Author Topic: Grasshopper Discussion (including Grasshopper 2, aka F9R-Dev1) Thread 1  (Read 300621 times)

Offline QuantumG

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As of a week ago (19 Jan 2014) we know Grasshopper 2, aka F9R-Dev1, is in McGregor. See the attached picture.

We were told it will fly from there shortly, before heading off to Spaceport America. If anyone has any less vague information, do tell.

I wonder how long it will be before we see Grasshopper 2 go supersonic, but after that I wonder if we'll see it fly above 100 km and do a retro-propulsive return to launch site. I wonder if we'll see this more than once. I wonder if we'll see this more than once a month.

Interesting times.  :D

« Last Edit: 08/20/2014 11:32 PM by Chris Bergin »
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Offline NovaSilisko

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It may be just me, but I swear GH1's nosecap looks taller than it did in the flight test videos. I'm guessing most likely just a weird camera angle, since side-on photos of GH1 look a lot taller. That or Bigfoot Syndrome.
« Last Edit: 01/25/2014 08:10 AM by NovaSilisko »

Online FutureSpaceTourist

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QuantumG, nice photo - thanks.

I've been wondering what implications the successful reentry of the first F9 v1.1 launch's 1st stage has for Grasshopper testing. In particular, with tests on and data from operational flights does that reduce the need for Grasshopper tests?

I imagine Grasshopper is good for exploring more of the flight envelope, trying more experimental software and/or control system changes etc and perhaps more frequent testing? But I got the feeling even SpaceX were a little surprised at how successful the 1st stage return was.
« Last Edit: 01/25/2014 08:17 AM by FutureSpaceTourist »

Online meekGee

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I agree that they were.  (Surprised).

IMO, GH2 has two goals.

The first is as an R&D tool, to learn about the reentry profile - both nominal and off-nominal conditions.
Some of that may have been trumped by the success of the last F9.1 flights.

The second is as a tool to put hours on the airframe, the engines, and the operating crew, to learn about flying reusable rockets - without being constrained to payloads, launch schedules, and without taking up pad time.

These two goals are sequential.  The success of the recent re-entry attempts, especially if it continues, will make the transition from the first goal to the second happen that much sooner.

I once suggested that if SpaceX encountered difficulty with customers in accepting "used" first stages, an aggressive flight campaign of GH2 can help by demonstrating a large number of cycles on one rocket. The way customers are responding to SpaceX, however, makes this a moot issue - they're showing enough enthusiasm that they might actually push to get to the front of the line...

QG - you're asking about once-per-month.  GH2 is the perfect tool to demonstrate just how fast they can turn around a stage, again without being tied to payload and pad timing issues.  So I think after they're well into goal #2, they'll push to see how "gas and go" they can get.
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Offline cambrianera

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It may be just me, but I swear GH1's nosecap looks taller than it did in the flight test videos. I'm guessing most likely just a weird camera angle, since side-on photos of GH1 look a lot taller. That or Bigfoot Syndrome.

A single pixel gained or lost in such low resolution pics makes a lot of difference.
This way different light conditions can greatly impact the visual width/length ratio (being width smaller than length, one pixel plus or minus has more effect proportionally).
« Last Edit: 01/25/2014 09:09 AM by cambrianera »
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Offline NovaSilisko

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It may be just me, but I swear GH1's nosecap looks taller than it did in the flight test videos. I'm guessing most likely just a weird camera angle, since side-on photos of GH1 look a lot taller. That or Bigfoot Syndrome.

A single pixel gained or lost in such low resolution pics makes a lot of difference.
This way different light conditions can greatly impact the visual width/length ratio (being width smaller than length, one pixel plus or minus has more effect proportionally).

Yeah, like I said. Bigfoot Syndrome (aka misinterpretation of extremely low-resolution images). The rockets in the aerial photo are quite overexposed, which might have something to do with it.
« Last Edit: 01/25/2014 10:54 AM by NovaSilisko »

Offline Karloss12

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I think GH2 will initially be used to learn and improve:
-the limits of the flight profiles, software, sensors etc.
-processes and procedures to turn the core around for re-launch as soon as possible.

Possibly more importantly, SpaceX needs to learn how many upward launches the rocket is good for.  This will involve putting a dummy 2nd stage and payload on top of GH2 and launching it beyond maxQ over and over again until the rockets fatigue limits are established.  The fatigue limits can of course be improved with refined design.  It would be irresponsible and take allot longer if SpaceX solely used the flights of paying customers to establish the fatigue limit.

