CAPE CANAVERAL, Fla. - The United States and Russia might be the most powerful players in the International Space Station program, but the future of the $60 billion construction project now hinges on an underrated partner: Canada.
Circling some 238 miles (381 kilometers) above Earth, the 17-story station -- which eventually will span an area as large as a city block -- simply can't be finished without a Canadian robotic servicing system also needed to maintain the outpost over the next two decades.
What's more, the ongoing assembly of the station will come to a quick halt if a critical Canadian construction crane isn't put in place by the visiting crew of shuttle Endeavour after its planned launch Thursday.
"The robot arm is absolutely essential to the rest of the space station assembly, as well as to operations after assembly is complete," said Endeavour mission specialist John Phillips.
"It's what's going to allow us to construct the greater portion of the station from now on," added U.S. astronaut Jim Voss, one of three tenants now serving a tour off duty aboard the outpost.
A joint project of 16 nations on four continents, the station initially consisted of a Russian space tug and the American Unity module, which were launched and linked in orbit in late 1998.
A long-delayed Russian command post that doubles as crew quarters finally was launched last July, and since then the station has undergone rapid expansion.The first piece of what eventually will be the station's 356-foot (108-meter) central truss was erected in October. A $600 million U.S. electric power tower - which features solar wings that measure 240 feet (73 meters) from tip to tip - was added in December.
Then a shuttle-borne construction crew delivered the station's first science center - the $1.4 billion U.S. Destiny laboratory - in February, doubling the size of the outpost, which now stretches 171 feet (52 meters) from end to end.
Coming up next: The so-called space station remote manipulator system, which is an advanced version of the shuttle's 50-foot (15-meter) Canadian robot arm.
Considered the heart of Canada's $1.4 billion (US$900 million) station investment, the sophisticated construction crane will be delivered by an international crew scheduled to blast off aboard Endeavour at 2:41 p.m. EDT (18:41 GMT) Thursday.
A marvel of modern technology, the 57-foot (17-meter) crane will be capable of moving from work site to work site outside the station, crawling to places that the shuttle's fixed robot arm cannot reach.
Snare-like hands on either end of the arm will be able to grasp so-called power and data grapple fixtures that will electrically connect the crane to computer control stations inside the complex. The crane then will be able to move end over end, from one pin-like anchor to the next, much like a toy Slinky rappelling down a staircase.
"It's a bit like an inchworm," said veteran Canadian astronaut Marc Garneau, now executive vice president of the Canadian Space Agency (CSA). "We've all seen an inchworm sort of put its nose down and then lift its whole body and then sort of flip over. And then its tail becomes like its nose and then it can flip end-over-end and move like that."
The crane will become even more mobile with the addition next year of a rail cart also built by the Canadians. Perched atop the cart, the robot arm will be able to move up and down the station's central truss.
Riding atop the so-called mobile transporter and its mobile base, which now are scheduled for launch in January 2002 and March 2002, respectively, the robot arm will be able to carry out assembly and servicing work anywhere along the station's metallic backbone.
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