PASADENA, Calif. -- Dec. 3 will mark the landing of not one, but two missions on Mars, although they will do so in dramatically different ways.
While the Mars Polar Lander will set down at a tame 5.4 miles per hour (8.6 kilometers per hour), the Deep Space 2 microprobes will plunge down on Mars about a minute earlier at nearly 75 times that velocity.
Crash-landing on purpose at 400 mph (644 kph) is the point, though.
The twin probes are designed to punch through the frosty polar layered terrain, making them the first mission to ever penetrate another planet.
Until now, planetary missions have only literally scratched the surface of Mars -- a tradition the Polar Lander will uphold with its robotic arm at its own landing site an estimated 60 miles (100 kilometers) away from the twin probes.
NASA hopes the probes, which are piggybacking to Mars aboard the Polar Lander, will plunge as deep as several feet into Mars upon impact.
Swathed in protective aeroshells the size of basketballs, the microprobes will awaken from an 11-month journey to Mars moments after they are jettisoned by the Polar Lander, or about five minutes before they hit the planets upper atmosphere.
As the probes hit the atmosphere, an accelerometer instrument will be switched on to record gravitational forces 20 times a second as the probes free-fall to the surface. Four minutes later, the accelerometer will begin reading those forces 25,000 times a second through the impact.
Scientists hope the measurements will allow them to characterize the density of the martian atmosphere and the hardness of the polar terrain they will dig into, including -- possibly -- the presence of any layering.
On impact, the gem-shaped aeroshells will shatter and each probe will separate into two parts, a forebody and aftbody. The bullet-shaped forebody -- about the size of a spice jar -- will penetrate the soil, but remain tethered to the aftbody, which will remain on the surface.
On Earth, NASA tested the devices by tossing them from airplanes and
shooting them from airguns.
All data collected by the penetrator will travel through the flexible-cable tether to the aftbody, which will beam it to the Mars Global Surveyor satellite, already in orbit around the planet.
The first data should be received on Earth by 12:30 a.m. ET Saturday, Dec. 4.
Once lodged in the ground, the probes will drill miniature soil samples, which they will then heat and sample for the presence of water vapor. They will also measure soil conductivity by gauging how long the forebodies take to cool once enveloped by the frigid - minus 184 Fahrenheit (minus 120 Celsius) - martian soil.
Since the $30 million mission is primarily a technology test bed, if the probes last two hours beyond impact it will be considered a success. At most, the probes batteries are expected to last for three days.
The mission is the second under NASAs New Millennium Program, which flight tests new technology that - if satisfactory - could then be applied to future missions. Deep Space 1, the first mission, has already successfully tested a dozen new technologies of its own.
A third mission, Space Technology 3, will attempt in 2003 to fly three
space-based telescopes in formation so they may work in unison.
If Deep Space 2 works - and the risks are enormous that it wont - NASA hopes it can become a model for a new way of exploring planets. Some envision sending swarms of microprobes to pepper a planet, forming a network of seismometers, weather stations or other miniaturized scientific stations.
The twin probes were recently named in honor of Antarctic explorers Roald Amundsen and Robert Falcon Scott as part of a NASA essay contest that drew 17,000 entries.
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