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Large Nasa (pay load) ships

Posted by: rinse - Wed Jan 06, 2010 4:20 pm
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Large Nasa (pay load) ships 
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Post Large Nasa (pay load) ships   Posted on: Wed Jan 06, 2010 4:20 pm
Is it cheaper in terms of gas economy to have horizontal lift off and climb to 40.000 foot in an angle. Than go vertical at 40.000 foot or so and drop off the wings on parachutes for reuse? Maybe small wings remain for Horizontal landing or no wings at all and make vertical landing.
(this for normal space flights without landing on other planets)


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Post Re: Large Nasa (pay load) ships   Posted on: Wed Jan 06, 2010 10:06 pm
If you're doing suborbital work, then that is a workable solution. Those first few kilometres of altitude where you have enough atmosphere to fly are actually a significant part of what you're trying to accomplish. So that is what Virgin Galactic does: they fly the first 15 kilometres, and then rocket the last 85 to the 100 km border. (There are other factors of course, safety for instance. Starting at 15km gives you much more time to solve a problem than starting on the ground.)

Going into orbit is a different game though. In principle, you can orbit the Earth at ground level. All you need is enough speed. Build a car that can go 7.9 km/s, and it will be weightless at top speed, because it will be in orbit like a satellite. Getting to that speed costs a lot of energy, much more than going 100km straight up costs.

The problem with orbiting at ground level of course is that the Earth has an atmosphere, which causes drag, and slows you down. It takes a lot of energy to keep pushing through the air, especially at high speeds, since the resistance rises with the square of the speed.

We solve that by not just accelerating our orbital spacecraft horizontally, but also lifting them up out of the atmosphere. That only takes a little bit of energy compared to what we need to get up to speed, and it saves a huge amount of energy that we would otherwise lose to drag.

So, with avoiding drag being more important than saving energy on gaining altitude, most rockets actually launch vertically, get up as quickly as they can, and then as they get higher and the atmosphere thins out, more or less gradually arc over. That way, the bulk of the speed they need to get for getting into orbit is obtained above the atmosphere.

Of course, the fact that the gain you would have by flying (with wings) the first few kilometres upwards rather than rocketing them is small compared to the energy you need to get up to orbital speed, doesn't mean that it's never a good idea to start with flying. Orbital Sciences' Pegasus rocket for example is air-launched from a carrier aircraft, and has its own wings too. This reduces cost of ground infrastructure (all you need is a fairly big airport, not an expensive tower), and makes it possible to fly around any adverse weather conditions. Larger rockets might very well do the same, if it were possible to build an aeroplane large enough to carry them.

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Post Re: "cheater" or half-stages   Posted on: Wed Jan 27, 2010 6:11 am
Quote:
rinse Jan 06, 2010
Is it cheaper in terms of gas economy to have horizontal lift off and climb to 40.000 foot in an angle. Than go vertical at 40.000 foot or so and drop off the wings on parachutes for reuse?
Maybe better to stick with carrier aircraft as a sort of "cheater" or zero-stage. Mavbe a winged parallel or series-burning first stage? If it drops back down fairly soon, it doesn't need as much complexity as a higher/faster stage would (It doesn't go far way, and doesn't need TPS for re-entry heating)

Plenty of other "Cheaters" work too.
I'd like to see more work into tri-propellant, maybe with jettisoned tankage.

Another idea, using EM catapult, of a smaller sort than usually envisioned:

Quote:
https://www.llnl.gov/str/Post.html
NASA is interested in maglev technology to help launch rockets at sharply reduced costs. As conceived, a track would use a reusable launcher to propel a rocket up a ramp to almost Mach 1 speeds before the rocket's main engines fire. According to Smith, the technology should be able to save about 30% of the weight of the launch vehicle. "Rocket engines are not fuel-efficient at low speed," he points out.

That's a big help right there, and since it can even be used at sea level, and doesn't go horrendously fast, it's lots easier than many other ways that have been tried to use EM catapults to achieve SSTO (or closer to it).

Also interesting is laser-thermal boost, using air-breathing engines at low-level, close to the launch site (the end of the EM track?)
Again, it's lots smaller/less complex than many other schemes for laser-thermal push to orbit.

Toss all of these together, with tri-propellent rockets to take it up the last bit to orbit, and we 're using each schemes only in the areas where it helps most, and losing it when it no longer is economical/simple.

Another good one that also uses a familiar concept, in a smaller way that only capitalizes on its strengths, is the Hypersonic Skyhook or HASTOL variation of the space tether/space elevator.
Most tether/elevator schemes have lots of problems/hurdles to overcome, but simplify it to the Hypersonic Skyhook, and we have a "cheater" upper stage, to add onto all of the other "cheats" we've employed.

http://adsabs.harvard.edu/abs/1995JBIS...48..123Z


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Post Re: Large Nasa (pay load) ships   Posted on: Wed Jan 27, 2010 6:21 am
In the early shuttle designs the Et Fuel tank and SRBs were part of the same flyback booster with their own wings and crew.

That was all dropped when the shuttles budget was cut by two thirds.

But even then, take-off was (usually) vertical.

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