Author Topic: Why the lack of SSTO projects?  (Read 15392 times)

Offline john smith 19

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Re: Why the lack of SSTO projects?
« Reply #120 on: 03/07/2017 10:10 AM »
JS19: The word or system you're looking for it "RENE" or "Rocket Engine Nozzle Ejector" system that was played with during the mid-60s.
Noted. And welcome back.
Quote from: RanulfC

You end up with something similar to the Atlas 1.5 stage system, (duct drops off around Mach-2) with around double the nominal payload-to-orbit. The same concept gave the Soviet GNOM pretty much the same payload/range of a Minuteman at half the size/mass. Performance peaks between Mach-1 and Mach-1.5 and tops out at Mach-2 unless you have a non-fixed inlet geometry which gets heavy fast. You get better performance at the top end with fuel-rich or fuel injection but need a bit longer duct or active injectors again which adds complexity but not much mass.
This suggests the best simple approach for reusability would be to close the duct off this Mach range.
Quote from: RanulfC

One thing that was not looked at in any studies directly but highly suggestive in past studies, (mid-to-late-60s) was "pre-cooling" intake air, (various methods but an interesting 'passive' system used a lightly insulated LH2 tank structure) to increase the mass flow through the ejector duct. A water injection system integral to the duct was suggested and I'd note that that can increase static thrust of a standard jet engine by 2 or more so there would be no reason to think it wouldn't work similarly in an ejector or ramjet duct. (This would be somewhere around 100 or so pounds of water if I recall the figures correctly for the whole take-off-to-Mach-2 flight)
A 100lbs is pretty small. I guess it depends what the thrust of the base engine was.
Quote from: RanulfC

Again those this is NOT an "SSTO" in a purist sense, but add some parachutes and recover down-range it is a VERY simple, cheap and effective 'boost' option for a NEAR-SSTO vehicle.
Good point. SSTO (especially VTOL) has always been tightly constrained by both the mass ratio and the Isp, and it's a vicious combination, with the best Isp coming from the propellant with traditionally the worst T/W.

As always the question is could these (perhaps coupled with HTOL) be enough to do SSTO with more or less a conventional rocket engine?
« Last Edit: 03/07/2017 11:10 PM by john smith 19 »
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline Rei

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Re: Why the lack of SSTO projects?
« Reply #121 on: 03/07/2017 11:21 AM »
Last time I looked into the concept (it's been a while), the duct tends to be a mass-limiting factor, hence the reason for getting rid of it when it's no longer needed, rather than just closing it off.

The water cooling concept makes no sense to me. How is the effect of an injection amount of water supposed to have a significant cooling effect on incoming air unless its mass is somewhat comparable to the incoming air (wherein the mass penalty would be large)? And if you're going to bring something with high specific heat, why not hydrogen, which in addition to being much colder, and much easier to mix rapidly, has a far lower molecular weight, aka more moles of light gas in the exhaust?

I do like the concept of thrust augmentation with air in general, though. It reminds me of the optimization issues one encounters with propellers. You get more thrust per unit power with a larger prop than a smaller prop because the larger one moves much more air, at a slower speed, to yield the same thrust; the slipstream is at lower velocity, and thus less energy is wasted to creating a fast slipstream.  It seems to be the same sort of optimization here: increase the thrust to power ratio by swapping mass for velocity.


Offline RanulfC

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Re: Why the lack of SSTO projects?
« Reply #122 on: 03/07/2017 10:48 PM »
Last time I looked into the concept (it's been a while), the duct tends to be a mass-limiting factor, hence the reason for getting rid of it when it's no longer needed, rather than just closing it off.

Exactly, but I'll point out that in some cases it was suggested that keeping the duct, (only loosing part of it to allow altitude compensation as an expander duct for the rocket array) was quite effective. It was studied under the "Reusable NOVA" (ReNOVA) concept and helped with the recovery of the stage by protecting the rocket engines on the way down. (ReNOVA's front end and aft expansion cone had it recovering like a the Mercury capsule it looked like)

Quote
The water cooling concept makes no sense to me. How is the effect of an injection amount of water supposed to have a significant cooling effect on incoming air unless its mass is somewhat comparable to the incoming air (wherein the mass penalty would be large)? And if you're going to bring something with high specific heat, why not hydrogen, which in addition to being much colder, and much easier to mix rapidly, has a far lower molecular weight, aka more moles of light gas in the exhaust?

