The crew patch for Endeavour's STS-100 mission. Photo: NASA

The space shuttle Endeavour rocketed into orbit today on a tricky, make-or-break flight to install a $900 million Canadian robot arm on the international space station, a high-tech space crane able to creep about the outpost like a mechanical inchworm.

Its three main engines roaring at full throttle, Endeavour blasted off from pad 39A on time at 2:40:42 p.m., majestically climbing through a partly cloudy sky and thundering away on a course paralleling the East Coast.

Two minutes later, its spent solid-fuel boosters were jettisoned for a parachute descent to waiting downrange recovery ships and Endeavour continued an uneventful climb to space on the power of its three hydrogen-fueled main engines.

At the moment of liftoff, Endeavour's quarry was passing over the equator south of India. If all goes well, shuttle commander Kent Rominger will guide the spaceplane to a docking with the international space station around 9:30 a.m. Saturday.

Joining Rominger for the 104th shuttle mission are pilot Jeffrey Ashby, flight engineer John Phillips, physician-astronaut Scott Parazynski, European Space Agency astronaut Umberto Guidoni, Canadian astronaut Chris Hadfield and Russian cosmonaut Yuri Lonchakov.

The primary goal of the flight is to install the "Canadarm 2," a 57-foot-long multi-joint space crane that is required to be in place and operational before the next assembly mission can be launched in June.

The goal of that flight is to attach the station's main airlock to the starboard hatch of the U.S. Unity module. But the shuttle's 50-foot-long arm - also built in Canada - cannot reach far enough to install the airlock. And so the new crane a requirement for assembly to proceed.

Parazynski and Hadfield are scheduled to install the the Canadarm 2 during two six-and-a-half-hour spacewalks Sunday and Tuesday.

The arm can be anchored to the station at either end, locking onto sockets mounted along the hull that provide power and relay video and telemetry to computer workstations inside the station.

Only one such "power and data grapple fixture," or PDGF, is currently in place. But additional sockets will be installed later and eventually, the arm will be able to move about the station end over end, from socket to socket.

Increasing its mobility even more, a motorized cart ultimately will be mounted on the station's main truss that will be able to carry the arm out to the facility's huge solar arrays on each end.

"As a Canadian, it's just an amazing opportunity for me personally, and as a representative of my country, to be riding on one arm that says 'Canada' and unfolding another arm that says 'Canada' as our prime contribution to the international space station," Hadfield said.

Hadfield will assist station astronaut Susan Helms during the arm's initial checkout and activation, using one of two robotic workstations in the Destiny laboratory module.

Among her other checkout tasks, Helms will carry out a dry run of the airlock installation procedure next week, putting the arm through the same maneuvers that will be required during the actual installation in June.

"The arm is probably a couple of generations evolved beyond the arm that is part of the space shuttle," Hadfield said during a pre-flight briefing. "The new one has a hand on both ends. Not really a hand, but the equivalent of a hand, the ability to grab and grapple.

"That hand not only grabs on, but it also plugs in electrically and connects video and connects data when it grabs on, so the arm can be operated from either end. And the arm can move itself around the station as required so it can far exceed the reach the arm on the shuttle would have."

The second objective of Endeavour's mission is to deliver 7,500 pounds of equipment and supplies, including two experiment racks and a two-month supply of food for Helms and her two crewmates.

The logistics are housed in an Italian-built cargo module named Raffaello. Parazynski, operating Endeavour's robot arm, will unberth the cargo module Monday and attach it to Unity's Earth-facing hatch.

It will be unpacked over the next four days and reloaded with station trash and discarded equipment for return to Earth.

Endeavour is scheduled to undock from the space station April 28, the same day the Russians plan to launch a new Soyuz spacecraft to replace the station's current emergency lifeboat, which is nearing the end of its certified 180-day orbital lifetime.

The crew of this so-called Soyuz taxi flight is expected to include U.S. businessman Dennis Tito, who reportedly paid the Russians some $20 million to become the first space tourist. Tito and his crewmates plan to spend about six days aboard the station before returning to Earth in the Soyuz currently attached to the outpost.

NASA managers and the station's other international partners unanimously oppose Tito's visit, arguing his visit should be delayed to October to permit additional training time and to minimize distractions to the station's crew at a particularly busy time.

But NASA and the other partners appear powerless to stop the Russians, who argue Tito is properly trained, launching on a Russian spacecraft that will dock with a Russian module.

Assuming NASA fails in last-minute attempts to persuade the Russians to delay Tito's visit, the American businessman and his two Soyuz crewmates will dock with the international space station on April 30, just a few hours before Endeavour's planned landing.