Poll

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

Component tests - 2017
3 (0.6%)
Component tests - 2018
21 (4.2%)
Integrated tests -  2017
19 (3.8%)
Integrated tests -  2018
237 (47%)
Integrated tests -  2019
181 (35.9%)
Raptor is not physically scaled up
33 (6.5%)
Never
10 (2%)

Total Members Voted: 504


Author Topic: SpaceX Raptor engine (Super Heavy/Starship Propulsion) - General Thread 1  (Read 947052 times)

Offline Zed_Noir

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #1180 on: 09/29/2018 07:48 pm »
@livingjw

Just out of curiosity. If the Raptor have higher chamber pressure (like for example 315 bar or 330 bar) in the future and the rest of the engine is mostly unchanged. What would be the changes to the thrust and the ISP of the engine?

Offline tdperk

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #1181 on: 09/29/2018 08:07 pm »
@livingjw

Just out of curiosity. If the Raptor have higher chamber pressure (like for example 315 bar or 330 bar) in the future and the rest of the engine is mostly unchanged. What would be the changes to the thrust and the ISP of the engine?

I believe that within a certain small % range of pressure increase, thrust and Isp all go up quite linearly with pressure, that does not whole true for example for a 100% increase.

Offline aero

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #1182 on: 09/30/2018 12:08 am »
@livingjw

Just out of curiosity. If the Raptor have higher chamber pressure (like for example 315 bar or 330 bar) in the future and the rest of the engine is mostly unchanged. What would be the changes to the thrust and the ISP of the engine?

I believe that within a certain small % range of pressure increase, thrust and Isp all go up quite linearly with pressure, that does not whole true for example for a 100% increase.

Linearly OK, but at what rate of change, isp/delta-bar? I hope it is 42!
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Offline MikeM8891

@livingjw

Just out of curiosity. If the Raptor have higher chamber pressure (like for example 315 bar or 330 bar) in the future and the rest of the engine is mostly unchanged. What would be the changes to the thrust and the ISP of the engine?

I believe that within a certain small % range of pressure increase, thrust and Isp all go up quite linearly with pressure, that does not whole true for example for a 100% increase.

Linearly OK, but at what rate of change, isp/delta-bar? I hope it is 42!

Here are some rough estimates. I expect these are accurate to within 2%. Basically the vacuum thrust scales linearly with chamber pressure, something like ~7.4 kN/bar. The sea level thrust is going to be 134 kN less than the vacuum thrust; this is based on the 1.3 m nozzle exit diameter. Vacuum Isp is not affected by chamber pressure.

Chamber Pressure250 bar300 bar315bar330bar
Thrust at sea level1,700 kN2,095 kN2,206 kN2,318 kN
Thrust in vacuum1,834 kN2,229 kN2,340 kN2,452 kN
Specific Impusle at sea level330.0 sec334.6 sec335.6 sec336.5 sec
Specific Impusle in vacuum356 sec356 sec356 sec356 sec
« Last Edit: 09/30/2018 01:31 am by MikeM8891 »

Offline livingjw

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #1184 on: 09/30/2018 05:17 pm »
Looks about about right to me. The only way to increase the vacuum Isp is to increase the expansion ratio. You need about 200:1 er to get close to 380 sec.

John

Offline IainMcClatchie

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #1185 on: 10/02/2018 02:58 am »
Jon, how did you estimate the fuel:oxy mass ratios for the preburners?  Your preburner outputs look quite hot, with a full flow design that's an absurd amount of thermal power going into the turbines....

Offline Hominans Kosmos

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #1186 on: 10/02/2018 07:03 am »
. Vacuum Isp is not affected by chamber pressure.

Chamber Pressure250 bar300 bar315bar330bar
Thrust at sea level1,700 kN2,095 kN2,206 kN2,318 kN
Thrust in vacuum1,834 kN2,229 kN2,340 kN2,452 kN
Specific Impusle at sea level330.0 sec334.6 sec335.6 sec336.5 sec
Specific Impusle in vacuum356 sec356 sec356 sec356 sec

What about improvements in combustion efficiency when running the engine further still from stoichiometric? Does higher chamber pressure enable running even more methane-rich?

Other question: does increased chamber pressure mean decreased throat area? For a theoretical const-mdot engine?

Offline livingjw

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #1187 on: 10/02/2018 12:15 pm »
Jon, how did you estimate the fuel:oxy mass ratios for the preburners?  Your preburner outputs look quite hot, with a full flow design that's an absurd amount of thermal power going into the turbines....

I chose 1000 F to minimize the pressure drop across the turbines needed to drive the pumps. The higher the turbine inlet temperature, the lower the pressure drop, the lower the overall pressure rise required of the pumps. Turbine materials are able to handle 100's of degrees higher temperatures, uncooled.

