Shuttle To Have Just 5-Minutes To Launch Rendezvous With Russian Space Station Requires Exacting Schedule For Discovery
NASA has five minutes Thursday to launch Discovery on a trip to Russia’s space station.
That’s it. Five minutes, less time than it takes for a space shuttle to reach orbit, less time than it takes, in fact, for an astronaut to crawl into the crew compartment and strap in.
And that’s the way it will be the next day and every day until Discovery soars.
It is NASA’s shortest shuttle launch window in 10 years and it comes in the middle of the night because of the unprecedented rendezvous with Russia’s orbiting Mir station.
The countdown began Sunday.
Discovery’s exact launch time won’t be known until 1-1/2 hours before liftoff, but it will be close to 12:48 a.m. EST on Thursday. That time was chosen to put Discovery and its crew of six on the right path to meet up with Mir, using the least amount of fuel. The Mir flyby is scheduled for Day 4 of the eight-day mission.
Commander James Wetherbee plans to bring Discovery within 35 feet of the Mir station as practice for Atlantis’ first docking with Mir in June. Atlantis will dock again in October and at least five more times through 1997 under a cooperative agreement with Russia.
NASA typically allows 2-1/2 hours to launch its shuttles. Any time a shuttle is bound for Mir, however, the launch window will shrink to about five minutes and the time of launch will move up nearly a half-hour with every passing day. The same restrictions will apply when it comes time to build a new space station with Russia and other countries later this decade.
NASA could stretch its launch windows by 10 to 15 minutes for these missions, but the price would be steep in terms of fuel. By launching at the proper time - i.e. within five minutes of the appointed moment - the shuttle uses a minimum amount of fuel in orbit to catch up to Mir. The longer the window the more fuel that’s needed, and the shuttle will have little if any to spare.
Launch managers have dealt with this before.
In the mid-1960s, NASA had less than a minute each day to launch the Gemini rendezvous missions. And in the mid-1980s, there were two less than five-minute launch windows for shuttles.
NASA had just 3-1/2 minutes to launch Challenger on a satellite-repair mission in 1984 and four minutes to launch Discovery on a satellitei-delivery mission in 1985. Both began right on time.
Eighteen of NASA’s 66 shuttle launches, in fact, have occurred in the first five minutes of the first launch attempt.
To improve its chances, NASA has reorganized its launch countdown for the Mir missions, adding an extra hour here and an extra half-hour there in case of last-minute equipment trouble. Fueling will begin a half-hour earlier than usual, and the astronauts will board a half-hour earlier, too.
NASA test director Al Sofge keeps reminding the launch team that if problems pop up in the final hours of the countdown, “You don’t want to rush. Don’t want to waste any time, but you don’t want to rush.”
“If you try to rush and do something stupid to make a 5-minute launch window, the benefit is infinitesimal,” Sofge says. ‘It’s better to be sitting on the ground wishing you were flying than flying wishing you were sitting on the ground.”
As for Florida’s fickle weather, mission managers have made one allowance. NASA rules prohibit shuttles from launching if thick clouds cover the emergency landing strip at Kennedy Space Center. That cloud ceiling used to be 8,000 feet; it’s now 6,000 feet because of improved shuttle navigation.