Poll

When will full-scale hot-fire testing of Raptor begin?

Component tests - 2017
2 (0.7%)
Component tests - 2018
12 (4.5%)
Integrated tests -  2017
15 (5.6%)
Integrated tests -  2018
187 (69.5%)
Integrated tests -  2019
35 (13%)
Raptor is not physically scaled up
15 (5.6%)
Never
3 (1.1%)

Total Members Voted: 269


Author Topic: ITS Propulsion – The evolution of the SpaceX Raptor engine  (Read 230705 times)

Offline livingjw

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #820 on: 03/03/2018 02:05 PM »
There is some misunderstanding here. The sea level thrust scale up is about 70%. The throat, combustion chamber and pumps is about 15% linear scale increase. Throat area scale is 1.15^2 = 1.32. Chamber pressure goes from 2000 psi to 2500 psi for an increased pressure ratio of 1.25. This would require about a 12% increase in pump speed. The thrust scale up due to the increased pressure and throat area is 1.25 x 1.32 = 1.65. An increased expansion ratio from about 26 to 35 gets you to 1.7 SL thrust scale ratio.

John

Online meekGee

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #821 on: 03/03/2018 02:07 PM »
Didn't they scale down the size of the production engines to be very close to the engine they already had under test?  Or did I just dream that 2017 IAC presentation?

I don't think 'scale down' is the right word.
BFS/R was scaled down to fit market needs.
This meant that for engine out and packing reasons, you pretty much need that size of engine.

I read it as "scaled down", but not because of engine size, or else they'd have ended up at the development engine size.

They first chose a development engine size long before detail design of the ship was done.

They later chose a ship size which makes sense as a first generation. 12 m was larger than necessary and introduced difficulties that they chose to avoid.

Larger ships will follow, but all in good time.

The chosen ship size dictated the flight engines will be larger than development engines by said 15%.

----
ABCD: Always Be Counting Down
« Last Edit: 03/03/2018 02:14 PM by meekGee »
ABCD - Always Be Counting Down

Offline livingjw

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #822 on: 03/03/2018 02:09 PM »
That makes no sense.

It makes a little sense. BFR's engines seem to be under design for the mission they have in mind, rather than the vehicle being specifically scaled to the engines they have available. This hypothesis does require the ability to scale the engine almost arbitrarily once they have the basic design worked out, though.

Didn't they scale down the size of the production engines to be very close to the engine they already had under test?  Or did I just dream that 2017 IAC presentation?

I think they did.  See the size comparison on my chart.

John

Offline su27k

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #823 on: 03/03/2018 02:12 PM »
The sub-scale engine size is determined by the Stennis test stand size, it's in the article started this thread: https://www.nasaspaceflight.com/2016/10/its-propulsion-evolution-raptor-engine/

Quote
While incapable of handling the full size of the expected Raptor engine unit, the Stennis test stand enabled the individual testing of each subcomponent of the 1MN scaled prototype that SpaceX currently has at its test facility in McGregor, Texas.

Quote
Since the final thrust level of the Raptor had not been settled, it was decided that the first integrated test engine would be a 1MN sub-scale engine.

It enabled the full testing at Stennis E2 and allowed for the development of robust startup and shutdown sequences, characterize hardware durability and anchor analytical models that would be used for future designs.

Online Hominans Kosmos

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #824 on: 03/09/2018 09:55 PM »
That makes no sense.

It makes a little sense. BFR's engines seem to be under design for the mission they have in mind, rather than the vehicle being specifically scaled to the engines they have available. This hypothesis does require the ability to scale the engine almost arbitrarily once they have the basic design worked out, though.

Didn't they scale down the size of the production engines to be very close to the engine they already had under test?  Or did I just dream that 2017 IAC presentation?

I think they did.  See the size comparison on my chart.

John

Correlation is not causation. The vehicle architecture is not being designed to match the engine, but the expected economic of the entire operation. Looking it from the opposite direction is the path to being mislead. Size of vehicle is not determined by one parameter (difficulty of engine scaling) but by a hundred.

Offline OneSpeed

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #825 on: 03/10/2018 11:07 AM »
Didn't they scale down the size of the production engines to be very close to the engine they already had under test?  Or did I just dream that 2017 IAC presentation?

I think they did.  See the size comparison on my chart.