A little water goes a long way or so the studies said :) A surprisingly long way but highly dependent on the airflow, vaporization, particle size and injection position which despite MIPCC being a 90s concept was actually studied and figured out in the early-60s. The concept later in flight injected liquid oxygen, (again a small amount compared to a rocket of course) to increase cooling at higher Mach, (2 to 4 in the original concept, here probably 1.5 to 2 if required at all, it was actually found that liquid nitrogen had a similar effect if you weren't needing the combustion chamber stabilization) and stabilize the combustion chamber temperature and combustion stability. Might not need that for a booster concept such as this.

Frankly one of the advantages is simply pushing more mass through the system and of course the more mass flow, which you get by 'cooling' the intake air to any degree, the better so you COULD use whatever you're using for fuel to burn with the air but if you're running fuel rich that's going to be overkill so why not use something dense, easy to store and easy to inject? The entire concept is based on historic use of water-injection in early turbojet engines, the trick was/is to use it in front of the compressor rather than in the exhaust providing more thrust, more air ingested, AND a higher compressor face Mach range. (The last has no place in the booster of course :) )

Quote
I do like the concept of thrust augmentation with air in general, though. It reminds me of the optimization issues one encounters with propellers. You get more thrust per unit power with a larger prop than a smaller prop because the larger one moves much more air, at a slower speed, to yield the same thrust; the slipstream is at lower velocity, and thus less energy is wasted to creating a fast slipstream.  It seems to be the same sort of optimization here: increase the thrust to power ratio by swapping mass for velocity.

That's the reason we have 'high-bypass' turbofans instead of turbojets :) The fans provide a much higher mass flow for less fuel consumption. Problem is, (like the propellers they resemble-ish :) ) they present a much larger area and so getting them to go faster is proportionally more difficult as the drag builds up. Hence we use low-or-medium bypass turbofans in aircraft we want to be able to go fast and high bypass in ones we don't need to.

Randy
From The Amazing Catstronaut on the Black Arrow LV:
British physics, old chap. It's undignified to belch flames and effluvia all over the pad, what. A true gentlemen's orbital conveyance lifts itself into the air unostentatiously, with the minimum of spectacle and a modicum of grace. Not like our American cousins' launch vehicles, eh?

Offline RanulfC

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Re: Why the lack of SSTO projects?
« Reply #123 on: 03/09/2017 02:02 AM »
Oh hullnuts! While we were all talking up the past we TOTALLY forgot to suggest the DIY method!
http://quantumg.net/mockingbird.pdf

You, a couple of buddy's, your CnC and 3D printer, a pickup truck and your personal 10kg to LEO SSTO! Sure it's PROBABLY going to be a bit on the expensive side and you'll PROBABLY find all sort of governments after your hide after a few launches but that's the FUN part, right?

Hey but that's not all! Switch things up a bit and you can probably milk at least half as much payload through various methods:
(I'm guessing since google is coming up empty no matter which keywords I use Dr. Dunn's alternate SSTO propellant paper is finally gone away :( )

Alternate propellants! Sure H2O2/Kerosene is nice and dense and needs no insulation but switch it out for LOX and Cryo-Propane instead! Bit trickier to work with but still well within the DIY range! And you can tell the authorities it's JUST for a barbecue! (Yes LOX cooking IS a thing :) )

Hey this baby is compact enough you really CAN use some "small" SRBs for it!
(https://engineering.purdue.edu/~propulsi/propulsion/rockets/solids.html)
Sure it's now an "assisted" SSTO but the motors for an AIM-9 or AMRAAM burn out pretty quick so they might fall in a friendly neighbors back-yard. Make space launch a community event!

Hey what about RENE, (Rocket-Engine-Nozzle-Ejector) for some extra "oomph" in your launch! Some re-arranging of parts and more of a "near-SSTO" effort and you can have your very own Mini-Me-NOVA... ER that is Mini-RE-NOVA! As in "reusable NOVA"!
(http://up-ship.com/blog/?p=9462)
You 'might' have to lose some of the shroud on the way up but maybe not as adding a water or liquid nitrogen intake cooling system might make up for the initial launch inefficiency. Don't forget to put a return address and postage on that main stage though as it will come down quite a ways down range! And then a small 'kick' motor on the payload puts it into orbit! But how to get it back? Well don't fret because in the late 60s a sintered carbon nosecap underwent an HOUR of reentry level heating cooled only by a couple of ounces of water and transpiration cooling and we're WAY more capable today! (And as per usual all my sites with that note are no longer valid, the paper used to be on tethers.com but no luck)

Lets face it the ability to get into loads of trouble at the drop of a launch vehicle is very much in range of todays DIY crowd so lets get out there and get launching!

