Phoenix Mars Lander Due To Enter Martian Atmosphere May 25
Three Mars spacecraft are adjusting their orbits to be over the
right place at the right time to listen to NASA's Phoenix Mars
Lander as it enters the Martian atmosphere on May 25.
Every landing on Mars is difficult. Having three orbiters track
Phoenix as it streaks through Mars' atmosphere will set a new
standard for coverage of critical events during a robotic landing.
The data stream from Phoenix will be relayed to Earth throughout
the spacecraft's entry, descent and landing events. If all goes
well, the flow of information will continue for one minute after
touchdown.
"We will have diagnostic information from the top of the
atmosphere to the ground that will give us insight into the landing
sequence," said David Spencer of NASA's Jet Propulsion Laboratory,
Pasadena, CA deputy project manager for the Phoenix Mars Lander
project. This information would be valuable in the event of a
problem with the landing and has the potential to benefit the
design of future landers.
Bob Mase, mission manager at JPL for
NASA's Mars Odyssey orbiter, said, "We have been precisely managing
the trajectory to position Odyssey overhead when Phoenix arrives,
to ensure we are ready for communications. Without those
adjustments, we would be almost exactly on the opposite side of the
planet when Phoenix arrives."
NASA's Mars Reconnaissance Orbiter is making adjustments in
bigger increments, with one firing of thrusters on Feb. 6 and at
least one more planned in April. The European Space Agency's Mars
Express orbiter has also maneuvered to be in place to record
transmissions from Phoenix during the landing. Even the NASA rovers
Spirit and Opportunity have been aiding preparations, simulating
transmissions from Phoenix for tests with the orbiters.
Launched August 4, 2007,
Phoenix will land farther north than any previous mission to Mars,
at a site expected to have frozen water mixed with soil just below
the surface. The lander will use a robotic arm to put samples of
soil and ice into laboratory instruments. One goal is to study
whether the site has ever had conditions favorable for supporting
microbial life.
Phoenix will hit the top of the Martian atmosphere at 5.7
kilometers per second (12,750 miles per hour). In the next seven
minutes, it will use heat-shield friction, a parachute, then
descent rockets to slow to about 2.4 meters per second (5.4 mph)
before landing on three legs.
Odyssey will tilt from its normally downward-looking orientation
to turn its ultrahigh-frequency (UHF) antenna toward the descending
Phoenix. As Odyssey receives a stream of information from Phoenix,
it will immediately relay the stream to Earth with a more capable
high-gain antenna. The other two orbiters, Mars Reconnaissance
Orbiter and Mars Express, will record transmissions from Phoenix
during the descent, as backup to ensure that all data is captured,
then transmit the whole files to Earth after the landing. "We will
begin recording about 10 minutes before the landing," said JPL's
Ben Jai, mission manager for Mars Reconnaissance Orbiter.
The orbiters' advance support for the Phoenix mission also
includes examination of potential landing sites, which is
continuing. After landing, the support will include relaying
communication between Phoenix and Earth during the three months
that Phoenix is scheduled to operate on the surface. Additionally,
NASA and European Space Agency ground stations are performing
measurements to determine the trajectory of Phoenix with high
precision.
With about 160 million kilometers (100 million miles) still to
fly as of late February, Phoenix continues to carry out testing and
other preparations of its instruments. The pressure and temperature
sensors of the meteorological station provided by the Canadian
Space Agency were calibrated Feb. 27 for the final time before
landing. "The spacecraft has been behaving so well that we have
been able to focus much of the team's attention on preparations for
landing and surface operations," Spencer said.