NASA plans on launching its first Mars Scout mission in 2007 at a cost capped at $325 million. But what that mission will actually be is still unknown. It's up to a jury of experts to choose from among four mission concepts: Phoenix, Marvel, Ares, and Scim.
May the best concept win.
Phoenix, a project headed by Peter Smith at the University of Arizona Lunar and Planetary Lab, uses technology developed for the 1999 Mars Polar Lander, which disappeared on descent to Mars. From the ashes of that program, researchers will resurrect and reuse a stereo-imaging camera and robotic arm. It will also carry a thermal-gas spectrometer.
A Delta II rocket will send the Phoenix to Mars, where it will aerobrake into the atmosphere, deploy a parachute to further slow its descent, then fire guided thrusters to cushion its touch down in the polar region. Exactly where it lands is important, so Smith and his team are conducting extensive premission planning using images from the previous Mars mission. Fortunately, a guided-entry system, also developed for the Polar Lander, will help assure Phoenix lands relatively close to the target area they stake out.
Once on Mars, the robotic arm, guided by a fully pointable, stereo-imaging camera mounted on its "wrist," will dig a trench 2 ft long, 4 in. wide, and up to 3 ft deep. The camera will photograph the trench's sides and bottom and assist in taking samples at various levels. "We need stereoscopic imaging to provide a 3D map of the digging area," says Smith. "The arm is stupid and must be told exactly where the surface is. Stereo will give us distances to nearby features and let us calculate their sizes."
The arm is strong enough to dig through hard soils and scrape into ices, but it can't overpower solid rock. "So if it lands on a slab of granite, only samples of surface dust will be possible."
Each sample, and there will be up to eight of them, is heated in an oven, which should vaporize any organic molecules and some inorganic ones as well. A mass spectrometer determines the exact composition of the gases from the samples. And although the heat and vaporization may make it difficult to determine the exact composition or biology of the samples, organic samples will leave telltale signatures.
"If the trench descends through an organically depleted layer, one that's dry and UV irradiated, to an organically rich, icy layer, then we will have established that a habitat suitable for life exists on Mars," says Smith. "But whether there are living organisms in our samples may be impossible to determine."
The solar-powered Phoenix relays data back to Earth via the Mars Reconnaissance or Odyssey Orbiters, which will be orbiting Mars. As a backup, Phoenix carries a steerable antenna for direct-to-Earth communications, which are possible anywhere on the sunlit portion of Mars. The mission should last 180 sols. (A sol is a Martian day, which is about 40 min longer than an Earth day.) And although the lander should make it through the polar summer, it probably won't survive the winter. There are no plans to recover the Phoenix once its mission is complete.
Mark Allen, a scientist a NASA's Jet Propulsion Lab in Pasadena is proposing the Mars Volcanic Emission and Life Scout mission, Marvel for short. It places a spacecraft in a near polar orbit, one that crosses close to both poles and almost perpendicular to the equator. The craft carries a solar occultation infrared spectrometer that takes measurements by looking at light from sunrises or sunsets as it shines through particles in the thin Martian atmosphere. That's one reason it will be in a polar orbit. It gives the spectrometer a sunrise and sunset on every orbit. Polar orbits also guarantee the craft eventually flies over the entire Martian surface.
The spectrometer detects a variety of substances indicative of life or hydrothermal activity. It's said to be so sensitive it can detect the presence of three cows on the planet by the methane they produce, a by-product of their digestion. (A cow produces 600 liters of methane per day.) Hydrothermal systems would reveal their presence by emitting plumes, which would change the near-surface humidity.
Marvel also carries a submillimeter spectrometer for detecting near-surface water and other signs of life and hydrothermal activity in airborne dust and water vapor. It should work in all Martian weather, including major dust storms. And if the occultations spectrometer detects traces of interesting compounds, scientists can retune the submillimeter instrument to look for them.
There's also a camera onboard for showing scientists what the cloud cover looked like when atmospheric readings were taken. Marvel is a close copy of the 2001 Mars Odyssey that has been successfully operating in Martian orbit for over a year. But Marvel's scientific instruments put it in position to detect signs of both life and volcanic activity. And if it doesn't detect these signs, it severely limits the likelihood of life or volcanism near the surface
Radiation-hardened computers on the satellite will process some data to reduce the amount sent to Earth. And at the end of its mission, a full Martian year, (687 days), the spacecraft will be boosted into a higher, quarantine orbit to prevent its entry into Mars' atmosphere.
The Ares mission (Aerial Regional-scale Environmental Survey of Mars) involves a rocket journeying to Mars and ejecting a capsule containing a folded up aircraft. Then, according to project leader Joel Levine, an atmospheric scientist at NASA, the shell slows using a parachute and deploys the Ares aircraft while still falling. The craft unfolds and fires its rocket engine to begin its flight mapping magnetism embedded in the Martian crust and gathering data on the composition of the surface and atmosphere.
