NASA scientists say they are confident that the Mars Odyssey鈥檚 entry into Martian orbit will proceed flawlessly next week. After losing two Mars-bound spacecraft in 1999, the space agency said on Thursday that it has done every test possible to ensure a successful mission.
鈥淲e could not be more ready for the events that are about to unfold,鈥� says David Spencer, Odyssey mission manager at the Jet Propulsion Laboratory, Pasadena.
鈥淢ars likes to befuddle us,鈥� says Jim Garvin, NASA Mars program scientist. 鈥淲e need Odyssey to be successful to lay the groundwork for future Mars missions programs.鈥�
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Mars Odyssey鈥檚 goals are to probe for near-surface water, map topography and measure radiation levels that might affect future human missions.
Photo: JPL/NASA
The mission鈥檚 moment of truth comes at 0226 GMT on Wednesday 24 October, by which time Mars Odyssey will have spent 200 days travelling more than 460 million kilometres.
However, orbital insertion has a low margin for error and the craft must hit its retrorocket brakes at just the right time and place. As it passes 300 kilometers above Mars, it will fire its main engine to slow down and slip into orbit.
In the 20 minutes that follow, the spacecraft will burn 258 kilograms of fuel and reduce its speed by about 175 meters per second. This will put it into a highly elliptical orbit that ranges from 300 to 28,000 km above Mars.
鈥淭he spacecraft is right on course,鈥� to pass within 25 kilometers of the target altitude says lead navigator Bob Mase of JPL.
Burn up
The spacecraft could survive a passage higher or somewhat lower, but it must stay above about 150 kilometers to avoid falling out of control into the Martian atmosphere and burning up.
That was the fate NASA鈥檚 Mars Climate Orbiter met two years ago after mission planners failed to convert imperial units properly into metric units.
Ten minutes after the engines start to fire, Mars Odyssey鈥檚 path will take it behind the planet, and controllers will lose track of it for a critical 20 minutes.
鈥淚f all goes well, shortly before 0300 GMT, Mars Odyssey will emerge from behind Mars and you鈥檒l see a lot of happy faces,鈥� Spencer told a press conference.
Aerobraking manoeuvre
Controllers plan to spend three days fine-tuning the eccentric 19-hour orbit before directing the spacecraft to dip into the upper fringes of the Martian atmosphere to slow the probe and adjust its orbit.
Over the three months that follow, a series of these passes, called aerobraking, will move Mars Odyssey toward a circular two-hour orbit, 400 km above the surface.
This is the orbit from which the craft will begin collecting data, starting in early February 2002.