Author Topic: SpaceX: General Falcon and Dragon discussion (Thread 9)  (Read 408144 times)

Offline Robotbeat

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Re: SpaceX: General Falcon and Dragon discussion (Thread 9)
« Reply #40 on: 09/02/2013 01:41 am »
The SpaceX press release was about a single Merlin 1d engine achieving the equivalent firing time of 10 full missions. Are you going to tell me that a single /ablative/ RS-68 was fired for more than 10 times a full mission duration burn? If so, can you give a press release?

EDIT: Looking at the actual figures, it looks like an RS-68 was fired for 4000s, and the maximum flight duration (allowed) is about 1200s, so it was about 3 times the maximum flight duration. No single RS-68 engine was qualified for over 4000s that I can tell.
« Last Edit: 09/02/2013 01:52 am by Robotbeat »
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Offline ChrisWilson68

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Re: SpaceX: General Falcon and Dragon discussion (Thread 9)
« Reply #41 on: 09/02/2013 01:42 am »
It's always safer, for any individual mission, to take all the performance the first stage has got.  So the customer has to accept that in return for a cheaper launch, they are accepting a higher chance of mission failure. 

That just means it's safer to use the same launcher but not do reuse versus that same launcher with reuse.  That doesn't mean it's safer versus another launcher.

There are many factors that go into safety, and having lots of extra margin in the first stage that can be applied to give the second stage lots more margin is only one of them.  It's far from clear that this is the biggest factor determining which of two launchers is safer.

In other words, Falcon 9v1.1 expendable might be 1.0001x as safe as Faclon 9R, but both might be 1.5x or 5x as safe as their competition (or 0.2x as safe, for that matter).

Online LouScheffer

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Re: SpaceX: General Falcon and Dragon discussion (Thread 9)
« Reply #42 on: 09/02/2013 01:50 am »

But otherwise, the customer is explicitly accepting a lower chance of mission success in return for a cheaper launch.  And if they have somehow missed this point, I'm certain the competitors will be happy to point it out, and the insurance companies will use it as a reason to raise premiums.
BOTH the first and second stages have a lot of margin. The second stage is going to do another very long burn after putting the payload into orbit. 200m/s would be fine. The odds are much greater that it simply wouldn't restart, which wouldn't affect the main payload.

The main payload is tiny. It's comical how over-sized Falcon 9 v1.1 is for this mission. It's about 25 times more powerful than necessary. What the stages plan on doing after separation isn't likely to make any difference to the primary payload.
Sure, for this mission I agree.  But this will not be true for a mission using the full capacity of a 9R.  In this case you have the risk that a second stage underperformance (as happened on a Delta a few months ago) could doom a mission which would have worked if re-usability was not attempted.

Offline pippin

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Re: SpaceX: General Falcon and Dragon discussion (Thread 9)
« Reply #43 on: 09/02/2013 01:52 am »
The SpaceX press release was about a single Merlin 1d engine achieving the equivalent firing time of 10 full missions. Are you going to tell me that a single /ablative/ RS-68 was fired for more than 10 times a full mission duration burn? If so, can you give a press release?

See the paper above (I edited my post)

And no, the SpaceX press release was not about a single engine (unless they built only one for the test program), it was about "the Merlin 1D":
Quote
Through a 28 test qualification program, the Merlin 1D accumulated 1,970 seconds of total test time, the equivalent run time of over 10 full mission durations, and is now fully qualified to fly on the Falcon 9 rocket.
The program included four tests at or above the power (147,000 pounds of thrust) and duration (185 seconds) required for a Falcon 9 rocket launch.

Offline Robotbeat

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Re: SpaceX: General Falcon and Dragon discussion (Thread 9)
« Reply #44 on: 09/02/2013 01:55 am »

But otherwise, the customer is explicitly accepting a lower chance of mission success in return for a cheaper launch.  And if they have somehow missed this point, I'm certain the competitors will be happy to point it out, and the insurance companies will use it as a reason to raise premiums.
BOTH the first and second stages have a lot of margin. The second stage is going to do another very long burn after putting the payload into orbit. 200m/s would be fine. The odds are much greater that it simply wouldn't restart, which wouldn't affect the main payload.

The main payload is tiny. It's comical how over-sized Falcon 9 v1.1 is for this mission. It's about 25 times more powerful than necessary. What the stages plan on doing after separation isn't likely to make any difference to the primary payload.
Sure, for this mission I agree.  But this will not be true for a mission using the full capacity of a 9R.  In this case you have the risk that a second stage underperformance (as happened on a Delta a few months ago) could doom a mission which would have worked if re-usability was not attempted.
But if you have reusability, if you do it right, it's also possible to have greater confidence in the flight hardware than expendable, since the flight hardware has actually flown multiple missions already and proven itself many times in flight which can be said of no expendable launch vehicle airframes. Would you rather fly on the first or the fortieth flight of a newly minted 737?

