Author Topic: ITS Propulsion – The evolution of the SpaceX Raptor engine  (Read 110748 times)

Offline RedLineTrain

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #500 on: 10/08/2017 03:07 PM »
What are the industry norms on development testing?  Was the SSME Block III proposal especially gold-plated?  Or do some substitute testing of production engines for development testing -- i.e., like I assume SpaceX did with Merlin 1D?

Some things to educate yourself with:

Test and Evaluation Guideline for Liquid Rocket Engines

Liquid Rocket Engine Flight Certification

In general, look at the acceptance criteria of contracts for vehicles engines.

Very interesting, thanks. One thing I picked up is "Testing should demonstrate margin on maximum specified operating life." If you read that literally and simplistically, then all the claims for BFR booster design life imply an extremely long test program.

For sure, it is interesting to take those two documents together, because it shows that none of the engines detailed in the NASA/Richards document (SSME, F-1, J-2, RL-10, LR87, and LR91) had qualification requirements that demonstrated margin.  The SSME had a design life of 27,000 seconds, but a qualification requirement of only 5,000 seconds, at least for the first iteration in the late 70s/early 80s.

That said, a NASA 2011 powerpoint at page 15 appears to show a development/qualification/testing program taken in its entirety to be robust.  Before its first flight, SSME had on the order of 145,000 seconds over 700 test firings.  The design program seems to have been a bit rocky.  Perhaps that necessitated starting over the design testing a lot.

The NASA/Richards document is very good and succinct.  It states clearly that well into the modern rocket age (it is undated but perhaps in the late 80s), there were no industry/government-wide rules and requirements for design and certification and that processes were historically based and heuristic.  Basically, you do design testing until you are satisfied that you are done.  And so no two design testing campaigns are identical.

Edit:  The NASA/Richards document also shows that none of the rocket engines listed were tested for FOD ingestion.
« Last Edit: 10/08/2017 03:16 PM by RedLineTrain »

Offline livingjw

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #501 on: 10/08/2017 03:13 PM »
Question for the thread:  I know the Block 5 merlin has been tested to 145% thrust without issue- assuming the raptor had an equivilant level of engineered reserve, Given the expansion ratio of the Raptor vac, could you use the RaptorVacs to get useful emergency thrust during a near-sea level Abort scenerio?

What’s the Block 5 Merlin ?
Is it Merlin 1E ?

Is it 145% more heavy?

The latest version of Merlin (M-1D) is a standard engine with upgrades for human rating the Falcon 9.  It is basically the same mass engine AFAIK.  The test to 145% power was a validation of margin, I believe, not a new rating for the engine or even a planned operating 'option.'

A long life engine will experience "plastic creep" of its hot and highly stressed parts. (turbines, combustion chamber coolant passages). Running engines at higher than rated temperatures, pressures and speeds greatly reduces life. Running at these conditions during development testing shows margin and provides information about plastic creep and other failure modes.

John

Offline rakaydos

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #502 on: 10/08/2017 05:43 PM »
Question for the thread:  I know the Block 5 merlin has been tested to 145% thrust without issue- assuming the raptor had an equivilant level of engineered reserve, Given the expansion ratio of the Raptor vac, could you use the RaptorVacs to get useful emergency thrust during a near-sea level Abort scenerio?

What’s the Block 5 Merlin ?
Is it Merlin 1E ?

Is it 145% more heavy?

The latest version of Merlin (M-1D) is a standard engine with upgrades for human rating the Falcon 9.  It is basically the same mass engine AFAIK.  The test to 145% power was a validation of margin, I believe, not a new rating for the engine or even a planned operating 'option.'

A long life engine will experience "plastic creep" of its hot and highly stressed parts. (turbines, combustion chamber coolant passages). Running engines at higher than rated temperatures, pressures and speeds greatly reduces life. Running at these conditions during development testing shows margin and provides information about plastic creep and other failure modes.

John

Understood, but the original question was asking for the BFS Abort system thread. While running engines at higher than rated values greatly reduces the life of the engine, I am asking whether it may, in a dramatic situation, contribute to an increase in the life of the payload, given what we know about expansion ratios and TWR. :p

Online Peter.Colin

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #503 on: 10/08/2017 06:13 PM »
Question for the thread:  I know the Block 5 merlin has been tested to 145% thrust without issue- assuming the raptor had an equivilant level of engineered reserve, Given the expansion ratio of the Raptor vac, could you use the RaptorVacs to get useful emergency thrust during a near-sea level Abort scenerio?

What’s the Block 5 Merlin ?
Is it Merlin 1E ?

Is it 145% more heavy?

