Small Planetary Science Missions

The Vision for Space Exploration included a strong component of HSF robotic precursor missions and robotic science missions to exploration destinations.  Robotic precursor missions are a worthy topic, but today I'll discuss the status of robotic Planetary Science missions at NASA.  The status of the Mars program has been well-publicized, with NASA's withdrawal from ExoMars participation, near-term cuts to Mars mission funding, and the decision to initiate Mars-2020, a mission like the one that delivered the Mars Surface Laboratory Curiosity rover, but with an instrument suite that is yet to be determined.  The status of other NASA Planetary Science missions has not received nearly as much attention.  However, with recent and expected budget cuts, there will be no outer planets flagship missions, and the smaller Discovery and New Frontiers mission lines will be slowed.  Lunar Quest and Mars Scout small missions are already gone. Future Planetary Exploration gives some insight into the direction Discovery and New Frontiers are heading:

I picked up one key point in Monday’s meeting while listening to James Green, the head of NASA’s planetary science program.  In reviewing his program’s projected budget, his team believes that it can start two additional New Frontiers missions ($1B each) and a single Discovery mission ($500M) in the next ten years. The balance between the two programs is NASA's choice; for approximately the same funding it could select one New Frontiers and three Discovery instead.

The recent Planetary Science Decadal Survey anticipated 5 Discovery mission starts and 2 New Frontier mission starts over the course of a decade.  In its first decade, the Discovery program was able to start even more missions than that.  Now we could be looking at only a single competitively selected Discovery mission in a decade.  That's a going-out-of-business pace for Discovery, the backbone of NASA Planetary Science.

It is interesting that NASA has decided to implement the highest priority Flagship mission of the Decadal Survey.  However, Flagship missions are not the highest priority of the Survey:

It is also possible that the budget picture could turn out to be less favorable than the committee has assumed.  This could happen, for example, if the actual budget for solar system exploration is smaller than the projections the committee used.  If cuts to the program are necessary, the committee recommends that the first approach should be descoping or delaying Flagship missions.  Changes to the New Frontiers or Discovery programs should be considered only if adjustments to Flagship missions cannot solve the problem.  And high priority should be placed on preserving funding for research and analysis programs and for technology development.

The bold is the Survey's, as this is one of their key points.

The budget cuts are harming NASA Planetary Science, but ignoring the Decadal Survey and implementing a Flagship mission at the expense of most of the remnants of the Discovery mission line is not helpful.

Since we are already ignoring the Decadal Survey, I have a suggestion designed for these budget-challenged times.  That suggestion is to initiate a new line of "very small" Planetary Science missions.  With the possibility of a decade where Mars-2020 and 3 other missions are the only new starts, and the prospect of even more budget cuts to Planetary Science in the years ahead, something drastic is needed to keep the program and the associated science community in business once the missions that are currently in operation and under construction go silent.  Incoming data will be needed in future years.  Imagine if one of the rare future missions fails?  Something is needed for survival in the data-lean years, and I suggest that be a new line of competitively selected, low-cost, highly-focused Planetary Science missions.  These would be cost-capped at a level that is considerable lower than Discovery ($500M plus launch and possible NASA-furnished equipment in some cases).  Maybe the figure would be $200M, or maybe even $50M or much lower.  The goal would be to have frequent new mission starts, perhaps one per year or 2.  This mission line could be like NASA's new orbital Earth Ventures line (the line includes orbital, suborbital, and instrument mission series) or the Heliophysics and Astrophysics Explorers.  An example mission is CYGNSS.  The line would be for independent missions, and not for adding instruments to other organizations' planetary missions, since NASA already has such Missions of Opportunity.  In today's budget situation, implementing such a mission series would likely mean sacrificing one of the large missions, like one of the New Frontiers missions, which would certainly not be an easy choice to make.

One objection to such a proposal is that even though the cost of such missions would be lower, the corresponding reduction in science returned would be even greater.  Either mission risk would be increased unacceptably, or mission capability would decrease unacceptably.  Small missions may work for Astrophysics, Heliophysics, and Earth Science, but missions in those fields have a much easier time because they don't need to go to other planets, with all of the associated difficulties of communication bandwidth, long mission life, propulsion requirements, and more for flyby and orbiting planetary missions, let alone the challenges of landers and sample return.

One response to that objection is that Planetary Missions don't all have to go far.  Discovery shows this.  There could be "very remote" sensing missions like Kepler or NASA's proposed Near Earth Asteroid survey instrument that don't come close to their subjects.  There could be sample missions like Genesis that don't need to approach a distant planetary body.  A mission could wait for a NEO to approach us.  A lander could use a "less gentle landing" style like the ill-fated Deep Space 2 impactors.  Starting a line of such competitive procurements would likely generate many new low-cost mission ideas.

My main response to this argument, however, may take a bit of a leap of faith for the skeptical critic.  That response is that mission capabilities for small missions are increasing rapidly, and Planetary Science should not leave itself out of this trend.  Cubesats are becoming more powerful and a low-cost industry is growing around that standard.  Multiple cubes can be combined for more ambitious missions.  The Interplanetary Cubesat Workshop is evidence of the effort to increase the reach of Cubesats.  Planetary Resources is a company developing low-cost spacecraft capable of investigating asteroids.  An announcement is expected tomorrow for Deep Space Industries; we will have to wait to see what their vision is.  Multiple Google Lunar X PRIZE teams are striving to send missions to the lunar surface.  That is a largely private competition, but some teams may also be interested in having a government customer.  NASA has a space technology program that may be interested in demonstrating technologies like aerocapture or solar electric propulsion at other planets.  Perhaps some sort of collaboration could occur with that organization on a small Planetary Science mission.  Many other small spacecraft efforts are in progress for Earth environment observation, military, technology development, and other purposes, perhaps representing a combined wave of efforts unlike any that has come before.  NASA Planetary Science can ride this wave, and at the same time help it grow, or it can ignore it and struggle, perhaps successfully, to scrape up the funding for each one of the small remaining handful of large missions it now expects.