The rocket failing during re-entry is much less of a commercial and reputational concern compared to the rocket failing on its upward leg with a satellite on board.
« Last Edit: 01/25/2014 11:23 AM by Karloss12 »

Online guckyfan

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Possibly more importantly, SpaceX needs to learn how many upward launches the rocket is good for.  This will involve putting a dummy 2nd stage and payload on top of GH2 and launching it beyond maxQ over and over again until the rockets fatigue limits are established.  The fatigue limits can of course be improved with refined design.  It would be irresponsible and take allot longer if SpaceX solely used the flights of paying customers to establish the fatigue limit.

The rocket failing during re-entry is much less of a commercial and reputational concern compared to the rocket failing on its upward leg with a satellite on board.

If they do that, where would they do it? Dropping a dummy second stage on a typical launch trajectory would require a free range. It seems to me Vandenberg would be a good option. I doubt they can do it in New Mexico.


Offline Avron

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I was wondering what the max velocity/ downrange profile would look like for GH2.
In terms of testing the envelope, it is an ideal test vehicle.
I was also wondering if GH2 would gain more engines over time ( assuming they don't break this one), allow the lofting and test recovery of say the second stage in time. In terms of lofting, I can think of a dozen items that could be launched via a GH2. So it could go from test bed to test support equipment.
All of this would provide inputs to longevity, availability, repeatably, processes and procedures for re-usability. 
One item I would like to see is the added use of some drogue chute to the returning vehicle so that its max velocity is reduced at landing time. I.e. would the mass of a chute offset and provide more capability than the same mass in propellants. I can still see a returning stage gaining a lot of return distance  from downrange and control in x and y axis by steering itself to the landing pad under some chute, thus giving the range more time and confidence, in allowing the  stage to enter the landing area. I.e. if the the control is not there and the stage is not on glide slope, then press the button well before the stage comes close to the LZ. I still see the final breaking burn to touchdown, however, I see that initiated at a much reduced velocity in both z and x axis.

Online Roy_H

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I think GH2 will initially be used to learn and improve:
-the limits of the flight profiles, software, sensors etc.
-processes and procedures to turn the core around for re-launch as soon as possible.

Possibly more importantly, SpaceX needs to learn how many upward launches the rocket is good for.  This will involve putting a dummy 2nd stage and payload on top of GH2 and launching it beyond maxQ over and over again until the rockets fatigue limits are established.  The fatigue limits can of course be improved with refined design.  It would be irresponsible and take allot longer if SpaceX solely used the flights of paying customers to establish the fatigue limit.

The rocket failing during re-entry is much less of a commercial and reputational concern compared to the rocket failing on its upward leg with a satellite on board.

No 2nd stage required. GH2 has only 3 engines.
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Offline Avron

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Re: Grasshopper Discussion (including Grasshopper 2, aka F9R-1)
« Reply #10 on: 01/25/2014 01:04 PM »
Possibly more importantly, SpaceX needs to learn how many upward launches the rocket is good for.  This will involve putting a dummy 2nd stage and payload on top of GH2 and launching it beyond maxQ over and over again until the rockets fatigue limits are established.  The fatigue limits can of course be improved with refined design.  It would be irresponsible and take allot longer if SpaceX solely used the flights of paying customers to establish the fatigue limit.

The rocket failing during re-entry is much less of a commercial and reputational concern compared to the rocket failing on its upward leg with a satellite on board.

If they do that, where would they do it? Dropping a dummy second stage on a typical launch trajectory would require a free range. It seems to me Vandenberg would be a good option. I doubt they can do it in New Mexico.



I dont see then trying the typical trajectory for the second stage tests, as that would need orbital speed, I see them test some of the return path of that stage.

Offline kirghizstan

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Re: Grasshopper Discussion (including Grasshopper 2, aka F9R-1)
« Reply #11 on: 01/25/2014 01:29 PM »
With only three engines you cannot put a dummy stage on it that would do anything to simulate anything important. You need 9 engines for that which could be GH2.5

Offline cuddihy

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Grasshopper Discussion (including Grasshopper 2, aka F9R-1)
« Reply #12 on: 01/25/2014 01:38 PM »
That seems like a silly way to test fatigue limits. Why wouldn't they just qualify the stage on a stand and then do metal sample tests?

You can do thousands of fatigue cycles in the time to prep the GH for one flight. Flights are more useful for operational issues like how the stage performs under various flight conditions, and identifying failure-prone parts or subsystems.
« Last Edit: 01/25/2014 01:46 PM by cuddihy »

Offline Avron

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Re: Grasshopper Discussion (including Grasshopper 2, aka F9R-1)
« Reply #13 on: 01/25/2014 01:58 PM »
That seems like a silly way to test fatigue limits. Why wouldn't they just qualify the stage on a stand and then do metal sample tests?

You can do thousands of fatigue cycles in the time to prep the GH for one flight. Flights are more useful for operational issues like how the stage performs under various flight conditions, and identifying failure-prone parts or subsystems.

