Discussion SpaceX's Grasshopper RLV

[Andy44]

Did a quick calculation by watching one of the launch videos and listening to the telemetry read-outs. The upshot is that with a purely ballistic trajectory after 1st stage sep, the stage would only land 600 km or so downrange (and air resistance would mitigate even that distance), so a landing at KSC from a VAFB take-off is probably not a possibility.

VAFB is in California, not Texas.

However, Texas Gulf Coast to Florida Gulf Coast is well over 1000 km.

 

[Deleted Orbinaut]

VAFB is in California, not Texas.

However, Texas Gulf Coast to Florida Gulf Coast is well over 1000 km.

Right.. smacks forehead. I'd just been looking at the SpaceflightNow launch schedule and think I had Vandenberg in mind. I'm in San Diego, so if the conditions are right, I can actually see VAFB launches.

 

[MattBaker]

But isn't launching from Texas over Florida or even other Southern states a big risk, too? Failure is always possible and I wouldn't want a Falcon 9 and especially not a Falcon Heavy failing and falling onto my property...

 

[Urwumpe]

But isn't launching from Texas over Florida or even other Southern states a big risk, too? Failure is always possible and I wouldn't want a Falcon 9 and especially not a Falcon Heavy failing and falling onto my property...

Well, I would have to check this better, but it looks like a 90° azimuth launch would pass approximately between Florida and Cuba from there. A launch into an ISS orbit would go between Cuba and Mexico.

With a small push of the engines, you could change the trajectory of the almost empty stage a lot and increase range effectively or divert laterally to a landing site. But it seems doubtful that the stage would do a RTLS. This would mean around 3500 m/s DV if you also want optimal second stage conditions.

 

[Cosmic Penguin]

Grasshopper featuring Texas Cows (TM):

 

[orb]

Grasshopper featuring Texas Cows (TM):

Get SpaceX Grasshopper! You won't need a herding dog anymore!

 

[Donamy]

That will make for some really tough steak.

 

[DaveS]

Has anyone besides me noticed the fire on the bottom right of the vehicle during the descent stage? I'm not talking about the Merlin 1D exhaust, but a sustained black smoke producing flame on the bottom right of the GH test vehicle that starts during the final few seconds of descent.

 

[Urwumpe]

Has anyone besides me noticed the fire on the bottom right of the vehicle during the descent stage? I'm not talking about the Merlin 1D exhaust, but a sustained black smoke producing flame on the bottom right of the GH test vehicle that starts during the final few seconds of descent.

Not sure what you mean there... it only looks like the gas generator exhaust was scorching something during the descent.

 

[DaveS]

Not sure what you mean there... it only looks like the gas generator exhaust was scorching something during the descent.

That's the gas generator? It almost looks like it's on fire with that kind of exhaust!

 

[Urwumpe]

That's the gas generator? It almost looks like it's on fire with that kind of exhaust!

Yes, it is a lot of rather cold exhaust, simply dumped through a tube without any attempt to generate thrust, you also see that kind of flame on the similar early Atlas launches.

Just look here behind the right exhaust: That is just the gas generator.

 

[kamaz]

Get SpaceX Grasshopper! You won't need a herding dog anymore!

I see great potential for a technology spin-off company...

 

[Alfastar]

I see great potential for a technology spin-off company...

Sorry, but I think Musk already go steal that idea from your mind :lol:

 

[Thunder Chicken]

That's the gas generator? It almost looks like it's on fire with that kind of exhaust!

The trusses on the landing legs seem to be getting a bit scorched due to radiational heating from the thrust and gas generator flame. You can see smoke coming off of them occaisionally. Nothing a little tinfoil won't fix

 

[RGClark]

An appropriate time for these Grasshopper tests, when the DC-X is being celebrated:

20 years ago: Novel DC-X reusable rocket launched into history.
Megan Gannon Space.com
Aug. 16, 2013 at 3:23 PM ET
http://t.nbcnews.com/science/20-years-ago-novel-dc-x-reusable-rocket-launched-history-6C10936007

Bob Clark

 

[Arrowstar]

I notice two distinct exhaust plumes coming from the base of the rocket. Can someone describe what these are?

 

[Thunder Chicken]

One plume is the rocket exhaust from the nozzle, the second is the exhaust from the gas generator.

In Gas Generator Cycle rockets, a small portion of the fuel and oxidizer is burned and used to drive a turbine which in turn drives the fuel and oxidizer pumps.

 

[Arrowstar]

Interesting. Propulsion is one of those disciples that are noticeably missing from an astrodynamics curriculum, so always happy to learn something new. Is the gas generator exhaust used to control the vehicle along side the engine itself or is it considered a fixed perturbation to be accounted for when developing the rocket's control law?

 

[Thunder Chicken]

Interesting. Propulsion is one of those disciples that are noticeably missing from an astrodynamics curriculum, so always happy to learn something new. Is the gas generator exhaust used to control the vehicle along side the engine itself or is it considered a fixed perturbation to be accounted for when developing the rocket's control law?

The gas generator exhaust generally produces a very small amount of thrust, and it generally is in proportion to the main thrust. The control valves that control the flow to the engine also controls the flow to the gas generator, as the gas generator needs to provide more power to the turbopumps as the overall thrust increases.

Practically they can estimate the amount of thrust produced by the generator and account for it. I don't know whether the gas generator nozzle is fixed or gimballed. I'd guess that it would be fixed and they would handle any off-axis moments by gimballing the main nozzle.

 

[C3PO]

The Merlin on SpaceX's upper stages gimbals the gas generator exhaust for roll control.