CAPE CANAVERAL, Fla. -- While NASA struggled this week to get Space Shuttle Atlantis off the launch pad on a mission to revive a stalled International Space Station (ISS) project, a half a world away, Russia raced against time to prepare another crucial launch in the project.

Although the Atlantis crew will prolong the life of the already-flying elements of the ISS, any further construction of the multibillion-dollar outpost hangs on Russias ability to meet a long string of deadlines in the near future.

The Proton booster returned to flight in February and so far has successfully delivered three payloads into orbit. However, to ensure the success of the Zvezda launch, the Russian Aviation and Space Agency, Rosaviacosmos, decided to use modified second-stage engines in Proton rocket number 39801 -- the one which will lift Zvezda.

Both Russian and U.S. space officials have said that a July 12 launch date for Zvezda -- a date confirmed by Rosaviacosmos -- imposed a very tough deadline on Khrunichev, Proton's manufacturer.

Nevertheless, Valeri Alaverdov, first deputy general director of Rosaviacosmos, said that Russia would meet the July 12 launch date. Tommy Holloway, the ISS program manager at Johnson Space Center in Houston, echoed Alaverdov, saying that he is confident Zvezda would take off between July 8 and 14.

A depiction of the International Space Station

The modified second-stage engines for the Proton rocket that will carry Zvezda arrived at Moscows Khrunichev on April 1. The rocket is expected to be completely assembled around May 15. On May 28, Khrunichev expects to ship it to the Baikonur Cosmodrome in Kazakhstan, Russia's primary launch facility.

Before it lofts Zvezda, Rosaviacosmos currently plans two launches of the modified Proton rocket. Successful liftoffs would then verify the reliability of the upgraded second-stage engines for the Zvezda launch.

Alaverdov said that the first Proton with modified engines would take off at the end of May or beginning of June, carrying a Gorizont 45 communications satellite. Khrunichev is scheduled to ship the Proton on Wednesday, April 26. A new Breeze upper stage will also be tested on this launch. The original Breeze was launched atop a Proton booster last July, but it never had a chance to demonstrate its performance due to a launch failure.

If this attempt succeeds, the second launch to test Protons upgraded engines will take place in the second half of June. This time, the rocket will carry a Geyser data-relay satellite for Russias Ministry of Defense.

Two other Proton launches -- equipped with older second-stage engines carrying Russian Express A-3 and U.S. Sirius 1 communications satellites -- have been planned for June 8 and June 18, respectively. However, Zvezda's tight schedule might push both of these launches into the second half of summer 2000.

Although the Zvezda service module has been virtually flight-ready for the last several months, Russian engineers have tried to improve the spacecraft during the delay. The most important upgrade was related to the modules software. The new computer code for Zvezdas flight-control system will improve the spacecrafts chances of surviving should communication with the ground break down.

According to the latest work-plan, the electrical testing on Zvezda currently conducted in Baikonur will be completed on April 29. Following the May Day holiday celebrated in Russia, the module will go through a four-day test in the vacuum chamber.

Around May 20, the international resident crews will visit Baikonur for familiarization training with their future orbital home.

Zvezda will reach a critical milestone around June 16, when the modules launch date will be finalized. By that time both test launches of the Protons, with their modified engines, should have been completed. Once a launch date is established, the so-called irreversible operations will begin, such as fueling the spacecraft with toxic and highly corrosive propellants. This critical operation is currently scheduled for June 27.

Around July 3, the fully assembled Zvezda and its protective shroud will be mated to the Proton launch vehicle and the whole system will be transported to the launch pad for final preparation before takeoff.