Stoke Space Technologies: General Company and Development Updates and Discussions

[TorenAltair]

Full power, all engines:

https://twitter.com/stoke_space/status/1569868769153142787

[john smith 19]

Full power, all engines:

https://twitter.com/stoke_space/status/1569868769153142787

Full reusability, plug nozzle (or "truncated aerospike" depending on your terminology) and LH2.

Now these guys actually are doing something different.

[Asteroza]

So this seems to be one pump pack feeding all chambers?

[john smith 19]

So this seems to be one pump pack feeding all chambers?

That's the implication. Of course it could just be one at the moment, to fire up the ring.

This recalls the 25Klb dual expander plug nozzle Rocketdyne did for the USAF in 1974 by one of the authors of "Huzel & Hwang. "

Despite Bono's fondness for pitching differential throttling it was designed to gimbal.

Not sure if this one is though.

[sevenperforce]

So this seems to be one pump pack feeding all chambers?

I believe in their latest tweet they said they had "both pumps" and "all chambers" firing which suggests exactly two pumps and fifteen chambers.

However the ring looks like it has extra space and a hole between each engine for an extra combustion nozzle so thirty total makes more sense. That way, too, they can be turned off in pairs to help reduce deep throttle requirements during the landing burn.

Despite Bono's fondness for pitching differential throttling it was designed to gimbal.

Not sure if this one is though.

The patent disclosure talks about the entire engine assembly gimbaling but it's in the "in addition to, or as an alternative to" section so it may or may not be plan A. But there's no talk of differential throttling.

"The vehicle is an upper stage rocket. The centerbody is a truncated toroidal aerospike having a centerbody base that partially defines the aft end of the vehicle. The engine is recessed into a base surface of the vehicle. The outer expansion surface is integrally connected to the vehicle, and the augmented aerospike nozzle includes a seal that allows the centerbody to gimbal while allowing the outer expansion surface to remain fixed with respect to the vehicle."

It later notes, "The nozzle includes a seal (e.g., hot gas seal formed by metal bellows) that allows the centerbody to gimbal while allowing the outer expansion surface to remain fixed with respect to the second stage rocket. The seal extends between [the] forward end of the outer expansion surface and the outer aft end of the initial nozzle portion." It goes on to state that it's also possible to have the seal in another place so that both the inner and outer expansion surfaces gimbal together.

[Robotbeat]

The Dec21 posts had them targeting $250kg launch cost on 1650kg RLV. Think they are way to optimistic. If they can do $5000-10000 should have chance of competing.

The better market to go after with reuseable 2nd stage is downmass. This can be cargo from spacestations or just on it own where experiments or 0g manufacturing is done in 2nd stage over few weeks. Could easily charge $20m a flight not have any competition.

Theyll need $250/kg to compete fully against F9 (which can do $1000/kg marginal cost) or early Starship and Terran-R.

[Robotbeat]

https://twitter.com/JoelSercel/status/1563168808793018370

Not my place to say what it is, but STOKE has the most advanced rocket technology in the world but it is based on sound engineering. A full generation beyond Starship and vastly better.  I am very positive about STOKE.

I think people get pretty enamored by aerospikes. There’s little advantage over just a high chamber pressure, and basically no real advantage for an upper stage. At the expense of low thrust to weight ratio. The reentry method playing well with the aero spike concept is clever, but I’m not sure it’s really so much better than a conventional approach.

People also get too enamored with hydrogen. Besides the handling difficulties, the dry mass of the tanks and the pumps just is much worse for hydrolox than other fuels, largely negating the Isp advantage (especially if you use it fuel rich on both first and second stages).


All that said, they avoided the biggest pitfall of all by choosing two stages instead of the usual single stage that this aerospike/reentry concept had been paired with in the past. Two stages means that the poor thrust to weight ratio of an aerospike, and the really bad dry mass of hydrolox won’t hurt them too much. It’ll still be able to get to orbit even when their optimistic assumptions meet reality. And choosing to tackle full reuse is awesome; just like with Falcon 9 and partial reuse, anyone that doesn’t eventually go full reuse will be outcompeted by those who do.

I worry a little that it suffers from the too-clever-by-half, novelty for novelty’s sake approach to RLVs, part of what killed X-33 so completely (and which likely would’ve kept it from even achieving F9’s cost per kg even if they had managed to get VentureStar to orbit). (And Starship isn’t completely immune to this, honestly… we’ll see if the chopsticks end up working well for them or not.)

But making it two stages means they can do several things suboptimally and still achieve orbit.

[sevenperforce]

I think people get pretty enamored by aerospikes. There’s little advantage over just a high chamber pressure, and basically no real advantage for an upper stage. At the expense of low thrust to weight ratio. The reentry method playing well with the aero spike concept is clever, but I’m not sure it’s really so much better than a conventional approach.

