Author Topic: SpaceX COTS Demo 1 Updates  (Read 638947 times)

Offline Jim

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Re: COTS Demo 1
« Reply #220 on: 09/18/2010 03:41 am »

1.  other similar class vehicles is hardly an abnormal type of test.


2. They don't want it to be expendable, they want to recover the first stage.

3. And even if it has been hot fired, there were tweaks to their system to eliminate roll off the pad. Perhaps they want to test pad loads or something. Also they had a problem previously with their test stand not having the exact same configuration as the pad. What's wrong with being extra careful knowing there is precedent for issues there?

1.  Yes it is abnormal.  Any more than one is

2.  That has nothing to do with it

3. roll can't be fixed by static firing.  Test pad loads used weights and hydraulic cylinders.

Offline spacetraveler

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Re: COTS Demo 1
« Reply #221 on: 09/18/2010 03:48 am »
I don't know why they are doing it. I'm just saying I think you are being a bit presumptuous to take the opinion that there could be no valid reason whatsoever for them doing it.

During the last flights static fire they uncovered a valve issue which was different from the test stand. So there is precedent for this procedure uncovering problems for them.

If they continue to do it and find no more issues, perhaps they will drop it on future flights. But there's nothing wrong with being extra cautious towards the beginning with the vehicle's history so new.
« Last Edit: 09/18/2010 03:50 am by spacetraveler »

Offline Antares

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Re: COTS Demo 1
« Reply #222 on: 09/18/2010 04:18 pm »
1) There are valid reasons, but the trade is poor.  I mean, there's ALWAYS something more that could be done.  But every step has a cost.  There are cheaper (albeit less foolproof) ways to do what they're doing.  The increase in mission success for an on-pad static fire and some of the other things they do are negligible IMEO.

2) That was a first-use issue, which could have been uncovered in ways that did not risk the flight hardware.  There shouldn't be other similar problems this time, though I grant that all launch systems need a 3-4 flows to shake things down.
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Offline Ben the Space Brit

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Re: COTS Demo 1
« Reply #223 on: 09/18/2010 04:50 pm »
I think that one thing to remember is that Falcon-9 Flight-2 is not a flight by a mature launch vehicle by a mature space launch organisation.  SpaceX are still feeling their way on some things, including debugging their LVs.  So, understandably, they're doing as many tests as possible in an attempt to ensure (as far as this can be ensured) that they won't lose possibly a year because of a launch failure on this mission.

Test fires will probably vanish from the schedule after they have developed more confidence in the vehicle and their own proceedures.
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Offline SpacexULA

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Re: COTS Demo 1
« Reply #224 on: 09/18/2010 05:23 pm »
Static fires are not for software testing.  They are only for propulsion system testing

Could this be a test of the Vibration/Acoustic environment that the Dragon will experience?  You would think that this information could have been collected from the 1st launch, but if as you say, the test serves to purpose for the launcher it' has to be the payload right?

I have a hard time belieiving that SpaceX does not have folks just as smart as Jim & Antares working for them, so they must know this test is not needed for the launcher, no way they are just doing this for the fun of it.
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Offline mmeijeri

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Re: COTS Demo 1
« Reply #225 on: 09/18/2010 05:26 pm »
Static fires are not for software testing.  They are only for propulsion system testing

End to end is further than you think <-- software testing maxim.

Not saying that is the reason in this case.
« Last Edit: 09/18/2010 05:31 pm by mmeijeri »
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Offline R.Simko

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Re: COTS Demo 1
« Reply #226 on: 09/18/2010 06:06 pm »
Before the first flight of Falcon 9 Elon talked about the importance of that first flight and that they were going to do as much testing as possible.  I'm sure that flights 1-3 of Falcon one was in his mind.  This second flight and first COTS test flight could be considdered every bit as important.  SpaceX needs a very good flight, if they are going to have any chance of having COTS test flights 2 and 3 combined into a single flight, thereby saving them time and money.

