Slashdot Mirror
Paul Allen Launches Commercial Spaceship Project
smitty777 writes "The phrase 'Where do you want to go today?' takes on a whole new meaning as Paul Allen, Microsoft co-founder and the world's 57th richest man in the world, looks to create a new spaceship company. Stratolaunch Systems plans to bring 'airport like operations' to the world of private space travel. Partnering with Burt Rutan, the plan is to field a test within five years and commercially available flights within ten. Spacecraft will be air-launched from a giant, six-engined aircraft. There is more information available on the Stratolaunch homepage."
*crash*
...Department comes:
the world's 57th richest man in the world
Paul Allen for the money spigot, Burt Rutan for the carrier aircraft, and Elon Musk/SpaceX for the rocket stages. When I worked on such concepts many years ago at Boeing, we generally found that launching from altitude like that doubles the payload compared to the same rocket starting from the ground, so it makes a lot of sense from an engineering and cost sense, as long as the carrier aircraft costs less than the rocket stages per flight (normally easy to do).
This design overcomes one limitation we had at Boeing, which was the 747 was not quite large enough in it's current form. By going to six engines of the same size as the 747 uses, they solved that problem. Eventually they can also look at flying back the first rocket stage, for even more savings. Once it is empty of fuel, the rocket stage does not weigh much, so it would not take much in the way of wings, landing gear, and some small jet engines so it can fly to a landing. Without knowing how far it will go on a ballistic arc doing it's launch job, it is hard to say if it should fly back to the launch site, or fly forward to another landing location.
Getting into orbit isn't about altitude - it's about velocity. If you look at the energetics of any rocket, about 95% of the energy produced goes into the kinetic energy of velocity - with only about 5% going into the potential energy of increased altitude. Having a jet impart the initial ~600mph to the rocket stage is a huge savings, particularly given the non-linear nature of the propellant economics.
I have wondered why we don't just use massive helium balloons to carry rockets much closer to space
Check out JP Aerospace who have been working on the "Airship to Orbit" concept.
Atmospheric airships using both buoyancy and lift go from ground to 140K feet. There they dock with "Dark Sky Stations" where cargo is transferred to the massive airship-to-orbit craft that can only exist at this altitude and will use buoyancy to rise to 200K feet, then uses electric propulsion to speed up over several days to orbital velocity.
High bypass turbofans like the ones they will be using are about 20 times as fuel-efficient as rocket engines. For one thing, they get oxygen from the air, and then the turbine pushes 6-8 times more air with the big fan, which goes around the combustion part of the engine.
Starting at altitude helps you in three ways: (1) the velocity and altitude you are starting at, (2) less air drag flying through the remainder of the atmosphere, and (3) less back-pressure loss in the rocket engine. At sea level, the loss is 1 atmosphere times the area of the back end of the nozzle, which is significant.
...perhaps we should have some better places to go?
Unfortunately, it really does have to work the other way around. It's a very unfortunate Catch-22. Until getting to orbit stops breaking the bank, there's not much you can do to put a livable space in orbit, let alone the moon or mars; until there is a place to go, it's not commercially viable to research spaceflight.
Getting to space is a cost-per-pound proposition. How many pounds of material does it take to make a sustainable habitat on the moon? How many pounds of fuel to get it there? How many pounds of fuel will they keep on the moon in reserve in case someone needs to come home? Without lifting capabilities that far surpass what we have, it won't be practical.
That leaves us with two options for research and development: Convince government to waste money on something the majority of their constituents will never benefit from, or convince millionaires to part with their money for a joyride. As long as the latter works, more power to them. Personally, I wouldn't mind my tax dollars going to space research either, but there are a lot of people in this country who would be better served with a lower tax rate (let alone an actual public service, you know, like health care or the post office) than with space travel.
Just saw an interview on the news with Burt and Paul. Paul made a point of saying he would not be one of the first to go up. In fact he would wait for many launches before he would go. I guess he learned something from his time at Microsoft!
You are incorrect. A carrier aircraft doubles the payload to orbit relative to the same rocket starting from the ground. The energy and fuel saved might be only 3%, but if your payload to orbit of the rocket is 3% to start with, then saving 3% will double the payload to 6%.
A carrier aircraft helps in several ways:
* The actual altitude and velocity at the time you light up the rocket
* Reduced g-losses. A conventional rocket starts by going straight up in order to get above most of the atmosphere quickly. When you are thrusting up, gravity fights you by trying to pull you down. This is lost energy. When you thrust horizontally, gravity is perpendicular so does not slow you down. With air-launch, you spend more of your thrust near horizontal
* Reduced drag loss. You are starting above about 80% of the atmosphere, so reduce drag by that much.
* Reduced pressure loss in the rocket nozzle. At sea level, you have to fight 1 atmosphere of air times the area of the nozzle exit. It reduces the rocket engine thrust by that amount. Starting up higher gives you more thrust for the same fuel used.
You need to factor in all of those items to find out the true value of getting launched off an aircraft.
747-400 engines have thrust between 265 and 282 kN (depending on engine model). 777 engines have thrust between 338 and 514 kN. You can get more thrust out of four 777 engines than you can six 747 engines. The design has a high wing, so engine diameter isn't an issue. Why use six engines instead of four?
(A330 and A380 engines have only a small advantage over 747, at 310-320 kN.)
The 747-400 has been around 6 more years than the 777, and 747-300 much longer again. Maybe they can get six used 747 engines much cheaper than four used 777 engines. As a low-usage aircraft, it makes sense to have increased maintenance costs if it saves enough on capital costs.
Quattuor res in hoc mundo sanctae sunt: libri, liberi, libertas et liberalitas.