Airbreathing SSTO

If polywell fusion is developed, in what ways will the world change for better or worse? Discuss.

Moderators: tonybarry, MSimon

93143
Posts: 1131
Joined: Fri Oct 19, 2007 7:51 pm

Postby 93143 » Wed Mar 05, 2008 1:50 am

But then he started complaining about ozone production, and that design doesn't really have any way to dump the heat from the reactor (unless you want to go with my big glowing panels idea).

Furthermore, that drive only works at hypersonic speed.

I'd prefer something that's a bit more versatile. Currently I'm thinking ejector ramscram (doesn't have to be super big and heavy because combustion isn't an issue) with hydrogen injection from the cooling system. The big glowing panels then have less to do until you reach space, which is good for safety and runway integrity and such. The ejector rocket doubles as a space drive, and since the engine as a whole is cylindrical you can magnetically shield it so as to get very high exhaust temperatures, like VASIMR. The dumped hydrogen should scavenge any ozone, even if it doesn't burn inside the engine due to mixing issues.

On the other hand, the raster-scan drive probably has advantages too. I'm not familiar enough with high-speed propulsion technology to say (maybe I should find out when the Air-Breathing Propulsion class is and sit in on it).

djolds1
Posts: 1296
Joined: Fri Jul 13, 2007 8:03 am

Postby djolds1 » Wed Mar 05, 2008 5:09 am

93143 wrote:But then he started complaining about ozone production, and that design doesn't really have any way to dump the heat from the reactor (unless you want to go with my big glowing panels idea).


Its similar to QED/ARC. Dump the heat into the working remass.

93143 wrote:Furthermore, that drive only works at hypersonic speed.


I'd think it could work at even ram-air pulsejet speeds (think the engine on the German V1), albeit in slightly modified form. Build it like an RBCC engine (Rocket Based Combined Cycle). Perhaps use the ARC rocket mode for the initial burst of thrust, with a conical centerbody diffuser blocking the inlet. Raster scan the REB (relativistic electron beam) into the rocket remass injected into the thrust tube. Once you get to operational speed, the diffuser and rocket fuel injector retract, and the REB scans the through-flowing air, superheating it. Use the air-breathing mode from say Mach 0.3 to Mach 10, and then reengage the conical centerbody and rocket fuel injectors for ARC mode final injection to orbit.

Tho in this modified concept, the raster scan may be superfluous.

93143 wrote:I'd prefer something that's a bit more versatile. Currently I'm thinking ejector ramscram (doesn't have to be super big and heavy because combustion isn't an issue) with hydrogen injection from the cooling system. The big glowing panels then have less to do until you reach space, which is good for safety and runway integrity and such. The ejector rocket doubles as a space drive, and since the engine as a whole is cylindrical you can magnetically shield it so as to get very high exhaust temperatures, like VASIMR. The dumped hydrogen should scavenge any ozone, even if it doesn't burn inside the engine due to mixing issues.


Sounds like my idea above, albeit that mine doesn't use H2 or H2O injection for the airbreathing mode. However, I prefer separating SSTO and in-space propulsion. Use the airbreathing/ARC SSTOs as analogues of the C130 and C17 cargo planes. 20-75 metric tonnes to orbit. Use separate ARC and CSR vessels in space beyond LEO.

IIRC, Bussard was selling the ozone creation as a good thing, "replenishing" ozone losses in the upper atmosphere.

And with a (quasi)ARC mode, radiators aren't necessary until you shut down the drive in space. The ejected remass/working mass is the radiator. In space, I prefer droplet radiators. Far less risk during the takeoff and E/LEO boost phases. Extend the droplet booms once in orbit. And its safer in space - only the booms can be damaged, there are no big solid radiator panels for micro-meteoroids to hit. Also, you can delay deployment of the radiators for awhile, dumping heat into on-board sodium or lithium heat sinks.

93143 wrote:On the other hand, the raster-scan drive probably has advantages too. I'm not familiar enough with high-speed propulsion technology to say (maybe I should find out when the Air-Breathing Propulsion class is and sit in on it).


Scramjets are called "scamjets" (NOT sp) for good reason. Perusal of Google Groups threads should be informative.

Duane
Vae Victis

93143
Posts: 1131
Joined: Fri Oct 19, 2007 7:51 pm

Postby 93143 » Tue Mar 11, 2008 9:37 pm

djolds1 wrote:Its similar to QED/ARC. Dump the heat into the working remass.


