Two-stage Spaceplane with LOX collection

[DDE]

7 hours ago, DerekL1963 said:

(Actually, if you haven't yet and you need a laugh...  you should go read the original.)

Quote

With level flight and good control surfaces we can get into ground effect at the runway.  We still want a gentle touchdown with minimal mass.  So we effect a half-vertical landing.

With all these thrusters, the orbiter should be using them on final approach.  In ground effect this may allow a “Soyuz” like cushion, reverse thrust, and little or no actual skid on the landing feet.  This becomes a hybrid semi-vertical landing, but on a wide stable base.

SO WITH THRUSTERS WE CAN DO THIS TOO.  ON A WIDE STABLE BASE.

SO WHO NEEDS LANDING GEAR?

YOUR FRAGILE AND HIGHLY EXPENSIVE THERMAL PROTECTION SYSTEM!

Grrrrr...

Edited August 7, 2017 by DDE

[YNM]

40 minutes ago, DDE said:

YOUR FRAGILE AND HIGHLY EXPENSIVE THERMAL PROTECTION SYSTEM!

Grrrrr...

Financier not happy, airport owner not happy.

 

Edited August 7, 2017 by YNM

[magnemoe]

1 hour ago, DDE said:

YOUR FRAGILE AND HIGHLY EXPENSIVE THERMAL PROTECTION SYSTEM!

Grrrrr...

Why, just why, if you have an plane you land as an plane, landing wheels are light. Vertical landing makes sense on an marginal lifting body setup like the ITS upper stage, if so get rid of the wings. 

[wumpus]

Oh dear.  Some really basic questions...

Where are you staging?  Inside the atmosphere is notoriously difficult to stage, but exiting the atmosphere kills performance for air breathing engines (you don't need immediate staging, but you hardly want to wait between flameout and negligible aero issues).  Will it have an afterburner that includes an oxidizer to go between flameout and staging?  This doesn't begin to look at CoM/CoL issues.

How much delta-v?  Mach 3 (1km/s) is the record for shipping jet engines, and that pretty much "used up" its designer.  Mach 6 (1km/s) might be possible for something like the X-43, but don't think it's anywhere near ready to carry an additional stage (and "mach 9" was pretty much maintaining speed with only a blip of "acceleration" to prove that it could sustain such speeds).

What velocity/altittude are you collecting LOX at?  If subsonic, you may have finally found a load for the stratolauncher (don't collect, just launch from the stratolauncher), if supersonic (especially for mach values over 2), just what are you using as a heat sink?  Do you need the air-air intercooler from SABRE to do this?  Is there a particular reason that Reaction Engines didn't hype this while they hyped everything else under the Sun (their main claim to making things work is a heat exchanger after all)?

Does it really need to be a plane/have lift?  The shuttle's wings were a real problem, and you need some outrageous thrust for high mach values.  Is there some reason not to just lift off vertically or possibly launch down a rail that includes a ramp (possibly with a bit of a push)?  This is an even better question if the upper stage doesn't have any oxidizer in it, and remember the story is that the SR-71 had reserve power even at maximum speed (the limit was the airframe, not the engine.  Presumably such power could be converted to climbing).  If the system can't work with the weight of the LOX (and has to collect LOX at near maximum speed) there is a problem.

The elephant in the room really doesn't have to do with any of these.  It is simply the reason that rockets are used for spaceflight at all.  Rockets are cheap (compare ICBMs vs. cruise missiles, especially in payload/$).  The closest we can come to the cost of a first stage booster (to LEO) is that Spacex "ballpark figure" for using a "flight proven" booster is ~$30Million.  $30M might get you one high-bypass turbofan engine for a Boeing 777, but you really need a supersonic designed jet engine (GE builds a lot of high-bypass turbofans and presumably can build them cheaper than something typically only bought by military organisations).  I suspect that such a thing won't be reusable rockets without a daily launch cadence (I was similarly amused by Elon Musk's "thousands of flights" using ITS).

I think a better question are "where are the ramjet first stages"?  A ramjet should be able to get a real speed of mach 3-5, easily more than 2km/s of delta-v (including aero/gravity losses).  They aren't *that* outragous to build (and have been used in deployed missiles).  You might still need two more stages, but they will presumably much smaller.  I'd prefer air launch (B-52, Orbital's L-1011, Stratolaunch) for the ability to simply get up to speed with a simple dive, but ground launch with SRBs providing a ".1 stage" is probably cheaper.  My guess is that simply scaling up a 2 stage rocket makes it too cheap to bother with an expensive and highly limited first stage.  Also since most ramjets have been single use (see missile deployment), there isn't much more motivation than with rockets.

[DDE]

4 hours ago, magnemoe said:

Why, just why, if you have an plane you land as an plane, landing wheels are light. Vertical landing makes sense on an marginal lifting body setup like the ITS upper stage, if so get rid of the wings. 

