An article reviewing the circumstances that led to the accident of the space shuttle "Columbia" which was lost during its return to the atmosphere with seven crew members on board including the first Israeli astronaut. Courtesy of the author, Asaf Brewald from the Israeli Astronomical Society and the Astronomy Forum in Nene
Assaf Brewald, Israel Astronomical Society
The following article is mainly based on information from the report of the commission of inquiry that investigated the Columbia accident. The report is available to the public and can be downloaded from the website: http://www.caib.us/
All the images appearing in the article originate from the report of the Commission of Inquiry (NASA)
introductionThe space shuttle Columbia - designated OV-102 - was the first in the space shuttle fleet of the American space agency NASA and took off for its maiden flight on April 12, 1981.
Back in June 1997, NASA received recommendations to use several shuttle flights for research in the field of life sciences and microgravity. In March 1998, the director of the space agency at the time, Daniel Goldin, announced that mission STS-107 would be dedicated to research purposes and announced that in principle the mission was planned for launch in May 2000.
Finally, the launch date was set as January 11, 2001. From this stage, the launch date was postponed no less than 13 times. Some of the reasons were administrative and some were technical. The administrative reasons include the changes in priorities for NASA missions (missions to the International Space Station, for example) and changes in planning the preparation of the shuttle's trunk, which includes the experimental laboratory. Some of the technical reasons that led to the postponement of the launch date were an unplanned extension of the duration of the periodic treatments the ferry underwent as well as grounding of the ferry fleet for 4 months following the discovery of cracks in the fuel piping of the ferries - cracks that required repair.
The STS-107 mission included a wide variety of scientific experiments designed to be performed aboard the shuttle during flight. These experiments included, among others, MEIDEX - (Mediterranean Israeli Dust Experiment) - an experiment whose purpose is to observe dust in the atmosphere in the Middle East region - as well as the "Chemical Garden" experiment, in the preparation of which middle school students from the Ort Kiryat-Mutzkin school participated, and which was designed to examine the development of Crystals in zero-gravity conditions.
As part of the Israeli-American cooperation, it was decided that an Israeli astronaut would take part in the flight for the first time. The chosen candidate was Ilan Ramon: a lieutenant colonel in the Israeli Air Force and a degree in computer and electronics engineering at Tel Aviv University.
The shuttle that was chosen to carry these experiments on board was the Columbia since this shuttle is limited to carrying relatively light cargo (compared to the other shuttles in the fleet) and is therefore not "busy" with the assembly tasks of the International Space Station which was in progress at the time the mission was planned.
The flight took off on January 16, 2003 and lasted 16 days. Once the scientific experiments planned for the course of the mission were completed, the shuttle began entering the Earth's atmosphere on its way to landing at the Kennedy Space Center in Florida.
During the entry into the atmosphere, huge forces are exerted on the shuttles and it is exposed to very high temperatures as a result of the entry into more and more compressed layers of air at high speed. The shuttle's heat protection system is designed to protect the shuttle from the enormous heat generated at this stage. However, when Columbia entered the atmosphere, something went wrong: within a few minutes, several alerts were received from various sensors in the area of the shuttle's left wing, which provided unusual experiences. Shortly thereafter, contact with the shuttle was lost and at the same time reports began to be received from eyewitnesses who observed what appeared to be fragments disintegrating and moving away from the shuttle entering the atmosphere.
In a short time, the difficult picture became clear: while the shuttle was over the state of Texas at an altitude of about 70 km and at a speed of about 20 thousand km/h, it disintegrated and its remains were scattered over a large area of several states in the USA. The seven Columbia crew members on mission STS-107 perished.
Rick Husband, 45, mission commander.
William McCall, 40, pilot.
David Brown, 46, mission specialist.
Laurel Clark, 41, mission specialist.
Kalpana Chawla, 41, mission specialist.
Michael Anderson, 42, mission specialist and cargo handler.
Ilan Ramon, 47 years old, cargo expert.