Randy
From The Amazing Catstronaut on the Black Arrow LV:
British physics, old chap. It's undignified to belch flames and effluvia all over the pad, what. A true gentlemen's orbital conveyance lifts itself into the air unostentatiously, with the minimum of spectacle and a modicum of grace. Not like our American cousins' launch vehicles, eh?

Offline john smith 19

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Re: Why the lack of SSTO projects?
« Reply #124 on: 03/10/2017 09:27 PM »
Oh hullnuts! While we were all talking up the past we TOTALLY forgot to suggest the DIY method!
http://quantumg.net/mockingbird.pdf
Kare's powerpoint was certainly comprehensive both in the how and the why you would do it.  :) He definitely had access to Whiteheads work on pumped propulsion.
Quote from: RanulfC
You, a couple of buddy's, your CnC and 3D printer, a pickup truck and your personal 10kg to LEO SSTO! Sure it's PROBABLY going to be a bit on the expensive side and you'll PROBABLY find all sort of governments after your hide after a few launches but that's the FUN part, right?

Depending on launch site in the CONUS I'd expect a visit within 2 hours of a whole of USG departments, several of them with guns.
Quote from: RanulfC
Hey but that's not all! Switch things up a bit and you can probably milk at least half as much payload through various methods:
(I'm guessing since google is coming up empty no matter which keywords I use Dr. Dunn's alternate SSTO propellant paper is finally gone away :( )

Alternate propellants! Sure H2O2/Kerosene is nice and dense and needs no insulation but switch it out for LOX and Cryo-Propane instead! Bit trickier to work with but still well within the DIY range! And you can tell the authorities it's JUST for a barbecue! (Yes LOX cooking IS a thing :) )
Really? turning "Flambe" up to 11?
IIRC the standout from Dunn's paper was MethylAcetylene, or Propyne to give it its systemic name. The strained ring added several seconds to the Isp over Butane and Propane. Unfortunately I'm not sure they've ever cleared it from being carcinogenic.  :(
I think peroxide Propulsion in Sweden are still in business so a cat pack is potentially not too big a challenge (although work on Meso scale cat packs for cubesats suggests getting a small design right is tricky).
Quote from: RanulfC
Hey this baby is compact enough you really CAN use some "small" SRBs for it!
(https://engineering.purdue.edu/~propulsi/propulsion/rockets/solids.html)
Sure it's now an "assisted" SSTO but the motors for an AIM-9 or AMRAAM burn out pretty quick so they might fall in a friendly neighbors back-yard. Make space launch a community event!
True, but quite tough to get hold unless you're on an actual AFB.
Quote from: RanulfC
Hey what about RENE, (Rocket-Engine-Nozzle-Ejector) for some extra "oomph" in your launch! Some re-arranging of parts and more of a "near-SSTO" effort and you can have your very own Mini-Me-NOVA... ER that is Mini-RE-NOVA! As in "reusable NOVA"!
(http://up-ship.com/blog/?p=9462)
You 'might' have to lose some of the shroud on the way up but maybe not as adding a water or liquid nitrogen intake cooling system might make up for the initial launch inefficiency. Don't forget to put a return address and postage on that main stage though as it will come down quite a ways down range! And then a small 'kick' motor on the payload puts it into orbit! But how to get it back? Well don't fret because in the late 60s a sintered carbon nosecap underwent an HOUR of reentry level heating cooled only by a couple of ounces of water and transpiration cooling and we're WAY more capable today! (And as per usual all my sites with that note are no longer valid, the paper used to be on tethers.com but no luck)
 
 
I could have sworn those tests were done sometime in the mid 70's.  The problem has always seemed to be distributing the water and finding some kind of feedback mechanism to increase the flow to the hotter parts. I though of it as an "artificial sweat gland," but I've never seen any design that can implement it.  :(
Quote from: RanulfC
Lets face it the ability to get into loads of trouble at the drop of a launch vehicle is very much in range of todays DIY crowd so lets get out there and get launching!
Ah but the real challenge is bringing it down afterward.  :(

Mockingbird used a sort of TPS "umbrella" to substantially raise the the surface area and hence the re-entry altitude.

