Author Topic: SpaceX Reusable Falcon 9 (Grasshopper ONLY) DISCUSSION Thread (4)  (Read 293317 times)


Offline Robotbeat

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Note number one: The next grasshopper isn't supposed to be called "Grasshopper," from what I hear.
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Offline tigerade

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Note number one: The next grasshopper isn't supposed to be called "Grasshopper," from what I hear.

What will it be called?  F9R?

Offline IRobot

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Think I read F9R-1 somewhere.

Offline AnalogMan

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Note number one: The next grasshopper isn't supposed to be called "Grasshopper," from what I hear.

What will it be called?  F9R?

In correspondence copied to the FCC in support of an application for a radio license for use with a test launch vehicle at Spaceport America, SpaceX refer to this vehicle variously as:

"STA for Grasshopper in Las Cruces New Mexico"
"SpaceX Falcon-9 "reusable" "
"Falcon 9R test vehicle in Spaceport America"


This dates from July this year - I'm sure its got other names too!
« Last Edit: 09/17/2013 06:20 pm by AnalogMan »

Offline go4mars

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How far could Grasshopper 2 translate, land, and return to base? 
Could you send it a few hundred miles, land it briefly, drop off an oilfield part (or something), and then off it goes back to base?    All 9 1D's are restartable IIRC. 

I was reminded this week how much offshore rig time is worth per hour.  A lot! 

Oh, and consider this the obligatory post for thread 4 reminding about potential for use of Grasshopper 2 in fighting forest fires by creating burn lines. 
Elasmotherium; hurlyburly Doggerlandic Jentilak steeds insouciantly gallop in viridescent taiga, eluding deluginal Burckle's abyssal excavation.

Offline ChrisWilson68

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How far could Grasshopper 2 translate, land, and return to base? 
Could you send it a few hundred miles, land it briefly, drop off an oilfield part (or something), and then off it goes back to base?    All 9 1D's are restartable IIRC. 

I was reminded this week how much offshore rig time is worth per hour.  A lot! 

Oh, and consider this the obligatory post for thread 4 reminding about potential for use of Grasshopper 2 in fighting forest fires by creating burn lines. 

The legs are probably too weak to hold the stage up when it has anything close to a full load of fuel.  They're designed only to hold it up when landing nearly empty.  So it can't take off from those legs with much fuel.

And the fuel costs to fly it a few hundred miles are going to be very high compared with a helicopter or fixed-wing aircraft.  Plus, running the engines puts a lot of wear and tear on them.  F9R could be incredibly successful if each engine is good for 20 flights.  A point-to-point transport like you're talking about would be pretty costly if the engines had to be replaced after 20 flights, or even after 200.

Offline douglas100

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How far could Grasshopper 2 translate, land, and return to base? 
Could you send it a few hundred miles, land it briefly, drop off an oilfield part (or something), and then off it goes back to base?    All 9 1D's are restartable IIRC. 

I was reminded this week how much offshore rig time is worth per hour.  A lot! 

Oh, and consider this the obligatory post for thread 4 reminding about potential for use of Grasshopper 2 in fighting forest fires by creating burn lines. 

Grasshopper 2/F9R-1 is a engineering development vehicle. Its purpose is not to deliver anything to anywhere. This thread is not about point-to-point rocket powered vehicles. Your post is OT. If you want to discuss point to point rocket delivery, start another thread.
Douglas Clark

Offline go4mars

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...thread is not about point-to-point rocket powered vehicles. Your post is OT...
I'll start over with no applications suggested.

Grasshopper 1 translated 100 m recently. 
I imagine that Grasshopper 2 could translate a lot further, given 9 Merlins and full tanks.  Any speculations as to how far it could go sideways in the following cases:

1) Return to launch pad like the recent Grasshopper 1 test.
2) Landing on a different pad elsewhere. 
Elasmotherium; hurlyburly Doggerlandic Jentilak steeds insouciantly gallop in viridescent taiga, eluding deluginal Burckle's abyssal excavation.

Offline malu5531

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Grasshopper 1 translated 100 m recently. 
I imagine that Grasshopper 2 could translate a lot further, given 9 Merlins and full tanks.  Any speculations as to how far it could go sideways in the following cases:

1) Return to launch pad like the recent Grasshopper 1 test.
2) Landing on a different pad elsewhere. 

I calculate a single Grasshopper 2 (F9R / v1.1 first stage) would have ~9173 m/s delta-v capacity (4% dry/wet ratio + 0.5% residual fuel). => max possible hoover time: 9173 / 9.81 = 935 seconds.

I'm not sure what a reasonable horizontal speed might be, but let's keep it the same as Grasshopper; ~100m/min or say 2 m/s. Maintaining this speed will require some fuel and slightly lower the actual hoover time, but let's ignore this and get maximums;

1) 935/2*2 => ~935 m
2) 935*2 => ~1870 m

Note; This is for a "slow horizontal translate" type of transport / flight, per request.

However, ballistic transport would be much more efficient, since hoover basically is 100% gravity loss. With ballistic trajectory, it could probably self-ferry anywhere within north america and perhaps even to Europe, Africa and South America (guesstimate).

