The docking ports of space station Alpha and shuttle Endeavour make contact high above the south Pacific. Photo: NASA TV/Spaceflight Now

Shuttle skipper Kent Rominger guided Endeavour to a glacial docking with the international space station today as the two spacecraft sailed 243 miles above the south Pacific Ocean at five miles per second.

The successful linkup sets the stage for a critical spacewalk Sunday by astronauts Scott Parazynski and Canadian Chris Hadfield to install the new Canadarm 2 space crane on the station's hull.

"The delivery of the Canadarm is really crucial to mthe remaining assembly of the space station," said lead flight director Phil Engelauf. "We're now at the point in the assembly where the components to be added to the station cannot be installed without the additional reach capability that's provided by this new arm."

Starting with the next assembly mission in June.

During that flight, the station's main airlock will be installed, a job that cannot be accomplished using the shuttle's shorter robot arm. The airlock will enable station crews to stage assembly and maintenance spacewalks between shuttle visits.

Endeavour approaches the station with the Sahara Desert in the background. Photo: NASA TV/Spaceflight Now

The new Canadarm 2, mounted on the Destiny laboratory module, must be checked out and operational before the airlock can be launched. But if today 's docking was any indication, the flight is off to a near perfect start.

"Everything went great, we are right on the timeline and looking forward to starting a really aggressive period over the next few days of deploying the Canadarm 2 and transferring the contents of the (Raffaello cargo module) into the station," said Engelauf. "Everything's going great so far."

Positioned directly ahead of the station, flying tail toward Earth with its payload bay facing the lab complex, Endeavour's docking system engaged its counterpart on the station at 9:59 a.m. to cap a two-day orbital chase.

About a half hour later, leak checks between the shuttle and the station's PMA-2 docking port were complete and the station's four massive gyroscopes assumed attitude control of the combined spacecraft.

But the Endeavour astronauts were not able to enter the station today because the shuttle's cabin air pressure was lowered from 14.7 psi to 10.2 psi Friday to help Hadfield and Parazynski purge nitrogen from their bloodstreams.

The space station is pictured by the center-line camera in the shuttle's docking port during the rendezvous. Photo: NASA TV/Spaceflight Now

The astronauts did, however, open the hatches leading into the PMA-2 docking port to position supplies needed by the station crew before Sunday's spacewalk. The Alpha astronauts - commander Yuri Usachev, Susan Helms and James Voss - floated into PMA-2 later to retrieve the items delivered by the shuttle's crew.

The major item was electrical cabling needed to bypass an overly sensitive ground fault interrupt circuit that was tripping breakers in the power supply used by the robotic work station needed to operate the new Canadarm 2 crane.

Endeavour's crew also left the station astronauts a bit of fresh coffee, fruit and vegetables, welcome additions to their typically freeze-dried menu.

Station flight director John Curry said Alpha's complex systems are in good shape, including a Russian carbon dioxide removal device that was acting up Friday.

Endeavour's astronauts cram into the PMA-2 docking adapter to greet the Expedition 2 crew through a porthole in the closed hatch. Photo: NASA TV/Spaceflight Now

THe Vozdukh system can operate in a variety of modes depending on how many crew members it is supporting. On Friday, it was stuck in Mode 3, meaning it could support the station's three-person crew but no more.

That wasn't an issue for Endeavour's docking because the shuttle's CO2-absorbing lithium hydroxide canisters can handle the full load on their own. But flight controllers wanted to fix the problem before arrival of a Soyuz spacecraft April 30 carrying U.S. businessman Dennis Tito and two crewmates.

Working in Mode 3, the Vozdukh would not have been able to handle the load of the increased six-member crew, forcing them to tap into the station's own supply of lithium hydroxide canisters. Eighteen such canisters currently are on board the station, enough for 15 days. Endeavour's crew is delivering 10 more.

The space station towers above shuttle Endeavour in this view from a payload bay camera. Photo: NASA TV/Spaceflight Now

Overnight Friday, however, the Vozdukh suddenly shifted into Mode 5, providing enough CO2 scrubbing for five crew members

"There was some troubleshooting planned (today), but Vozdukh overnight started working a little bit more efficiently in what we call Mode 5, which means it can maintain the levels for a three-person crew and we decided not to do any major maintenance on that today," Curry said.

If the Vozdukh stays in Mode 5, the crew will still need to use lithium hydroxide during the upcoming visit by Tito and company. But Curry said only one or two of the 28 canisters that will be on board will be needed.