At this scale my instinct is that TPS and GNC are the biggest problems. GPS will shut down due to DoD restrictions (unless you want to home brew a GPS receiver. Quite feasible given a published design for a Transputer based unit needed about 10MIPS over 20 years ago). Likewise the challenge of a light but robust (ideally flexible) TPS. I note that NASA have developed flexible versions of its PICA and SIRCA ablatives. There's also something called "stunt gel"which is basically 99% water. I'll also note today high end brake pads are made of RCC.

The other issue that the Whitehead team noted was the lack of a small size high pressure thrust chamber as most had been inherited from pressure fed hypergolic designs for station keeping on comm sats. That suggests this is a key missing element for pump fed systems, going to 1000-1500psi 
« Last Edit: 03/11/2017 01:57 PM by john smith 19 »
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline strangequark

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Re: Why the lack of SSTO projects?
« Reply #125 on: 03/10/2017 09:46 PM »
Oh hullnuts! While we were all talking up the past we TOTALLY forgot to suggest the DIY method!
http://quantumg.net/mockingbird.pdf

You, a couple of buddy's, your CnC and 3D printer, a pickup truck and your personal 10kg to LEO SSTO! Sure it's PROBABLY going to be a bit on the expensive side and you'll PROBABLY find all sort of governments after your hide after a few launches but that's the FUN part, right?

Hey but that's not all! Switch things up a bit and you can probably milk at least half as much payload through various methods:
(I'm guessing since google is coming up empty no matter which keywords I use Dr. Dunn's alternate SSTO propellant paper is finally gone away :( )

Alternate propellants! Sure H2O2/Kerosene is nice and dense and needs no insulation but switch it out for LOX and Cryo-Propane instead! Bit trickier to work with but still well within the DIY range! And you can tell the authorities it's JUST for a barbecue! (Yes LOX cooking IS a thing :) )

Hey this baby is compact enough you really CAN use some "small" SRBs for it!
(https://engineering.purdue.edu/~propulsi/propulsion/rockets/solids.html)
Sure it's now an "assisted" SSTO but the motors for an AIM-9 or AMRAAM burn out pretty quick so they might fall in a friendly neighbors back-yard. Make space launch a community event!

Hey what about RENE, (Rocket-Engine-Nozzle-Ejector) for some extra "oomph" in your launch! Some re-arranging of parts and more of a "near-SSTO" effort and you can have your very own Mini-Me-NOVA... ER that is Mini-RE-NOVA! As in "reusable NOVA"!
(http://up-ship.com/blog/?p=9462)
You 'might' have to lose some of the shroud on the way up but maybe not as adding a water or liquid nitrogen intake cooling system might make up for the initial launch inefficiency. Don't forget to put a return address and postage on that main stage though as it will come down quite a ways down range! And then a small 'kick' motor on the payload puts it into orbit! But how to get it back? Well don't fret because in the late 60s a sintered carbon nosecap underwent an HOUR of reentry level heating cooled only by a couple of ounces of water and transpiration cooling and we're WAY more capable today! (And as per usual all my sites with that note are no longer valid, the paper used to be on tethers.com but no luck)

Lets face it the ability to get into loads of trouble at the drop of a launch vehicle is very much in range of todays DIY crowd so lets get out there and get launching!

Randy

Working with vehicles almost exactly the size of Mockingbird, and knowing the masses of the various parts makes it amazingly hilarious to read through.
Gravity's just a habit that you're pretty sure you can't break.

Offline Proponent

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Re: Why the lack of SSTO projects?
« Reply #126 on: 03/11/2017 09:52 AM »
I'd like to turn the question in the OP around and ask not why there is so little interest in SSTO now but why there was so much interest in the 1990's.  If it was thinkable then, shouldn't it be even plausible now, with the benefit of 25 years' worth of technological advances?

My guess is that the answer lies more in Keynes's animal spirits than in technology or economics:  the economic boom of the 1990's led people to dream a little more and worry a little less.  But maybe I'm wrong.  Were there, for example, specific technological or economic lessons learned from the projects in the nineties that have curtailed enthusiasm today?