And again, the first stage will carry a lot of excess propellant that could be used in case of engine-out instead of flyback maneuvers even in reusable flights, so every "Reusable" flight will have significant margin that can be used at the expense of the first stage (if it were an expendable flight, you might instead include a secondary payload).
« Last Edit: 09/02/2013 02:13 am by Robotbeat »
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Offline Robotbeat

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Re: SpaceX: General Falcon and Dragon discussion (Thread 9)
« Reply #45 on: 09/02/2013 02:01 am »
The SpaceX press release was about a single Merlin 1d engine achieving the equivalent firing time of 10 full missions. Are you going to tell me that a single /ablative/ RS-68 was fired for more than 10 times a full mission duration burn? If so, can you give a press release?

See the paper above (I edited my post)

And no, the SpaceX press release was not about a single engine (unless they built only one for the test program), it was about "the Merlin 1D":
Quote
Through a 28 test qualification program, the Merlin 1D accumulated 1,970 seconds of total test time, the equivalent run time of over 10 full mission durations, and is now fully qualified to fly on the Falcon 9 rocket.
The program included four tests at or above the power (147,000 pounds of thrust) and duration (185 seconds) required for a Falcon 9 rocket launch.
Okay, so the qualification program was shorter. How is that a problem? RS-68's flight qualification program was much shorter than SSME's and Boeing/Rocketdyne bragged about it being so much shorter. But remember, the flight time of a Merlin 1D is also shorter, about half of what a core RS-68 engine does in a Delta IV Heavy launch.
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Offline Robotbeat

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Re: SpaceX: General Falcon and Dragon discussion (Thread 9)
« Reply #46 on: 09/02/2013 02:10 am »
They've done at least two or three equivalent mission durations of firings of the integrated first stage. Cumulatively, that's 18-27 mission-duration firings for the engines, not counting individual firing. I would guess if you include every time they test-fired a Merlin 1D or a development Merlin 1D, the total cumulative time may be over 100 mission duration firings. They've built several dozen of these engines, now.

And I believe Vulcain 2 was "qualified in flight," as will the new Merlin Vacuum, since vacuum testing is quite expensive. (though obviously full-duration non-vacuum ground tests were done)
« Last Edit: 09/02/2013 02:14 am by Robotbeat »
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Offline pippin

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Re: SpaceX: General Falcon and Dragon discussion (Thread 9)
« Reply #47 on: 09/02/2013 03:26 am »
Okay, so the qualification program was shorter. How is that a problem?

It isn't a problem _except_ for that they _claimed_ that it was longer than usual, not shorter.
And the differences are dramatic.

So I don't believe their other claims right away neither. That's all I said, I never said there's a technical issue.
What I said is: If SpaceX says "we do something better or more prudent than others" then I don't believe a word they say unless I have an independent confirmation.

And that's where the discussion started. You said they test better than others so their risk will be lower and I asked what you base that on.
« Last Edit: 09/02/2013 03:28 am by pippin »

Offline Robotbeat

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Re: SpaceX: General Falcon and Dragon discussion (Thread 9)
« Reply #48 on: 09/02/2013 03:35 am »
Okay, so the qualification program was shorter. How is that a problem?

It isn't a problem _except_ for that they _claimed_ that it was longer than usual, not shorter.
And the differences are dramatic....
The industry standard may be 2:1, even if people in industry often exceed it. I read Boeing/Rocketdyne also bragging about exceeding the standard testing margin standard, but I don't see people jumping on them.
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Offline Robotbeat

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Re: SpaceX: General Falcon and Dragon discussion (Thread 9)
« Reply #49 on: 09/02/2013 03:36 am »
You don't have to believe their claims. No one else in industry does acceptance testing of each rocket stage, that is plain.
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Offline tobi453

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Re: SpaceX: General Falcon and Dragon discussion (Thread 9)
« Reply #50 on: 09/02/2013 05:09 am »
You need to keep in mind, that SpaceX only published the total time of qualification testing. Before that is development testing and that time is unknown.

Also they tested the first stage core for nearly two complete burns, thats 2 x 9 x 180=3240 seconds. If you add the nearly 2000 seconds qualification testing you are at 5000 seconds.

