Discussion SpaceX's Grasshopper RLV

[Andy44]

I may be mistaken but I think the Titan upper stage used the gas generator exhaust for roll axis control.

 

[Keatah]

Well do SOMETHING with the gas generator exhaust. In this context its like free energy.

 

[Urwumpe]

Well do SOMETHING with the gas generator exhaust. In this context its like free energy.

Wrong - the lower the pressure of the gas generator exhaust is after passing the turbine, the more effective you used this exhaust.

If you also want to use the turbine exhaust for producing thrust with it, you need to keep a higher exhaust pressure after the turbine, thus lower the effectivity and in effect, the overall specific impulse.

 

[Keatah]

Very well.

 

[Urwumpe]

Very well.

Come on, you used the words "free energy"... you are aware that I had the right to fully TANSTAAFL you for that, so please be a bit more thankful for me not executing my rights. :rofl:

 

[Thunder Chicken]

I don't even think that the gas generator nozzle is choked (allowing supersonic speeds in exhaust, like in the main thruster bell). It really is a draft tube to recover some pressure and decelerate the gas. Ideally you'd love the gas to exit at atmospheric pressure and near zero velocity as that would minimize the loss of energy, but practically you have to have a little velocity to keep the gas moving out of the system.

 

[MaverickSawyer]

I may be mistaken but I think the Titan upper stage used the gas generator exhaust for roll axis control.

You are correct. LR-91s did gimbal the GG exhaust.

 

[Cosmic Penguin]

While we wait for new videos of the last Falcon 9 launch..... we got THIS! :blink:

[ame="http://www.youtube.com/watch?v=9ZDkItO-0a4"]Grasshopper 744m Test | Single Camera (Hexacopter)[/ame]

The Grasshopper reached 744m altitude on this launch on October 7.

 

[N_Molson]

+1 for the precision landing. But I'm still unconvinced. No second stage, no payload, and propellant tanks are probably completely drained by that 700-meters hop.

 

[Urwumpe]

+1 for the precision landing. But I'm still unconvinced. No second stage, no payload, and propellant tanks are probably completely drained by that 700-meters hop.

I would say, it is still an impressive R&D achievement. I agree to your accessment, it isn't anything with an instant application. But as technology precursor, it is still one magnitude better than what the DC-X did.

Also, the propellant tanks should still have a lot of capacity left - the engine does not consume that much fuel per second at full thrust and the DV of such a flight profile is the same for big and small rockets.

 

[N_Molson]

Also, the propellant tanks should still have a lot of capacity left - the engine does not consume that much fuel per second at full thrust and the DV of such a flight profile is the same for big and small rockets.

Hmm... But full tanks would mean more mass and probably more engines which means more consumption...

 

[Urwumpe]

Hmm... But full tanks would mean more mass and probably more engines which means more consumption...

Well, yes - thats the price for the second next step towards suborbital space missions with it = exceed Mach 3.5 and 100 km altitude.

Luckily, only one engine needs to be restartable and full throttleable for that, they could use simpler and lighter boost engines for launch.


But as it is now, they should have enough propellant capacity for short supersonic flights - which would be the real next step, since vehicle performance is much different at supersonic speeds.

 

[Andy44]

That video is amazing, the rocket got a lot closer to the camera than I was expecting, I was waiting for turbulence from the rocket to flip the camera copter over.

 

[Donamy]

Outstanding !!!:thumbup:

 

[N_Molson]

which would be the real next step, since vehicle performance is much different at supersonic speeds.

Yes, and I guess that some aerodynamic work is going to be required to make the legs hypersonic-ready.

 

[Mader Levap]

+1 for the precision landing. But I'm still unconvinced. No second stage, no payload, and propellant tanks are probably completely drained by that 700-meters hop.

Unconvinced by what? You know about next version of Grasshopper that will start flying in 2014, riiight?

 

[N_Molson]

Unconvinced by what? You know about next version of Grasshopper that will start flying in 2014, riiight?

About the viability of the concept. The point of the thing is not only to do fleahops, you know ? Maybe you want a drawing ? :dry:

 

[Kyle]

+1 for the precision landing. But I'm still unconvinced. No second stage, no payload, and propellant tanks are probably completely drained by that 700-meters hop.

This was the final flight of Grasshopper, next one is the F9R hops. Perhaps, if those are successful, you may be more convinced. If not then we'll see how CRS3's first stage performs in February.

 

[N_Molson]

I'll be convinced when I'll see that concept of first stage integrated with a whole rocket and a payload. Which is the point.

 

[Kyle]

I hadn't seen these before: