Bringing an Asteroid Home

Conceptual design for an asteroid capture and retrieval spacecraft.  Credit: Rick Sternbach/Keck Institute for Space Studies

Aviation Week and Space Technology reports that the President’s next budget request for NASA will include funds to begin developing a mission to bring an asteroid to the Earth-moon system.  The initial goal will be to provide a destination for a manned mission to an asteroid, but if the idea works, it could kick start asteroid mining.

The insight behind the mission is that it’s technically easier and cheaper to bring a small asteroid to where it can easily be reached by a manned mission than it is to send astronauts to an asteroid.  This may seem counter-intuitive.  The feasibility study that proposed the idea defined a small asteroid as around 7 meters in diameter with a mass of 250,000 to 1,000,000 kg.  The robotic spacecraft will have to travel to the asteroid, match its spin, net it, de-spin it, and then drag it back to the Earth-moon system.  However, robotic spacecraft and asteroids don’t require complex life support systems and near fail safe engineering systems.  If the robotic mission fails, it’s a shame.  If a human mission fails with the loss of the astronauts, it’s a catastrophe.

This concept was originally proposed last year in a study carried out by the Keck Institute for Space Studies at the California Institute for Technology (which is also home to the Jet Propulsion Laboratory).  The study participants included scientists and engineers from a wide range of institutions.  You can read the report here.

The mission would be enabled by three key developments.  First, we need the technology to be able to find a number of very small asteroids so that one can be selected with the optimum trajectory, size, and spin.  (An asteroid spinning too fast would exceed a spacecraft’s capacity to de-spin it.)  The desired C-type of asteroids would be dark and spotting them is considered by at least one of the authors of the feasibility study as the toughest part of the concept.  The size of the target asteroid was selected as the smallest that was believed to be detectable in large enough numbers to find a good candidate.

Second, high powered solar electric engines would be needed to be able to transport the asteroid back to the Earth-moon system.  The spacecraft will need to simultaneously operate four 10-kW engines to enable the mission.  For comparison, the total power system for the Dawn spacecraft, which also uses ion propulsion, is 10-kW.  Bringing the asteroid to the vicinity of the moon puts it near the top of the Earth-moon system’s gravity well and greatly diminishes the propulsion requirements for the mission compared to bringing the asteroid to lower Earth orbit.  A near lunar destination also minimizes the risk of impact with the Earth (it’s impolite, to say the least, to drop a small asteroid in someone’s back yard, although a C-type asteroid would likely disintegrate before reaching the Earth’s surface).

The final key development will be the launch system and spacecraft needed to deliver astronauts to the asteroid.  NASA already is working on these – the Space Launch System and Orion spacecraft.  What it has lacked has been a credible use for the system.  Flights to near Earth asteroids require months or years to a destination that lacks drama, lunar missions require landers that aren’t funded, and Mars is a distant dream.  What the proposers of this scheme – and now NASA, apparently – believe is that a relatively short flight to an asteroid brought to our backyard would be a winning combination.

Once an asteroid is returned, what would the astronauts do?  The proposers suggest that early missions would be focused on scientific examination, testing operations near and on a tiny body, and validation of methods that eventually could lead to mining and processing the asteroid’s material.  C-type asteroids are rich in volatiles and conveniently have the consistency of dried mud, simplifying mining.  A 7 m carbonaceous asteroid is estimated to contain 100 tons of water, a similar amount of carbon-rich compounds, and 90 tons of metals (mostly iron).  A key problem with enabling human exploration beyond the moon is the cost of delivering fuel and water beyond low Earth orbit.  One or more small asteroids could become fueling stations for missions two or three decades from now.

The cost to deliver the asteroid to the vicinity of the moon was estimated at $2.65 billion, or somewhat more than the cost of the Curiosity Mars rover mission.  The human spaceflight system is being paid for separately.  The proposers do not give a cost estimate for developing and operating the mining equipment.  For the coming year, NASA reportedly will ask to $100M to refine the technical requirements of the asteroid capture spacecraft and operations.  A launch to an asteroid presumably would not occur until the end of this decade or early in the next.  

