Author Topic: SpaceX Reusable Falcon 9 (Grasshopper) DISCUSSION Thread (2)  (Read 351044 times)

Offline mr. mark

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Realigned thread to allow for discussion.

Update thread:
http://forum.nasaspaceflight.com/index.php?topic=30708.0

This thread below is a mix of news and discussion, but we needed two seperate threads.
« Last Edit: 12/27/2012 12:33 am by Chris Bergin »

Offline Crispy

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Yes, but now that test flights are underway, it's good to separate the updates from the chatter, as is done with other with other topics.

Offline Chris Bergin

Thread 2. Follow on from:
http://forum.nasaspaceflight.com/index.php?topic=27748.0 - Over 200,000 reads.

Based on the article by some fella called Chris Bergin.

http://www.nasaspaceflight.com/2012/01/spacex-testing-reusable-falcon-9-technology-this-year/

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Offline aero

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So it finally dawns on me that SpaceX already has a resusable Falcon 9 core and Falcon Heavy Booster in the form of the Grasshopper. It has flown twice, (reusable) and except for replacing 8 engines with landing legs for ballast, it's configuration is the same.  As for the argument that Grasshopper has not yet reached staging velocity, well, that is just a controls problem.

I wonder how much refurbishment Grasshopper needs between flights?
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Offline Lars_J

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Grasshopper is NOT a reusable Falcon 9 core. Not even close.

Offline Hauerg

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...
I wonder how much refurbishment Grasshopper needs between flights?
Irrelevant. (As Jim might say.)
Grasshopper is not a booster stage.

Offline aero

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Grasshopper is NOT a reusable Falcon 9 core. Not even close.

Well, it had better be close, else what's the point? There already are several "toy" (sub scale) machines that have launched, landed and re-launched successfully but no one would use their flight controls on a reusable core or booster stage.

Grasshopper does use the tanks and one real engine, so the form factor is close as a result. So are you saying that SpaceX must attach 8 dead engines to Grasshopper before it can stand in for a Falcon 9 core or booster stage? :p

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Offline Crispy

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Grasshopper will not experience anything like the full flight conditions of a F9R 1st stage. The point of it is to learn about the subset of those conditions that can be met with (relatively) low altitude hops and boilerplate landing gear.

Online oldAtlas_Eguy

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Unless I am mistaken the Grasshopper is made up of:


1) A v1.0 tank (probably the qualification flight test tank which would be sitting in storage at McGregor).

2) A v1.0 thrust structure (probably the qualification flight test thrust structure which would be sitting in storage at McGregor). This thrust structure would not need any modifications other than capping off the other 8 prop lines for the other 8 engines not being attached. The legs would be attached at the hold-down pin locations on the thrust structure. Also the add-on engine fairings and other engine compartment covers would not be installed.


3) Of course a set of landing legs which are new and are much heavier than what would be used on a F9R.


4) The addition of SII avionics (IMU, GPS receivers, triple redundant CPU's and other avionics items that in a F9 only exist on SII but are required to be able to fly the Grasshopper). These would probably be new flight certified avionics that would otherwise have actually flown on an F9.


5) A M1D engine probably a test article engine with minimal refurbishment. My guess here would be the first production unit used to do the qualification testing.


You are correct that the Grasshopper is not a F9R version of a v1.1 core since about everything will be different except avionics and a M1D engine. Reuse of hardware that is test articles of real flight hardware would make costs for Grasshopper very low and still achieve the goals of the project which is to develop the software and experience in doing vertical landing with a tall slim structure, measure the forces and other items in the flight performance not easily mathematically modeled without real data. This will gain them the data necessary to do the engineering to define the LV capabilities for a F9R version that reuses only the 1st stage based on a modified F9v1.1 core.

Offline Mongo62

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So would SpaceX eventually build a "Grasshopper 2" based on a F9 v1.1 fuselage, possibly with a methane-burning Merlin engine, or go straight to a F9R 1st stage for use in actual launches?  In their position I would certainly build a second, more advanced Grasshopper, but SpaceX may feel that the original Grasshopper flights provide adequate verification of the fly-back idea.

Offline Elmar Moelzer

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I think it has more in common with the final RF9 than the oh so glorious Ares 1X had with the final Ares1 or the X33 would have had with the final Venture Star.
That said, it is clearly a testbed for the technology needed to do a reusable first stage and NOT a reusable first stage. They can still gather a lot of experience with flight profiles and controls and control software. IIRC they are already working on the next version of grasshopper that will have a full Falcon 9 1.1 first stage tank instead of the F9 1.0 first stage tank and landing legs that are more representative of the final legs. I guess they will start testing that one soon after they (pretty much inevitably) will crash the first one into the ground during a (subsequently infamous) testflight that critics will doubtlessly use to ripp the whole project apart (since for some reason it has become unacceptable to loose a test vehicle these days).
;)
« Last Edit: 11/23/2012 07:02 pm by Elmar Moelzer »

Offline cambrianera

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oldAtlas_Eguy, I agree with you on everything except for:


2) A v1.0 thrust structure (probably the qualification flight test thrust structure which would be sitting in storage at McGregor). This thrust structure would not need any modifications other than capping off the other 8 prop lines for the other 8 engines not being attached. The legs would be attached at the hold-down pin locations on the thrust structure. Also the add-on engine fairings and other engine compartment covers would not be installed.


