MatterBeam

Two-stage Spaceplane with LOX collection

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Hi!

I came across a very well thought-out design for re-usable launch vehicles, describes in this article: VISION.

b18.jpg

The concept involves solving the problems SSTO spaceplanes have by separating the vehicle into two sections: a hypersonic carrier plane and a nose-mounted rocket-plane. The innovative part is to mount them end-to-end.

The booster plane carries the rocketplane to a high altitude and gives it about 3km/s initial velocity. The rocketplane stages and completes the climb into orbit, unburdened with air-breathing jet engines. The propellants selected were RP-1 and H2O2 for their density and non-cryogenic storage, important factors for an airplane that needs to fit its propellant tanks into wings.

g1.jpg

For overall simplicity and technology readiness, no scramjets are used. Instead, simple turboramjets bring the booster plane up to supersonic speeds. Rocket engines take over at high altitude and add about 2km/s until the booster stage runs out of propellants. The second stage is a pure rocketplane that can deliver 6km/s of deltaV. Payload is about 450kg.

e4.jpg

Re-entry is made easier with the massive airbrakes the rocketplanes has on the back.

https://exospace.files.wordpress.com/2017/03/a14.jpg

My suggestion is that we slightly modify the propellant choices and the ascent profile for a massive boost in performance.
Due to the propellant choices, air cannot be cooled and liquefied like in a SABRE engine. There needs to be a reserve of liquid hydrogen to provide the heatsink for this to happen.

However, there is a way to liquefy air without using liquid hydrogen. Heat pumps can be used to cool a metal heat sink down to cryogenic temperatures, using evaporation and compression cycles. When air is run through the heat sink, which acts as a heat exchanger, oxygen condenses on it and can be collected. This costs power to run... power which can be derived from the turbo-ramjet's turbines.

Of course, equipping heat pumps large enough to fill the entire booster and rocketplane with liquid oxygen as it flies up through the atmosphere instead of simply using liquid hydrogen as a heat sink is a massive mass and power penalty. This penalty can become minor if we only equip pumps capable enough to fill up only the rocketplane with liquid oxygen. About 5 times less liquid oxygen would be needed.

By collected liquid oxygen this way, you can launch the upper stage with RP-1 tanks full and liquid oxygen tanks empty. The liquid oxygen tanks would be larger than peroxide tanks by about 22% in volume and be slightly heavier due to insulation. The benefit is a 30 to 50 second jump in Isp and about a 50% drop in rocketplane mass on liftoff. This means smaller booster plane engines and wings, larger payload and so on.

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Posted (edited)

The original concept looks cool, no doubt about it. It seems like a lot of effort for a 450kg payload though. Horizontal staging also looks tricky - and I'm wondering what's going to happen to the carrier plane aerodynamics at 3km/s once it loses that nice streamlined space plane.

As for generating LOX on the fly (haha) - where are you dumping the heat from your heat pumps and how? Your aircraft skin - and any radiators you attach to it - are going to get toasty at 3km/s, even at altitude, so I'd think your heat pump efficiency will be lousy.

Edited by KSK
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1 hour ago, KSK said:

Horizontal staging also looks tricky - and I'm wondering what's going to happen to the carrier plane aerodynamics at 3km/s once it loses that nice streamlined space plane.

Splat.

1 hour ago, KSK said:

where are you dumping the heat from your heat pumps and how? Your aircraft skin - and any radiators you attach to it - are going to get toasty at 3km/s

The heat pumps operate at significantly less than Mach 3, while turbojets are still operational.

Ultimately, I doubt the math will check out once you account for the massive onboard cryogenic plant and the dramatically increased duration of flight given that turbojets don't generate that much power.

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Nice design, looks fairly doable, staging should probably work to. Remember you would be pretty much in vacuum at separation. 
Forget lox collection, use lox tanks instead, have it in the body then rp1 in the wings. 
you need special hangar to mate upper stage anyway. One issue is takeoff, I assume you need at least one wheel on the rocket part to not make it to front heavy, option is to pump fuel forward after takeoff or an takeoff trolley who is dropped on takeoff. 

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450 kg ? ISRO can launch them cheaper...

"Collecting LOX in-flight" - look, LOX at boiling point is ~1 g cm^-3 , your air is only 1 mg cm^-3, and that's only 20% of them oxygen, where are you getting them again ?

Seriously, spaceplanes are cool, sure, but I'm pessimistic about payload fraction. Unless we go to space so often it's still terrible at best.

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Posted (edited)

1959, research program ROLS (Recoverable Orbital Launch System) - a winged SSTO, condensing the air and storing LOx in flight (at 100-110 km altitude).
Would start from a runway with small amount of LOx (just to reach the gathering altitude) and collect it in flight.

Would be powered by LACES (Liquid Air Collection Engine System), which was being designed by Marquardt and General Dynamics.
This would close the gap between a low-speed jet and a high-speed rocket engine.

