Stratolaunch: General Company and Development Updates and Discussions

[Robotbeat]

Physics says (conventional) hydrolox is bad for SSTO. Physics says hydrogen is the lowest density liquid there is, and density is proportional to thrust and inversely proportional to dry mass.

The inverse proportion law is a good hypothesis but it doesn't seem to apply to actual rockets. For instance, if we take the Delta IV CBC with a dry mass of 26,000 kg and a propellant load of 200,400 kg, we could surmise the dry mass of a corresponding kerolox booster like the Atlas V CCB. With a propellant load of 284,089 and 2.87x the fuel density, the 7.7:1 fuel:dry mass of the Atlas V CCB should be 22.1:1 or a dry mass of 12,854 kg. Actual dry mass is 21,054 kg.  Something that seems to fit actual real life rockets of which there are myriad examples seems to suggest a more complicated relationship than a 1:1 relationship between volume and dry mass. For instance, keeping volume fixed, but varying mass of the load probably has structural implications.

edit: We should also look at single stage performance of the hydrolox CBC and the kerolox CCB using their vacuum isp numbers.

Delta IV CBC: 8738 m/s
Atlas V CCB: 8851 m/s

Surprisingly close.

Look at earlier Atlas variants, and you’ll see mass ratios closer to what I was saying.

Original mass ratio of the Atlas booster was over 20:1, very close to the 22 you might calculate.


(Also, look at falcon 9).

[ncb1397]

Physics says (conventional) hydrolox is bad for SSTO. Physics says hydrogen is the lowest density liquid there is, and density is proportional to thrust and inversely proportional to dry mass.

The inverse proportion law is a good hypothesis but it doesn't seem to apply to actual rockets. For instance, if we take the Delta IV CBC with a dry mass of 26,000 kg and a propellant load of 200,400 kg, we could surmise the dry mass of a corresponding kerolox booster like the Atlas V CCB. With a propellant load of 284,089 and 2.87x the fuel density, the 7.7:1 fuel:dry mass of the Atlas V CCB should be 22.1:1 or a dry mass of 12,854 kg. Actual dry mass is 21,054 kg.  Something that seems to fit actual real life rockets of which there are myriad examples seems to suggest a more complicated relationship than a 1:1 relationship between volume and dry mass. For instance, keeping volume fixed, but varying mass of the load probably has structural implications.

edit: We should also look at single stage performance of the hydrolox CBC and the kerolox CCB using their vacuum isp numbers.

Delta IV CBC: 8738 m/s
Atlas V CCB: 8851 m/s

Surprisingly close.

Look at earlier Atlas variants, and you’ll see mass ratios closer to what I was saying.

Original mass ratio of the Atlas booster was over 20:1, very close to the 22 you might calculate.


(Also, look at falcon 9).

IF you want to look at sensitivity to propellant choice, you should control for other variables. Atlas V and Delta IV use similar aluminum isogrid tank construction. Falcon 9 uses Aluminum-Lithium while previous Atlas vehicles used steel balloon tanks that couldn't support their own weight.

[envy887]

Physics says (conventional) hydrolox is bad for SSTO. Physics says hydrogen is the lowest density liquid there is, and density is proportional to thrust and inversely proportional to dry mass.

The inverse proportion law is a good hypothesis but it doesn't seem to apply to actual rockets. For instance, if we take the Delta IV CBC with a dry mass of 26,000 kg and a propellant load of 200,400 kg, we could surmise the dry mass of a corresponding kerolox booster like the Atlas V CCB. With a propellant load of 284,089 and 2.87x the fuel density, the 7.7:1 fuel:dry mass of the Atlas V CCB should be 22.1:1 or a dry mass of 12,854 kg. Actual dry mass is 21,054 kg.  Something that seems to fit actual real life rockets of which there are myriad examples seems to suggest a more complicated relationship than a 1:1 relationship between volume and dry mass. For instance, keeping volume fixed, but varying mass of the load probably has structural implications.

edit: We should also look at single stage performance of the hydrolox CBC and the kerolox CCB using their vacuum isp numbers.

Delta IV CBC: 8738 m/s
Atlas V CCB: 8851 m/s

Surprisingly close.

Look at earlier Atlas variants, and you’ll see mass ratios closer to what I was saying.

Original mass ratio of the Atlas booster was over 20:1, very close to the 22 you might calculate.


(Also, look at falcon 9).

IF you want to look at sensitivity to propellant choice, you should control for other variables. Atlas V and Delta IV use similar aluminum isogrid tank construction. Falcon 9 uses Aluminum-Lithium while previous Atlas vehicles used steel balloon tanks that couldn't support their own weight.

