10 × 10 centimeters, weighs approximately a kilogram, and can cost as little as $60,000 to build.  Large CubeSats expand the length to 60 centimeters and the mass to approximately 6 kg.

While over a hundred CubeSats have been placed in Earth orbit, their small size poses challenges for planetary missions.   A CubeSat that would travel to and orbit Mars, for example, must deal with the harsher radiation environment beyond Earth’s magnetosphere, carry a propulsion system to make course corrections and brake into Martian orbit, have a beefed up communications system to return data from up to 300M kilometers away, and provide solar panels large enough to collect sufficient sunlight at Mars’ greater distance from the sun.  There’s just not enough mass or space to do all that within the CubeSat form factor

CubeSats are likely to play a role in future planetary missions, but most frequently as daughter craft carried to their destination by larger spacecraft.  (I’ll explore possible concepts in a future post.)

An emerging class of spacecraft – I’ll call them SmallSats – would fit between LargeSats and CubeSats.  These spacecraft make use of the design techniques of CubeSats but scale the form factor up to a meter or so and the mass up to 50 to 100 kg or so.  At this size, the spacecraft could meet the challenges of interplanetary missions.

I’ll also note that the potential for SmallSats isn’t limited to planetary missions.  At least two commercial companies are planning spacecraft in this class for high resolution (3 to 5 m) imaging of the Earth.  If successful, they would compete with current companies such as WorldView that are currently using traditional LargeSat designs that cost and weigh an order of magnitude more than their planned SmallSat equivalents.  (See articles at The New York Times and Wired Magazine.)

At the Low Cost Planetary Mission conference last June, several concepts for SmallSat planetary spacecraft were presented.  I’ll use the concepts presented to explore the potential and limitations of this class of spacecraft for future planetary exploration.

Engineers from JPL presented their concept for one class of these spacecraft, the Micro Surveyor, for missions in the inner solar system.  While the first planetary SmallSat may cost around $40M, their goal is to create a design for spacecraft in the $20M range to enable  total mission costs to eventually be around $100M (compared to $450 to $500M for NASA’s Discovery missions and $750M to $1B for New Frontiers missions).

Conceptual design for JPL’s Micro Surveyor planetary spacecraft that would stand just 0.9 m high.  The design is sized to fit within the space allocated for secondary payloads adapter ring (ESPA) on the launch of larger spacecraft (insert figure in the upper right).  Propulsion would be provided by an electric propulsion system (EP).  Credit: JPL.

The design is sized to be carried as a small secondary payload on the launch of a larger spacecraft such as a communications satellite to enable low cost launches.  Once in Earth orbit, a Micro Surveyor would use an electric propulsion system (similar to, but much smaller than the ion engine being used by the Dawn spacecraft) to gradually change its orbit to flyby the Earth’s moon.  Encounters with the moon would provide gravity assists that would put the spacecraft on a trajectory to Venus, Mars, or an asteroid or comet near Earth.  (While not mentioned in the presentation, the moon itself could be a mission target.)

The flight times to Venus or Mars illustrate one of the limitations that this approach has.  While LargeSat missions to these planets can arrive in less than a year (thanks to a dedicated launch that puts the spacecraft on a direct trajectory), a Micro Surveyor spacecraft would take ~16 months to reach Venus and ~36 months to reach Mars.  Once the spacecraft reaches its target world, the electric propulsion system would allow a slow spiral into the science orbit.  Patience may be a virtue, but the longer flight times mean that mission operation costs will build up during the longer flights.

The small size of the spacecraft also would limit the scientific payload.  While a LargeSat Discovery mission might have 50 kilograms or more in instruments, the Micro Surveyor spacecraft is being designed to carry just 15 kg of instruments.  The mission planned for the Micro Surveyor would also need to fit within the limited power available to the instruments and the restricted bandwidth of data the tiny spacecraft could return to Earth.  A Micro Surveyor could, for example, carry a camera to Mars for high resolution imaging (3 to 5 m) of the surface, but the mission would be severely limited in how many images could be returned per day. 

Also, Venus, the moon, Mars, and near Earth asteroids have been (or are planned to be) visited by many spacecraft.  Much of the low hanging fruit in terms of science has been done.  With an estimated cost of ~$100M per Micro Surveyor missions, finding a new, compelling scientific missions that fit within the mass, power, and data limitations of the spacecraft may prove to be a challenge. 

