Zepplin Theroy

[Xyphos]

another weird and out-there idea came to my mind, what if we could tether ultra-light SSTO's to a Zepplin, float it up to 16kM with out using any fuel, then undock it, nose-dive to Mach and orbit?

Edited August 5, 2015 by Xyphos

[Yukon0009]

It's a used-before in an experiment.

[Whirligig Girl]

Balookets are real designs. Balloon-rockets. In fact, I would imagine if the steampunk space program wants to launch heavy things to space, they HAVE to use rockoons.

[Xyphos]

Balookets are real designs. Balloon-rockets. In fact, I would imagine if the steampunk space program wants to launch heavy things to space, they HAVE to use rockoons.

heh, would be cool for a mod.

[Tex_NL]

On Kerbin the dV required for vertical altitude is only a fraction of what's required for horizontal speed. On Eve balloons could lift you above the thickest atmosphere but on Kerbin it's hardly worth the effort.

[AbacusWizard]

I imagine getting up to 16 km for "free" (those balloons do cost something) would save a layer or two of booster rockets, but the important thing is it would look cool.

[Nich]

Not to mention you would need a balloon the size of KSA to lift a 1t satalite

[GoSlash27]

Surprisingly (or perhaps not) it really wouldn't save much. Atmospheric effects don't give much of a penalty on Kerbin.

Best,

-Slashy

[Geschosskopf]

heh, would be cool for a mod.

Go find the Hooligan Labs airships mod and give it a try.

[Kerbart]

another weird and out-there idea came to my mind, what if we could tether ultra-light SSTO's to a Zepplin, float it up to 16kM with out using any fuel, then undock it, nose-dive to Mach and orbit?

Let's entertain the idea for a second. And let's for simplicity sake there's no air resistance because that would totally break our model. So, our rocket dives to sea level, gaining, for arguments sake, a velocity of mach 3. And now we're using THAT to try to get into orbit. I'm pretty sure that once you point your rocket upward (again assuming no losses that would happen in real life) you will lose speed due to gravity, and at an altitude of 16km be back at speed 0.

Unless I'm missing something.

[Bill Phil]

Surprisingly (or perhaps not) it really wouldn't save much. Atmospheric effects don't give much of a penalty on Kerbin.

Best,

-Slashy

Same for Earth, actually. Atmospheric drag accounts for a few percent in the total delta V breakdown.

Most of it is getting up to orbital speed. The next most is getting up to altitude and gravity losses.

- - - Updated - - -

Let's entertain the idea for a second. And let's for simplicity sake there's no air resistance because that would totally break our model. So, our rocket dives to sea level, gaining, for arguments sake, a velocity of mach 3. And now we're using THAT to try to get into orbit. I'm pretty sure that once you point your rocket upward (again assuming no losses that would happen in real life) you will lose speed due to gravity, and at an altitude of 16km be back at speed 0.

Unless I'm missing something.

Why sea level? If you use an aircraft with propulsion, diving a little bit could help you get to a decent fraction of orbital speed. You then pull up slowly and activate the rocket thrusters at the correct altitude.

[LostOblivion]

On Kerbin the dV required for vertical altitude is only a fraction of what's required for horizontal speed.

Isn't this even more so IRL?

[Xyphos]

Let's entertain the idea for a second. And let's for simplicity sake there's no air resistance because that would totally break our model. So, our rocket dives to sea level, gaining, for arguments sake, a velocity of mach 3. And now we're using THAT to try to get into orbit. I'm pretty sure that once you point your rocket upward (again assuming no losses that would happen in real life) you will lose speed due to gravity, and at an altitude of 16km be back at speed 0.

Unless I'm missing something.

yeah, you don't dive down to sea level. the atmosphere is it's thickest below 8kM.

16kM--->9kM @ -10* pitch is plenty enough for RAPIERS to build up enough thrust and Mach. I've done quite a few aerodynamic stall-out recoveries around this area, with 9kM being the very bottom of the dive, not when you begin to pitch up.

once RAPIERS start to Mach, they will begin snowballing their thrust until around 15kM-16kM then they start to wane, so you'll want to achieve hypersonic speeds between 8.5kM-9.5kM (1200dV-1400dV surface / 1500dV-1800dV orbital) until your parts begin to seriously overheat then carefully pitch up 30* and use the gained momentum to climb, very much like a roller-coaster.

yes, you will lose dV to drag forces and gravity but as a counter that, RAPIERS will continue to burn until their evidential flame-out at 32kM-38kM, depending on your intake setup.

at 32kM-38kM the atmosphere is so thin, drag is drastically reduced, you would have only lost 100dV-250dV depending on your piloting skill.

just kick in rocket mode and close intakes after flame-out, set an AP of 70kM-72kM then slow-burn your circularization early, around 55kM-60kM - Nervas work well for this task.

I would also like to point out, that you should only bring enough oxidizer to get your vessel to orbit, and in multiple RAPIER setups, it's perfectly OK to keep a few of them in jet-only mode; not all of them have to be rockets.

recently, I've been building my own aerodynamic nose cones out of radiators, which deflect the hot air away from the craft, preventing many parts from overheating which allows me to gain an extra 150dV-200dV to compensate for the losses when climbing.

Edited August 6, 2015 by Xyphos

[tsotha]

Not to mention you would need a balloon the size of KSA to lift a 1t satalite

On earth you get about a kg of lift for every m3 of hydrogen. So your 1 ton sat is a little more than a 10m cube (assuming the envelop weighs something). The Hindenburg weighed something like 232 metric tons.

[Goddess Bhavani]

Here I was daydreaming we'd have Zeppelin-like spaceships the size of a Star Destroyer deploying hundreds of Valkyr flying saucer strike craft in a meteorblitzkrieg against the planet below.

[Tex_NL]

Obviously there is a much more economic solution to oversized Zeppelins: a carrier plane. SpaceshipOne and WhiteKnight.

It does work to go suborbital (barely) but without much more dV to spend on horizontal velocity you won't reach orbit.

[SkyRender]

I always wondered why rocket launches are done at sea level. Wouldn't it make more sense to find the highest point possible (or even better, engineer one)? I realize there's falling debris concerns if the launch fails, but an artificial near-coastal mountain could solve that well enough. Even if you only saved a few hundred dV on the launch, that adds up to an awful lot of fuel thanks to the Rocket Equation.

[Red Iron Crown]

I always wondered why rocket launches are done at sea level.

It's for barge access. Rocket stages are bulky and difficult to move by rail or road.

[Tex_NL]

I always wondered why rocket launches are done at sea level. Wouldn't it make more sense to find the highest point possible (or even better, engineer one)? I realize there's falling debris concerns if the launch fails, but an artificial near-coastal mountain could solve that well enough. Even if you only saved a few hundred dV on the launch, that adds up to an awful lot of fuel thanks to the Rocket Equation.

Getting all that equipment and pre-assembled rocket parts up a high enough mountain would be a logistical nightmare.

[Brofessional]

You don't actually gain all that much over just launching from the ground. Most of the delta-v cost in getting to orbit is spent acquiring horizontal velocity, not vertical.

You would get through the thickest part of the atmosphere for "free", but you could do that just as easily with LF drop tanks.

[selfish_meme]

The Graf Zeppelin had a lifting capacity of 87 tons, (did you know it made 590 flights, not bad eh) most first stages burn out by 16km (on Kerbin), I'm thinking there should be an efficiency gain there somewhere

[PB666]

On Kerbin the dV required for vertical altitude is only a fraction of what's required for horizontal speed. On Eve balloons could lift you above the thickest atmosphere but on Kerbin it's hardly worth the effort.

^^^^^^^