Author Topic: SpaceX Raptor engine - General Thread 4  (Read 802213 times)

Offline InterestedEngineer

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Re: SpaceX Raptor engine - General Thread 4
« Reply #660 on: 08/30/2021 04:06 pm »

125 GW is the kinetic energy. [snip]

1 kg of methane has a lower heating value of ~50.3 MJ. One watt is one Joule per second. Therefore, burning 134 kg/s results in 6740 MJ per second or 6.74 GW of energy output! For one engine. So this times 33 (the currently planned final engine count for Booster) results in 222.4 GW of energy output! That's quite a bit.

So the efficiency of thermal-kinetic is  125GW/222GW =56%

What is theoretical max?  56% is off the charts good for thermal-mechanical conversion (e.g. nuke plant is 42% on a very good day)

Offline rsdavis9

Re: SpaceX Raptor engine - General Thread 4
« Reply #661 on: 08/30/2021 04:20 pm »

125 GW is the kinetic energy. [snip]

1 kg of methane has a lower heating value of ~50.3 MJ. One watt is one Joule per second. Therefore, burning 134 kg/s results in 6740 MJ per second or 6.74 GW of energy output! For one engine. So this times 33 (the currently planned final engine count for Booster) results in 222.4 GW of energy output! That's quite a bit.

So the efficiency of thermal-kinetic is  125GW/222GW =56%

What is theoretical max?  56% is off the charts good for thermal-mechanical conversion (e.g. nuke plant is 42% on a very good day)

As high of a temp as you want to go.
Something like delta-T/absolute-T
So by making delta-T large you approach one.
With ELV best efficiency was the paradigm. The new paradigm is reusable, good enough, and commonality of design.
Same engines. Design once. Same vehicle. Design once. Reusable. Build once.

Offline livingjw

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Re: SpaceX Raptor engine - General Thread 4
« Reply #662 on: 08/30/2021 04:28 pm »

125 GW is the kinetic energy. [snip]

1 kg of methane has a lower heating value of ~50.3 MJ. One watt is one Joule per second. Therefore, burning 134 kg/s results in 6740 MJ per second or 6.74 GW of energy output! For one engine. So this times 33 (the currently planned final engine count for Booster) results in 222.4 GW of energy output! That's quite a bit.

So the efficiency of thermal-kinetic is  125GW/222GW =56%

What is theoretical max?  56% is off the charts good for thermal-mechanical conversion (e.g. nuke plant is 42% on a very good day)

This is about as good as it gets for a heat engine with waste heat utilization. Large ship engines are typically in the 50-57% range, and they try really hard for every extra percent.


John
« Last Edit: 08/30/2021 04:30 pm by livingjw »

Offline spacenut

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Re: SpaceX Raptor engine - General Thread 4
« Reply #663 on: 08/30/2021 07:08 pm »
Has the Raptor reached 230 tons of thrust now? 

Are the 230 ton thrust Raptors the 20 that are on the outer rim of the Superheavy booster?

And, are the inner 9 Raptors the 200 ton thrust versions?

If this is true then the Starship has around 14 million lbs thrust in English units?  I was thinking musk was pushing for 15-16 million lbs thrust. 

Offline xvel

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Re: SpaceX Raptor engine - General Thread 4
« Reply #664 on: 08/30/2021 07:28 pm »
Has the Raptor reached 230 tons of thrust now? 

Are the 230 ton thrust Raptors the 20 that are on the outer rim of the Superheavy booster?

And, are the inner 9 Raptors the 200 ton thrust versions?

If this is true then the Starship has around 14 million lbs thrust in English units?  I was thinking musk was pushing for 15-16 million lbs thrust.

No, current raptors are all 200t, but I'm not 100% sure, current prototypes will fly without much payload so they don't need that much thrust as final version.
« Last Edit: 08/30/2021 07:28 pm by xvel »
And God said: "Let there be a metric system". And there was the metric system.
And God saw that it was a good system.

Offline spacenut

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Re: SpaceX Raptor engine - General Thread 4
« Reply #665 on: 08/30/2021 07:36 pm »
Has the Raptor reached 230 tons of thrust now? 

Are the 230 ton thrust Raptors the 20 that are on the outer rim of the Superheavy booster?

