Stoke Space

[tater]

7 minutes ago, JoeSchmuckatelli said:

They're certainly doing interesting stuff, have a cool name and fun vids

They have a decent chance to succeed as well. I think their concept of stage 2 reuse is simpler/better than Starship, tbh.

[JoeSchmuckatelli]

20 minutes ago, tater said:

They have a decent chance to succeed as well. I think their concept of stage 2 reuse is simpler/better than Starship, tbh.

One of the things I've seen from them is that they appear to be keen students of SX.  Inspired by certain SX choices, cautioned, informed and imitative while still innovating in their own right.

It's one sign of SX's success, and I hope a harbinger of good things to come.

--- the thing I've liked about SX is they're taking Rocket Science from being something wholly in the realm of the wizards of government/academia/contractors and making it look a lot more blue collar / shade-tree-mechanic.  The 'common as commercial air' idea is actually a good one.  Stoke seems to be a beneficiary of the changing attitudes.

[Royalswissarmyknife]

I only have one question for stoke.

Wen Hop?

[sevenperforce]

WHOAAAAAA

They're doing differential throttle control after all!

Go Stoke!

[tater]

1 hour ago, sevenperforce said:

Go Stoke!

I frickin love these guys.

There's a nonzero chance this vehicle gets the first stage 2 rapid reuse.

[Exoscientist]

 Mystified why Stokes Space won’t consider using the aerospike on the first stage. Literally  the only thing it would require is using a longer spike beneath the stage, so you get the full adaptive nozzle capabilities of the aerospike, i.e., operable at sea level while getting high vacuum optimized ISP in vacuum.

 NASA showed with the XRS-2200 twenty years ago this works.

https://en.wikipedia.org/wiki/Rocketdyne_XRS-2200

 

    Bob Clark

[tater]

36 minutes ago, Exoscientist said:

 Mystified why Stokes Space won’t consider using the aerospike on the first stage. Literally  the only thing it would require is using a longer spike beneath the stage, so you get the full adaptive nozzle capabilities of the aerospike, i.e., operable at sea level while getting high vacuum optimized ISP in vacuum.

Why?

The booster is only giving the thing a couple km/s. Yes, they'd save a few percent of booster props from the average I_sp being higher.  It doesn't buy enough. Vacuum I_sp for methalox is an upper limit something like 380s. Sea level is ~330s. A SL methalox engine running in vacuum gets maybe 350s. So the difference is ~30s of I_sp, and the average will be somewhere in the middle.

I'd be mystified if they did an aerospike.

[sevenperforce]

34 minutes ago, tater said:

I'd be mystified if they did an aerospike.

Same. It wouldn't make any sense at all to use an aerospike on the first stage.

1 hour ago, Exoscientist said:

Mystified why Stokes Space won’t consider using the aerospike on the first stage. Literally  the only thing it would require is using a longer spike beneath the stage

This doesn't really make sense. There can't be a "longer spike" beneath the first stage because there isn't a spike beneath the first stage.

And for the record, the term "aerospike" really refers to a truncated plug engine, because the entrained air under the plug acts like a virtual spike. What you're referring to is a non-truncated plug nozzle, which looks like a lance.

But anyway, there isn't any spike beneath the first stage right now, so converting from conventional engines to an aerospike is nontrivial. There are seven engines on the first stage. Do you propose converting all seven to individual annular aerospike engines, or are you envisioning a single plug nozzle with the engine combustion chambers wrapped around it?  If the former, how do you suggest Stoke solve the combustion problems that have plagued all annular aerospike engines to date? If the latter, how do you suggest Stoke handle vertical landing?

1 hour ago, Exoscientist said:

so you get the full adaptive nozzle capabilities of the aerospike, i.e., operable at sea level while getting high vacuum optimized ISP in vacuum.

Well, that's not exactly how an aerospike works. An aerospike isn't vacuum-optimized in vacuum; it is simply better than a sea level nozzle. Similarly, while an aerospike is operable at sea level, it is not nearly as efficient at sea level as a sea level nozzle, so you end up with a thrust shortfall and specific impulse shortfall at liftoff. This couples destructively with the enormous weight penalty of an aerospike design to increase gravity drag. In most designs this seriously obviates any advantages from slightly increased specific impulse in vacuum.

[magnemoe]

1 hour ago, tater said:

Why?

The booster is only giving the thing a couple km/s. Yes, they'd save a few percent of booster props from the average I_sp being higher.  It doesn't buy enough. Vacuum I_sp for methalox is an upper limit something like 380s. Sea level is ~330s. A SL methalox engine running in vacuum gets maybe 350s. So the difference is ~30s of I_sp, and the average will be somewhere in the middle.