If you assume that the development testing was at least that much you arrive at 10.000 seconds total test time, which would be my guess.
« Last Edit: 09/02/2013 05:16 am by tobi453 »

Offline blazotron

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Re: SpaceX: General Falcon and Dragon discussion (Thread 9)
« Reply #51 on: 09/02/2013 06:23 am »
You need to keep in mind, that SpaceX only published the total time of qualification testing. Before that is development testing and that time is unknown.

Also they tested the first stage core for nearly two complete burns, thats 2 x 9 x 180=3240 seconds. If you add the nearly 2000 seconds qualification testing you are at 5000 seconds.

If you assume that the development testing was at least that much you arrive at 10.000 seconds total test time, which would be my guess.

Agreed.  The paper on RS-68 development lists 18945 seconds of total time for development AND certification.  The SpaceX news release specifically states 1970 seconds for qualification (i.e. certification).  There is certainly a large amount of development time to get to the point of certification that is not included in that total.  Same with the Vulcain stat listed by Pippin, which includes development time.

It's also worth pointing out a few more things:
1) For a regeneratively cooled engine, most engine components are not life sensitive as they do not ablate.  Typically life limited items are seals and bearings in pumps.  Beyond those components, it is the number of starts that matters most to engine life and reusability.  Thermal cycles are typically much more of an issue in combustion devices as they typically cause low cycle fatigue that might be measured in the 10s of starts before things start to wear out.  Valve cycles and component pressure cycles are also start based, although those tend to be less limiting.  Once you get through the startup thermal cycle, running the engine for additional time usually doesn't cause as much life reducing fatigue on these components, and so shorter tests may be preferred to demonstrate tolerance to starts.

2) For an ablative engine, burn time is important, because there is a life limit on total time due to material removal.  Thus longer tests may be preferred to show tolerance to ablation.

3) RS-68's average test length during the previously mentioned 18945 seconds of development and certification is about 105 seconds per test.  Because this includes development tests, which tend to be shorter when they are cut do to problems and during the initial ramp up to full power/full duration operation, the average certification test length was probably longer.  SpaceX's average qualification test length is about 70 seconds.  These ratios roughly match the ratio of burn time for the engines, which makes sense, and make sense per points 1 and 2. 

4) SpaceX states that the M1D qualification testing achieved a >10:1 ratio on mission duration.  They also state that the tested life and start margin was >4:1.  This implies that they budget a "standard life" for each engine if approximately 10/4=2.5 * 185 seconds = 462.5 seconds.  This number would include any engine acceptance testing, stage acceptance testing, static fire on the pad, and any launch aborts, in addition to the actual 185 seconds in flight.  It also implies that they budget 28/4=7 starts per engine as its "standard starts".  These numbers only make sense if demonstrated on a single engine, as the point of demonstrating 4:1 margin on "standard life and starts" is to show that you have 4:1 margin on fatigue life and wear life in your design.  If you use multiple engines for this, you aren't showing the same margin.

5) I agree with tobi453 that development testing would add a significant amount of total test time to the Merlin 1D total and thus the comparisons that have been made to RS-68 and Vulcain are apples to oranges.

<edited to add some whitespace to make it easier to read>
« Last Edit: 09/02/2013 06:25 am by blazotron »

Offline apace

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Re: SpaceX: General Falcon and Dragon discussion (Thread 9)
« Reply #52 on: 09/02/2013 06:30 am »
Unneeded remark. I sent him an email and get back to this a soon as I have an answer from Bernd.
Thanks, look forward to his response.

I contacted the author of the article and he confirmed, that the part with the Munich Re is fiction and NOT based on facts.

Offline pippin

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Re: SpaceX: General Falcon and Dragon discussion (Thread 9)
« Reply #53 on: 09/02/2013 08:40 am »
Unneeded remark. I sent him an email and get back to this a soon as I have an answer from Bernd.
Thanks, look forward to his response.

I contacted the author of the article and he confirmed, that the part with the Munich Re is fiction and NOT based on facts.

Ha, I stand corrected then.
Good to know! Thanks.

Offline pippin

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Re: SpaceX: General Falcon and Dragon discussion (Thread 9)
« Reply #54 on: 09/02/2013 08:47 am »
You need to keep in mind, that SpaceX only published the total time of qualification testing. Before that is development testing and that time is unknown.

Also they tested the first stage core for nearly two complete burns, thats 2 x 9 x 180=3240 seconds. If you add the nearly 2000 seconds qualification testing you are at 5000 seconds.

If you assume that the development testing was at least that much you arrive at 10.000 seconds total test time, which would be my guess.

You can always assume a lot if you want to believe that they are the greatest thing since sliced bread but it's not what they said. And sorry, but they are not known for understating their achievements.

