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…
What do you think of the proposals for a “space elevator”? If that worked, the variable cost of getting stuff into orbit would fall by orders of magnitude. I have seen things written by enthusiasts, but I do not know if the thing is simply too far-fetched from an engineering standpoint.
Biggest question: what if it falls down? Don’t forget that even if you’ve got a good answer, you’ve got to sell it to people with way more power than sense that are paid to be excessively paranoid.
Another problem is that, while a single rocket can carry a handful of people into space, half a giant beanstalk doesn’t bring anyone anywhere useful. It’s an enormous investment that has zero payoff until it’s all done. And endless opportunity for any official within range to put this massive project on hold and bring the whole project, and everyone’s entire investment, crashing down. This becomes an even bigger problem if we try to build it on the equator, which makes the most sense from a technical point of view.
I’ll agree that if the thing gets built, bringing payloads up gets a lot easier since you don’t waste such large amounts of fuel on simply lifting the rest of the fuel. But it’s one of those “I’ll believe it when I see it” deals.
Yeah, Jim Bennett wrote somewhere that it is bad enough trying to write the environment impact statement for a single private rocket launch — a space elevator would never get past that stage.
Still, these guys, Liftport Group, seem serious. They offer these responses to the question “what if the cable breaks?” Sounds reasonable to me, but I’m no engineer.
I do think that rocketry is too expensive to really get us out into space. Something like the space elevator, or something really SF like an anti-gravity “truck” are the only way we’ll do it on a massive scale.
I would think an eletromagnetic railgun would make an outstanding launcher for materiel. Humans would not survive the acceleration, however. For them, “old fashioned” SSTO’s would be necessary, joining up with their materiel in orbit. One could even launch an upperstage booster into orbit for tranfer to an interplanetary vehicle.
Hey. What’s this below? An antispam device? Cool.
Gas Core Nuclear Rockets
Advanced nuclear electric propulsion (NEP) systems. INSPI envisions a fully integrated ultralight and ultracompact power and propulsion system that would be capable of safely transporting a human crew to other planets of our solar system.
Good collection of links on nuclear powered space exploration.
Michael is right, a railgun would do the trick. You could use nuclear power plants to drive that, at least.
I don’t think that you’d launch a completely booster using a rail gun, though. Too big a gun needed, and don’t forget the athmospheric friction on the way up. You would have to develop special projectiles with heat shields. So you’d get the components up there that way, and assemble your booster in orbit.
You could send your crew into orbit using a shuttle, have them assemble their interplanetary vehicle from the components launched with the rail gun, and the advantage wouldn’t just be the consumption of less energy per pound and bigger payloads, but also much less restrictions in constructing your ship. You could build a huge interplanetary mothership to fly to Mars or beyond, and then use shuttles or Apollo like capsules to get to the planet or moons you want to visit.
If you don’t want to launch that much stuff from Earth you can mine some Asteroids, at L5, for example. Even a small M-type asteroid contains more metal than ever had been mined in human history.
Sky’s (not) the limit, dude.
That should have been ‘nuclear power plants to drive material’ and ‘than ever has been mined in human history’, respectively.
(Damnit, I don’t have time to dig for a link, but y’all are partly incorrect about the fuel situation.
First, most recent spaceflight operations research and development in the West has been in the use of hydrogen, which is actually worse than hydrocarbon fuels; in the shuttle, it winds up being hydrogen combined with solid rocket boosters… which I think was a particularly bad solution… but I’m getting distracted.
The Russians do have much better engines than we do, and they haven’t even been developing new ones for the past fifteen years or so. The US has spent the last thirty where the only new engines we’ve built have been liquid hydrogen fueled.
And there’s a persuasive (to me at least) argument by Mitchell Burnside Clapp (IF you could find it on the web; I know the paper’s out there) that hydrocarbons are a better fuel to use for an RLV than liquid hydrogen/oxygen.
It turns out that if you run a nominal kerosene-fueled RLV through the trajectory optimization programs like POST you wind up with a lower delta-V needed overall to reach orbit, because gravity losses are less (hydrocarbon engines generally weigh less and produce more thrust), tankage weighs less (hydrogen is too fluffy a fuel), and there’s less aerodynamic drag.
Not to mention the operational problems with hydrogen even if all things were equal and it were as good as hydrocarbons. (Metal embrittlement and all that jazz).
(I’m trying to summarize because I’m in a hurry. I’ll write something decent, with links and stuff, when I get home.)
But even the argument above is besides the point.
IF you had (for instance) a two-stage RLV that could launch stuff to orbit for only five times the cost of refuelling it you could put all other launch vehicles on the market out of business. Fuel (and oxidizer) costs are a _very_ small fraction of current launch vehicle costs.
More later…
Here’s a link to a discussion on the subject at usenet, with MBC as a participant:
http://yarchive.net/space/rocket/fuels/hydrogen_deltav.html.
The author of the linked-to piece you mentioned is stating his opinion about SSTO as if it’s fact. But I don’t think we’ve seriously tried to make a decent SSTO or even TSTO RLV. And I don’t think the political boondoggles like X-33 were serious.
I’m with Phil. There’s lots of ways to solve the problem. The article linked was beating up strawmen. The DCX had a 50% mass fraction because it was never intended to go to orbit, so mocking it just showed the author’s ignorance (or malice). The “92%” he kept throwing around assumes the specific impulse of the engines and delta-V to get to orbit are both constant, which is BS–they’re both a function of what system architecture you’re using.
Plus there’s no need to use an SSTO to get to orbit. The original shuttle concept (two fully reusable stages) would work fine. Or we can go with MBC’s concept of aerial refueling on the way up.
I’ve wondered for some time how difficult it would be to hit orbit with a 2-stage system, the first one being an air-breathing launcher for the upper rocket stage. Never analyzed it. I suppose that the staging velocity is well below optimal.
Just a quick followup, and not anything in depth, according to this post at Space Transport News, Elon Musk (the founder of Paypal who’s working on a family of small launch vehicles) has stated that for the Falcon 1 (the initial vehicle in the family) the cost of the fuel for a Falcon 1 launch is something like $ 30,000.00, which is ” $48 per kg out of ~$12K per kg total cost to get to LEO” with that vehicle. Most of that cost is the kerosene and hydrogen; the liquid oxygen is ridiculously cheap compared to that. IF they can work out ways to reuse their hardware (which they plan to try) they think they can bring that price down.
E-P, getting to orbit with two stages is very doable. Having an air-breathing first stage may make it easier, depending on how big a payload you’re trying to put up. I worked on one at Pioneer Rocketplane.
I think that the rocket eqn means that SSTO is a very difficult problem [1] but if you look at where the money goes in rockets, that’s not necessarily a deal killer. As I recall, most of the moolah goes to the wages of the huge teams of people needed to launch and operate space vehicle, to the tune of a trained engineer per
You know, the fastest way to discover the truth is to post an incorrect one online
every couple of kilograms. At least, I think that’s the number.
Fuel is cheap. ISTR from sci.space.* a discussion of a hypothetical fuel cost for a kerosene/LOX orbit rocket of around $3/kg delivered to LEO, most of which is the hydrocarbons used. LOX is almost as free as air.
1: Ignoring things like nuclear thermal because, hey, good luck of getting by the PR problems.