Thursday, February 20, 2014

Boundaries for the Next Discovery Mission Selection

In my post a couple of weeks ago on the selection of NASA’s next low cost planetary mission, I said that the conditions NASA imposed on scientists proposing missions would determine much of what kind of missions scientists could impose.

Yesterday, NASA released a preview for the next competition.  There are some important innovations and a major limitation.

NASA will accept proposals to study any solar system body except the sun and the Earth.  Scientists cannot propose missions to study planetary systems around other stars (NASA astrophysics program funds these missions.)

NASA announced that the budget for the spacecraft, instruments, and data analysis (the Principal Investigator (PI) budget) would be $450M (FY15 dollars).   This is a small increase from the last competition’s PI budget of $425M, and by itself would not keep up with inflation. 

Outside of the PI’s budget, NASA will pay for the cost of the mission launch.  For the first time, NASA will pay for the cost of the mission’s operation outside of the PI budget.  In past competitions, missions with long flight times, and hence high operations costs, were at a disadvantage to missions with low operations costs.  This appears to be an effort to equalize operations costs.  Missions that would benefit are any with flight times of several years compared to the weeks or months to reach Venus, the moon, or Mars.  With operations costs not counted against the PI’s budget, the new competition probably keeps up with inflation compared to the previous competition.  (NASA’s announcement does emphasize that the operations costs projected for a mission must be ‘reasonable’.)

The major limitation for this competition is that NASA will not provide a radioisotope power system for this competition.  While recent NASA presentations suggests it has sufficient plutonium-238 fuel to support a Discovery mission, that fuel could not be prepared in time to meet the expect launch date for this competition.  As a result, any mission that cannot use solar power is effectively eliminated.  This would include missions beyond Jupiter, to the permanently shadowed lunar polar craters, or where large solar panels just won’t work like for a mission that would make multiple landings on a comet (see this description of the CHOPPER mission proposed for the last competition).

NASA traditionally offers scientists various technologies at the space agency’s cost that it would like to see tested in space.  For this competition, NASA says it is considering providing a version of the NASA Evolutionary Xenon Thruster (NEXT) ion propulsion engine as well as heat shield technology for missions that would send a probe into planetary atmosphere.  These former would benefit missions that would require large amounts of thrust such as main belt asteroid missions or comet rendezvous missions.  The latter would benefit missions such as Venus atmospheric probes.

NASA also is considering requiring proposals to include carrying its Deep Space Laser Communications (DSLO) package.  This technology was tested on the LADEE mission currently orbiting the moon and showed that lasers could return much larger volumes of data than traditional radio systems.  NASA would now like to try this technology from a spacecraft in deep space.  Missions with low data rates such as Venus atmospheric probes probably would see little benefit from the DSLO system.  Missions with lots of imaging data such as Venus radar mappers or Io multi-flyby missions would make good use of the DSLO system.

One other new requirement is a limitation on how much of the cost of instruments foreign space agencies can contribute.  NASA has had a limitation that foreign governments could not contribute more than one-third the cost of the total mission.  That cap now also applies to the contribution to the cost of the science payload, too.  This appears to be a way of preventing a proposal team from minimizing its PI costs by filling most of the payload with instruments paid for by other governments.  NASA apparently wants US planetary missions to provide opportunities for US scientists to fly their instruments.

All in all, this looks to be a nice opportunity that keeps the Discovery program on track to continue to support innovative missions to a variety of destinations in the solar system.

Key dates (subject to change)

May 2014 – release of draft Announcement of Opportunity with details for proposers

September 2014 – release of final Announcement of Opportunity

December 2014 – proposals due

May 2105 – selection of two to three finalists for further study

October 2016 – selection of winning mission

December 2021 – launch by this date

Tuesday, February 18, 2014

Mission to a Metallic World: A Discovery Proposal to Fly to the Asteroid Psyche

Imagine flying deep within the asteroid belt to study the most unreachable location in the solar system: the deep core of a terrestrial world.

That will be one asteroid mission that will be proposed for NASA’s upcoming competition to select its next Discovery mission to explore the solar system.

