Using Fuel Depots Instead of Giant Rockets 202
EccentricAnomaly writes "The New York Times has a story about a leaked NASA study that showed it would cost $80 BIllion less and get astronauts to an asteroid sooner if NASA used fuel depots instead of developing a new rocket. According to the article, NASA's response to the leaked study is to start developing fuel depots in addition to continuing its new rocket program. Because, after all, who doesn't need more cool stuff."
Re:Let's have both. (Score:5, Informative)
Umm, no.
You added eight years worth of supplemental and emergency appropriations ($900 B) onto last year's military budget.
The same article showed the correct amount to add for this year: $37 billion.
Which would make the correct value $700.3 billion, less than half what you asserted.
Re:Uhm... (Score:5, Informative)
The Apollo J-2 was designed to restarted way back in 1967, as was the Aerojet AJ-10 from the late 1950's.
AJ-10 variants were used for both the Apollo SM engine, and the Shuttle OMS pods. They were designed to remain fueled for long periods of time and be re-ignightable. This is a solvable problem.
Re: Guns, lots of guns... (Score:5, Informative)
Fuel is a good candidate to launch with a high-g device, but a mass driver is not the most economical way to get it off the Earth. It is fairly easy to show that a pipe will cost less per foot than induction coils and a frigging huge power supply to feed it, for the same job of accelerating a projectile. Generally, these type of devices are called "hypervelocity guns", defined as when the muzzle velocity is hypersonic (ie more than Mach 5 or 1500 m/s). This is roughly twice the muzzle velocity of large military guns.
In 1993 I was the study manager at Boeing for using a large gun to deliver fuel to a depot, which then was used to send communications satellites to GEO. The savings was you needed 75% less conventional rocket to launch the satellite dry. Hypervelocity guns are not new, they have been used for ballistic and re-entry testing for about 40 years now. NASA owns several of them. Mainly they need scaling up and "industrializing" - setting them up for regular operations, rather than research use.
To reach the highest muzzle velocity, you want to use the lightest gas (Hydrogen), and heat it, so the speed of sound is as high as possible. Speed of sound is the same as speed of pressure waves in the gas, and when your projectile exceeds that speed, there is no way for the gas at the back end to affect the projectile any more, because it outruns the pressure waves. So the gun gets very inefficient at that point. To make hot hydrogen, it is easiest to store it at room temperature in pressure tanks, then run it through a heat exchanger before it gets to the barrel. There is nothing that goes "boom" like a small gun, it's closer to natural gas pipeline operations (in fact, we sourced the gun barrel from a pipeline maker in the study). Find a suitable mountain, such as Cayembe in Ecuador (the highest point on the equator, and the right slope), and put a 2 km long x 60 cm I.D. pipe pointing up. Load a 600 kg projectile about 4 meters long into it, and it will accelerate at 900 g's, and come out with a muzzle velocity of around 5600 m/s. You lose around 1 km/s of that to air drag, and then use an onboard rocket to finish getting to orbit. Net payload to orbit is around 100 kg, which does not sound like much, but if your launcher is at the equator, you can potentially launch 15 times a day to a single depot destination. Over the course of a year that comes to 550 tons (minus downtime for maintenance).
For launching people and delicate cargo, Hawaii is the best location. Assume a 20 km pipe x 10 m diameter, pushing a 500 ton vehicle. It works out the pressure in the barrel needs to be 2 atmospheres (200kPa, 30 psi). That gives you 3 g's acceleration, safe for humans and satellite parts. Muzzle velocity is 1100 m/s (Mach 3.6), which is not a huge fraction of orbit velocity, but a nice running start before you light up your on-board rocket. Given those starting conditions, a reuseable non-cryogenic rocket should have a payload of around 35 tons, which along with a 10 meter diameter should be plenty for any cargo or people you want to launch. This is the upper end of what you might want to build, for your first low-g cargo launcher you can go a lot smaller.
