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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."
http://www.2r2s.com/irdt_concept.html
My wife's sketchblog Blob[p]: Gastrono-me
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.
The same way as SS1.
SS1 was a revolutionary design that, when coming back down, folded and came into the atmosphere like a shuttlecock, then when velocity was low enough, unfolded and landed like a plane.
Damned impressive engineering. No reason it won't scale from a 3 seater to a 7 seater.
As I understand it the third working design in the series was always intended to be an orbital craft. First an X-Prize winner, then a larger passenger version for sub-orbital tourism, and then an orbital design. I've been hearing this pretty much from the beginning. So how is this in any way recent?
Difference in notation systems: Dutch: The dot is a thousands seperator, the comma is the decimal seperator.
My wife's sketchblog Blob[p]: Gastrono-me
I hope you're not talking about SS3 because you could not be more wrong.
The reason SS1 was so simple was because it didn't have reach the speeds needed for orbit. It went up and fell back down. Simplicity.
An orbital craft will need to reach much higher speeds. As a result when it reenters the atmosphere, it will have to bleed off that high speed somehow. Most reentry vehicles trade their speed for heat energy by using the atmosphere for braking.
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!
The saving is SFA compared to the kinetic energy required.
1 kg mass at 10 km height = 98.1 kJ
1 kg mass at 7600 m/s = 28.9 MJ
Wow, your potential energy saving is 0.34% of the kinetic energy.
Different people use different punctuation to separate digit groupings. In North America, commas are used to separate groupings of three digits and periods separte integers from decimals (100,000.00 USD). In Europe, it tends to be the other way around (100.000,00 EUR).
The "more correct" way, IIRC, is to separate groups of three with spaces and use commans or periods for the decimal point as you see fit (100 000.00 or 100 000,00).
Those are reasons for wanting a magical SSTO, I'll grant you, if we're talking about "ideal" spacecraft. However, with any given level of technology short of magical, the SSTO is going to cost more (being made of pure unobtanium) and be less safe (with no margin for engineering slack with every component pared the the minimum possible wieght). As long as we're stuck with chemical rockets, multiple stages let you work with cheaper materials and use more weight for redundancy and engineering slack. Being able to allow for reasonable tolerances in manufacturing variation makes a *huge* difference in price and safety. (After all, the second thing a young engineer learns is "the vendor is a lying bastard, nothing on this spec sheet is accurate!" I still can't understand how NASA gets product that actually meets spec.)
...
Sadly, an SSTO *has* to be the pinnacle of efficiency until someone invents better propulsion than liquid hydrogen + LOX.
BTW, WTF is your sig about? I've been wondering for years
Socialism: a lie told by totalitarians and believed by fools.
The obvious design change is a swing wing. You need the wings to not produce too much drag during launch in order to get up to the speeds needed, so you'll probably have them folded back most of the way.
During landing, AFAIK, the larger the surface area, the more gradual the descent angle should be, and thus the less heating you'll get. (This assumes you descend quickly enough that you don't end up skpping off the atmosphere like a stone across a pond, of course, but....) Anyway, if you can slow the descent angle enough... say a dozen times around the planet before you enter usable air space instead of---what does the shuttle do... about half an orbit from deorbit burn to the ground, give or take?---less than one time around, you would see a lot less surface heating... I think....
Just a thought.
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The simple fact is that you can re-enter the atmosphere with little or no heating ... all you have to do is SLOW DOWN!
Close, but not entirely true.
An orbiting object's energy is one half kinetic energy, one half potential energy, and so slowing down to zero orbital speed relative to the atmosphere still leaves you with 50% of your energy to burn off.
So to a first approximation, slowing down reduces your heat by only 50%. You've still got to deal with what's left. If you can at that point manage to fall into the atmosphere very slowly instead of ballistically, you'll give yourself more time to burn off the energy, but of course this again brings up the problem you mention of needing the fuel to do it.