Even the Soviets, terrified of creating a hole through the heat shield, managed.

[MatterBeam]

I must pre-face that I started this thread to propose a modification to a concept I found. I didn't intend to discuss the plausibility of the design itself or the viability of space-planes in general. Trying to ridicule the entire thing by picking on flaws in the original proposal is just pathetic. It doesn't advance the discussion and just marks you as a dishonest participant. 

On 06/08/2017 at 11:22 PM, Steel said:

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.

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

Probably not. I was basing myself on the work done on the LACE and Skylon engines and assumed that developing these engines to function in much less extreme environments would be simpler. 

The data that supports a TSTO that collects up to 72% of its reaction mass while in flight is the simple rocket equation. For a hrydrolox rocket, this fraction can be as high as 89%, hence the incredible advantage that comes from in-flight oxygen collection. I thought that a small collection plant that only fills up the second stage's oxygen tanks would fit into the proposal's general theme of using less advanced, lower development costs systems. 

18 hours ago, YNM said:

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.

The heat pump efficiency equation for moving heat from a cold source to a hotter environment is T(cold)/[(Thot)-T(cold)]. Any inefficiency on top of that is due to the pump's design... a pump which is based on a Stirling engine working in reverse can approach 50% efficiency, hence the numbers I posted above.

The wing shape and the overall shape of the concept is based off Concorde and it's vortex lift wing-tips.

Why would you assume and ask me to stop drinking schnapps?

16 hours ago, DerekL1963 said:

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.)

?

7 hours ago, magnemoe said:

Why, just why, if you have an plane you land as an plane, landing wheels are light. Vertical landing makes sense on an marginal lifting body setup like the ITS upper stage, if so get rid of the wings. 

I agree with this - Skylon's design managed to reduce landing gear mass to 1.5% of take-off mass, so there is no need for the awkward launch cradles and un-safe landing skids.

6 hours ago, wumpus said:

Oh dear.  Some really basic questions...

Where are you staging?  Inside the atmosphere is notoriously difficult to stage, but exiting the atmosphere kills performance for air breathing engines (you don't need immediate staging, but you hardly want to wait between flameout and negligible aero issues).  Will it have an afterburner that includes an oxidizer to go between flameout and staging?  This doesn't begin to look at CoM/CoL issues.

How much delta-v?  Mach 3 (1km/s) is the record for shipping jet engines, and that pretty much "used up" its designer.  Mach 6 (1km/s) might be possible for something like the X-43, but don't think it's anywhere near ready to carry an additional stage (and "mach 9" was pretty much maintaining speed with only a blip of "acceleration" to prove that it could sustain such speeds).

What velocity/altittude are you collecting LOX at?  If subsonic, you may have finally found a load for the stratolauncher (don't collect, just launch from the stratolauncher), if supersonic (especially for mach values over 2), just what are you using as a heat sink?  Do you need the air-air intercooler from SABRE to do this?  Is there a particular reason that Reaction Engines didn't hype this while they hyped everything else under the Sun (their main claim to making things work is a heat exchanger after all)?

Does it really need to be a plane/have lift?  The shuttle's wings were a real problem, and you need some outrageous thrust for high mach values.  Is there some reason not to just lift off vertically or possibly launch down a rail that includes a ramp (possibly with a bit of a push)?  This is an even better question if the upper stage doesn't have any oxidizer in it, and remember the story is that the SR-71 had reserve power even at maximum speed (the limit was the airframe, not the engine.  Presumably such power could be converted to climbing).  If the system can't work with the weight of the LOX (and has to collect LOX at near maximum speed) there is a problem.

The elephant in the room really doesn't have to do with any of these.  It is simply the reason that rockets are used for spaceflight at all.  Rockets are cheap (compare ICBMs vs. cruise missiles, especially in payload/$).  The closest we can come to the cost of a first stage booster (to LEO) is that Spacex "ballpark figure" for using a "flight proven" booster is ~$30Million.  $30M might get you one high-bypass turbofan engine for a Boeing 777, but you really need a supersonic designed jet engine (GE builds a lot of high-bypass turbofans and presumably can build them cheaper than something typically only bought by military organisations).  I suspect that such a thing won't be reusable rockets without a daily launch cadence (I was similarly amused by Elon Musk's "thousands of flights" using ITS).

I think a better question are "where are the ramjet first stages"?  A ramjet should be able to get a real speed of mach 3-5, easily more than 2km/s of delta-v (including aero/gravity losses).  They aren't *that* outragous to build (and have been used in deployed missiles).  You might still need two more stages, but they will presumably much smaller.  I'd prefer air launch (B-52, Orbital's L-1011, Stratolaunch) for the ability to simply get up to speed with a simple dive, but ground launch with SRBs providing a ".1 stage" is probably cheaper.  My guess is that simply scaling up a 2 stage rocket makes it too cheap to bother with an expensive and highly limited first stage.  Also since most ramjets have been single use (see missile deployment), there isn't much more motivation than with rockets.

