NASA's last-minute thumbs-up to send a US astronaut to the space station Mir represents a vote of confidence in Russia's aging orbital outpost.
But it also may signal a lingering concern over the impact a nyet would have had on Russia's willingness to fulfill its role in the International Space Station project. Construction is scheduled to begin late next year, and Moscow is on the hook for several of the station's key elements.
"It is a decision that all of us at NASA did not take lightly," said Daniel Goldin, the space agency administrator, in announcing the go-ahead to send astronaut David Wolf up to Mir Thursday.
Not since the aftermath of the Challenger explosion in 1986 has the safety of US astronauts received such high-profile attention. This time, however, the hardware belongs to someone else.
So far this year Mir has endured a fire, a collision, power shortages, and coolant leaks. Its woes continued this week: On Monday, the station's computer failed for the fourth time since July, forcing the crew to cobble together a machine from spare parts. The carbon-dioxide removal system also needed minor repairs, and the crew noticed a "brown substance" floating from the station.
In making his decision to send Wolf, Mr. Goldin drew on two independent studies of the space station's safety, NASA's own internal evaluation, plus face-to-face talks with counterparts in Russia.
The decision does carry considerable risk, however. If something serious were to happen during the astronaut's planned four-month stay, it might not only jeopardize his safety but could also shake overall US confidence in the space program.
Critics on Capitol Hill are closely watching the mission. One, House Science Committee chairman James Sensenbrenner (R) of Wisconsin, says the US has learned a lot from trips to Mir, but argues the risks now outnumber the potential rewards.
Ironically, the shuttle mission carrying Dr. Wolf and six colleagues - including a Russian and an astronaut from the European Space Agency - was to have shut the hatch on long-term Mir visits by US astronauts. When the shuttle-Mir missions began, NASA was aiming to build a new orbiting outpost, the International Space Station, beginning this November. Shuttle resources would be needed for the construction effort.
By the end of 1995, however, Russia's financial crisis prompted some parliament members to propose using Mir to replace - at least temporarily - the ISS service module Moscow had agreed to build. The Russian space program was too broke to meet its ISS commitments and maintain the unmanned rockets needed to keep Mir's crew in groceries.
Mindful of Moscow's concerns, NASA announced in January 1996 a new agreement with the Russian Space Agency that, among other things, turned the shuttle into a freighter for Mir. The US space agency added two shuttle-Mir flights in 1998. In exchange, the Russians reaffirmed their commitment to the delivery schedule of ISS components. Since then, however, budget problems have delayed Moscow's ISS effort yet again.
For the Russians, talk of keeping Wolf on the ground has been disturbing. If it had happened, Americans would be viewed as "sunshine space explorers," says Valery Ryuminof RSC Energia, which is building ISS components. "Factions in Russia oppose joint operations. Such a decision ... would delay work on the International Space Station."
NASA officials maintain that the ISS effort has much to gain from remaining Mir visits. One, Frank Culbertson, notes that remaining long-duration missions will allow scientists to test upgrades to research equipment. The aim is to iron out bugs now - before devices are installed on the ISS. Goldin says his decision to go ahead with the mission was based in part on the "additional experience and knowledge that cannot be gained elsewhere."
Wolf's schedule is packed with some 35 experiments. "We're just at that point in the learning curve where things are ready to take off," Mr. Culbertson says.