There might be some concerns with changes they have made since F9 flight one, or SpaceX might see it as just one more precaution to take.  I agree with Ben and others, that this test will eventually be eliminated.

Offline mr. mark

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Re: COTS Demo 1
« Reply #227 on: 09/18/2010 08:53 pm »
Here is a link to a Spaceref.com article that includes the first picture of the Dragon cargo capsule along with some pictures of the 2nd Falcon 9.

http://www.spaceref.com/news/viewnews.html?id=1438
« Last Edit: 09/19/2010 12:07 am by mr. mark »

Offline simonbp

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Re: COTS Demo 1
« Reply #228 on: 09/18/2010 11:02 pm »
+19 EELVs with only 1 pad test firings
+100 Delta II's with none

+1 Delta IV H that failed due to software on first flight
+1 Delta III that failed due to software on first flight
+1 Ariane V that failed due to software on first flight

Notice a trend?

And yes, static fires do provide info for the GNC folks, especially on Falcon 9 where guidance is through differential thrust (unlike Delta or Atlas)...

Online ugordan

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Re: COTS Demo 1
« Reply #229 on: 09/18/2010 11:10 pm »
+1 Delta IV H that failed due to software on first flight

Really?

Quote
And yes, static fires do provide info for the GNC folks, especially on Falcon 9 where guidance is through differential thrust (unlike Delta or Atlas)...

???

Offline kevin-rf

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Re: COTS Demo 1
« Reply #230 on: 09/18/2010 11:55 pm »
+1 Delta IV H that failed due to software on first flight

Really?


Even Wiki lists it as:

Due to Cavitation in the propellant lines causing sensors registered depletion of propellant. The strap-on, and later core CBC engines shut down prematurely.

Yes it was a software commanded shutdown, but it had a real hardware based cause.
« Last Edit: 09/18/2010 11:56 pm by kevin-rf »
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Offline Lars_J

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Re: COTS Demo 1
« Reply #231 on: 09/19/2010 12:00 am »
+19 EELVs with only 1 pad test firings
+100 Delta II's with none

+1 Delta IV H that failed due to software on first flight
+1 Delta III that failed due to software on first flight
+1 Ariane V that failed due to software on first flight

Notice a trend?

And yes, static fires do provide info for the GNC folks, especially on Falcon 9 where guidance is through differential thrust (unlike Delta or Atlas)...

I don't think so... All 9 engines gimbal. (at least the outer 8 do) - doing differential thrust would cause too much of a payload penalty, but I could be wrong. The Merlin 1C's in the F9 1st stage are designed to run at full thrust for the entire running time. They even shut off two engines before MECO instead of throttling down.
« Last Edit: 09/19/2010 12:10 am by Lars_J »

Online ugordan

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Re: COTS Demo 1
« Reply #232 on: 09/19/2010 12:37 am »
Yes it was a software commanded shutdown, but it had a real hardware based cause.

In other words, the software acted as expected. The D-IVH premature shutdowns were not software faults.

Offline Jim

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Re: COTS Demo 1
« Reply #233 on: 09/19/2010 03:51 am »
Static fires are not for software testing.  They are only for propulsion system testing

End to end is further than you think <-- software testing maxim.

Not saying that is the reason in this case.

flight software is not tested in static firing, the vehicle is not moving

Offline Jim

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Re: COTS Demo 1
« Reply #234 on: 09/19/2010 03:54 am »
+19 EELVs with only 1 pad test firings
+100 Delta II's with none

+1 Delta IV H that failed due to software on first flight
+1 Delta III that failed due to software on first flight
+1 Ariane V that failed due to software on first flight

Notice a trend?

And yes, static fires do provide info for the GNC folks, especially on Falcon 9 where guidance is through differential thrust (unlike Delta or Atlas)...

Incorrect.  GNC software is not tested with static fires.  None of those errors would have been uncovered with a static fire. 

