WASHINGTON NASA has moved up the deadline for submission of the "final four" proposals for its planned Mars Scout mission. The four finalists are now expected to submit their designs for remote exploration systems, blending advanced robotics with lab-on-chip technology, by May 15 instead of July.
The finalists have each been given an extra $100,000, on top of the $500,000 already promised, to get their designs and feasibility studies in to the agency by the new deadline. NASA has set aside $325 million to build the winning system for a Scout mission to Mars in 2007.
"The goal of the Mars Scout program is to complement the existing Mars Exploration program, which is already putting either an orbiter around Mars or a lander on Mars every two years," said Joel Levine, principal investigator for a remote-control airplane designed to fly in the thin Martian atmosphere. The Mars Scout program, Levine said, is expected to fill in scientific gaps in the Mars Exploration program by answering questions about Mars that will not be addressed by the core mission.
An original series of 25 entries was narrowed down to the four finalists. The judges will consider the scientific merit of each proposal as well as the final implementation feasibility study for each. The feasibility studies will focus on cost, management and technical plans, including educational outreach and small-business involvement. The mission is slated to be launched in 2007 and to arrive at Mars in 2008.
"Each of the selected missions pursues some of the greatest unknowns about potential biological activity on Mars, including such issues as the presence of organic molecules or their by-products," said Jim Gargin, NASA's lead scientist for Mars exploration.
Of the four finalists, two are from outside NASA. Professor Laurie Leshin of Arizona State University (Tempe) is proposing a near-miss fly-by that would scoop up part of the atmosphere and sling-shot it around Mars for the return trip to to Earth.
Leshin earned her "Mars reputation" by studying meteors, allegedly from Mars, found near Earth's polar cap. On this mission called the Sample Collection for Investigation of Mars (SCIM) probe an aerogel would sample atmospheric dust and gas from 40 miles up before using what Leshin calls its "free-return trajectory" to sling-shot the samples back to Earth.
University of Arizona (Tucson) researcher Peter Smith, who previously designed the imager for the Mars Pathfinder program, proposes a rerun of the failed Mars Polar Lander, which apparently crashed on Mars in 1999. His "in situ" study of volatiles, water vapor, organic molecules and climate, called Phoenix, would carry the instruments that have already been built, but never used, for the canceled Mars Surveyor Lander. The Phoenix would take a close-up look at the water detected at the poles by the now-orbiting Mars Odyssey.
Scout Program finalist Mark Allen, a researcher at NASA's Jet Propulsion Laboratory (Pasadena, Calif.), has proposed a Mars Volcanic Emission and Life mission. The mission would conduct a global survey from orbit of the photochemistry of Mars' atmosphere in a search for traces of volcanic and microbial activity. It would also map the movement of water vapor through a full-annual cycle.
The orbiting lab proposed by Allen would house an infrared solar occultation spectrometer a device that makes supersensitive measurements by viewing through the atmosphere sideways as the Sun rises and sets.
The only "airplane" proposal comes from NASA's Levine, whose team has designed and tested an unmanned flyer, Ares (for "aerial regional-scale environmental survey"). The aircraft would be folded up for the trip to Mars but would be deployed into the atmosphere for a 500-kilometer flight just 1 mile above the Mars surface.
"One of NASA's themes for Mars exploration is 'following the water,' which we are literally going to do." Levine said. "We are also going to study the other chemically active gases in the air with a mass spectrometer." Since the Ares craft would fly only a mile from the surface of Mars, it would be able to measure the water vapor while simultaneously pinpointing possible sources of that water on the surface.
As a part of the instrument payload, a mass spectrometer would analyze the atmospheric gases the Ares flyer passes through in real-time, streaming the data back to Earth. The science payload would also include a magnetometer in each wing-tip, to measure the variations in the magnetic field in Mars' crust. A "point" spectrometer would be focused on the surface passing beneath the flyer in order to record its mineralogy and composition of the surface of Mars. For each of these measurements, a camera would record the visual features of the surface that correspond to the measurement.