Offline su27k

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Re: Why the lack of SSTO projects?
« Reply #127 on: 03/11/2017 12:39 PM »
I'd like to turn the question in the OP around and ask not why there is so little interest in SSTO now but why there was so much interest in the 1990's.  If it was thinkable then, shouldn't it be even plausible now, with the benefit of 25 years' worth of technological advances?

Well all the SSTO projects since then have crashed and burned may have something to do with it... Also back then NASA is still flying a partially reusable vehicle, it may be uneconomical but it is reusable, so a SSTO may be seen as a natural next step. Nowadays NASA has pretty much given up on reusable and retreated to throw away everything, so SSTO seems to be further away then ever if you just considering NASA and traditional aerospace.

If this hypothesis is true, I think we may see renewed interest in SSTO if current crop of partial reusable launch vehicles prove themselves.

Offline john smith 19

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Re: Why the lack of SSTO projects?
« Reply #128 on: 03/11/2017 01:53 PM »
Well all the SSTO projects since then have crashed and burned may have something to do with it...
Which ones were you thinking of?

I can only think of the X33, which was a masterclass in poor design selection compounded by poor staffing and uncaring management.
Quote from: su27k
Also back then NASA is still flying a partially reusable vehicle, it may be uneconomical but it is reusable, so a SSTO may be seen as a natural next step. Nowadays NASA has pretty much given up on reusable and retreated to throw away everything, so SSTO seems to be further away then ever if you just considering NASA and traditional aerospace.
Things may change.
Quote from: su27k
If this hypothesis is true, I think we may see renewed interest in SSTO if current crop of partial reusable launch vehicles prove themselves.
Unlikely for the same reason that existed then. VTOL SSTO delivers 1/3 to 1/2 the payload weight to orbit.  Only designs substantially outside the rocket paradigm can do better and that makes investors very nervous.

That won't change until a much better engine is tested.
Unlikely
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline Archibald

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Re: Why the lack of SSTO projects?
« Reply #129 on: 03/11/2017 02:08 PM »
Would the Mockingbird ever works ? I thought SSTOs scaled pretty bad.

Offline HMXHMX

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Re: Why the lack of SSTO projects?
« Reply #130 on: 03/11/2017 04:17 PM »
Would the Mockingbird ever works ? I thought SSTOs scaled pretty bad.

SSTOs do scale badly.  I was always dubious about Mockingbird for a number of reasons but at the same time, in the early 1990s, having any one-stage reusable VTOL demonstrator was better than having none, so I supported it.  If it had been built, it would have had similar utility to DC-X, which was a much larger project.

(Bit of background: I was a hired consultant to Livermore's O-Group for the project, along with Max Hunter, Thor and S-IVB Chief Engineer, and George R. Sutton, yes, of Rocket Propulsion Elements.)

Offline HMXHMX

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Re: Why the lack of SSTO projects?
« Reply #131 on: 03/11/2017 04:19 PM »
Well all the SSTO projects since then have crashed and burned may have something to do with it...
Which ones were you thinking of?

I can only think of the X33, which was a masterclass in poor design selection compounded by poor staffing and uncaring management.
Quote from: su27k
Also back then NASA is still flying a partially reusable vehicle, it may be uneconomical but it is reusable, so a SSTO may be seen as a natural next step. Nowadays NASA has pretty much given up on reusable and retreated to throw away everything, so SSTO seems to be further away then ever if you just considering NASA and traditional aerospace.
Things may change.
Quote from: su27k
If this hypothesis is true, I think we may see renewed interest in SSTO if current crop of partial reusable launch vehicles prove themselves.
Unlikely for the same reason that existed then. VTOL SSTO delivers 1/3 to 1/2 the payload weight to orbit.  Only designs substantially outside the rocket paradigm can do better and that makes investors very nervous.

That won't change until a much better engine is tested.
Unlikely

It's not a better engine that is required since chemical engines are at the peak of their development and performance; it's a better propellant mass fraction.

Offline john smith 19

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Re: Why the lack of SSTO projects?
« Reply #132 on: 03/11/2017 10:40 PM »
SSTOs do scale badly.  I was always dubious about Mockingbird for a number of reasons but at the same time, in the early 1990s, having any one-stage reusable VTOL demonstrator was better than having none, so I supported it.  If it had been built, it would have had similar utility to DC-X, which was a much larger project.

(Bit of background: I was a hired consultant to Livermore's O-Group for the project, along with Max Hunter, Thor and S-IVB Chief Engineer, and George R. Sutton, yes, of Rocket Propulsion Elements.)
That suggests that any design choices should have been well informed although I recall Charles Pooley (microlaunchers) did note that scale down (for single or multi stage vehicles) is tough. 