At the conference, the JPL presenter did not suggest any specific mission concepts for the Micro Surveyor.  I’ll suggest three possible mission concepts that occurred to me that might meet the goals of conducting interesting new science while fitting into the mass, power, and data constraints.  I want to emphasize that this is amateur armchair mission architecture; none of these concepts may pass technical muster when examined by real mission architects.

The first concept would target Venus.  The clouds of Venus have made observation of the surface difficult by orbiting spacecraft.  While larger missions can carry heavy and power hungry radar systems to image the surface, mapping the surface composition has been largely impossible because the clouds block the view.  A series of spectral windows in the near-infrared (between 0.8 and 1.8 μm), however, allow observation of the surface.  The VIRTIS instrument on the Venus Express spacecraft has mapped portions of the planet using these windows to examine surface areas for different compositions and look for temperature differences suggesting volcanic activity. 

Red-orange colors in this VIRTIS image of Venus’ Idunn Mons volcanic peak indicate warmer areas suggesting different surface compositions and younger ages than surrounding material.  Press release describing the science available here and image caption here.  Credit: ESA.

The VIRTIS instrument, however, was designed for analyzing the cloud deck, and has low resolution (~150 kilometers) and isn’t optimized for observations at the wavelengths of the spectral windows.  A follow on instrument optimized for surface mapping (along with further cloud studies) has been proposed for future European Venus missions.  The proposed Venus emissivity mapper would weigh just five kilograms, easily fitting within the mass constraints of a Micro Surveyor mission.  (In fact, on a dedicated mission, a more capable instrument might be flown than has been proposed.)  Fitting within the data constraints of a SmallSat mission, though, might require creative mixing of low resolution global mapping with targeted higher resolution mapping for priority targets.

A second  concept would explore the diversity of comets.  Visits of several comets by spacecraft have shown that these relics from the formation of the solar system are widely varied.  The spacecraft that made the observations to date carried different sets of instruments, making systematic comparisons difficult.  One NASA Discovery mission, CONTOUR, planned to address this problem by visiting two or more comets with the same spacecraft and instrument suite.  Unfortunately, the CONTOUR mission failed early in its mission while leaving Earth orbit. 

The CONTOUR spacecraft carried a diverse suite of instruments: a remote imager/spectrograph (12.0 kg), an aft imager for post encounter images (1.8 kg), a mass spectrometer (9.3 kg), and a dust analyzer (11 kg).  Based on these masses, a Micro Surveyor comet mission could carry any one of the three larger instruments plus the equivalent of the aft imager.  (Because more than a decade has passed since CONTOUR’s launch, new versions of these instruments could be developed that would have less mass.  However, the small budgets foreseen for SmallSats probably would allow for only minimal tweaking of current instrument designs.  The soon-to-be-launched lunar LADEE mass spectrometer derived from the CONTOUR instrument, for example, is 11.3 kg.  Budgeting something around 10 kg for a SmallSat-scale mission mass spectrometer seems reasonable.)  The limited payload available for a SmallSat means that their science goals must be tightly focused.

A tweak on the comet mission concept would be to send a spacecraft to pass by one of the main belt asteroids that have been observed to emit gasses like comets, suggesting that they are either captured comets or very volatile rich asteroids (at which point, there may not be much of a difference).

At the same conference, researchers presented a concept for an outer solar system SmallSat mission.  This work was done to investigate the power requirements for such a mission to determine whether a small version of a radioisotope power system could meet the electric power requirements.  To gauge the spacecraft and power system, the team investigated a flyby of one or more Centaur objects, which have orbits within those of the outer planets.  The study team selected just two instruments, a narrow angle camera (2.4 kg) a hyperspectral infrared spectrometer (4 kg).  As a baseline, the study team looked at two SmallSat-scale spacecraft encountering the asteroid 2060 Chiron and a second pair encountering a second asteroid.  To reach the outer solar system, the mission would have a dedicated launch that would send the four craft two Jupiter where gravity assists would redirect the spacecraft to their final destinations.

Conceptual design for an outer solar system SmallSat spacecraft that would be 1.76 m high.  Multiple copies of this design could be launched together (insert) to provide redundancy or allow targeting of multiple destinations.  Credit: NASA, JPL.

