LOGAN, UTAH – Small may soon be big for NASA.

"It’s not the solution for everything, but the proper mix of small and large [spacecraft] is the way to go in planetary exploration," said Charles Elachi, director of Earth and space science at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California. He said the failure of recent Mars missions made the National Aeronautics and Space Administration "risk-shy," so the agency’s headquarters is "not completely on the bandwagon" of small spacecraft.

Elachi said technical advances during the past decade make it possible for small spacecraft to perform planetary science missions.

"Smaller does not mean less capable," Elachi said, noting that miniaturization of attitude-control systems means that "within the next decade, you’ll be able to put the gyroscopes on a chip."

He said the camera on NASA’s Deep Space 1 spacecraft weighs less than 15 pounds (7 kilograms), compared with older spacecraft cameras weighing hundreds of pounds (kilograms).

Spacecraft structures are also shrinking, thanks to advances like propellant tanks made of ultralight composite materials. Antennas, radar dishes and other equipment that can be inflated or unrolled may reduce weights of those components by an order of magnitude, Elachi said.

Miniaturizing interplanetary propulsion systems remains a challenge, he said, citing the need to reduce the size of ion engines or to use solar sails.

He indicated the best bet for launching small planetary spacecraft would be as piggyback payloads on rockets carrying large primary payloads. For example, a European Ariane 5 rocket can carry eight 265-pound (120-kilogram) microspacecraft in addition to the main payload, at a cost of about $1 million for each of the smaller payloads, he said.

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The small (220-pound, or 100-kilogram) spacecraft would be used to reconnoiter terrain that a larger, more expensive and capable mission could study later in greater detail.

Barry Goldstein led a recent JPL study on the Scout concept for the 2003 timeframe.

"We had an excellent concept," Goldstein said. "One of the reasons we did not proceed for 2003 was the perceived risk of not getting together a quality project in time for launch," adding that the class of spacecraft could go to the Red Planet as soon as 2005.

A proposal to fly a Mars glider in December 2003, on the 100th anniversary of the Wright brothers' first airplane flight, was killed by NASA for fear ofan embarrassing public failure.
     

At Mars, other future missions may rely on the same technologies used on the Deep Space 2 (DS-2) microprobes, which failed after purposefully slamming into Mars last December. Peppering a planet with tiny probes modeled on the tiny spacecraft could enable scientists to do work in ways any single, larger mission could not.

For example, probes could provide the backbone of a scientific network, where each miniature spacecraft takes calibrated and simultaneous measurements across a broad area, tracking everything from the weather to seismic activity.

"You can’t just go to one place if you want to do that type of science," said Sarah Gavit, the former Deep Space 2 project manager, in a recent interview. "The idea is not going to go away: it’s too good."

Indeed, Gavit said she and her colleagues were proposing further tests of the DS-2 technology, in order to smooth the way for other mission concepts to make use of it.

During his talk, Elachi gave several other examples of proposals for small spacecraft explorations and said, "There is no doubt in my mind that five years from now these will be real."

• One idea is to place a network of six small satellites in Martian orbit over six or seven years so data can be relayed to Earth almost any time from Mars-landing craft.

"I have no doubt over the next decade we will have a network of that nature, but some people are not ready for it yet," Elachi said. "The key concern is the reliability of the satellites."

• A 19-pound (8.5-kilogram) fold-up glider could be deployed from a 28-inch-long (70-centimeter-long) entry probe, unfurl its wings to a span of 5.7 feet (1.75 meters), then fly over the surface of Mars.

A proposal to fly a Mars glider in December 2003, on the 100th anniversary of the Wright brothers’ first airplane flight, was killed by NASA for fear of an embarrassing public failure, Elachi said.

• Entry capsules on parachutes could plunge through Martian skies, then release instrument-laden floating balloons to make measurements.
• More small Martian rover vehicles are likely, similar to the Sojourner rover deployed from the Pathfinder lander.
• The proposed Japanese MUSES-C spacecraft would make a touch-and-go landing on an asteroid to pick up samples and deploy a U.S.-built rover. The robot would measure 5.5-by-5.5-by-2.8 inches (14-by-14-by-7 centimeters) and weigh only 2.9 pounds (1.3 kilograms), including a camera.

Elachi raised the possibility that diminutive spacecraft with solar sails might be launched toward the edge of our solar system in the next 20 years. He also speculated that in 25 to 30 years a small craft might leave on a 4-light-year (23.5 trillion-mile or 37.8 trillion-kilometer) trip to the nearest star, Alpha Centauri.