Agreed, once you know the loading the subsystem will need to endure, the testing must be done in a lab, if needed. In most cases the MTBF can be calculated, knowing the material properties and expected loading. However, there is nothing that beats real world tests. 

Online RonM

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Re: Grasshopper Discussion (including Grasshopper 2, aka F9R-1)
« Reply #14 on: 01/25/2014 02:11 PM »
That seems like a silly way to test fatigue limits. Why wouldn't they just qualify the stage on a stand and then do metal sample tests?

You can do thousands of fatigue cycles in the time to prep the GH for one flight. Flights are more useful for operational issues like how the stage performs under various flight conditions, and identifying failure-prone parts or subsystems.

Agreed, once you know the loading the subsystem will need to endure, the testing must be done in a lab, if needed. In most cases the MTBF can be calculated, knowing the material properties and expected loading. However, there is nothing that beats real world tests.

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Offline ChefPat

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Re: Grasshopper Discussion (including Grasshopper 2, aka F9R-1)
« Reply #15 on: 01/25/2014 02:14 PM »
With the tests done on F9v1.1/CASIOPE, SES-8 & possibly THAICOM-6 is it possible that F9R-1 has become superfluous?
I did read (but can't find again) that SES-8 successfully re entered unpowered & broke up on the ocean surface.
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Offline Okie_Steve

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Re: Grasshopper Discussion (including Grasshopper 2, aka F9R-1)
« Reply #16 on: 01/25/2014 02:20 PM »
I've been wondering what implications the successful reentry of the first F9 v1.1 launch's 1st stage has for Grasshopper testing.
I agree that getting down to the surface on the first try was a big surprise - for every one. I expect that launching with legs through max-Q and repeated reuse i.e. "gas and go" will continue for quite a while to collect reliability data. However, future Grasshopper tests may be in the peculiar situation of using the landing data from the first stage recovery attempt rather than generating it as originally planned.

Online guckyfan

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Re: Grasshopper Discussion (including Grasshopper 2, aka F9R-1)
« Reply #17 on: 01/25/2014 02:28 PM »
It has been speculated that Falcon 9R flights will be needed to show precision landing as a prerequisite for permission for land landing of incoming stages. That sounds reasonable to me and can be shown with the test vehicle.

Doing repeated flights with dummy second stages emulating real life trajectories and loads seems more sensible done with real stages that have come back from commercial flights.

Online AncientU

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Re: Grasshopper Discussion (including Grasshopper 2, aka F9R-1)
« Reply #18 on: 01/25/2014 02:34 PM »
That seems like a silly way to test fatigue limits. Why wouldn't they just qualify the stage on a stand and then do metal sample tests?

You can do thousands of fatigue cycles in the time to prep the GH for one flight. Flights are more useful for operational issues like how the stage performs under various flight conditions, and identifying failure-prone parts or subsystems.

Agreed, once you know the loading the subsystem will need to endure, the testing must be done in a lab, if needed. In most cases the MTBF can be calculated, knowing the material properties and expected loading. However, there is nothing that beats real world tests.
Putting the first returned stage back on the test stand will be the real test of core structural integrity.  I believe that GH2/F9R-1 will again be a software development test bed.
« Last Edit: 01/25/2014 02:35 PM by AncientU »
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Offline macpacheco

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Re: Grasshopper Discussion (including Grasshopper 2, aka F9R-1)
« Reply #19 on: 01/25/2014 04:09 PM »
I think GH2 will initially be used to learn and improve:
-the limits of the flight profiles, software, sensors etc.
-processes and procedures to turn the core around for re-launch as soon as possible.

Possibly more importantly, SpaceX needs to learn how many upward launches the rocket is good for.  This will involve putting a dummy 2nd stage and payload on top of GH2 and launching it beyond maxQ over and over again until the rockets fatigue limits are established.  The fatigue limits can of course be improved with refined design.  It would be irresponsible and take allot longer if SpaceX solely used the flights of paying customers to establish the fatigue limit.

The rocket failing during re-entry is much less of a commercial and reputational concern compared to the rocket failing on its upward leg with a satellite on board.

True, but this would make more sense using a complete F9R first stage.
If you need to test the full structural tolerance of the vehicle on repeated cycles, you need the full thrust of 9 engines at liftoff, nominal MaxQ conditions, also requiring full fuel on the first stage and something heavy enough to make up for the 2nd stage + a good size payload, perhaps the mass simulator should be 99% water, that gets dumped at max altitude, otherwise the vehicle will be too heavy for the retro burns.
As soon as SpaceX gets the first few S1's recovered, they will have plenty of F9R S1 to add a mass simulator perhaps call it GH3.
It's interesting that the vehicle goes high enough and on a typical launch profile that re-entry is fast/hot enough to test the way back fully too, testing the whole stage one launch cycle.
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