The Centaur mission again shows the limitations of small payload masses.  Chiron has active gas emissions.  Being able to include a mass spectrometer to measure the composition of those gasses could greatly enrich our understanding of the formation of the outer solar system.  This is especially true if Centaurs were once Kuiper-Belt worlds that were later captured within the outer solar system. 

(If I can play armchair mission architect for a bit longer, the instrument masses for the Centaur concept are low enough that they could be paired with a mass spectrometer and almost fit within the payload of a Micro Surveyor.  A camera, imaging spectrometer, and a mass spectrometer would be a very nice payload for a comet, outgassing asteroid, or Centaur mission.)

While the presentation discussed only the Centaur mission concept, similar flyby missions could be done to any outer solar system body.   (A favorite of mine would be a flyby of Neptune’s moon, Triton.) 

The Centaur mission presentation brought up interesting questions on how to think about these missions.  Traditional planetary missions have sized a single spacecraft to carry all the instruments necessary to meet the science goals.  SmallSat-scale spacecraft are cheap enough each ($10M to$20M was mentioned at the conference) that perhaps you fly two or more to a single target.  For a comet or Centaur mission, perhaps one craft carries a camera and imaging spectrometer and a second carries a mass spectrometer.

Traditional planetary spacecraft have also carried dual copies of most critical systems so that if one fails, the spacecraft can continue operating on the second.  To keep mass and per spacecraft costs low, the concepts presented at the conference envisioned a single copy of each system.  Would risk management be better preserved by duplicating key systems within a single spacecraft or by flying two copies of the spacecraft?  For the Centaur mission concept, the mission architects suggest that two craft could be targeted to the high priority Chiron object and the other two craft could be targeted to separate objects.  If all craft succeed, three objects are visited.  If half fail, you would likely get Chiron and/or flybys of two different Centaur objects.

The Centaur mission presentation had one slide that suggests that building planetary spacecraft on tiny budgets only addresses part of the costs of a planetary mission.  The team estimated that the total mission cost would be $511M, only 20% of which would be for four copies of the spacecraft hardware.  (The design exercise was trying to hit the mission costs for a Discovery-class mission (~$500M in the future), rather than hitting a lower cost target.)  The rest of the costs were for design, testing, launch, mission operations, and budget reserves.  At the conference, presenters suggested that total mission costs for an inner solar system SmallSat-scale mission might be approximately $100M using a standard spacecraft designs such as the Micro Surveyor.  If that target can be hit, the cost of the spacecraft hardware would represent 20% to 40% of the mission costs.

At the moment, engineers and scientists are beginning to explore what might be accomplished by SmallSat-scale missions using today’s technology.  As technology progresses, the potential for these spacecraft will grow.  Another JPL team presented a concept for a near-Earth object hunter-seeker mission.  This mission would use a next generation micro-electro-fluidic-spray propulsion technology.  The spacecraft would first maneuver itself into an orbit just inside Earth’s orbit to begin a search for asteroids as small as a few meters across.  As interesting objects are found, the spacecraft would rendezvous with five to six of them for close up examination by a camera and imaging spectrometer and with surface contact to probe the asteroids structural cohesion.  Total mass for the spacecraft with fuel is estimated to be just 50 kilograms within a body (not counting solar panels) just 60 centimeters on a side. 

Conceptual design for a next generation SmallSat spacecraft for the near-Earth asteroid Hunter-Seeker mission.  Credit: JPL.

Editorial Thoughts:  SmallSats for planetary exploration are an exciting concept, especially when NASA’s planetary program faces tight budgets for new missions.  As I’ve tried to emphasize, though, they would complement, not replace larger missions.  The goals for many planetary missions need multiple instruments that each would approach or break the limits for a SmallSat.  The Mars MAVEN Discovery mission, for example, requires the simultaneous operation of a suite of instruments that together have a mass several times what a Micro Surveyer spacecraft could carry to understand the composition and processes in the upper atmosphere.  The HiRise camera on board the Mars Reconnaissance Orbiter has a mass of 64 kg, approaching the mass for an entire Micro Surveyor spacecraft (~75 kg).