Another example: S-IVB vs Falcon 9 upper stage: they have comparable wet mass, thrust, wet TWR, engine cycles, and the F9 US has slightly better delta-v with a 6000 kg payload (~8400 m/s vs ~8100). But the F9 US has less than half the dry mass, in a much smaller footprint of 3.7x12 m instead of 6.7x18 m. Both factors would make it much easier to return from space: everything related to control, entry, and landing can be smaller and lighter.

Granted, the F9 US is Al-Li alloy instead of Al alloy, and uses FSW instead of arc welding. But the S-IVB is still a good example of a excellent dry mass fraction among restartable LH2 upper stages, so new tech hasn't improved the SOA that much to date.

Using LH2 ties up a lot of dry mass in tanks, insulation, engines, and subsystems to support those larger and heavier components.

[Star One]

Stratolaunch Reveals Hypersonic Testbed Concepts

[Olaf]

https://twitter.com/DigitalGlobe/status/1045000645986734083

We spotted the @Stratolaunch aircraft at the Mojave Air & Space Port in California. Reported to be the largest airplane (by wingspan) ever created at 385 feet, tripling that of a Boeing 737. @PaulGAllen http://ow.ly/ZLii30lZ7jg

[envy887]

They are building a half-size SSME...

Designed to power the family of air-launched vehicles unveiled by the company in August, the emergence of the PGA marks a major gambit in Stratolaunch’s bid to take a slice of the growing small- and medium-payload space-launch market.

The PGA is a liquid oxygen and hydrogen engine with fuel-rich staged-combustion.

Tests of the PGA engine are set to begin at NASA Stennis in October.

Designed for air-launch from the Stratolaunch aircraft, the PGA is designed to produce 200,000 lb. thrust.

http://aviationweek.com/future-aerospace/pictures-stratolaunch-pga-rocket-engine-revealed#slide-4-field_images-1856521

[Tomness]

They are building a half-size SSME...

Designed to power the family of air-launched vehicles unveiled by the company in August, the emergence of the PGA marks a major gambit in Stratolaunch’s bid to take a slice of the growing small- and medium-payload space-launch market.

The PGA is a liquid oxygen and hydrogen engine with fuel-rich staged-combustion.

Tests of the PGA engine are set to begin at NASA Stennis in October.

Designed for air-launch from the Stratolaunch aircraft, the PGA is designed to produce 200,000 lb. thrust.

http://aviationweek.com/future-aerospace/pictures-stratolaunch-pga-rocket-engine-revealed#slide-4-field_images-1856521

Like a Raptor/BE-4 hybrid not surpising if Jeff was working on Hydrogen Raptor  at SpaceX & BE-3 at Blue

[GWH]

Looks like a pretty big engine bell, I would imagine they are trying for a fairly high expansion ratio due to air launch?

[envy887]

They are building a half-size SSME...

Designed to power the family of air-launched vehicles unveiled by the company in August, the emergence of the PGA marks a major gambit in Stratolaunch’s bid to take a slice of the growing small- and medium-payload space-launch market.

The PGA is a liquid oxygen and hydrogen engine with fuel-rich staged-combustion.

Tests of the PGA engine are set to begin at NASA Stennis in October.

Designed for air-launch from the Stratolaunch aircraft, the PGA is designed to produce 200,000 lb. thrust.

http://aviationweek.com/future-aerospace/pictures-stratolaunch-pga-rocket-engine-revealed#slide-4-field_images-1856521

Like a Raptor/BE-4 hybrid not surpising if Jeff was working on Hydrogen Raptor  at SpaceX & BE-3 at Blue

It doesn't appear to share a whole lot with either Raptor, which has a two-stage fuel pump, separate preburners, and all the complications of an ox-rich side, but with the ox preburner/turbine/pump built atop the main injector. It's also quite different from BE-3, which is a combustion tapoff with both pumps on a single shaft. This engine has single stage pumps, but on separate shafts.

It does appear a lot simpler than the SSME which had 4 pumps and 2 preburners. This only has 2 turbopumps and apparently 1 preburner, located behind the ox turbopump, on the left side of the photo.

For a clean sheet design from a company new to the engine game, I like it. High performance but relatively simple.

[HMXHMX]

They are building a half-size SSME...

Designed to power the family of air-launched vehicles unveiled by the company in August, the emergence of the PGA marks a major gambit in Stratolaunch’s bid to take a slice of the growing small- and medium-payload space-launch market.

The PGA is a liquid oxygen and hydrogen engine with fuel-rich staged-combustion.

Tests of the PGA engine are set to begin at NASA Stennis in October.

