Europeans fix radar antenna over Mars

HOUSTON - European space controllers have successfully completed the extension of the first of three radar antennas on the Mars Express spacecraft now orbiting the Red Planet, after encountering a temporary glitch. The antennas are to be used in an experiment that would look for water beneath the Martian surface.

Engineers confirmed overnight that the first radar boom, which had been partially deployed a week earlier, was now completely out and locked. Deployment of the second boom will be delayed "a few weeks" while engineers study last week's anomaly, the European Space Agency reported Wednesday.

Mars Express has been in orbit for well more than a year, but deployment of the MARSIS ground-penetrating radar had been delayed due to concerns that the flexible antenna structures might whip around violently and damage the spacecraft during their release. Such violent gyrations apparently did not happen, and in fact the initial deployment now seems to have had inadequate force to snap all the antenna segments into alignment.

After the coiled-up antenna was released, engineers at ESA's Mission Control Center in Darmstadt, Germany, indirectly monitored the boom's status by noting subtle vibration patterns, sources told MSNBC.com on condition of anonymity.

Subtle cues
The simple, multisegmented boom had no sensors or other instruments, and the craft's cameras were pointed in another direction.  However, the spacecraft did have very sensitive accelerometers on board, and by measuring the extent and timing of the spacecraft's rocking motions, these instruments provided subtle cues as to how far out the boom had extended and how stiff it was.

"Careful examination of the numbers led to approximately where the boom was bent and how much," one program source told MSNBC.com.  "Indirect evidence of what was going on was unambiguous."

Over the past week, the ESA team developed a plan to respond to the anomaly.

"As prolonged storage in the cold conditions of outer space could affect the fibreglass and Kevlar material of the boom, the mission team decided to ‘slew’ (or swing) the 680-kilogram [1,496-pound] spacecraft so that the sun would heat the cold side of the boom," ESA reported on its Web site. "This was done so that thermal expansion would force the unlocked segment into place."

ESA said the maneuver began at about 4:20 p.m. ET Tuesday, and when controllers re-established contact with Mars Express at 1:50 a.m. ET Wednesday, an analysis of the data showed that the boom was fully locked.

No further deployments will be attempted until "after a thorough analysis and investigation of the Boom 1 deployment characteristics," ESA said. This will result in the loss of some of the best observational periods: The radar is most effective when it is passing over the dark side of Mars, but as the probe's orbit shifts, it will eventually be lowest over regions that will start becoming sunlit.

Even if all three booms are rolled out successfully, the MARSIS experiment would have to be tested for several weeks. Only then would the radar antenna's 15-watt transmitter begin its scientific work in earnest. Most of the signals would be reflected directly back from the surface, but scientists hope the fraction that penetrates the surface will then be bounced back by layers of materials much farther underground.

High hopes for deep views
The MARSIS team's science goals range from "modest to ambitious," said Jeffrey Plaut, a researcher at NASA's Jet Propulsion Laboratory who is one of the principal investigators for the experiment.

NASA / JPL Radar signals from the MARSIS experiment could be reflected back by a water table, as shown in this cutaway graphic.

"On the modest side, we are eager to see the interactions of our signals with the ionosphere and the surface of Mars," Plaut wrote in an e-mail to MSNBC.com. "The echoes detected from these two environments will be unlike any data obtained at Mars, and will undoubtedly contain some surprises.

“A bit more ambitious is to detect echoes (layer boundaries) that are unambiguously from the subsurface. This will be a major accomplishment for the experiment,” he continued.

“The fully ambitious goal is to characterize these detected boundaries,” he said — in other words, to “say something about their nature. This is where the search for water comes in.”

Plaut is cautious in his expectations: “It is not at all simple to look at a radar echo history and identify the composition of the reflecting layers. However, if there is a shallow water table in the right geometry, it may have a distinctive radar signature.” The experiment could conceivably detect water that is two or three miles (a few kilometers) beneath the surface.

“Convincing ourselves and our colleagues that this is a verified water detection will be quite a task,” he admitted, “but if we can do it, you might call it hitting a home run.”

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