However, SmallSats are promising to carry out highly focused investigations with smaller instruments or to visit objects that wouldn’t make the cut for $500M to $1B missions. 

Planeatary SmallSat missions could also provide opportunities for a new generation of scientists and engineers to take lead positions on smaller missions and gain the experience necessary to manager larger projects.  Currently, the pool of scientists and engineers with flight mission experience who can take lead positions for future Discovery and New Frontiers missions is shrinking as flight opportunities have dwindled.

For approximately half the cost of a Discovery mission with launch, NASA could fly two to three SmallSat-class missions.  I hope that NASA pursues the opportunity.  I expect that the planetary science community would show considerable creativity in finding ways to use missions in this class.

Resources:

The following links are to the presentations from the Low Cost Planetary Science 10 conference that discussed planetary SmallSat designs

Enabling Low Cost Planetary Missions Through Rideshare Opportunities (Micro Surveyor)

A Low-Cost Small Radioisotope Power System Centaur Flyby SmallSat Mission Concept (Outer planets SmallSat)

A Low-Cost NEO Micro Hunter-Seeker Mission Concept

Mars Rover 2020: Astrobiology and Caching

NASA’s planned Mars 2020 rover likely will both continue the astrobiological exploration of Mars begun by the Curiosity rover and provide stepping stones to the next stages of Martian exploration. 

Two weeks ago, NASA’s Mars 2020 rover Science Definition Team (SDT) delivered its report recommending the science goals for the mission.  Probably to the surprise of no one, the team recommended essentially the same science goals as had several previous SDT’s on what NASA’s next mission to Mars should do.  Like the Curiosity rover currently on Mars and the planned European and Russian ExoMars rover mission, the 2020 rover will look for clues as to whether Mars ever contained the conditions to enable life and whether traces of life or pre-biotic chemistry remain.

The mission will also provide an important transition to the next phases of Mars exploration by caching samples that could eventually be returned to Earth and testing technologies for future human and robotic missions.

The challenge the SDT faced was how to do all of this on a budget (~$1.5B) that with inflation may be just somewhat more than the half cost of the initial Curiosity rover.  To fit within the budget, a key tradeoff would have to be made that will make the 2020 rover less capable in a key respect than the Curiosity and ExoMars rovers.

The 2020 rover will be enabled by the substantial investment NASA made in the design of the Curiosity rover and its entry, descent, and landing system.  NASA and the Jet Propulsion Laboratory that built the Curiosity rover also retain substantial stockpiles of spare parts and engineering expertise that can be used in rebuilding substantial portions of the spacecraft. 

I’ve read many press summaries of the SDT’s recommendations, which tend to focus on the proposed caching of samples for possible return to Earth.  If NASA follows through, this will be the first concrete step towards a goal that Mars scientists have made their top priority for decades.  However, the caching is just one aspect of the proposed mission.

Summary of the goals for the 2020 rover mission as envisioned by the SDT.  This and all images in this post are from the briefing to the Mars Exploration Program Analysis Group (MEPAG) July 23, 2013 presentation by the SDT chair, Jack Mustard (Brown University).  Credit: JPL

Double click on any image for a larger view.

To understand the full promise of this mission, I’ll go through each of the SDT’s proposed goals for the mission (which closely parallel those NASA asked the SDT to consider).  First, though, the proposed mission implementation to meet those goals makes more sense with some background on how rovers are used as scientific platforms.

In the course of driving several kilometers, a rover will pass by thousands of potential spots for more detailed examination.  Each of those examinations, though, can take days to weeks complete.  There is a tradeoff between driving distance, and hence number of locales that can be explored and the number of spots where in-depth data can be gathered.

To make the best trade possible between these two goals, the mission team employs a hierarchy of scientific assessments with those at the top taking the least time and those at the bottom the most.  First, the team uses orbital observations to select the locales it would like to visit.  Then as the rover arrives at each locale (and also during the drives between them), the rover’s remote sensing instruments are used to get the “big picture.”  From these images, the science selects a small number of targets for the next level of investigation by the contact instruments.  As the name implies, these instruments are placed in contact with a rock or soil sample target.  Instruments in this class include the microscopic imagers and alpha-particle X-ray spectrometers carried by the MER Spirit and Opportunity rovers and the Curiosity rover.  For a still smaller number of extremely interesting targets, the time is taken to collect a sample.  On the Curiosity rover and the planned 2018 ExoMars rover, these samples are delivered to highly sophisticated analytical instruments inside the rovers for more detailed measurements.  The 2020 rover will collect the samples and place them in a cache, which may eventually be returned to Earth for more detailed measurements than can be made within a rover.  (The MER rovers do not have the capability to collect samples.)