On the upside the scale of such a vehicle opens up various mfg and materials possibilities.

What particular areas did you think Mockingbird was going to have trouble with?

It's not a better engine that is required since chemical engines are at the peak of their development and performance; it's a better propellant mass fraction.
If you're looking at a rocket powered SSTO then you need to put the whole structure into less than 10% of the GTOW. Not using LH2 may reduce the gravity losses (I normally knock 100m/s off) but OTOH you lose a substantial amount of Isp in the process, lowering the average Isp by quite a lot.

My instinct is that no pure rocket SSTO can deliver a payload fraction equal to a TSTO. That fact alone severely limits investor interest.  If you can't match a TSTO what does your vehicle do that outweighs that disadvantage?

Only moving away from a pure rocket system seems to offer a chance of delivering the kind of Isp that can accommodate a payload fraction at least equal to that of a TSTO.
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline jongoff

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Re: Why the lack of SSTO projects?
« Reply #133 on: 03/11/2017 11:49 PM »
It's not a better engine that is required since chemical engines are at the peak of their development and performance; it's a better propellant mass fraction.

Well, engine T/W ratio and mission-averaged Isp are ones where there are still room for improvement, even if Isp at a specific exit condition has already neared practical limits. Engine T/W ratio is an important part of overall dry mass especially on SSTOs. But yeah, there are a lot of other areas that could use improvement.

~Jon

Offline HMXHMX

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Re: Why the lack of SSTO projects?
« Reply #134 on: 03/12/2017 12:46 AM »
SSTOs do scale badly.  I was always dubious about Mockingbird for a number of reasons but at the same time, in the early 1990s, having any one-stage reusable VTOL demonstrator was better than having none, so I supported it.  If it had been built, it would have had similar utility to DC-X, which was a much larger project.

(Bit of background: I was a hired consultant to Livermore's O-Group for the project, along with Max Hunter, Thor and S-IVB Chief Engineer, and George R. Sutton, yes, of Rocket Propulsion Elements.)
That suggests that any design choices should have been well informed although I recall Charles Pooley (microlaunchers) did note that scale down (for single or multi stage vehicles) is tough. 

On the upside the scale of such a vehicle opens up various mfg and materials possibilities.

What particular areas did you think Mockingbird was going to have trouble with?

It's not a better engine that is required since chemical engines are at the peak of their development and performance; it's a better propellant mass fraction.
If you're looking at a rocket powered SSTO then you need to put the whole structure into less than 10% of the GTOW. Not using LH2 may reduce the gravity losses (I normally knock 100m/s off) but OTOH you lose a substantial amount of Isp in the process, lowering the average Isp by quite a lot.

My instinct is that no pure rocket SSTO can deliver a payload fraction equal to a TSTO. That fact alone severely limits investor interest.  If you can't match a TSTO what does your vehicle do that outweighs that disadvantage?

Only moving away from a pure rocket system seems to offer a chance of delivering the kind of Isp that can accommodate a payload fraction at least equal to that of a TSTO.

Interestingly, there was a study done by some NASA Langley folks in the mid-1980s (can't place the time any better memory fades) where they showed (to their, my and Hunter's satisfaction) that one-stage systems could directly match payload performance of two-stage systems to LEO, when a detailed analysis took into account the penalty of the mass of the interstage plus extra altitude engine propulsion mass.  What I don't recall is where the two concepts crossed over, but the basic message was to refute the "two stages are always better than one" assertion.  The analysis also required pretty high mass fractions, but not higher than what SpaceX and others have approached or achieved.  I do recall that the analysis was a briefed at pretty high levels in the gov't which helped kick off the program (SSRT) that became DC-X.  (And then DC-X didn't address the most critical issue, i.e., propellant mass fraction.)

I've wanted to write a formal paper on the matter for a long while but never had the time, and my motivation to do so is largely gone.  And first I'd have to find the hardcopy of their memo/briefing, which might be a near-impossible task.

Offline Katana

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Re: Why the lack of SSTO projects?
« Reply #135 on: 03/12/2017 02:39 AM »
Would the Mockingbird ever works ? I thought SSTOs scaled pretty bad.
In my own calculations, a tiny pump fed launcher capable of 10kg payload need 2.5 or 3 stages and 1~2 ton GTOW. Structure mass fractions of stages varies from 1/6 to 1/12 (instead of 1/20 of Mockingbird ) depending on propellants.

