Three Cheers for the Magellan Control Team
MAGELLAN'S radar images, which now cover 11 percent of Venus, bring us new knowledge of a largely unknown planet. But behind this stunning scientific breakthrough lies the equally impressive work of the spacecraft control team. Magellan's sophisticated observing capability would be for naught if operational glitches spoiled the mission. Thanks to the control team's insight in diagnosing trouble and its skill in dealing with it, the mission is off to a near flawless start.
The first serious glitches occurred Aug. 16 and 21. Responding to some still unknown threat, the on-board computers followed programmed procedures and put the spacecraft into a ``protected state.'' They oriented Magellan so that its solar arrays pointed at the sun and its batteries would not run down. This involved turning the high-gain antenna away from Earth. Controllers lost contact with the craft for 14.5 hours in the first instance and 17.7 hours in the second.
The $744-million mission could have ended there. Happily, Magellan is managed by computers that Earth-based controllers can reprogram. The team turned off the fault protection in a way that does not endanger the spacecraft but reduces its tendency to break communications.
Having solved that mission threat, controllers continue to face a succession of potential glitches. A spacecraft transmitter may shut down. Ground equipment may malfunction. And so on. Handling such problems keeps control-team members on their toes as much as the in-flow of radar images keeps the scientific team on the edge of excitement.
Then there are the unexpected problems that, with hindsight, should have been foreseen. Next week, on Nov. 1, Venus will be in what astronomers call superior conjunction, passing behind the sun as seen from Earth. Mission planners expected to lose contact with Magellan during conjunction. But they did not expect confusion in the spacecraft's ability to point its solar arrays.
Yet as Venus neared the sun, Magellan's sun sensors told it to point one way while its orientation program told it something else. Once again, controllers figured out the trouble and reprogrammed the computers. Now Magellen should keep its batteries charged when it moves behind the sun.
Magellan's controllers have scarcely begun their task. There's a great deal riding on their being able to continue to meet problems with the outstanding skill and insight they have already shown.
Scientists want the spacecraft to function for at least several years. Magellan's nominal mission runs well into 1991. This will give scientists a near complete map of the Venus surface. But polar regions will be left out. Also, it won't yield information needed to decide whether, and to what extent, Venus has plate-tectonic activity like the movement of crustal plates on Earth.
Thus, scientists very much want Magellan to carry on what planner's call an extended mission. This means functioning years beyond the nominal mapping mission. For example, the longer the spacecraft works at Venus, the more data scientists can gather on the gravity anomalies that affect Magellan's orbit. These anomalies, in turn, will reveal how mass is distributed on the planet. This will give insight into Venus's tectonic activity.
Magellan will be a success even if it fails after completing its nominal mission. But its biggest payoff can come only after several years of observations. The key to realizing that payoff is the controllers' success in keeping the spacecraft running.
As we admire the images the spacecraft has sent after reaching Venus on Aug. 10, let's hear a few cheers for the control team.