As I understand it, the separation between the stages occurs after the booster plane reaches Mach 3 or so on turbo-ramjets then switches to rocket mode and lifts itself well out of the atmosphere. It is in this vacuum environment, going at about 2.5-3km/s that staging occurs. 

During this rocket boost phase, the center of mass necessarily moves forwards as the front-mounted second stage remains fully fuelled while the rear booster stage empties its tanks. 

The only issue I have is that after separation, the booster plane's COM might be too far aft due to the mass of its engines and the empty fuel tanks for stable flight back to the ground. 

DeltaV breakdown was not specified in the proposal I linked to, I had to work it out from a single table of data. Mach 3 is achieved on ramjet power, then the rockets ignite and start climbing for a final velocity around 3km/s and an apoapsis above the atmosphere. The second stage does the bulk of the work by delivering about >5km/s. 

I've determined that the best velocity/altitude for collecting LOX is during the climb from subsonic to Mach 3, where the ramjets cut off. At high intake temperatures, the heat pump efficiency drops, going from a COP of 0.3 to about 0.1... the heat sink is the heat exchanger block cooled to about 70K by compression/expansion cycles of the heat pump's nitrogen working fluid. The heat of the air is moved into the oxygen-devoid exhaust at the cost of a lot of energy. 

The SABRE's heat exchanger is a much more complex version of my proposal despite the seemingly simpler mechanism: super-cool the exchanger by circulating LH2 over and and just scoop up the liquid oxygen that condenses out of the air. The problem is that Skylon is trying to do that at hypersonic speeds, so cooling must take place in milliseconds, and then recover the boiling H2 for use as propellant in a scramjet that shares a reaction chamber with a closed rocket engine...

The wings allow a take-off TWR of less than 0.5.

Rockets are cheap but a recoverable craft only has to count the propellant and refurbishment costs as the mission price. Unless refurbishment costs more than throwing a rocket engine stack away (Shuttle?), it will be massively cheaper.

The problem with rail launch is that you lose the airliner-like flexibility of flying the craft between the construction point and the payload delivery, mating and launch airport. You'd need to build a special space-port that services that exact craft in that specific configuration, making it a very inflexible investment. This sort of reasoning is why SpaceX is not building its own launch site and instead using existing infrastructure. 

As I understand from missile propulsion, you can only really push a ramjet to Mach 4+ if you intend to use it once. Mach 3 and below allows for more reusable ramjet designs, hence the need to switch to rocket mode after Mach 3. 

[Steel]

On 06/08/2017 at 1:40 AM, MatterBeam said:

...

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. 

...

I've found the problem I'm afraid. Your calculations are out by a factor of 1000. 81 tons (i.e 81,000 kg) of air being cooled 630 K will take 51 GJ, not MJ (1x10³ . 81x10³ . 630 = 5.1x10¹⁰), which means your heat pumps will need require almost a terajoule at your quoted efficiency. 

This is why most of the concepts for this that I'd seen were LH₂ based I guess, heat pumps just don't work well enough.

Edited August 8, 2017 by Steel

[wumpus]

As far as I know, the only attempt to make a first stage separate at mach 3 was the blackbird M-21/D-21 program (basically launching a supersonic drone from a blackbird).  On the second test, the release of the drone caused the plane to pitch down eventually crashing the plane.  Both crew ejected but the launch control officer died.  Kelly Johnson canceled the M-21/D-21 program immediately after this (I have no idea if it was clear already if a blackbird could fly anywhere the drone could - it was only limited by treaties, not enemy fire).

This is the reason initial replies basically said "thud".  The implications of the launch are the system can fly as stage 1+2, stage 1, stage 2 (presumably, it looks like it comes down as a shuttle X-37), and all intermediate staging configurations.  That last bit is the killer.  You can run tiny models in a wind tunnel, you can compute the air flow in a super computer, but computing the air flow as they separate is going to be a nightmare.  Getting the thing to be stable in stage 1+2, stage 1, and stage 2 already puts so many restrictions on it you will likely have a very specific configuration to test for staging, and won't be able to make any changes once disasters happen.  I really don't think you can reliably separate at mach 3 with real lift, and you don't want the mass of the wings anyway.

Could a ramjet be sufficiently powerful for vertical flight?  It can't take off without assistance as ramjets don't start until near mach 1, but flight from mach 1-3 is the main issue.  It also couldn't do a vertically powered landing without additional engines, but that really wouldn't be much of an issue.  It all comes down to just how much thrust you can convince the ramjets to produce (I'm guessing the things launches from a (horizontalish?) rail, if only to get many ramjets to light while getting up to speed).  Judging from Steel's reply above, I don't expect the "lox collection" to ever work (its only advantage is to reduce the thrust needed from the ramjets, hopefully "moar (and bigger) boosters" can solve that.  Trying to reduce the fuel consumed by a ramjet stage doesn't make sense until you can have a ramjet stage).