Rovers on Mars follow a hierarchical strategy for selecting a small number of targets for in-depth exploration.

The SDT described their proposal for the 2020 mission in terms of fulfilling four goals, and I’ll present their recommendations for each of those four goals.

Goal A: “Explore an astrobiologically relevant ancient environment on Mars to decipher its geological processes and history, including the assessment of past habitability.”

The 2020 rover would follow a hierarchical strategy to explore a location on Mars believed to have been habitable.  The definitive identification of past signs of life is likely to require the testing of returned samples in Earth laboratories.

Every NASA landed Mars mission – except the 1996 Pathfinder mission that focused on technology demonstration – has had the goal of exploring Mars’ past and current potential for life or pre-biotic chemistry.  For the MER rovers, the goal was simply to determine whether water – an essential ingredient for life – was present at the surface early in Mars’ history.  The Curiosity rover is exploring Gale Crater to examine soils from many eras of Martian history to determine whether or not environments for life existed and to determine whether biosignatures of past life remain.  The 2018 ExoMars rover will explore another site on Mars for its astrobiology potential.

The SDT has proposed that the 2020 rover continue the strategy and pursue astrobiology as the mission’s defining goal.  Its proposed strategy breaks into two parts.  The first is to have the rover carry a suite of instruments capable of a exploring site’s geologic history in-depth with an emphasis on how that history affected the possible presence of past life.

The team proposes that the rover carry multispectral cameras for obtaining images and an imaging spectrometer for analyzing composition across entire sites.  These instruments would provide the context to interpreting each locale’s history as well as allowing the science team to select specific targets for more detailed exploration.

For most of the contact science, the SDT is proposing that the rover carry a new generation of instruments.  Current Mars rover contact spectrometers measure mean composition over an approximately two centimeter contact area.  The new generation of instruments under development can make composition measurements for spots as small as a tenth of a millimeter.  With that resolution, the contact spectrometers would make dozens to hundreds of measurements across the contact area.

If you take a close look at soils and most rocks, you’ll see that most are composites of many fragments that each have their own geological story to tell.  The contact spectrometers that are likely to be proposed for the 2020 rover will be capable of exploring each of those fragments individually.  (The SDT also proposes that the rover carry an imaging microscope to study the morphology and texture of each contact area.)

The remote sensing and contact instruments listed above are included in the baseline recommendations and are expected to be affordable at the low end of the expected budget (~$90M to $125M) for the science instruments.  If the budget becomes plusher, the SDT recommends two additional instruments to study the shallow subsurface beneath the rover.  A ground penetrating radar would detect subsurface rock and soil layers, providing better context for understanding the geology exposed at the surface.  A gamma ray spectrometer would measure the composition of soil in the upper few centimeters and could alert scientists to interesting substances just below the upper veneer of soil.

A capable instrument suite enables scientific exploration; the rover still must be delivered to a location that orbital instruments show might have been a location for life or pre-biotic chemistry.  A number of such locations are known, and more are being searched for.  However, these sites often lie within rough terrains with just a small area free of large rocks that would end the mission should the rover be unlucky enough to land on one.  The 2020 rover mission will inherit the precision landing system developed for the Curiosity rover that reduced the area of the landing ellipse to a fraction of what it had been for previous landers.  

The SDT recommends shrinking that ellipse further to allow more landing sites to be considered.  On past missions, the parachute has opened at the earliest possible time during the descent.  For the 2020 descent, the SDT recommends that the entry system have the ability to vary the time of opening based on its estimate of its position relative to the landing zone. This relatively simple enhancement could reduce the size of the landing ellipse by 25% to 50%.

Many potentially interesting astrobiology sites on Mars lack any area the size of a landing ellipse free of large rocks or dangerously steep slopes.  A second enhancement the SDT asked NASA to consider is terrain recognition navigation (TRN) that would enable the lander to compare images of the landing area stored on board with real-time images taken during the descent.  This capability would allow the descent system to determine its actual location and steer free of hazardous terrain in the moments of final descent. 

