Though it survived two congressional attempts to kill it in the last two years, the Galileo mission the United States plans to launch toward Jupiter in 1982 is running into a rash of unforeseen and threatening problems.
Galileo, the first spacecraft designed to use the space shuttle as a launch platform, for flight to another planet is suffering because the shuttle has run into snags. The delays could push the mission back into 1983 or force planners to split it into two missions, one to orbit Jupiter and the second to drop a probe into the giant planet's turbulent atmosphere.
There are ways to fly the full Galileo mission on time in 1982 but they cost money. One option is to forgo the shuttle launch.The space agency could buy from the Air Force a stretched version of its Titan-Centaur rocket to launch Galileo.
That, however, would add at least $125 million to the $285 million cost of Galileo. In part, this is because the launch pad at Cape Canaveral would have to be rebuilt to accommodate the stretched version of the Titan-Centaur.
A more attractive option is to attach a Centaur rocket to Galileo inside the shuttle. That wouldn't cost as much as buying a Titan-Centaur but would introduce an element of risk into the mission. The Centaur is fueled with liquid hydrogen, which could endanger the lives of the astronauts flying the shuttle.
It would cost money to modify the Centaur engine so the astronauts could carry it in the shuttle "but it would be worth it," said one source close to the Galileo project. "The Centaur would give us such good rocket performance that we wouldn't even have to go in 1982, we could wait a year and still do the whole mission."
The way things originally were planned, Galileo would be carried into Earth orbit in January 1982 by the space shuttle. The shuttle would drop it off in orbit, where it would blast off to Jupiter using a solid-fueled rocket engine called the Interim Upper Stage (IUS), which Boeing Co. is developing for the Air Force.
The Air Force version of the IUS is in fine shape, but the version that the National Aeronautics and Space Administration wants to buy from Boeing is not, The reason is that the device built into the shuttle to hold the rocket in place is overweight, meaning that as much as 7,000 pounds of rocket fuel must be taken out of the IUS to accommodate the overweight support device.
"If we have to take rocket fuel out of the IUS, it means we won't be able to carry the fuel we'd need aboard Galileo to fly a full mission," the Galileo project source said."It might mean we could carry a probe to Jupiter but not be able to go into orbit around the planet when we got there."
Of even more concern to Galileo scientists is the trouble the space agency has had testing the main shuttle engines.The shuttle engine test program is so far behind that the space agency has had to postpone development of an advanced engine the shuttle will need to carry Galileo into Earth orbit.
The advanced engine is called the "109 percent engine," which means it will be burned on takeoff at 109 percent of its rated thrust, It does that by burning the exhaust gases at a higher temperature that normal, which gives the shuttle more lift but requires a more elaborate cooling system.
"The shuttle engine guys tell us that if they get the go-ahead to develop the 109 percent engine they can have it certified by November of 1980, which is a year before we'd need it," the Galileo source said. "Maybe that's true, but all I know now is that they don't have the go-head."
Without the 109 percent engine, Galileo would probably have to be delayed at least until 1983. That creates a new difficulty. The 1982 launch date was chosen so Galileo could take advantage of the fact that Jupiter aligns with Mars that year. The way the mission was planned, the Galileo spacecraft would fly by Mars and use that planet's gravity to give it an extra push toward Jupiter.
If Galileo can't get that push, it will have a fuel problem. That would mean a drastic cut in the mission -- instead of making 11 orbits of Jupiter and its four moons, Galileo would make only five.
Under consideration is a move to scrap the old plan and substitute a Centaur engine for IUS. Not only could the Centaur carry the 4,500-pound Galileo all the way to Jupiter, it would not need the assist of the 109 percent engine to get into Earth orbit and would not need the help of Mars to get it to Jupiter.
"We could even wait a year or two years while we made sure the Centaur was safe," the Galileo source said. "It would cost money, but we could take our time and do it right."
Also under consideration is a plan to fly to Jupiter without the probe that was to be dropped into the atmosphere of the huge planet. Galileo would then be just an orbiting mission. A probe could be sent by itself a year later and the orbiting spacecraft would still be there to act as a a radio relay to Earth.
The Galileo mission has survived tough times before. Two years ago, the House Appropriations Committee voted to kill it, but after a bitter battle the mission was reinstated on the House floor. This year, Sen; William Proxmire (D-Wis.), chairman of the Senate Appropriations subcommittee with jurisdiction over space, tried to kill it but couldn't muster the votes in his own subcommittee.