Still, this cuts the fuel budget in half (a pretty hard limit on the cost of space flight).  At a $50,000 fuel savings, I'm guessing that the breakeven point is somewhere between weekly and daily flights (daily flights would cross the billion dollar savings in about 5 years, which seems a no brainer.  Scale it back from there).

[MatterBeam]

24 minutes ago, Steel said:

I've found the problem I'm afraid. Your calculations are out by a factor of 1000. 81 tons (i.e 81,000 kg) of air being cooled 630 K will take 51 GJ, not MJ (1x10³ . 81x10³ . 630 = 5.1x10¹⁰), which means your heat pumps will need require almost a terajoule at your quoted efficiency. 

This is why most of the concepts for this that I'd seen were LH₂ based I guess, heat pumps just don't work well enough.

Damn! You're quite right. Even if we start collecting LOX at subsonic speeds at low altitude, where air temperature is closer to 270K and heat pump efficiency is 17.5% instead of 5.6%, and continue the collection for 30 minutes instead of 10 minutes, we'd still need 51MW of pump power or 102MW of shaft horsepower, with equipment massing tens of tons.

The only way that would be worthwhile is if the entire craft was converted into LOX/RP-1 and launched with empty LOX tanks and an excess of RP-1. The excess RP-1 is burned in the turbo-ramjets and the moment the LOX tanks are filled, we switch the rocket mode. Problem is, you'd then need to collect and process 603 tons of air and the equipment mass would explode to hundreds of tons. 

I think this concludes it. 

Mechanical heat-pumps are not worthwhile until they become massively more powerful per kg, in the range of 50-100kW/kg.

16 minutes ago, wumpus said:

As far as I know, the only attempt to make a first stage separate at mach 3 was the blackbird M-21/D-21 program (basically launching a supersonic drone from a blackbird).  On the second test, the release of the drone caused the plane to pitch down eventually crashing the plane.  Both crew ejected but the launch control officer died.  Kelly Johnson canceled the M-21/D-21 program immediately after this (I have no idea if it was clear already if a blackbird could fly anywhere the drone could - it was only limited by treaties, not enemy fire).

This is the reason initial replies basically said "thud".  The implications of the launch are the system can fly as stage 1+2, stage 1, stage 2 (presumably, it looks like it comes down as a shuttle X-37), and all intermediate staging configurations.  That last bit is the killer.  You can run tiny models in a wind tunnel, you can compute the air flow in a super computer, but computing the air flow as they separate is going to be a nightmare.  Getting the thing to be stable in stage 1+2, stage 1, and stage 2 already puts so many restrictions on it you will likely have a very specific configuration to test for staging, and won't be able to make any changes once disasters happen.  I really don't think you can reliably separate at mach 3 with real lift, and you don't want the mass of the wings anyway.

Could a ramjet be sufficiently powerful for vertical flight?  It can't take off without assistance as ramjets don't start until near mach 1, but flight from mach 1-3 is the main issue.  It also couldn't do a vertically powered landing without additional engines, but that really wouldn't be much of an issue.  It all comes down to just how much thrust you can convince the ramjets to produce (I'm guessing the things launches from a (horizontalish?) rail, if only to get many ramjets to light while getting up to speed).  Judging from Steel's reply above, I don't expect the "lox collection" to ever work (its only advantage is to reduce the thrust needed from the ramjets, hopefully "moar (and bigger) boosters" can solve that.  Trying to reduce the fuel consumed by a ramjet stage doesn't make sense until you can have a ramjet stage).

Still, this cuts the fuel budget in half (a pretty hard limit on the cost of space flight).  At a $50,000 fuel savings, I'm guessing that the breakeven point is somewhere between weekly and daily flights (daily flights would cross the billion dollar savings in about 5 years, which seems a no brainer.  Scale it back from there).

I think that the separation event being described here is very close to a vertical stack separation, much like what rockets perform regularly. The difference is that the bodies are not cylinders but blended wings... but in the near-vacuum it should not make a big difference. 

The ramjets are actually turbo-ramjets. They lift off horizontally on turbojet mode, probably with a TWR of 0.4 or so. As the velocity increases, the turbo-ramjets only need to maintain a TWR high enough to overcome drag forces. At Mach 3, they are operating in pure ramjet mode, at which point the craft pitches up and ignites its TWR >1 rocket boosters. No vertical ramjet flight is involved. 

[wumpus]

11 minutes ago, MatterBeam said:

I think that the separation event being described here is very close to a vertical stack separation, much like what rockets perform regularly. The difference is that the bodies are not cylinders but blended wings... but in the near-vacuum it should not make a big difference. 

