In the wake of Sundays failed attempt to relay signals from Mars Polar Lander via a second orbiting spacecraft, the silence from Mars is starting to seem interminable. And in that silence, controllers at the Jet Propulsion Laboratory are narrowing their strategies on how to contact the lander.
So far, the strategies have assumed the lander was functioning, carrying out a set of pre-programmed instructions for sending back data, but that it was having trouble pointing its main antenna at Earth. This so-called medium-gain antenna, which transmits and receives in a frequency range called X-band, needs to be pointed with an accuracy of 5 degrees. Thats like hunting for a star in the sky by looking through a cardboard tube.
To correct for a small pointing error, controllers have already tried a technique called "raster scan," in which the X-band antenna scans the sky near the place where the Earth is expected to be. The hope was that tracking stations on Earth would "see" the landers signals sweep across their field of view, and make contact.
The lander has a second antenna, which uses UHF frequencies. This antenna does not need to be pointed because it transmits over the entire sky, although at lower power. It is the UHF antenna that was used in Sundays relay attempt via the orbiting Mars Global Surveyor.
The fact that this relay didnt work makes it all but certain that the Polar Lander, if it arrived safely on the surface, is in "safe mode," a protective state of non-activity that could have been triggered by a variety of abnormal conditions aboard the spacecraft. If so, the lander would not have been able to carry out the previous attempts at the raster scan or the relay.
That leaves two options: try the scan and the relay again, this time in safe mode.
Theres one hitch: In safe mode, the lander is not programmed for either the raster scan or the relay. But it can receive commands from Earth using a third, low-power X-band antenna. That means controllers can tell the lander to amend its safe-mode software so that the scan technique, and the UHF relay, can be tried.
Early Monday ET, the Polar Lander will try the second raster scan with its medium-gain antenna. This time the antenna will cover a wider portion of the martian sky, increasing the chances of finding Earth. A third raster scan, covering the entire sky above the lander, can be tried early Tuesday ET, if Mondays scan is unsuccessful.
Finally, there is a chance late Tuesday ET for the lander to make another relay attempt via Mars Global Surveyor. If that fails, says Project Manager Richard Cook, then all of the "big cards" will have been played. "When we get through those," Cook added, "we are really at a point of diminishing returns."
"The team is getting more frustrated and tense about all this," Cook said. But he maintained that he and his colleagues are still in fair spirits.
Meanwhile, there is no word from the twin Deep Space 2 microprobes that impacted Mars on Friday, not far from the Polar Lander. Deep Space 2 Project Manager Sarah Gavit confessed that "if we havent heard from them in the next 24 hours, the odds of ever hearing from them really diminish." However, the DS2 team will continue to listen for the next week.
advertisement