Offline mmeijeri

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Re: COTS Demo 1
« Reply #235 on: 09/19/2010 09:35 am »
flight software is not tested in static firing, the vehicle is not moving

I don't understand the logic. Obviously the flight software has been thoroughly and continually tested since long before the static test (and if they're doing it right even before it was written). And obviously there any many important areas that don't get tested with a static test. But every test helps. The vehicle still shakes, sensors are measuring things, valves move. Things could possibly go wrong at this stage. And those are the things you test for. Again, I'm not saying this is their reason and I'm not saying other companies are doing it wrong. I'm just saying that as a software guy I would consider such a test valuable. Depending on the cost of such a test, which I don't know, it may or may not be worth it.
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Offline Jim

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Re: COTS Demo 1
« Reply #236 on: 09/19/2010 03:02 pm »
flight software is not tested in static firing, the vehicle is not moving

I don't understand the logic. Obviously the flight software has been thoroughly and continually tested since long before the static test (and if they're doing it right even before it was written). And obviously there any many important areas that don't get tested with a static test. But every test helps. The vehicle still shakes, sensors are measuring things, valves move. Things could possibly go wrong at this stage. And those are the things you test for. Again, I'm not saying this is their reason and I'm not saying other companies are doing it wrong. I'm just saying that as a software guy I would consider such a test valuable. Depending on the cost of such a test, which I don't know, it may or may not be worth it.

I.  non flight software is usually use for static tests.
2.  Most sensors on a vehicle are not used in the  guidance (flight) software, the data is just telemetered to the ground.
3.  There is very little of the guidance software that deals with the propulsion system.  Other than thrust chamber ok switches/chamber pressures and occasionally propellant utilization, there is little interaction of the flight software with the rest of the vehicle.

4.  Guidance (flight) software steers the vehicle and controls events.  Most vehicles have separate engine controllers that operate the engine.  The guidance system only issues start, shutdown and throttle level commands. The engine controller does all the other necessary computations for valve movements.


Offline Antares

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Re: COTS Demo 1
« Reply #237 on: 09/19/2010 06:56 pm »
The Delta III wasn't a (edit:) testable software problem either.  Sheesh, Simon, I usually disagree with you on policies; but you did yourself no favors with that post.
« Last Edit: 09/19/2010 11:55 pm by Antares »
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Offline mmeijeri

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Re: COTS Demo 1
« Reply #238 on: 09/19/2010 07:10 pm »
I.  non flight software is usually use for static tests.
2.  Most sensors on a vehicle are not used in the  guidance (flight) software, the data is just telemetered to the ground.
3.  There is very little of the guidance software that deals with the propulsion system.  Other than thrust chamber ok switches/chamber pressures and occasionally propellant utilization, there is little interaction of the flight software with the rest of the vehicle.

4.  Guidance (flight) software steers the vehicle and controls events.  Most vehicles have separate engine controllers that operate the engine.  The guidance system only issues start, shutdown and throttle level commands. The engine controller does all the other necessary computations for valve movements.

Thanks for that detailed information! About the software for the engine controller: in a vertically integrated company like SpaceX, is there a particular reason for the engine controller to be physically located on the engine? Couldn't the controller be run on the same processor as the flight software? It's software after all.
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Offline kkattula

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Re: COTS Demo 1
« Reply #239 on: 09/20/2010 04:36 am »
Quote from: mmeijeri
Thanks for that detailed information! About the software for the engine controller: in a vertically integrated company like SpaceX, is there a particular reason for the engine controller to be physically located on the engine? Couldn't the controller be run on the same processor as the flight software? It's software after all.

There are multiple sensor inputs and actuator outputs to each engine.
Why would you run all those lines back to the LV guidance computer?

IIRC, each Merlin has just one ethernet connection plus power from the batteries.

« Last Edit: 09/20/2010 04:36 am by kkattula »

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