It will also measure isotopic ratios of carbon, oxygen nitrogen, and noble gases to reconstruct the atmospheric and climactic evolution on Mars. "Lighter gases escape from the atmosphere faster than heavy ones," explains Levin. "So by measuring two isotopes of the same gas, we can calculate how much atmosphere has escaped over time. This could help establish whether Mars once had a thick, warm atmosphere or if it was always as cold and thin as it is today."
Ares will fly 300 mph and 1 km above magnetic anomalies discovered by Mars Global Surveyor, making three parallel laps around a racetrack pattern above Mars' Southern Highlands. Then it goes on to other preplanned areas before the rocket runs out of fuel and the plane crashes. Although it will take only an hour to accomplish its primary tasks, Levine and his team hope the plane stays aloft longer.
A pair of magnetometers record residual magnetism in the crust, repeating a task done by Surveyor. "But a magnetometer's resolution is proportional to the distance between the instrument and the object being measured," says Levine. "Surveyor flew 400 km high, so we'll have a 400-fold increase, more than two orders of magnitude, in spatial resolution."
Although there are areas of crust with magnetism, Mars has no planetary magnetic field. Scientists believe crustal magnetism is left over from when Mars did have a planetary field, and those portions of crust could date back 4.6 billion years and the birth of the planet. Earth, which is just as old, has no crust that old due to plate tectonics and continental drift constantly recycling the surface.
Ares carries a downward-looking point spectrometer to further examine the crust. It unravels the mineralogy and composition of the surface based on changes in reflected sunlight. A nose camera photographs areas being examined by the point spectrometer. A second, tail-mounted video camera gives a pilot's view of the flying craft to its Earth-bound handlers.
Ares also carries a mass spectrometer, one capable of analyzing an atmospheric sample every 10 sec. It will look at the atmosphere and how it interacts with the surface. Specifically, it will search for varying concentrations of water vapor, biogenic gases such as methane, ammonia, and nitrous oxide, that are generated by microorganisms, and chemically active gases such as hydrogen peroxide and ozone. "These last two gases could explain why the Martian surface is so chemically reactive," explains Levine.
Data will be relayed through the "bus," the rocket that carries Ares from Earth to Mars. It will drop Ares into the Martian atmosphere without going into orbit around Mars, but it won't have time to get too far off before Ares starts sending back data. As a backup, Ares transmits data through one of the three orbiters that will be circling Mars in 2008, the Global Surveyor, Odyssey, and Reconnaissance Orbiter.
At Arizona State Univ., Laurie Leshin and her team are working out the details of their Sample Collection for Investigation of Mars (Scim) proposal. They want to send a spacecraft to Mars, where it will swoop into the atmosphere, grab some air and dust samples, then hightail it back to Earth. They reason that bringing samples back to Earth will let scientists use the best scientific instruments and techniques to examine them for information on Martian climate and geology. The samples could also help determine if meteorites currently thought of as being from Mars really are of Martian origin.
The mission begins with a fuel-efficient trajectory to Mars, where the spacecraft will make a high-speed flyby over the area it will be sampling one year later. The craft will scan the area, letting Leshin and her crew confirm that its atmosphere is laden with dust. On its next close pass of Mars one year later, it will dip into the atmosphere and take dust and air samples. Flying 40 miles high, it will collect a liter of atmosphere and, according to Leshin's calculations, at least 1,000 dust particles measuring 10 microns or more in diameter, along with millions of smaller particles.
"The dust particles should be representative of the Martian surface," says Leshin. "Dust on that planet is broadly homogenized in global dust storms. Thus, a scoop' of this dust, when examined one grain at a time, will tell us about the variety of material on or near the surface."
To ensure dust isn't harmed or altered while being collected, Scim uses aerogel modules to cushion the impact as particles enter the spacecraft. Silicon-based aerogel, manufactured at NASA's Jet Propulsion Lab, is solid but has a porous, spongelike structure in which 99% of the volume is empty space. The collection vessels are also cooled to prevent atmospheric heating from "cooking" the samples.
The spacecraft carries a Light Flash In-situ Dust Counter that will provide data on the number of dust particles in Mars' atmosphere. When a particle hits a sensor in the device, a small flash of light is generated and counted. This will be the first direct measurement of dust density in that planet's atmosphere.
The space capsule is aerodynamically stable and uses no thrusters on its short trip past Mars. It does, however, uses small thrusters about 10 months later to set up the return trajectory to Earth. Once close to Earth, a two-year journey from Mars, it will eject the capsule holding the samples. "We have a small landing ellipse or target area, and the capsule will be tracked on reentry," explains Leshin. "And we hope to get permission to land in the Utah Test and Training Range, just like other NASA missions. Given the navigational accuracy in today's spacecraft, there' s no chance of it going down where we don't expect it to, such as in the ocean, for example."
Once on Earth, samples will be stored in a dedicated clean room in the Astromaterials Lab at the NASA Johnson Space Center in Houston. JSC also houses the Apollo moon rocks, meteorites, and other space materials. Scim's dust and gas samples will be available for study by qualified investigators worldwide.