NASA has outlined its testing plan for the entry, descent and landing system that it hopes will get its Phoenix lander safely to the Martian surface on 25 May.

Phoenix will dig for water ice in Mars' north polar region, study the ice's history, monitor polar weather and investigate if microbial life could have survived underground. The mission is also part of NASA's preparations for human exploration.

Its main systems were built for the Mars Surveyor 2001 Lander, but that mission was cancelled in February 2000 after the Mars Polar Lander crash-landed in 1999. Correcting vulnerabilities identified by the crash investigation was a focus for the Phoenix team.

 Phoenix Lander
 © NASA
An artist's impression of the Pheonix lander on the surface of Mars

"We evaluated the [vehicle's] robustness...most notably the entry, descent and landing [system]," says NASA's California based-Jet Propulsion Laboratory's Phoenix project manager, Barry Goldstein. According to NASA, less than half of all Mars landers have successfully landed.

The entry, descent and landing testing included more than 60h of flight testing of the craft's radar, which NASA says is more than all the previous NASA Mars missions combined. Originally an altimeter radar, the system will determine vertical and horizontal velocity and altitude during the descent's final minutes. The computer will adjust the firing of 12 descent thrusters using the radar's data.

Two problems posed during descent include the possibility that the jettisoned heat shield may confuse the radar, making it think Phoenix was at a much lower altitude, and the 5% probability that the parachute would contact the lander after it separated, 40s before touchdown.

At 39.5s to touchdown the lander's rocket motors will pulse to control its orientation and vertical and horizontal velocity, so the Phoenix team programmed a manoeuvre to avoid any parachute contact.

Phoenix was launched by a Delta II rocket from Cape Canaveral air force station on 4 August 2007. The mission is being operated for NASA by the Lunar and Planetary Laboratory at the University of Arizona in partnership with the Jet Propulsion Laboratory, Lockheed Martin, and the Canadian Space Agency.

Source: Flight International

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