After a journey of 10-months and more than 400 million miles, Phoenix is set to arrive at the Red Planet just before 8 p.m. EDT this Sunday, beginning its study of water and possible conditions for life in the Martian arctic. Brent Shockley, Phoenix Configuration and Information Management Engineer, noted on the mission blog, that the Phoenix remains in good health and the navigation team is having daily meetings to evaluate the trajectory of the spacecraft to determine whether a final trajectory correction maneuver will be required on Saturday night.

NASA plans a press conference for tomorrow to relay the status of the spacecraft and the decision for a final trajectory correction maneuver tomorrow night.

Phoenix will land in an arctic plain comparable in latitude to central Greenland or northern Alaska. The selected landing area is centered at 68.16 degrees north latitude, 233.35 degrees east longitude. Topographical mapping by Mars Global Surveyor’s laser altimeter indicates a broad, shallow valley about 50 kilometers (about 30 miles) wide and only about 250 meters (about 800 feet) deep.

The intense period from three hours before the spacecraft enters Mars’ atmosphere until it reaches the ground safely is the mission phase called entry, descent and landing. The craft will hit the top of the atmosphere at a speed of 5.7 kilometers per second (12,750 miles per hour). Within the next six and a half minutes, it will use heat-generating atmospheric friction, then a parachute, then firings of descent thrusters, to bring that velocity down to about 2.4 meters per second (5.4 miles per hour) just before touchdown.

There is no guarantee of a successful landing, despite extensive analysis, testing and review of the entry, descent and landing system. In the international history of the space age, only five of 13 attempts to land on Mars have succeeded.

The entry, descent and landing system for Phoenix weighs less than the systems for earlier Mars missions, such as the air bags that cushioned the impacts for Mars Pathfinder and the Spirit and Opportunity rovers. This helps give Phoenix a higher ratio of science-instrument payload (59 kilograms or 130 pounds) to total launch weight (664 kilograms or 1,464 pounds) than any spacecraft that has previously landed on Mars.

Like NASA’s twin Viking landers in 1976, Phoenix will use descent thrusters in the final seconds down to the surface and will set down onto three legs. The system on Phoenix resembles Mars Polar Lander’s more than Viking’s. Mars Polar Lander reached Mars in 1999 but did not land successfully. Engineers for Phoenix have remedied all the vulnerabilities identified in reviews of Mars Polar Lander, and have also identified and addressed dozens of other potential issues.

Seven minutes before it reaches the top of Mars’ atmosphere, Phoenix will jettison the cruise stage hardware that it has relied on during the long flight from Earth to Mars. Half a minute later, the spacecraft will begin a 90-second process of pivoting to turn its heat shield forward. Five minutes after completing that turn, Phoenix will start sensing the top of the atmosphere, at an altitude of about 125 kilometers (78 miles). Friction from the atmosphere during the next three minutes will take most of the velocity out of the descent. Friction will heat the forward-facing surface of the heat shield to a peak of about 1,420 degrees Celsius (2,600 degrees Fahrenheit) at an altitude of 41 kilometers (25.5 miles).

Posted by Zoov on 24 May 2008 03:38 pm
Filed Under: Sci-Tech |