All the space shuttles were grounded following the accident. A special investigative committee appointed to investigate the circumstances of the disaster found a series of technical and administrative deficiencies in the space shuttle project and submitted recommendations to improve and streamline the American manned space program. As of writing these lines, the ferries have not yet returned to flight. The next ferry flight is scheduled for May this year.
what went wrong?
After many delays in the launch, the shuttle's engines were finally ignited on January 16, 2003, at 17:39 (Israel time). This mission was the 28th flight of Columbia and the 113th flight in the overall count of American space shuttle missions.
The launch course of each space shuttle is documented using a wide variety of cameras and tracking devices. The collected data is not, for the most part, checked in real time but is collected for the purpose of building a database for analysis and making future improvements to the ferries.
Some of the surveillance cameras near the launch site picked up, at about the 82nd second after launch, the detachment of at least two pieces of insulation foam from the external fuel tank. The insulating material is designed to isolate the air surrounding the external fuel tank and its contents: liquid hydrogen and liquid oxygen at extremely low temperatures.
Apparently, imperfect adhesion of the insulation foam to the fuel tank left air bubbles between the tank wall and the insulation layer. The pressure changes as well as the loads applied during the launch resulted in the "falling out" of one small and one larger piece of the insulation. Similar events of disintegrating pieces of foam from the external fuel tank have been documented on at least six different occasions during previous space shuttle launches but never caused serious damage to the shuttle.
The piece of insulation foam that came off during the STS-107 launch was about half a meter in size - larger than any piece that came loose on previous launches - and came off from the area where the nose of the shuttle connects to the external fuel tank via two struts.
At the time when the piece of insulation broke off, the shuttle was at an altitude of about 22 kilometers and at a speed of about 2,500 km/h. The low mass of the piece of foam relative to its size caused it to suddenly slow down and be swept to the left by the fast air flow around the shuttle. The shuttle itself hit the piece of foam at a relative speed of about 800 km/h when the point of impact was critical: in the front area of the shuttle's left wing root.
The piece of foam disintegrated upon impact and the shuttle continued its flight and entered, as planned, the orbit around the Earth. A day after the launch, during the examination of the data received from the surveillance cameras, the damage was detected.
Inaccurate assessmentThe data that was available to the control teams when they were trying to assess the severity of the damage was quite meager. The nature of the impact and its severity depend greatly on the speed of the impact, the mass and shape of the piece of foam that broke off, as well as the exact location and angle of the impact. That data was not available in the days before the shuttle's expected reentry into the atmosphere on Feb. 1, when its science missions end.
The general assessment during the next two weeks of the mission was that the damage caused during the launch of the shuttle is not critical and does not pose a safety hazard to the continuation of the flight. In retrospect, it turns out that the damage to the insulation foam was more severe than what was initially estimated.
The impact area is one of the centers where the heat load is the most extreme during the shuttle's reentry into the atmosphere. In this area of the shuttle wing, tiles made of carbon compounds are installed (tiles called "RCC-Reinforced Carbon-Carbon tiles). These tiles reach temperatures of about 1,600 degrees Celsius during entry into the atmosphere. The purpose of the tiles is to insulate the hot gases surrounding the shuttle during entry into the atmosphere and the aluminum structure of the shuttle's body.
The piece of insulating foam severely damaged the number 8 RCC tile on the shuttle's left wing. The impact created a hole about 40 cm wide in the lower part of tile 8-left and also created cracks in the gasket that closes the gap between tiles 8 and 9 as well as in tile 9.
The investigative committee that looked into the circumstances of the accident initiated a series of experiments to test the durability of the damaged tiles in the event of an impact with insulating foam. The goal was to prove that serious damage could indeed be caused as a result of such an event.
To carry out the experiments, a part of a shuttle wing corresponding to the one that was damaged in the last flight of Columbia was used. To reproduce as accurately as possible the state of the tiles that were installed in Columbia, parallel tiles were used that were disassembled from the space shuttle Discovery's wing after about 28 flights.
