Originally Posted by
balsa model
I don't have to get the cost where you want it, to win this argument.
The only known mass market for spaceflight requires launch costs below $100 a kilo. At that point tourism starts to become viable enough to sustain a huge increase in payload to orbit, and your flight rate can be high enough to make an SSTO more profitable than an expendable.
Saying 'I can prove SSTOs don't make sense so long as I define the question so that SSTOs don't make sense' seems rather silly. In the medium term they're the only things that make sense if your goal is to build a sizable human population in space (longer than that and something like a space elevator may be viable and cheaper).
The big problem with launcher development right now is that there's no proven large market between communication satellites and tourists. If you're launching a billion-dollar comsat which will produce billions in revenue over its lifetime, then the difference between paying $200 million or $20 million to launch it is small, whereas if you're in the launch business, the difference between charging $200 million or $20 million a launch is enormous if it won't result in any significant increase in the number of launches.
So there is little economic incentive for developing new technologies to dramatically reduce launch costs until you can get them down to levels where ordinary mortals can afford them. Skylon, if I remember correctly, was estimated to cost around $500 per kilo back in the 90s, which puts it squarely into the 'who do you think your customer is?' range. Put a $10,000,000,000 price tag on developing a launcher with no known profitable use, and no-one in their right mind is going to fund it... particularly when you consider that the development cost is almost certainly optimistic.
Which is presumably why RE are now pushing for work on a hypersonic airliner instead of an SSTO. The problem is that there's not much more of a proven market for hypersonic airliners than for spaceflight at $500 a kilo.
I just have to point out that all reusable options have shown to be more expensive than using the throw-away variants. By a lot.
The only operational 'reusable' launcher is the shuttle, which is barely reusable and has to carry a human crew with all the extra cost that entails yet still costs less per flight than a comparable expendable launcher. The problem with the shuttle is the huge fixed costs of the facilities and standing army required to support it; the variable cost of flying an extra shuttle launch is around $200,000,000 while the average cost over the entire program is closer to ten times that amount because the fixed costs have to be spread over a small number of launches.
That is why both reusability and high flight rate are important if you want to dramatically cut costs. So, for that matter, is not running your own 'spaceport' that adds a couple of billion dollars a year to your fixed costs when you could just buy launch slots elsewhere when you need them.
Our propulsion technology hasn't seen any revolutionary invention since the 60's. That's our limit.
No, that's as far as we've had any incentive to go. When the only real markets for your services are happy to pay $200,000,000+ a launch with a 98% success rate, there's simply no incentive to do any better.
Absolutely! If it cost less to produce a new expandable one than to recover and overhaul a reusable one that carries the same payload, then Yes!
And even the shuttle, which is at best refurbishable and throws away around $100,000,000 in hardware each flight, costs less to overhaul than the cost of building an equivalent expendable launcher.
Should I even need to add that SpaceX are aiming to recover and reuse both stages of their Falcon launchers because they believe it will reduce costs compared building new ones each time?