How? This is air at hypersonic speed, and you're trying to heat it with a heat exchanger? We have enough trouble doing it with hydrogen combustion, as you pointed out with that 'scamjet' crack... A heat exchanger hot enough to do it would be similar to the 'big glowing panels' idea but with the added problem that it would be useless in space. No, I think we're better off dumping at least some hydrogen. We have full internal control of the heat transfer process that way...

djolds1 wrote:I prefer separating SSTO and in-space propulsion. Use the airbreathing/ARC SSTOs as analogues of the C130 and C17 cargo planes. 20-75 metric tonnes to orbit. Use separate ARC and CSR vessels in space beyond LEO.


Maybe. You could make an economic case for it. But you could make a much stronger economic case for not going to space at all, even with BFRs to power the ships. This reactor technology would make it possible (I didn't say optimal) to get in a spaceship on Earth, take off and go land on one of Saturn's moons, do something useful there, take off again and go back to land the entire, intact original spaceship on Earth. I say we go for it.

Not exclusively, of course. If this really works there's going to be something you could plausibly call a manned spaceflight infrastructure, rather than the ridiculous money hole we have now.

djolds1 wrote:IIRC, Bussard was selling the ozone creation as a good thing, "replenishing" ozone losses in the upper atmosphere.


Okay. I didn't get that impression from the paper I was reading, but that could have been the delivery. It was the last thing he said before switching to discussion of rockets, so it sounded dismissive. In any case, it's not something you want happening at ground level.

djolds1 wrote:In space, I prefer droplet radiators. Far less risk during the takeoff and E/LEO boost phases. Extend the droplet booms once in orbit. And its safer in space - only the booms can be damaged, there are no big solid radiator panels for micro-meteoroids to hit. Also, you can delay deployment of the radiators for awhile, dumping heat into on-board sodium or lithium heat sinks.


I'm dubious about droplet radiators. They preclude high-thrust vacuum operation, and the potential for mass loss (by boiloff, splashing, etc.) is worrying for long missions. This is one of the things I hoped BFR-powered spacecraft would get rid of - the overriding need to save weight at the cost of durability and versatility.

On the other hand, if you use pure ARC to get to orbit, you will definitely need deployable radiators of some kind. The advantages may outweigh the problems.

...The one big intrinsic flaw in the idea of spaceframe-integrated super-high-temperature radiators (assuming you could do it within a reasonable mass budget) is the fact that they would present a hazard to nearby personnel and technology, not only while operating but for a significant amount of time after shutdown. For certain applications the trade might be worth it...

...You know, we've had the potential for SSTA capability since the '60s. The idea has been so thoroughly swept under the rug (and with good reason) that NASA's new capsule shares its name...

djolds1
Posts: 1296
Joined: Fri Jul 13, 2007 8:03 am

Postby djolds1 » Wed Mar 12, 2008 4:05 am

93143 wrote:How? This is air at hypersonic speed, and you're trying to heat it with a heat exchanger? We have enough trouble doing it with hydrogen combustion, as you pointed out with that 'scamjet' crack... A heat exchanger hot enough to do it would be similar to the 'big glowing panels' idea but with the added problem that it would be useless in space. No, I think we're better off dumping at least some hydrogen. We have full internal control of the heat transfer process that way...


Bleed off some air for bypass, slow it down, and dump heat into it. Also, the all-airbreathing mode would only operate in the ramjet & low-scramjet velocity range, which we have already achieved. So dumping heat into the working mass shouldn't be too difficult. Also, it should be possible to use on-board heat sinks for the brief all-airbreathing phase if necessary.

Besides, for in-atmosphere application, all you really need to dump heat from is the engine operation itself. If you can do that raster-scanning a hull undercut, you can probably do it in a cylindrically shaped RBCC variant.

I in no way advocate the "scramjet to Mach 25" airbreathing to orbit idea. Airbreathing might or might not be useful for E/LEO interface craft, but would probably be useful for suborbital passenger travel.

93143 wrote:Maybe. You could make an economic case for it. But you could make a much stronger economic case for not going to space at all, even with BFRs to power the ships. This reactor technology would make it possible (I didn't say optimal) to get in a spaceship on Earth, take off and go land on one of Saturn's moons, do something useful there, take off again and go back to land the entire, intact original spaceship on Earth. I say we go for it.