Inside a large intake (by Garret AiResearch) there were several heat exchangers where LH2 was cooling the intake air making it to condense. The liquid air would be stored in oxidizer tanks.

1960-1961. Marquardt shows the LACES prototype in Saugus, CA.
The liquid-fuel engine achieved 275 lb thrust, working for 5 minutes and more using condensed air as oxidizer.

SSTO would have engines of 3 types:

  • turbojets for 0..3 Mach,
  • ramjets for 3..8-10 mach (reaching 100..110 km altitude and storing LO2)
  • rocket engine for >8 Mach.

All use LH2 as fuel.

SSTO could get from its its orbit down to 100 km, to refill its oxygen tanks and return to the orbit again.

Would contain a liquid air separator to get pure LO2, without nitrogen.

Total mass when reaching the orbit would be twice greater than total mass when starting from runway.

But research program SR.651 (research of aerodynamics, blah-blah-blah) demonstrated that required technologies would become available only in 1970s.
So, instead of the described, all of them began to compete in atomic SSTO.projects. With the known result.

(From Space Wings, ISBN 978-5-85247-317-2)

(Btw, using LH2 was the key feature here, because of its enormous heat capacity)

Edited by kerbiloid
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3 hours ago, YNM said:

450 kg ? ISRO can launch them cheaper...

"Collecting LOX in-flight" - look, LOX at boiling point is ~1 g cm^-3 , your air is only 1 mg cm^-3, and that's only 20% of them oxygen, where are you getting them again ?

Seriously, spaceplanes are cool, sure, but I'm pessimistic about payload fraction. Unless we go to space so often it's still terrible at best.

We could use beamed power for spaceplanes...

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Collecting LOX?  Spectacularly bad idea.  LOX is cheap on the ground, or you could possibly do in-air refueling if it weighed too much.

You also might want to play RO/RSS (or even just stock+aircraft) for awhile to get the feel of the real problems.  You need 9km/s delta-v for orbit.  While a first stage doesn't provide all that much delta-v (spacex first stages provide 2*km/s for expendable launches and 1.4km/s for returning flights), that is still vastly more speed than you can expect to get out of a jet engine (mach 3 is ~1km/s).  The final huge problem is that you really want to exit the atmosphere before detaching.  I'm guessing this involves dumping both fuel+oxidizer into a "scram[notlonger]jet" engine or some other kludge.

As mentioned above it is going to crash (without crazy design features).  The center of mass of stage1+2 has to line up with the center of lift of stage1+2.  The center of mass of just stage 1 must line up with the center of lift of stage 1.  The obvious way is to simply mount the rocket on top/below the plane, but you could concievably do tricks like keeping the fuel of the rocket in the tail and then pumping it into stage 2 above the atmosphere and before superation.  In reality, the amount of complexity and kludge for just about any way to do this will kill the project.

The reason nobody suggests this outside of newbie space enthusiasts is that the only reason to build such a spaceplane is to save on fuel costs.  While this is a worthy goal (since you use at least $20k/head in fuel to get people into space, that is a hard limit on the price of a ticket), the industry simply isn't ready.  While I'm sure the cost for the SR-71 blackbird is extremely classified (and it didn't really hit the performance characteristics we need for a first stage), I'm absolutely sure that they would need a ton of flights to match space-x's ~$100,000 fuel bil (Spacex's entire fleet only cost a few billion to make all the rockets.  Don't expect to build a blackbird for a few billion a pop, and then only if you build a large fleet).

PS: google NASA's (now Air Force's) X-43 for the absolute state of the art in high-speed flight.  2km/s isn't *quite* out of the question, but it still needs a ton of development.

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3 hours ago, wumpus said:

Collecting LOX?  Spectacularly bad idea.  LOX is cheap on the ground, or you could possibly do in-air refueling if it weighed too much.


Back in the 90's, on a space newsgroup, we spent quite a bit of time trying to work out how to air-to-air refuel LOX without a) crapping up the LOX system on the receiving aircraft or, b) freezing the two aircraft together where the boom connected with the receiver.  (The problem of chilling and purging the boom and the piping on the receiving aircraft to maximize the quality of the LOX that reached the tank we left for another time.)  Our semi-professional opinion (as there were actual rocket scientists weighing in) was that it would be an extraordinarily difficult thing to do.

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1 hour ago, DerekL1963 said:


Back in the 90's, on a space newsgroup, we spent quite a bit of time trying to work out how to air-to-air refuel LOX without a) crapping up the LOX system on the receiving aircraft or, b) freezing the two aircraft together where the boom connected with the receiver.  (The problem of chilling and purging the boom and the piping on the receiving aircraft to maximize the quality of the LOX that reached the tank we left for another time.)  Our semi-professional opinion (as there were actual rocket scientists weighing in) was that it would be an extraordinarily difficult thing to do.

