The little satellite that could
Marisat, 24 years old, takes on new duties over Antarctica
WASHINGTON — The numbers change slowly on the glowing screens in the control room as technicians keep watch on the health of the oldest commercial satellite in space, drifting slowly westward in the silence of space 22,300 miles above the equator. The space trek has just begun; some travel hazards lie ahead.
But after almost 24 years of service, the little satellite that won't quit, the redoubtable Marisat, has embarked on a new mission, one to enhance communications for scientists working in Antarctica at the remote Amundsen-Scott station, South Pole.
Marisat is uniquely qualified for the new mission. Ground controllers tightly maintain Marisat in an east-west direction in geosynchronous orbit, so it crosses the equator at the same spot above the earth. But it is allowed to roam harmlessly north and south in a huge looping gait, weaving back and forth, above and below, the line of the equator. This conserves fuel. So, at one point, Marisat slides about 13 degrees below the equator, allowing it to look over the curvature of the earth and "see" the South Pole, which other geosynchronous satellites do not serve.
The National Science Foundation (NSF), which coordinates all US scientific research in the Antarctic, finds the wandering ways of this senior space citizen to its advantage. The NSF plans to join Marisat with other communications links to relay scientific data, as well as voice communications, from the South Pole outpost, one of the remotest points on a continent that today is a giant scientific laboratory.
Data collected at the polar station shapes mankind's knowledge and understanding of basic climatic changes in the world.
"We are conducting aggressive, hi-tech science there," declares Patrick Smith, technology-development manager in the NSF's Office of Polar Programs. The relatively small South Pole station, operating year-round through what one wag dubbed Antarctica's two seasons - dark winter and light winter - also is inhabited by other US scientific and support personnel conducting a broad spectrum of work in astronomy, biology, environmental science, geology, glaciology, marine biology, geophysics, and other sciences. They accumulate mountains of data faster than trees makes little green apples.
The space trek begins at NSF's request. Comsat Corp., owner of the satellite, is repositioning Marisat from its station of almost a quarter of a century at 72.50 East longitude over the Indian Ocean, to a new station over the Atlantic Ocean at 33.90 West longitude.
As part of an illustrious past before its new assignment, Marisat formed the third and final link in a global mobile satellite system that provided the first commercial space communications to ships at sea in the mid-1970s. The US Navy, which inelegantly called the system "Gapfiller," because it filled a gap in the Navy's arsenal of satellite resources at the time, used UHF links from Marisat for its worldwide gray fleet of combat and supply ships; the drum-shaped little bird even saw service years later as a backup during the 1990-91 Gulf War.
The satellite has defiantly outlived experts' estimates at birth of a five-year design life. Since being hurled into an evening sky aboard a Thor Delta rocket from Cape Kennedy on Oct. 14, 1976, orbital engineers at Comsat estimate it has made more than 8,500 trips around the world. That's a lot of mileage, something over 1.4 billion miles if you're counting, and Marisat is still ticking.
Its Atlantic and Pacific Marisat sisters have long departed, been sent to satellite heaven, or been deorbited by thrusting them above geosynchronous altitude and burning up all remaining on-board fuel.
The trek west began last February.
"We raised the orbit of the satellite about 50 kilometers," explains Dan Swearingen, vice president for advanced engineering and planning at Comsat. "Because it is now not in sync with the earth, the earth is passing below it, rotating east to west of course, so the satellite appears to drift westward. We'll stop it when it reaches station over the Atlantic, sometime in August." Marisat loafs along at a leisurely pace (actual velocity: about 6,900 m.p.h.), ambling westward about two-thirds of a degree a day.
There are some traffic problems up there. Because of potential signal interference, Comsat must notify owners of other satellites stationed along the way in the geosynchronous orbital path, if Marisat should come within 1 degree of any of them, in order to coordinate use of the satellite beacon frequency. And at least two maneuvers will be required to halt the drift and position Marisat over the Atlantic in August, if all goes well.
Once settled in its new orbital home, Marisat will be visible to the South Pole for high-quality voice and data services approximately five to six hours a day. NSF fills gaps with two other aging satellites, each non-geostationary or inclined orbit satellites that provide three to five hours each of service a day during passes: the GOES III and TDRS I.
Marisat, with the equivalent of about 48 voice (telephone) circuits or capacity for about 2.8 million bits of data per second, adds needed communications resources to the isolated US South Pole inhabitants.
Last year, these communications links served a vital function for Jerri Nielsen, wintering (dark) at the South Pole station, became ill in July.
Unable to leave, Dr. Nielsen consulted doctors in the United States via Internet e-mail and conference calls. They helped her treat herself until the first flight of the polar "summer" could reach her on the edge of the world and lift her out in mid-October.
Meanwhile, Marisat just keeps movin' along. Optimistic technicians now expect it to have another five to seven years of useful life.
(c) Copyright 2000. The Christian Science Publishing Society