Progress requires setbacks; the only sure way to avoid failure is not to try.
Henry Spencer
Sometimes a malfunctioning test setup actually gives the tested system a chance to show what it can do in an unrehearsed emergency. During a test of an Apollo escape system in the 1960s, the escape system successfully got the capsule clear of a malfunctioning test rocket.
Rocket engines generally are simpler than jet engines, not more complicated.
Liquid oxygen is one of the cheapest manufactured substances on Earth. In large quantities, it costs pennies per kilogram - cheaper than milk or beer.
SpaceX does seem to have had a run of bad luck, with its first three launches all failing.
Is manned space exploration important? Yes - not least because it simply works much better than sending robots.
In the long run, it's impossible to make progress without sometimes having setbacks, although people who get lucky on their first attempt sometimes forget this.
Technically and financially, it might still make sense to give up on Ares I and simply write off the money spent on it, but politically, that's probably impossible.
Testing a parachute drop of a heavy object is not simple.
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.
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.
Spaceflight, especially in the Mercury spacecraft, clearly wasn't going to be much like flying an airplane.
The Apollo programme of the 1960s had some weight problems, too; in particular, the lunar lander needed some fairly drastic weight-reduction work.
In the first few years, it was at least plausible to come in in the morning and read all the Usenet traffic that had come in, and 15 minutes later be off doing something useful.
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.
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.
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.
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.
The demise of Constellation is not the death of a dream. It's just the end of an illusion.
My one concern is that when money gets tight, it's easy to cut R&D funding that isn't tied to a specific project - look at what's happened to NASA's aviation research.
The communications delays between Earth and Mars can be half an hour or more, so the people on the ground can't participate minute by minute in Mars surface activities.
The Moon may not be quite as appealing as Mars, but it's still a complex and poorly understood world, with many questions still unanswered.
In 1960-61, a small group of female pilots went through many of the same medical tests as the Mercury astronauts and scored very well on them - in fact, better than some of the astronauts did.
NASA has never had a problem finding capable people to be astronauts. NASA's problem was, and still is, finding ways to cut the list of capable applicants down to a manageable length.
Not until the space shuttle started flying did NASA concede that some astronauts didn't have to be fast-jet pilots. And at that point, sure enough, women started becoming astronauts.
Since SpaceX's very beginnings, they have talked about recovering and reusing at least the first stages of their rockets.
Solid-fuel rockets can't easily be shut down on command.
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.
Trying to build a spaceship by making an aeroplane fly faster and higher is like trying to build an aeroplane by making locomotives faster and lighter - with a lot of effort, perhaps you could get something that more or less works, but it really isn't the right way to proceed.
As plans for the first lunar landing started to be made, nobody had really thought about who would be out first.
The original specifications for Apollo navigation called for the ability to fly a complete mission, including a lunar landing, with no help from Earth - none, not even voice communications.
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.
Speaking of photography, while the Apollo 8 crew shot hundreds of photos, there was one that got everybody's attention: a blue-and-white Earth rising over a gray moonscape.
In a small spacecraft, it was hard for the other two guys to sleep when the on-duty man was talking to Mission Control regularly.
Claiming that solid rockets are necessary for a heavy-lift launcher is obvious nonsense.
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.
It's true that Apollo 10's lander was overweight. Late in the craft's development, it became clear that its ballooning weight was endangering the whole mission.
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.
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.
If your goal is to change the world, you can't start by doing things the same old way because it sells better.
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.
Historically, the U.S.'s big launchers fly seldom enough that their costs are dominated by annual upkeep of facilities and staff, not by the actual cost of each launch. The expensive part is maintaining the launch capability, not actually conducting launches.
Foul-ups in testing are not uncommon, especially when the test setup is being tried for the first time.
One of the headaches of high-tech test programmes is having to debug the test arrangements before you can start debugging the things you're trying to test.
