Comments on: More on Grasshopper’s “Johnny Cash hover slam” test

By: John

John — Tue, 01 Oct 2013 06:11:52 +0000

The fuel mass needed to decelerate from Mach 6 or Mach 10 is not the same as the fuel mass to get to those speeds. The rocket weighs 18,000 kg empty and carries 372,000 kg of fuel – about 20kg fuel for every kg of rocket. Going up the rocket equation works against you, you need to use fuel to lift fuel. Coming down you just need to reduce horizontal delta v, of a much lighter rocket, say carrying a fuel load approximately equal to the rocket empty weight. Slow down and your now even lighter rocket falls back to earth. Fire the engines again close to the ground and you can touch down.

By: SpaceX shows off Grasshopper rocket’s hop | News Leech

SpaceX shows off Grasshopper rocket’s hop | News Leech — Fri, 12 Apr 2013 07:51:58 +0000

[…] joked that this flight was the “Johnny Cash hover slam,” according to an account from NewSpace Journal. Johnny Cash’s song about a “burning ring of fire” was playing in the background […]

By: Michael Spacex

Michael Spacex — Wed, 20 Mar 2013 22:32:15 +0000

After seperation of the second stage and entire payload plus using up ~80-90% of its own fuel up til stage seperation, the then you have no need to decelerat anything but an almost empty stage and by the last 1000 feet you basically are lifting an empty tank and it’s engines/landing gear which requires low throttle and I believe one engine at that point which only needs a thrust to mass ratio of just >1.

By: Aresia

Aresia — Wed, 13 Mar 2013 00:10:22 +0000

NOt an expert either but I think the point here is that Musk is looking for cost efficiency, not flight efficiency. You have a rocket that can be reused several times, and there are huge savings as a result.

But I also suspect he intends to fly one to Mars and use that as an Earth return vehicle.

By: Kevin

Kevin — Tue, 12 Mar 2013 14:35:33 +0000

Wow! That was awesome! Thanks so much for posting DocM.
I have a question regarding the SpaceX reusability design that I haven’t seen addressed anywhere and I’m wondering whether any of you folk might have some ideas. I would love to hear an explanation of how the extra mass needed for reusability (fuel, legs etc) affects the payload and economics of mass delivery to orbit. From a strictly amateur basis it seems to me that the fuel mass needed to decelerate from near orbit should be the same mass needed to accelerate to that same velocity. How can this work?

By: Stuart

Stuart — Tue, 12 Mar 2013 13:47:29 +0000

A fascinating insider discussion, 2013 is really looking exciting.

By: Stuart

Stuart — Tue, 12 Mar 2013 10:42:34 +0000

I have to ask, has anybody contravened their confidentiality employment agreement?

By: DocM

DocM — Mon, 11 Mar 2013 22:58:21 +0000

You guys really need to read this NSF post

http://forum.nasaspaceflight.com/index.php?topic=30385.msg1023706#msg1023706

Now….pick your jaws off the floor and read these.

http://forum.nasaspaceflight.com/index.php?topic=31075.msg1024620#msg1024620

http://forum.nasaspaceflight.com/index.php?topic=31075.msg1024640#msg1024640

By: Musk on the Dragon glitch, Texas spaceport plans, and needling Bezos « NewSpace Journal

Sun, 10 Mar 2013 14:50:17 +0000

[…] More on Grasshopper’s “Johnny Cash hover slam” test […]

By: Stuart

Stuart — Sun, 10 Mar 2013 09:44:29 +0000

(Corrected version)

An excellent test. The obvious result a rocket stage being able to hover and land safely.

The less obvious result proving the new Merlin 1D engine and the software and sensor suite to control it. I appreciate the opportunity to see the continuing development of this project.
I imagine a system with retractable landing legs is next, I must admit the current landing rig looks pretty heavy. Did anyone notice it appearing to be smoking a bit? Was the stetson wearing manekin there for scale or to find out if it ignited?
The results are very useful whatever comes of this test cycle.If only to sell them to Blue Origin (joke!).
Aresia I believe that you are quite right with your rather insightful comment the results can easily be used as a foundation for the â€œbig prizeâ€ Mars.