Author Topic: SpaceX Falcon 9 : CRS-11 : NET 31 May 2017 : DISCUSSION  (Read 21613 times)

Online Mike_1179

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Re: SpaceX Falcon 9 : CRS-11 : NET April 2017 : DISCUSSION
« Reply #40 on: 03/29/2017 02:13 PM »

I don't think liquid engines are the same in this regard as SRMs.  The performance characteristics don't vary as much and engine performance is constrained by the rate of flow of fuel/oxidizer to the engines.  SRMs just light off and go, so there is no ability to control the rate of burn dynamically once the motor is cast.

In any case, no Merlin-1D has yet flown with the full qualified thrust, that will come with Block 5 (or the ever-mysterious Block 4 perhaps).  I would expect that all engines at that point will be able to perform to that level and will not be run "hotter".

So for shuttle, they would only choose SRBs that were higher performing (based on the performance of the fuel mix that went into the casting) for missions that needed it?

Offline ChrisGebhardt

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Re: SpaceX Falcon 9 : CRS-11 : NET April 2017 : DISCUSSION
« Reply #41 on: 03/29/2017 02:32 PM »

I don't think liquid engines are the same in this regard as SRMs.  The performance characteristics don't vary as much and engine performance is constrained by the rate of flow of fuel/oxidizer to the engines.  SRMs just light off and go, so there is no ability to control the rate of burn dynamically once the motor is cast.

In any case, no Merlin-1D has yet flown with the full qualified thrust, that will come with Block 5 (or the ever-mysterious Block 4 perhaps).  I would expect that all engines at that point will be able to perform to that level and will not be run "hotter".

So for shuttle, they would only choose SRBs that were higher performing (based on the performance of the fuel mix that went into the casting) for missions that needed it?

Yes.  There was some degree of "choice" here.  It could be mission specific or based on season of projected launch.  Missions in winter had these higher performance SRBs since the atmosphere is denser in winter.  IIRC, it was a difference of burning ~10,000lbs of propellant per second vs. ~11,000lbs of propellant per second.

Online mn

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Re: SpaceX Falcon 9 : CRS-11 : NET April 2017 : DISCUSSION
« Reply #42 on: 03/29/2017 02:56 PM »

I don't think liquid engines are the same in this regard as SRMs.  The performance characteristics don't vary as much and engine performance is constrained by the rate of flow of fuel/oxidizer to the engines.  SRMs just light off and go, so there is no ability to control the rate of burn dynamically once the motor is cast.

In any case, no Merlin-1D has yet flown with the full qualified thrust, that will come with Block 5 (or the ever-mysterious Block 4 perhaps).  I would expect that all engines at that point will be able to perform to that level and will not be run "hotter".

So for shuttle, they would only choose SRBs that were higher performing (based on the performance of the fuel mix that went into the casting) for missions that needed it?

Yes.  There was some degree of "choice" here.  It could be mission specific or based on season of projected launch.  Missions in winter had these higher performance SRBs since the atmosphere is denser in winter.  IIRC, it was a difference of burning ~10,000lbs of propellant per second vs. ~11,000lbs of propellant per second.

So how did we veer off from SSME to SRB?

Mike's original post said "I remember that shuttle missions would choose  SSMEs that were "hotter" for missions that were heavier..."

So do SSME's AND SRB's have performance differences? and they were choosing for both?

P.S. yes this is off topic so feel free to ignore, and we can move on.

Online Mike_1179

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Re: SpaceX Falcon 9 : CRS-11 : NET April 2017 : DISCUSSION
« Reply #43 on: 03/29/2017 03:53 PM »

So how did we veer off from SSME to SRB?

Mike's original post said "I remember that shuttle missions would choose  SSMEs that were "hotter" for missions that were heavier..."

So do SSME's AND SRB's have performance differences? and they were choosing for both?

P.S. yes this is off topic so feel free to ignore, and we can move on.


We got here because I incorrectly thought that SSMEs were sometimes chosen specifically for a mission if additional performance was needed. Turns out I was wrong and that specific SRBs were sometimes identified for individual shuttle missions.

