Restart after the Inferno

NASA resumes shuttle flights after the tragic accident of the space shuttle Colum-bia:Astronaut Ulrich Walter explains the background and safety measures – and he gives us reasons why human spaceflight is so important.

Slightly abridged version published in: Bild der Wissenschaft, issue June 2005

On February 1, 2003 at 3pm Central European Time something incredible happened: During the re-entry phase into the earth atmosphere, the shuttle Columbia broke and large parts of it burnt up. All seven astronauts on board lost their lives ... .

How could this happen? Had the NASA not learnt any lessons from the Challenger disaster in January 1986, where all astronauts lost their lives, too? The reason for the Challenger disaster during ascent was packing rings, which, as a result of the frosty night before, had lost their capacity to expand, had become brittle, and thus were no longer able to block the heat of the burning solid fuel rockets during the launch. This resulted in a jet of fire, which continued through the shell of a booster and led to the explosion of the liquid oxygen and hydrogen tank.
The reason of the Columbia disaster on February 1 however was a totally different one: During the ascent an insulation foam component of about 3/4 kg and with a diameter of about half a metre, became detached from the external tank with the liquid fuel, and crashed on the front edge of the left wing with about 800 km/h. This resulted in an impact hole of approximately the same size. Neither mission control nor the crew knew anything about it, and after their mission they started their return flight without any suspicions. Re-entry causes a lot of heat of up to 1,400°C, which severed the wing from the shuttle on the spot where the hole was, just like a flame cutter; the shuttle became uncontrollable, broke and burnt up.
The appointed Columbia Accident Investigation Board (CAIB) found out later that the di-saster had two more profound reasons: Wrong assessment of risks, caused by similar events without serious consequences of past missions, and a working culture, which admits these things. This indeed results in a sense of déjà-vu, just like the former NASA astronaut Sally Ride explained in view of the Challenger disaster. To avoid such a disaster in the future, NASA is working to solve the technical reason of the problem as well as to define a new organisation structure for a new safety culture.

Flight path of the foam component, which damaged the wing of the space shuttle Columbia during the disaster in 2003 (computer animation)

The New Rules

The first flight after the Columbia disaster is scheduled for May 15. What will be new? First of all, there is not going to be any replacement for the Columbia, as the three shuttles in charge of the supply flights to the ISS are the only ones NASA still has. Columbia had also been in charge of other tasks not related to the ISS, like repairs of the Hubble telescope. As of now, these non ISS tasks will have the lowest priority. That is one reason why Hubble will not be repaired in the future. Another reason for not having a follow-up shuttle is, that the shuttle is to be used only until 2010, afterwards it is to be replaced by a subsequent system. And until then it is not worth having a replacement for the Columbia. Instead, the funds are to be invested in the development of the new system.

The new NASA safety rules provide that for all future shuttle flights the ISS has to be available as a safe haven. Apart from that, a second, so-called LON shuttle (Launch on Need) has to be ready for lift-off within 40 days at the latest to be able to bring back a crew stranded on the ISS. Such a LON shuttle will be available for the first time for the next mission. The faulty shuttle would then be undocked from the ISS, and, just like the MIR station in the past, it would burn up by means of a targeted re-entry manoeuvre above an uninhabited part of the Pacific Ocean.
As Hubble circles the Earth at a totally different orbit level compared with the ISS, and there is no fuel available to change the orbit level – the shuttle was not dimensioned for these tasks –, it is no longer possible to fly to the Hubble telescope because of the risk that the ISS as a safe haven could not be reached. That is the other reason for the discontinuation of the NASA repair flights of the Hubble telescope.

Technical Innovations

Measures were taken to avoid similar disasters, also to avoid the occurrence of foam components in the future, as well as measures to detect and diminish damages, if any impacts occur, and measures to repair possible impacts. In concrete terms, this means: that the so-called bipod flange-mount and some other spots of the external tank have been newly designed and equipped with heaters, as the detachment of foam as a result of so-called cryo-pumping have occurred mainly in these spots. During cryo-pumping the nitrogen of the air becomes liquid at extremely cold spots such as the bipod, it then migrates into the pores of the insulation foam and blows it off by means of evaporation, when frictional heat occurs during the ascent through the atmosphere.
There will be an arm of 12 metres, the so-called Orbiter Boom Sensor System (OBSS), to inspect possible damages; it will be placed upon the 15 metres long Canada arm of the shuttle as an extension. Its tip is equipped with a laser installation for distance measures as well as a laser camera. It may also carry an astronaut during the inspection. It will be used to meticulously examine those parts of the shuttle critical to heat, the nose cap and the front edge of the wings The OBSS is to be verified on the first two flights, and will then be available for all further flights.
Four digital cameras will be installed on the external tank of the solid fuel rockets for damage inspection, and they will transmit the images immediately to the Earth; so the images will be available immediately, not only after the mission as it is the case with the hand cameras used today.
22 temperature sensors and 66 impact sensors have been integrated into the front edges of the wing to be able to also recognise possible damages by micro meteorites.

