Author Topic: SpaceX Reusable Falcon 9 (Grasshopper ONLY) DISCUSSION Thread (5)  (Read 8209 times)


Online aero

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We've seen this picture before and been wow'ed by the crane. But have we looked closely at the landing legs on the stage.

https://twitter.com/elonmusk/status/413772104786780160/photo/1

I dismissed the rocket until today as just the old Grasshopper but on closer examination of the legs, it does not appear to me to be the same set-up as before. And I did see what looks like wheels which obviously cannot be part of the rocket (the tires would burn up) so are ground equipment, unless they are ground crew people standing in the line of sight. Also, I don't see anything resembling what we're sure the flight legs will look like.
Retired, working interesting problems

Offline Avron

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We've seen this picture before and been wow'ed by the crane. But have we looked closely at the landing legs on the stage.

https://twitter.com/elonmusk/status/413772104786780160/photo/1

I dismissed the rocket until today as just the old Grasshopper but on closer examination of the legs, it does not appear to me to be the same set-up as before. And I did see what looks like wheels which obviously cannot be part of the rocket (the tires would burn up) so are ground equipment, unless they are ground crew people standing in the line of sight. Also, I don't see anything resembling what we're sure the flight legs will look like.

I looked. its just the old GH.. and the cowboy.. same legs.. I would know :)

Offline ArbitraryConstant

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Something occurred to me which is obvious but I haven't seen discussed...

With the velocity reduction burn they ALREADY HAVE EVERYTHING needed for the original parachute/splashdown concept to work. Throw a parachute on Cassiope and the worst thing that happens to the stage is salt water.

This may have implications for others that try to retrofit reusability with larger monolithic engines, as I'm pretty sure just about any competent space program could make the velocity reduction burn happen.

Offline Garrett

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With the velocity reduction burn they ALREADY HAVE EVERYTHING needed for the original parachute/splashdown concept to work.
You're forgetting the problem with spin.
- "Nothing shocks me. I'm a scientist." - Indiana Jones

Offline ArbitraryConstant

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You're forgetting the problem with spin.
I'm not. That was the final landing burn. There was no spin problem with the velocity reduction/reentry burn. They reentered fine and the stage was intact until it hit the water at terminal velocity.

What didn't work with passive parachute recovery was reentry. If reentry works, the parachute step is trivial.

Offline ChrisWilson68

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You're forgetting the problem with spin.
I'm not. That was the final landing burn. There was no spin problem with the velocity reduction/reentry burn. They reentered fine and the stage was intact until it hit the water at terminal velocity.

What didn't work with passive parachute recovery was reentry. If reentry works, the parachute step is trivial.

There's some debate about when the spin began.  I'm of the opinion that the spin was established well before the final landing burn, and if the stage had deployed a parachute, it would have been spinning at the time of deployment, leading to a failure of the parachute system.

Offline ArbitraryConstant

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There's some debate about when the spin began.  I'm of the opinion that the spin was established well before the final landing burn, and if the stage had deployed a parachute, it would have been spinning at the time of deployment, leading to a failure of the parachute system.
That's a solvable problem, no?

Even just a drogue parachute deployed at higher altitude would have prevented a lot of the aerodynamic spinup.

Offline Okie_Steve

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Aerial photo of two Grasshopper type vehicles. Credit here http://www.reddit.com/r/spacex/comments/1vkhu1/aerial_photo_of_two_grasshopper_type_vehicles_at/
Picture of F9R/GH2 on McGregor thread. Let the leg speculation begin!

Offline AJW

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The base of the leg will be attached to the octaweb, which we know is structurally very strong.  But the base of the leg is a pivot point during leg deployment so there will be significant force directed inward onto the tank from the upper mount point where the piston is attached.  Once fully extended, the piston arms appear to be nearly parallel with the side of the tank, putting the landing force from the upper mount back along the length of the tank rather than towards the center.

These GH2 leg tests will be very interesting to watch.

Offline Jcc

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The base of the leg will be attached to the octaweb, which we know is structurally very strong.  But the base of the leg is a pivot point during leg deployment so there will be significant force directed inward onto the tank from the upper mount point where the piston is attached.  Once fully extended, the piston arms appear to be nearly parallel with the side of the tank, putting the landing force from the upper mount back along the length of the tank rather than towards the center.

These GH2 leg tests will be very interesting to watch.

The legs in your picture are an old design and different from the final legs, in particular, I think the final legs are longer, and have a wider stance than the ones shown. The deployed angle will be closer to 45 degrees, I think.
http://www.spacex.com/falcon9

Offline rpapo

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The legs in your picture are an old design and different from the final legs, in particular, I think the final legs are longer, and have a wider stance than the ones shown. The deployed angle will be closer to 45 degrees, I think.
http://www.spacex.com/falcon9
That picture was also a Falcon 9 1.0 with legs.  Notice the bumps over the corner engines.  Yes, it is an outdated picture.
An Apollo fanboy . . . fifty years ago.

Offline AJW

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Agreed. Clearly the 1.0 design was for the legs to only extend outwards only a short distance.  GH2 uses the new design but we haven't seen them attached or extended so it will be interesting to see the physics of the new design.  I am very interested in how the piston mechanism works since if the wider the legs are extend the more landing force they will have to absorb.  The old vertical design channeled this force more into what is now the octaweb.  Think how easy it is to crush an empty soda can from the sides vs. from the top and bottom.  You will want as much of the force to go into the octaweb and vertically along the core and not directed perpendicularly against the sides of the core.

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