I don't doubt that.  But did you even consider the issue of trying to liquify OX captured in flight?  The only real difference is the lack of a break in the system (pretty big) but you now have to deal with all the cryogenics.  The catch is that you wouldn't only have to add a 1km/s or two delta v to the LOX, you would have to add a delta-v to the LOX+crygenics mass.

Did anybody think of a "reverse-bomb-bay"?  Simply transfer the entire tank from the boom to the "rocket"?  It might be extreme, but I understand the boom has a wing and is essentially self supporting.  It might be possible to manuever the tank into a place the "rocket" can dock, remove the tank, and scoop it in.  Once released, the boom can go to a more reasonable level of lift and be returned.  I suspect that it is a bomb waiting to happen, but it woudl cover most the the issues brought up (while adding plenty of its own issues).

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Drop tanks anyone? Does that count as staging?

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7 minutes ago, wumpus said:

I don't doubt that.  But did you even consider the issue of trying to liquify OX captured in flight?  The only real difference is the lack of a break in the system (pretty big) but you now have to deal with all the cryogenics.  The catch is that you wouldn't only have to add a 1km/s or two delta v to the LOX, you would have to add a delta-v to the LOX+crygenics mass.

Our considered opinion was that is seriously stupid way to go about things.  A great deal of mass, volume, and power spent for very little return.  LOX is cheap, and so is Al-Li.    It doesn't make sense to spend gigabucks developing a system to save a few tens of thousands of dollars.

That's the basic problem with a lot of these schemes, the proponents thereof get blinded by their technical brilliance and forget what the point of the exercise was in the first place.  As I've long said, "cheap access isn't just an engineering exercise - it's also a beancounter exercise".
 

12 minutes ago, wumpus said:

Did anybody think of a "reverse-bomb-bay"?  Simply transfer the entire tank from the boom to the "rocket"?  It might be extreme, but I understand the boom has a wing and is essentially self supporting.  It might be possible to manuever the tank into a place the "rocket" can dock, remove the tank, and scoop it in.  Once released, the boom can go to a more reasonable level of lift and be returned.  I suspect that it is a bomb waiting to happen, but it woudl cover most the the issues brought up (while adding plenty of its own issues).

Thinking about the aerodynamics of that makes my head hurt.

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I will try to answer everyone.

13 hours ago, KSK said:

The original concept looks cool, no doubt about it. It seems like a lot of effort for a 450kg payload though. Horizontal staging also looks tricky - and I'm wondering what's going to happen to the carrier plane aerodynamics at 3km/s once it loses that nice streamlined space plane.

As for generating LOX on the fly (haha) - where are you dumping the heat from your heat pumps and how? Your aircraft skin - and any radiators you attach to it - are going to get toasty at 3km/s, even at altitude, so I'd think your heat pump efficiency will be lousy.

I believe the payload is so small because the author used real world data on wing area to estimate if the craft could fly with its wing loading. To fit within this data set, the wings cannot be gigantic, so the final craft must be small. Once a demonstrator for the technology is made to work, I am certain larger payloads can be scaled up. 

The carrier planes after separation only needs to remain stable as it decelerates down from high speed flight. Its natural half-saucer teardrop flying wing/blended body shape does contribute towards stability at high speed, even if its engines will not be able to overcome the drag. 

On the subject of heat pumps: LOX is created from air cooled down to 90K. The working fluid is likely to be liquid nitrogen, so the cold end of the heat pump is at about 70K. The hot end is the incoming air. At Mach 3, this is about 700K. A perfectly efficient heat pump would need 9 watts of power to move 1 watt of heat across this temperature range. A more realistic heat pump would maybe need about 18 watts.

In the rocketplane, the only data provided is a propellant mass figure of about 52000 pounds. Assuming a 2.5:1 oxidizer to RP-1 ratio, we'll need about 17 tons of liquid oxygen. This means we'd have to process about 81 tons of air.

Air has a heat capacity of roughly 1kJ/kg/K, so to cool down 81 tons of air from 700 to 70K, the heat pump must remove 51MJ of heat. At the efficiency quoted above, it will consume up to 923MJ. RP-1 delivers 43.5MJ/kg upon combustion so this shouldn't be a problem.

How long do we take to collect the liquid oxygen?

Minimizing flight time reduces fuel consumption but increases the power rating of the heat pumps necessary.

A 10 minute flight time translates into 1.6MW heat pumps. They could mass about 4.6 tons, but it is extremely likely that the data from here is not optimized for power density at all. The aerospace grade heat pumps could mass under a ton. A dynamo would need to convert 3MW of shaft power into electricity. This would mass between 300 and 600kg. Add insulation and tanks of another 400kg and we'll round up the assembly to 2 tons. In return, we can save 17 tons of liftoff mass and gain 10% Isp on the second stage. 

12 hours ago, DDE said:

Splat.

The heat pumps operate at significantly less than Mach 3, while turbojets are still operational.

