Updated November 11, 2016
Remarks on the Recent Explosion of a Falcon 9 Rocket at Cape Canaveral
On September 1 a Falcon 9 rocket of the company Space X exploded on the launch pad during fueling for a static firing test. The spectacular explosion completely destroyed the rocket and its satellite payload, whose launch had been planned for September 4. This is the latest of a string of failures which have afflicted the ambitious efforts of SpaceX company to greatly reduce the costs of space missions, through development of new generations of launch vehicles. On June 28 last year a Falcon 9 exploded in flight as a result of a structural failure. Earlier that year, on February 11, a Falcon 9 first stage was destroyed in a failed attempt to land vertically on an ocean platform after completing its boost mission. The explosion on September 1 is a particularly hard blow to the plans to use Falcon 9 vehicles for launching manned missions into space.
Spectacular failures are of course not uncommon in the history of rocket technology, and the lessons learned from them have contributed much to improving the reliability of launch systems. Also, despite the recent failures, the Falcon 9 has carried out 28 successful unmanned missions, including the transport of supplies to the International Space Station as well as launching communication satellites into orbit. Nevertheless, the difficulties experienced by Space X provide a useful occasion to reflect upon the present state of space technology and of science and technology generally.
There is no reason to doubt that travel into space will one day become as normal and routine as passenger air travel today. Overall, human beings have already spent a total of more than 133 man-years in orbit. The Russian cosmonaut Gennady Padalka has spent a record total of 879 days – nearly two and a half years -- in orbit, including a mission on the Russian space station Mir in 1998, followed by four longer stays on the International Space Station in 2004, 2009, 2012 and 2015. Three cosmonauts have remained in orbit continuously for a year before returning to Earth. The problems of living and working for substantial periods in an orbiting station under weightless (or microgravity) have to a large extent been solved. The International Space Station (ISS) has been continuously manned since the year 2000. A total of 244 people have lived on the ISS. Many of them visited the space station twice or even more times. Up to now there have been over 80 flights carrying passengers from the Earth to the ISS. Since the retirement of the U.S. Space Shuttle in 2011, travel to and from the space station has been done exclusive with Russian Soyuz launchers and reentry vehicles, now operating almost with the regularity of a “space railroad”. There have been 94 unmanned missions delivering supplies and equipment to the station. SpaceX has already carried out 7 of these unmanned resupply missions with its Falcon 9 vehicle, and is striving to become a main transporter of passengers as well as cargo to the ISS in the future. That includes capturing an projected commercial market for “space tourism”. Already seven “space tourists” having spent time on the ISS, taken there by Russian Soyuz vehicles and paying $20-40 million for the exciting trip.
All of this could easily lead to the impression that human travel into Earth orbit has already become a routine affair. But in reality this is very far from being true. The critical issue for space travel today -- and the main reason why it is still very far from “routine” – is transport to and from orbit, which today still involves a combination of very high cost and significant risks to the passengers.
Both problems are connected above all with the extraordinary complexity of orbital launch vehicles and the fact that critical components of these systems must operate flawlessly under extreme, rapidly changing conditions -- often near the farthest limit of what can be technically mastered -- in terms of extremes of temperature, pressure, mechanical loads and stresses, vibration, aerodynamic effects etc. The design constraints are extremely severe, especially given the need to minimize the weight of the vehicle. There are many points in the system where a serious malfunction will lead to catastrophic results within seconds or fractions of a second, with little or no time for correction. Given that a manned orbital launch vehicle is launched with hundreds of tons of fuel and liquid oxygen on board, in close proximity to each other, it is not surprising that malfunctions tend to end in explosions. Naturally there tends to be an inverse relationship between cost and risk. Given all these factors, the progress of human space flight from Yuri Gagarin’s flight 55 years ago up to the International Space Station today, has been a very, very remarkable achievement. There has been a price in human lives, however. 546 human beings have been in orbit, but 18 people have died during transport to or from orbit. From a purely statistical point of view that would imply a probability of more than 3% for not surviving the trip. Would you decide to go?