Not exclusively, of course. If this really works there's going to be something you could plausibly call a manned spaceflight infrastructure, rather than the ridiculous money hole we have now.


IIRC, the ARC mode (the only high-thrust QED rocket mode) is only good for Earth to Mars or so at most. To get past the asteroid belt requires the CSR mode at least. And CSR is low-thrust using a radiator. So Earth surface to Titan isn't really practical. But if you can get 20-75 tonnes to orbit cheaply several times a day, if not more often, the usual "build in orbit is difficult" objections don't hold. This is like a fast deployment of military assets by air. Hundreds or thousands of tonnes of cargo per day. Not a RoRo cargo ship, but much better than the limits for space access we labor under today.

93143 wrote:Okay. I didn't get that impression from the paper I was reading, but that could have been the delivery. It was the last thing he said before switching to discussion of rockets, so it sounded dismissive. In any case, it's not something you want happening at ground level.


I saw it as mostly PR, tho he made the claim.

93143 wrote:I'm dubious about droplet radiators. They preclude high-thrust vacuum operation, and the potential for mass loss (by boiloff, splashing, etc.) is worrying for long missions. This is one of the things I hoped BFR-powered spacecraft would get rid of - the overriding need to save weight at the cost of durability and versatility.

On the other hand, if you use pure ARC to get to orbit, you will definitely need deployable radiators of some kind. The advantages may outweigh the problems.


Using ARC, you dump heat into the remass while under thrust. That's what ARC means (All Regenerative Cooling). When not under thrust at constant velocity (coast between say Earth and Mars - the Mars Transfer Orbit stage) its a non-concern. And the medium-efficiency CSR mode is low- thrust anyway; again a non-concern.

Plus, you can recycle the droplet material as on-board lithium or sodium heat sink fuel for periods when the "radiator halyards" need to be stowed. Tertius, droplet radiators are easier to store, needing only space for the "radiator halyards." Fourth, they are more survivable, with only the halyards vulnerable.

93143 wrote:...You know, we've had the potential for SSTA capability since the '60s. The idea has been so thoroughly swept under the rug (and with good reason) that NASA's new capsule shares its name...


More than just nuclear pulse propulsion (ye olde bang bang). Look up "Sea Dragon" at astronautix. And if the Polywell fails, Google "paraffin hybrid rocket."

Duane
Vae Victis

ANTIcarrot
Posts: 62
Joined: Wed Aug 15, 2007 11:47 pm
Contact:

Postby ANTIcarrot » Wed Mar 12, 2008 2:24 pm

This topic has been discussed before.

Firstly, the sample design that Mr Bussard actually proposed:
http://www.longwood.edu/chemistry/Stude ... _Compr.ppt

A polywell is a low-neutron, not no-neutron source. In the multi GW range (as required by polywell SSTO proposals) that small percentage of power outputted as neutrons starts to become VERY significant.

In space this isn't a problem, but while flying through the atmosphere, or sitting on the ground, there are significant problems. (Like turning the runway radioactive.) Large aircraft (especially hypersonic delta wing monstrosities) also suffer from a number of operational issues that are a simple function of their size and flight envelope, and which polywell will not help solve.

It also faces thermal problems during reentry because of its shear size. Chemical SSTO use their light structures as an advantage, because it means they can slow down quickly and have light weight/robust thermal protection systems.

Lastly, it is blithely assumed that experimental electric rockets that struggle to produce thrust in the Newton range can easily be scaled up to produce thrust in the tons range. This seems unlikely.
Some light reading material: Half Way To Anywhere, The Rocket Company, Space Technology, The High Fronter, Of Wolves And Men, Light On Shattered Water, The Ultimate Weapon, any Janes Guide, GURPS Bio-Tech, ALIENS Technical Manual, The God Delusion.

93143
Posts: 1131
Joined: Fri Oct 19, 2007 7:51 pm

Postby 93143 » Wed Mar 12, 2008 10:04 pm

djolds1 wrote:Besides, for in-atmosphere application, all you really need to dump heat from is the engine operation itself.


Okay, I think I see the misunderstanding. A 6 GW BFR is going to produce well over a gigawatt of waste heat just from alpha bombardment of the grid. If you slow down air at Mach 10 to subsonic speed, it gets pretty hot, and even with the increase in specific heat of air at high temperature, this starts to look a bit extreme. If you can dump over a gigawatt at an exchanger temperature of several thousand degrees, great - but I doubt it. Slush hydrogen, on the other hand...

djolds1 wrote:I in no way advocate the "scramjet to Mach 25" airbreathing to orbit idea.


