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Planetary News: Mars (2006)Mars Reconnaissance Orbiter (MRO) on Final Approach to Red PlanetBy A.J.S. RaylMarch 8, 2006
The Mars Reconnaissance Orbiter (MRO) – which is carrying the most technically advanced payload ever sent to another planet -- began its final approach to the Red Planet yesterday after activating a sequence of commands designed to get the spacecraft successfully into orbit; today all systems are looking good for a seamless – albeit partially blind -- orbit insertion on Friday, March 10, mission officials announced at a press conference held today at the Jet Propulsion Laboratory (JPL). MRO, which launched on August 12, 2005 from Cape Canaveral and has traveled more than 493 million kilometers (306 million miles) to get to Mars -- is currently traveling at 10,300 kilometers (6,400 miles) per hour on a precision trajectory. As it gets closer and closer to the planet in the next two days it will double its speed. When the NASA spacecraft -- which was designed and developed by JPL and Lockheed Martin Space Systems -- pulls into the Martian port Friday, it will join two other American orbiters – Mars Global Surveyor and 2001 Mars Odyssey, twin Mars Exploration Rovers Spirit and Opportunity, and one European Space Agency (ESA) orbiter, Mars Express, each of which has been investigating Mars for two years or more. While the Martian port may be getting a little crowded, there is no chance that MRO will get lost in the crowd. Rather, this “next generation” spacecraft promises to make its presence known both in terms of size and technological capability. The final approach sequence, which MRO initiated Tuesday, will culminate when it fires its main thrusters for about 27 minutes on Friday – an action that puts “a foot on the brakes,” so to speak, to reduce the spacecraft’s velocity by about 20 percent as it swings around Mars at about 5,000 meters per second (about 11,000 miles per hour) just enough so that it can be captured by Mars’ gravity. "We have been preparing for years for the critical events the spacecraft must execute on Friday," said Jim Graf, MRO project manager at JPL. "By all indications, we're in great shape to succeed, but Mars has taught us never to get overconfident. Two of the last four orbiters NASA sent to Mars did not survive final approach."
That said or disclaimed, everything really is looking good, and a sense of calm surrounded the team this morning at the press conference where the tenor was low-key, subdued compared to the high-octane anxiety that permeated the Lab during the Mars Exploration Rovers (MER) landings (due in large part to a sudden increase in dust and hence density of Mars atmosphere just before the arrival of the twin robots). When Graf says MRO has been operating superbly, it isn’t spin. Although four trajectory correction maneuvers (TCMS) -- fine adjustments or tweaks to the course of the spacecraft – had been planned, the navigators were so on it that the last two were cancelled. Instead of expending 35 kilograms (77 pounds) of fuel, they only expended 10 (22 pounds), leaving more fuel for operations once the spacecraft gets into orbit. Moreover, MRO has already completed one of its mission objectives by flying the Optical Navigation camera in a technology demonstration. Weighing in at 2.8 kilograms (6.1 pounds), the OpNav “opens up a new way of positioning ourselves, a new way of finding out where we are relative to the planets and heretofore have not had,” said Graf. Historically, mission teams have relied on radiometrics, but with this camera, he noted, “we now have an optical way of confirming our position down to about a kilometer, which is pretty astounding.” Nevertheless, the concern is and it was evident today. “MRO is entering a very dangerous phase in the next several days,” cautioned Fuk Li, Mars program manager at JPL. The numbers of successes to failures “are sobering to us,” he said. “We have a tremendous amount of anxiety and concern at this particular point in time, which is what you want us to be – you want us to be concerned and worried,” said Graf. “We’re worried about making sure we can get in right – that means turning over that last rock and looking for a problem and solving it.” Mars Orbit Insertion (MOI) will be, after all, like getting MRO to sail through a keyhole. Anything can happen at any point. “An unsuspecting spacecraft, for example, that may not know a dust storm has just sprung up finds that the density of the atmosphere is much increased at this altitude where we’re collecting just a few impacts, if you will, of atmospheric molecules and slowing down just a bit,” noted Dan McCleese, Mars chief scientist at JPL, and principal investigator of the Mars Climate Sounder (MCS), one of the eight science experiments onboard MRO. “If the dust quantities increase dramatically and we don’t compensate the altitude of the spacecraft then we can find ourselves in considerable difficulty.” Indeed, that was what the MER team was confronting in January 2004. Fortunately, for MRO, the other spacecraft in operation there are watching the dust activity and can offer up forewarning should a storm come on the scene. Beyond the potential for being greeted by a hostile Mars, MRO will be going it alone in the final critical minutes. “Since we will be doubling our speed as we approach the planet, there is no time for the team as a whole to react,” said Graf. “The light time is about 12 minutes Earth to Mars, so there really will be no time. We have now onboard all of the programs needed to carry out MOI and the spacecraft is all on its own.” While programming and trajectory changes can still be made for a while now, MRO is basically on autopilot and pending any unforeseen events will carry out its tasks with no further changes to its commands.