I strongly suspect that the SR-71 crash happened at "full ramjet mode" and "near vacuum".  And if you have a blended wing body traveling below ramjet flameout, I really don't think it can be a "vertical stack separation".  A steep enough pitch to be stalled across the entire range might make things possible, however.  I really doubt anyone intentionally stalled a SR-71 (I'm pretty sure stalling a U2 was certain death).  Modern post-stall operation might make it possible (presumably with a bunch of RCS to regain control).

Decades ago, one of the reasons for more and more powerful supercomputers was to do a full simulation of a plane's aerodynmaics.  I have to wonder how many Nvidia Tesla P100 cards it takes to calculate the speration of stages nowadays (possibly even just one lesser card)?

I still don't like the idea of wings or turbocompessors (you'll still have the CoL/CoM issues no matter what, plus the mass of the wings).  You'll need a launch cadence high enough to justify a rail-launch, possibly rail-gun style.  It isn't happening without a massive investment, so try to make the per-vehicle costs lower.

[Steel]

6 minutes ago, wumpus said:

Decades ago, one of the reasons for more and more powerful supercomputers was to do a full simulation of a plane's aerodynmaics.  I have to wonder how many Nvidia Tesla P100 cards it takes to calculate the speration of stages nowadays (possibly even just one lesser card)?

A little off topic, but even today we can't do a high fidelity simulation of full aircraft in any sort of reasonable time. Modern airliners, in all their myriad complexity, still only have really high-quality CFD done on sensitive aerodynamic areas of the wings, they only do those small sections at a time, and even then only at certain flight conditions. Aerodynamics are pretty complicated as it turns out!

[YNM]

2 hours ago, MatterBeam said:

The heat pump efficiency equation for moving heat from a cold source to a hotter environment is T(cold)/[(Thot)-T(cold)]. Any inefficiency on top of that is due to the pump's design... a pump which is based on a Stirling engine working in reverse can approach 50% efficiency, hence the numbers I posted above.

Good luck finding one like so... also, where's the cold reservoir ?

2 hours ago, MatterBeam said:

The wing shape and the overall shape of the concept is based off Concorde and it's vortex lift wing-tips.

I don't think they allowed truncating. And separation can still go wrong - there's a good reason they never stage anywhere near low altitude or max Q. Most conventional rockets stages far above stratosphere.

2 hours ago, MatterBeam said:

Why would you assume and ask me to stop drinking schnapps?

Kool-aid. Whatever.

Edited August 8, 2017 by YNM

[DerekL1963]

2 hours ago, MatterBeam said:

I must pre-face that I started this thread to propose a modification to a concept I found. I didn't intend to discuss the plausibility of the design itself or the viability of space-planes in general.  Trying to ridicule the entire thing by picking on flaws in the original proposal is just pathetic.

If your design is a modification of the existing design - that means you're importing the flaws and problems of that design into your design.  That opens them up for discussion.  (Not to mention it's not up to you to limit what other people discuss.  If you don't don't want to discuss those things, don't reply to messages on those things.)

[wumpus]

2 hours ago, Steel said:

A little off topic, but even today we can't do a high fidelity simulation of full aircraft in any sort of reasonable time. Modern airliners, in all their myriad complexity, still only have really high-quality CFD done on sensitive aerodynamic areas of the wings, they only do those small sections at a time, and even then only at certain flight conditions. Aerodynamics are pretty complicated as it turns out!

I'd have expect to get there already.  I suspect it is more a data transportation issue (chaotic calculations means each calculation needs too much data) and not an issue of machoflops.  Then again, that idea that we were "getting close" may have been right before chaos theory took off.

Mach 3 staging is going to need that type of measurement.  Obviously it might happen after a pure veritcal staging of an SRB pre-first stage (which delivered aerodynmaic mockups to the mach 3 staging altitude), but you will need that measurement.  Or simply don't do mach 3 staging.  Of course, if someone wants thousand-bird LEO wireless communication networks, this type of thing is likely to be a real possibility.  But you need at *least* a weekly cadence, probably more (and the real money is getting the other launch-overhead costs down.  Right now they seem to cost more than it takes spacex to build a rocket, presumably because they are all built on assuming Apollo-level costs, and nobody has had sufficient reason to examine them all (expect to lose rockets when changing those procedures without knowing why each was put in place).

[insert_name]

On 8/7/2017 at 6:29 AM, DDE said:

YOUR FRAGILE AND HIGHLY EXPENSIVE THERMAL PROTECTION SYSTEM!

Grrrrr...

I was under the impression that the TPS was ablative, and would be trashed anyways.