And that full-up stage testing was AFTER the qualification testing, this is done for other engines, too.

And to all others: I'm tired of answering to people making "assumptions" about what the stuff others do without reading the links I gave. RS-68 might be an ablative engine but it's been tested LESS than other engines before, not MORE. It was an example of another engine with LITTLE testing and it was fired in only a single burn for twice as long as SpaceX' allegedly superior qualification program.
Dream of what you want, the facts look different to me.

Offline Ben the Space Brit

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Re: SpaceX: General Falcon and Dragon discussion (Thread 9)
« Reply #55 on: 09/02/2013 10:09 am »
The admonition to fly rather than propagandise in my signature is directed at SpaceX, I'm afraid.  As much as I admire their ambition and Elon Musk's technological vision, I have noticed that they are much better at promising, scheduling and offering visions of the future than they are in actually launching rockets that meet their stated performance goals in anything approaching a timely manner.

Seriously now, guys: the time for talk is over and the total focus must be on showing that there is substance behind it.
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Offline ChrisWilson68

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Re: SpaceX: General Falcon and Dragon discussion (Thread 9)
« Reply #56 on: 09/02/2013 12:50 pm »
The admonition to fly rather than propagandise in my signature is directed at SpaceX, I'm afraid.  As much as I admire their ambition and Elon Musk's technological vision, I have noticed that they are much better at promising, scheduling and offering visions of the future than they are in actually launching rockets that meet their stated performance goals in anything approaching a timely manner.

Seriously now, guys: the time for talk is over and the total focus must be on showing that there is substance behind it.

Let's compare the Falcon 9 ramp-up rate to Atlas V and Delta IV

Atlas V:

2nd flight: 9 months after 1st
3rd flight: 11 months after 1st
4th flight: 28 months after 1st
5th flight: 31 months after 1st
6th flight: 36 months after 1st

Delta IV:

2nd flight: 4 months after 1st
3rd flight: 9 months after 1st
4th flight: 25 months after 1st
5th flight: 30 months after 1st
6th flight: 43 months after 1st

Falcon 9:

2nd flight: 6 months after 1st
3rd flight: 19 months after 1st
4th flight: 28 months after 1st
5th flight: 33 months after 1st
6th flight: currently scheduled for 39 months after 1st

So, SpaceX's ramp-up rate is pretty similar to those for both Atlas V and Delta IV.  And that's in spite of SpaceX bring out a redesign of their vehicle along the way, and not starting with an organization that had been doing launches at a steady rate for a long time, unlike Atlas V or Delta IV.

I have to say this complaining that SpaceX is has been all talk and needs to start delivering rings hollow.  SpaceX has been delivering very well so far.

Offline clongton

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Re: SpaceX: General Falcon and Dragon discussion (Thread 9)
« Reply #57 on: 09/02/2013 12:51 pm »
If the second stage underperforms by 200 m/sec (a made up number) and the mission fails ...

 ??? Seriously? Either you really don't get it or you are deliberately ignoring cherry-picked facts. That 2nd stage has been thoroughly tested and flight qualified based on that hot-fire test. Everything about the stage is tested and certified before it is ever mated with the 1st stage at the launch site, and then it is tested AGAIN as an integrated part of the whole, except for the hot-fire.
« Last Edit: 09/02/2013 12:51 pm by clongton »
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Offline Jim

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Re: SpaceX: General Falcon and Dragon discussion (Thread 9)
« Reply #58 on: 09/02/2013 01:15 pm »

So, SpaceX's ramp-up rate is pretty similar to those for both Atlas V and Delta IV.  And that's in spite of SpaceX bring out a redesign of their vehicle along the way, and not starting with an organization that had been doing launches at a steady rate for a long time, unlike Atlas V or Delta IV.

I have to say this complaining that SpaceX is has been all talk and needs to start delivering rings hollow.  SpaceX has been delivering very well so far.


There were 11 Atlas II/III's and 5 Titan IV's that flew after the first Atlas V and Delta IV.  There was a transition plan. 

Offline Jim

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Re: SpaceX: General Falcon and Dragon discussion (Thread 9)
« Reply #59 on: 09/02/2013 01:16 pm »
If the second stage underperforms by 200 m/sec (a made up number) and the mission fails ...

 ??? Seriously? Either you really don't get it or you are deliberately ignoring cherry-picked facts. That 2nd stage has been thoroughly tested and flight qualified based on that hot-fire test. Everything about the stage is tested and certified before it is ever mated with the 1st stage at the launch site, and then it is tested AGAIN as an integrated part of the whole, except for the hot-fire.


The hot fired was done without the nozzle extension

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