The thrust structure of grasshopper is completely new, integrated in the frame of the legs, there is no trace of the composite skirt of v1.0, no trace of the v1.0 thrust bearing frame (see pic, you can see the dome of the tank through the frame)
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Offline hrissan

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I think it has more in common with the final RF9 than the oh so glorious Ares 1X had with the final Ares1 or the X33 would have had with the final Venture Star.
That said, it is clearly a testbed for the technology needed to do a reusable first stage and NOT a reusable first stage. They can still gather a lot of experience with flight profiles and controls and control software. IIRC they are already working on the next version of grasshopper that will have a full Falcon 9 1.1 first stage tank instead of the F9 1.0 first stage tank and landing legs that are more representative of the final legs. I guess they will start testing that one soon after they (pretty much inevitably) will crash the first one into the ground during a (subsequently infamous) testflight that critics will doubtlessly use to ripp the whole project apart (since for some reason it has become unacceptable to loose a test vehicle these days).
;)
In the video posted in "Elon Muslk talk in aerospace society" Musk actually says he expects one or two craters as a result of Grasshopper test program. :)

It seems the problem with stage reusability is not in hardware itself (Different legs? Different tank?), but in the algorithms. The thing must know how to fly and how to land.

Flight software must undertand how its current flight differs from desired one and know what to do. And once it understands what to do in every situation, it can fly any comparable vehicle, no matter what parameters it has. Just enter them correctly, and it will land it.

It makes sense to spend time for more general software landing algorithm and then reuse it for every slightly or drastically new core.

Offline Jason1701

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So would SpaceX eventually build a "Grasshopper 2" based on a F9 v1.1 fuselage, possibly with a methane-burning Merlin engine, or go straight to a F9R 1st stage for use in actual launches?  In their position I would certainly build a second, more advanced Grasshopper, but SpaceX may feel that the original Grasshopper flights provide adequate verification of the fly-back idea.

Yes, they have stated they will build a second version of Grasshopper eventually. Or replace the first one if it crashes.

Offline Elmar Moelzer

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hrissan, that is my thoughts exactly. I guess they dont really care that much about the hardware differences for the first version. That one will probably die while they are trying to find all the kinks in the software.

Offline Jim

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I think it has more in common with the final RF9 than the oh so glorious Ares 1X had with the final Ares1 or the X33 would have had with the final Venture Star.


That is far from the truth.  More amazing people nonsense.  The X-33 was as close to the Venturestar as the V1 is to V1.1
« Last Edit: 11/23/2012 08:54 pm by Jim »

Offline Elmar Moelzer

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Quote
The X-33 was as close to the Venturestar as the V1 is to V1.1
How could they be? The X-33 was only suborbital and much smaller. The airframe was going to look very different for Venture Star (in later design iterations, anyway, when the "wings" on VS grew larger and larger). IIRC, the TPS had to be changed too. The manufacturing process would have been completely different because of all that. In later design iterations the VS was envisioned to carry the payload in an external paylaod shroud, which was also different from the X-33.
« Last Edit: 11/23/2012 09:34 pm by Elmar Moelzer »

Offline RocketEconomist327

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It is completely impossible to say that SpaceX (Spacex) will fail with this project just as it is completely impossible to say that SpaceX (Spacex) will succeed with this project.

We should be enjoying the ride and just saying - ya know what man, that #&*^ right there was pretty cool.  Clearly the odds are against them.  However, the mindset, not to mention the superior brain power behind things like this is staggering and enjoyable.

Don't count the chickens before they hatch.  That being said, don't be surprised when they hatch.

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RE327
You can talk about all the great things you can do, or want to do, in space; but unless the rocket scientists get a sound understanding of economics (and quickly), the US space program will never achieve the greatness it should.

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Offline Norm38

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A post in the old thread stated that the next hop would be to 100 feet, and be soon.  Now that it's flown twice, I wonder what sets the flight rate?  Just the time to inspect the engine and refuel?

Now I imagine they'll want to take time to review the previous flight telemetry and plan the objectives of the next flight.  But that could easily mean one hop a week, or more.  It will be interesting to see how close Grasshopper can operate as a "gas-n-go" test bed.
« Last Edit: 11/24/2012 03:06 pm by Norm38 »

Online oldAtlas_Eguy

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By counting the days between the first and second you will have a good measure as to when the next would take place. The actions between flights will be analysis of the data and adjustment of the algorithims , mostly the gain values in the digital feedback control software.

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