The tiles were installed on a test structure that included a complex array of sensors. The "wing" was used as a target for a gas cannon that fired "bullets" of insulation foam - the same material that was used in the fuel tank of the Columbia - at high speeds and at different angles against the "wing". High-speed cameras combined with data received from the various sensors in the "wing" provided a detailed situational picture of the resistance of the Columbia wing against a foam impact in the layout that probably occurred during the launch on January 16, 2003.
As mentioned, the estimates regarding the damage during the days between the first diagnosis of the foam impact on the wing and the planned landing date were based on models only and not on accurate observations. NASA engineers, as well as the shuttle crew, did not have the opportunity to directly observe the damaged area and assess the severity of the damage.
On several occasions, various inspection teams requested to arrange for photographs of the shuttle to be obtained by means of a spy satellite in order to obtain more information about the damage caused to the tiles. The most serious assessments regarding the possibility of damage spoke of "local damage" to the shuttle's wing. Damage that will require repair after landing but does not pose a safety risk to the ferry and its crew.
Failures in the way different inspection teams communicated with each other as well as in their communication with the management of the shuttle program meant that such requests never reached their destination (the Department of Defense responsible for operating American spy satellites). The test teams had to base themselves on a mathematical model used to calculate and evaluate collision damage with "space-debris" as well as with micro-meteoroids of very small mass and dimensions. This model was initially not designed to assess damage that would result from a large piece of insulating material being hit during launch.
On the second day of the STS-107 flight, a radar of the US Air Force detected some object that detached from the shuttle (while in orbit) and slowly moved away from it. The object continued to appear on the radar screen for two days until it disappeared and probably burned up in the atmosphere. This observation was not known to the Columbia flight control team and its existence was only learned in a later examination of the data during the accident investigation. The hypothesis is that the object that moved away from the shuttle was a fragment of tile 8 which was damaged during the launch and was probably thrown into the wing structure of the shuttle. The same fragment apparently floated out of the wing on the second day of the flight and was then detected by the radar. The continuation of the mission was carried out without special events.
The last day of the flight
On February 1st, shortly after 15:15, shuttle pilot William McCall activated the shuttle's maneuvering engines to slow its movement and begin its descent into the atmosphere. The engines were started when the ferry was over the Indian Ocean and, as mentioned, was moving east towards landing in Florida.
About half an hour later, at 15:44:09, the shuttle descended to an altitude of 400,000 feet (about 130 km). This time is defined as the beginning of the "Entry-Interface" because at about this point the shuttle begins to be affected by the upper layers of the atmosphere. At this point the air around the shuttle begins to heat up and light up while surrounding the shuttle with a bright glow. The air temperature rises, at several critical points, to 1,600 degrees. These points include the bow of the shuttle and the leading edges of the shuttle's wings - including the area of tiles 8 and 9 which were damaged in the launch.
At 15:49:32 the shuttle began rolling to the right. This maneuver is part of a series of pre-planned rolls that the shuttle performs to lose additional speed while maintaining a uniform rate of descent which prevents it from overheating.
At 15:50:53 the shuttle passed below an altitude of 243,000 feet and entered a period of about 10 minutes in which the forces exerted on the shuttle are the strongest during descent.
At 15:53:56 the ferry passed over the coastline of the state of California.
The hot plasma surrounding the shuttle is largely isolated from the shuttle's aluminum body by the insulating tiles that surround it. However, through the hole in tile number 8-left, a hot stream of gas manages to penetrate and reach the structure of the left wing of the shuttle.
Starting at 15:52:17, the mission control center in Houston, Texas receives telemetry data from the shuttle indicating abnormal readings of various indicators in the area of the shuttle's left wing.
The first reading that was diagnosed was a "fall" of a temperature sensor installed on the side of the shuttle's left passenger compartment (close to the connection between the shuttle's wing and the shuttle's body).
In the next picture you can see the wing chassis and the location of the left passenger seat.
42 seconds later, another "fall" indication is received, this time from a sensor in the balancer area on the left wing (balancer - an aerodynamic steering surface used to steer the shuttle while gliding through the atmosphere before landing).
During the next few minutes, similar data are received from several additional sensors. In the control center, the project engineers try to assess the reasons for the abnormal and unexplained readings. In retrospect, it will turn out that the hot plasma stream that ate its way inside the wing of the shuttle damaged the wiring of the sensors in the wing and disconnected them.