Editorial thoughts: As a scientific mission, I don’t know how the science community would rank an asteroid retrieval.  For the same price as the $2.65B cost estimate, NASA could fly a Europa mission, conduct sample returns from several types of asteroids, cover much of the cost of a Mars sample return, or fly an orbiter and probe to Uranus.  (In reading the proposer’s report, it appears that the technical analysis of the mission is in the early stages.  I would not be surprised to see the final cost of the mission be substantially more than the current estimate.)

However, if humanity is to move into deep space, then this mission, I believe, could a brilliant interim step.  It would provide a target for sustained operation at the cusp of deep space, much as the early Gemini missions tested the technology and operations that led to the success of the Apollo mission.  The asteroids brought back could also provide the raw materials needed to enable missions deeper into the solar system.  (Bringing back other types of asteroids could also provide more valuable metals that might be mined for return to Earth.) 

At the moment, political leaders have not been willing to fund bold initiatives for human spaceflight.  Perhaps the greatest value of this mission would be that it would enable forward momentum so that future politicians can make the bold choice.

LPSC Highlights

At the end of March, planetary scientists will gather for the 44^th Lunar and Planetary Science Conference.  This is one of the top scientific conferences held every year for planetary science, with thousands of oral presentations and posters presenting the latest results from on on-going missions or analyzing data from past missions.  (A good source for the meeting’s highlights will be the Planetary Society’s blog.)

A tiny fraction of the presentations at LPSC will deal with future missions.  However, this is still one of the best sources for insights into details of missions under development.   In this post, I’ll cover some of the abstracts for the presentations that give a flavor of the breadth of the proposals.  (Abstracts are typically two pages and qualify as mini papers, so there’s plenty of detail.  The abstracts are also published on the web well ahead of the meeting, so I was able to write this post prior to the meeting.) 

Narrowing down the abstracts proved to be hard.  There are abstracts that provide the first detailed descriptions I’ve seen of the instruments that will fly on future missions.  Examples in this category include the cameras and visible to near-infrared spectrometer for NASA’s upcoming OSIRIS-Rex asteroid mission (launch in 2016).  In some cases, I’ve already written about the proposed missions or very similar versions, such as the European Inspire concept for multiple geophysical stations on Mars, landers for Venus, or flyby spacecraft for Jupiter’s moon Io. 

What follows are summaries of my selection of abstracts that present concepts new to this blog and that I found most interesting.

You can explore all the abstracts at http://www.lpi.usra.edu/meetings/lpsc2013/pdf/program.pdf.  You can read about future instrument concepts at http://www.lpi.usra.edu/meetings/lpsc2013/pdf/sess641.pdf , future missions and concepts at http://www.lpi.usra.edu/meetings/lpsc2013/pdf/sess638.pdf, and asteroid future mission concepts at http://www.lpi.usra.edu/meetings/lpsc2013/pdf/sess735.pdf

At the end of March, planetary scientists will gather for the 44^th Lunar and Planetary Science Conference.  This is one of the top scientific conferences held every year for planetary science, with thousands of oral presentations and posters presenting the latest results from on on-going missions or analyzing data from past missions.  (A good source for the meeting’s highlights will be the Planetary Society’s blog.)

A tiny fraction of the presentations at LPSC will deal with future missions.  However, this is still one of the best sources for insights into details of missions under development.   In this post, I’ll cover some of the abstracts for the presentations that give a flavor of the breadth of the proposals.  (Abstracts are typically two pages and qualify as mini papers, so there’s plenty of detail.  The abstracts are also published on the web well ahead of the meeting, so I was able to write this post prior to the meeting.) 