People also get too enamored with hydrogen. Besides the handling difficulties, the dry mass of the tanks and the pumps just is much worse for hydrolox than other fuels, largely negating the Isp advantage (especially if you use it fuel rich on both first and second stages).

I agree that people get too enamored with aerospikes, generally, but this isn't really a traditional aerospike; it has an outer expansion nozzle. In a low-pressure environment, the outer expansion region is going to act just like the engine bell of a conventional de Laval nozzle.

The revolutionary idea here is a truly actively-cooled heat shield, something that has never been attempted. And on top of that, it gets to use the same heat exchangers, turbines, and pumps that the engines use, so there's no added weight penalty. Using active cooling without any heavy heat shield is a novel route to rapid reusability.

[Robotbeat]

Actively cooled heatshields have been done before. On the base of the F9 booster, no less.

Again, there’s not necessarily any big gains from novelty. Using 2 pumps for a dozen engines has plumbing overhead unless you’re planning on operating at low pressure, in which case there’s a pressure overhead.

And you don’t need much pressure for active cooling of a heatshield.

(Active cooling of a heatshield is a good idea, of course, for enabling fast turnaround for a reusable upper stage.)

[HMXHMX]

I think people get pretty enamored by aerospikes. There’s little advantage over just a high chamber pressure, and basically no real advantage for an upper stage. At the expense of low thrust to weight ratio. The reentry method playing well with the aero spike concept is clever, but I’m not sure it’s really so much better than a conventional approach.

People also get too enamored with hydrogen. Besides the handling difficulties, the dry mass of the tanks and the pumps just is much worse for hydrolox than other fuels, largely negating the Isp advantage (especially if you use it fuel rich on both first and second stages).

I agree that people get too enamored with aerospikes, generally, but this isn't really a traditional aerospike; it has an outer expansion nozzle. In a low-pressure environment, the outer expansion region is going to act just like the engine bell of a conventional de Laval nozzle.

The revolutionary idea here is a truly actively-cooled heat shield, something that has never been attempted. And on top of that, it gets to use the same heat exchangers, turbines, and pumps that the engines use, so there's no added weight penalty. Using active cooling without any heavy heat shield is a novel route to rapid reusability.

Ah, a number of us have proposed and even built components for actively cooled heat shield integrated with plug-type propulsion...it is a good idea but not novel.

[HMXHMX]

Single J-2S class pump, multiple chambers, 15 ft diameter actively cooled plug with short Delta II fairing (8 ft dia) on top.  Thousand pound payload. 

Designed in 1977.

[Elmar Moelzer]

Single J-2S class pump, multiple chambers, 15 ft diameter actively cooled plug with short Delta II fairing (8 ft dia) on top.  Thousand pound payload. 

Designed in 1977.

I noted earlier how much their upper stage reminds me of the Phoenix SSTO. Maybe they are thinking about taking it to an SSTO once they have a TSTO that makes profit (if).

[Robotbeat]

I think people get pretty enamored by aerospikes. There’s little advantage over just a high chamber pressure, and basically no real advantage for an upper stage. At the expense of low thrust to weight ratio. The reentry method playing well with the aero spike concept is clever, but I’m not sure it’s really so much better than a conventional approach.

People also get too enamored with hydrogen. Besides the handling difficulties, the dry mass of the tanks and the pumps just is much worse for hydrolox than other fuels, largely negating the Isp advantage (especially if you use it fuel rich on both first and second stages).

I agree that people get too enamored with aerospikes, generally, but this isn't really a traditional aerospike; it has an outer expansion nozzle. In a low-pressure environment, the outer expansion region is going to act just like the engine bell of a conventional de Laval nozzle.

The revolutionary idea here is a truly actively-cooled heat shield, something that has never been attempted. And on top of that, it gets to use the same heat exchangers, turbines, and pumps that the engines use, so there's no added weight penalty. Using active cooling without any heavy heat shield is a novel route to rapid reusability.

Ah, a number of us have proposed and even built components for actively cooled heat shield integrated with plug-type propulsion...it is a good idea but not novel.

Yup.

Stoke is really putting these SSTO concepts to the test....
And by putting it on top of a reusable first stage, they'll be basically guaranteed to have enough performance to reach orbit... at least if their stuff works!

[ddspaceman]

https://twitter.com/stoke_space/status/1570159779485732865

[Robert_the_Doll]

Single-stage Earth-orbital Reusable Vehicle (SERV) and its Manned Upper-stage Reusable Payload (MURP) spaceplane was designed in 1969-1971 as one of the many proposed Space Shuttle designs.

A twelve module LH2/LOX aerospike engine was arranged around the rim of the base, covered by movable metal shields. During the ascent the shields would move out from the body to adjust for decreasing air pressure, forming a large altitude compensating nozzle. The module was fed from a set of four cross-linked turbopumps that in normal operations would run at 75% of their design capacity, if one turbopump failed then throttling up the remaining 3 to 100% would allow full power to be maintained. The engine as a whole would provide 7,454,000 lbf (25.8 MN) of thrust, about the same as the S-IC, the first stage of the Saturn V.