I agree that it's probably not a good idea using a SCRAMjet as such. The combustion thing just gets too marginal. However, I am of the opinion that QED heating (which is independent of mixing length) would shrink the size of a hypersonic airbreathing engine sufficiently to make it a reasonable proposition. A number of things that make scramjets so hard to build just stop being problems, particularly if it proves possible to magnetically shield the engine from the high-temperature exhaust (which is pretty much a plasma).

djolds1 wrote:IIRC, the ARC mode (the only high-thrust QED rocket mode) is only good for Earth to Mars or so at most. To get past the asteroid belt requires the CSR mode at least. And CSR is low-thrust using a radiator. So Earth surface to Titan isn't really practical. But if you can get 20-75 tonnes to orbit cheaply several times a day, if not more often, the usual "build in orbit is difficult" objections don't hold. This is like a fast deployment of military assets by air. Hundreds or thousands of tonnes of cargo per day. Not a RoRo cargo ship, but much better than the limits for space access we labor under today.


True, but you're assuming that (a) one spacecraft can't carry two engine types, and (b) that an ARC engine can't be designed for 'combined-cycle' operation, so that you could simply go to orbit, deploy the radiators, and cut the mass flow rate to the engine like in VASIMR. I think a CSR-B engine might be light enough that it would be plausible to just lug one up - but combined-cycle is more elegant.

...maybe you could design it so the reactor chamber has big clamshell doors that open up and turn your ARC system into a DFP engine...

The SSTO cargo ship is a great idea. I'm all for it. But i believe Bussard himself stated (Tom Ligon certainly did) that with this reactor, Single Stage To Anywhere was technically possible. It'd be a shame if no one tried it.

djolds1 wrote:Using ARC, you dump heat into the remass while under thrust. That's what ARC means (All Regenerative Cooling). When not under thrust at constant velocity (coast between say Earth and Mars - the Mars Transfer Orbit stage) its a non-concern. And the medium-efficiency CSR mode is low- thrust anyway; again a non-concern.


Okay, good point. I wasn't thinking. Besides, the only radiator system that allows you to go to high thrust suddenly is the 'glowing panels' one. Solid deployables do have more margin for medium-thrust, though...

I stilll have concerns regarding mass loss. I know you recycle the liquid, but that doesn't help with boiloff and splashing losses...

djolds1 wrote:Look up "Sea Dragon" at astronautix. And if the Polywell fails, Google "paraffin hybrid rocket."


I've heard of the Sea Dragon, but I didn't know there was an SSTO spinoff along the lines of SASSTO (crazy stuff). Look up Skylon for a more recent SSTO concept...

...but I didn't say SSTO. The Orion is the only drive we currently know how to build that qualifies as Single Stage To Anywhere - supposedly it could take a large manned expedition to Pluto and back in a year, or power a multigenerational starship to a nearby star. Kind of a shame that it makes such a mess when it launches...

ANTIcarrot wrote:Firstly, the sample design that Mr Bussard actually proposed: [link]


Thanks for the link. That is essentially the design I read about in one of the papers. It uses conventional turbojets to go to Mach 2 or 3 and rockets the rest of the way. I'm trying to get rid of all that unnecessary rocket delta-v and replace it with air thrust so we have more propellant left over to do other stuff once we reach orbit.

ANTIcarrot wrote:A polywell is a low-neutron, not no-neutron source. In the multi GW range (as required by polywell SSTO proposals) that small percentage of power outputted as neutrons starts to become VERY significant.

In space this isn't a problem, but while flying through the atmosphere, or sitting on the ground, there are significant problems. (Like turning the runway radioactive.)


Surround the reactor with six inches of water (IIRC) and a thin layer of boron-10 and you're good to go. If you use air thrust to get to orbit, there should be no problem with the extra mass.

ANTIcarrot wrote:Large aircraft (especially hypersonic delta wing monstrosities) also suffer from a number of operational issues that are a simple function of their size and flight envelope, and which polywell will not help solve.


Yes, but if we're contemplating building them with chemically-fueled engines (which we are), the number of problems Polywell DOES solve (including the requirement for precisely matched altitude and speed) probably pushes them over the edge into 'good idea' territory...