Narrowing down the abstracts proved to be hard.  There are abstracts that provide the first detailed descriptions I’ve seen of the instruments that will fly on future missions.  Examples in this category include the cameras and visible to near-infrared spectrometer for NASA’s upcoming OSIRIS-Rex asteroid mission (launch in 2016).  In some cases, I’ve already written about the proposed missions or very similar versions, such as the European Inspire concept for multiple geophysical stations on Mars, landers for Venus, or flyby spacecraft for Jupiter’s moon Io. 

What follows are summaries of my selection of abstracts that present concepts new to this blog and that I found most interesting.

You can explore all the abstracts at http://www.lpi.usra.edu/meetings/lpsc2013/pdf/program.pdf.  You can read about future instrument concepts at http://www.lpi.usra.edu/meetings/lpsc2013/pdf/sess641.pdf , future missions and concepts at http://www.lpi.usra.edu/meetings/lpsc2013/pdf/sess638.pdf, and asteroid future mission concepts at http://www.lpi.usra.edu/meetings/lpsc2013/pdf/sess735.pdf

Components of the Selene-2 mission, from LSPC 2013 Abstract 183

Abstract 1838: SELENE-2 – The Japanese space agency has been studying a follow on mission to their highly successful SELENE lunar orbiter since 2009.  SELENE-2 would place a lander and rover on the lunar surface, and would be Japan’s first major lander on another world.  (The Hayabusa missions include tiny landers for asteroids.)  In addition to developing the lander and rover technology, the mission would conduct serious science.  The lander would be a geophysical station with a seismometer, a heat flow probe, a magnetometer, precise radio tracking, and a laser reflector.  (The last would allow precise measurements of the distance between the Earth and lunar surfaces by reflecting laser pulses from Earth-bound telescopes.  Combined with radio tracking, this will help study tiny wobbles in the moon’s position giving clues to the interior structure.)  The rover would study the chemistry of the lunar surface with a number of spectrometers to study composition.  An orbiter with a small number of instruments would complete the mission.  Unfortunately, it appears from the abstract that the Japanese space agency has lacked funds to move the mission out of the study phase and into development.  As a result, the launch date has slipped from 2015 to 2018 at the earliest.   If this mission does fly, it will join a number of others from China, Russia, and India in the coming decade.  The moon could prove to be even more crowded with spacecraft than Mars will be.

The following two abstracts propose missions for very small spacecraft, built on the CubeSat paradigm.  CubeSats are designed around small, standard building blocks (cubes).  Depending on the mission, a spacecraft may use one or several cube building blocks.  CubeSats have become popular for Earth orbital missions for implementing very focused science on small budgets.  Various teams are now looking at potential uses of CubeSats for planetary missions.  Many instruments cannot be hosted on these tiny platforms, so these craft won’t replace larger spacecraft.  However, CubeSats may enable a new class of standalone missions or as auxiliary spacecraft carried by much more capable mother ships.

Abstract 1233: LunarCube – This abstract highlights the challenges of adapting CubeSats to missions beyond the Earth and the limitations on the science they can do.  The authors point out that advances in consumer electronics have led to reductions in size, mass, and power while processing capabilities have increased.  However, to operate beyond Earth orbit, CubeSats must be enhanced for longer mission lives, require navigation and propulsion systems, more robust communications systems, and hardening for more severe radiation and thermal environments.  (These are the reasons that planetary missions of all sizes cost substantially more than equivalent Earth observing satellites.)  Once these challenges are met, the resources for the instrument(s) will be constrained.  A Lunar Water Distribution LunarCube could carry a near infrared spectrometer to map water in lunar soils that would be limited to 2 kilograms, 2 Watts of power, and 1500 bytes of data returned per day.   Two other mission concepts are listed with similarly constrained payloads: a craft to analyze plumes kicked off the lunar surface by a separate impact craft and a proof of concept radio astronomy mission that would operate from the surface.   The ultimate goal for the LunarCube project is to create a design for a “virtual ‘smart phone’ with a variety of experiments.”   Editorial Thoughts: Despite the limitations, missions like these to the moon or perhaps to near Earth asteroids would perform real science.  They would be especially useful for training new researchers on how to develop and manage missions at relatively low cost. 