I'd be mystified if they did an aerospike.

Would aerospikes make more sense on an first stage with SRB so it runs for longer, think SLS rater than two stage rockets?

[JoeSchmuckatelli]

31 minutes ago, sevenperforce said:

, that's not exactly how an aerospike works

Can you (or someone) point me to a decent resource on what aerospikes are good for? 

I thought it was a clever design that increases efficiency, but the only drawback was current materials science... Sounds like there is more to it than I suspected. 

[darthgently]

45 minutes ago, JoeSchmuckatelli said:

Can you (or someone) point me to a decent resource on what aerospikes are good for? 

I thought it was a clever design that increases efficiency, but the only drawback was current materials science... Sounds like there is more to it than I suspected. 

From what I've gathered from your posts, you do get what they are good for.  But for a first stage where the vacuum advantages are short lived if any it may not be worth the extra combustion chamber complexity.  Advances in the circular detonation stuff may change that is what I'm thinking, but even that is more complex than a standard engine+nozzle

[tater]

Plug/aerospikes have been proposed for a long time, generally for SSTO designs. The point being that since you're dragging the engines from the launch pad to orbit, you should make them closer to optimal for both use cases (sea level, and vacuum).

Putting them on a booster for a 2 stage design gains so little it's not worth even thinking about, the engines are not being carried to orbit.

1 hour ago, magnemoe said:

Would aerospikes make more sense on an first stage with SRB so it runs for longer, think SLS rater than two stage rockets?

RS-25 actually has a decent I_sp. Looks like the various aerospikes tested have lower SL Isp than RS-25, and similar I_sp in vacuum. So probably doesn't help—and even if it would, such a small amount that it makes no useful difference. The problem with SLS is that it has no path to ever get the payload to orbit it must to be useful with Orion on top (useful here defined as the ability to do single stack missions to the lunar surface and back).

On topic for Stoke, the plug engine on stage 2 is incidental. They are optimizing for an actively cooled heatshield that happens to have engines (cause it needs them ).

[magnemoe]

25 minutes ago, tater said:

Plug/aerospikes have been proposed for a long time, generally for SSTO designs. The point being that since you're dragging the engines from the launch pad to orbit, you should make them closer to optimal for both use cases (sea level, and vacuum).

Putting them on a booster for a 2 stage design gains so little it's not worth even thinking about, the engines are not being carried to orbit.

RS-25 actually has a decent I_sp. Looks like the various aerospikes tested have lower SL Isp than RS-25, and similar I_sp in vacuum. So probably doesn't help—and even if it would, such a small amount that it makes no useful difference. The problem with SLS is that it has no path to ever get the payload to orbit it must to be useful with Orion on top (useful here defined as the ability to do single stack missions to the lunar surface and back).

On topic for Stoke, the plug engine on stage 2 is incidental. They are optimizing for an actively cooled heatshield that happens to have engines (cause it needs them ).

Yes the RS-25 is amazing, has anybody thought on extending nozzles on long burning first stage engines? Shuttle is all the way to orbit after all. 

[tater]

35 minutes ago, magnemoe said:

Yes the RS-25 is amazing, has anybody thought on extending nozzles on long burning first stage engines? Shuttle is all the way to orbit after all. 

At 453s, I don't see much room for improvement on those engines.

The only reason for a sustainer is to reuse the engines—something only Shuttle ever did, and refurb cost for those made it pretty much pointless.

[sevenperforce]

2 hours ago, magnemoe said:

Yes the RS-25 is amazing, has anybody thought on extending nozzles on long burning first stage engines? Shuttle is all the way to orbit after all. 

The RS-25 does have a vacuum-sized nozzle. That's why it is able to get over 450 seconds of specific impulse in vacuum. That's also why it has such a low thrust/area ratio. If you look at an RS-25 in person, you'll see that the powerhead itself is very small compared to the nozzle.

The only reason that the RS-25 can fire at sea level without ripping itself apart is that the end of the nozzle angles back in toward the center, creating a high-pressure region at the outer lip which prevents flow separation. Unfortunately this results in a pretty severe loss of thrust and specific impulse at sea level.  The RS-68 gets a nice respectable 365 seconds of specific impulse at sea level despite being a gas generator engine, while the RS-25 only gets 366 seconds -- just a single second of specific impulse more -- despite having a vastly more efficient turbopump cycle and much larger nozzle.

