Via James Nicoll, the number that causes the cost of orbital flight to, well, skyrocket.
For a SSTO boosteer using LH2 fuel and LO2 oxidizer, 92% of the take-off weight will be fuel. That leaves 8% for the rocket and everything else in it.
That’s a steep climb. Every single pound of anything brought on board means the ship needs to also accomodate almost 12 more pounds of fuel. And of course it does that by having a bigger, and therefore heavier, fuel tank, and thus needing to accomodate even more fuel.
You can save some fuel (and thus needed fuel capacity) by ditching parts of your ship as soon as they’re no longer needed to get you the rest of the way to orbit rather than bring them the whole way up, but those bits need to be replaced if you want to make another trip.
Add to that the fact that the structural strength needed to stand up to several g’s at takeoff and thousands of degrees of frictional heat at reentry, and complete self-contained ecosystems and/or consumable oxygen, water and food all tend to be kind of heavy, and what you’ve got is an assurance that anything you ride to orbit is going to be massive and expensive.
And it’s never going to get much better. We’re never going to get a better fuel for leaving Earth, not in our present society.
Don’t we already have something better than chemical fuel?
Of course not, and we never will. Our fearless leaders, and their licensed friends in the nuclear industry, have much better fuel to work with, but you can be sure that we will never get our hands on it without major political changes. The problem is that anything that’s good for making a rocket go is also good for blasting stuff on Earth. Getting propellant to shoot out of the back of the rocket involves lots of heat applied to that propellant, causing pressure to get really high and forcing lots of propellant out of the rocket nozzle at high speed. Getting buildings to fall down involves lots of heat applied to a bomb casing, causing pressure to get really high and forcing lots of hot air and hot bomb casing parts and hot bomb explosive parts to go flying at high speeds to knock down, melt, shred, and otherwise ruin whatever they encounter before their energy dissipates.
Lots of heat is also a good way to ruin water treatment plants, bridges, railroads, and other things that people for miles around depend on to keep them supplied with the necessities of life.
This leads democratic governments and tyrants alike to enact laws requiring the unwashed masses to keep their mitts off of anything that can release significantly more energy per pound or more energy per liter than gasoline. So we’re stuck with the chemical fuels, and it’s only the government and their heavily restricted set of license holders that get to play with the good stuff. And we all know how efficiently they bring down costs over time.
So what can be done?
Some wealthy entity can, at great expense, send a small crew representing all of the major genders into space along with a self-contained ecosystem – on a one-way trip. Then in a couple of hundred years, they’ll be a force to be reckoned with, especially since they’ll have about 99.9999% of the Solar System’s proven reserves of energy, hydrocarbons, metals, and other natural resources. They can, among other things, flood the market with extra-cheap full rocket fuel tanks and thus give us cheaper access to their new society even without recourse to better fuel. (Although we might still have trouble getting permission to use giant tanks full of fuel…) And, if they don’t repeat our legal and regulatory mistakes, they’ll have lots of really nifty technology to sell that can’t be gotten anywhere on Earth. Assuming, of course, that they bring along lots of frozen embroys or genetic engineering technology… otherwise, they’ll be heavily inbred before any of that cool stuff happens.
Don’t forget, though, that our fearless leaders may be reluctant to sign onto or leave unmolested a project that gives them or their successors the exciting opportunity to be the next King George III. (This may be one of the reasons why the original manned space program attracted little support overall.)
Can we do something a little faster than that?
Sure. We can massively deregulate everything once enough voters are finally convinced that 19th Century America was among humanity’s greatest success stories of all time, and its living conditions horrify us only because we managed to build on that achievement in the 20th Century. We stand on the shoulders of giants and call them pygmies. Following their example and standing on their shoulders would allow us to reach higher still. Anyway, letting the unwashed masses have the good fuel and letting them commute in personal aircraft and freely buy and sell radio spectrum for communication and run big water condensers/purifiers off of their cheap nuclear energy (rather than having it piped in over a sparse network) and so on would make us all safer – it’s easier to build a big bomb, of course, but it’s easier still to live outside any likely bomb’s blast radius and still effectively trade and socialize with lots of other people. And remain supplied with power and water even if things nearby do get smashed or blown up or flooded or otherwise messed with. And trade with space-based populations, who have access to more abundant resources than anyone’s ever seen, gets cheaper as well. Basically, we get all of the good effects of plan (1) and then some without waiting for a handful of people to multiply for several generations first.
But it looks like we’ll probably just sit here until the next asteroid or Directive 10-289 or whatever sends us back to the Dark Ages. Maybe in the next renaissance they’ll get it right…