John

Correlation is not causation. The vehicle architecture is not being designed to match the engine, but the expected economic of the entire operation. Looking it from the opposite direction is the path to being mislead. Size of vehicle is not determined by one parameter (difficulty of engine scaling) but by a hundred.

The 2017 BFR is fundamentally a 3/4 scale model of the 2016 ITS.

DimensionRatio
Linear0.75
Area0.5625
Mass0.421875

Thrust is proportional to area, so if you scale the ITS engines by 0.75, the thrust is scaled by 0.5625.
The ITS SL engines were 3000 kN, and the BFR SL engines will be 1700 kN.
3000 * 0.5625 = 1687 kN, pretty close to 1700.

The ITS liftoff mass was 10500 mT, so multiply by 0.421875 for a 0.75 scale model.
10500 * 0.421875 = 4429 mT, also pretty close to 4400 mT.

42 * 3000 kN engines would have given ITS a T/W ratio of 42 * 3000 / 10500 * 9.8 = 1.22.
For BFR, the number of engines required for the same T/W ratio would be 4400 * 1.22 * 9.8 / 1700 = 30.95, very close to 31.

I suspect the correlation is no accident ;)

Offline livingjw

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #826 on: 03/10/2018 01:21 PM »
That makes no sense.

It makes a little sense. BFR's engines seem to be under design for the mission they have in mind, rather than the vehicle being specifically scaled to the engines they have available. This hypothesis does require the ability to scale the engine almost arbitrarily once they have the basic design worked out, though.

Didn't they scale down the size of the production engines to be very close to the engine they already had under test?  Or did I just dream that 2017 IAC presentation?

I think they did.  See the size comparison on my chart.

John

Correlation is not causation. The vehicle architecture is not being designed to match the engine, but the expected economic of the entire operation. Looking it from the opposite direction is the path to being mislead. Size of vehicle is not determined by one parameter (difficulty of engine scaling) but by a hundred.

Didn't mean to imply it was the only reason, just one of many.

John

Online Hitech

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #827 on: 03/17/2018 07:34 PM »
Is it possible that some of the pre-burner( or main injectors) structure is copper like many other engines. and some local impingement occurs during start and shutdown?
« Last Edit: 03/17/2018 07:46 PM by Hitech »

Offline livingjw

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #828 on: 03/23/2018 12:44 PM »
Is it possible that some of the pre-burner( or main injectors) structure is copper like many other engines. and some local impingement occurs during start and shutdown?

Don't know about the pre-burners, but the main chamber is a a copper alloy. Probably GRCo-84 or similar.

John

Offline Navier–Stokes

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #829 on: 03/26/2018 03:59 PM »
Jeff Foust‏ @jeff_foust 

If you squint at this chart, you can see ongoing and planned test activity at Stennis by Aerojet Rocketdyne, Relativity, Stratolaunch and SpaceX, among others.

8:41 AM - 26 Mar 2018

Offline jpo234

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #830 on: 03/26/2018 06:58 PM »
Jeff Foust‏ @jeff_foust 

If you squint at this chart, you can see ongoing and planned test activity at Stennis by Aerojet Rocketdyne, Relativity, Stratolaunch and SpaceX, among others.

8:41 AM - 26 Mar 2018
What is the "SpaceX combustion device"?
You want to be inspired by things. You want to wake up in the morning and think the future is going to be great. That's what being a spacefaring civilization is all about. It's about believing in the future and believing the future will be better than the past. And I can't think of anything more exciting than being out there among the stars.

Offline Rabidpanda

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #831 on: 03/26/2018 07:06 PM »
Jeff Foust‏ @jeff_foust 

If you squint at this chart, you can see ongoing and planned test activity at Stennis by Aerojet Rocketdyne, Relativity, Stratolaunch and SpaceX, among others.

8:41 AM - 26 Mar 2018
What is the "SpaceX combustion device"?

Most likely full scale preburners, or subscale injector testing for Raptor.

Offline Robotbeat

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #832 on: 03/27/2018 12:23 AM »
I thought this was more interesting. What's "Mars Lander"?
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

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Offline gongora

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #833 on: 03/27/2018 12:38 AM »
I thought this was more interesting. What's "Mars Lander"?

Whatever it is, it's not likely to have anything to do with Raptor.

Offline Robotbeat

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #834 on: 03/27/2018 12:50 AM »
I thought this was more interesting. What's "Mars Lander"?