Concept for small Uranus spacecraft based on CubeSat form factor.  From LSPC 2013 Abstract 1860

Abstract 1860: Small Spacecraft Exploration of Uranian Moons – This abstract proposes a solution for an eventual Flagship (~$2B) Uranus orbiter.  To fully observe Uranus and its magnetosphere, the spacecraft will need an orbit that carries it over Uranus’ poles.  The moons, however, orbit above the equator and will be difficult to observe.  The authors of this abstract propose that the main spacecraft would carry four large CubeSat-based daughter spacecraft that would examine the moons.  (CubeSats designs can be enlarged by ‘stacking’ multiple cubes; this design would have the volume of six cubes.)  These small spacecraft would operate in pairs.  As a pair approaches a moon, they would image its surface and measure its gravity by monitoring each other’s relative speed (much as the two GRAIL spacecraft did for our moon).  These craft would need advanced technologies.  Their solar panels would need to convert approximately 50% of the light striking them to electricity.  (This is much higher than current production solar panels can do, but the technology is under development and in the lab has reached 42%.)  The daughter craft would use very small ion (“electrospray”) engines to set up their encounters with the moons.  The craft would need to be able to carefully manage their power use and storage and largely operate autonomously.

Abtract 1291: Mars Aerial Vehicle – Airplanes have been proposed for Martian exploration since at least the late 1970s.  The extremely thin atmosphere of Mars makes flight difficult, and the proposals I recall all had lives measured in hours before they exhausted their power reserves and crashed.  This proposal would make the craft part balloon and part aircraft.  The shape would be that of an aircraft, but the body and winds would be filled with helium, giving the craft 70% neutral buoyancy.  The rest of the necessary lift would come from a propeller powered by batteries that would be recharged by solar cells on the wings.  While the abstract doesn’t discuss how long the craft might operate, it would seem that it could operate for at least days and perhaps much longer until too much helium had leaked out.  The aircraft would carry a ground penetrating radar and a magnetometer to search subsurface ice and hydrated soils.  Because the aircraft would be much closer to the surface than orbital spacecraft, resolution would be much higher, allowing it to pinpoint local deposits.

Several instruments that would date Mars material could measure dates for a diversity of rock and soil fragments within a sample.  This image shows the laser operating in a grid pattern.  Note that each sample is a small fraction of a square millimeter. From LSPC 2013 Abstract 1762.

Abstract 1762: Rb-Sr  Dating – Over the last few years, several research teams have made good progress in developing instruments that could date rocks and soils and be carried on Mars rovers.  Unlike most worlds whose rocks formed within a few hundred million years of the birth of the solar system, Martian rocks have formed over billions of years.  Unfortunately, establishing the chronology of Mars’ geologic history has been tough and subject to large errors.  (The current method depends on counting craters, with surfaces that are older having more craters.  However, the rate at which craters are formed is uncertain and craters on Mars can be buried by dust or eroded away.)  The instruments under development would examine rocks on Mars and fix their age to within tens of millions of years.  Most of the instruments, such as the one described in this abstract, would use micro lasers to melt tiny (~75x5 microns in this case) samples of rock or soil.  The instruments would then measure the ratios of key isotopes in the released vapor to establish ages.   One of the elements would be the radioactive decay product of the other; since the rate of decay is well known, the ratio of the two would establish the age.  This abstract is one of several at the LPSC meeting describing progress.  I’ve highlighted this one because it is more descriptive (i.e., less technical) than the others and probably would be the most readable for many of the readers of this blog.  Editorial Note: The next opportunity for one of these instruments to fly to Mars would be on NASA’s 2020 rover.  I don’t know if any will be technically ready in time or whether the limited instrument budget for that mission can afford the cost of completing development for a flight ready instrument.

