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Registered Member #4266
Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874
Thought it would be obvious, that if to get to Geo orbit is 90-95% rocket fuel, using a plane that takes half the fuel from the atmosphere, you would be in the range of 50%
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Delta-V is a relative thing sure enough, but escape velocity from the Earth's gravitational field is absolute, and as Dr. Slack points out, an aircraft or balloon isn't really any help in achieving it.
The only advantage of the air-launched approach is that it allows the rocket to start off in a thinner atmosphere and experience less drag. But the atmospheric drag really isn't that significant compared to the "drag" of the Earth's gravity on the rocket's mass.
Once you are out of the Earth's gravitational field, then you can start talking about delta-V, firing up ion thrusters and so on.
Thought it would be obvious, that if to get to Geo orbit is 90-95% rocket fuel, using a plane that takes half the fuel from the atmosphere, you would be in the range of 50%.
For near earth orbit you need about 8km/s as BigBad pointed out. In order to utilise atmospheric oxygen the rocket needs to stay in the atmosphere and accelerate to that speed. Drag prohibits that.
8 km/s is a lot. If you'd throw a rock vertically up with that speed it would rise up to about 6000km height neglecting air resistance. Potential energy gained from starting 10 or 30km up is comparatively little.
Registered Member #4266
Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874
Mark 27 is enough to reach escape velocity, a air breathing plane like jet engine or balloon(not realistic but sticking to the point), can gain most of that speed using mass from the atmosphere.
I designed a 2 meter thimite rocket that can fly 8300km, from NZ to almost US, a solid fuel rocket wouldn't get half that distance.
A ballon would allow it to get high enought were less eff engines can take over, but has high speed.
A jet engine is more eff than a rocket, but a rocket is fast, a prop is more eff than a jet....etc
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Ok i think i have a better way of stating things.
Assume in both cases i want to lift the same 1kg payload to the same simple orbit. And the rocket is 90% propellant and 10% airframe.
For the rockoon case: we let it go at 100,000 feet, 0 speed.
For the traditional case: It stands on the ground sea level, 0 speed.
obviously the rockoon rocket will be smaller and need less propellant. but by how much of a difference ? a wee bit, a lot, or a huge amount ?
Now as stated previously,
Uspring wrote ...
8 km/s is a lot. If you'd throw a rock vertically up with that speed it would rise up to about 6000km height neglecting air resistance. Potential energy gained from starting 10 or 30km up is comparatively little.
is this true if we throw a rock upward also from 30km ?
His idea uses 3 semi-ridged airships. A small one from ground to 100k ft, a 2nd large 1 mile diameter asterisk like a permanent station in a static position somehow, then the final 1 mile "V" shaped hypersonic balloon that accelerates to mach 25 over the course of 20 to 30 hours, based on a MHD type solar - chemical rocket system. They also have plans to use "active drag reduction" on the leading and upper surface of the wing.
These vids are short so please watch and give me some advice.
From the US military industrial complex with infinite amounts of tax dollars . .. Lockheed's fabulous propaganda video.
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4059
What about a balloon/Lifter/turbofan solar powered hybrid, initially lifted by laser but then the solar panel "flips over" via magnetic or piezo motors and tracks the Sun during acceleration and boost phase? Onboard fuel cell gas generator and distributor provides thrust above 30K feet and the ion drive only turns on quite high up using residual H gas from the actual balloon, the Lifter, drone and balloon section then detaches via 4 point Curie point heater and magnet pulse which doubles as the interconnects then returns for reuse via 'chute and green blinkenlights for optical tracking. Any excess energy not used is stored in the fuel cell(s) or onboard single charge Li batteries.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Conundrum wrote ...
What about a balloon/Lifter/turbofan solar powered hybrid, initially lifted by laser but then the solar panel "flips over" via magnetic or piezo motors and tracks the Sun during acceleration and boost phase? Onboard fuel cell gas generator and distributor provides thrust above 30K feet and the ion drive only turns on quite high up using residual H gas from the actual balloon, the Lifter, drone and balloon section then detaches via 4 point Curie point heater and magnet pulse which doubles as the interconnects then returns for reuse via 'chute and green blinkenlights for optical tracking. Any excess energy not used is stored in the fuel cell(s) or onboard single charge Li batteries.
Im building a discrongtificated, bipolar field modulated quantum accelerator for propulsion, and the langly / tesla electrostatic disc fringe field effect for stability of the power control flux capacitor.
A tiny bit more, but still only a little difference compared to throwing from 0m. If you add air drag, the difference would be _much_ bigger.
The advantage of a high altitude start is, that you can launch the rocket almost horizontally. For low earth orbits more than 95% of a satellites energy is in its velocity and not in its altitude. So that is where you need to aim it. For a surface launch not all energy spent in getting the rocket up to 30km height is lost, since it will have gathered speed and be angled into the orbits direction, but the vertical speed component is wasted.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
I'm seeing from your opinions that their advantage is nozzle expansion efficiency, not having a billion $ launch facility and weather is less of a restriction along with some orbital directions.
Registered Member #61406
Joined: Thu Jan 05 2017, 11:31PM
Location:
Posts: 268
Upspring that's not internally true. You could go straight up at 27km/hr and you escape earth, but the orbit won't be much good. Rather than just the earth there is the sun. compare vacuum to sea level, is like compare water to air. the only thing that would make this a bad idea, is the second stage rocket at its weight, a balloon can't lift much. Patrick keep it kiss, potassium clorate charcoal and a binder, then switch to a expensive high ISP, thrust engine. workout the first stage to as cheap as business practical then you'll bet NASA, but then you need them for the second stage.
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Rockoons and Propellent Mass Fractions.