What? (Score:5, Informative)
Did you read the report? It was comparing the cost of SLS launched missions to the moon or an asteroid, with depot enabled versions of missions to the moon or an asteroid. They weren't trying to argue that every rocket in the world is refuellable, nor even most, they were saying that launching a LTO transfer stage empty, then fuelling it in orbit, is cheaper to develop and fly than building a Really Big Rocket.
You can launch a 100 ton lunar transfer stage on SLS, say, with a 25 ton dry weight and 75 tons of fuel.
Or, you can launch the 25 ton stage empty on a Falcon Heavy or a Delta IV Heavy, plus three fuel missions on similar rockets, and it will cost billions of dollars less. (Their scenario is more detailed, obviously.)
SLS is an expensive and harmful way to do these missions. It actually makes us less likely to go beyond Earth orbit, and wastes two to three decades and many tens of billions of dollars doing so.
Prior art (Score:5, Informative)
The fuel depot on orbit of course is ISS Zarya or better known as FGB. It gets fuelled up by Proton's on a regular basis, and ISS uses the propellant for station keeping. Considering the mass of ISS, boosting its orbit is no small feat.
Russians also have a spare module, used to be called FGB-2 sitting somewhere in the hangar. It was proposed as various additions to ISS at some point.
In summary, storable hypergolic orbital propellant transfer is a well known, well developed and currently used technology. Yes you need quite a bit more of it to do burns with delta-v in order of km/s, but the maturity of the solution and abundance of off the shelf engines and propulsion module designs using hypergols may well outweigh cryogenics in overall system designs.
Propellant is also relatively cheap, even nasty stuff like hydrazine, and just lifting more of it would provide the much needed demand side for the globally stagnant launch industry, which has been in the oversupply mode for years, i.e. there are far more operational rockets than there are paid payloads.
The point that "propellant depots" is nothing new, and in fact NASA's current flagship HSF program uses it needs to be made more often. Switching to cryogenics would be a new development even if not that complicated, and may or may not be worth it, depending on overall mission requirements and other elements of system architecture.
Re:How do you get to fuel depots without a rocket? (Score:5, Informative)
As others have said, you use smaller rockets to launch the mission payload "dry", and to launch the fuel separately. But to explain the cost savings, let me use an example:
The SLS is projected to cost over $60 billion to develop and around $1.5 billion per launch. The biggest version is supposed to launch 130 tons, but the first version will only launch 70 tons. (And remember, $60 billion is only for the rocket, it doesn't include the cost of the actual mission hardware.)
SpaceX's Falcon Heavy will probably cost less that $0.5 billion to develop, and is already taking commercial orders at something like $0.125 billion per launch. It is intended to launch over 50 tons.
For the price one 130 ton SLS launch, you could pay the entire development costs for Falcon Heavy and still have enough to buy 8 launches of 50 tons, or 400 tons total. And once Falcon Heavy is developed, each subsequent $1.5 billion could buy 12 FH launches, or 600 tons.
600 tons for the same price as 130 tons.
So instead of spending $60 billion to develop SLS, it could be spent on actual missions. Isn't that a more intelligent way to run a space program?
Re:NASA has no choice on SLS (Score:5, Informative)
Falcon Heavy simply does not have the payload capability for manned, deep space flight.
You didn't read the report? Or the summary? Or the headline?
Nothing intended to launch on the 130 ton SLS has more than 50 tons dryweight. So instead of launching it fuelled on a $1.5 billion launcher, you launch it dry on a $0.125 billion launcher, and launch the fuel on some other $0.125 million launchers. $1.5 billion worth of mission for less than half price. Bargain!
Even assuming Falcon Heavy is ready on time, SpaceX is still in business in 2014
What chance do you think the SLS has of every reaching its first mission? On time, on budget. After burning through its $60 billion development budget?
and they haven't started multiplying their prices after they have gone public
They are signing commercial contracts at a list price of $125 million per launch. (Less if you don't need the entire 50 tons.)