Also, you need to clear less airspace with a vertical launch.
Brian
Quoth Padeye:
Technically, yes, but that orbit will intersect the surface of the Earth. In other words, it’ll crash (or at least land) before it even finishes a single orbit. I don’t think that’s what you had in mind.
Now, if you give it enough power, then it’ll never return to Earth, but it’ll get very far away, and the orbit won’t exactly be “around” the Earth. Interestingly, if you don’t have to worry about the atmosphere, the initial speed required for this doesn’t depend on where you’re aiming: It’s not actually escape velocity, it’s escape speed.
You can also put some sort of rocket on your projectile, so it can change to a more permanent orbit once it reaches the appropriate height. This takes much less fuel than the initial launch, so it can be practical.
But notice that I specified “if you don’t have to worry about the atmosphere”. Launches from Earth to space, by any means, do unfortunately have to worry about the atmosphere, and the easiest way to deat with the atmosphere is to start off going straight up, so as to deal with as little of it as possible.
To correct a slight misapprehension…
Rockets, or anything else in orbit, are NOT free of Earth’s gravity. The gravitational force in a low orbit, say 140 miles, is around 93% of the value at the surface. Hence the high speed (5 Miles/sec) that is required to stay in orbit.
And to add to G. Cornelius’ remark regarding a substantial velocity being required: approximately 80% of the Shuttle’s energy is expended on orbital velocity. The remainder is all that is needed to achieve the exoatmospheric altitude.
Carry on.
The idea is simply to get up above the atmosphere as quickly as possible. The atmosphere is a huge energy drag.
I never thought about that before. I imagine pre-space travel there was no height maximum to air rights. When did that change? Is there a treaty?
What I was looking for, even if my original post wasn’t super clear on that, was why you couldent launch like an airplane to say 30.000 ft then climb like a rocket. Like the pegasus but in a single stage. But the pegasus is, if I remeber correctly, a very small vehicle compared to the shuttle.
So my idea was to get out of the thicker part of the atmosphere with minimum thrust and a slow climb, before you start the big throttle up, and go for orbit. It seems like such a waste to burn all that fuel on a vertical climb. I sure most of you undrerstood that, but I just wanted to make things clear.
But the same obstacles still apply I suppose. To use jet engines for atmospheric flight would use less fuel, but would add weight and cost. You would also need a wing structure, that has to be protected on reentry, witch adds more weight. The load on the wings would also be huge.
Pioneer Rocketplane …
http://www.rocketplane.com/
…has an interesting solution to the problem. It has two jet engines, and a rocket engine but only fuel for the jet engines on takeoff. It climbs to 30.000 ft were it meets a tanker which transfers kerosine, and oxygen for the rocket engine. It then lights the rocket engine and starts the climb to sub-orbit. I wonder if it can be applied to an orbital vehicle as well?
Some experimental fighter planes have been flown to sub-orbital altitudes using a similar technique - but they would still have a long way to go with a lot of fuel to carry to get into orbit. And they don’t carry a payload.
As you point out, the problem is really the weight of the fuel. You can only fly like an airplane to a limited altitude, after which there is not enough lift. Once you get there, you’d need still need a massive amount of fuel to get into orbit.
Not only that but the structure of an airplane is very different than that of a rocket…as I’m sure you are aware the space shuttle is just a glider in reentry, it could never take-off like an airplane. Any normal airplane or jet would be torn apart in reentry (and presumably in a liftoff as well).
The cost of a non-reusable rocket launch is primarily determined by the complexity of the rocket, and only minorly affected by the cost of the fuel. A big simple rocket that uses a lot of fuel is cheaper than a complex rocket that gets the same payload into space more efficiently. Rocket launch companies are in business to make money, and the most economical solution at the moment is simple launch vehicles that don’t try to use the atmosphere for additional lift in any way. No jet engines or wings, not much more than a big set of fuel tanks with a few engines at the bottom.
When someone develops a practical reusable launch vehicle that doesn’t require six months of inspection and rebuilding between launches, the cost of fuel may be a bigger factor, and air-assisted lift and jet engines may become the more economical choice. Or maybe not - even a reusable rocket should be kept as simple as practical, to keep development costs down and reliability up. Adding a whose seperate thrust system adds a lot more potential failure points to your launch vehicle.
No, I was specifically referring to the X-15 that preceeded the Pegasus by a few decades. It didn’t achieve orbatal flight but that’s a matter of available power and parameters rather than design. If we had followed that path rather than the Mercury/Redstone/Atlas to get a human into space it would have given us a very different ideas of what “proper” space flight is.
Chronos, thanks for the correction. I was trying to get a concept across but was misleading in the process.
