Dienstag, 30. Juni 2015 - 08:52 Uhr
Rockets are bombs, and after 60 years spaceflight remains a nascent, experimental enterprise
Space lies a mere 60 miles above the planet’s surface, so tantalizingly close.
Space shuttle Atlantis enters the Earth’s atmosphere. (Mike Fossum/NASA)
It shouldn’t be that hard to reach, right? After all, humans have sent rockets into space for nearly six decades.
Yet as American (SpaceX), Russian (Progress) and American-Russian (Orbital Sciences) industry have found out during the last eight months, with rocket and spacecraft failures, putting a vehicle into orbit around Earth remains no easy feat.
It calls to mind what O. Glenn Smith, a former space shuttle engineer, wrote about about the challenge of reaching orbit five years ago as the space shuttle program wound down.
Consider the following observations about launch vehicles:
Rockets are essentially big bombs. In a typical launch to orbit, only about 1 to 4 percent of total launch weight is payload and 10 to 15 percent structure and engines. The rest, 80 to 85 percent, is combustible fuel.
Extraordinary energy is required to break out of Earth’s gravity well. The space shuttle was roughly equivalent in size to a Boeing 737. The amount of energy it expended in eight minutes to reach orbit is comparable to that of a 737 traveling around the world, a 50-hour flight.
The failure of many components in a rocket lead to a catastrophe. When a belt breaks on your car, you get it towed. When a belt breaks on a rocket, it explodes. Examples of potential failures include stuck fuel valves, autopilot or navigation failures, stuck air vents, auxiliary power unit failures and engine fires.
The failure of an 38-foot O-ring in the Space Shuttle Challenger’s solid rocket booster caused a total loss in 1986. (NASA)
The expense of launching prohibits a full test flight program. All early launches of a new rocket system are by definition test flights and are relatively risky, and therefore all launchers stay in this flight test mode for their entire lives. The Falcon 9 had flown only 17 times prior to Sunday’s launch attempt.
Attaining aviation levels of safety is nearly impossible. Even if a commercial human launcher could attain a goal of 999 successes out of 1,000 attempts — an enviable safety record as yet unheard of — it is still a very risky endeavor, and 10,000 times as risky as a trip on a scheduled commercial airline.
Orbital spaceflight remains a nascent industry. Although NASA has been flying into space for more than half a century, the country has still has only performed about 500 or 600 crewed and uncrewed orbital flights. Think about how many accidents there were in the first 600 airplane flights.
The bottom line is that launch failures have occurred across both government and private space industry. It is almost a cliche to say “space is hard,” but the engineering challenge of getting a lot of mass off planet Earth is non-trivial. And although humans have been at it a long time, with only perhaps 1,000 or so global attempts to do so, the spaceflight industry remains a very experimental business indeed.
Bear that in mind when judging SpaceX and other private companies trying to do something very difficult, in different ways.