Static View of Columbia after STS-73 landing on 11/05/95 at 6:45am EDT
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The launch of STS-73 started with the countdown clock picking up at 7:30pm at the T-11 hour mark with a scheduled T-0 at 9:50 a.m. Loading of fuel was completed at 3:53am. The crew suited up at 6:00am and traveled out to Launch Pad LC-39B. (Reference KSC Shuttle Status 10/18/1995).
At the post-launch press conference, Jim Harrington, Director of Shuttle Operations mentioned the launch countdown went relatively smoothly. At the beginning of the count there was a problem with one of 3 redundant sensors on Liquid Oxygen (LOX) portion of the external tank toggling from wet to dry. The sensor was bypassed. After tanking, one of the relief valves in the LOX storage area had a slow leak internally that will be fixed during ground operations. There was also a fire alarm that went off accidently at the 155ft level during the later part of the count while the close out crew was still on the pad. No fire was detected. Also, a right hand mid joint heater trimmed down and the launch team switched over to the backup system. Finally, the range command destruct system lost communications between the ROCC and the antenna. A contingency plan was work and the count was picked back up.
The launch scheduled for October 15 10:46 a.m EDT was scrubbed at 1:25pm EDT due to weather conditions at KSC that were unacceptabledue for launch. Due to the scheduled launch of the Atlas launch vehicle on Tuesday morning (10/17/95), the next available time frame in which Columbia could have been launched was Thursday, Oct. 19 at 9:49 a.m. EDT. Bad weather delayed the Atlas launch which slipped the launch of Columbia till Friday. The launch window extended until 12:19 p.m. that day. (Reference KSC Shuttle Status 10/16/1995). Fueling operations had started around 1:20 a.m. EDT with the loading of 1/2 million gallons of liquid hydrogen and liquid oxygen into the external tank and were completed at 4:03am. Since the available launch period extended to 1:35 p.m. EDT based on the Transoceanic Abort Landing (TAL) lighting conditions at Ben Guerir, Morocco the crew was boarded one hour later than planned to provide a increased opportunity for favorable weather towards the end of the launch window. They departed the Operations and Checkout Building (O&C) at 7:20am EDT.
On 10/14/95, the Mission Management Team closed the two open issues with flight hardware which caused a one day postponement of the launch of Columbia on Mission STS-73. The issue with a duct on the main engines was resolved by technicians taking ultrasonic measurements of the duct to verify adequate wall thickness. That work along with additional data analysis have allowed engine managers to conclude that there are 3 good SSMEs on Columbia. The issue with a General Purpose Computer (GPC) was resolved by removing and replacing the suspect unit. The new GPC installed in Columbia has been tested and approved for flight support. (Reference KSC Shuttle Status 10/14/1995).
On 10/13/95, NASA managers postponed the launch of Space Shuttle Columbia on Mission STS-73 to 10/15/95 in order to work an issue with the Space Shuttle Main Engine (SSME) and another with the orbiter's onboard computer (GPC). The issue with the Shuttle main engines involves inspection work that is required because of a crack found in a high pressure oxidizer duct on a main engine (SSME SN# 2015) being tested at the Stennis Space Center in Bay St. Louis, Mississippi on 10/11/95. Inspection of the failed duct indicates the crack happened in a weld area and was due to the duct wall being too thin. The work on Columbia involves ultrasonic inspection of the welds on each engine's high pressure oxidizer duct to ensure proper wall thickness. There are seven different welds on each engine duct.
A separate issue was worked by the launch team with one of Columbia's General Purpose Computers (GPC). During prelaunch testing, the ground crew noticed an unusual response in the data transmission between the GPC and associated electronics hardware.
The launch scheduled for Saturday, 10/7/95 at 9:41am EDT was scrubbed at 10:05am EDT ( T-minus 20 minute mark ) by KSC Launch Director Jim Harrington and the Mission Management Team due to a problem with one of Columbia's two Master Events Controllers (MEC). The MECs control all critical functions that occur on the Shuttle at T-0 and through flight, including routing commands from the Shuttle s onboard computers to fire the explosive bolts that hold the solid rocket boosters to the Mobile Launch Platform (MLP) and the pyrotechnics that separate the boosters from the external tank during flight. (Reference KSC Shuttle Status 10/07/1995).