Ultimately, I doubt the math will check out once you account for the massive onboard cryogenic plant and the dramatically increased duration of flight given that turbojets don't generate that much power.

Good point. If we collect the liquid oxygen at subsonic or low supersonic speeds, the air temperature would be about 300K instead of 700K, bringing the heat pump efficiency up to 6 W per watt moved. This makes them three times smaller.

Since we do not need to hold the liquid oxygen for long and losses can be compensated for by just collecting more air, simple insulated tanks with boil-off valves can replace a 'massive onboard cryogenic plant'. 3MW is 4000 shaft horsepower. 

9 hours ago, magnemoe said:

Nice design, looks fairly doable, staging should probably work to. Remember you would be pretty much in vacuum at separation. 
Forget lox collection, use lox tanks instead, have it in the body then rp1 in the wings. 
you need special hangar to mate upper stage anyway. One issue is takeoff, I assume you need at least one wheel on the rocket part to not make it to front heavy, option is to pump fuel forward after takeoff or an takeoff trolley who is dropped on takeoff. 

The main reason for the whole LOX collection concept is that you can lift off with the LOX tanks empty and fill them while flying for 'free'. Filling them up on the ground would negate this advantage.

9 hours ago, YNM said:

450 kg ? ISRO can launch them cheaper...

"Collecting LOX in-flight" - look, LOX at boiling point is ~1 g cm^-3 , your air is only 1 mg cm^-3, and that's only 20% of them oxygen, where are you getting them again ?

Seriously, spaceplanes are cool, sure, but I'm pessimistic about payload fraction. Unless we go to space so often it's still terrible at best.

If the two-stage spaceplane concept is proven, then you'll only be paying fuel costs. ISRO throws away its engines, tanks and stages for a strictly higher cost per launch. This is why it is not so bad if the spaceplane has a bad payload fraction.

As for actually collecting 81 tons of air for processing, you'd need maybe 50 to 100kg/s flow rate. At Mach 3.2 (1088m/s) and an altitude of 25.9km and external air temp of -50 degrees C (0.039kg/m^3), intakes will take in 42kg/m^2/s. Two inlets of 1.12m diameter will do the job. At Mach 1 (330m/s), an altitude of 4.5km and an external air temp of -20 degrees C (0.791kg/m^3), an intake will take in 261kg/m^2/s. 

Considering all the above factors, it might just be worthwhile to collect LOX at near-supersonic speeds at relatively low altitude and just use more thrust to boost up to Mach 3.

6 hours ago, kerbiloid said:

1959, research program ROLS (Recoverable Orbital Launch System) - a winged SSTO, condensing the air and storing LOx in flight (at 100-110 km altitude).
Would start from a runway with small amount of LOx (just to reach the gathering altitude) and collect it in flight.

Would be powered by LACES (Liquid Air Collection Engine System), which was being designed by Marquardt and General Dynamics.
This would close the gap between a low-speed jet and a high-speed rocket engine.

Inside a large intake (by Garret AiResearch) there were several heat exchangers where LH2 was cooling the intake air making it to condense. The liquid air would be stored in oxidizer tanks.

1960-1961. Marquardt shows the LACES prototype in Saugus, CA.
The liquid-fuel engine achieved 275 lb thrust, working for 5 minutes and more using condensed air as oxidizer.

SSTO would have engines of 3 types:

  • turbojets for 0..3 Mach,
  • ramjets for 3..8-10 mach (reaching 100..110 km altitude and storing LO2)
  • rocket engine for >8 Mach.

All use LH2 as fuel.

SSTO could get from its its orbit down to 100 km, to refill its oxygen tanks and return to the orbit again.

Would contain a liquid air separator to get pure LO2, without nitrogen.

Total mass when reaching the orbit would be twice greater than total mass when starting from runway.

But research program SR.651 (research of aerodynamics, blah-blah-blah) demonstrated that required technologies would become available only in 1970s.
So, instead of the described, all of them began to compete in atomic SSTO.projects. With the known result.

(From Space Wings, ISBN 978-5-85247-317-2)

(Btw, using LH2 was the key feature here, because of its enormous heat capacity)

LH2 is extremely problematic for flying vehicles. It requires massive fuselages that must also be insulated against high temperatures, large engines to overcome the drag and heavy structure to keep them rigid enough in flight. Also, the scramjet requirement for Mach 3 to 8 flight is just something we do not have, so that's gambling on technologies currently unavailable.

Despite recent advances in lightweight structural materials, I do not think we will have the technology to make an LH2 spaceplane work. The advantages are not currently great enough to compete with a less efficient by simply cheaper 'brute force' solution of using a heavier spaceplane with RP-1 fuels. 

Thank you for the references though. I personally am very interested in spaceplane concepts since the 70's, with the Star Raker being the pinnacle of re-usable design. 

6 hours ago, Bill Phil said:

We could use beamed power for spaceplanes...

