HOUSTON, April 21 — This weekend’s blastoff of a Russian Soyuz spacecraft will mark the first human space mission since the loss of the shuttle Columbia and its seven astronauts almost three months ago. In the intervening time, this space mission has been completely redesigned to reflect the new realities of a grounded space shuttle fleet and the urgent demands of the high-maintenance international space station.

Russian cosmonaut Yuri Malenchenko and NASA astronaut Edward Lu will rocket into orbit from Russia’s Baikonur space center in Kazakhstan, just east of the Aral Sea. The countdown will reach zero at midmorning local time on Saturday (11:54 p.m. ET Friday). They will then spend two days chasing after the space station and will dock about 2 a.m. ET Monday.

After a week of conferring with the crew they are replacing, the two new station caretakers (who have already visited the station once on a shuttle construction mission, when they did a spacewalk together) will assume full responsibility for operating the 130-ton orbital outpost.

HOMECOMING FOR CURRENT CREW
Currently on board NASA are astronauts Ken Bowersox and Don Pettit, and Russian cosmonaut Nikolai Budarin, who had their duty tour extended for two months. Instead of landing by shuttle, as originally planned, they will return to Earth on May 4 in the Soyuz TMA-1 escape craft already attached to the station.

They are fully trained for this option, and Budarin is a veteran civilian cosmonaut who has landed in Soyuz vehicles twice before. But on those earlier missions, the flight engineer was an assistant to military pilot-cosmonauts who sat in the center control seat, where Budarin will now control the descent.

Only twice before in the history of the Russian human space program has a non-pilot cosmonaut commanded a Soyuz vehicle. Both missions, in 1979 and 1980, turned out to be very unlucky. On one, a maneuvering engine exploded, and the men had to make an emergency landing. On the other, a seemingly routine landing suddenly turned hazardous when the soft-landing engine failed and the capsule smashed into the ground with bone-jarring force.

These failures were only coincidentally associated with who was in charge of the mission. So unless Budarin is overly superstitious, he and his shipmates should have nothing to worry about.

If there is any reason for concern, it rests with the novelty of their new-model Soyuz TMA-1 spacecraft, which had never been flight-tested before its current mission — and with any possible quality repercussions on its manufacture due to the near-bankrupt state of the Russian space industry

CHANGE OF PLANS -- The change of plans for the Soyuz could conceivably add to the financial crisis. The original “taxi crew” was supposed to have consisted of a Russian pilot and two paying “guest cosmonauts.” One, a professional astronaut from the European Space Agency named Pedro Duque, would have assisted in flying the ship, while the other was supposed to have been a “space tourist.” The sale of both those seats would have brought in a badly needed $20 million to $30 million.

In response to the crisis, the Europeans agreed to delay Duque’s flight until the next Soyuz swap in October, while still paying for it according to the original schedule. But the expected money from space tourist tickets has vanished.

If the Columbia tragedy hadn’t occurred on Feb. 1, Malenchenko, Lu and a third crewmate would have been delivered to the station aboard a shuttle mission in early March, and by now the trio would have been nearly halfway through their Expedition 7 mission. But for now, the Soyuz TMA spacecraft represents the only way station astronauts can get back and forth.

William Gerstenmaier, NASA’s space station program manager, described some of the Soyuz TMA modifications at the preflight press conference last week. The final braking system, which fires in the last few feet of the parachute descent to soften the impact, has been rebuilt completely. To allow taller astronauts to fit inside, a small “bump” on the side of the Soyuz provides several extra inches of leg room, and that different shape has been covered by a modified thermal protection system.

“The structural modifications to the descent module were tested using several hangar-based drop tests,” NASA press official Rob Navias explained to MSNBC.com. Other landing system modifications — including the descent computer control system, explosive bolts sequencer, improved altimeters and soft-landing rocket engines — “were tested using several airborne drop tests.”

“The Russians are very test-intensive,” Gerstenmaier stressed at the news conference. He said that the new control computers and software have been subjected to extensive verification, and that there was complete redundancy to the new systems.

“Behind all this is a backup analog computer,” he continued, “the same one that’s been flown on Soyuz for a long time — and it can handle the entire entry and landing if the new hardware or software can’t.”

The Russians, too, will pay more attention than usual to the coming landing. For the first time in their space program, they plan to make observations of the Soyuz TMA-1’s entry fireball from space with a special ultraviolet camera in the space station’s main down-facing window. The new twist comes as a coincidence, following the loss of Columbia during this same phase of flight.

TRAVEL DOCUMENTS -- The change in landing plans has created more than mere scheduling problems, noted Melissa Gard, NASA’s manager for the current expedition operations. In response to a question from MSNBC.com, she described how a fellow astronaut will be at the landing site in Central Asia with passports and visas for the two Americans, who had not expected to need them when they blasted off last fall.

Kazakh immigration and customs officials have been sticky in the past about unexpected space visitors with uninspected baggage, but NASA has learned from experience and expects no bureaucratic problems — or any other kind — this time.

James Oberg, space analyst for NBC News, spent 22 years at the Johnson Space Center as a Mission Control operator and an orbital designer.