[meteorite-list] NASA Probes Shifting Orbits for Curiosity Rover Landing

[Ron Baalke]

http://www.spaceflightnow.com/news/n1203/06marsorbiters/

NASA probes shifting orbits for Curiosity rover landing
BY STEPHEN CLARK 
SPACEFLIGHT NOW
March 6, 2012

Two NASA spacecraft circling Mars have begun repositioning their orbits
to provide engineering insight into the landing of the Curiosity rover
on the red planet in August, supplying engineers on Earth with vital
data during the robot's dramatic rocket-assisted touchdown.
 
Engineers are shifting the orbits of the Mars Reconnaissance Orbiter and
Odyssey probes, ensuring they have line-of-sight communications with
Curiosity as it lands at Gale crater, a 96-mile-wide impact site adorned
with rugged rock formations and a colossal central peak.

Landing is scheduled for early Aug. 6, U.S. Eastern time.

"Odyssey and MRO have begun positioning their orbits so that they will
be overflying [the Mars Science Laboratory] during entry, descent and
landing," said Fuk Li, director of Mars exploration at the Jet
Propulsion Laboratory in Pasadena, Calif.

Without MRO and Odyssey, controllers would lose crucial information on
how the $2.5 billion mission performs as it plunges through the Martian
atmosphere at hypersonic speeds, deploys parachutes, fires a rocket back
and lowers the six-wheeled rover to the surface on a bridle.

NASA has never tried such a landing system before, and if it works, it
will allow the space agency to place much larger, and heavier, payloads
on Mars. Live insight into the landing will yield crucial information on
how the system works, and would give NASA reams of data in the event of
a mishap or failure.
 
The Odyssey spacecraft, which has orbited Mars since late 2001, will be
the primary means of monitoring Curiosity's progress during landing.
Odyssey will be in view of both Curiosity and Earth, so the orbiter will
offer bent-pipe communications, receiving transmissions from the rover
and relaying them directly to Earth.

Traveling at the speed of light, the signals will reach Earth several
minutes later.

The rover carries its own X-band direct-to-Earth transmitter, but it
only provides a communications rate of about 1 bit per second, just
enough to send status tones back to mission control at JPL.

"It will only tell us roughly what it is doing," Li said.

With Odyssey, engineers will receive a stream of data at 8,000 bits per
second.

After losing the Mars Polar Lander mission on descent to the red planet
in 1999, NASA began requiring live communications with probes heading
for the Martian surface, according to the space agency. NASA received no
data from MPL during landing, challenging an engineering investigation
tasked with finding a cause of the failure.
 
Launched in 2005, MRO will collect data from Curiosity and play it back
to Earth about an hour after landing.

The European Space Agency's Mars Express spacecraft will also listen to
Curiosity during the landing, giving NASA four methods of obtaining
information on how the lander performed.

"Spacecraft all around Mars will be listening as we enter that day," Li
said.

Odyssey also provided real-time bent-pipe communications from NASA's
Phoenix lander when it touched down on the northern polar plains of Mars
in 2008.

The Spirit and Opportunity rovers, which arrived at Mars in 2004, only
communicated with a direct-to-Earth transmitter.

The Mars orbiter fleet will also be essential during Curiosity's science
operations. Odyssey and MRO will relay commands to the rover and
research data, imagery and health information back to Earth.

"For MSL, they are instrumental to make it work," Li said. "Without
them, MSL's operation would probably slow down by a factor of ten."