This would very likely work, but the initial set-up cost of deploying hundreds of megawatt lasers is just impossible to cover unless the US/EU/China decide it is a matter of national interest or if laser power per $ cost drops rapidly.

5 hours ago, wumpus said:

Collecting LOX?  Spectacularly bad idea.  LOX is cheap on the ground, or you could possibly do in-air refueling if it weighed too much.

You also might want to play RO/RSS (or even just stock+aircraft) for awhile to get the feel of the real problems.  You need 9km/s delta-v for orbit.  While a first stage doesn't provide all that much delta-v (spacex first stages provide 2*km/s for expendable launches and 1.4km/s for returning flights), that is still vastly more speed than you can expect to get out of a jet engine (mach 3 is ~1km/s).  The final huge problem is that you really want to exit the atmosphere before detaching.  I'm guessing this involves dumping both fuel+oxidizer into a "scram[notlonger]jet" engine or some other kludge.

As mentioned above it is going to crash (without crazy design features).  The center of mass of stage1+2 has to line up with the center of lift of stage1+2.  The center of mass of just stage 1 must line up with the center of lift of stage 1.  The obvious way is to simply mount the rocket on top/below the plane, but you could concievably do tricks like keeping the fuel of the rocket in the tail and then pumping it into stage 2 above the atmosphere and before superation.  In reality, the amount of complexity and kludge for just about any way to do this will kill the project.

The reason nobody suggests this outside of newbie space enthusiasts is that the only reason to build such a spaceplane is to save on fuel costs.  While this is a worthy goal (since you use at least $20k/head in fuel to get people into space, that is a hard limit on the price of a ticket), the industry simply isn't ready.  While I'm sure the cost for the SR-71 blackbird is extremely classified (and it didn't really hit the performance characteristics we need for a first stage), I'm absolutely sure that they would need a ton of flights to match space-x's ~$100,000 fuel bil (Spacex's entire fleet only cost a few billion to make all the rockets.  Don't expect to build a blackbird for a few billion a pop, and then only if you build a large fleet).

PS: google NASA's (now Air Force's) X-43 for the absolute state of the art in high-speed flight.  2km/s isn't *quite* out of the question, but it still needs a ton of development.

I do play RSS exclusively and I do have a good feel for the deltaVs and mass ratios required. The booster plane here is supposed to reach Mach 3 on turbo-ramjet power while collecting LOX for the second-stage rocketplane. The booster plane then switches to rocket mode and adds another 2.5km/s to its velocity, adding up to around 3.5km/s. Orbital velocity is 3km/s. Upon separation, the second stage needs to deliver another 4.8 to 5km/s to circularize. With a 320s Isp engine, this requires a mass ratio of 4.9, with an RP-1/LOX alternative, the mass ratio required drops to 4.2.

Center of mass/center of lift is not a big problem. Flight controls can correct imbalances in the lower atmosphere while it is quite neutral. As Mach 1 is passed, the center of lift is dragged backwards due to mach tuck while the center of mass moves forwards as the second stage rocketplane's LOX tanks are filled. The whole plane presented above is modelled quite around the wing shape of a Concorde for extra lift at the rear.

The point of a spaceplane is that you recover 100% of the equipment that leaves the runway. Your marginal cost is just the propellants, which as you mentioned, is very cheap.

1 hour ago, DerekL1963 said:


Back in the 90's, on a space newsgroup, we spent quite a bit of time trying to work out how to air-to-air refuel LOX without a) crapping up the LOX system on the receiving aircraft or, b) freezing the two aircraft together where the boom connected with the receiver.  (The problem of chilling and purging the boom and the piping on the receiving aircraft to maximize the quality of the LOX that reached the tank we left for another time.)  Our semi-professional opinion (as there were actual rocket scientists weighing in) was that it would be an extraordinarily difficult thing to do.

The two stages can have an integrated fuel line running back to front through the entire craft. Nothing would be exposed to the exterior environment.

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3 hours ago, MatterBeam said:

he main reason for the whole LOX collection concept is that you can lift off with the LOX tanks empty and fill them while flying for 'free'.

No, it's not 'free' - you pay a great deal of money and weight for the hardware.

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Posted (edited)

10 hours ago, MatterBeam said:

If the two-stage spaceplane concept is proven, then you'll only be paying fuel costs. ISRO throws away its engines, tanks and stages for a strictly higher cost per launch. This is why it is not so bad if the spaceplane has a bad payload fraction.

As for actually collecting 81 tons of air for processing, you'd need maybe 50 to 100kg/s flow rate. At Mach 3.2 (1088m/s) and an altitude of 25.9km and external air temp of -50 degrees C (0.039kg/m^3), intakes will take in 42kg/m^2/s. Two inlets of 1.12m diameter will do the job. At Mach 1 (330m/s), an altitude of 4.5km and an external air temp of -20 degrees C (0.791kg/m^3), an intake will take in 261kg/m^2/s. 