Goal B: “Assess the biosignature preservation potential within the selected geological environment and search for potential biosignatures.”

Examples of potential biosignatures and measurements the 2020 rover could make to find them.

Much of the scientific attraction of Mars comes from its preservation of ancient surfaces and rocks that might retain records of conditions that could have led to life or even records past life itself.  The second proposed goal for the 2020 mission would have the rover actively assess whether biosignatures could have been preserved and to search for those biosignatures.

What would be a biosignature?  If we were extremely lucky, it might be fossilized layers from algae-like micro-organisms visible to the cameras.  More likely, it would be the alteration of rock or soil chemistry in a way that would be best explained by complex organic chemistry or the actions of life.  Again, if we were lucky, it could be the presence of organic matter preserved for billions of years.

The rover would seek biosignatures using all of the instruments listed above and with one or two instruments that would be selected for their ability to detect organic material.  The Viking and Phoenix landers and the Curiosity rover (and the future ExoMars rover) have relied on sophisticated analytical instruments such as mass spectrometers to detect organic molecules.  These instruments are capable of much more sophisticated measurements than is possible with contact instruments that must operate directly in the harsh Martian environment.  Analytical instruments have soil samples delivered to them where they can be analyzed with numerous techniques and altered through heating or wetting to release gasses or induce chemical reactions.

Unfortunately, the budget for the 2020 rover does not include funding for analytical instruments.  Instead, the SDT proposes that the rover carry one or two spectrometers capable of detecting the presence organic matter.  The authors of the SDT report are clear that the strategy they propose will result in the 2020 rover having significantly less capabilities to analyze potential organic material than other missions with analytical instruments.

The SDT points out a compensating new capability for the 2020 rover: sample caching.  As described below, if the cache is eventually returned to Earth, terrestrial laboratories could perform far more sophisticated measurements than would ever be possible on a rover or lander.

Goal C: “Demonstrate significant technical progress towards the future return of scientifically selected, well-documented samples to Earth.”

Priorities for samples to be collected.  The E2E-iSAG was a previous mission assessment for a rover mission focused on selecting and caching samples.

Returning a carefully selected set of Martian samples has long been a goal of the Mars science community.  The last planetary Decadal Survey ranked a mission to select and cache a set of samples for future return to Earth as its highest priority large mission for the coming decade.  A follow on mission would collect the samples and take them into Martian orbit, and a third mission would retrieve the samples from that orbit and bring them back to Earth.

The President’s Office of Management and Budget balked at beginning a sequence of missions that in combination could cost $6B to $8B.  They agreed to the 2020 rover mission to continue the in situ exploration of Mars and to demonstrate technical progress towards future robotic and manned missions, including caching samples.

The SDT concluded that the difference between demonstrating the technical capability to select and cache samples and actually leaving a returnable cache would be minimal.  They recommend the rover assemble a sample cache of up to 31 to 38 five centimeter long core samples of rock and soil acquired by the rovers drill.  Once collected, the cache would be placed on the surface for a future mission to collect in a few years or even a few decades.

Goal D: “Provide an opportunity for contributed Human Exploration & Operations Mission Directorate (HEOMD) or Space Technology Program (STP) participation, compatible with the science payload and within the mission’s payload capacity.”

When the 2020 rover mission was approved by the President’s office, one of the requirements was that it demonstrates technologies that would be useful for future robotic and human missions.  The SDT recommended four options be considered (in priority order):

• Demonstrate the ability to capture and compress Martian air (which is primarily CO₂) and extract liquefied oxygen for use as the oxidizer for the fuel for future a robotic or manned ascent stage from the Martian surface (commonly called in-situ resource utilization or ISRL).  While many parts of this technology can be demonstrated on Earth, key issues of collecting CO₂ under varying dust conditions, winds, atmospheric pressure, and temperatures can be best demonstrated on Mars
• Better instrument the entry and descent system to collect information on the conditions of descent and parachute performance.  (The Curiosity entry and descent system collected extensive information during its landing; the proposed 2020 system would collect that information and new information.)   The technologies discussed earlier to reduce the risk of landing by timing the parachute opening and using terrain recognition would also benefit future missions. 
• Collect extensive weather information including atmospheric temperature profiles and atmospheric dust profiles to better understand atmospheric behavior.  Collecting this information would better characterize the atmosphere and reduce risk for future landings on Mars.
• A biomarker system to “demonstrate detection of microbial contamination for future human missions.”