Electric pumps and batteries are light, but overall weight of all systems are heavy. Piston pumps of Mockingbird are heavier, especially more valves. 0.02 inch Al skin is also too thin to weld.

For using low weight traditional rocket as (expendable) SSTO, the old Atlas I with balloon tanks should be promising. The original version only jettison 2 engines and send 1.3t Mercury capsule to orbit with 120t GTOW, rather good. Replacing 1950s low isp kerosene engines with Merlin may make it complete SSTO.

Though less economic than F9R.
« Last Edit: 03/12/2017 05:23 AM by Katana »

Online sevenperforce

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Re: Why the lack of SSTO projects?
« Reply #136 on: 03/22/2017 08:27 PM »
Just for the hell of it, how about I crunch the numbers on a mini-ITS SSTO powered by a production version of the 1000 kN dev Raptor with an ejector shroud?

Suppose the engine masses roughly 550 kg and develops 102 tonnes of thrust. Add an ejector shroud (mass: 2 tonnes) and the static thrust jumps to 117.3 tonnes thrust. Let's set GLOW at 100 tonnes exactly, both to have a nice round number and to give us a launch TWR of just under 1.2. The ITS tanker's carbon-fiber body has a structural tankage ratio of 97.4% including TPS. I'll drop that to 96% as an expected square-cube loss, but that means a "pure fuel" ship would give us 93.6 tonnes of fuel. So whatever we have left once we reach orbit, re-enter, and land is our round-trip payload.

Rather than trying to compute a pure mathematical solution, I'll just define the following discrete velocity regimes for thrust augmentation and compute iteratively:

under 170 m/s: 15% augmentation, eff isp 384.1 s
170 to 430 m/s: 25% augmentation, eff isp 417.5 s
430 to 670 m/s: 40% augmentation, eff isp 467.5 s
670 to 1500 m/s: 50% augmentation, eff isp 501 s
1500 to 2000 m/s: 40% augmentation, eff isp 467.6 s
2000 to 2500 m/s: 30% augmentation, eff isp 434.2 s
2500 to 3000 m/s: 20% augmentation, eff isp 400.8 s
3000 to 3400 m/s: 10% augmentation, eff isp 367.4 s
over 3400 m/s: 8% vacuum thrust boost, eff isp 361 s

landing: 0% boost, isp 334 s.

As the ship will rapidly gain speed due to the ejector duct, gravity drag losses will be minimal, but drag losses will be a little higher. I'll estimate 1.1 km/s total, with 100 m/s of drag added to each of the above acceleration regimes (300 m/s on the last one).

GLOW: 100 tonnes
At 170 m/s: 93.1 tonnes
At 430 m/s: 85.23 tonnes
At 670 m/s: 79.14 tonnes
At 1500 m/s: 65.49 tonnes
At 2000 m/s: 57.45 tonnes
At 2500 m/s: 49.89 tonnes
At 3000 m/s: 42.83 tonnes
At 3400 m/s: 37.27 tonnes
At 7800 m/s: 10.75 tonnes
After landing (500 m/s): 9.22 tonnes

Since our dry mass is 6.4 tonnes, this means the payload is 2.82 tonnes with a fully reusable SSTO at a GLOW of 100 tonnes.

Any further improvement...like SSME-derived altitude compensation to push up the vacuum specific impulse, or a parallel launch assist booster...makes this quite viable.

A "quasi-SSTO" with low cost small boosters (booster GTOW < 0.5* sustainer GTOW) could be better than either pure SSTO (high tech, low margin) or typical TSTO (or 1.5 stage) systems (booster GTOW > 2 * sustainer GTOW).
This is precisely my feeling on the matter.

Quote from: Robotbeat
Also, drag. You have to accelerate all that reaction mass from a standstill to near your flight speed, JUST like a regular launch vehicle except you have to use inlets to do so.

This is kind of a subtle point that I haven't seen many people actually grok (and interestingly, keeping the airflow supersonic like in a SCRAMjet doesn't actually help you much... Energy is conserved).
Yeah, the curve for air augmentation or other airbreathing modes goes up with ram compression, then starts to drop as the forward airspeed approaches the exhaust velocity. There would be a very specific ascent profile for a partial airbreather.