The latest version of Merlin (M-1D) is a standard engine with upgrades for human rating the Falcon 9.  It is basically the same mass engine AFAIK.  The test to 145% power was a validation of margin, I believe, not a new rating for the engine or even a planned operating 'option.'

A long life engine will experience "plastic creep" of its hot and highly stressed parts. (turbines, combustion chamber coolant passages). Running engines at higher than rated temperatures, pressures and speeds greatly reduces life. Running at these conditions during development testing shows margin and provides information about plastic creep and other failure modes.

John

Understood, but the original question was asking for the BFS Abort system thread. While running engines at higher than rated values greatly reduces the life of the engine, I am asking whether it may, in a dramatic situation, contribute to an increase in the life of the payload, given what we know about expansion ratios and TWR. :p

Falcon 9 Block 5 will have higher thrust than Falcon 9 Full Thrust. We don’t know if the 145%, is higher than planned operation.  Since we don’t know how much more thrust the Fuller than Full thrust will be...



Offline MP99

Very nice drawing  :) I like it!

How high T/W? why is it not made public?
Musk said it was the best ever, so better than M1D.

Cheers, Martin

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Offline AncientU

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #505 on: 10/09/2017 04:33 PM »
Question for the thread:  I know the Block 5 merlin has been tested to 145% thrust without issue- assuming the raptor had an equivilant level of engineered reserve, Given the expansion ratio of the Raptor vac, could you use the RaptorVacs to get useful emergency thrust during a near-sea level Abort scenerio?

What’s the Block 5 Merlin ?
Is it Merlin 1E ?

Is it 145% more heavy?

The latest version of Merlin (M-1D) is a standard engine with upgrades for human rating the Falcon 9.  It is basically the same mass engine AFAIK.  The test to 145% power was a validation of margin, I believe, not a new rating for the engine or even a planned operating 'option.'

A long life engine will experience "plastic creep" of its hot and highly stressed parts. (turbines, combustion chamber coolant passages). Running engines at higher than rated temperatures, pressures and speeds greatly reduces life. Running at these conditions during development testing shows margin and provides information about plastic creep and other failure modes.

John

Understood, but the original question was asking for the BFS Abort system thread. While running engines at higher than rated values greatly reduces the life of the engine, I am asking whether it may, in a dramatic situation, contribute to an increase in the life of the payload, given what we know about expansion ratios and TWR. :p

Falcon 9 Block 5 will have higher thrust than Falcon 9 Full Thrust. We don’t know if the 145%, is higher than planned operation.  Since we don’t know how much more thrust the Fuller than Full thrust will be...

But we do know -- the Block 5 engines are to provide 190,000 lbf of thrust.  The 145% is just a test to destruction (or margin verification) as previously stated.  Please stop trying to make the Block 5 M-1D a 145% rating.
"If we shared everything [we are working on] people would think we are insane!"
-- SpaceX friend of mlindner

Offline Nilof

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #506 on: 10/11/2017 04:02 AM »
Question for the thread:  I know the Block 5 merlin has been tested to 145% thrust without issue- assuming the raptor had an equivilant level of engineered reserve, Given the expansion ratio of the Raptor vac, could you use the RaptorVacs to get useful emergency thrust during a near-sea level Abort scenerio?
Raptor vac. could be designed with a detachable nozzle extension which can be jettisoned in an emergency abort situation. This would allow it to operate at SL along with an emergency thrust reserve to push the ship safely away in an emergency.

Given it is a full regen nozzle, you'd need to set up the plumbing to allow this (upper and lower circuits?) and have valves that shut off in an emergency- otherwise you'll be spewing unburned fuel into the exhaust, within the relatively enclosed interstage area. I'd imagine the base heating would ramp up extremely quickly in this scenario, limiting how long you could burn the RapVacs.
Keep in mind spewing unburnt fuel isnt exactly a drawback when you're struggling to raise your TWR as quickly as possible.

But it wouldn't contribute to thrust, it would be ejected from the severed regen channels and burn somewhere behind the vehicle.
It would also cut off cooling to the remaining part of the nozzle and the chamber, leading to very rapid engine failure.
So any sort of jettisonable nozzle is going to have to address this anyway by redirecting the coolant pathway.

Edited to add: simply chopping off the nozzle would actually lower T:W because all that fuel is lost rather than going to the combustion chamber. So I would assert that even if it is only for use in dire emergencies, it is essential that any sort of nozzle jettison capability must be accompanied by a redirect of the regen pathway. Not impossible, I'm sure, just an added complication.