2 hours ago, tater said:

RS-25 actually has a decent I_sp. Looks like the various aerospikes tested have lower SL Isp than RS-25, and similar I_sp in vacuum.

Aerospikes (especially multi-chamber aerospikes) usually suffer from being overweight, so combustion chamber pressures are kept low to avoid making the chambers too heavy; the designs rely on the large nozzle to get respectable specific impulse despite the low chamber pressure. Thanks to staged combustion, the RS-25 has a pretty phenomenal chamber pressure at 206 bar, compared to the paltry 58 bar of a design like the XRS-2200.

[Exoscientist]

On 6/14/2023 at 11:42 AM, tater said:

Why?

The booster is only giving the thing a couple km/s. Yes, they'd save a few percent of booster props from the average I_sp being higher.  It doesn't buy enough. Vacuum I_sp for methalox is an upper limit something like 380s. Sea level is ~330s. A SL methalox engine running in vacuum gets maybe 350s. So the difference is ~30s of I_sp, and the average will be somewhere in the middle.

I'd be mystified if they did an aerospike.

 They will first test the upper stage on the ground, a “hopper”.  The upper stage will use hydrogen so these first hopper experiments will use hydrogen. The XRS-2200 engine showed you can get quite high vacuum ISP of even a first stage engine by using an aero spike. Then quite key is to recognize a large portion of the flight of even a first stage is under near vacuum conditions so an aero spike can increase performance of a first stage of a two stage vehicle, thereby increasing the performance of the rocket overall.

  Robert Clark

Edited June 19, 2023 by Exoscientist

[Exoscientist]

On 6/14/2023 at 2:09 PM, darthgently said:

From what I've gathered from your posts, you do get what they are good for.  But for a first stage where the vacuum advantages are short lived if any it may not be worth the extra combustion chamber complexity.  Advances in the circular detonation stuff may change that is what I'm thinking, but even that is more complex than a standard engine+nozzle

 

 Actually a key fact is a significant proportion of a first stage firing is under near vacuum conditions, where a vacuum optimized engine would improve its performance. See this graphic of a Delta IV flight for example. The first stage fires all the way to 120 km altitude.

 The Falcon 9 first stage also fires until quite high altitude, nearly at vacuum, at ca. 80 km.

   Bob Clark

[tater]

57 minutes ago, Exoscientist said:

 They will first test the upper stage on the ground, a “hopper”.  The upper stage will use hydrogen so these first hopper experiments will use hydrogen. The XRS-2200 engine showed you can get quite high vacuum ISP of even a first stage engine by using an aero spike. Then quite key is to recognize a large portion of the flight of even a first stage is under near vacuum conditions so an aero spike can increase performance of a first stage of a two stage vehicle, thereby increasing the performance of the rocket overall.

Not necessarily. Mass matters, TWR matters. Buying a few seconds of I_sp doesn't matter if you burn more on gravity losses. All for maybe 30s of I_sp.

9 minutes ago, Exoscientist said:

 Actually a key fact is a significant proportion of a first stage firing is under near vacuum conditions, where a vacuum optimized engine would improve its performance. See this graphic of a Delta IV flight for example. The first stage fires all the way to 120 km altitude.

Not even remotely comparable. DIV stages at 4.72 km/s, more than twice what a reusuable stage 1 stages at. Even assuming downrange landing (vs boostback to the launch site) it needs to either be built to deal with much higher entry temps (increasing mass, killing small I_sp gains), or it has to do a F9 style entry burn (reserving more prop mass). Pretty much all the booster reuse concepts are following the lead of SpaceX as they have to deal with the same issue. You want minimal TPS on the booster and min prop reserves for EDL. S2 reuse requires much more effort, and has to be done regardless of S1 reuse difficulty, so concentrate on that, don't burden the booster with reuse mass it doesn't need.

[magnemoe]

4 hours ago, Exoscientist said:

 They will first test the upper stage on the ground, a “hopper”.  The upper stage will use hydrogen so these first hopper experiments will use hydrogen. The XRS-2200 engine showed you can get quite high vacuum ISP of even a first stage engine by using an aero spike. Then quite key is to recognize a large portion of the flight of even a first stage is under near vacuum conditions so an aero spike can increase performance of a first stage of a two stage vehicle, thereby increasing the performance of the rocket overall.

  Robert Clark

Hopping tests is to test the real life braking and landings with turbulence and wind also wind over the engines, like the Starship hops or the grasshopper for testing falcon 9 landings .
If they want more airtime, they can do an two stage suborbital flight like new Shepard if it was an second stage (how about triggering the launch abort system after first stage separation  (Yes you will be billed for replacing it or the capsule or you burn up together with the innocent passengers ))  
But at this point you might just as well go for orbit. Launch empty so first stage can do an boost back and have lots of room to land. Second stage will also get the reentry system tested, it likely fails the first time. 

