One of them, the $542 million Propulsion Module, is so far over budget -- by several hundred million dollars -- that Congress has ordered an investigation by its watchdog agency, the General Accounting Office.
"NASA has failed to learn any lessons from the cost overruns and delays experienced during the seven-year development phase of the International Space Station," said Sen. John McCain, (R-Arizona), who chairs the Senate Commerce, Science and Transportation Committee.
"This situation clearly indicates that NASA needs to spend more time on technical management of its program instead of counting its appropriation funds," McCain said.
NASA believed that it had technical management in mind when it first began thinking more than four years ago about how to recover from a potential service-module disaster.
In late 1996, the agency began considering the idea of the ICM to keep the station stable at a safe altitude above Earth. The ICM could not, however, house any people.
"By no means is it a service-module replacement," said Kirsten Williams, a NASA spokeswoman. "It has no crew quarters and none of the life-sustaining functions that the service module has."
The $210 million ICM was built by the Naval Research Laboratory in Washington, D.C. It employs the same sort of spacecraft frame structure used for Navy surveillance satellites.
But the ICM has had delays due to design problems. In April, parts of it failed an electrical test before shipment for checkout at the Patuxent River Naval Air Station in Maryland.
The ICM is now set to be launched in April 2001, "which still fits in with our contingency plans," Williams said.
Once in orbit, the module is expected to provide one to three years of propulsive capability, depending on how often its thrusters are used. It holds 12,000 pounds (5,445 kilograms) of fuel.
The second U.S. tug, the Propulsion Module, is essentially a big gas tank with thruster rockets.
It was first considered in 1998 as sort of a backup to the ICM. The Propulsion Module also holds about 12,000 pounds of fuel within its 27-foot- (8.2-meter-) long structure.
NASA had wanted the Propulsion Module to be designed for refueling in orbit. But that and other requirements pushed the cost well beyond the $542 million contract with Boeing.
NASA since has decided that the Propulsion Module could be returned to Earth periodically aboard the space shuttle for refueling and then re-docked with the ISS.
The space agency has asked Boeing to submit a new design and a revised cost estimate based on the lesser requirements. NASA also is having aerospace company TRW to review the design.
"We are working very closely with NASA to simplify the design of the Propulsion Module and reduce its price to meet NASA's funding targets," said Alan Buis, a Boeing spokesman in Huntington Beach, California.
The aerospace giant plans to submit a new technical design for the module in August. A date for a firm cost estimate has yet to be determined.
As it stands, the Propulsion Module now is set to be launched in the summer or fall of 2004 with an expected performance life of 10 years.
The two tugs may provide a little breathing room in case the Russian Zvezda service module fails for whatever reason to show up for duty at the ISS.
But nothing short of a second service module -- which NASA also has been thinking about -- would truly make the station an occupied outpost in space.
"We have to keep our fingers crossed that this baby -- the service module -- goes to orbit as designed," said Charles Vick, a space analyst with the Federation of American Scientists in Washington.
"Even with the interim things NASA has planned, the space station's future really rests with this launch. It's nail-biting time," Vick said.
advertisement
