Saturn's Deep, Dark Secret
Titan, the only major body in the solar system that we haven't gotten a good look at, is about to be outed.
- By Craig Mellow
- Air & Space magazine, July 2004
(Page 3 of 4)
With Cassini-Huygens well beyond repairman range, the only solution left was to attempt to reduce the Doppler shift so that the transmitted signals would fall within the receiver’s designed bandwidth. That required ESA and NASA’s Jet Propulsion Laboratory in southern California to remap much of the Saturn mission, so that Cassini would be moving past Titan on the right track to receive the data transmitted from Huygens.
The long-distance adjustments took three years, as the two mission controls modeled possible trajectories, then programmers furiously wrote software instructing the spacecraft in their new routines. Huygens will now disengage from Cassini on the mothership’s third pass by Titan after entering orbit around Saturn. That will happen this December 25, about six weeks later than originally planned. At the time of separation, both craft will be on a course to collide with the moon. The lander will coast another 2.5 million miles to do just that, but five days after the separation, Cassini will fire maneuvering thrusters—“slam on the brakes,” as deputy program manager Earl Maize puts it—to change course and orient itself so that when Huygens starts transmitting, Cassini’s high-gain antenna will be pointed toward Titan. The success of the Huygens mission depends on this maneuver.
In the meantime, Huygens will sleep until an onboard timer, set at separation, wakes up the craft’s batteries and computers as Huygens approaches Titan’s atmosphere. The batteries have enough power for the two-and-a-half-hour trip to the surface—plus an adequate reserve, in case the fall doesn’t pulverize the probe.
Huygens folk say they were compensated for the labor and stress of redesigning the mission by the Americans’ helpful attitude. “NASA’s cooperation has been magnificent,” says David Salt at Darmstadt. “JPL altered its whole four-year tour of Saturn to accommodate us. At this level it’s not just a design problem. It’s a political compromise too.”
To core Cassini-Huygens scientists, the partnership between Darmstadt and Pasadena is nearly as thrilling as the lander’s experience on Titan’s surface will be—and, they fear, as ephemeral. “We thought we would open a new era of international planetary enterprise,” says Toby Owen, a University of Hawaii astronomer who in 1980, with French colleague Daniel Gautier, championed what would eventually become Cassini-Huygens. “But it didn’t happen, and it’s a little sad that it didn’t. Now America and Europe are each planning their own missions to Mercury. Why do we need two?”
Though necessary for ambitious space missions like Cassini-Huygens, international collaborations are now jeopardized by the U.S. security climate—in particular, stepped-up enforcement of the International Technology and Arms Restrictions, or ITAR, regulations. Even as the Internet makes sharing research much simpler technically, planetary scientists fear that paranoia will squelch future global space coordination. “The fact that I had to take my clothes off and be searched on a U.S. domestic flight because of my British accent creates an unpleasant impression,” says David Southwood, the Imperial College of London physicist who is ESA’s chief scientist. “But when we’re securing a box of electronics for NASA on board the International Space Station without being allowed to know what’s in it, that really makes the working climate difficult.”
ESA depends on NASA’s cooperation for its broader ambitions. European planetary craft would be helpless, for instance, without the U.S. Deep Space Network of communication radar antennas. But the ITAR regulations are discouraging. “Cooperation with NASA is more and more difficult,” says Jean-Pierre Lebreton. “They don’t want Europe working on any subsystems which they see as on a critical path.”
The Planetary Society’s Louis Friedman believes that Cassini-Huygens could probably not have been done without international cooperation, and he worries about the new U.S. policy of going it alone. “The recently announced lunar mission and Mars sample return are all being planned domestically without international involvement,” he says, “which I think is a huge mistake.”