News | June 3, 2009
Relying on the Deep Space Network
Todd J. Barber, Cassini lead propulsion engineer
As "May Gray" seamlessly changes to "June Gloom" in Southern California, our thoughts turn to another murky vista -- the atmosphere and surface of Saturn's largest moon, Titan. Even though I haven't found time to pen this column for over six weeks, the spacecraft insisted on keeping its many rendezvous with the solar system's second-largest satellite. As I've said many times, Cassini science waits for no one! Unfortunately, this will lead to me having to rehash some old news as I attempt to get caught up over the next few weeks. I hope you'll bear with me as I relive a busy but productive few months at Saturn. Before I can do that, though, I must tell the tale of a challenge a bit closer to home.
In mid-April, the 70-meter antenna at Goldstone, CA (Deep Space Station 14, or DSS-14) started having some issues at the bearing interface. I'm amazed at how quickly the Deep Space Network (DSN) team was able to return DSS-14 to operation after some significant hardware issues. Each 70-meter DSN antenna weighs almost 3000 tons (that's 6 million pounds, folks!), or nearly 3 million kilograms. Despite this enormous mass, the antenna itself must move in both azimuth ("side to side") and elevation ("up and down") with incredible precision, pointing to distant targets literally billions of miles away. Motion is enabled via hydraulic bearings, but to say the tolerances are tight is a vast understatement. This 3000-ton antenna floats on a pool of high-viscosity oil, with an oil film-height roughly equal to the thickness of a sheet of paper! As you might imagine, if this thin lubrication layer were to be compromised for any reason, the potential for severe hardware damage is definitely there. This makes it even more amazing that the DSS-14 downtime was as short as it was. Cassini and many other spacecraft rely on the 98+% data return that typifies the DSN, decade after decade. After all, without the DSN we might be able take thousands of pictures of Saturn -- but no one would ever see them!
I'm sure I mentioned the nomination of the Cassini website for a "Webby," an Internet award competition, in my previous column. In closing, I'm happy to report that our website was honored with this award, and some of our team members will soon depart for New York to accept this honor! If I were of slighter build and a smaller girth, I would surely try to squeeze into their carry-on luggage to be a part of this momentous event. Of course, though, this would only serve to put me further behind in writing this column. I'll see you next week as I pick up with the torrent of Titan science during the last half of April 2009.