We know nothing about what the geology of metal world would be like.  Could the impact crater look like frozen splats?  Credit: JPL/Corby Waste

Asteroids are found scattered across the solar system like artifacts strewn across an archaeological site.  Just as a delicate gold necklace and simple rough potsherd can speak the different strata of an ancient society, the many types of asteroids speak of the strata of conditions in the earliest eon of the solar system.  Stony bodies, for example, formed closer to the sun while icy bodies formed further away. 

By studying asteroids (and their cousins, the comets), scientists can study the remains of conditions from the earliest solar system. 

Most asteroids are smallish affairs with diameters measured in meters to kilometers or at most a few tens of kilometers and are usually chips knocked from larger protoplanets by impacts from still other asteroids.  In a few cases, though, the original protoplanets remain largely intact.  By studying these worlds with spacecraft, geologists can examine how the terrestrial planets formed.  On the true planets, that early history is long lost because of geologic activity.

Some of the protoplanets have a familiar structure like Vesta with its rocky mantle and metallic core that resembles the structure of the terrestrial planets.  Others are unlike any world we have explored to date.  Massive Ceres is a rock-ice world with a deep mantle of ice and is a member of a family of asteroids that emit water vapor (some are even comet like with full dust and ice vapor trails).  The asteroid Psyche is a metal world that may be the remnant core of protoplanet. 

(When I first began reading about the solar system several decades ago, comets were icy balls with some dust and asteroids were rocky.  Now we know that comets and asteroids are a continuum and many asteroids contain substantial amounts of ice that would have been water when these bodies still retained the heat form their formation.) 

Asteroids have been popular targets for solar system missions.  NASA has flown two asteroid missions and is building a third with a fourth listed as high priority.  Japan’s JAXA space agency has flown one mission, is building a second, and is planning for a third.  American and European scientists have proposed numerous additional missions.  In the last competition for NASA’s low-cost Discovery program (~$425M missions), over a quarter of the 28 missions proposed would have flown to an asteroid or observed them with a space telescope.

In the competition for the next Discovery mission expected to begin this year, we can expect a similar enthusiasm from the scientific community.  A good portion of the proposals will probably be to fly to one or more of the small asteroids whose orbits are near the Earth’s.  Flights to these worlds are relatively easy, making the missions that orbit them and even land budget bargains and low risk.  In addition, collisions, gravitational influences of the true planets (especially Jupiter), and even the pressure of the sun’s light have scattered the smaller asteroids across the solar system. Within easy reach from Earth are bodies representing a plethora of conditions that were found across the early solar system. 

Scientists who want to study protoplanets have to look to the asteroid belt between Mars and Jupiter.   There the Discovery Dawn spacecraft has finished its studies of the rocky protoplanet Vesta and is headed towards the rock-ice dwarf planet Ceres.

While the Dawn mission picked off two of the most exciting protoplanets, there are plenty more.  European scientists in their last mission competition proposed two main belt asteroid missions (neither selected).    They focused on two classes of asteroids.  The first were asteroids that have been observed to eject jets of water vapor.  The second class was actually a single asteroid – the metal world Psyche.

Scientists planning to propose Discovery missions usually are reluctant to say much about their ideas.  The competition is tough and missions usually are proposed several times.  Why say something that would give a competing team a good idea?  So of the eight asteroid Discovery missions proposed last time, we know very little about what was actually proposed.

Even with the stiff competition, though, some scientists try to build support for their proposals by making some disclosures in public.  It can’t hurt to have the members of the review panels already excited by a mission before they evaluate the proposal.  In general, we hear more about how scientifically interesting a destination is (those facts are widely known) and less about the spacecraft and instruments (what I know many of the readers of this blog are most interested in).  The few times we hear about detailed implementation, it generally is to a destination that seems beyond the reach of a Discovery-class mission where building technical credibility before the review likely helps.  All three of the teams that have proposed missions to the Saturn system, for example, have revealed a fair amount about the implementation.

The team preparing to propose a mission to the metal world Psyche has been relatively open about their proposal although they talk more about the destination than their spacecraft and instruments.

The asteroid Psyche is one of the larger asteroids.  Credit: Lindy T. Elkins-Tanton

Fortunately, the destination is worth learning about.  Stop for a second and ask yourself – what location for all the planets do we know least about?

