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Planetary News: Mars (2006)Mars Reconnaissance Orbiter Gets Ready to RockBy A.J.S. RaylSeptember 27, 2006
The Mars Reconnaissance Orbiter (MRO) has completed the 6-month process of aerobraking to circularize its orbit for the mission's main, 2-year science phase and as of today all 6 instruments that will be used to study the atmosphere, surface, and subsurface have checked out and are operational. Although the science phase of the mission won't begin until November 8, the action gets underway this Friday, September 29, when the instrument teams will begin putting their devices through a one-week exercise collecting test data. MRO features the largest radio antenna ever sent to Mars, with a transmitter powered by large solar panels, giving it the capability to send home 10 times as much data per minute as any previous spacecraft. The reality is setting in amongst the members of the science teams. "It's thrilling and a little unreal," said Sue Smrekar, MRO deputy project scientist, during an interview with The Planetary Society. "We're realizing now that we're not practicing anymore." On September 11, MRO fired its 6 intermediate-size thrusters for 12.5 minutes, shifting the low and high points of its orbit. The spacecraft is now in locked in the nearly circular, low-altitude orbital pattern where the periapsis -- the point where the spacecraft is closest to the planet -- is over Mars' south pole and the apoapsis -- or farthest point -- over the north pole. The altitude of the orbit ranges from 250 kilometers (155 miles) to 316 kilometers (196 miles) above the surface. Earlier today, the Compact Reconnaissance Imaging Spectrometers for Mars (CRISM) "popped its cover" and took its "first light" image, the last of the orbiter's 6 instruments to undergo its check-out. The CRISM 'first light' image will be smeared, and a second image taken immediately after will be in twilight, according to Richard Zurek, MRO project scientist. "While they are good enough to confirm that the telescope cover is open, they will not be useful for science," he pointed out. CRISM’s spring-loaded cover had been closed since the orbiter’s launch in August 2005, protecting the imager’s sensitive telescope optics from fuel residue and heat as the spacecraft eased into orbit around Mars. Today, a day after turning on CRISM’s power and putting the device through a series of performance tests, instrument opeerators opened the cover and verified that it had deployed properly. “Everything went smoothly and our team is looking forward to our first images later this week,” announced Scott Murchie, CRISM principal investigator from the Applied Physics Laboratory (APL) in an official press release. CRISM will break down the visible and near-infrared light (with wavelengths from 400 to 4,050 nanometers) reflected from areas on the Martian surface as small as 18-meters (59 feet) across, with the orbiter at its average altitude of about 190 miles (300 kilometers). In essence, the instrument will read 544 “colors” in reflected sunlight to detect minerals in the surface, and it offers a greater capability to map spectral variations than any similar instrument sent to another planet. Its highest resolution is about 20 times sharper than any previous look at Mars in near-infrared wavelengths. Designed to look for areas that were wet long enough to leave a mineral signature on the surface, CRISM wil be searching for the spectral traces of aqueous and hydrothermal deposits, and mapping the geology, composition, and stratigraphy of surface features. By identifying sites most likely to have contained water, CRISM data will help determine the best potential landing sites for future Mars missions seeking fossils or even traces of life. The instrument will also be used to examine seasonal variations in dust and ice in the atmosphere.
Since the CRISM team will have only a couple of days to look at the first data, it could take them several days to release even raw images. Mineral maps could take weeks, even though key "indices" (ratios of various spectral channels) could suggest something earlier, Zurek added. Last week, there was a lot of excitement about the deployment the 10-meter long (33-foot long) antenna of the Shallow Subsurface Radar instrument, especially among the Italians. More simply known as SHARAD, this instrument, which is provided by the Italian Space Agency, will search to depths of about one kilometer (a little more than half a mile) to find and map layers of ice, rock and, if present, liquid water. "We will use the Shallow Radar to map buried channels, to study the internal structure of ice caps, and to see boundaries between layers of different materials," elaborated Roberto Seu of the University of Rome La Sapienza, leader of the instrument's science team. "The data will provide our first detailed look just under the Martian surface, where ices might reside that would be accessible for future explorers." But the process of opening up any antenna in space is nerve-wracking. SHARAD had been folded and tucked away throughout the flight to Mars (from August 12, 2005 to March 10, 2006) and for the past 6 months, while the orbiter was aerobraking to shrink the size of its orbit. Add to that its 10-meter (33-foot) size, and it is easy to understand that a number of things had to go right and not go wrong for the antenna to be properly extended. September 16 was d-day. The latches on the restraints were popped open. And the spring-loaded twin arms of the antenna unfolded themselves, apparently, just as designed, since subsequent information from the spacecraft indicated that each arm properly extended to its 5 meter (16.4 feet) length. The radar instrument received its first radio echo from the Martian surface during a test on September 18, providing the first demonstration that the instrument is working properly. "Now the excitement builds about what the radar will find hiding beneath the surface of Mars," Enrico Flamini, the Italian Space Agency's program manager for SHARAD, said as the team announced its success. SHARAD complements a similar instrument that went into use last year on the European Space Agency's Mars Express orbiter, the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) instrument, and both are the result of an Italian and American partnership in planetary radar probes. The 2 instruments use different radar frequencies -- while the SHARAD on MRO can discriminate between thinner layers, it cannot penetrate as deep underground like MARSIS on Mars Express can. MRO's 3 cameras underwent checkouts earlier in the mission, in fact, just days after Mars Orbit Insertion (MOI) on March 10.