(OT, but cool application of F9R; Aircraft-like ballistic transport of Cargo and Passengers (using a ~50-100mT transporter-pod for F9R to launch into a ballistic trajectory). Anyone see a business case for less than 30 minutes across the atlantic?;))
« Last Edit: 09/03/2013 02:47 pm by malu5531 »

Offline VatTas

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(OT, but cool application of F9R; Aircraft-like ballistic transport of Cargo and Passengers (using a ~50-100mT transporter-pod for F9R to launch into a ballistic trajectory). Anyone see a business case for less than 30 minutes across the atlantic?;))

Ridiculously slow, ridiculously expensive mean of point-to-point transport. If you have 50mT on top of F9R first stage, you will end up several hundred km downrange, not across Atlantic.
Even if viewed from self-ferry perspective, it doesn't make a lot of sense. If you want to move F9R stage more than few hundred km, you will have to deal with near-orbital reentry forces and heating. So just get it onto truck or barge instead...

Please, move this discussion about p2p suborbital transportation somewhere else. It is really OT in Grasshopper thread.

Offline Norm38

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From this article:  http://www.spacenews.com/article/launch-report/37094musk-says-spacex-being-%E2%80%9Cextremely-paranoid%E2%80%9D-as-it-readies-for-falcon-9%E2%80%99s

Quote
ďWeíve never attempted to land Grasshopper on water. We donít know if the radar system will detect the water surface level accurately. We donít know all sorts of things, so I really give it a very tiny chance of success. But weíre going to see what data we can learn,Ē Musk said.

Is this the first direct confirmation we have that Grasshopper uses radar in the control loop?
« Last Edit: 09/06/2013 04:35 pm by Norm38 »

Offline Joel

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I find it interesting that Musk thinks that there's a 10 % possibility to "land" the stage on water.

We've heard that the legs will also be used as flight control surfaces (right?), but this stage doesn't have any legs. Does it mean that the legs are only used for flight control during the last portion of the trajectory, to steer the stage to the pad (or away from the pad, should the engine fail)?

Offline Joel

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Is this the first direct confirmation we have that Grasshopper uses radar in the control loop?

Nope, that was known. See e.g. https://twitter.com/elonmusk/status/353309492131278848

Offline simonbp

I'm not sure what he means about the radar's ability to detect water; this isn't exactly the first time someone has pointed a radar at the ocean! On the other hand, restarting the engine sounds like a much larger risk.

Offline Robotbeat

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I'm not sure what he means about the radar's ability to detect water; this isn't exactly the first time someone has pointed a radar at the ocean! On the other hand, restarting the engine sounds like a much larger risk.

It's not about radar's ability to work, it's about this specific implementation. Just because something works in principle doesn't mean it's proven to work in a specific implementation. Also, what are the exact conditions at the splashdown site? Sea state? Angle? Humidity? You also have to ensure no false-positives.

Engine restarts, on the other hand, can be tested quite a lot with plenty of extra oomph. But still, it's an extra thing to go wrong.
« Last Edit: 09/06/2013 05:38 pm by Robotbeat »
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

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Online JBF

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I'm not sure what he means about the radar's ability to detect water; this isn't exactly the first time someone has pointed a radar at the ocean! On the other hand, restarting the engine sounds like a much larger risk.

False returns are common with radar pointing at a fluid surface. 
"In principle, rocket engines are simple, but thatís the last place rocket engines are ever simple." Jeff Bezos

Offline simonbp

Yes, but it's something that is easily handled by statistical signals processing. Ocean-hugging anti-ship missiles have been doing this for decades. There are probably numerous AIAA and IEEE papers on the subject. Again, relative to the Merlin relight, the radar is of minimal concern.

Online JBF

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Yes, but it's something that is easily handled by statistical signals processing. Ocean-hugging anti-ship missiles have been doing this for decades. There are probably numerous AIAA and IEEE papers on the subject. Again, relative to the Merlin relight, the radar is of minimal concern.

Depends on how tight the timing is. Remember that the landing profile is engines on at the last possible minute so that it lands exactly when velocity is killed, no hovering.
"In principle, rocket engines are simple, but thatís the last place rocket engines are ever simple." Jeff Bezos

Offline PreferToLurk

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Yes, but it's something that is easily handled by statistical signals processing. Ocean-hugging anti-ship missiles have been doing this for decades. There are probably numerous AIAA and IEEE papers on the subject. Again, relative to the Merlin relight, the radar is of minimal concern.

I am sure they have a solution they feel comfortable with or they wouldn't even make the attempt.  Point being that it hasn't been tested.  They expect to detect the water. They also expected to be able to approach the ISS on their first attempt, but the dragon eye software just couldn't get a clean reading and they had to patch it.  There will be no time for a software patch on this test. 

The larger point is that Must was merely using one example to illustrate the fact that they have many unknowns and any one of them could prevent a successful soft touchdown.  Just because he picked one example over another is no indication of which one might be most risky. Besides, he likely intentionally brought up an example which might not be particularly obvious just to emphasize the number of critical systems that have to work perfectly for them to pull this off.

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