Russia’s Soyuz orbital launch vehicles are doubtless the most reliable that have been developed so far, functioning presently as “workhorses” for manned space activity internationally. Their high reliability is connected with the very long experience in building and operating rockets based on essentially the same design -- going back to the Soviet ICBM development in the 1950s -- and the unparalleled number of launchings of launch vehicles developed as variations on that same basic design. The total of more than 1700 manned and unmanned missions includes over 870 launches of vehicles belonging to the official “Soyuz” family, including the ones that have transported all crew members to the ISS since 2010, plus a large part of the cargo supplies to the station. Since the first launching of a Soyuz vehicle in 1966 there have 22 failed missions, amounting to a success rate of about 97.4%. Only one failure occurred with a manned mission, when a Soyuz vehicle exploded during countdown in 1983. Fortunately, the crew survived, thanks to a rocket-powered launch escape system which dragged their capsule away from the launch vehicle just 2 seconds before it exploded.
Paradoxically, the high degree of reliability of the Soyuz launchers has much to do with the fact that there have been no major changes in its basic technology and robust design for more than 40 years. Reliability through technological stagnation? At the same time, without major innovations there is hardly any hope of substantially reducing the cost of orbital missions compared to the Soyuz or similar launch vehicles, which have been optimized in the course of long experience. But how can spaceflight become routine, if it requires a giant, 45 meter-long vehicle, and costs over $10 million per person, to transport half a dozen people into orbit?
This is what SpaceX is trying to change. An obvious strategy is to create launch vehicles that can be recovered and used again many times -- as opposed to the Soyuz and other so-called expendible, “throwaway” systems in which the entire hardware, including the engines and other extremely expensive components, is discarded during the ascent trajectory, burns up in the atmosphere or is destroyed by ground impact. Building reusable or all least partially reusable launch vehicles is an old idea, of course, but it has proved so far to be difficult and risky in practice. The most serious effort in this direction, prior to SpaceX’s development of the Falcon launchers, was the U.S. Space Shuttle. Much can be learned from the history of the Shuttle.
Like the Falcon 9 today, the Space Shuttle was created with the main goal of drastically reducing the cost of orbital missions compared with conventional rockets. It is important, as background, to keep in mind that following the first successful manned landing on the Moon in 1969, the budget of the U.S. space agency NASA began to be drastically reduced. (The last Apollo mission to the Moon was in 1972, and Man has still not returned!) By 1975 NASA’s budget was less than 50% of what it had been at the height of the Apollo program. NASA was under enormous pressure to cut costs. The hope was that this could be done by creating a launch vehicle which could return to Earth, landing like a glider, and be used again many times. Although the basic facts about the Shuttle are widely known, it is useful to briefly review some of them here.
For various reasons a compromise was made with respect to reusability. The Space Shuttle consisted of the so-called Orbiter, an external liquid fuel tank and two solid-fuel booster rockets. The winged Orbiter carried the crew, a cargo port and the powerful main engine. It was designed to reenter the atmosphere, glide to the Earth and land on a runway. The Orbiter was intended to be reused more than 50 times. The two solid-fuel booster rockets provided extra thrust for the lift-off and initial phase of the launch trajectory. After the solid fuel was used up, the boosters were jettisoned and returned to the ground by parachute, where they could be recovered and used again. The external fuel tank, which was needed to fuel the main engine up to the point when orbital parameters were achieved, was then jettisoned and burned up in the atmosphere. It was the major non-reusable component.
Today SpaceX is pursuing a similar strategy in a different way. The Falcon 9 is a two stage rocket, where the first stage – which makes up a large part of the launch cost of rocket-based launching systems – returns to Earth, landing vertically onto a platform. Both approaches pose enormous technical challenges, and also demand very careful maintenance of the rocket engines and other systems before they can be reliably re-used.
