In May 1988 there was a series of huge explosions at Henderson, Nevada, on the edge of urban Las Vegas. The biggest had the force of a small nuclear device, (over 1kt — the Hiroshima bomb was 15kt) but it was all caused by an accident with ammonium perchlorate. This chemical is the oxidizer part of the fuel for the Space Shuttle solid-fuel boosters, and when the loss of the shuttle Challenger caused the shuttle programme to be suspended, a backlog stockpile began to grow at the factory.
When the company ran out of storage in the proper metal canisters, they began to fill plastic drums. That’s a curious choice for a rocket fuel company to make, given that a combination of polymer and oxidizer is one common design for solid rocket fuel. All you have to do is light it. In this case, a guy with a welding torch caused the fire, but luckily, it took time to spread to the stockpiles and most employees were able to escape to a safe distance. (There were two fatalities.)
There was a total of seven explosions during the accident. The two largest registered 3.0 and 3.5 on the Richter scale. The oxidizer factory and its neighbour, Kidd’s marshmallow factory, were both completely levelled.
I was indirectly reminded of this event, (known as the PEPCON disaster after the name of the company, the Pacific Engineering Production Company of Nevada), by the news of the successful first launch yesterday of the SpaceX Dragon spacecraft.
I hasten to emphasise “indirectly reminded”. Dragon was launched by the Falcon 9 rocket, which does not use solid fuel boosters. Its first stage has nine (count ’em) liquid-fuelled Merlin 1C engines. Liquid fuel is an inherently more complex design than solid fuel, which is exactly like a firework rocket, but arguably safer, because the two components of the fuel have to be pumped together into the combustion chamber rather than being permanently mixed. The Merlin rocket engine uses liquid oxygen and kerosene.
Dragon is the first commercial spacecraft to reach orbit, and after two orbits it was successfully brought back to Earth and parachuted into the sea off Mexico. SpaceX are developing it under a contract with NASA to develop technology for cargo flights to the International Space Station, but originally Dragon was conceived as a manned spacecraft, and has a pressurized cabin/cargo bay. According to the company, continued development towards a crewed configuration would be straightforward. Seven astronauts would be accommodated, but it’s space capsule style seating. You can’t get up and walk around.
Don’t go thinking that you’ll be able to get a commercial flight into space a year from now anyway, on the Virgin Galactic SpaceShipTwo, even if you have the $200,000 for a ticket. In spite of the name, SpaceShipTwo is really just a high-altitude aircraft. It is intended to reach a height of over 100km for a few minutes, officially “in space”, but it can never reach orbit.
SpaceShipTwo uses neither a solid-fuel nor liquid-fuel rocket motor, but a hybrid, the RocketMotorTwo, which burns a synthetic rubber with a liquid oxidizer, nitrous oxide (or laughing gas). (How quaint those mixed-case names will look in the future. The near future.) Hybrid engines have safety advantages over solid-fuel ones because, like a liquid-fuel design, the two parts of the fuel aren’t in contact except at the point of ignition.
The predecessor SpaceShipOne won the X-Prize for being the first commercial, reusable craft to top 100km, and although that was a superb accomplishment, it falls far short of what SpaceX achieved yesterday. While suborbital flight isn’t easy, it’s much, much easier than attaining orbit, and much, much easier to get back from. But future space flight will probably use a combination of the technologies being developed today.
People often compare the state of space flight today with some aspect or other of early aviation. It’s now just over a hundred years since the first manned powered flight, and fifty years since the first manned spaceflight. If the two activities were really parallel, then we’d be in the space equivalent of aviation of the 1950s, the first era of passenger jets and air travel for the masses. (Or at least, the affluent masses.)
Clearly, that’s not the case, and not likely to happen for decades at least. Maybe real progress will depend on technological breakthroughs as yet unforseen. But the flawless operation of Dragon yesterday was definitely a step in the right direction.
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