Does the extension skirt actually need active cooling, or is it radiatively cooled? I'd expect the exhaust to be rather cold when it has expanded 30 times or so...
For a variable Isp spacecraft running at constant power and constant acceleration, the mass ratio is linear in delta-v.   Δv = ve0(MR-1). Or equivalently: Δv = vef PMF. Also, this is energy-optimal for a fixed delta-v and mass ratio.

Offline Kaputnik

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #507 on: 10/11/2017 08:03 AM »
Question for the thread:  I know the Block 5 merlin has been tested to 145% thrust without issue- assuming the raptor had an equivilant level of engineered reserve, Given the expansion ratio of the Raptor vac, could you use the RaptorVacs to get useful emergency thrust during a near-sea level Abort scenerio?
Raptor vac. could be designed with a detachable nozzle extension which can be jettisoned in an emergency abort situation. This would allow it to operate at SL along with an emergency thrust reserve to push the ship safely away in an emergency.

Given it is a full regen nozzle, you'd need to set up the plumbing to allow this (upper and lower circuits?) and have valves that shut off in an emergency- otherwise you'll be spewing unburned fuel into the exhaust, within the relatively enclosed interstage area. I'd imagine the base heating would ramp up extremely quickly in this scenario, limiting how long you could burn the RapVacs.
Keep in mind spewing unburnt fuel isnt exactly a drawback when you're struggling to raise your TWR as quickly as possible.

But it wouldn't contribute to thrust, it would be ejected from the severed regen channels and burn somewhere behind the vehicle.
It would also cut off cooling to the remaining part of the nozzle and the chamber, leading to very rapid engine failure.
So any sort of jettisonable nozzle is going to have to address this anyway by redirecting the coolant pathway.

Edited to add: simply chopping off the nozzle would actually lower T:W because all that fuel is lost rather than going to the combustion chamber. So I would assert that even if it is only for use in dire emergencies, it is essential that any sort of nozzle jettison capability must be accompanied by a redirect of the regen pathway. Not impossible, I'm sure, just an added complication.

Does the extension skirt actually need active cooling, or is it radiatively cooled? I'd expect the exhaust to be rather cold when it has expanded 30 times or so...

Quote
Will be full regen cooled all the way out to the 3 meter (10 ft) nozzle diameter. Heat flux is nuts & radiative view factor is low.

https://mobile.twitter.com/elonmusk/status/877341165808361472?lang=en-gb
Waiting for joy and raptor

Online Oersted

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #508 on: 10/12/2017 07:52 PM »
Gwynne Shotwell Q&A. The quote below is not verbatim but from notes by Reddit-user "Sticklefront": https://www.reddit.com/r/spacex/comments/75ufq9/interesting_items_from_gwynne_shotwells_talk_at/

"What is the biggest obstacle to the BFR's success?

The composite tanks will be challenge, but we are doing it already. We are currently building a larger raptor right now, and currently have a scaled version of raptor on the test stands. Harder than the rocket, though, will be where poeple are going to live, what will life be like, what will they do there? Also, while the choice of fuel for the BFR was constrained by resource availability on Mars, it is no accident that the final choice of methane is the cheapest energy source here on earth. This will greatly facilitate the economics side of things."

Offline Manabu

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #509 on: 10/13/2017 03:25 PM »
Historically rocket builders have frequently launched extremely expensive engine development programs in search of larger engines. Were they wrong to do so?
Probably not.

Historically, rockets used analog computers to control the engines. More engines increase complexity more than linearly, which means both heavier and more difficult to design avionics. Think N1 KORD as an extreme and failed example.

Miniaturized digital computers you can program, optical cables, etc, diminish the mass and complexity of such systems significantly, allowing more engines to be used economically. So, probably since the 90s, multiple engine rockets became more viable.

Online Lars-J

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #510 on: 10/13/2017 04:25 PM »
Historically rocket builders have frequently launched extremely expensive engine development programs in search of larger engines. Were they wrong to do so?
Probably not.

Historically, rockets used analog computers to control the engines. More engines increase complexity more than linearly, which means both heavier and more difficult to design avionics. Think N1 KORD as an extreme and failed example.

Miniaturized digital computers you can program, optical cables, etc, diminish the mass and complexity of such systems significantly, allowing more engines to be used economically. So, probably since the 90s, multiple engine rockets became more viable.

I disagree... Many engines have been a viable option since the beginning of the space age.