That means the entire premise of my question is moot as SpaceX selecting hardware for CRS-11 would not be driven by some performance goals but by other things (like scheduling among the missions on their manifest)
« Last Edit: 03/29/2017 03:55 PM by Mike_1179 »

Online Steven Pietrobon

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Re: SpaceX Falcon 9 : CRS-11 : NET May 2017 : DISCUSSION
« Reply #44 on: 03/30/2017 09:33 AM »
Yes, each engine has its own personality with slightly differing Isp's. Here are the Isp values for Saturn V used on Apollo 14. You can see they used the highest performing engine for the S-IVB.

S-IC
1 264.7
2 263.9
3 264.9
4 264.3
5 264.8

S-II
1 423.3
2 424.1
3 424.8
4 424.1
5 426.0

I-IVB
1 427.1
Akin's Laws of Spacecraft Design #1:  Engineering is done with numbers.  Analysis without numbers is only an opinion.

Offline Ben the Space Brit

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Re: SpaceX Falcon 9 : CRS-11 : NET May 2017 : DISCUSSION
« Reply #45 on: 03/31/2017 12:26 PM »
So, it is my understanding that this mission will mark the first reuse of a Dragon Mk1 (and may also mark the wind-down of the Mk1 production line). Has any indication been given yet as to which spacecraft will be used?
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Offline Skyrocket

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Re: SpaceX Falcon 9 : CRS-11 : NET May 2017 : DISCUSSION
« Reply #46 on: 03/31/2017 12:28 PM »
So, it is my understanding that this mission will mark the first reuse of a Dragon Mk1 (and may also mark the wind-down of the Mk1 production line). Has any indication been given yet as to which spacecraft will be used?

It is capsule C106, which had flown the SpX 4 mission.

Offline stcks

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Re: SpaceX Falcon 9 : CRS-11 : NET May 2017 : DISCUSSION
« Reply #47 on: 03/31/2017 12:30 PM »
So, it is my understanding that this mission will mark the first reuse of a Dragon Mk1 (and may also mark the wind-down of the Mk1 production line). Has any indication been given yet as to which spacecraft will be used?

It is generally understood to be using the Dragon from the CRS-4 mission. I'm not sure if that has been de-facto confirmed yet though.

Online mn

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Re: SpaceX Falcon 9 : CRS-11 : NET May 2017 : DISCUSSION
« Reply #48 on: 03/31/2017 02:39 PM »
So, it is my understanding that this mission will mark the first reuse of a Dragon Mk1 (and may also mark the wind-down of the Mk1 production line). Has any indication been given yet as to which spacecraft will be used?

It is generally understood to be using the Dragon from the CRS-4 mission. I'm not sure if that has been de-facto confirmed yet though.

Confirmed by NASA: https://forum.nasaspaceflight.com/index.php?topic=42229.msg1659526#msg1659526

Online FutureSpaceTourist

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Re: SpaceX Falcon 9 : CRS-11 : NET May 2017 : DISCUSSION
« Reply #49 on: 03/31/2017 10:14 PM »
My emphasis:

Quote
In office today: 1st reflown booster on mission cntrl screen, many flown Merlins, 1st reused Dragon ready to ship out ..I'm sensing a theme♻️

https://twitter.com/rocketjoy/status/847931487437570048

Offline Norm38

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Re: SpaceX Falcon 9 : CRS-11 : NET May 2017 : DISCUSSION
« Reply #50 on: 03/31/2017 11:36 PM »
Cool, I've been waiting for a used Dragon to fly again, they have enough of them, probably don't need to build any more, if they can turn them around fast enough.

Offline Herb Schaltegger

My emphasis:

Quote
In office today: 1st reflown booster on mission cntrl screen, many flown Merlins, 1st reused Dragon ready to ship out ..I'm sensing a theme♻️

https://twitter.com/rocketjoy/status/847931487437570048

Has there yet been any reasonably-reliable information about what beyond the pressure vessel is being reused for certain? I'd imaging the Dracos are probably fairly easily refurbished and likely reusable. I have long wondered what the thermal environment during re-entry does to exposed CBM interface and top hatch, for instance.
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Offline Bob Shaw

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Re: SpaceX Falcon 9 : CRS-11 : NET May 2017 : DISCUSSION
« Reply #52 on: 03/31/2017 11:51 PM »
It'll be interesting to see how much they actually refly - IIRC, it is basically only the pressure vessel. No plumbing, heat shield, recovery or docking gear.

