Derby and District Astronomical Society
The Journal of the Derby and District Astronomical Society
September - December 2005
STS-114/Discovery: Return To Flight
By Anthony R. Southwell
After a wait of about 2½ years and after numerous launch date slips, the Space Shuttle Discovery took off on STS-114, the Return to Flight mission on 26th July 2005. The flight was due to launch on 13th July, but the launch was scrubbed at T - three hours, due to erroneous readings from one of four fuel sensors in the External Tank (ET). These sensors tell the Shuttle’s onboard General Purpose Computers (GPCs) when the ET is getting low on fuel, at that point the GPCs automatically shut down the Shuttle main engines.
|The launch of STS-114/Discovery from Pad 39-B at the Kennedy Space Center, Florida at 10:39 am EST (15:39 BST) on 26th July 2005. Image Credit: NASA|
On the day of the of the first launch attempt, the fuel cells were tested and it was found that one of the sensors was giving a false reading. It was reading ‘dry’ when it should be reading ‘wet.’ In other words the sensor was convinced that the ET was empty or nearly empty, when in reality it was completely covered in super cold liquid hydrogen fuel. Mission rules stated that the Shuttle could not be launched if all four sensors were not in agreement. So, the launch was scrubbed and STS-114 was delayed for about a week, while NASA management and engineers worked to resolve the problem.
The problem proved to be more difficult to track down, let alone solve. It was determined that the sensor was suffering from an intermittent electrical failure, and that no physical cause for this an anomaly could be found. So with no clear resolution to this problem, NASA management decided to, against its own flight rules, launch Space Shuttle Discovery on the STS-114 mission on July 26th. As it turned out, the fuel sensor never again gave any sign of trouble and Discovery was able to launch.
The crew for this mission were:
Commander: Colonel (USAF Retired) Eileen M. Collins. Collins was the first woman to fly as Pilot and last as Commander on a Space Shuttle mission. STS-114/Discovery would be Collins' fourth spaceflight.
Pilot: Colonel (USAF) James M. Kelly. STS-114 was Kelly’s second spaceflight.
Mission Specialist 1: Soichi Noguchi of the Japanese Space Agency. Noguchi was making his first spaceflight.
Mission Specialist 2: Stephen K. Robinson. Robinson was making his third spaceflight.
Mission Specialist 3: Andrew S. W. Thomas. Thomas was making his fourth spaceflight.
Mission Specialist 4: Wendy B. Lawrence. STS-114 was Lawrence’s fourth spaceflight.
Mission Specialist 5: Charles J. Camarda. Camarda was making his first spaceflight.
|The STS-114 crew. From left Steve Robinson, Jim Kelly, Andy Thomas, Wendy Lawrence, Charlie Camarda, Eileen Collins and Soichi Noguchi. Image Credit: NASA|
The main objective of the STS-114/Discovery mission was not only to get the Shuttle flying again, but also to test the technology developed as a response to the 15 Return to Flight (RTF) recommendations that came out of the Columbia Accident Investigation Report (CAIB) of August 2003. Discovery was also to pay a visit to the International Space Station (ISS) to transfer some 15 tonnes of supplies via the Rafaello logistics module, which was housed in Discovery’s payload bay.
The launch itself was text book as far as it went, but it was not without incident. Shortly after liftoff, a bird struck the top of the ET. This was really not that much of a concern because the Shuttle was not traveling very fast at this point, so the bird strike did not cause any damage. One of 107 cameras that were to document Discovery’s ascent into orbit imaged the bird strike. At 66 seconds into the flight a small piece of Thermal Protection System (TPS) tile came away from an area near to the nose landing gear doors. This fragment of tile did not hit Discovery and a camera attached to the ET looking back at the Shuttle imaged it. Then at 2 minutes and 10 seconds, came an event that made my blood run cold, a large piece of foam detached from the ET and fell away, it did not strike Discovery, it fell between the right wing and the ET. The foam came off the PAL ramp on the ET and was comparable in size to the piece of foam which came off the bipod area on Columbia’s ET during its final mission. That was worrying, NASA had grounded the Shuttle fleet for two and a half years and spent a billion dollars on trying to implement the CAIB recommendations, but we still have foam coming off a different area of the ET! The imagery from the ET camera was live, but you did not see the PAL Ramp foam debris detach. That only came to light at a post-launch press briefing.