The countdown had started and proceeded with little difficulty. During tanking operations, the only minor problem was an overvoltage failure of a ground pump (Primary Pump 126). Tanking was picked up using the backup pump 127 and the count proceeded normally. The flight crew had departed the Operations and Checkout Building for Pad 39-B at 6:25am EDT and was onboard Columbia. At 8:56am (T-minus 29 minute mark), the launch team called a Launch Commit Criteria violation due to a failed self test on B-Core (Port 1, bit 5) of Columbia's Master Events Controller #1. The four cores are all redundant allowing the Shuttle quad-redundancy. Launch commit criteria rules require all four cores to be operating properly for safe flight. The launch countdown was placed on hold at the T-minus 20 minute mark while commands were issued to determine if the problem was with the controller or with instrumentation. It was determined the problem was with the controller which will need to be replaced.
At this time, the external tank will be drained and purged, the Rotating Service Structure (RSS) moved back around the vehicle and preparations made to gain access to the aft engine compartment to remove and replace the MEC. The MEC is scheduled to be removed on Monday 10/9/95 and the replacement MEC tested on Tuesday 10/10/95. Some of the experiments in the USML-2 spacelab module must be serviced before another launch attempt can be made and the onboard cryogenic tanks must be off-loaded and then re-loaded with liquid hydrogen and liquid oxygen reactants.
The launch on 10/6/95 was scrubbed at 3:33am for a minimum of 24 hours due to a problem in the orbiters #1 hydraulic system which services Columbia's nose wheel steering system. On 10/6/95, during pre-launch checkout, engineers noticed a problem with the volume of hydraulic fluid in the system. They will cycle the hydraulic system's fill and dump valve and run a compressibility test. (Reference KSC Shuttle Status 10/06/1995).
The launch scheduled for 10/5/95 was posponed 24 hours due to bad weather from Hurricane Opal. (Reference KSC Shuttle Status 10/05/1995) The launch attempt of Columbia on September 28, 1995 at 9:35 a.m was scrubbed due to indications of a hydrogen leak in Space Shuttle Main Engine (SSME) #1 (SN#-2037) . The scrub was called at 4 a.m. on 9/28/95. The hydrogen main fuel valve needed to be replaced which delayed the launch approximately one week. (Reference KSC Shuttle Status 9/28/1995).
During the launch postponement press conference, Jim Harrington, KSC Launch Director and John Plowden, Rocketdyne Site Director reported that Tanking operations had begun approximately an hour later than planned primarily due to lightning in the area of the launch pad. Liquid hydrogen was in recirculation for about 30 minutes and the main fuel valve had begun to chill down. When it reached the temperature of -10F degrees the valve started to leak. Tanking operations were stopped when the temperature on the valve reached the Launch Commit Criteria cuttoff limit of -250F degrees at the downstream side of the valve. Normal temperature on the valve runs at -100F to -150F degrees.
This would have been the first launch of SSME engine SN#-2037 and the failed valve but it had been thru 7 static firings during ground tests. The engine and valve were last tested at cryogenic temperatures during hot firing June 15, 1995 at Stennis Space Center in Mississippi. A failure of this nature has occured only once before during the STS-2 tanking test. That failure was due to metallic contamination in the downstream seal of the valve. The valve is accessable via the AFT engine compartment. It weighs about 75 pounds with a flow path of 2.5 inches. It will be replaced at the pad. The bad valve will be sent back to the Rocketdyne factory in California for testing.
The launch countdown had begun at 4am on Monday, September 25, 1995 and the crew arrived at the KSC Shuttle Landing Facility (SLF) at 8:20 a.m. (Reference KSC Shuttle Status 9/25/1995).
RTV backfilling for both solid rocket boosters of Space Shuttle Columbia was performed on 9/5/95. (Reference KSC Shuttle Status 9/05/1995). Earlier, on 8/8/95, engineering analysis indicated that the No. 2 main engine on Columbia was unacceptable for flight and was removed and replaced with an engine originally slated to fly on mission STS-74. (Reference KSC Shuttle Status 8/08/1995). The replacement engine does not have a block one liquid oxygen pump. (Reference KSC Shuttle Status 8/15/1995).
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