Also on-board the Ares flyer would be a full complement of "flight instrumentation" to measure the pressure, density, temperature, and three-dimensional structure of the wind as it flies. Finally, a lipstick-sized camera, placed in the tail but pointing forward, would record the flyer itself with Mars in the background. All of the data would stream back by relaying it to the orbiter, which has a radio antenna big enough to broadcast all the way to Earth.
The flyer would also simultaneously scan for the chemically active molecules on the surface of Mars that make it so highly chemically reactive. Scientists believe the Mars surface is so highly chemically active because gases from the atmosphere have condensed on the surface. Ares would test that hypothesis as it flies over Mars' surface.
If microbes exist on the surface of Mars, according to Levine, his instrumentation would be able to detect them from a mile up.
In particular, there are a variety gases that the aircraft's mass spectrometer could identify as the "signature" gases of biological activity. "Our mass spectrometer will be capable of detecting and searching for gases that indicate the presence of life of Mars," Levine said. "Microbes produce a whole suite of gases that serve as indicators of the microbes' being there: methane, ammonia, nitrous oxide . . . If there is life, it is on the surface, and we [would be] so close to the surface that these gases would be sucked into the mass spectrometer, where we could determine every gas that is there."
The 20-foot wingspan of the 200-kilogram (440-pound) Ares flyer must fit into the 8-foot diameter of the aeroshell that would take it to Mars. Consequently, both wings and the tail-section must be folded up for the trip to Mars, which takes about nine or 10 months. The aeroshell would then be deployed from Mars orbit into the atmosphere.
When the aeroshell reaches optimal altitude, a parachute would open to slow it. The aeroshell would be jettisoned, leaving the parachute holding the folded airplane by its tail, nose down. The Ares flyer's rocket engine would then be started up and the parachute detached.
"We believe that the most challenging engineering part of the mission is the deployment of the plane . . . in the thin Mars atmosphere," said Levine.
Late last year, Levine's team shipped a half-scale prototype of the Ares flyer to Oregon, where a weather balloon carried the flyer to an altitude of 110,000 feet in about 90 minutes. It then simulated the aeroshell's being jettisoned. The plane unfolded and detached from the balloon according to plan, Levine said.
It took just seven months to move from concept to successful test of the half-scale prototype, Levine said. The first two prototypes were spent in the two dozen wind tunnels at the NASA's Langley Research Center. By adjusting the air pressure and density to approximate the Mars atmosphere, Levine's team of atmospheric engineers was able to validate a specific design for a plane that could fly in the thin Martian air (1/200th the density of Earth's atmosphere).
"We tested the prototype at 103,000 feet that's over 20 miles above the Earth. The air there is like the air that we are going to have to fly through on Mars; the pressure per square inch and the density are comparable to what's on Mars. The flyer deployed and flew perfectly, landing directly on the white center line at the balloon test facility," said Levine.
The test flight was not powered but was just allowed to glide down under the control of an engineer manning a radio control set used by model-plane flyers. The engine design had not been finalized in time for the initial test, which was designed to prove that a folded plane could unfold and glide from a parachute deployment inside a small aeroshell. Levine said the rocket fuel type has still not been chosen.
The duration of the flight would be highly dependent on the weight of the plane the heavier it is, the shorter its total flight path. To determine how much fuel to take with the flyer, Levine called in a team of knowledgeable Mars scientists and told them of the Ares' instrument payload and the kinds of measurements that were to be made. He then asked them what distance the Ares would have to fly in order to make the mission scientifically worthwhile. The answer was 500 km (300 miles).
"Our feeling is that we can fly considerably longer and make considerably more measurements," Levine said. "But we call 500 kilometers our scientific baseline and we are confident that it is no problem."
An audio recording of reporter R. Colin Johnson's full interview with principal investigator Joel Levine can be found online at AmpCast.com/RColinJohnson.