MRO on course for its dangerous Mars rendezvous
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: March 10, 2006
After a seven-month voyage from Earth, timers aboard NASA's Mars Reconnaissance Orbiter are counting down to a make-or-break 27-minute rocket firing this afternoon to slow the craft enough to slip into a looping elliptical orbit around the Red Planet.
If the burn is too short by just a few minutes, the $720 million mission will sail past Mars and into a useless orbit around the sun. But mission managers say they are confident everything will work as planned for the most sophisticated science satellite ever sent to Mars.
"We are very excited and naturally, because it's part of our job, we're very worried," said project manager James Graf at the Jet Propulsion Laboratory in Pasadena, Calif. "Worried about the things that could jump out and bite us that we don't know are out there right now. At the same time, we're very optimistic, we're optimistic that we've done everything to make sure we're ready to go forward and get MOI (Mars orbit insertion) accomplished successfully."
But, he added in an interview with CBS News, "the thing you've gotta recognize is in the last 15 years, we've lost two orbiters out of four and one lander out of four. We have a lower success rate with the orbiters than we do with the landers. So although we think we've just gotta fire the engines and we're in, there's an awful lot that still has to go on and go on properly for us to make orbit work."
Approaching Mars from below, the solar-powered Mars Reconnaissance Orbiter - MRO for short - will pressurize its propulsion system at 3:50 p.m., a critical milestone and the point where NASA's Mars Observer spacecraft failed in 1993. MRO's flight computer has been programmed to fire up the craft's six 38-pound-thrust main engines main engines about 4:24 p.m. to begin the critical braking maneuver. About 21 minutes into the burn, MRO will disappear behind the limb of Mars and flight controllers at JPL will lose contact with the spacecraft.
If there are no problems, the engines will shut down around 4:51 p.m. and the satellite will emerge from behind Mars at 5:16 p.m. It could take flight controllers up to a half hour to confirm MRO did, in fact, get captured in the proper orbit.
"We're going to burn for about 27 minutes and we have to have a burn of about 23 or 24 minutes just to get into orbit," Graf said. "Otherwise, we're going to go right by. Now, we do have a view of the spacecraft for the first 21-and-a-half minutes, then we become occulted by the planet and so if something happens the last five or six minutes during the course of that burn, we won't know about it until we come out from behind the planet."
The goal is to slow MRO by 2,200 mph, putting the craft in an elliptical orbit with a low point of about 250 miles and a high point of nearly 30,000 miles.
Using a variety of clever tracking techniques, controllers knew MRO was on the proper course going into today's braking maneuver. And unlike any previous robotic mission, MRO's computer can reboot itself in the event of a major problem and restart the rocket firing on its own. But so far, the flight has gone like clockwork.
"At the current time, Mars Reconnaissance Orbiter is safe and stable, with fully charged batteries, pointing at the Earth in full communication with us," flight systems manager Howard Eisen said earlier today. "We have good gyroscopes and a good star tracker and the flight teams ... are working no issues whatsoever."
A timeline of major events is available here.
Assuming a successful MOI, flight controllers will spend the next six to seven months slowly lowering the high point of MRO's orbit by making repeated low-altitude passes through the planet's extreme upper atmosphere. The idea is to use friction with the martian atmosphere to provide the energy necessary to achieve a roughly circular polar orbit.
To guard against overheating the costly spacecraft, flight controllers will proceed very cautiously. Beginning in late March or early April, the low point of the orbit will be slowly 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.
"The first part is there are some practice runs where we just test out the environment, the engines, in this configuration," said project scientist Richard Zurek. "It's like stepping into the pool when you're not sure about the temperature of the water, you put your toe in first and gradually go in. So we go through a series of altitudes to 200 kilometers (124 miles) and then we'll start stepping down from there. It's not until you get to around 160 kilometers (100 miles) of the surface of the planet that youčre really going to start feeling the effects of the atmosphere and even then we've got plenty of margin against overheating.
"So you see what that density is and now you've got your first point correlating altitude with what you're seeing. As we get to the lowest altitude, we'll take smaller steps. So step by step, that's what we call the walk in."
During peak aerobraking, Zurek said, the atmospheric forces acting on the spacecraft will be roughly comparable to what one would feel sticking a hand out a car window at a speed of about 40 mph. But it is heat, not the aerodynamic forces, that pose the biggest concern. Engineers do not want MRO to experience anything higher than about 340 degrees Fahrenheit.
"It's kind of a high wire balancing act," Zurek said. "You want to go deep, and in a reasonable amount of time, to get down to the orbit you want and yet you're not going so deep that you're going to overheat some component of the spacecraft."
Once aerobraking is complete, science operations will begin in earnest.
"In 1964, Mariner 4 flew by Mars taking a stark set of 24 images showing a surprisingly barren, cold and dry planet," Michael Meyer, NASA's lead Mars scientist at agency headquarters, said during a recent news conference. "Over 40 years later, we're now poised to collect more data than all the previous missions combined. MRO ... 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 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."