When it comes to investing in new technology for space science missions, NASA’s philosophy is that science is in the driver’s seat.

“We’ve decided we’re not investing in technology for technology’s sake and we need to make sure that these technologies we invest in [support] our mission set,” said Jim Green, director of NASA’s planetary science division.

Green manages a $1.3 billion annual


that funds the development, launch and operation of orbiting observers and robotic landers sent to investigate the planets, moons, asteroids and comets of our solar system.

Within that

portfolio, only about $70 million is carved out solely and explicitly for the development of new technologies. And the technologies that pot of money goes toward

have some of the broadest applications to the planetary science division’s mission set.


division’s technology program is focused primarily on

advanced propulsion and new radioisotope

systems that can generate power in the absence of the sun’s rays. In the area of propulsion, a good example is a

next-generation version of the ion thrusters currently propelling NASA’s

Dawn spacecraft on its lengthy voyage to two of the solar system’s oldest surviving protoplanets, Vesta and Ceres.

Radioisotope power systems – long-lasting spacecraft batteries that convert heat from decaying plutonium-238 into electricity –

likely will

remain a major focus of NASA’s space science technology development efforts in the years ahead.

Today’s radioisotope power systems, such as the

radioisotope thermoelectric generator being built to supply power to the 2009 Mars Science Laboratory, are only about 4 percent efficient, according to Green. But a so-called Stirling-cycle system that Lockheed Martin has been working on for years in Valley Forge, Pa

., with NASA’s help is expected to be closer to 32 percent efficient and is

considered just about ready for prime time.

NASA put out a call for Discovery- and Mars Scout-class mission concepts this fall that would take advantage of recent breakthroughs in radioisotope power to explore

hard-to-reach solar system destinations previously considered off limits to all but the most complex


. Green said he expected at least 40 proposals to come in by the Nov. 30 deadline.

He hopes to select between eight and 10 of the mission concepts for

further study

and take the results to his boss, NASA Associate Administrator for Science Alan Stern, to make the case that the next Discovery solicitation – still more than a year away – should invite scientists to propose missions that would be powered by NASA-provided Stirling engines.

By making radioisotope power more affordable, Stirling-cycle engines have the potential to open up “new vistas

” for a budget-minded program that some scientists would say already has “picked all the low-hanging fruit,” Green said.

“If the Stirling engine works out for us, now we’ve got some new low-hanging fruit,” he said. “You are able to go to some places where the sun don’t shine. And there’s a ton of those.”

Green also said quite a bit of technology development occurs within the planetary science division’s various mission-focused programs and as part of its roughly $300 million

annual investment in research. The latter is

a broad category that pays for everything from extended mission operations and grant-based research and analysis to some of the early design

work on new classes of instruments.

Green cited the Planetary Instrument Definition and Development Program, or PIDDP, as a “fantastic workhorse” for taking immature instrument technologies and bringing them

to a higher level of


“A number of instruments we’ve flown have grown up through the PIDDP,” Green said. “Unfortunately in the past we haven’t put much money into it. And I am bound and determined to put more money into it. It’s oversubscribed and there’s so many good ideas out there that indeed starting this year we will be investing more money in basic instrument technologies like that.” Green said.

Green also wants to invest

more in


technologies considered too mature for PIDDP funding

but still not ready to be assigned to a mission.

“We’ve done that in the Mars program already. The Mars instrument development program has allowed these higher [technology readiness-level] instruments in and much to its credit it’s really seen some positive results,” he said.

Astronomers, whose focus often is far beyond the reaches of our solar system, also


thinking about the technology investments

needed to

enable the big missions of the future.

During a recent conference in Baltimore focused on


space telescope missions, Jon Morse, who manages

NASA’s $1.5 billion-per-year

astrophysics program

, spoke about the importance of letting science drive technology development rather than the other way around.

For at least some of the technologists present, that approach is just fine, since nearly all astronomers can agree that when it comes to space telescopes: bigger is better.

Ron Polidan,

former chief technologist at NASA’s Goddard Space Flight Center in Greenbelt, Md., and now

chief architect for civil space at Northrop Grumman Space Technology, said during the conference and in a subsequent interview that 20-meter-aperture space telescopes are feasible

by 2020 with the right investments.

The James Webb Space Telescope, which Northrop Grumman Space Technology of Redondo Beach, Calif., is building for NASA, will deploy a 6.5-meter segmented mirror after

it is launched in 2013.

Webb’s basic design was locked down several years ago but

Northrop Grumman has continued to invest


deployable optics research in order to make the most of any given rocket’s

payload shroud, Polidan said. Some of the

new approaches being studied, he said, would enable NASA’s planned

Ares 5 heavy-lift rocket to launch observatories

with primary mirrors nearly 10 times larger than the Hubble Space Telescope’s powerful main optic.

Polidan said he favors one approach called hexagonal stacking, in which six-sided segments are stacked for launch and then unfolded once in space. If it wants to demonstrate the technology on a smaller telescope before committing to a 20-meter behemoth, NASA could use the same hexagonal stacking approach to put a fairly substantial telescope on a rocket as small as a Delta 2, he said.

Harold Reitsema, director for space science

advanced programs at Ball Aerospace & Technologies Corp. of

Boulder, Colo.,

agreed that Ares 5’s huge 10-meter fairing is a potential bonanza for astronomers, with 20-meter apertures probably representing the upper limit of what is doable in the next 15 to 20 years.

“The problem with really large launch vehicles is it takes a tremendous amount of money to fill it with the best technology,” Reitsema said in an interview. He noted that

investments would be needed in new sensors and data-handling capabilities to take full advantage of the light-gathering potential of the very-large-aperture telescopes now being studied.