Offline Arch Admiral

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Re: Why the lack of SSTO projects?
« Reply #137 on: 03/22/2017 08:49 PM »
The reason SSTO was so popular in the 1980s and the early 90s was that there was a high-priority national program that couldn't work without cheaper access to LEO -- namely the Strategic Defense Initiative. X-30/NASP and DC-X/DC-Y were directly funded by SDIO to launch and maintain anti-ICBM systems. ALS/NLS and X-33/VentureStar were less directly influenced by SDIO, but clearly considered orbital battle stations (like the Soviet Polyus) as a major part of their market.

The reason SSTO has dropped from sight since then is that those programs clearly showed that the idea was unworkable in the real world of real engineering (just like the proposed payloads). The preliminary work done on the test vehicles X-30, DC-X, and X-33 demonstrated that the operational versions NASP, DC-Y, and VentureStar would come out far to heavy to reach orbit.

Offline john smith 19

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Re: Why the lack of SSTO projects?
« Reply #138 on: 03/22/2017 11:08 PM »
The reason SSTO was so popular in the 1980s and the early 90s was that there was a high-priority national program that couldn't work without cheaper access to LEO -- namely the Strategic Defense Initiative. X-30/NASP and DC-X/DC-Y were directly funded by SDIO to launch and maintain anti-ICBM systems. ALS/NLS and X-33/VentureStar were less directly influenced by SDIO, but clearly considered orbital battle stations (like the Soviet Polyus) as a major part of their market.

The reason SSTO has dropped from sight since then is that those programs clearly showed that the idea was unworkable in the real world of real engineering (just like the proposed payloads).
Actually DC-X showed that with a properly designed vehicle you could turn it around in  26 hours (and that would have been about 9 if the range crew had been willing to work a bit later) without engine removal or dis assembly despite having the most difficult to handle (but highest Isp) fuel  available.

The X33 programme demonstrated only that NASA was that a company keen to retain the status quo could effectively game the NASA procurement process by making promises it had no intention of keeping then ensuring project failure by packing the staff with staff who lacked either the skills or the intelligence (or both) to make it succeed.

All the X33 programme demonstrated about SSTO was that if  you choose the most complex way to carry out a task, with the most amount of untested (and unnecessary) technology in the critical path you have a very high likelyhood of failure. Compound that by staffing the project with inexperienced or under qualified staff and you can practically guarantee failure.

Otherwise it demonstrated that LM are very good at extracting money from the USG.
Quote from: Arch Admiral
The preliminary work done on the test vehicles X-30, DC-X, and X-33 demonstrated that the operational versions NASP, DC-Y, and VentureStar would come out far to heavy to reach orbit.
I'd suggest you read TA Heppenheimers "Facing The Heat Barrier." What the X30 programme demonstrated is that without effective oversight a great deal of money can be wasted on something that, had the proper thermophysical properties been used from the onset, would probably have never been started. I'll leave others to speculate on how that came about.

DC-X did not in fact address vehicle weight. That was to be handled by DC-Y.  Curiously there seems to have been an anonymous campaign in Congress to prevent this from ever being funded, as described in G Harry Stine's "Half Way to Anywhere."
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline Asteroza

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Re: Why the lack of SSTO projects?
« Reply #139 on: 03/23/2017 05:57 AM »

The other issue that the Whitehead team noted was the lack of a small size high pressure thrust chamber as most had been inherited from pressure fed hypergolic designs for station keeping on comm sats. That suggests this is a key missing element for pump fed systems, going to 1000-1500psi 

I wonder for the Rocketlabs Electron what the Rutherford engine's chamber pressure is a max electric pumping?


So for a mockingbird/bricklifter/3U cubesat lifter redux, the pump system and associated chamber get pretty important. At these scales though, what kind of pumping systems are available now that look attractive enough to use? Rocketlabs is bringing electric pump power source into vogue, but what about the physical pumps themselves? Whitehead advocated an advanced piston design. Some piston systems use a non-propellant high pressure drive gas (dump the gas as verniers?).  Rotaries range from traditional centrifugal to axial, plus rampressors and lobed rotors like gerotors/wankel/"liquid piston" inverse wankel. Other piston oddballs might include electric drive free pistons.

At these scales, is using active cooling to assist the pump cycle generally not worth it, or is it terribly application specific? Rutherford appears to use active cooling for the nozzle at least.

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