Mars Reconnaissance Orbiter nears arrival at red planet
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: February 24, 2006
If the burn doesn't work or is too short, the 4,800-pound solar-powered MRO will race past Mars and on into a useless orbit around the sun. Given the spacecraft's excellent health after a seven-month, 310-million-mile cruise to Mars, mission managers are confident everything will work as advertised.
But they'll still have their fingers crossed.
"We are right on the money right now heading towards our encounter with Mars on the 10th," said James Graf, MRO project manager at NASA's Jet Propulsion Laboratory. "I have to say, we're getting into the dangerous portion of the mission. The cruise has not been easy, we've accomplished an awful lot during that, but now we're starting to enter into the realm where we've lost two spacecraft in the last 15 years."
That first orbit will have a low point of about 250 miles and a high point of nearly 30,000 miles. Over the next seven months, MRO will make repeated low-altitude passes through the planet's extreme upper atmosphere. This aerobraking process will provide the atmospheric friction needed to slowly bleed off energy and circularize the orbit at an altitude of less than 200 miles.
Mars orbit insertion is a critical maneuver with little margin for error. NASA's Mars Climate Orbiter was lost during orbit insertion in 1999, victim of an embarrassing navigation error, and the Mars Observer was lost in 1993 when its propulsion system was pressurized just before arrival.
"We will be approaching the southern pole of Mars and the spacecraft will be pointing directly to Earth at that point in time," Graf said. "We will rotate the spacecraft about 120 degrees to keep the low gain antenna pointed in the manner that we can continue to communicate back to Earth. Then we fire the thrusters.
"If we don't succeed in firing the thrusters, we will fly right by the (planet). So this is obviously the critical maneuver. We have to decrease our speed by 18 percent during that phase."
Twenty-one minutes into the rocket firing, MRO will disappear behind Mars as seen from Earth and remain out of contact for a half hour.
"So we will not see the end of the burn itself," Graf said. "We will be doing all of this automatically on the spacecraft, that is, to terminate the burn. We will slew back to an attitude so that we can view back to Earth the minute we come out from behind Mars."
Flight controllers at JPL will regain radio contact at the point, but it will take another 30 minutes or so to analyze how the spacecraft's velocity is affecting the signal and thus, whether MRO successfully achieved orbit. The goal is a 35-hour orbit with a low point of about 249 miles and a high point of some 27,340 miles.
The spacecraft's cameras will be used to take a few test shots during the initial orbit, but the instruments will be put into hibernation for the remainder of the spring and summer while aerobraking runs its course.
To take full advantage of atmospheric braking, the low point of the orbit will be carefully reduced to around 62 miles. It will be raised, or "walked out," later, with the ultimate goal being a roughly circular orbit with a high point of at most 199 miles and a low point as close as 158 miles to the surface.
Here is a timeline of major events on March 10 (in Earth-received Eastern Time):
10:24 a.m.: Final trajectory correction maneuver if needed
04:07 p.m.: Start spacecraft turn to orbit-insertion orientation
04:19 p.m.: Turn complete
04:24 p.m.: Orbit insertion rocket firing begins
04:45 p.m.: Spacecraft enters martian shadow; on battery power
04:47 p.m.: Loss of signal as MRO passes behnd Mars
04:51 p.m.: End of orbit insertion burn
05:13 p.m.: Spacecraft turns for Earth pointing
05:16 p.m.: Acquisition of signal
Once in its planned orbit next fall, science operations will commence.
"In 1964, Mariner 4 flew by Mars taking a stark set of 24 images showing a surprisingly barren, cold and dry planet," said Michael Meyer, NASA's lead Mars scientist at agency headquarters. "Over 40 years later, we're now poised to collect more data than all the previous missions combined. MRO is set to enter Mars orbit on (March) 10th and is expected to return 34 terabytes of information. This is about as much information as in a video store. I can only imagine the number of exciting things we're going to find on the planet.
The Mars Reconnaissance Orbiter began its journey Aug. 12, 2005, with a ground-shaking launch atop a Lockheed Martin Atlas 5 rocket. The spacecraft is the latest in a series of robotic probes designed to explore Mars at ever-increasing levels of detail.
Equipped with a suite of sophisticated cameras and other instruments, MRO will sniff out underground ice deposits, map the red planet's geology with unprecedented clarity and monitor its tenuous, dusty atmosphere.
It also will serve as a communications satellite, relaying measurements and observations from future Mars landers while using its own ultra-high-resolution camera and other instruments to identify possible landing sites.
With six sophisticated instruments, including a giant 1.2-gigapixel camera capable of photographing objects as small as a kitchen table, the Mars Climate Orbiter is expected to beam back three to four times the combined output of two NASA spacecraft already in orbit around Mars, along with NASA's Cassini Saturn orbiter and the old Magellan Venus orbiter.
"Since Mariner 4, we've learned that Mars was once warmer and wetter," Meyer said. "But when, and for how long, remains to be the central question in our understanding of the biological potential of Mars. MRO will be multitasking. It's going to be a weather satellite, it's going to be a surveyor, able to identify geological features, minerals, the subsurface structure, it's going to be a communications relay and a guide to the next decade of exploration. The instrument capabilities are unprecedented.
"So after the hair-raising Mars orbit insertion and several months of aerobraking, MRO will start the science orbit and acquire a tremendous amount of data. We will be well placed in finding exciting new features on Mars, places to go and the wherewithal to unveil the past and potential future of Mars."