The new external tank on its way to the integration hall

Repairing the Tiles

Tiles can only be repaired with the support of the ISS. During the approximation stage, the ISS will first of all photograph and inspect the shuttle. Then the shuttle will be docked onto the ISS with its arm, and it will turn in a way that from the ISS there will be access to the tiles on the lower part. Astronauts, supported and guided by the arm of the ISS, will then be able to repair the tiles. A pink, silicon-based ablator material (to reduce the heat by means of evaporation instead of insulation of the material) is to be used for repairs. The problem here are the small blisters that might form in the vacuum of weightlessness, which might make the ablator heat-permeable at these spots.

Astronaut Carlos I. Noriega, on board the 0g aircraft KC-135, injecting material into a special glass bulge to study the sliding properties of the material in weightlessness.

This procedure can however not be used to repair the very sensitive mechanical RCC insulations (reinforced carbon-carbon) at the front edge of the wings. There are two possible procedures for this problem: holes of up to 15 cm are to be closed by a heat-resistant cover plate. For smaller cracks, a kind of spatula is to be used. A metallic protective coating to avoid also larger holes in case of an impact during the launch was discarded not long ago. Only the spatula method will be available for the next flight. This means that at the moment it would not be possible to repair a damage the size of the damage of the Columbia disaster, and the shuttle would have to be abandoned as described above. NASA is investigating and working to find a solution for these cases.
These solutions are however only interim solutions. A fully redesigned and far safer thermal protection system, which may also be repaired in space, will be available in two years at the earliest. NASA is working on such a system, of course also in the framework of the subsequent system.
If the shuttle had to return to the Earth with an insulation beyond repair, according to NASA the heat load could be reduced by releasing the payload, by changing the entry trajectory or by modifying the angle of attack. Personally I think the two latter possibilities can only be used to a limited extent, as the present entry path has already been optimised with regard to heat.

NASA established an independent group to critically and independently supervise the innovations, the so-called Return to Flight Task Group, headed by two former astronauts, Kathryn C. Thornton, and Thomas Stafford.

The New NASA Culture

But NASA's largest task still lies ahead: The CAIB had asked them to introduce new corporate structures and a new corporate culture to guarantee the safety of space travel and to increase the safety awareness of the staff. The first step may have been to contract Behavioral Science Technology Inc. to compile and change the behaviour of the NASA staff. But just to have a nice and colourful image, which is the result today and which is supposed to show the future aware-ness, does not really change a corporate culture. It has to be alive and perceived for decades. This is quite a large challenge, as the experience from the 17 years between the Challenger and the Columbia disaster shows that routines develop very fast and easily lead to overlooking real dangers.

Preliminary plan of Behavioral Science Technology Inc. with regard to the new NASA culture

People often ask me whether as an astronaut you are not afraid to enter the shuttle as it is so risky. I think the answer David Brown, one of the astronauts killed in the Columbia disaster, gave to his brother Douglas Brown on Christmas 2003, just two months before the flight, when he asked him what he should say to the public in case he were killed, is quite symptomatic for all astronauts: "I accepted the risk when I took on the job, just as I did when I became a Navy pilot." Every astronaut, and that includes me, thinks about the possibility of a deadly end of the mission before the selection, and when he / she starts the training, he / she assumes a calculated risk. But it is a conscious and convinced decision, everybody has the freedom to decide for him- / herself. The decision is supported by a special, bizarre logic sometimes difficult to understand for non-technicians: Every problem that has been solved makes the shuttle safer. With its flight on 15 May the shuttle will be safer than ever. I flew in the shuttle in 1993, so why would I say no if they asked me today? I am convinced that not only I but also all my colleagues would fly again without thinking twice.

Do We Need Astronauts?

But will we need astronauts risking their lives during these missions? Do we really need human spaceflight? In Germany you hear that question very often, usually what people want to say is that it is very expensive and that these things could actually also be done with robotic missions. "High costs" is a favourite argument of those people who are generally against human spaceflight, and thus thoughtlessly put it forward. Whenever you ask these people how expensive such a manned mission actually is, and how much money could be saved by an unmanned mission, they usually just shrug their shoulders. Just let me give you two examples where this would be possible, as there are hardly any manned and unmanned missions that are really comparable. One example is the D2 mission where I participated. It was the second German science mission in the science laboratory Spacelab on the Columbia. The overall costs for the experiment payload of 6.3 tons, which corresponds to 88 experiments, was 442 million euros. Can Germany actually afford such a mission? Well, let's calculate a little bit: The Germans had the lion's share with 330 million euros, the US, Japan and other European countries also paid for their own experiments. The German costs were distributed over six years of preparation time, and for the 80 million German citizens this meant 70 cents/year/citizen. So, that answers the question of whether we can afford it.

Now we want to weigh up manned and unmanned space travel. It is quite interesting that at that time there was a parallel development in the field of weightlessness research, which is hardly known: Eureka. Eureka was a freely floating, unmanned, reusable platform, which was used to carry out fully automated experiments. Eureka flew from August 1992 until June 1993, just at the same time when my mission flew, it had an overall experiment payload of 4.4 tons on board consisting of 15 experiments. Overall costs: 412 million euros. The costs per experiment were more than five times higher than the costs of a comparable manned mission. No wonder that Eureka was never used again, as it could not compete against the far more economical manned alternative.