Although they are “always concerned,” team members are ready, Graf said. “We have two teams that are ready – one here at JPL and one up in Denver at Lockheed Martin ready to step in and move forward if they have to. I feel confident. We have a very good spacecraft that’s been performing extraordinarily well and we have an excellent well-trained team that’s ready to come forward. So I am concerned, because I have to be as a good project manager, but I’m also confident that we have done the right things and we have the right people in place to be successful.” MRO will expand the flotilla at Mars not just by number, but also by size, design, and state-of-the-art technologies. It is a humongous spacecraft compared to its immediate orbiting predecessors, bigger than Mars Global Surveyor and Mars Odyssey combined. “Its size is representative of a lot of other changes that we’ve made relative to the design of the spacecraft,” Graf pointed out. “We have a major departure from the [type of] spacecraft we built previously and what we’re flying now with MRO. It’s a much more capable spacecraft and its pointing is much more capable. The payload itself is a large departure, because it is the most technically advanced payload we’ve ever sent to another planet, and it’s a demanding payload that puts demands on the spacecraft that required us to build essentially the next generation spacecraft for exploration at Mars.” The sophisticated suite of state-of-the-art instruments and communications gear onboard give MRO the capability of returning – in its two year primary mission -- more than 10 times the amount of data returned by all previous Mars missions combined, including the Mars Exploration Rovers (MER). “One image from the High Resolution Imaging Science Experiment (HiRISE) camera can be as large as 28 gigabits,” Richard Zurek, project scientist for the mission, pointed out. “Think of that in terms of your digital camera.” Added Graf: “One 28 gigabit image is more data than both rovers returned to Earth in the first 90 days of operation.” The quality, they say, will put you on Mars. “Being able to get high resolution from 200 miles above the surface is not quite but almost like being able to look at the planet at the scale you could do if you were at the surface itself,” said Zurek. MRO will build upon discoveries by the five successful missions currently active at Mars by examining Mars' surface, atmosphere, and underground layers in great detail from a low orbit, with eight scientific investigations being carried out by six instruments and the spacecraft itself. Since MRO will be getting close-in detail, it will aid future missions by scouting possible landing sites and relaying communications that will send 10 times as much data per minute as any previous Mars mission. “We’re following the water just as the previous missions have done and we’re bringing more capability in terms of resolution whether we look at the atmosphere or the surface or into the surface and that’s a major reason for the design of this spacecraft,” Zurek noted. Although the official science phase of the mission won't begin until November, “we will actually be studying the changeable structure of Mars' atmosphere by sensing the density of the atmosphere at different altitudes each time we fly through it during aerobraking," he clarified.
While previous NASA missions have focused more on geology, MRO will take an unprecedented look at Mars atmosphere and its weather. The key instrument being used to carry out this much-anticipated research is the Mars Climate Sounder (MCS), which will be making its long-awaited debut on MRO after flying in earlier incarnations on two unsuccessful missions to Mars. “Mars is a dynamic planet today,” said McCleese, the principal investigator of MCS. “Most of the features we see on the surface have been the way they are for a very long while, but the climate continues to change, the weather continues to change. What we’re trying to do with this aspect of the program is to observe and better understand that climate and weather on Mars.” MCS will observe the atmosphere not only to characterize the weather and climate on Mars, but especially to better understand the famous Martian dust, which, said McCleese, drives the way in which Mars’ atmosphere behaves and is “perhaps the most alien aspect of Mars.” The long-term objective of the MCS is, he said, “to contribute a beginning to the process of developing enough understanding of the Martian weather system to be able to predict it” for future arriving missions, specifically landers, and eventually for human visitors in the future. The MCS data will also inform the forthcoming robotic missions that will want to aerobrake or aerocapture, “so getting that database and validating the models that we are building now,” added Zurek, “will give us indications of what the atmosphere might be like in those times and place we can’t observe.” [Read more about Dan McCleese, his life-long dream to study the weather on Mars, and the MCS here at planetary.org tomorrow. Hear more now on Planetary Radio.] But before the science can begin, there is, as Zurek duly noted, “this little matter of turning from a cruiser to Mars into a true orbiter at Mars.” The schedule for Friday, according to Graf, is as follows: “MRO will approach the South Hemisphere of Mars and perform a roll. This is critical so we can maintain communication from the low-gain antenna back to Earth. About 1:25 pm Pacific Standard Time (PST) on Friday, we will fire the thrusters. They will operate for about 27 minutes. We will watch that burn for 21 minutes and at that point the spacecraft goes behind the planet and we no longer get a signal from it.” That means the spacecraft will complete the burn behind the planet on autopilot and out of sight of the ground team. So, for the last 6 minutes, the MRO team members will essentially be in “white-knuckle” time wondering if the spacecraft is going to actually complete the burn and go into orbit. “If we don’t get several of those last minutes, we will not be able to get into Mars orbit,” said Graf. “We will be behind the planet for about 30 minutes. After we complete the burn, MRO will still be out of radio contact.” Engineers designed the burn to slow the spacecraft just enough for Mars' gravity to capture it into a very elongated elliptical orbit. Mission controllers at JPL and Lockheed Martin Space Systems in Denver, will continue from here on out to monitor the spacecraft and all the coming events closely – but after a certain point Friday it will be up to MRO and Mars. MRO is to emerge from behind the dark side of Mars at about 2:16 pm (PST). “It will reconfigure itself, do some maneuvers, and point back to Earth and try and make contact immediately with us,” said Graf. Even then, however, they won’t know for sure that MRO has been captured by Mars’ gravity. It will take engineers some time to review Doppler data and other data to make that judgment, so there could be anywhere from a half hour to an hour or more delay in knowing whether Mars cooperated and MRO is safely in orbit. Provided MOI goes like the rest of the mission has, once MRO is in orbit it will spend six months gradually adjusting the shape of that orbit by aerobraking, making it rounder, and closer in to the planet. “We do that by slowly grazing the atmosphere and allowing the friction of the molecules in the atmosphere to slow us down,” explained Graf. During this period, MRO will make more than 500 of these carefully calculated dips into Mars' atmosphere – which is the process called aerobraking or using friction with the atmosphere to gradually shrink the orbit to the size and nearly-circular shape chosen as the most advantageous for science instruments. And then MRO’s official science phase will begin. |
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