Spaceflight Now: STS-92 Mission Report

High winds conspire to scrub shuttle Discovery launch
BY WILLIAM HARWOOD
SPACEFLIGHT NOW

Posted: October 9, 2000

  Arm
A file image of the gaseous oxygen vent arm in position atop of the external fuel tank. Winds prevented workers from extended the arm to the tank today. Photo: NASA TV
 
After weekend work to resolve two technical issues, the hard-luck shuttle Discovery was grounded again today, this time by high winds at the launch pad that prevented engineers from completing preparations to fuel the ship for take off.

Launch of the 100th shuttle flight, the most complex space station assembly mission yet attempted, is now targeted for 7:40 p.m. Tuesday, weather permitting.

Forecasters with the 45th Space Wing at the Cape Canaveral Air Force Station are predicting a 70 percent chance of low clouds and high winds Tuesday evening that could prompt yet another delay.

Conditions are expected to improve dramatically by Wednesday, with a 70 percent chance of acceptable conditions.

NASA typically makes two back-to-back launch attempts before standing down a day to give engineers time to rest. But agency managers said three attempts in a row might be considered, depending on the weather and other factors.

NASA initially had until Wednesday to get Discovery off the ground before standing down until Oct. 14 to make way for the Oct. 12 launch of an Atlas rocket carrying an Air Force communications satellite.

Shuttles and unmanned rockets launched from the Cape Canaveral Air Force Station share the same military tracking systems and it takes a day or more to reconfigure the Eastern Range to support a different mission.

Early today, Air Force officials confirmed the Atlas flight would be delayed until next week because of a technical problem, giving NASA additional options for getting Discovery off the ground this week.

The current strategy, NASA officials said, is to press ahead for a launch try Tuesday and again Wednesday, if necessary. At that point, the team could either stand down a day and try again Friday or press ahead for a third-straight launch attempt Thursday.

Today's scrub was ordered after engineers were unable to move a rotating gaseous oxygen vent hood into position over the tip of Discovery's external fuel tank.

  Arm
A file image of the gaseous oxygen vent arm being removed from the top of the external fuel tank prior to launch. Photo: NASA TV
 
The so-called "beanie cap" is used to carry oxygen vapor away from the tank after it is loaded with supercold propellants to prevent potentially dangerous ice from building up. It is rotated away from the tank two minutes and 55 seconds before launch.

The beany cap normally would have been moved into place by 2 a.m. or so, but high winds at the pad in the wake of a weekend cold front made that impossible. Gusts as high as 44.6 knots were recorded, violating NASA's 42-knot safety limit.

Had the arm been in place by 5 a.m., fueling could have started on time. But by 8 a.m., time had run out for even a delayed fueling start and one hour later, NASA's mission management team ordered the 24-hour delay.

Discovery's launch flow is shaping up to be one of the most difficult in recent memory.

An attempt to get the spaceship into orbit last Thursday was delayed a minimum of 24 hours because of concern about the status of critical bolts used to hold the external tank to the shuttle.

Later that night, engineers decided a sluggish valve in Discovery's engine compartment needed to be replaced and launch was delayed an additional two days to Monday.

A new valve was installed over the weekend and on Sunday, mission managers decided the external tank attachment bolts were safe to launch as is, leaving weather the only concern.

  Station
The international space station as photographed against Earth's horizon during a fly-around by shuttle Atlantis last month. Photo: NASA
 
NASA needs to get Discovery off the ground as soon as possible to attach a new shuttle docking port to the international space station and an 18,300-pound truss that houses four stabilizing gyroscopes.

The Z1 truss also will serve as a temporary mounting point for a huge solar array scheduled for delivery in December.

The space station's first full-time crew is scheduled for launch atop a Soyuz rocket on Oct. 30. Discovery must be back on the ground at least two days before the Soyuz takes off to give NASA personnel supporting both missions time to fly to Russia.

The station crew needs the Z1 and the new solar array to provide additional power.

The truss will be mounted atop the U.S. Unity module. But the gyroscopes will not be activated until early next year, after arrival of the U.S. laboratory module Destiny.

To keep the gyros from getting too cold between now and the end of the year, the station will be oriented to provide additional solar heating.

As a result, the Unity module will be too warm for the station crew to enter until the solar arrays scheduled for attachment in December are in place and providing the electricity needed to power heaters on the gyroscopes.

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