Designed for air-launch from the Stratolaunch aircraft, the PGA is designed to produce 200,000 lb. thrust.

http://aviationweek.com/future-aerospace/pictures-stratolaunch-pga-rocket-engine-revealed#slide-4-field_images-1856521

Like a Raptor/BE-4 hybrid not surpising if Jeff was working on Hydrogen Raptor  at SpaceX & BE-3 at Blue

It doesn't appear to share a whole lot with either Raptor, which has a two-stage fuel pump, separate preburners, and all the complications of an ox-rich side, but with the ox preburner/turbine/pump built atop the main injector. It's also quite different from BE-3, which is a combustion tapoff with both pumps on a single shaft. This engine has single stage pumps, but on separate shafts.

It does appear a lot simpler than the SSME which had 4 pumps and 2 preburners. This only has 2 turbopumps and apparently 1 preburner, located behind the ox turbopump, on the left side of the photo.

For a clean sheet design from a company new to the engine game, I like it. High performance but relatively simple.

If one is air-launching then high chamber pressure isn't needed, so reliability and safety rule the design specification.

[Gliderflyer]

There is an article on Geekwire (here: https://www.geekwire.com/2018/paul-g-allens-stratolaunch-space-venture-lifts-veil-pga-rocket-engine/) that has some pictures of hardware and a higher resolution render of the engine.

[envy887]

My first take at labeling the components.

[SDSmith]

Air & Space magazine has a short article.

An engineer at Scaled Composites in Mojave, California, Mason Hutchison is working on Stratolaunch, a flying platform for launching payloads into low Earth orbit. The enormous vehicle is a testament to recycling: It’s made from two Boeing 747s. Hutchison spoke with Terry Dunn in June.

https://www.airspacemag.com/as-interview/space-masses-interview-scaled-composites-180970361/

[HMXHMX]

My first take at labeling the components.

I haven't been following this as closely I perhaps should, but that engine looks to me like an expander cycle, not a pre-burner or GG cycle.  A fair amount of similarity to the Blue BE-3U upper stage version...

[Steven Pietrobon]

I haven't been following this as closely I perhaps should, but that engine looks to me like an expander cycle, not a pre-burner or GG cycle.  A fair amount of similarity to the Blue BE-3U upper stage version...

The Aviation Week article says it is fuel rich staged combustion.

"The PGA is a liquid oxygen and hydrogen engine with fuel-rich staged-combustion."

[HMXHMX]

I haven't been following this as closely I perhaps should, but that engine looks to me like an expander cycle, not a pre-burner or GG cycle.  A fair amount of similarity to the Blue BE-3U upper stage version...

The Aviation Week article says it is fuel rich staged combustion.

"The PGA is a liquid oxygen and hydrogen engine with fuel-rich staged-combustion."

I know. 

In any case, my real point is that for an altitude-started and operating engine, where elevated Pc doesn't do much for you, staged combustion is really not useful and complicates development.  I think it is telling that Blue converted to an open expander cycle for BE-3U.

[envy887]

The turbines exhaust into the injector, so it is closed cycle. If it is a closed cycle expander it is unique since it had a short chamber and is some 5 times larger by thrust than any other closed cycle expander.

[russianhalo117]

My first take at labeling the components.

I haven't been following this as closely I perhaps should, but that engine looks to me like an expander cycle, not a pre-burner or GG cycle.  A fair amount of similarity to the Blue BE-3U upper stage version...

The turbines exhaust into the injector, so it is closed cycle. If it is a closed cycle expander it is unique since it had a short chamber and is some 5 times larger by thrust than any other closed cycle expander.

The article explicitly says there are preburners on board and the the PGA engine (Family) is an FRSC engine.

[envy887]

My first take at labeling the components.

I haven't been following this as closely I perhaps should, but that engine looks to me like an expander cycle, not a pre-burner or GG cycle.  A fair amount of similarity to the Blue BE-3U upper stage version...

The turbines exhaust into the injector, so it is closed cycle. If it is a closed cycle expander it is unique since it had a short chamber and is some 5 times larger by thrust than any other closed cycle expander.

The article explicitly says there are preburners on board and the the PGA engine (Family) is an FRSC engine.

I know, and the renders agree with that - except for the plurality of preburners. There is only one duct which splits to feed both of the turbines, so there is only one preburner. Unless they are using serial preburners, which I have never heard of anyone doing and can't think of any reason to do so.

[Davidthefat]

I think it is telling that Blue converted to an open expander cycle for BE-3U.

Yea, but BE3 was never a staged combustion cycle to begin with. It was a dual turbopump tap off cycle, which has difficulties of its own.