 

Mars 2020 Rover: Science There, Here, or Both

By July 1, a group of scientists will define the goals of the rover NASA will launch in 2020 to Mars.  The rover will be a near twin of the Curiosity rover that is currently on Mars.  (Since Curiosity is nuclear powered, it may still be operating when its sibling arrives.)  The Curiosity design will ensure that the rover is highly capable.  What the Science Definition Team (SDT) will determine is what its scientific goals are.  From those goals, NASA will select a suite of instruments to fulfill those goals.

What I’ll attempt to do in today’s post is to discuss some of the tradeoffs that I think may be considered in selecting the science goals.  I won’t attempt to discuss potential individual instrument selections – the scientific community is tremendously creative in developing instrument concepts, many of which lie outside my expertise.

The most basic question will be whether to do detailed composition analysis there, here, or both.  There means on the surface of Mars, and here means returning samples to the laboratories of Earth.  The Phoenix lander, Curiosity rover, and the planned European and Russian 2018 ExoMars rover will carry highly sophisticated chemical laboratories rovers (science there).  However, while the instruments on those rovers are engineering marvels, they are pale imitations of the incredibly more varied and sensitive instruments in laboratories here on Earth (science here). 

The Mars community has decided (formally through the last Decadal Survey) that answering the key questions about Mars requires the sophistication of Earth-based instruments.  The goal identified in the Survey for the next Mars rover was to find and cache samples for eventual return to Earth.  Science instruments on the rover would serve primarily to identify interesting samples to collect.  The catch, though, is that returning those samples will require two additional missions costing $4-6B.  In an era of shrinking US federal budgets, any samples collected may languish on Mars for a decade, perhaps several, and possibly forever

In a world of plush budgets, focusing the 2020 rover on simple sample collection would be the obvious choice (as it was for the members of the Decadal Survey in days of rosier budget forecasts).  In a world of shrinking US Federal budgets, though, the SDT members may decide that equipping the rover with highly capable – but expensive ($10s of millions) – instruments may be a better choice.  With this strategy, whether samples are returned or not, the rover will have conducted sophisticated analyses of rocks and soils:  A guaranteed science return.

So why not just do both?  Collect samples and carry a sophisticated science laboratory?  The answer is a limited budget and conflicting operational strategies.  The former is simpler to explain.  The science instrumentation budget for the 2020 rover is expected to be $80-100M, approximately half that available for developing the Curiosity rover’s instruments.  NASA’s managers have stated that the budget won’t provide the funds for developing a full suite of complex new instruments.

The conflict in the operational strategies arises from how to maximize the use of time.  (While the 2020 rover may operate for many years, planners can count on only the two it is designed for.)  For a caching-focused mission, the goal is to visit as many locations as possible, assess their potential for samples worthy of return to Earth, and move on quickly from the many that don’t make the cut.  For a science on Mars-focused mission, the preparation and analysis of each sample requires long periods parked in one spot.  (Think of the weeks Curiosity has spent parked in each of the two locations it has analyzed samples (although the process should speed up as the rover’s operators gain experience).) 

For either mission strategy, two sets of instruments might be the same.  The first suite will consist of remote sensing instruments that study the surrounding landscape without physically touching any of it.  Cameras will serve as the eyes of geologists (and armchair explorers on Earth).  The rover may carry one or more spectrometers that analyze different portions of the electromagnetic spectrum to map composition.  The Spirit, Opportunity, and the ExoMars rover used or will use this approach.  An alternative would be to use a laser to vaporize rock and soil surfaces to enable chemical analysis of the briefly glowing vapor as the Curiosity rover does.  Whatever the instruments selected, their goal will be to select specific locations for study or sampling and to understand the geological context.