A data recording system known as the Modular Auxiliary Data System Recorder was also discovered among the remains of the shuttle. This system records data from a large number of sensors installed on the shuttle for later analysis. Most of this data is not transmitted in real time as part of the shuttle's telemetry transmissions, so locating the system and extracting the information stored in it was essential to understanding the latest events on the last Columbia flight.
According to the data received from this system, the shuttle's flight control computer detected a higher than normal aerodynamic drag that diverted the shuttle from its planned glide path. The excess drag was created as a result of the worsening damage to the aerodynamic structure of the left wing. The flight control computer automatically activated the shuttle's rudder flaps to maintain the pre-planned glide path.
Meanwhile, eyewitnesses watching the shuttle enter the atmosphere began to notice points of light moving away from the shuttle. These points were created by fragments that broke off from the wing of the shuttle.
At 15:59:15, the control center contact in Houston reported to the crew on board the shuttle about the abnormal sensor readings received at the control center. The response received 17 seconds later was from Mission Commander Rick Husband "Roger..." and cut off. It was the last voice transmission received from the shuttle Columbia.
At about the same time (according to the data from the data recording system on the shuttle) the computer diagnosed an abnormal load that roughly affected the shuttle's sailing direction. A correction that the computer fed into the shuttle's steering flaps failed to maintain the gliding direction and as a result the flight control computer also activated the shuttle's steering rockets in a desperate attempt to stabilize it on its course. Seconds later, the main warning light in the shuttle's crew compartment was activated. The direct reason for the activation of the alarm was never known, but apparently the flight control computer was no longer able to maintain the proper gliding direction of the shuttle.
Films taken both by amateurs, as well as film obtained from a cannon camera on an American Apache helicopter that was on a training flight in Texas, showed the shuttle disintegrating 18 seconds after 4:XNUMX p.m., Israel time.
At the stage when the shuttle was destroyed, the control center in Houston still did not have the evidence of the shuttle's disintegration. At the center, they engaged in repeated attempts to renew contact with the shuttle and to re-locate it using the radar after it disappeared from the tracking screen. At the same time, the evaluations continued regarding the nature of the readings received by the sensors on the shuttle in the last minutes before contact with it was lost.
It wasn't until around 16:16 PM - the time when the ferry was scheduled to land in Florida - that an emergency plan was activated at the control center in Houston after it was realized that the ferry was lost.
The pre-prepared emergency plan includes the closing of the control center for the purpose of secure storage of all the data contained therein to enable a thorough investigation of the circumstances of the accident. At the same time, calls were received at the center, initially on cell phones, telling of television broadcasts showing what appeared to be the disintegration of the shuttle and the sooty remains that were discovered throughout several states in the USA.
In a short time, a very extensive operation was launched to collect the remains of Colombia. US President George Bush declared the state of Texas - in whose territory most of the remains of the ferry fell - as a national disaster area.
At the same time as searching for remains to assist in the investigation, NASA made sure to warn the general public to avoid contact with shuttle remains. The space shuttle carries on board highly toxic substances such as hyperbolic fuels, coolants and explosives used in various pyrotechnic installations. Such parts might have survived the disintegration of the shuttle, reached the ground and landed in populated areas, so it was necessary to neutralize them by skilled professionals. At the same time, various emergency authorities were activated to prepare for the possibility of contamination of food, water or air sources by dangerous substances from the ferry.
More than 25,000 people - most of them volunteers - participated in the extensive search operation, searching for the remains of a foot. 37 helicopters and 7 planes also participated in the search.
At the end of the operation, approximately 84,000 remains of the shuttle were located, which accounted for approximately 38% of the shuttle's mass.
The investigative committee that looked into the circumstances of the disaster, CAIB - Columbia Accident Investigation Board, made a series of serious findings of poor conduct by the American space agency in general, and of the space shuttle program during the 16 days of the last flight in particular. The committee counted no less than eight different opportunities to obtain useful information regarding the damage caused to the shuttle wing - eight opportunities that were missed due to poor communication between the various inspection teams and the management teams of the shuttle program. Messages that were passed between the various teams - and which in retrospect turned out to be critical - were passed informally, thereby preventing the possibility of a thorough and essential assessment for a useful decision-making process regarding the treatment of the problem.