Considering all the above factors, it might just be worthwhile to collect LOX at near-supersonic speeds at relatively low altitude and just use more thrust to boost up to Mach 3.

Have you not look up air density and composition at operating altitude ? Also, what advantage does this all have over just simply having scramjets, which is function-wise the same thing ? Then there's the question of efficiency, which can easily change the magnitude of the problem you're facing.

Also, don't forget sunken cost and service cost. Things at edges of engineering tends not to last that long. Hence unless we go really often to space, to the point that we're hard-pressed to make them "looks conventional", it's not worth it.

Also, too often at normal rockets your payload will simply be lofted along with other payloads, you only pay half of the whole thing or so.

17 hours ago, Bill Phil said:

We could use beamed power for spaceplanes...

... and burn everything on the path.

Edited by YNM
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7 hours ago, DerekL1963 said:

No, it's not 'free' - you pay a great deal of money and weight for the hardware.

And you need to burn fuel to power the process and fuel to keep you in the air while collecting, an smaller converter weight less but you would need more fuel for flying.
You have the same oxygen tank issues as if you launched with oxygen, the only benefit is that you can have an more lightweight landing gear and weaker engines depending on condenser weight and fuel used. 
With stronger engine you could climb faster reducing boil off. 

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9 hours ago, DerekL1963 said:

No, it's not 'free' - you pay a great deal of money and weight for the hardware.

'Free' meaning that you do not have to 'pay' in propellants, engine thrust, landing gear and wing area to get them up to the altitude and speed where they start being used. 

Due to the rocket equation, 17 tons less mass at liftoff is actually a much greater saving once the booster plane is at Mach 3 and switching to rocket mode. 

2 hours ago, YNM said:

Have you not look up air density and composition at operating altitude ? Also, what advantage does this all have over just simply having scramjets, which is function-wise the same thing ? Then there's the question of efficiency, which can easily change the magnitude of the problem you're facing.

Also, don't forget sunken cost and service cost. Things at edges of engineering tends not to last that long. Hence unless we go really often to space, to the point that we're hard-pressed to make them "looks conventional", it's not worth it.

Also, too often at normal rockets your payload will simply be lofted along with other payloads, you only pay half of the whole thing or so.

... and burn everything on the path.

Yes, I found the correct temperatures and pressures at the altitudes I noted and calculated the air density using online calculators. 

Scramjets is not a currently available technology and will not be mature enough for routine spaceflight for a very long time. It is better to focus on existing tech, like ramjets and cryo-collection of air at moderate velocities, for cost and development time reasons. 

Which efficiency are you referring to?

This design is far from the 'edges of engineering'. I don't understand what you mean by 'looks conventional'. If you mean the overall shape of the plane, it is based on a Concorde.  

2 hours ago, magnemoe said:

And you need to burn fuel to power the process and fuel to keep you in the air while collecting, an smaller converter weight less but you would need more fuel for flying.
You have the same oxygen tank issues as if you launched with oxygen, the only benefit is that you can have an more lightweight landing gear and weaker engines depending on condenser weight and fuel used. 
With stronger engine you could climb faster reducing boil off. 

The fuel consumption increase from using a multi-megawatt generator is truly insignificant. As noted above, 4000 horsepower would have to drawn from a turbo-jet's shaft. According to this source, the old J-58s produced up to 160000 shaft horsepower each.

The advantages are more Isp, lighter gear, smaller wings, less drag, less thrust, less fuel consumption in flight and use of existing LOX/RP-1 engines instead of developing a modern HTP/RP-1 engine.

The boiloff as noted before would be low and easily compensated for by just scooping up more oxygen. You only have to hold the oxygen liquid for the few minutes between stage separation and circularization, which should not last more than a handful of minutes. 

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Posted (edited)

2 hours ago, MatterBeam said:

Yes, I found the correct temperatures and pressures at the altitudes I noted and calculated the air density using online calculators. 

Scramjets is not a currently available technology and will not be mature enough for routine spaceflight for a very long time. It is better to focus on existing tech, like ramjets and cryo-collection of air at moderate velocities, for cost and development time reasons. 

Which efficiency are you referring to?

This design is far from the 'edges of engineering'. I don't understand what you mean by 'looks conventional'. If you mean the overall shape of the plane, it is based on a Concorde.  

Cyro-collection of air at high speeds isn't a well-tested thing AFAIK. Air liquidation at land plants, sure, turbofan intake liquidation, nowhere.

I'm referring to the efficiency of the oxygen extraction method. If you haven't noticed, the flow anywhere inside this extraction will have to stay continuous. You're not bagging air around.

The tech is not at the edge ? Dude, they only have done supersonic separation for single-component cylinders (which are easy and quite strong) and between two lifting bodies, but the later has only been done a few times and more often they fails...