Just look at the Saturn I(B), it flew fine with 8 engines in the 60's. R-7 has flown with 5 engines for decades. The problem with the N-1 was primarily a lack of testing. More engines have been a viable option for many decades, and it took SpaceX to break that industry trend of "fewer is better, one is best" that was reaching absurd levels in the last few decades.
« Last Edit: 10/13/2017 04:26 PM by Lars-J »

Offline intrepidpursuit

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #511 on: 10/13/2017 10:40 PM »
The F1 was built by hand with people welding thousands of parts together to make mechanical works of art. The RL-10 was made basically the same way. When the manufacturing method and complexity doesn't scale, you want to make as big an engine as you can so there are fewer places to go wrong.

Now we have the capability to mass produce something the size of a Raptor, which brings the cost per unit down dramatically. The effort goes into building the tooling rather than the engine. Now, if you build a bigger engine you are building bigger tooling that will get less use, so you get more cost and less reliability inherently. If you can build a smaller engine that is an order of magnitude more reliable than the old hand built engines then you want to design for manufacturability.

I think the difference is in the way engines are built now and the way they can be modeled. Economy of scale shifts to favoring quantity over size.

Offline matthewkantar

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #512 on: 10/13/2017 11:38 PM »
As has been noted about the Merlin engines in the F-9, lots of engines means a much more rapid acquisition of reliability data. A successful flight of the booster will pile up somewhere around 4500 seconds of engine time. Engine data will be amassed three plus times faster than on the F-9, 31 times faster than on Atlas or Vulcan.

Matthew

Offline DJPledger

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #513 on: 10/15/2017 08:08 PM »
Future BFR’s with 200 or much more engines really wouldn’t surprise me at all.
Raptor no. on BFR system has been determined by the need for the ship to have engine out capability for landing and using single engine design throughout the system while keeping complexity to the minimum required level. For future larger BFR's just scale up Raptor thrust with BFR system mass to keep engine no. same as current BFR.

EM said in his recent Reddit AMA that Raptor can easily be scaled from 1MN to 1.7MN at SL so further scale ups of Raptor for future larger BFR systems should not be too difficult.

Offline RedLineTrain

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #514 on: 10/15/2017 08:37 PM »
Excerpts from Musk's AMA yesterday related to Raptor.

------

Q:  Why was Raptor thrust reduced from ~300 tons-force to ~170 tons-force?
A:  We chickened out
A:  The engine thrust dropped roughly in proportion to the vehicle mass reduction from the first IAC talk. In order to be able to land the BF Ship with an engine failure at the worst possible moment, you have to have multiple engines. The difficulty of deep throttling an engine increases in a non-linear way, so 2:1 is fairly easy, but a deep 5:1 is very hard. Granularity is also a big factor. If you just have two engines that do everything, the engine complexity is much higher and, if one fails, you've lost half your power. Btw, we modified the BFS design since IAC to add a third medium area ratio Raptor engine partly for that reason (lose only 1/3 thrust in engine out) and allow landings with higher payload mass for the Earth to Earth transport function.

Q:  Could you update us on the status of scaling up the Raptor prototype to the final size?
A:  Thrust scaling is the easy part. Very simple to scale the dev Raptor to 170 tons.

The flight engine design is much lighter and tighter, and is extremely focused on reliability. The objective is to meet or exceed passenger airline levels of safety. If our engine is even close to a jet engine in reliability, has a flak shield to protect against a rapid unscheduled disassembly and we have more engines than the typical two of most airliners, then exceeding airline safety should be possible.

That will be especially important for point to point journeys on Earth. The advantage of getting somewhere in 30 mins by rocket instead of 15 hours by plane will be negatively affected if "but also, you might die" is on the ticket.

Q:  Will the BFS methalox control thrusters be derived from Raptor or from SuperDraco engines?
A:  The control thrusters will be closer in design to the Raptor main chamber than SuperDraco and will be pressure-fed to enable lowest possible impulse bit (no turbopump spin delay).

Q:  Will the BFR autogenous pressurization system be heat exchanger based?  You told us previously that the BFR will eliminate the use of Helium and use hot oxygen and hot CH4 to auto-pressurize the propellant tanks.  Can you tell us more about this new system, will it involve heating the propellants at the engines via heat exchangers and routing the hot gas back to the tanks via pipes, or will they use some other method?  If it's heat exchanger based, will all Raptor engines have heat exchangers?
A:  We plan to use the Incendio spell from Harry Potter
A:  But, yes and probably

Q:  Will Raptor engines be (metal-) 3D printed?
A:  Some parts of Raptor will be printed, but most of it will be machined forgings. We developed a new metal alloy for the oxygen pump that has both high strength at temperature and won't burn. Pretty much anything will burn in high pressure, hot, almost pure oxygen.