Whatever it is, it's not likely to have anything to do with Raptor.
Why the heck not?
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

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Offline Robotbeat

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #835 on: 03/27/2018 01:05 AM »
The first flight of Falcon 9 had a failed restart of the Vacuum Merlin because roll control froze up in vacuum, a problem they probably could've caught in a test like this. At the time (correct me if I'm wrong), this facility had been basically mothballed, thus they would've had to spend like hundreds of millions to restart it or something vs the ~$40 million price of another Falcon 9 launch which they may have had to do anyway. So at the time, it was a good trade, even especially in retrospect.

Apparently now the facility is being used by upper stages again, which means SpaceX won't have to pay the full cost of un-mothballing. Also, a BFR and BFS cost about an order of magnitude more than a Falcon 9 v1.0, and SpaceX would have to wait another 26 months to try again, thus pushing back their crewed flight another synod.

Pretty sure it makes sense to test for integrated-Raptor landing failure modes in Mars-like conditions.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline gongora

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #836 on: 03/27/2018 01:17 AM »
The first flight of Falcon 9 had a failed restart of the Vacuum Merlin because roll control froze up in vacuum, a problem they probably could've caught in a test like this. At the time (correct me if I'm wrong), this facility had been basically mothballed, thus they would've had to spend like hundreds of millions to restart it or something vs the ~$40 million price of another Falcon 9 launch which they may have had to do anyway. So at the time, it was a good trade, even especially in retrospect.

Apparently now the facility is being used by upper stages again, which means SpaceX won't have to pay the full cost of un-mothballing. Also, a BFR and BFS cost about an order of magnitude more than a Falcon 9 v1.0, and SpaceX would have to wait another 26 months to try again, thus pushing back their crewed flight another synod.

Pretty sure it makes sense to test for integrated-Raptor landing failure modes in Mars-like conditions.

That facility won't support a single Raptor.

Offline Robotbeat

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #837 on: 03/27/2018 01:26 AM »
The first flight of Falcon 9 had a failed restart of the Vacuum Merlin because roll control froze up in vacuum, a problem they probably could've caught in a test like this. At the time (correct me if I'm wrong), this facility had been basically mothballed, thus they would've had to spend like hundreds of millions to restart it or something vs the ~$40 million price of another Falcon 9 launch which they may have had to do anyway. So at the time, it was a good trade, even especially in retrospect.

Apparently now the facility is being used by upper stages again, which means SpaceX won't have to pay the full cost of un-mothballing. Also, a BFR and BFS cost about an order of magnitude more than a Falcon 9 v1.0, and SpaceX would have to wait another 26 months to try again, thus pushing back their crewed flight another synod.

Pretty sure it makes sense to test for integrated-Raptor landing failure modes in Mars-like conditions.

That facility won't support a single Raptor.
Based on what, exactly?

And keep in mind: The facility CAN be upgraded, and the slide directly implies that it will.

The facility can handle up to 400,000lbf, which is roughly the same as a vacuum Raptor: https://www1.grc.nasa.gov/facilities/isp/

...and, like Merlin, Raptor will almost certainly start life out at lower thrust. (and the initial Mars landing will involve throttling down the engines)
« Last Edit: 03/27/2018 01:28 AM by Robotbeat »
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

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Offline docmordrid

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #838 on: 03/27/2018 02:39 AM »
Adjusting the fiscal year quarters to actual calendar dates, doesn't that test window close at the end of March 2020? Additionally, doesn't the Mars 2020 rover have a NET of July 2020?

3-4 months to button up and ship it?
« Last Edit: 03/27/2018 02:42 AM by docmordrid »
DM

Offline Robotbeat

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #839 on: 03/27/2018 03:28 AM »
Adjusting the fiscal year quarters to actual calendar dates, doesn't that test window close at the end of March 2020? Additionally, doesn't the Mars 2020 rover have a NET of July 2020?

3-4 months to button up and ship it?
That would be the Mars rover, not the "Mars Lander." The 2020 rover uses the Skycrane stage, just like MSL, therefore there is no "lander" part.

The only US "Mars Lander" I can think of, then, is BFS.

...there is the European/Russian lander, but that is, as you say, a 2020 mission (July) so there wouldn't be enough time to test it there in 2020.
« Last Edit: 03/27/2018 03:31 AM by Robotbeat »
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

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