[MatterBeam]

23 hours ago, wumpus said:

I strongly suspect that the SR-71 crash happened at "full ramjet mode" and "near vacuum".  And if you have a blended wing body traveling below ramjet flameout, I really don't think it can be a "vertical stack separation".  A steep enough pitch to be stalled across the entire range might make things possible, however.  I really doubt anyone intentionally stalled a SR-71 (I'm pretty sure stalling a U2 was certain death).  Modern post-stall operation might make it possible (presumably with a bunch of RCS to regain control).

Decades ago, one of the reasons for more and more powerful supercomputers was to do a full simulation of a plane's aerodynmaics.  I have to wonder how many Nvidia Tesla P100 cards it takes to calculate the speration of stages nowadays (possibly even just one lesser card)?

I still don't like the idea of wings or turbocompessors (you'll still have the CoL/CoM issues no matter what, plus the mass of the wings).  You'll need a launch cadence high enough to justify a rail-launch, possibly rail-gun style.  It isn't happening without a massive investment, so try to make the per-vehicle costs lower.

The ramjet flameout and switch to rocket engines happens within the atmosphere. The booster plane expends its propellants and reaches 100km+ altitudes travelling at about 3 to 3.5km/s. It is in this airless above-the-atmosphere environment that separation will happen. Both stages will be on a ballistic trajectory with mostly negligible aerodynamic effects.

Blended wings where fuel is stored within the wings with very little 'empty space' means that the booster plane should not mass much more than a vertical, cylindrical rocket stack with the same engines. Are you advocating for or against rail-launch in the last sentence?

23 hours ago, YNM said:

Good luck finding one like so... also, where's the cold reservoir ?

I don't think they allowed truncating. And separation can still go wrong - there's a good reason they never stage anywhere near low altitude or max Q. Most conventional rockets stages far above stratosphere.

Kool-aid. Whatever.

The cold reservoir would have been the 270 to 700K air. The hot source is the 70K liquid oxygen. The point of a heat pump is to move heat against the temperature gradient, requiring energy input to do so. 

The point is moot now: an error in my calculations gave an unreasonably good estimate of the equipment masses involved. Collecting LOX with a mechanical heat pump requires massive increases in pump kW/kg ratings to become competitive with liquid-hydrogen heat exchangers.

11 hours ago, insert_name said:

I was under the impression that the TPS was ablative, and would be trashed anyways.

The empty booster plane would re-enter the atmosphere at about 3km/s and it will have an excellent lift-to-drag ratio. Together, these factors greatly reduce the heat load compared to a full 7.5km/s re-entry and would not require ablative thermal protection.

[RuBisCO]

Here are the rough calculations I get for a two stage to orbit space plane, first stage Kereosene-LOX, second stage LH-LOX.

    First Stage    Second Stage    
Fuel    1500    200    t
Ratio    10%    30%    
Cargo    285    25    t
Wet    1935    285    t
Dry    435    85    t
ISP    320    450    s
Delta V    4684    5339    m/s
    Total    10023    m/s
Prop. Density    1    0.28    t/m^3
Volume    1500    714    m^3
Tank D    5    5    m
Tank R    2.5    2.5    m
Length    45    25    m
# of Tanks    2    2    
Volume    17012    916   m^3
Vol. Ratio    113%    128%   

Looks very doable, would not require atmosphere compensating engines, a structure to mass ratio of 10% is realistic for a kerosene-LOX space plane. First stage would consist of two 5 m wide tanks strapped together (side by side) that are 45 m long, second stage would consist of two 5 m wide tanks 25 m long. First stage may be able to glide back or use jet engines and residual fuel to fly back, second stage would enter orbit and glide back. 

Edited August 9, 2017 by RuBisCO

[MatterBeam]

42 minutes ago, RuBisCO said:

Here are the rough calculations I get for a two stage to orbit space plane, first stage Kereosene-LOX, second stage LH-LOX.

    First Stage    Second Stage    
Fuel    1500    200    t
Ratio    10%    30%    
Cargo    285    25    t
Wet    1935    285    t
Dry    435    85    t
ISP    320    450    s
Delta V    4684    5339    m/s
    Total    10023    m/s
Prop. Density    1    0.28    t/m^3
Volume    1500    714    m^3
Tank D    5    5    m
Tank R    2.5    2.5    m
Length    45    25    m
# of Tanks    2    2    
Volume    17012    916   m^3
Vol. Ratio    113%    128%   

Looks very doable, would not require atmosphere compensating engines, a structure to mass ratio of 10% is realistic for a kerosene-LOX space plane. First stage would consist of two 5 m wide tanks strapped together (side by side) that are 45 m long, second stage would consist of two 5 m wide tanks 25 m long. First stage may be able to glide back or use jet engines and residual fuel to fly back, second stage would enter orbit and glide back. 

Good work. 

Just note, that for comparison, the Chinese Long March 5 also puts 25 tons into orbit but has a liftoff weight of 879 tons. The Ariane 5 ES puts 20 tons into orbit with a liftoff weight of 777 tons while the Delta IV Heavy puts 28.8 tons into orbit while lifting off at only 733 tons.