Hubble is another example. Until know there have been four successful repair missions with the shuttle. If you exclude the expensive Hubble devices, which had to be installed, every mission cost about 1.5 billion dollars. As with a pending Hubble repair mission in an emergency case the shuttle would not be able to reach the space station as a safe haven, and as the successor James Webb telescope is almost ready, NASA decided not to repair Hubble. Over the years, Hubble has developed into a national icon, so there were numerous protests, especially among scientists. But why do we need a manned repair mission, as an unmanned mission would be just as good and even less expensive? NASA summoned a commission of the National Academy of Sciences, which is also called Lanzerotti panel after its chairman Lanzerotti. The first smoke signals came up at the end of last year, when the panel's interim report stated: "The Hubble telescope is too valuable to expose it to the risks of an unmanned mission." Instead they called upon the then NASA administrator O’Keefe to keep open a slot for a manned shuttle mission in order to fulfill this job. Should the risk of a Hubble all of a sudden be more important than the risk of the astronauts? What was the reason for this swing of opinion of the scientists, which are normally rather against human spaceflight? Just a few weeks had been enough to realise that robotic missions are far riskier with regard to their success compared with manned missions. And apart from that, more often than not they are more expensive than people thought. The costs for a Hubble robotic mission are about 1.3 billion dollars, and according to NASA this is a conservative estimate; an independent estimate of the private space development and consulting company Aerospace Cooperation headquartered in El Segundo, California considered the price tag to be rather 2 billion dollars. Why is it so expensive? The problem is flexibility and redundancy. Technology can go wrong or fail. If you have to make plans for a second solution for every imaginable case, these additional costs for redundancy solutions may quickly rise above those for providing an environment for astronauts. And even with a very generous redundancy factor you can never be sure that you have taken into consideration all emergencies, and that everything will go smoothly. Aerospace Coop. correspondingly calculated the success rate to a mere 58%. That is not really flattering compared with the up to now four successful manned repair missions. The flexibility of a person is simply unbeatable in a very complex working environment. This is why today and certainly also in the near future there won't be any robots in a garage repairing cars.

Do we really need human spaceflight? To be honest I have never really understood the meaning of this question. If you have a manned and alternatively an unmanned solution for a pending mission, then we should just choose the less expensive one, as we do on the Earth as well .... if we have the alternative. If flexibility and intelligence on the spot are required, there is usually no getting around the human being. Apart from the Hubble repair, this is especially true for scientific experiments. The so-called principle investigator, i.e. the one who proposes an experiment, does not know the result of the experiment, otherwise he would not propose it. As the result is not known, during the experiment it is often necessary to interact with an experimenter, who may intervene if something unexpected occurs, and who is able to change the experiment again and again until the unexpected result has been brought out perfectly. This kind of optimisation during an experiment is the skill of an experimenter, and this is why even on the Earth there will never be a laboratory without people. So why should this make sense in outer space? Neither on the Earth nor in outer space fully automated laboratories have become accepted (see Eureka), and, as long as research will be done in weightlessness, there will also always be facilities such as the ISS.
And we should not forget those manned missions, where it is not important if robotic alternatives exist or not, as the target is simply that human beings are present: The first human in outer space (Gargarin), the first spacewalk (Leonov), the first human on the moon (Armstrong), the first human on the Mars (...). I think you will agree that these missions are not absolutely necessary, just like the opera, pop concerts, football championships or Formula One races, or any cultural event. They don't have a real benefit. And still this is where billions of taxes go to. By the way, we invest more taxes in German opera houses than in German spaceflight. I think the money is well invested as you cannot evaluate what humans do and need just according to utilitarian principles. Sport, culture, and science, including spaceflight culture and science, are human accomplishments, which form the quality of life of our society. It satisfies the original questions of mankind with regard to themselves and their position in this world. It just makes a big difference whether a planet is explored with telescopes, with robots, or finally by humans. Humans are interested in humans. Every tennis game, every Formula One race, even pop and piano concerts would not be that important to us if they did not have their stars. And quite apart from scientific research results, the day when the first human will step on another planet, Mars, will be a day of great international interest. And at that moment, nobody will want to know if the cost-benefit relation was adequate for this step. The nation that will make such a thing possible, will again be the nation that has been using this transutilitarian benefit very consciously to demonstrate its political weight and technical know-how. The world will watch in front of the TV and in the Internet, and everybody will say: Yes, they are the greatest nation. Once again, they will be the greatest, because they realised that only the future and its technologies will be able to solve our problems, not the past we are so proud of. So once again, the young people will be on their side, and because of these fascinating demonstrations they will always know the name of their space agency, but they will never know the name of the German space agency. This grand nation will seduce the graduating students, the doctoral students, and postdocs also in the future, making their and its dream come true, and they know that they can only make them come true in that country. Which brings us again into the spiral of success.

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ULRICH WALTER is professor of astronautics at the Technische Universität München. In 1993 he was an astronaut of the mission STS-55 (D2) on board the space shuttle Columbia.