Could they have been saved?
During the sixteen days of the mission no solid information was received regarding dangerous damage to the shuttle's thermal protection system. If there was such information, could anything be done?
The investigative committee suggested that if there was indeed such information, two possible courses of action could be indicated.
1) Repairing the damage by the astronauts.
This way of doing it talked about carrying out an extra-vehicular activity (EVA-Extra Vehicular Activity) to accurately check the nature of the damage to the heat shield and then to install an improvised patch to plug the hole that was created. That patch might have been made up of various metal parts that are in the shuttle's crew compartment and that will be held in place using bags and cases filled with water that will freeze at the low temperature in space and become solid enough to protect the damaged wing structure.
The patch was not expected to hold up ideally but might – perhaps – allow the shuttle to enter the atmosphere using an entry profile that would reduce the strain on its damaged left wing. In this way, it is possible that the shuttle would have been able to slow down and reach a low altitude that would allow the abandonment of its crew through the escape system and fall safely to the ground.
However, many factors may hinder the success of this operation. The dimensions of the hole, its exact location, as well as the possibility that the same patch will not, after all, last - all of these made the possibility of repair having a very high risk factor and relatively low chances of success.
2) Launching a rescue shuttle
The preferred course of action would have been to use the space shuttle Atlantis to rescue the crew of the Columbia.
Aboard the Columbia were the seven crewmen who might survive for a full month (that is, an additional two weeks after February 1). Beyond this time the oxygen in the shuttle was running out and so was the lithium hydroxide. This material is used to remove carbon dioxide (the gas emitted when crew members breathe) from the shuttle's crew compartment.
The space shuttle Atlantis was scheduled for launch in early March and was in advanced stages of preparation. With the declaration of a state of emergency, preparations for the launch could be completed on February 10 - five days before the time left for the Columbia crew.
Atlantis would take off with four crew members on board: a commander, a pilot and two astronauts trained for extravehicular activity. Atlantis would dock with Columbia and approach within a few meters of it when the two "rescue" astronauts would transfer the Columbia crew members to Atlantis.
Prior to Columbia's abandonment, its crew members would activate an automatic sequence of operations that would return the shuttle to burn in the atmosphere above the Pacific Ocean or, alternatively, raise it to a higher orbit where it would await a future repair flight.
This script is also problematic. The preparation of Atlantis required a round of preparation-for a very quick launch and free of any malfunctions and delays both for the shuttle and therefore for the launch. Let's also not forget that the space shuttles are very similar to each other. The failure that caused the initial damage in Columbia could have been repeated during the launch of Atlantis.
Some of the recommendations of the commission of inquiry into the accident discuss adding the possibility of in-orbit repair of a space shuttle that suffered damage to its heat shield. Such a repair capability may exist by docking with the International Space Station (an operation that Columbia could not perform due to the differences in its orbits and the station's and the lack of sufficient fuel to perform such a drastic orbit change) or by kits that will be on board each shuttle and allow its crew to examine and repair such damages Without connecting to the space station or in the event that the shuttle cannot connect to the space station as a result of some malfunction or if the damage was discovered only after the shuttle had already left the station.
As of today, the space shuttle is the only means that allows the launch of heavy cargo together with crew members to the coffee route around Kadu. There is no doubt that the loss of the Columbia, and the conclusions and recommendations of the commission of inquiry established as a result will accelerate the moves to switch to other means of launch. As of this writing, the next shuttle flight is scheduled for May 2005. All upcoming flights will probably be essential flights for work on the International Space Station.
It must be remembered that in our current era, the development of a new means of space transportation is an extremely expensive task that will be difficult to implement in the near future. The days are no longer the days of the Cold War and the days of the space race when it was easy for the space agencies to obtain budgets for the development of projects on a scale like that of the space shuttle.