The figures you propose are 1500 tons liftoff for 25 tons into orbit... not only would this be nearly twice less efficient than the Long March 5, which also uses a RP-1/hydrolox scheme, but it would have to take off from a runway. The heaviest plane to ever take off is the Antonov 225 with a maximum take-off weight of 640 tons. The Antonov struggles with 120 tons of turbofans just getting by with a TWR of 0.23... 

Due to the numbers you suggest, I strongly think that a purely rocket-powered spaceplane would not be economical for many flights compared to expendable rockets, and even less so compared to a re-usable rocket stack like the Falcon 9 Heavy plans to be.

Try maybe taking off on jet power and climbing to an altitude where a vacuum optimised RP-1/LOX engine can produce thrust at an Isp of 353 seconds. Also, reduce the dry to wet mass ratio to closer to 5% than 10%, to take into account the fact that the booster plane will likely be built like a horizontal rocket than a plane. The Star-Raker program proposed pressurized tanks to supplement the structural strength of the wings on take-off. 

[RuBisCO]

3 hours ago, MatterBeam said:

Good work. 

Just note, that for comparison, the Chinese Long March 5 also puts 25 tons into orbit but has a liftoff weight of 879 tons. The Ariane 5 ES puts 20 tons into orbit with a liftoff weight of 777 tons while the Delta IV Heavy puts 28.8 tons into orbit while lifting off at only 733 tons.

The figures you propose are 1500 tons liftoff for 25 tons into orbit... not only would this be nearly twice less efficient than the Long March 5, which also uses a RP-1/hydrolox scheme, but it would have to take off from a runway. The heaviest plane to ever take off is the Antonov 225 with a maximum take-off weight of 640 tons. The Antonov struggles with 120 tons of turbofans just getting by with a TWR of 0.23... 

Due to the numbers you suggest, I strongly think that a purely rocket-powered spaceplane would not be economical for many flights compared to expendable rockets, and even less so compared to a re-usable rocket stack like the Falcon 9 Heavy plans to be.

Try maybe taking off on jet power and climbing to an altitude where a vacuum optimised RP-1/LOX engine can produce thrust at an Isp of 353 seconds. Also, reduce the dry to wet mass ratio to closer to 5% than 10%, to take into account the fact that the booster plane will likely be built like a horizontal rocket than a plane. The Star-Raker program proposed pressurized tanks to supplement the structural strength of the wings on take-off. 

Look at the weight of the space shuttle, ~25 tons of cargo to orbit with a on pad weight of 2,030 tons. 

No, my proposal is simply a fully reusable space shuttle, as it had been originally proposed, two winged stages would take-off, first stage would glide back and second stage would enter orbit, drop off cargo and glide back. My belief is had they actually built that, instead of the semi-reusuable POS they created, the space-shuttle would not have been the utter failure it had become.

As for the fuel use, according to Elon Musk the fueling cost for the Falcon 9 is $200,000, I'm hypothesizing a rocket that uses 3 times as much propellant, so that is $600,000 for the first stage in propellant.

http://excrementselonsays.com/transcript/spacex-press-conference-at-the-national-press-club-2014-04-25

The second stage propellant cost using $3.66 per kg of LH2 and $0.16 per kg of LO2 and a O2:H2 mass ratio of 6 = $151,722 

https://www.quora.com/How-much-does-NASA-pay-per-kg-for-hydrogen-and-oxygen-in-rocket-fuel

http://www.astronautix.com/l/loxlh2.html

So total costs in fuel would not exceed $1 million, for 25 tons to orbit that is a cost of $30 per kg.

I think that focusing on the more efficient design would require soo much development dollars upfront it simply would not be worth a much simpler design using older technology.

 

[DerekL1963]

42 minutes ago, RuBisCO said:

So total costs in fuel would not exceed $1 million, for 25 tons to orbit that is a cost of $30 per kg.

Fuel has never been the cost driver in the first place...  So, no offense, this is a totally useless metric.

[Nibb31]

2 hours ago, RuBisCO said:

So total costs in fuel would not exceed $1 million, for 25 tons to orbit that is a cost of $30 per kg.

Do you think the only cost of running an airline is kerosene or that the only cost of running Google is their electricity bill ?

Edited August 10, 2017 by Nibb31

[RuBisCO]

5 hours ago, Nibb31 said:

Do you think the only cost of running an airline is kerosene or that the only cost of running Google is their electricity bill ?

Nope, I never said such a thing, only that fuel cost are not the concern, $30 a kg clearly would mean the fuel cost is going to be far lower then simply the maintenance and launching costs, regardless of the fact is consumes a lot of fuel. They were hoping for launch costs with a space shuttle in adjusted dollars of ~$1000 per kg, so the fuel costs would be 0.3% of that cost. There is clearly no need to make a more fuel efficient spacecraft for getting to LEO. What matters more is turn around time, maintenance and launch costs.

