Countdown for Key Shuttle Test Resumes

A two-part countdown resumed Sunday for the test-firing of space shuttle Discovery’s engines after engineers repaired a hydrogen leak and a balky oxygen pump.

The problems that cropped up Friday caused the fourth postponement in 10 days for the test, which is considered critical to certifying Discovery for the first shuttle flight since the Challenger disaster.

The test-firing is now scheduled to take place Thursday.

Expect Postponement

Officials believe that the delays, combined with an unresolved leak in Discovery’s steering-engine system, will postpone the launch date from mid-September to October.

The leak and pump problems developed soon after technicians began pouring more than half a million gallons of liquid hydrogen and liquid oxygen propellant into the spaceship’s external fuel tank.

It was the first attempt to fuel a space shuttle since Challenger exploded on Jan. 28, 1986, killing the crew of seven.

Secured on Pad

The exercise leading to the firing of the three main engines, with Discovery secured firmly on the launch pad, is divided into two parts.

The first part, now under way, involves fully fueling the tank and simulating a problem that forces a postponement with the countdown at 10 seconds before a mock liftoff. That will take place today.

The launch team then will empty the tank, restart the countdown, refill the tank and aim for a 20-second ignition of the engines at 7:30 a.m. Thursday.

The purpose is to check several modifications made to the engines and launch pad since the Challenger accident and to provide countdown practice for the launch team.

Gas Leak Remains

When the test is completed, the National Aeronautics and Space Administration still must cope with the small gas leak in the steering-engine system that is separate from the main engines.

Engineers have come up with a plan to reach and repair the leak by entering Discovery’s cargo bay and cutting a hole through the rear bulkhead into the steering engine compartment.

Another option, with a decision that will be made after the test-firing, is to take Discovery off the launch pad and back to a hangar for repair, a move that could postpone the launch until November.