It’s the cores of the planets.  We can infer much about the size of the cores from seismic data (so far available only for the Earth and the moon but soon also for Mars), gravitational studies that reveal the mass of the core, and measurements of the magnetic field when present.  No one, though, has ever seen a planetary core or directly measured its composition.

The asteroid Psyche may give us that opportunity.  As bodies coalesced in the early solar system, initially random chance brought dust and ice to clump together.  Once a body reach a kilometer or more in diameter (what is called a planetesimal), its gravity became strong enough to pull more material in to it.  At a critical size, the heat from radioactive elements, collisions, and gravitational pressure melted the interiors of these worlds and they became protoplanets. Iron and nickel metals sank to the cores, mantles formed from the lighter silicate materials or ices, and a crust may have formed of either unmelted primitive materials, or by volcanism from the interior flooding the surface. 

Three possible origins have been suggested for the metallic asteroid Psyche (~250 km diameter), all of them intriguing.

Psyche could be an asteroid in which repeated collisions chipped off the crust and mantle, leaving the core a naked body.  If this is the case, then a mission to this world would be the equivalent to a mission deep below the surface of any of the terrestrial planets to examine their cores.  It’s a journey that is possible only because chance created and then preserved from ultimate destruction by further collisions Psyche’s naked core. 

Psyche could be the remnant of the collision of two protoplanets that shattered and expelled the core of the smaller body to become Psyche.  In this case, we wouldn’t get to examine an intact protoplanet’s core.  We’d still get to examine the composition of a protoplanet’s core, though, and also see how a world composed almost purely of metal formed itself following a collision.  Collisions such as this would be been common in the early solar system.  One is believed to have created the Earth-moon system. All planetary cores, in fact, almost certainly formed from multiple generations of fragmentation, differentiation, and merging of previous cores.

And finally, Psyche could have formed so close to the early sun that all materials other than metals (and some silicates) would have been evaporated and have been unavailable for planet building.  Later migrations of Jupiter and Saturn in and out of the inner solar system could have moved this world to its present location in the asteroid belt.  In this case, a mission to Psyche would show us an entirely new class of world.

Telescopic observations reveal that Psyche’s surface is 90% metallic and 10% silicate rock.  A spacecraft orbiting Psyche likely could distinguish between these scenarios by measuring the composition in detail and looking at the arrangement of the silicate material.  If the silicate material is primarily high-magnesian pyroxene or olivine, then these silicates are likely the remnants of a crystallizing magma ocean, and indicate that Psyche started as a differentiated planetesimal and had its mantle stripped, validating the mission’s prime hypothesis for this body. If the silicates are all primitive chondritic material, then they were likely added as later impacts, and Psyche may have started life as a highly reduced metallic body without a significant silicate mantle, or, the nature of impact flux and its consequences are far more significant than our current models indicate. The numbers and shapes of craters on Psyche’s surface may help decipher that story.

Here are some of the key questions a spacecraft would explore at Psyche:  How did this large metal world form?  If it is a remnant core, what is the composition and structure of a terrestrial world’s core?  If Psyche was once molten, did it solidify from the inside out, or the outside in?  We have a number of meteorites from a single metallic asteroid (the group IVA iron meteorites); is Psyche their source?  The metallic asteroids appear to be much less dense than the metallic meteorites; are these asteroids rubble piles? 

We know a great deal about the geology and surface features of rocky worlds, icy worlds, and will learn about rock-ice worlds when the Dawn spacecraft reaches Ceres next year. Metal worlds may differ significantly in their appearance. What does the surface of a metal world look like?  Imagine how strange a crater might appear. Laboratory tests of craters in metal show that sometimes the ejecta flaps freeze before they fall; could this happen on a planetesimal?

Like the Dawn spacecraft, the Psyche spacecraft would use solar electric propulsion.  As for instruments, the proposal team’s Principal Investigator, Dr. Lindy T. Elkins-Tanton of the Carnegie Institution for Science,  told me, “We hope to learn not just about the surface of this metal body, but also about its interior, which requires geophysics. We'll be carrying a magnetometer, and we'll use the spacecraft itself to develop a detailed model of the body's gravity field. With these measurements and knowledge of topography, we'll get information on internal structure.