John

Offline livingjw

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #1188 on: 10/02/2018 12:27 pm »
. Vacuum Isp is not affected by chamber pressure.

Chamber Pressure250 bar300 bar315bar330bar
Thrust at sea level1,700 kN2,095 kN2,206 kN2,318 kN
Thrust in vacuum1,834 kN2,229 kN2,340 kN2,452 kN
Specific Impusle at sea level330.0 sec334.6 sec335.6 sec336.5 sec
Specific Impusle in vacuum356 sec356 sec356 sec356 sec

What about improvements in combustion efficiency when running the engine further still from stoichiometric? Does higher chamber pressure enable running even more methane-rich?

Other question: does increased chamber pressure mean decreased throat area? For a theoretical const-mdot engine?

- Once you distance your mixture ratio from stoichiometric (3.7 should do it), high combustion efficiencies are easier to achieve. More distance from stoichiometric will probably not help.
 
- If you want to maintain constant mass flow with increasing pressure, you will have to decrease throat size. You usually wouldn't have to do this since increased pressure from the pumps (spinning faster) would normally increase mass flow.

John

Offline acsawdey

Jon, how did you estimate the fuel:oxy mass ratios for the preburners?  Your preburner outputs look quite hot, with a full flow design that's an absurd amount of thermal power going into the turbines....

I chose 1000 F to minimize the pressure drop across the turbines needed to drive the pumps. The higher the turbine inlet temperature, the lower the pressure drop, the lower the overall pressure rise required of the pumps. Turbine materials are able to handle 100's of degrees higher temperatures, uncooled.

John

Evolution of Rolls-Royce air-cooled turbine blades and feature analysis

Even the materials in the very earliest turbojets could handle 1000K (1340F) turbine inlet temperature. To me this feels like one of the big advantages of full-flow -- the temperatures are low compared to gas turbines.



Offline Elmar Moelzer

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #1190 on: 10/07/2018 09:04 pm »
Here are some rough estimates. I expect these are accurate to within 2%. Basically the vacuum thrust scales linearly with chamber pressure, something like ~7.4 kN/bar. The sea level thrust is going to be 134 kN less than the vacuum thrust; this is based on the 1.3 m nozzle exit diameter. Vacuum Isp is not affected by chamber pressure.

Chamber Pressure250 bar300 bar315bar330bar
Thrust at sea level1,700 kN2,095 kN2,206 kN2,318 kN
Thrust in vacuum1,834 kN2,229 kN2,340 kN2,452 kN
Specific Impusle at sea level330.0 sec334.6 sec335.6 sec336.5 sec
Specific Impusle in vacuum356 sec356 sec356 sec356 sec
What would 300, 315 and 330 bar look like with 2.4 m and 1.7 m exit diameter bells?
I assume that the higher chamber pressure would improve the performance of larger ER nozzles at SL as well? Or am I wrong here?

Offline Hominans Kosmos

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #1191 on: 10/09/2018 12:23 pm »
Isn't 1.7 m too large?

Offline Elmar Moelzer

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #1192 on: 10/10/2018 05:14 am »
Isn't 1.7 m too large?
I thought they would have nozzles with up to 2.4 meters diameter for the vac version?

Offline RobLynn

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #1193 on: 10/11/2018 09:53 am »
Isn't 1.7 m too large?

SSME has a huge Ø2.3m nozzle with 1860kN thrust at 363s SL ISp and a huge 77.5 expansion ratio.  Mass flow not that much different from the Raptor, and chamber pressure only 20.5MPa

SSME used a hooked trailing edge to increase pressure near nozzle rim to 30-40kPa far above the 14kPa found in centre of the outlet flow.

There is obviously a lot of scope for further optimisation of Raptor nozzles for both booster and spaceship.  I think the Ø9m booster suffers badly from being too small a diameter.  If not constrained by the tooling they would probably prefer to go for a much larger diameter ~6x the optimised nozzle diameter + spacing pitch (assuming outer ring directly aligned with tank walls) to allow 37 engines, thicker tank walls, a shorter stack, reduced booster surface area, and create more drag on re-entry to lower terminal velocity and reduce landing burn fuel requirements.  Or they might prefer to run even more (61 engines) at significantly lower pressures to improve thrust chamber life and minimize lifetime costs.  But at the moment getting it flying as cheaply as possible is for sure the right approach.
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Offline speedevil

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #1194 on: 10/11/2018 10:09 am »
There is obviously a lot of scope for further optimisation of Raptor nozzles for both booster and spaceship.  I think the Ø9m booster suffers badly from being too small a diameter.
The booster tail seems to not be 9m.
Most of the flare visible in some images is due to the fins, but not all.