The Space Shuttle was a masterpiece of engineering. During the 30 years from 1981 to 2011 – when the Shuttle program was discontinued -- four Orbiters flew a total of 133 successful orbital missions. Unfortunately, there were also two major disasters: the explosion of the Shuttle “Challenger” 73 seconds after its launch on January 28, 1986, and the disintegration of the Shuttle “Columbia” during reentry to the Earth on February 1, 2003. In each case the entire crew was lost, resulting in 14 deaths.
Investigations of the background and causes of these disasters cast light on the dangers inherent in the use of rockets for space travel in general, while revealing the risks involved in attempting to minimize costs, and the fateful effects of errors and biases in the decision-making process at all levels of such a complex undertaking. In a deeper sense, the causes of the two accidents are inseparably connected with a fundamental weakness in the whole mode of economic growth which has prevailed in the United States and most other nations of the world since the 1970s.
It is particularly instructive, in this respect, to read the short document “Personal observations on the reliability of the Shuttle” written by the famous physicist Richard Feynman and presented on June 11, 1986, one day after the release of official Rogers Commission Report on the Challenger disaster. Although Feynman himself was a member of the Rogers Commission, he carried out his own investigation, including discussions with engineers and others involved directly in the design, launching, operation and maintenance of the shuttle. Feynman is sharply critical of the way the project was managed, and of the way the NASA management downplayed the risks in order to “sell” the Shuttle project to the government and public. Here I will quote from some particularly interesting passages of his 13-page report, which is well worth reading in its entirety. Feynman begins his discussion of the Challenger disaster with the following observation:
“It appears that there are enormous differences of opinion as to the probability of a failure with loss of vehicle and of human life. The estimates range from roughly 1 in 100 to 1 in 100,000. The higher figures come from the working engineers, and the very low figures from management. What are the causes and consequences of this lack of agreement?”
As is now well-known, the immediate cause of the Challenger explosion was a material failure in an elastic ring (“O-ring”) used to seal a joint on one of the two solid-fuel booster rockets which supplemented the thrust of the shuttle’s main engine in the initial phase of the flight. A stream of hot gas thereby escaped from the booster (so-called blow-by) and damaged the structure of the adjacent external fuel tank, leading to the breakup and explosion of the whole vehicle. There had long been a controversy about the risks involved in using of solid-fuel engines in manned flights, but the designers of the shuttle system had nevertheless decided to use them. Feynman wrote:
“An estimate of the reliability of solid rockets was made … by studying the experience of all previous rocket flights. Out of a total of nearly 2,900 flights, 121 failed (1 in 25). This includes, however, what may be called early errors, rockets flown for the first few times in which design errors are discovered and fixed. A more reasonable figure for the mature rockets might be 1 in 50. With special care in the selection of parts and in inspection, a figure of below 1 in 100 might be achieved, but 1 in 1,000 is probably not attainable with today's technology. Since there are two rockets on the Shuttle, these rocket failure rates must be doubled to get Shuttle failure rates from Solid Rocket Booster failure. NASA officials argue that the figure is much lower. They point out that these figures are for unmanned rockets but since the Shuttle is a manned vehicle ‘the probability of mission success is necessarily very close to 1.0 ’ “
Feynman asks: How could NASA be sure about such an estimate? “Previous NASA experience had shown, on occasion… near accidents, and accidents, all giving warning that the probability of flight failure was not so very small.” He goes on to discuss the specific fact that erosion in seals used to join parts of the shuttle had already been found in previous flights. “The acceptance and success of these flights is taken as evidence of safety. But erosion and blow-by are not what the design expected. They are warnings that something is wrong. The equipment is not operating as expected, and therefore there is a danger that it can operate with even wider deviations in this unexpected and not thoroughly understood way.”
