Henry Spencer
Henry Spencer
Henry Spenceris a Canadian computer programmer and space enthusiast. He wrote "regex", a widely used software library for regular expressions, and co-wrote C News, a Usenet server program. He also wrote The Ten Commandments for C Programmers. He is coauthor, with David Lawrence, of the book Managing Usenet. While working at the University of Toronto he ran the first active Usenet site outside the U.S., starting in 1981. His records from that period were eventually acquired by Google to provide...
NationalityCanadian
ProfessionScientist
CountryCanada
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Whether solid rockets are more or less likely to fail than liquid-fuel rockets is debatable. More serious, though, is that when they do fail, it's usually violent and spectacular.
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Past experience, on the shuttle and the Titan rockets, suggests that large multi-segment solid rockets have a probability of failure of 0.5 to 1 per cent.
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Supplying fuel for a Mars expedition from the lunar surface is often suggested, but it's hard to make it pay off - Moon bases are expensive, and just buying more rockets to launch fuel from Earth is relatively cheap.
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Large solid rockets have never been a very good way to build launchers that might have crews on top, especially because of the problems in getting the crew away from a failing launcher.
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Developing expendable rockets is always going to be painful and expensive. Throwing the whole rocket away on each attempt not only costs a lot, it also hampers figuring out just what went wrong because you don't get the rocket back for inspection.
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An experienced designer with more freedom to act might have realised that there was just too much optimism in the Ares I concept: that a shuttle SRB was simply too small as a first stage for a rocket carrying the relatively heavy Orion spacecraft.
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Solid-fuel rockets can't easily be shut down on command.
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Claiming that solid rockets are necessary for a heavy-lift launcher is obvious nonsense.
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Sometimes people wonder why aeroplanes are so cheap and rockets are so expensive. Even the most superficial comparison shows one obvious difference: aeroplane engines use outside air to burn their fuel, while rockets have to carry their own oxidisers along.
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The Orion capsule uses an escape system quite like that of the Apollo spacecraft in the 1960s and 70s: an 'escape tower' containing a solid-fuel rocket that will pull it up and away from Ares I in a pinch.
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Reusable rockets promise much easier testing because you should usually get them back, and you can debug as you go rather than having to get everything perfect the first time.
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The key virtue of orbital assembly is that it eliminates the tight connection between the size of the expedition and the size of the rockets used to launch it.
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On the technical side, Apollo 8 was mainly a test flight for the Saturn V and the Apollo spacecraft. The main spacecraft system that needed testing on a real lunar flight was the onboard navigation system.
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Sure, there were hopes that Constellation's systems could later be adapted to support more ambitious goals. But Apollo had those hopes, too. It didn't work in 1970, and it wasn't going to work in 2020.