Provided that with today’s proliferating technology, a material feasible for structural stability pertaining to horizontal winged takeoff may become possible in the future. My inquiry is that if the previous statement comes to fruition would it be possible to use a rotating rocket propulsion system to provide the necessary thrust to achieve lift and reach the upper atmosphere then rotate the rockets to begin a more vertical ascent?
air friction.
the goal of launching a spacecraft is to get it going really fast. It has to be traveling at 17000 mph in order to stay in orbit. It can do that at any height (neglecting the variation of speed with orbital height. my point is that one can orbit at any height given enough speed). Going high is important, but not as important as going fast. The reason for vertical launch is to get away from the dense atmosphere as quickly as possible. It doesn’t do any good to stay low, and as speed increases, it begins to become a major problem.
In the ten years since this thread was originally started, some new designs have been developed. The Skylon spaceplane will take off horizontally, with air-breathing engines that switch to rocket mode as it leaves the atmosphere. Most of the acceleration needed to reach orbit is horizontal, but you usually don’t want to spend any more time in the atmosphere than you have to.
A tip, Amiable sloth94: The purpose of language is communication, and using big fancy words just because you can doesn’t help with that. You appear to be trying to impress us with your vocabulary-- Save that for the content.
Yeah, for some reason, I’m hearing W.C. Fields as I read that.
I’m a Doc Savage fan. “Johnny” (William Harper Littlejohn) used big words whenever he could, probably to piss off the other members team.
Spaceship 2 launches horizontally from a ‘mother plane’:
http://en.wikipedia.org/wiki/SpaceShipTwo
It seems like part of it may be where the ship is getting it’s oxidizer for the atmospheric portion of the burn. If it’s from the air, such as a jet engine, it tends towards horizontal launch (this would include using a mother plane, as that is sort of equivalent to a first state), if it’s from stored sources it tends to be a vertical launch.
One issue is ratio. All the SSTO designs (Single Stage to Orbit) were about minimizing the weight while maximizing the energy output, but regardless - even back-of-envelope calculations showed that an orbital craft using conventional current fuel would have to be 90% to 95% fuel to reach orbit.
If you add the complexity of multiple engines, wings and controls, landing gear to support that 95% extra, heat shield for the big wide wings for re-entry (remember the tiles?) and what you end up with is is an engineering monstrosity where each addition compunds the amount of other items you have to add.
So you go with the compromise - horizontal “first stage”. now you have 2 choices -
You take something like a Jumbo Jet and fill it with fuel, so it takes off carrying a second stage to orbit vehicle. This first stage can maybe get to a few miles up and about 600 mph unless you are going to use a rear rocket engine to get better results. Now what?
Spaceship Two and Whight Knight are designed for a small sub-orbital arc, nowhere near enough energy to get to orbit. For orbit, scale up the Spaceship Two to about 10 times the size and a lot fancier heat shielding, which means WK is about 20 times the size or more… Jumbo jet pairs territory or worse…
A 747 is not designed to fly at Mach 3, and if it climbs up to a really thing part of the atmosphere, above 50,000 feet, is there enough air-over-control-surfaces to maintain control? Will the wings rip off on the way down after launch at supersonic speeds?
So you need to design a special rocket plane to do the first stage; it can do mach 5 or more, get up to 100,000 feet like the ones the Virgin Space planes. Building supersonic or hypersonic jets and rocket planes is not a trivial exercise.
Orbital speed is in the neighbourhood of 18,000 mph. (25,000 around the world orbit in an hour and a half…) Even mach 5 - 3,000mph - is nowhere near the signifcant part of that speed. the second stage of an orbital craft is going to need to be pretty large if you are launching more than a 200-lb staellite.
Finally, theres the launch issue. To keep the launch vehicle balanced, the second stage has to sit over the center of gravity. Now you have to separate two aircraft in mid-air at extreme speed without one being bumped into the other by turbulence, or being separated at a funny angle where it starts tumbling. And the pair also has to be relatively aerodynamic… But the problem with heat shield damage on the shuttle was simple - the heat shield was downwind from part of the cryogenic fuel tank, so ice built up on the tank and the wind blew it into the shuttle tiles; or the foam used to prevent ice buildup tore loose at thousands of mph.
For a dozen different technical reasons it’s a heckuva lot simpler (but not as cool) to launch straight up, keep everything in line and drop off the bottom of the assembly when its fuel is gone…
Sapceship 2 does not have even a fraction of the fuel needed to get to orbit - it just does a suborbital hop. To orbit, it would need enough fuel to get from 600mph (subsonic jet speed) to 18,000mph and it still needs to punch through substantial atmosphere. …which would mean it would be close to half or 3/4 fuel. (Look at the pegasus craft - however that is a 3-stage throw-away too).
I was hearing Cliff Claven, from Cheers.
To chronos. I’m sorry to look like I was showing off, that was not my intention. I was merely trying to be taken seriously.