Skipping over Feynman’s detailed discussion of the O-ring problem, I want to quote from the section in which he discusses the Shuttle main engine. This crucial component was not involved in the shuttle disasters, but his discussion points to the complexities of the system and the risks of trying to cut costs:
“The Shuttle Main Engine was designed and put together all at once with relatively little detailed preliminary study of the material and components. Then when troubles are found in the bearings, turbine blades, coolant pipes, etc., it is more expensive and difficult to discover the causes and make changes. For example, cracks have been found in the turbine blades of the high pressure oxygen turbopump. Are they caused by flaws in the material, the effect of the oxygen atmosphere on the properties of the material, the thermal stresses of startup or shutdown, the vibration and stresses of steady running, or mainly at some resonance at certain speeds, etc.? How long can we run from crack initiation to crack failure, and how does this depend on power level? Using the completed engine as a test bed to resolve such questions is extremely expensive. One does not wish to lose an entire engine in order to find out where and how failure occurs. Yet, an accurate knowledge of this information is essential to acquire a confidence in the engine reliability in use. Without detailed understanding, confidence can not be attained.
“The Space Shuttle Main Engine is a very remarkable machine. …. It is built at the edge of, or outside of, previous engineering experience. Therefore, as expected, many different kinds of flaws and difficulties have turned up. Because, unfortunately, it was built in the top‐down manner, they are difficult to find and fix. The design aim of a lifetime of 55 missions equivalent firings (27,000 seconds of operation, either in a mission of 500 seconds, or on a test stand) has not been obtained. The engine now requires very frequent maintenance and replacement of important parts, such as turbopumps, bearings, sheet metal housings, etc. The high‐pressure fuel turbopump had to be replaced every three or four mission equivalents (although that may have been fixed, now) and the high pressure oxygen turbopump every five or six. This is at most ten percent of the original specification. But our main concern here is the determination of reliability. In a total of about 250,000 seconds of operation, the engines have failed seriously perhaps 16 times.”
Feynman concludes his report with a now-famous remark:
“For a successful technology, reality must take precedence over public relations, for nature cannot be fooled.”
The experience with the Space Shuttle program and the difficulties of SpaceX today point to a fundamental issue in economics. Every basic technology has inherent limits. Beyond a certain point, attempting to increase its productivity further by gradual improvements and clever tricks – i.e. trying to “fool nature” – inevitably leads to diminishing returns and growing risks.
Fundamentally speaking, for example, all the launch vehicles used up to today for space travel are limited by two main realities: firstly, the “rocket equation” derived by Konstantin Tsiolkovsky in 1903, and secondly the use of chemical fuels, carried on the vehicle, as the source of energy for propulsion. In practice these two realities are reflected in the fact that in all the systems used up to now, the payload is only a small percentage of the total mass of the launch vehicle (including fuel) at the moment of launch. Falcon 9, for example, requires a starting mass of 550 tons in order to transport less than 22 tons into low Earth orbit (LEO). About 90% of the takeoff mass is fuel, so that a large percentage of the fuel and of the physical work performed by the engines is expended in order to lift and accelerate the mass of fuel which is consumed in the process of placing the payload into orbit. This puts enormous demands on the engine, whose performance is limited by the energy density and power density that can be reached using chemical reactions. The only practical way to “break out” of these limitations is to utilize a different principle than that of a rocket, and/or to utilize a different source of energy (e.g. nuclear reactions). That in turn requires a revolution in space technology.
Tsiolkovsky proposed one possibility already back in 1895: the so-called “space elevator”, which is based on a completely different principle than rocket-based transport. There are a number of other, very interesting possibilities for breaking free of the problems and limitations of chemical-rocket-based space transport. But realizing Tsiolkovsky’s idea or any of the other proposed alternatives will require revolutionary breakthroughs in science and technology.
Travel into space will surely become a normal and routine matter in the future, just as flying in airplanes today. Man is destined to colonize Mars and other regions of the solar system. But this will not be achieved by strategies focused primarily on cutting costs. Austerity policies lead to disasters. As I have discussed in my book on Physical Economy, we need instead a transition to what I call strongly nonlinear development: economic development “propelled” by an ongoing succession of fundamental discoveries and ensuing technological revolutions. We require this form of economic development not only for Man’s activity in space, but even more for the future of the human civilization on the Earth.