A second set of instruments would be located on the rover’s arm and would be physically placed in contact with soils and rocks to make their measurements.   The Spirit, Opportunity, and Curiosity rovers carried both microscopic imagers and spectrometers to measure composition.  (The ExoMars rover will not have a robotic arm and doesn't have equivalent instruments, although it will have an infrared spectrometer embedded in its drill bit.) The advantage of these instruments is that they conduct their measurements quickly, allowing fast assessments.  The downside is that the types of instruments and their sophistication are limited by the need to fit on the head of the robotic arm and be exposed to the harsh Martian environment.

For the 2020 rover, though, the compositional contact instruments may be much more sophisticated than those flown to date.  Previous instruments measured average composition across each sample area (1.7 cm for Curiosity).  If you look closely at soils and most rocks, you’ll see that they are composed of many smaller rock fragments, each with its own story.  The next generation contact images may be able to differences composition across the contact area as small as 0.5 mm or smaller.

Regardless of the science focus, the 2020 rover seems likely to carry instruments from these first two suites.  Depending on the science goals, it may also carry a third suite, an analytical laboratory.  These would be instruments within or mounted on the rover that receive samples delivered by the rover’s drill or scoop.  These instruments can be larger, allowing for more sophisticated measurements.  They can also manipulate the samples, say heating them to drive off organic molecules or wetting them to measure the resulting chemical reactions.  The Spirit and Opportunity rovers were too small to carry these instruments, but Curiosity carries two.  The Phoenix lander also had an analytic laboratory as will the ExoMars rover. 

The range of instruments possible for an analytical laboratory is wide, and I seem to find two or three new proposals with each scientific conference that includes discussions of future Mars missions.  One core instrument type is a mass spectrometer and gas chromatograph combination that can “taste” gases driven off a sample by heating a sample.  This is a standard technique for measuring carbon chemistry, including organic molecules.  The Curiosity rover carries one (the Sample Analysis at Mars, or SAM instrument) and the ExoMars rover will carry a more capable version.

An exciting new class of instruments that are maturing to become flight ready would perform geochronology on Mars rocks and soils to nail down their ages.  Understanding the age of key events in Mars’ history, recorded in its rocks and soils, is one of the motivating goals of returning samples to Earth.  The development of instruments that can be carried to Mars provides an opportunity to address key questions without the cost of returning samples.

However, NASA’s managers have already stated that the limited instrument budget for the 2020 rover will preclude development of a suite of new instruments.  That would seem to favor the remote sensing and contact instruments over the more capable but also much more complex and expensive laboratory instruments.  A previous science definition team that examined instruments for a caching rover called for only remote sensing and contact instruments.

Careful ‘shopping’, though, may be able to extend the budget.  NASA could fly copies of the Curiosity instruments, whose development has already been paid for.  It might also fly copies of one or more of the ExoMars instruments.  (The ExoMars MOMA instrument itself uses a copy of much of the Curiosity’s SAM instrument.)  NASA has also said it is open to instruments provided by – and very importantly, paid for – by other nations.

Editorial Thoughts: I have seen a multitude of proposals for Mars sample return over the past several decades and not one has come close to being funded.   I personally am wary of flying a rover mission that focuses too heavily on sample acquisition and caching.  Those samples may never reach Earth, and funds for major rover missions may come very infrequently.  While planetary scientists see sample return as the necessary next step, the long history of failed sample return proposals suggests that returning rocks exciting to geologists and astrobiologists doesn’t open the public checkbook for a many billion dollar outlay.  (My personal guess is that Congress will provide the funds for a sample return if a rover finds complex organic molecules suggesting past or present life. )

I will be shocked if the SDT doesn’t call for the rover to collect and cache samples in case governments come to feel generous.  However, I’d also like to see one or more complex analytical instruments fly, even if they are copies of previously flown instruments.  So do science there and enable science here.  That would guarantee more sophisticated measurements, and the measurements they do make may show that the samples exciting to the general public as well as scientists.