“We'll have an imager, of course, in the hopes of seeing some unforeseen new metal geology, and to count craters to measure the age of the surface, among other goals. Measuring the surface compositions of a metal object remotely is more difficult. Infrared spectrometers are great for silicates, but only gamma ray spectrometers can measure metal composition. We expect, though, to see some silicate materials along with the metals.”

I asked Dr. Elkins-Tanton about the possibility of flying to a second asteroid.  She told me that they looked at this and concluded that it wasn’t feasible.  No other asteroid visit would address their questions about metallic asteroids (and the instrument suite that would be wanted for a comet-like asteroid, for example, would be different).  It also would be difficult to fit second asteroid visit into a Discovery mission budget.

In my previous post, I wrote that Discovery mission competitions surprise and delight us with the cleverness of the missions proposed.  While we will hear little about many of the missions likely to be proposed for the asteroids, the Psyche mission gives an idea of what is possible.

You can read a two page summary of the science goals for the Psyche mission at this link.

My thanks to Dr. Lindy Elkins-Tanton for reading a draft of this post and making several useful suggestions.

Wednesday, February 5, 2014

Discovery Next

The Discovery program is unique in NASA’s planetary program.  Within the budget constraints of each selection, the scientific community is free to propose any mission to any destination.  In the last selection, the finalists were the Insight Mars geophysical station (which was selected), a mission to land on the lakes of Titan (TiME), and a mission to orbit and repeatedly land on the nucleus of a comet (CHOPPER).   To paraphrase Forest Gump, the Discovery program is like a box of chocolates – you never know what you’re going to get.  The creativity of the scientific community has given us a wide assortment of missions in the past and is likely to surprise and delight us again.

The missions of the Discovery program have visited a wide-range of solar system destinations.  Image from Historic Spacecraft and used under a creative commons license. 

A month so or so ago, it appeared that the selection of NASA’s next mission in this, its lowest cost planetary mission program, was on indefinite hold.  This program in its first decade produced an incredible wealth of missions of ten missions that studied Mercury, the moon, Mars, asteroids, comets, and the sun.  The program more than fulfilled its goal of ensuring that NASA’s planetary mission portfolio was diversified.

In the second decade, though, just two missions were approved, to the moon and Mars.  For the next decade it was uncertain when the next mission selection would begin.  It appeared that already approved missions in development would consume most of the foreseeable mission development budget. 

That has changed with the NASA budget that was just approved.  Congress directed NASA to accelerate the selection of the next, thirteenth Discovery mission.  Based on the proposals from the last Discovery mission (see list at the end), we can expect a good deal of creativity from the scientific community.

By contrast, the New Frontiers program ($750M to $1B missions) has a list of pre-selected, high priority missions (although creative solutions can be proposed).  The other class of missions, Flagship missions ($1.5B+) like Cassini or Curiosity, are selected by panels of scientists and fostered and developed over a decade or two.  The next two likely missions in this class, the 2020 Mars rover (already approved) and a Europa multi-flyby spacecraft (in study), are well known.

Realistically, there will be limits to the missions that can be proposed for the next Discovery mission.  NASA’s managers will have to decide on the budget they can afford for the mission.  In the past, scientists could propose missions with a total cost of ~$425M for the spacecraft, its operation, and the data analysis.  (NASA paid for the cost of the launch and some other expenses separately.)  Jim Green, head of NASA’s planetary program, said in a meeting recently that the budget will decide how ambitious missions could be.  To afford a mission to the outer solar system, the budget would need to be closer to $500M, but a smaller budget could be set for missions to the moon, Venus, or Mars.

There also will be other key programmatic decisions.  Will NASA pick up the costs of providing a plutonium power system to enable missions that can’t use solar panels for power such as spacecraft that would travel to Saturn, the permanently shadowed craters of the moon, or land repeatedly on a comet?  The latest count of available plutonium power systems suggests that one will be available for either a Discovery or a New Frontiers mission this decade.

A fixed budget also puts missions with long flights to their destinations at a disadvantage compared to missions that go to worlds next door.  Each year of flight to reach a destination costs the mission $7M to $10M, a big disadvantage if the voyage takes five to seven years.  The scientific community has proposed that NASA allow the budget to be flexible to cover costs of long flights.

