Game Plan for NASA's Planetary Missions

Planetary exploration at a crossroads. On one hand, right now the pace of discovery is head-spinningly rapid. Robotic explorers are orbiting Venus, Mars, Saturn, and the Moon, with another days away from arriving at Mercury. Spacecraft heading to solar-system destinations near and far are queued for launch later this year. It's a great time to be a planetary scientist.

But there's writing on the wall, and it isn't very positive. While the Obama administration has requested $1.54 billion for NASA's solar-system activity in fiscal 2012 budget, up 11% from fiscal 2011, it'll start dropping in the years thereafter. By 2016 NASA's planet-chasers will working with only $1.25 billion.

Against this backdrop, today the National Research Council's Space Studies Board (part of the U.S. National Academy of Sciences) released an exhaustive, 400-page report that lays out a strategy for planetary exploration from 2013 to 2022. The NRC released similar assessments for astrophysics and heliophysics last year.

Although technically these "decadal surveys" assess the entire scope of a space-science discipline — NSF-funded activities, new directions for research, and which new technologies are worth developing — their real raison d'être is to decide which space missions should be A-listed for funding. And NASA counts on the panels to represent the consensus of each particular scientific community — once the rankings are made, that's pretty much it.

You have to give credit to Steven Squyres and his 15-person steering committee: since getting their marching orders two years ago, they've collectively digested 199 position papers representing the views of nearly 1,700 individuals. For purposes of manageability, the task force carved up the solar system into five domains: Mars; other terrestrial worlds (Mercury, Venus, and the Moon); giant planets; satellites; and primitive bodies (comets and asteroids).

"First and foremost, we're trying to take the pulse of the community," Squyres explains. But at the same time it's all got to fit within NASA's projected budget, and to ensure that the candidates' costs were estimated both by their proponents and by an independent aerospace contractor. "The good news is that these costs are probably realistic," he notes. "The bad news is that you're going to see some sticker shock."

NASA flies three classes of interplanetary craft: low-cost Discovery missions; moderate-cost New Frontiers missions; and uber-costly Flagship missions. Although it didn't weigh in on Discovery candidates, the panel recommends continuing this highly productive program at its current level ($500 million per year). Also reaffirmed is the decision to build the Mars Trace Gas Orbiter in partnership with the European Space Agency.

For a suitable venue to unveil the report, titled Vision and Voyages for Planetary Science in the Decade 2013-2022, the Space Science Board chose the Lunar & Planetary Science Conference, whose 1,500 attendees have much to gain — or lose — from the panel's picks for Flagship and New Frontiers consideration. And here they are:

Flagship missions

The only two serious contenders were the same ones offered up during the previous go-round returning samples of Mars to Earth, and sending a dedicated orbiter to Jupiter's enigmatic moon Europa. Last time, Europa got top billing — this time, it's Mars.

The envisioned sample-return effort would actually entail three missions: one or two rovers to collect and cache samples, a rocket that boosts the samples into Martian orbit, and a ferry dispatched to Mars to return the samples to Earth. It's such an expensive undertaking to complete that only the first of these elements — the Mars Astrobiology Explorer-Cacher (MAX-C) — is being considered. But the panel admonishes NASA and ESA, its partner, that the price tag for MAX-C needs to come down to $2.5 billion to be viable &hellip and that likely will require leaving one rover behind.

"Some scientists in Houston voiced concern at the choice of a "Mars Sample Return or Bust" strategy — not only because there's no Plan B for long-term exploration of the Red Planet but also because the Jupiter Europa Orbiter has been under study for years and is considered technologically ready to go. There's no question JEO would produce amazing science, Squyres says, but its projected cost of $4.7 billion is "a scary big number" — the kind of budget-busting expense that would crowd out many smaller efforts.

Farther down on the wish list are Flagship missions to Uranus, Enceladus, and Venus. But, realistically, the crescendo for spending cuts in Washington likely means that NASA's budget will be hamstrung for years to come. That reality, combined with the ballooning cost overruns for the James Webb Space Telescope, likely means that none of these big-ticket undertakings are in the agency's foreseeable future.

"We'll have a challenge to execute a Flagship mission within the existing budget," admits James Green, who heads NASA's solar-system-exploration efforts. "Until a different budget is passed, those are my marching orders."

New Frontiers missions

So space-exploration junkies wanting a quicker science fix should instead keep tabs on the Discovery pipeline and get to know the proposed midsize missions, which have price tags at or below $1 billion (with launch rockets priced separately). Two approved spacecraft in this class are New Horizons, now en route to Pluto, and Juno, to be launched toward Jupiter this August. A third should be selected for funding within a few months.

Squyres' panel would extend the New Frontiers series with a fourth mission selected from one of these recommendations:

• a sample return from the surface of a comet
• a sample return from the giant basin South Pole-Aitken on the lunar farside
• a probe of Saturn's atmosphere
• a multi-destination tour of Trojan asteroids
• a Venus lander

Then the following two candidates would be added in prior to the selection of the fifth New Frontiers mission:

• a Jupiter orbiter optimized for frequent flybys of the volcanic moon Io
• a network of geophysical monitoring stations on the Moon's near- and farsides

Now that the recommendations are out, Squyres and his steering committee plan to take them on the road to build that all-important community consensus at a series of town-hall presentations. He then hopes droves of planetary scientists will contact their representatives in Congress — not only to draw attention to the great missions waiting to be flown, but also to try to keep NASA's solar-system budget from taking the nosedive projected for the years ahead.

Click here to watch a replay of tonight's presentations by Squyres and Green.