Although this 28th flight of America's space shuttle is nearly identical to the mission flown by Discovery in September, NASA officials consider it significant because it indicates the nation's manned space program is again functioning smoothly and efficiently following the January 1986 Challenger disaster. Discovery's latest flight is the third shuttle launch since then.
"It's a very organized program (and) the recovery is going extremely well," a confident Richard Truly, NASA's director of space flight, said at a pre-launch briefing yesterday. "It's going to be a great year."
NASA has planned seven launches for 1989, including next month's launch of the Magellan satellite to Venus and December's launch of the huge Hubble Space Telescope.
Truly said that he expected the agency to stick to its 1989 schedule but conceded that the lengthy reprocessing of the shuttle Columbia, which has not flown since Jan. 12, 1986, could result in a delay of that shuttle's July flight on a Defense Department mission.
NASA's "highest priority," Truly said, is meeting the launch windows of major planetary missions that have been delayed for years by the Challenger accident.
Although Discovery is making essentially the same flight it made last fall, this week's mission will be unique in several ways.
For the first time, NASA will have the option of using a new, Bermuda landing site in the event that two of three main shuttle engines fail shortly after launch. But the astronauts will still have the option of using a new bailout system if the orbiter cannot be landed, Truly said.
Discovery also will have several unique experiments on board, including ones exploring zero gravity's effect on the healing rate of broken rat bones and the growth rates of chicken embryos and plant roots. Discovery will carry four live rats and 32 fertilized chicken eggs.
Its main mission, though, will be the deployment of the satellite, called the Tracking and Data Relay Satellite System, into orbit above Earth.
This will be the fourth such satellite launched aboard the space shuttle. One was launched in 1983, one was lost aboard the Challenger and another was launched on Discovery last fall.
The network of the three communications satellites is designed to allow the space agency to communicate efficiently with all manned and unmanned spacecraft - which in the past were tracked with a large network of ground- based stations.
The Discovery crew has a Philadelphia connection: Bagian, an engineer, surgeon and pilot, was born in Philadelphia and received degrees from Drexel University and Thomas Jefferson University.
This weekend's three-day countdown leading to Discovery's launch was smooth. The shuttle had been plagued by serious mechanical problems that delayed its launch from late February until this week.
The main problem was a small crack discovered inside one of its main-engine liquid oxygen pumps after Discovery returned from its September mission. All three of the shuttle's liquid oxygen pumps were removed and replaced while the Discovery stood upright on its launch pad.
Last week, the launch was delayed again after a device that controls the separation of the orbiter vehicle from its two boosters and external fuel tank failed to work during a test. Borrowing parts from the shuttle Columbia, NASA engineers replaced the faulty device on Discovery and the countdown began.