Q:  Can BFS vacuum-Raptors be fired at sea level pressure?
A:  The "vacuum" or high area ratio Raptors can operate at full thrust at sea level. Not recommended.
« Last Edit: 10/16/2017 04:06 PM by RedLineTrain »

Offline RedLineTrain

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #515 on: 10/15/2017 09:05 PM »
Quote from: EM AMA
The flight engine design is much lighter and tighter, and is extremely focused on reliability. The objective is to meet or exceed passenger airline levels of safety. If our engine is even close to a jet engine in reliability, has a flak shield to protect against a rapid unscheduled disassembly and we have more engines than the typical two of most airliners, then exceeding airline safety should be possible.

The NASA/Richards document continues to be golden.  Thanks again, Space Ghost.  It shows a jet fighter engine qualification requirement to be 150 hours (540,000 seconds), or roughly two orders of magnitude more than the original SSME qualification requirement.

The 150 hour requirement also appears to be replicated in the FAA type certification requirements for endurance testing.  Perhaps because Raptor only fires for a short time compared to jet engines, the qualification requirements arrived at for Raptor may be less, at least in duration.

Edit:  Reliability for modern jet engines seems pretty extreme.  GE's G90 powerplant (used on the Boeing 777) is said to have an in-flight shutdown rate of one per million engine flight hours.
« Last Edit: 10/15/2017 09:18 PM by RedLineTrain »

Online yokem55

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #516 on: 10/15/2017 10:40 PM »
Quote
Q:  Will the BFS methalox control thrusters be derived from Raptor or from SuperDraco engines?
A:  The control thrusters will be closer in design to the Raptor main chamber than SuperDraco and will be pressure-fed to enable lowest possible impulse bit (no turbopump spin delay).
I'm curious what kind of ignition these will use. I would think even sparker ignition might be too slow. Could they have a hot ignition coil in the combustion chamber that stays heated when it is anticipated that they might need to be fired?

Offline envy887

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #517 on: 10/15/2017 10:43 PM »
Quote from: EM AMA
The flight engine design is much lighter and tighter, and is extremely focused on reliability. The objective is to meet or exceed passenger airline levels of safety. If our engine is even close to a jet engine in reliability, has a flak shield to protect against a rapid unscheduled disassembly and we have more engines than the typical two of most airliners, then exceeding airline safety should be possible.

The NASA/Richards document continues to be golden.  Thanks again, Space Ghost.  It shows a jet fighter engine qualification requirement to be 150 hours (540,000 seconds), or roughly two orders of magnitude more than the original SSME qualification requirement.

The 150 hour requirement also appears to be replicated in the FAA type certification requirements for endurance testing.  Perhaps because Raptor only fires for a short time compared to jet engines, the qualification requirements arrived at for Raptor may be less, at least in duration.

Edit:  Reliability for modern jet engines seems pretty extreme.  GE's G90 powerplant (used on the Boeing 777) is said to have an in-flight shutdown rate of one per million engine flight hours.
Long haul intercontinental jet flights run the engines 100 to 1000 times longer per flight then a P2P rocket would.

Offline Gliderflyer

Quote
Q:  Will the BFS methalox control thrusters be derived from Raptor or from SuperDraco engines?
A:  The control thrusters will be closer in design to the Raptor main chamber than SuperDraco and will be pressure-fed to enable lowest possible impulse bit (no turbopump spin delay).
I'm curious what kind of ignition these will use. I would think even sparker ignition might be too slow. Could they have a hot ignition coil in the combustion chamber that stays heated when it is anticipated that they might need to be fired?
I don't have any inside information, but I would bet they will use normal spark torch igniters. I have worked with them before, and they have a pretty fast response time that should be more than adequate for an RCS system.
I tried it at home

Offline guckyfan

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Re: ITS Propulsion – The evolution of the SpaceX Raptor engine
« Reply #519 on: 10/16/2017 09:51 AM »
Quote
Q:  Will the BFS methalox control thrusters be derived from Raptor or from SuperDraco engines?
A:  The control thrusters will be closer in design to the Raptor main chamber than SuperDraco and will be pressure-fed to enable lowest possible impulse bit (no turbopump spin delay).
I'm curious what kind of ignition these will use. I would think even sparker ignition might be too slow. Could they have a hot ignition coil in the combustion chamber that stays heated when it is anticipated that they might need to be fired?
I don't have any inside information, but I would bet they will use normal spark torch igniters. I have worked with them before, and they have a pretty fast response time that should be more than adequate for an RCS system.

The Morpheus moon lander testbed uses spark ignition and it does high frequency firing bursts. I guess a 5 or 10t thruster will not be quite as fast but it does not need to be.

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