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Planetary News: Mars (2006)Mars Reconnaissance Orbiter: Hi-RISE Camera Returns First Test ImagesBy A.J.S. RaylMarch 27, 2006
It was a test. Only a test. But it passed, and soon it will be released in flying colors. The first test images of Mars from the High Resolution Imaging Science Experiment (HiRISE) camera onboard the Mars Reconnaissance Orbiter (MRO) showed up on the monitors in the wee hours of the morning Friday, March 24, in clear, crisp form to an ecstatic team gathered in the HiRISE Operations Center on the University of Arizona (UA) campus in Tucson, and an almost equally thrilled group of MRO team members at the Jet Propulsion Laboratory (JPL). "It was very exciting to see our first images of Mars especially since they looked like such good images. They were well-focused, unsmeared, high signal-to-noise -- everything we wanted and hoped to see," Alfred McEwen, professor in the UA's Lunar and Planetary Laboratory and principal investigator of the instrument, told The Planetary Society today. It was especially good to see them, he said, "considering that if you take the speed of the spacecraft over the Martian surface and the altitude and scale it down to something in our experience, it's like photographing grains of sand along a highway going 120 miles per hour." The image showed a section of Mars approximately 50 x 19 kilometers (31 x 12 miles) in the mid-latitude southern highland region to the north/northwest of Agyre Planitia. An old, muted crater can be clearly seen in the middle of the scene, with sets of channels to the left and right. Superimposed on parts of this terrain is a much younger, layered mantle of debris, which is smooth in places, but rough in other areas where it may have partially sublimated. This suggests that the debris mantle is (or was) rich in volatiles such as ices of water, carbon dioxide, or both. Also superimposed on the landscape are many small sharp-rimmed impact craters and wind-blown dunes. Together these features illustrate processes that may have involved water both on ancient Mars (channels and eroded craters) and much more recently in Mars' history (volatile-rich debris mantle). The $42 million High Resolution Imaging Science Experiment is the most powerful camera ever to leave Earth's orbit and with a little help from MRO, HiRISE "pointed and clicked" at 8:36 p.m. Pacific Standard Time (PST) last Thursday, while the spacecraft orbited over Mars' southern Hemisphere and collected 40 minutes of engineering test data. To get desired groundspeeds and lighting conditions for the test images, researchers programmed the cameras to shoot while the spacecraft was flying about 2,489 kilometers (1,547 miles) or more above Mars' surface, about nine times the range planned for the orbiter's primary science mission. The data was then transmitted from MRO through the Deep Space Network (DSN) to JPL for processing and onto Arizona. The sharp, clear images of the Agyre Planitia and Dorsa Argentea region that came through at 12:31 a.m. PST on Friday and over the weekend prove the HiRISE is in good operating condition. They also offer up just a tantalizing hint of what it to come when the science mission officially begins in November and, in that sense, have had Mars people marveling, because this is only the beginning.
The highest resolution of these test images -- about 2.5 meters (8 feet) per pixel (an object 8 feet in diameter would appear as a dot) is comparable to some of the best resolution previously achieved from Mars orbit. But when MRO gets into its nearly-circular science orbit, the HiRISE images will show detail at 0.28 meters per pixel, resolution that will clearly show objects smaller than 40 inches wide from an altitude of some 320 kilometers (about 200 miles). Although the HiRISE is a color camera, the first image was released in black and white simply because of the time constraints involved in releasing it in color. "The images come back in separate black and white channels and it takes more work to get the color data to be properly registered and calibrated so that the image is in good color," McEwen explained. "The color variations on Mars are subtle. So we're working on that. We just haven't finished yet." The team currently plans to release the color images one week from Friday, on April 7. The team didn't select the region to the north/northwest of Agyre Planitia to image, rather it was just a random target, McEwen said. "Given the nature of the currently, highly elliptical orbit, we had to image at certain times in order to get decent images. We didn't even know which orbit it would be, so we couldn't even pick the longitude. We just planned a set of images with no idea of what it was going to cover." That made the images that appeared all that much more of a surprise. The second test series, taken last Saturday, was a bit different in that these images were taken while the Mars Climate Sounder (MCS) was turned on. "The Mars Climate Sounder has to gimbal back and forth when it's in operation and that induces vibrations that should cause some smear and some geometric distortions of our images, and so we wanted to measure the MCS-induced jitter," McEwen explained. "We do have a high stability mode where we pause the motion of MCS, but we want to also do some imaging while MCS is on. So we needed to get some measurements to see how severe this is and what we can do to compensate for it." Beyond just making sure HiRISE -- which is one of eight science investigations on MRO -- works, the test also enables the team to better prepare for the science phase of the mission. "It's a lot of work to so all this," said McEwen. "The tests give us something to work with in many ways. They help us a great deal to get these images and discover what are the real problems with processing this data and putting them together. We've already discovered a couple of problems in our software -- little things with the geometry and how to get images to line up properly -- and we're fixing those now. For the rehearsals and operational readiness tests, we have real data to process, and we can see how long it takes to process data and design our system. We can work on calibration and matching geometrics with real data and see whether we have gotten the precise corrections needed for color imaging and for high-resolution surface measurements from stereo pairs of images. We check our photometry models. It just helps us in so many ways, and once the primary science phase starts, we're just going to be swamped. Every two weeks, there will be another planning period and every day we'll be returning new images. There will be no time to work on this type of thing, so it's great to have these next six months of aerobraking to work on this." The HiRISE team is creating a website to allow anyone to suggest targets and locations for the camera and plan to open it this summer. "We hoped to have it up sooner, but we have to get rid of some bugs and increase the security before we open," said McEwen.
The images from HiRise, McEwen noted, will work with and complement the images from other cameras on other orbiters at Mars. "For topography, on a global scale, we have the Mars Orbiter Laser Altimeter data (from Mars Global Surveyor), on a regional scale, we have the High Resolution Stereo Camera stereo data (from Mars Express), and soon we'll have HiRISE for high-resolution of particular areas," he said. Two other camera systems onboard MRO -- the Context Camera and the Mars Color Imager -- also collected images during the past several days, at the same time as HiRISE. Those images, according to an official NASA press announcement, will be released in coming days. All told, more than 25 gigabits of imaging data, enough to nearly fill five CD-ROMs, were received through the Deep Space Network station at Canberra, Australia, and sent to JPL, and the camera teams at the UA and Malin Space Science Systems. MRO – which went into orbit around Mars on March 10 -- has been flying in elongated orbits around the Red Planet since then. Every 35 hours, it has swung about 44,000 kilometers (27,000 miles) away from the planet then come back within about 425 kilometers (264 miles) of Mars' surface. Mission operations teams at JPL and at Lockheed Martin Space Systems, Denver, continue preparing for aerobraking. That process will use about 550 careful dips into the atmosphere during the next 6 to 7 months to shrink the orbit to a near-circular shape less than 300 kilometers (200 miles) above the ground. For the University of Arizona team, HiRISE's success on MRO will be significant. NASA's next mission to Mars, Phoenix, which is slated for launch next year, will be overseen by the UA, the first NASA mission ever to be run entirely from a university. |
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