Also arranged around the base were forty 20,000 lbf (89 kN) jet engines, which were fired just prior to touchdown in order to slow the descent. Movable doors above the engines opened for feed air. Two RL-10's provided de-orbit thrust, so the main engine did not have to be restarted in space. Even on-orbit maneuvering, which was not extensive for the SERV (see below), was provided by small LOX/LH2 engines instead of thrusters using different fuels

[sevenperforce]

The revolutionary idea here is a truly actively-cooled heat shield, something that has never been attempted. And on top of that, it gets to use the same heat exchangers, turbines, and pumps that the engines use, so there's no added weight penalty. Using active cooling without any heavy heat shield is a novel route to rapid reusability.

Ah, a number of us have proposed and even built components for actively cooled heat shield integrated with plug-type propulsion...it is a good idea but not novel.

Single J-2S class pump, multiple chambers, 15 ft diameter actively cooled plug with short Delta II fairing (8 ft dia) on top.  Thousand pound payload. 

Designed in 1977.

Ah, yes, I forgot about that.

I believe the Phoenix L would have been water-cooled rather than using fuel. And the idea of using common heat exchangers, turbines, and pumps seems novel.

I also very much like what is essentially an annular-linear bell nozzle; it's not at all a traditional aerospike in the sense of having open expansion.

Single-stage Earth-orbital Reusable Vehicle (SERV) and its Manned Upper-stage Reusable Payload (MURP) spaceplane was designed in 1969-1971 as one of the many proposed Space Shuttle designs.

I do love SERV. And IIRC the engine shields functioned not dissimilarly from this, where they opened up larger and larger during ascent to act as an auxiliary expansion surface (see attached image).

[john smith 19]

Single-stage Earth-orbital Reusable Vehicle (SERV) and its Manned Upper-stage Reusable Payload (MURP) spaceplane was designed in 1969-1971 as one of the many proposed Space Shuttle designs.

BTW SERV was an unsolicited entry to the STS competition (because y'know Chrysler, what do they know abou building aircraft?)

It was actually a very conservative design (it assumed no better landing accuracy than the Apollo GNC, hence all the jet engines, and NASA demo'd GH2 powered jet engines (eliminating the kero tanks) in the mid 70's).

But it broke the unwritten requirement to have wings 

Stoke's plan is pretty neat. When you deal with these "novel" architectures you hav to consider the issues.

1) There are no VTO TSTO systems that have demonstrated US recovery except Shuttle (IE with wings). Everything else is just CGI.
2) Only LH2 gives the kind of Isp needed to have even a chance of US recovery.
3) A conventional US would be structure+engines+TPS as seperate, heavy components, while a plug nozzle (with appropriate US design) combines all of these components together, and (like SERV) can minimize the TPS needed on the backside of the stage, something that isn't really possible for a std pure cylindrical stage.

This is quite a radical design, and frankly only quite a radical design has a chance of achieving the goal of US reusabilty.

[Robotbeat]

Balooney, there’s no need for a radical design for making an upper stage of a multistage rocket reusable.

[Steven Pietrobon]

Single-stage Earth-orbital Reusable Vehicle (SERV) and its Manned Upper-stage Reusable Payload (MURP) spaceplane was designed in 1969-1971 as one of the many proposed Space Shuttle designs.

BTW SERV was an unsolicited entry to the STS competition (because y'know Chrysler, what do they know about building aircraft?)

I don't think that is quite correct. The Marshall Space Flight Center (MSFC) issued Alternate Space Shuttle Concepts (ASSC) studies to Chrysler, Lockheed and Grumman/Boeing. The ASSC was initiated on 6 July 1970. Chrysler's space launch experience came building the Saturn I and Saturn IB first stages for MSFC who did the actual design. Chrysler developed SERV (Single Stage Earth Orbital Reusable Vehicle).

See Dennis R. Jenkins excellent book "Space Shuttle: The History of Developing the National Space Transportation System; The Beginning Through STS-50" pages 85 to 87.

[john smith 19]

I don't think that is quite correct. The Marshall Space Flight Center (MSFC) issued Alternate Space Shuttle Concepts (ASSC) studies to Chrysler, Lockheed and Grumman/Boeing. The ASSC was initiated on 6 July 1970. Chrysler's space launch experience came building the Saturn I and Saturn IB first stages for MSFC who did the actual design. Chrysler developed SERV (Single Stage Earth Orbital Reusable Vehicle).

See Dennis R. Jenkins excellent book "Space Shuttle: The History of Developing the National Space Transportation System; The Beginning Through STS-50" pages 85 to 87.

Thank you. It's not a subject I've delved into in any great detail. What reading I've done suggests it was not really appreciated by TPTB. Still a clever approach that used a close reading of the actual spec to get the job done.

Thanks for setting the record straight