"Looks conventional" as in "we do this so often, it should be something more "normal" ". Like, dunno, airplanes when it was Wright Brothers compared to now. I know someone must fill the gap, but I'm not even sure if anyone is interested for the time being !

Edited by YNM
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2 hours ago, MatterBeam said:

'Free' meaning that you do not have to 'pay' in propellants, engine thrust, landing gear and wing area to get them up to the altitude and speed where they start being used.


0.o  And how, precisely, do you intend to get the cryo-collection machinery into position without spending propellants or requiring wing area?  Cavorite?

 

2 hours ago, MatterBeam said:

Scramjets is not a currently available technology and will not be mature enough for routine spaceflight for a very long time. It is better to focus on existing tech, like ramjets and cryo-collection of air at moderate velocities, for cost and development time reasons. 


0.o  Existing tech?  Please cite one example of an operating in flight cryo-collection system.

 

2 hours ago, MatterBeam said:

You only have to hold the oxygen liquid for the few minutes between stage separation and circularization, which should not last more than a handful of minutes. 


0.o  No, you have to hold the oxygen liquid from the moment you start collection.

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1 hour ago, YNM said:

Cyro-collection of air at high speeds isn't a well-tested thing AFAIK. Air liquidation at land plants, sure, turbofan intake liquidation, nowhere.

I'm referring to the efficiency of the oxygen extraction method. If you haven't noticed, the flow anywhere inside this extraction will have to stay continuous. You're not bagging air around.

The tech is not at the edge ? Dude, they only have done supersonic separation for single-component cylinders (which are easy and quite strong) and between two lifting bodies, but the later has only been done a few times and more often they fails...

"Looks conventional" as in "we do this so often, it should be something more "normal" ". Like, dunno, airplanes when it was Wright Brothers compared to now. I know someone must fill the gap, but I'm not even sure if anyone is interested for the time being !

You are correct about the state of high-speed cry-collection technology, but it is only one technology that must be developed instead of multiples, such as on the Skylon. Also, the range of operating parameters is not as extreme as what is being attempted by the LACE, so I'm guessing it would rather easier to collect oxygen at Mach 0.9-3 than Mach 5-8. 

The efficiency of the oxygen extraction method? Well how would you measure a loss of efficiency in this process? Condensed liquid oxygen being blown away or gasses escaping somehow? We can reduce it all to how much more kW is needed from the heat pump. I already gave that component a 50% cut to efficiency when it could approach instead be approaching ideal efficiency, to demonstrate that the scale of the task is manageable even with pessimistic predictions. 

My understanding of the concept proposed on the website I linked to is that every technology in use has been matured over decades. 'Edge of technology' would be stretching what we can do, such as taking a laboratory experiment (beaming laser power, cryo-cooling at hypersonic speeds) into a real world situation (HX laser thruster, Skylon Reaction Engines). Trying to perfect the in-line separation of two components on a ballistic trajectory in near-vacuum is very much easier than attempts at edge-of-technology R&D. 

The small payload low-cost launcher business is promising enough for companies such as Rocket Labs, Virgin Orbit and more to vie for the market. A fully reusable HTOL craft would beat expendable small rockets in the race to the lowest $/kg.

29 minutes ago, DerekL1963 said:


0.o  And how, precisely, do you intend to get the cryo-collection machinery into position without spending propellants or requiring wing area?  Cavorite?

0.o  Existing tech?  Please cite one example of an operating in flight cryo-collection system.
0.o  No, you have to hold the oxygen liquid from the moment you start collection.

The cryo-collection machinery and power generation equipment would mass much less than the savings of not having to lift off with a full load of oxidizer, for significant net savings. Please do not be disingenuous. 

The concept of in-flight cryo-collection of liquid oxygen has been seriously studied and experimental results are already available. Attempting to accomplish this in a supersonic regime is easier than in a hypersonic regime. 

Liquid oxygen is not liquid hydrogen. Storing it is much, much easier... so easy and safe that large tanks of liquid oxygen are proudly displayed behind hospital buildings. During the fill-up process, losses are compensated for by collecting more LOX than is needed. It is then held for a few minutes. I think you are vastly overestimating the losses involved in holding LOX for a couple of minutes - they should be on the order of 0.1% or less. Here is a commercial solution that holds LOX with a loss rate of 0.2 to 1.2% per day. ULA managed to bring LH2 losses to less than 0.1% per day, so LOX losses must be 0.05% per day or lower.

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3 hours ago, MatterBeam said:

The cryo-collection machinery and power generation equipment would mass much less than the savings of not having to lift off with a full load of oxidizer, for significant net savings. Please do not be disingenuous. 

If you're looking for someone disingenuous, you need to take a look in a mirror, because is now the second message where you've done nothing but handwave and blow smoke rather than addressing the issues I raised.

 

3 hours ago, MatterBeam said:

The concept of in-flight cryo-collection of liquid oxygen has been seriously studied and experimental results are already available.