[MatterBeam]

8 hours ago, DerekL1963 said:

Fuel has never been the cost driver in the first place...  So, no offense, this is a totally useless metric.

 

6 hours ago, Nibb31 said:

Do you think the only cost of running an airline is kerosene or that the only cost of running Google is their electricity bill ?

The point of re-usability and spaceplanes, which are 100% reusable, is that the cost of a mission gets reduced to the cost of fuel per mission plus the lifetime maintenance cost divided by the number of missions.

If a  25t payload two-stage spaceplane costs $1 million in propellants and $100 million in lifetime costs, and it performs 300 missions, then the cost per kg into orbit is $53. If we add in the billion dollar or so price tag, it'll still amount to $186/kg over its lifetime.

For comparable rockets, the lifetime is one single mission. Equipment is thrown away, which cannot be recovered, so you incur their full cost. Hence the current $20000/kg prices.

 

[wumpus]

8 hours ago, DerekL1963 said:

Fuel has never been the cost driver in the first place...  So, no offense, this is a totally useless metric.

It is an absolute hard limit, and a major consideration in airline costs.  But as mentioned it requires something like 300 missions (less than a number one Elon Musk used for his ICT) and there are a *lot* of lower lying fruit to be grabbed first (mainly get launch personnel down to baggage handler/customer service levels that airlines use).

Another issue is that it is so far out there (in required tech and infrastructure) that it might not reach 300 missions before a space elevator obsoletes it.  Build technology for an infrastructure that exists, not what you want it to be.  By the time tech exists, too much of it will surprise you and your old design won't be optimal.

One thing I would question is: is there any reason to stage at 1km/s?  Is your second stage sufficiently efficient to the other 7-8km/s?  This looks like a better job for either some baffles for an air-augmented rocket (a huge aero problem, but not as bad as building both the ramjets and doing in-air staging) or possibly simply having ramjets on stage 1 as auxiliary engines.  If you need a third stage to break up the 7-8km/s delta-v, your logistical costs will completely eat any fuel costs for the foreseeable future, and I suspect that even eating the dry weight of some ramjets will make save more fuel than dumping a stage at 1km/s.  Also ramjets would be ideal to place on asparagus staged boosters (no idea how high the "asparagus fruit" is on the try, but probably lower than the "air breather").  Using ramjets as auxiliaries to rockets also gets rid of the need for compressors and whatnot (the rockets handle 0-supersonic, then throttle down.  You might not want to launch purely vertically) and greatly simplifies the whole procedure.

[MatterBeam]

48 minutes ago, wumpus said:

It is an absolute hard limit, and a major consideration in airline costs.  But as mentioned it requires something like 300 missions (less than a number one Elon Musk used for his ICT) and there are a *lot* of lower lying fruit to be grabbed first (mainly get launch personnel down to baggage handler/customer service levels that airlines use).

Another issue is that it is so far out there (in required tech and infrastructure) that it might not reach 300 missions before a space elevator obsoletes it.  Build technology for an infrastructure that exists, not what you want it to be.  By the time tech exists, too much of it will surprise you and your old design won't be optimal.

One thing I would question is: is there any reason to stage at 1km/s?  Is your second stage sufficiently efficient to the other 7-8km/s?  This looks like a better job for either some baffles for an air-augmented rocket (a huge aero problem, but not as bad as building both the ramjets and doing in-air staging) or possibly simply having ramjets on stage 1 as auxiliary engines.  If you need a third stage to break up the 7-8km/s delta-v, your logistical costs will completely eat any fuel costs for the foreseeable future, and I suspect that even eating the dry weight of some ramjets will make save more fuel than dumping a stage at 1km/s.  Also ramjets would be ideal to place on asparagus staged boosters (no idea how high the "asparagus fruit" is on the try, but probably lower than the "air breather").  Using ramjets as auxiliaries to rockets also gets rid of the need for compressors and whatnot (the rockets handle 0-supersonic, then throttle down.  You might not want to launch purely vertically) and greatly simplifies the whole procedure.

I agree with your statement on fuel costs but the 300 mission figure I gave out was only to divide full cost of the vehicle over its service lifetime to provide a fairer price/kg comparison with expendable rockets. The only 'need' is for components to be used for more than one mission for them to massively win out against expendable rockets. Like the Falcon 9 booster: even if it only survives for 3 missions, it has already massively won out in prices against every single other rocket out there.

I'm confused however by the 1km/s figure? I thought it was clear that the booster plane did not stage at Mach 3, but after switching to rocket mode and reach 3km/s and an altitude of over 100km. 

It is extremely hard to make ramjets in a vertical launch vehicle useful. The traditional gravity turn launch trajectory gives them a very very small window of usefulness before the atmosphere becomes too thin.