Then there’s a question of how much risk NASA is willing to accept.  The more ambitious the proposal, the greater the chance it would bust its development budget or fail sometime after launch.  Commentators have said that NASA appears to have become risk adverse in its Discovery mission selections (see here).  On the other hand, where NASA once had the budget to select two missions every two years, it now is looking at perhaps just two Discovery missions a decade.  The relative cost of failure has grown, and low-risk, good-science missions have been available to select.

We will get answers to most of these questions (except the tolerance for risk) in a few months when NASA releases the draft Announcement of Opportunity (AO) for the next selection.  AO’s spell out what NASA is looking for, the budget it has set, the class of launch vehicles it will pay for, and what resources it will make available such as a plutonium power supply.  Proposers will decide to propose or not in response to the constraints placed on the selection.

Congress asked that the AO be released this May, but NASA’s managers have said that they and the scientific community couldn’t be ready by that date.  Instead, a draft AO will come out for the community to comment on in the next few months.  NASA has said that the final AO will be released before next October.

Once the final AO is released, we will still need patience to wait to find out which mission is selected and even longer to see it reach its destination.   The previous AO was released in June 2010, the three finalists were selected in May 2011, the winning InSight mission was selected in August 2012, and launch will come in 2016.  If the next selection follows the same pace and the AO is released in, say, September 2014, the finalists may be known in August 2015, the winner selected in November 2016, and launch in 2020.  If the mission goes to Venus, the moon, or Mars, it could arrive at its destination in weeks or months.  If it goes to Saturn, it could take seven years.

There’s also a question of how NASA will fit this mission into its budget, which is already largely spoken for by missions in development.  NASA had planned to release the AO for its next New Frontiers mission in 2015.  Will that be delayed or does NASA think it can select two new missions this decade?  We will know more when NASA’s proposed 2015 budget is released in March.

In the hopes that future budgets will support the selection and development of the next Discovery mission, this is the kick off post for what will be a semi-regular series of posts on missions that are likely to be proposed.

SpaceNews also has an article on the selection of the next Discovery mission.

I’ll close with a list of previous Discovery mission selections and what’s known about the list of missions that were proposed for the last selection.  This will give an idea of the range of creative missions that may be proposed for the next selection.

Selected DISCOVERY and Mars Scout missions

The Mars Scout program selected missions similar is scope to the Discovery program and has since been merged with the Discovery program.  I’ve indicated these missions with an asterisk.

The first two missions were selected by NASA without an AO
NEAR – near Earth asteroid rendezvous and landing
Pathfinder – Mars lander and rover

AO Date and Missions
1994:     Lunar Prospector - orbiter
1994:     Stardust comet sample return and 2 comet flybys
1996:     Genesis – returned samples of the solar wind
1996:     CONTOUR – multiple comet flybys (failed)
1998:     Deep Impact – Delivered impactor to comet & 2 comet flybys
1998:     MESSENGER – Mercury orbiter
2000:     Kepler – exoplanet hunter
2000:     Dawn – orbit asteroids Vesta and Ceres
2002:     *Phoenix – Mars polar lander
2006:     GRAIL – 2 lunar orbiters
2006:     *MAVEN – Mars orbiter
2010:     InSight – Mars geophysical station

Proposals in response to the 2010 AO

NASA does not release any information on missions proposed except for the three finalists (and then only limited information except for the winner).  The competition is tough and most scientists propose multiple times, so most want to keep their proposals as confidential as possible.  NASA did release the number of proposals for each class of destination.  Where I can, I’ve listed additional detail based on what proposers stated publicly and based on a list maintained by Blackstar at the forum

Venus – 7 proposals
4 proposals reportedly for radar mapping missions
At least one for an atmospheric probe
Moon – 3 proposals
Lunar seismic station
Lunar south pole ice prospector(s)
Mars and it's moons – 4 proposals
Mars geophysical station (InSight)
Asteroids – 8 proposals
A near Earth asteroid lander
Near Earth asteroid survey
Jupiter system – 1 proposals
Io multi-flyby
Saturn system – 2 proposals
Titan lake lander (TiME)
Titan and Enceladus multi-flyby (JET)
Comets – 3 proposals

Comet Hopper (CHOPPER)