The first test images from the High Resolution Imaging Science Experiment – more simply known as HiRISE -- the camera that will offer the best resolution of all the cameras on MRO -- were taken on March 24 and released in black and white by Alfred McEwen and colleagues at the University of Arizona immediately, and in color on April 7. HiRISE is the largest diameter telescopic camera ever sent to another planet and it will capture images at resolutions of 25-50 centimeters (9.8-19.6) inches per pixel, a higher resolution than ever before. One of its main functions is to map areas on Mars to be explored later by landers, and its data will give planetary scientists and engineers more information than they've ever had to work with before. The camera will be able to reveal rocks and layers as small as the width of an office desk, and will image more than 2% of Mars at resolutions of 1 meter (about 3 feet) per pixel or better. Stereo image pairs will be acquired over the highest-priority for even more compelling, 3-dimensional detail. Only landers have previously been capable of such high-resolution imaging. Not long after the first test HiRISE images hit the media, Michael Malin and colleagues at his Malin Space Science Systems released the first test images from the other two cameras onboard MRO, the Context Camera (CTX) and Mars Color Imager (MARCI), a descendant of a similar instrument that flew on the Mars Climate Orbiter that was lost in September 1999 during orbit insertion. The CTX -- a camera that will take wide-angle images to help place detailed HiRISE and CRISM measurements in their proper context on Mars -- will expand the present area of high-resolution coverage by a factor of 10, taking images that span 40 kilometers (25 miles) across at a resolution of 8 meters (26 feet) per pixel. MARCI, meanwhile, will be taking daily global images of Mars in 6 different colors, so that scientists can follow changes in weather and ultimately produce global maps of always fickle Martian weather. Although the CTX and MARCI images acquired were taken, like the HiRISE images, from nearly 10 times as far from the planet as MRO is now, they clearly showed that "both cameras will meet or exceed their performance requirements once they're in the low-altitude science orbit," Malin, team leader for the context camera and principal investigator for the MARCI, announced in April. Mars Climate Sounder (MCS) -- the radiometer or atmospheric profiler that will use visible and infrared light to detect vertical variations of temperature, dust, and water vapor concentrations in the Martian atmosphere and show how they change over the course of the mission -- also underwent some early testing. As with the cameras, the spacecraft was not then in its science orbit. Just this past week, however, the MCS team "acquired data in the right orbit to be able to do the scanning of the atmosphere," reported Smrekar.
MCS will be the first science investigation at Mars capable of performing a "4-dimensional" study of the key properties of Mars' atmosphere (3 spatial dimensions and time). Throughout the science phase of the mission, MCS will almost continuously acquire vertical profiles of the temperature, pressure, dust, and clouds of the lower 80 kilometers (50 miles) of Mars' atmosphere. In addition to the experiments planned with the spacecraft's 6 instruments, 2 additional scientific investigations will use the orbiter itself to analyze the motion of the spacecraft in orbit to study the structure of the upper atmosphere and the Martian gravity field. Right now, the focus is on the 6 instruments and the beastly amount of data that's about to flood the Jet Propulsion Laboratory (JPL), where the mission is being managed. "On Friday, we'll start taking test data, trying all different modes that we'll be using in the primary science phase," Smrekar said. "We will have a week-long set of observations that should run through all the different instrument settings and the spacecraft settings for observing, so we'll have a good amount of data to really get working with before the primary science phase starts." Then, as the scientists review their first real bounties and before the "firehose is turned on," things will quiet down on MRO during the solar conjunction -- October 18 through October 29 -- when Mars orbits around the other side of the Sun from Earth. During solar conjunctions, commands and data often get corrupted, because the radio waves are attempting to pass through the edge of the Sun, and that causes interference in communications. While downlinks can be stored onboard spacecraft and used at least to some degree after the corruptions are accounted for and corrected, uplinking and commanding in particular are generally avoided during solar conjunction. "Basically we will stop taking data due to solar conjunction, however, two of the instruments will continue to take data throughout October," Smrekar informed. "MARCI will be taking a daily picture and MCS will be scanning the atmosphere throughout that time. Since these are low-data rate instruments, we're able to store their data onboard, so it'll be safe during the conjunction time period. There will some limited downlinking, but we're planning on storing it in case any of it is corrupted." Once solar conjunction ends, MRO will be ready to rock. The flight operations team will conduct one more "clean-up" maneuver November 20. "This one last maneuver will get us exactly at the right inclination," Smrekar said. "But we're at the right altitude and close to our final time of day now, in our 2-hour orbit, and, with regard to how the instruments see the surface, we are in our primary science configuration." Even before that final maneuver, though, on November 8, "the fire hose will be on" and the science gathering will have begun. "We will be taking data indefinitely -- at least 2 years and, if all goes well, we're hoping NASA will give us funds to keep going, well beyond that," said Smrekar. Although November 8 is still more than a month away, the first deluge is already on the way. In the one week of test observations that begins Friday, Smrekar said, "we'll be getting more data than some of the past missions in entirety." Indeed. They expect to acquire -- get this -- about 350 Gigabits of data -- more than the Mars Exploration Rovers (MER) have acquired to date. Mars researchers will be, no doubt, giddy as all the new information begins pouring down from the Red Planet. But what's going to happen to all that data? "We'll be checking out the data and doing some analysis," said Smrekar, "but the main bulk of the analysis of the science data is going to be going at different sites, universities and institutions, around the country."For decades to come. |
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