Slashdot Mirror
SpaceShipThree to be Orbital Spacecraft
FleaPlus writes "The president of spaceflight company Virgin Galactic has recently
stated that if the upcoming suborbital service with SpaceShipTwo
is successful, the follow-up SpaceShipThree will be an orbital craft.
Although orbital spaceflights would be much longer and could
potentially dock with orbital
space stations, they are also considerably more difficult than
suborbital spaceflights. Other private firms working on orbital
spaceflight (and potentially in the running for Robert Bigelow's $50
million America's Space Prize for orbital flight) include t/Space
and SpaceX."
It is a big fuel saver. The use of the fuel is non-linear, So when you can save some fuel by having a higher starting point with less drag, it also has a non-linear saving as result.
Just calculate the needed potential energy to lift the crafts total mass for 10km up in the air, and you know what basic savings you get.
I also can not seem to find an image of a rocket trajectory, so a description will have to suffice: The first few kilometer the trajectory is as straight up as possible. The trajectory in the densist air layers is the shortest possible. Since speeding up in that part is costly (drag=speed^2), the speed is kept down, in multistage rockets by coasting, or with solid fuel rockets by designing the thrust in such a way that you do not spend to much fuel on speed. Once the air density is low enough (less drag), you will speed up again, and adjust the trajectoy to get to escape velocity. For a decaying orbital trajectory, you do not necessarily need escape velocity, you just need to be able to make it around the earth like one time. So going orbital is also still pretty free in interpretation and goal.
New designs for suborbital planes with ramjets almost all use this design principle for this reason (and they need to get up to speed to make the ramjet work).
The main problem stays though that the design is complex, the take-off of a combined craft like this is slow, and the payload the combined craft can take is low, not higher than current rocket techniques if you really want to get into orbit (Imagine the shuttle+fueltank minus thrusters being lifted to sufficient height)
My wife's sketchblog Blob[p]: Gastrono-me
"Fuels that are used in space must carry their own oxygen, but when going at high speeds in the earth's atmosphere, why not make like a jet engine and get oxygen from the atmosphere?"
Because rockets generally don't 'go at high speeds in the earth's atmosphere'. Typically the job of the first stage is to lob the second stage pretty much out of the atmosphere so it can accelerate to orbital velocity with very low drag and vacuum-optimised engines.
You really don't want to be flying at Mach 20 in an atmosphere thick enough to provide oxygen to your engines: I believe the NASP design would have required active cooling with liquid hydrogen to keep the skin from melting. Developing such a system is a lot more expensive than throwing some more liquid oxygen in the tanks, and fatal if the cooling fails.
There are ways around it - raise the chamber pressure like in the shuttle or use an altitude compensating nozzle like an aerospike or plug nozzle but the kinks are yet to be worked out of these approaches.
There are problems with using air-breathing launchers. That said the most interesting idea I've seen for a cheap launcher includes them.
SpaceShipOne is currently at the Udvar-Hazy Center at Dulles airport. I went there a couple of days ago and recognized it under a blue tarp by the hangar doors near the Concorde. It's a shame they don't uncover it, you can get pretty close to it. I guess they want to have a big unveiling when they move it downtown. http://www.spacealumni.com/index.php?option=com_co ntent&task=view&id=218&Itemid=9
My boy, my boy!