Concluding Thoughts

Capabilities of the 2020 rover proposed by the SDT.  Boxes without ‘+’ represent the recommended threshold capabilities below which the mission might not deliver sufficient value for the investment.  Boxes with ‘+’ represent highest priority additions beyond the threshold capabilities.  If more funding than the SDT were available, the mission could be further enhanced with either more capable instruments or additional instruments such as a weather station or additional instruments to characterize any organic matter.

The mission proposed by the SDT would meet the goals set out for a caching rover as the top priority in the last Decadal Survey.  It would also meet the goals recently set out by NASA for demonstrating key technologies for future missions.

At the same time, even if the samples not collected, the rover would carry out intensive geological and astrobiological exploration at a fifth site on Mars.  (The Viking landers explored two sites in the 1970s, the Phoenix lander explored the ice-rich northern plains, the Curiosity rover is exploring Gale Crater now, and the ExoMars rover will presumably explore yet another site.)  The new generation of contact instruments that will be ready for the 2020 rover will allow exploration of the composition of Martian soils and rocks at micro-scales that previous missions have not be able to do.  This is an exciting new capability.

While the SDT report doesn’t spend much time on the possible weather station that the 2020 rover may carry, I think this would be an important addition.  Scientists have long wanted to get a network of metrological stations on Mars to better explore weather patterns.  In 2020, there may still be three functioning weather stations already on Mars: Curiosity, NASA’s InSight lander, and the Russian surface station planned for the ExoMars mission.  A fourth station would be an important addition.

The 2020 rover is a mission that will be done on a tight budget.  The highly capable analytical laboratories of the Viking and Phoenix landers and the Curiosity and ExoMars rovers would not fly on the 2020 rover.  The capabilities the SDT recommends for the 2020 rover meet all the requirements previous SDT’s have laid out for a rover mission focused on sample selection and caching.  However, the 2020 rover would have less capability for science on Mars for characterizing organic matter and other volatiles than Curiosity or the ExoMars rover.

Of course, the need for the analytical laboratory would go away if the sample cache is returned to Earth laboratories.  The 2020 rover would make the investment in the first crucial step, selection and caching of samples, of the Holy Grail of Mars science: returning samples.  How long might those samples sit on the surface of Mars before being collected?  I expect that that will be a question for how compelling the discoveries by the rover’s instruments are and the generosity of future governments.  And it may not be American craft or only American craft that collect and return the samples.  In the coming two decades, several space agencies are likely to have the technology to participate in the sample return.

A second bet being made is to leave out a deep drill such as the ExoMars rover will carry.  The drill proposed for the 2020 rover will collect samples five centimeters (about two inches) in length, similar to that carried by the Curiosity rover.  This may not be deep enough to get below the surface radiation that is believed to destroy organic matter at Mars (see this post).  The ExoMars drill was designed with this problem in mind and will reach up to two meters below the surface.  Adding a similar drill to the 2020 rover would require a substantial modification to the Curiosity rover design isn’t possible within the budget.  However, if the Curiosity rover doesn’t find organic matter and the ExoMars rover does but deeper beneath the surface, then the bet on the shorter drill will look problematic.

Even with the current budget realities, though, the SDT has proposed a highly capable, exciting mission.  NASA’s officials warmly received the recommendations, indicating that their final choices for the mission are likely to be similar to those recommended by the SDT, but some changes are possible. 

A key decision by NASA will be on whether to fund the sample collection and caching system and the sophistication of that system.  Current news reports indicate that it intends to fly this system.

The next step for the mission will be for NASA to issue a call to solicit instrument proposals this coming fall.  The type of instruments NASA says it is interested in receiving proposals for is likely to be the definitive statement on the mission’s scientific goals.

For more information on the SDT’s recommendations you can read these documents.

MEPAG Briefing of Final Report of the 2020 Mars Rover Science Definition Team (SDT) (presentation)

Final Report of the Mars 2020 Science Definition Team and appendices