[magnemoe]

On 6/12/2023 at 9:53 PM, tater said:

I frickin love these guys.

There's a nonzero chance this vehicle gets the first stage 2 rapid reuse.

I bet they beat SpaceX on reuse. Simply as this upper stage you can put on an trailer after landing and you can land it in any remote area in the US designated for this stuff. 

Yes Starship is two order of magnitude more impressive but it not road portable in an economic sense outside prepared routes. 
Or can you land Starship at the KSC  complex? after 10 successful landings at multiple reentry trajectories?
Shuttle could and it came in to KSC in the same weight range and more shallow but it was not an private project from Musk. 
Bocka Chicka: No simply as you will overfly Mexico on most trajectories, even if Musk bribe the Mexican officials to allow it the US will mpt, the Chinese will pay more in bribes for access to the wreck also Mexicans might getting killed. 
I thought the oil rigs was for Starship catch and landing for reuse, you could then either load onto an ship or barge or later do an ballistic jump who is much safer as over sea and an fixed trajectory. 

[darthgently]

6 hours ago, Exoscientist said:

Actually a key fact is a significant proportion of a first stage firing is under near vacuum conditions, where a vacuum optimized engine would improve its performance. See this graphic of a Delta IV flight for example. The first stage fires all the way to 120 km altitude.

The first stage starts at 0m/s and ends somewhere much nearer to, but short of, orbital velocity, so the actual time spent at lower altitudes compared to higher altitudes is much greater than the diagram you posted suggests, as it is simply the path taken and the horizonal axis is not time

[tater]

I understand trying to come up with better variants of crappy rockets that suffer from design-by-politics (Ariane 6, SLS, etc), but I don't understand second guessing people who have clearly thought about all the trade offs for a vehicle like the one Stoke is building.

Andy Lapsa explains why an aerospike is a poor booster choice in the video posted up thread (the aerospike discussion is timestamped, but I linked at that timestamp):

 

Edited June 19, 2023 by tater

[JoeSchmuckatelli]

6 hours ago, tater said:

Andy Lapsa

I'm watching the video and listening to him... And can't help but see the depictions of the engineers and scientists in movies about the 50s and 60s in my mind's eye. 

The contrast is - well, punk rock comes to mind. 

"... You beat the crap out of them enough and work through the bugs, and you end up with something really resilient" 

 

Hell yeah! 

[Exoscientist]

22 hours ago, tater said:

Not necessarily. Mass matters, TWR matters. Buying a few seconds of I_sp doesn't matter if you burn more on gravity losses. All for maybe 30s of I_sp.

Not even remotely comparable. DIV stages at 4.72 km/s, more than twice what a reusuable stage 1 stages at. Even assuming downrange landing (vs boostback to the launch site) it needs to either be built to deal with much higher entry temps (increasing mass, killing small I_sp gains), or it has to do a F9 style entry burn (reserving more prop mass). Pretty much all the booster reuse concepts are following the lead of SpaceX as they have to deal with the same issue. You want minimal TPS on the booster and min prop reserves for EDL. S2 reuse requires much more effort, and has to be done regardless of S1 reuse difficulty, so concentrate on that, don't burden the booster with reuse mass it doesn't need.

 

 As I said even the Falcon 9 first stage fires into quite high altitude, ca. 80 km. It is the case for any two-stage vehicle the first stage fires into near vacuum altitude, where the vacuum ISP is the one that would obtain. Then an adaptive nozzle on a first stage that would give it the same vacuum Isp as a vacuum optimized nozzle of an upper stage would improve the overall rocket performance.

  Robert Clark

Edited June 20, 2023 by Exoscientist

[tater]

13 minutes ago, Exoscientist said:

 As I said even the Falcon 9 first stage fires into quite high altitude, ca. 80 km. It is the case for any two-stage vehicle the first stage fires into near vacuum altitude, where the vacuum ISP is the one that would obtain. Then an adaptive nozzle on a first stage that would give it the same vacuum Isp as a vacuum optimized nozzle of an upper stage would improve the overall rocket performance.

Except an aerospike masses more, and takes up more room. So in return for a few seconds of I_sp gain, it loses TWR, the trade is not worth it. Firefly started with a toroidal aerospike... and abandoned it.

The only use-case for an aerospike I think is for an SSTO.

But what does every single rocket company on earth know?