And, are the inner 9 Raptors the 200 ton thrust versions?

If this is true then the Starship has around 14 million lbs thrust in English units?  I was thinking musk was pushing for 15-16 million lbs thrust.

No, current raptors are all 200t, but I'm not 100% sure, current prototypes will fly without much payload so they don't need that much thrust as final version.

Does anyone know for sure?  I know this is what Musk was shooting for and I know the version 2 of Raptor is being produced. 

Offline rsdavis9

Re: SpaceX Raptor engine - General Thread 4
« Reply #666 on: 08/30/2021 07:52 pm »
Elon in his talk with everyday astronaut said that the V2 Raptors:
1. Same for RB and RC except RC has TVC
2. 230t
3. Should be hitting MacGregor next week.

That doesn't mean that it wont take a while to iron out any kinks.
So we really don't know.
With ELV best efficiency was the paradigm. The new paradigm is reusable, good enough, and commonality of design.
Same engines. Design once. Same vehicle. Design once. Reusable. Build once.

Offline xvel

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Re: SpaceX Raptor engine - General Thread 4
« Reply #667 on: 08/30/2021 07:52 pm »
All raptors on site are raptor 1 ~200t, raptor 2 230t has not been photographed yet, raptor 1 boost has also most likely 200t thrust.

No one is 100% sure about all of this and never will be.
And God said: "Let there be a metric system". And there was the metric system.
And God saw that it was a good system.

Offline ETurner

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Re: SpaceX Raptor engine - General Thread 4
« Reply #668 on: 08/30/2021 08:24 pm »

125 GW is the kinetic energy. [snip]

1 kg of methane has a lower heating value of ~50.3 MJ. One watt is one Joule per second. Therefore, burning 134 kg/s results in 6740 MJ per second or 6.74 GW of energy output! For one engine. So this times 33 (the currently planned final engine count for Booster) results in 222.4 GW of energy output! That's quite a bit.

So the efficiency of thermal-kinetic is  125GW/222GW =56%

What is theoretical max?  56% is off the charts good for thermal-mechanical conversion (e.g. nuke plant is 42% on a very good day)
A rocket engine that expands its exhaust to vacuum with an infinite expansion ratio and no frictional heating would ideally convert all the thermal energy in the exiting gas to kinetic energy. In other words, the theoretical limit for conversion of thermal energy to kinetic energy is 100%. Actual rocket engines can get close enough to this ideal that the exhaust is pretty cold (until it impinges on something!).

People seem to get confused about this, but the key thing to remember is that expansion cools a gas, and large expansion ratios can cool it to a low temperature even if it starts out very hot. (I had to search a bit to find a non-confused answer online: https://www.quora.com/Can-rocket-exhaust-be-colder-than-the-air.)

Heat-engine efficiency limits -- the Carnot limit, (Thot - Tcold)/Thot -- donít apply because rockets donít work by flowing heat through a device from a source (at Thot) to a sink (at Tcold). The system isnít closed, because it spews away mass.

Offline CorvusCorax

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Re: SpaceX Raptor engine - General Thread 4
« Reply #669 on: 08/30/2021 10:25 pm »

125 GW is the kinetic energy. To have a closer look. Raptor 2 will have a mass flow ...

Even just the pump power combined of a 33 engine superheavy (usable turbine shaft power of both oxygen and methane turbopumps combined) will reach 2.1 GW.

That's just in the same ballpark as a medium sized nuclear power plant.

Just to drive the pumps ;)



Offline Aeneas

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Re: SpaceX Raptor engine - General Thread 4
« Reply #670 on: 09/01/2021 08:30 am »
Has the Raptor reached 230 tons of thrust now? 

Are the 230 ton thrust Raptors the 20 that are on the outer rim of the Superheavy booster?

And, are the inner 9 Raptors the 200 ton thrust versions?

If this is true then the Starship has around 14 million lbs thrust in English units?  I was thinking musk was pushing for 15-16 million lbs thrust.

230 t (or Raptor 2) might get to the test stand in the coming months. Current design is about 185 t.
https://twitter.com/elonmusk/status/1420826978102435845?s=20
And yes, if you calculate the full thrust of the 29 Raptor test version, it'll have a terrible TWR. That's why it is most likely that they will fly underfilled. Which is definitely no problem when just carrying a wheel of cheese or just up to 100 t.