Online Lars-J

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Re: SpaceX Falcon 9 : CRS-11 : NET May 2017 : DISCUSSION
« Reply #53 on: 03/31/2017 11:58 PM »
It'll be interesting to see how much they actually refly - IIRC, it is basically only the pressure vessel. No plumbing, heat shield, recovery or docking gear.

They have already reused components from Dragons on previous flights, so I think it is more than you think that will be reused.

Offline Bob Shaw

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Re: SpaceX Falcon 9 : CRS-11 : NET May 2017 : DISCUSSION
« Reply #54 on: 04/01/2017 12:21 AM »
It'll be interesting to see how much they actually refly - IIRC, it is basically only the pressure vessel. No plumbing, heat shield, recovery or docking gear.

They have already reused components from Dragons on previous flights, so I think it is more than you think that will be reused.

I hope so - I'm not trying to minimise their plans. What has been reused previously? Even Apollo saw a surprising amount of reuse!

Offline MKremer

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Re: SpaceX Falcon 9 : CRS-11 : NET May 2017 : DISCUSSION
« Reply #55 on: 04/01/2017 04:16 AM »
It'll be interesting to see how much they actually refly - IIRC, it is basically only the pressure vessel. No plumbing, heat shield, recovery or docking gear.

They have already reused components from Dragons on previous flights, so I think it is more than you think that will be reused.
That's true, but to the general public "re-use" implies just refueling and loading some new cargo. Most people don't consider what needs to be refurbished/replaced (and why).

Online Galactic Penguin SST

So, it is my understanding that this mission will mark the first reuse of a Dragon Mk1 (and may also mark the wind-down of the Mk1 production line). Has any indication been given yet as to which spacecraft will be used?

It is capsule C106, which had flown the SpX 4 mission.

Do you have a source for the C1XX numbers?
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Offline rockets4life97

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Re: SpaceX Falcon 9 : CRS-11 : NET May 2017 : DISCUSSION
« Reply #57 on: 04/01/2017 12:00 PM »
So, it is my understanding that this mission will mark the first reuse of a Dragon Mk1 (and may also mark the wind-down of the Mk1 production line). Has any indication been given yet as to which spacecraft will be used?

It is capsule C106, which had flown the SpX 4 mission.

Do you have a source for the C1XX numbers?

The /r/spacex wiki has this info. I can't guarantee it is accurate.

Offline old_sellsword

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Re: SpaceX Falcon 9 : CRS-11 : NET May 2017 : DISCUSSION
« Reply #58 on: 04/01/2017 12:35 PM »
So, it is my understanding that this mission will mark the first reuse of a Dragon Mk1 (and may also mark the wind-down of the Mk1 production line). Has any indication been given yet as to which spacecraft will be used?

It is capsule C106, which had flown the SpX 4 mission.

Do you have a source for the C1XX numbers?

The /r/spacex wiki has this info. I can't guarantee it is accurate.

It's come from multiple sources, but employee u/Spiiice (who has since deleted their account) did mention it on r/SpaceX. Dragon 1 capsules are C1XX, Dragon 2 capsules are C2XX.

Offline intrepidpursuit

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Re: SpaceX Falcon 9 : CRS-11 : NET May 2017 : DISCUSSION
« Reply #59 on: 04/02/2017 04:09 AM »
It'll be interesting to see how much they actually refly - IIRC, it is basically only the pressure vessel. No plumbing, heat shield, recovery or docking gear.

They have already reused components from Dragons on previous flights, so I think it is more than you think that will be reused.

I'm pretty sure we've already heard that they reuse the CBM and much of the gear from the GNC bay such as the grapple fixture regularly. I would be interested to know though how much of the gear between the pressure vessel and the OML is being reused. I'm sure it is a new OML and heat shield.

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