After Discovery entered orbit and the ET was jettisoned, Andy Thomas took a few images of it, he imaged the PAL Ramp damage, and also two divots in the foam very near the bipod area. With the revelation that the ET is still shedding foam, NASA took the decision to ground the Shuttle fleet once more until the foam shedding issue was resolved. This means that at the time of writing Atlantis will not launch on STS-121 until March 2006.
|Handheld still image taken by Discovery's crew of the external fuel tank as it was jettisoned after launch. A large piece of foam separated from the tank during the Shuttle's ascent to orbit from an area called the Protuberance Air Load (PAL) Ramp. The area of missing foam on the tank is indicated by a light spot near the upper edge of the tank just below the liquid oxygen feedline. Image Credit: NASA|
Flight Day 2 saw the use of the laser inspection boom attachment for the Shuttle’s robot arm, this was to be used to inspect Discovery in orbit to assess how well the TPS tiles had survived the launch, taking particular interest in the wing leading edge areas and the black TPS tiles on the Shuttle’s belly. The boom showed Discovery to be in pretty good shape, although there were one or two scuffs located near the nose landing gear doors.
Flight Day 3 saw Discovery dock with the ISS. Before Discovery docked, the crew performed a back flip and exposed the Shuttle’s underside so that the Expedition 11 crew of the ISS, Sergei Krikalev (Commander) and John Phillips (Flight Engineer) could photograph Discovery and locate any further damage, to which they discovered two pieces of gap filler were protruding from tiles on the underside of Discovery. A debate then ensued over whether the crew should remove these gap fillers before they returned to Earth.
Flight Day 4 saw another round of inspections of Discovery by the robot arm boom, also the Rafaello module was docked with the ISS prior to the transfer of supplies. Flight Day 5 saw the first of three spacewalks conducted by astronauts Robinson and Noguchi. On this EVA the astronauts would test out TPS tile repair methods on a range of deliberately damaged tiles. The method employed was a putty-like filler that is used to fill voids in a tile and the other was a black paint that is used to cover scratches on the surface of TPS tiles that are located on the underside of the Orbiter. Flight Day Six saw more cargo transfer activities.
|Shuttle Discovery as taken from aboard the International Space Station during rendezvous and docking operations. The Italian-built Raffaello Multi-Purpose Logistics Module (MPLM) is visible in the Shuttle’s cargo bay and a Soyuz spacecraft docked to the Station is at right. Image Credit: NASA|
Flight Day 7 saw the second EVA of the mission, Robinson and Noguchi went out and replaced a Control Moment Gyroscope (CMG) that is used to maintain the ISS’ attitude, without using thruster fuel. By Flight Day 8 the decision had been made to make a third EVA to remove the gap fillers from the underside of Discovery, the EVA would take place the following day. Flight Day 9, astronaut Robinson went out and ‘rode’ the Shuttle’s robot arm and successfully removed the protruding gap fillers. Due to the decision taken by NASA to ground the Shuttle fleet in the light of continuing foam loss from the ET, an extra day was added to Discovery’s stay at the ISS to transfer as much material as they could to the ISS. Flight Day 10 saw a commemoration ceremony for STS-107, STS-51L, Apollo 1, Soyuz 1 and Soyuz 11, with each member of the STS-114 and Expedition 11 crews reciting a short prepared piece.
Flight Day 11 saw the Rafaello module undocked form the ISS and returned to Discovery and the shuttle and ISS parted company on Flight Day 12. After a day’s delay due to bad weather at KSC, Discovery returned to a safe landing at Edwards Air Force Base, California on Flight Day 14 at 8:11am EDT (13:11pm BST) on August 9th.
|Shuttle Discovery glides in for a landing at Edwards Airforce Base in California at 05:11 Pacific Daylight Time on the 9th August 2005. Image Credit: NASA|