It's around 10m.

Offline wannamoonbase

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #1195 on: 10/11/2018 04:25 pm »
I think the Ø9m booster suffers badly from being too small a diameter.  If not constrained by the tooling they would probably prefer to go for a much larger diameter ~6x the optimised nozzle diameter + spacing pitch (assuming outer ring directly aligned with tank walls) to allow 37 engines, thicker tank walls, a shorter stack, reduced booster surface area, and create more drag on re-entry to lower terminal velocity and reduce landing burn fuel requirements.

I agree on the problems with the smaller diameter.  There appears to be advantages to increasing the diameter beyond 9 meters.

Yes tooling is expensive, but they are just starting and are making foundational decisions they may live with for decades.

Maybe make the 1.0 model of the BFS at 9 meters and get flying.  But why not order another tool.

That's my 2 cents from my armchair.
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Online meekGee

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #1196 on: 10/11/2018 05:13 pm »
I think the Ø9m booster suffers badly from being too small a diameter.  If not constrained by the tooling they would probably prefer to go for a much larger diameter ~6x the optimised nozzle diameter + spacing pitch (assuming outer ring directly aligned with tank walls) to allow 37 engines, thicker tank walls, a shorter stack, reduced booster surface area, and create more drag on re-entry to lower terminal velocity and reduce landing burn fuel requirements.

I agree on the problems with the smaller diameter.  There appears to be advantages to increasing the diameter beyond 9 meters.

Yes tooling is expensive, but they are just starting and are making foundational decisions they may live with for decades.

Maybe make the 1.0 model of the BFS at 9 meters and get flying.  But why not order another tool.

That's my 2 cents from my armchair.

This is SpaceX.  The minute the 9 m flies, they'll be working on the 12, or the 15.

Why would it be "decades" if even the first design didn't take even a single decade?
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Offline Lars-J

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #1197 on: 10/11/2018 05:53 pm »
I think the Ø9m booster suffers badly from being too small a diameter.  If not constrained by the tooling they would probably prefer to go for a much larger diameter ~6x the optimised nozzle diameter + spacing pitch (assuming outer ring directly aligned with tank walls) to allow 37 engines, thicker tank walls, a shorter stack, reduced booster surface area, and create more drag on re-entry to lower terminal velocity and reduce landing burn fuel requirements.

I agree on the problems with the smaller diameter.  There appears to be advantages to increasing the diameter beyond 9 meters.

Yes tooling is expensive, but they are just starting and are making foundational decisions they may live with for decades.

Maybe make the 1.0 model of the BFS at 9 meters and get flying.  But why not order another tool.

That's my 2 cents from my armchair.

This is SpaceX.  The minute the 9 m flies, they'll be working on the 12, or the 15.

Why would it be "decades" if even the first design didn't take even a single decade?

Did SpaceX immediately start working on 4 and 5m diameter Falcon rockets after F9 flew in 2010?

Why would they when it is far easier to stretch the 9m? There is no real benefit for just going to 12m from 9m.

There are ground infrastructure issues that makes going larger than 9-10m difficult. If they plan on using existing launch sites, like 39A. And perhaps ANY land launch site in the continental US. I don't think they will be able to go bigger without a large floating launch infrastructure.
« Last Edit: 10/11/2018 05:55 pm by Lars-J »

Offline hkultala

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #1198 on: 10/12/2018 01:53 pm »
Is the planned expansion ratio still the same as in 2017 version? Or did they make the nozzle of the "sea level optimized" raptor slightly bigger in the 2018 version? (optimizing it for slightly higher than sea level to be better comphromize for vacuum, or optimizing it for higher chamber pressure even on sea level)

Increasing the nozzle size might explain the width increase in the base of the rocket?
« Last Edit: 10/12/2018 01:54 pm by hkultala »

Offline ZachF

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #1199 on: 10/12/2018 02:22 pm »
Is the planned expansion ratio still the same as in 2017 version? Or did they make the nozzle of the "sea level optimized" raptor slightly bigger in the 2018 version? (optimizing it for slightly higher than sea level to be better comphromize for vacuum, or optimizing it for higher chamber pressure even on sea level)

Increasing the nozzle size might explain the width increase in the base of the rocket?

I think it's mostly just a protective skirt for the engine bells. The size does not look to have changed much, perhaps a slight increase.

if you look at the 2017 BFR the outer ring of engine bells extends outside the diameter of the rocket, now it is inside.

That being said, I would not be surprised given the increase in pressure if the throat was narrowed somewhat and the ER pushed from ~35 to more like 40.
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