Offline Hog

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Re: SpaceX Raptor engine - General Thread 4
« Reply #671 on: 09/02/2021 12:58 am »
Who knows exactly what thrust they are commanding during these very early tests.
Paul

Offline StarshipTrooper

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Re: SpaceX Raptor engine - General Thread 4
« Reply #672 on: 09/02/2021 05:54 am »
Very interesting. So Booster 4, with 29 Raptor1 engines producing 185 tons each would be about 11.8 million lbs thrust.
ďI'm very confident that success is within the set of possible outcomes.Ē  Elon Musk

Offline LMT

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Re: SpaceX Raptor engine - General Thread 4
« Reply #673 on: 09/02/2021 01:55 pm »
just reading this blog about pintles, and it shows raptor pintle test, I am reading this correctly, there is only one pintle used in raptor?
( from this page https://pintleinjector.blogspot.com/2016/12/pintle-injector.html )
pic from that page of raptor pintle

- I don't think we know if there are any pintle injectors in the Raptor.

- I thought that was a picture of a cold flow test of a preburner.

- Does anyone know for sure?

John

Yes, it's a LOX preburner.  Popular photo, page 3.  You and I talked about that photo last year, re: soft-landing engine options. 

1 2 3 and 4.

Quote from: livingjw
"The top picture is an early test of a preburner..."
« Last Edit: 09/02/2021 02:21 pm by LMT »

Offline brettly2021

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Re: SpaceX Raptor engine - General Thread 4
« Reply #674 on: 09/04/2021 11:34 am »
thanks for clearing that up

Offline Hominans Kosmos

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Re: SpaceX Raptor engine - General Thread 4
« Reply #675 on: 09/06/2021 07:41 am »

It's an Elon "long" term goal.  It could be Twitter-war fodder with little basis in reality.

IIRC re-using the first stage of a rocket 10 times was once such a long term goal.
As was cross feed MPS.

Cross feed was a nice to have, rather than a central design requirement. Cross feed compares to original Raptor sizing plans and BFR diameter and other things that were thought as possible avenues for meeting requirements, but not requirements themselves.

Offline envy887

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Re: SpaceX Raptor engine - General Thread 4
« Reply #676 on: 09/17/2021 07:37 pm »
Some engine numbers in this post:

...
Appendix G. Exhaust Plume Calculations (PDF)

I haven't checked them against the KSC assessment to see if anything has changed. The nominal mass flow appears to be 525 kg/s, and engine pressure 253 bar.

Offline FutureSpaceTourist

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Re: SpaceX Raptor engine - General Thread 4
« Reply #677 on: 09/18/2021 02:35 pm »
twitter.com/vincent13031925/status/1414203506186100736

Quote
Elon Musk Shares SpaceX's Starship Raptor Production Plans To Colonize Mars By 2050

https://twitter.com/elonmusk/status/1439224823549411329

Quote
This engine needs to be 10X lower cost. Order of magnitude change is good reason for a new name.

What really matters is not yet another ďadvancedĒ rocket engine, as there are many such devices, but there has never been a cheap (<$1000/Ton-force) rocket engine. Not even close

Offline BT52

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Re: SpaceX Raptor engine - General Thread 4
« Reply #678 on: 09/18/2021 02:52 pm »
1) Guys just though experiment. What are ways that Raptor team could do to really simplify engine architecture?

I was thinking about casting manifolds around main chamber to eliminate all that piping (purge, bypases, regen). Some sort "octovalve" but for raptor system?. That would made (presumably) easier manufacturing, assembly and made whole engine much more reliable and maybe even more compact as is.

2) Other problem i can think off. How much electronic looms u really need and how made its installation robust and reliable enough to even get benefits from said simplifications. Ofc if there are benefits at all.

Offline Okie_Steve

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Re: SpaceX Raptor engine - General Thread 4
« Reply #679 on: 09/18/2021 04:47 pm »
One thing they are already pursuing is economics of scale with the new raptor factory and related volume production of the metallurgy required. Maybe someone with production experience can hazard a likely result on the relative cost going forward.

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