In other words, it doesn't constitute existing and available technology.  Take a look in that mirror again.

 

3 hours ago, MatterBeam said:

Liquid oxygen is not liquid hydrogen. Storing it is much, much easier... so easy and safe that large tanks of liquid oxygen are proudly displayed behind hospital buildings. During the fill-up process, losses are compensated for by collecting more LOX than is needed. It is then held for a few minutes.


Again, sidestepping the issues I raised.  Seriously, are you so dense you fail to grasp the difference between storage dewars that are already chilled - and your flight tankage which isn't.  And the same goes for the flight tankage in the ULA paper you linked.  It's pre chilled on the ground.  Once again the mirror beckons.

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Posted (edited)

Ok let's calm this down slightly, we don't want to get the thread locked. I'd like to think that no one is deliberately trying to be rude or disingenuous.

I do have a couple of questions though.

4 hours ago, MatterBeam said:

The concept of in-flight cryo-collection of liquid oxygen has been seriously studied and experimental results are already available. Attempting to accomplish this in a supersonic regime is easier than in a hypersonic regime. 

Are you sure it has been studied as well as you think? There aren't actually that many experimental results that I could find (I have only been looking for 20 minutes or so though), most of the papers in this area seem to be review papers, and at least two [1] [2] that I've skimmed tonight say something along the lines of "the success of this concept is contingent on the development of an efficient collection plant".  There's one study using vortex tubes which look dubious to say the least [3] (I can't even tell where, or if, this has been published), and then most of the other papers are studies that use LH2 to condense oxygen, which you've said you don't want. I'm also pretty sure there's absolutely no experimental data of this actually being done in-flight, so I can see why @DerekL1963 has reservations.

The more important question for me is why you'd want to do this, is there data that supports that TSTO with in-flight collection is better than a ground-fueled TSTO? I know there is for the SSTO case having read some of the reivew papers [2].

 

[1] P. Hendrick, M. Saint-Mard, P. Hendrick, M. Saint-Mard, "Saenger-type T.S.T.O. using in-flight LOX collection", 33rd Joint Propulsion Conference and Exhibit, Joint Propulsion Conferences

[2]V. Balepin, P. Czysz, M. Maita, J. Vandenkerckhove, "Assessment of SSTO Performance with In-Flight LOX Collection", Sixth AIAA International Space Planes and Hypersonic Systems and Technologies Conference

[3] https://www.researchgate.net/publication/234886776_LOX_SEPARATION_STUDIES_USING_CRYOGENIC_VORTEX_TUBE

Edited by Steel
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Please avoid accusing each other of lying. There's no need to treat each other so hostilely. 

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Posted (edited)

10 hours ago, MatterBeam said:

You are correct about the state of high-speed cry-collection technology, but it is only one technology that must be developed instead of multiples, such as on the Skylon. Also, the range of operating parameters is not as extreme as what is being attempted by the LACE, so I'm guessing it would rather easier to collect oxygen at Mach 0.9-3 than Mach 5-8. 

The efficiency of the oxygen extraction method? Well how would you measure a loss of efficiency in this process? Condensed liquid oxygen being blown away or gasses escaping somehow? We can reduce it all to how much more kW is needed from the heat pump. I already gave that component a 50% cut to efficiency when it could approach instead be approaching ideal efficiency, to demonstrate that the scale of the task is manageable even with pessimistic predictions. 

My understanding of the concept proposed on the website I linked to is that every technology in use has been matured over decades. 'Edge of technology' would be stretching what we can do, such as taking a laboratory experiment (beaming laser power, cryo-cooling at hypersonic speeds) into a real world situation (HX laser thruster, Skylon Reaction Engines). Trying to perfect the in-line separation of two components on a ballistic trajectory in near-vacuum is very much easier than attempts at edge-of-technology R&D. 

The small payload low-cost launcher business is promising enough for companies such as Rocket Labs, Virgin Orbit and more to vie for the market. A fully reusable HTOL craft would beat expendable small rockets in the race to the lowest $/kg.

Well, AFAIK we never loaded any generating machinery onto any flights. Oxygen Condensers that we found at hospitals and even homes are creating concentrated gaseous oxygen, not 100% LOX. Designing a heat pump is never easy - your fridge isn't as efficient as you think, let alone if it was in a room 1000K hot. I'm counting the efficiency based on flow of gaseous oxygen (theoretical maximum) vs amount of LOX actually produced. Without stalling the intake and make the contraption plummet to ground.

Also, calling this whole contraption "based off Concorde" is a bit like saying that the Shuttle is "based off 737".

Get off your schnapps mate.

Edited by YNM

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1 hour ago, YNM said:

Also, calling this whole contraption "based off Concorde" is a bit like saying that the Shuttle is "based off 737".

To be fair "based off Concorde" isn't quite what the original said.   (Actually, if you haven't yet and you need a laugh...  you should go read the original.)

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