ANTIcarrot wrote:It also faces thermal problems during reentry because of its shear size. Chemical SSTO use their light structures as an advantage, because it means they can slow down quickly and have light weight/robust thermal protection systems.


True as well. However, there are ways around this. Advanced materials may help. Airbreathing launch may also leave you with enough propellant for cooling purposes during reentry, or even a substantial retro burn.

ANTIcarrot wrote:Lastly, it is blithely assumed that experimental electric rockets that struggle to produce thrust in the Newton range can easily be scaled up to produce thrust in the tons range. This seems unlikely.


We're not talking about using conventional SEP engines and running 6 GW through them. The QED engine family is actually fairly well thought out, as I discovered when I tried to invent a superior alternative...

ANTIcarrot
Posts: 62
Joined: Wed Aug 15, 2007 11:47 pm
Contact:

Postby ANTIcarrot » Wed Mar 12, 2008 10:43 pm

93143 wrote:Surround the reactor with six inches of water (IIRC) and a thin layer of boron-10 and you're good to go. If you use air thrust to get to orbit, there should be no problem with the extra mass.


That's just moving the problem around. And arguably making it worse. With that kind of throughput you will have issues of some kind of neutron activation, and hence the production of radioactive waste and embrittlement.

Yes, but if we're contemplating building them with chemically-fueled engines (which we are)


Actually, no one today is considering such a proposal. Space X is going to try and hack the EELV market off at it's knees. NASA is aiming for a 'son of apollo' design as a safe bet. Ariane Space is concentrating on slow progressive improvements to their successful family of launchers, as is Russia. All professional studies into launching large amounts of payload have almost universally concluded that VTOL is better.

Absolutely no one is contemplating monster space planes. :) Well, apart from Reaction Engines Ltd, and I'm not sure if they count.

How does polywell solve noise/overflight issues? Or the problems that there are only about twenty runways world wide that could land such a large aircraft in an emergency? Or that HTOL vehicles cost 3x or 4x as much as VTOL to develop? They were originally suggested to make up for perceived (nonexistent/illusionary/fictional) shortfalls in rocket technology. But those perceptions are shrinking, while awareness of the problems of hypersonics is growing. How could polywell ever solve *these* problems? :(

True as well. However, there are ways around this. Advanced materials will help.


Let me put it this way: Space planes = ITER. Or a 'self licking lollipop' as someone else described it. If you want Cheap Access To Space, you can spend money on building a real CATS vehicle, or you can use it to push another agenda, like material/technology R&D, or polywell. There was until recently a page that listed every rocket proposal since 1960, and it made very damning reading for anything with wings.

We're not talking about using conventional SEP engines and running 6 GW through them. The QED engine family is actually fairly well thought out, as I discovered when I tried to invent a superior alternative...


True, but my point still stands anyway. Before seriously proposing a 4GW version of Engine X, you might want to build a 1kW version first. Or point to someone else who has, or someone completely independent of the polywell community and reputable who thinks it can be done.

Once in space, this would be a preferred engine for things like a trip to Mars. Or indeed, somewhere that's actually worth going to. But that airframe will cost tens of billions and take years to develop. A well designed chemical rocket will out compete it economically despite flight costs being ten times higher, simply because purchase costs will probably be several orders of magnitude lower. Just like Concorde.
Some light reading material: Half Way To Anywhere, The Rocket Company, Space Technology, The High Fronter, Of Wolves And Men, Light On Shattered Water, The Ultimate Weapon, any Janes Guide, GURPS Bio-Tech, ALIENS Technical Manual, The God Delusion.

djolds1
Posts: 1296
Joined: Fri Jul 13, 2007 8:03 am

Postby djolds1 » Thu Mar 13, 2008 2:07 am

ANTIcarrot wrote:This topic has been discussed before.

Firstly, the sample design that Mr Bussard actually proposed:
http://www.longwood.edu/chemistry/Stude ... _Compr.ppt


Actually the original raster-scan concept is from an older paper, not one on the askmar site. I think I've got a scan of it but the PDF I created is huge (16+ MB, IIRC).

ANTIcarrot wrote:A polywell is a low-neutron, not no-neutron source. In the multi GW range (as required by polywell SSTO proposals) that small percentage of power outputted as neutrons starts to become VERY significant.

In space this isn't a problem, but while flying through the atmosphere, or sitting on the ground, there are significant problems. (Like turning the runway radioactive.) Large aircraft (especially hypersonic delta wing monstrosities) also suffer from a number of operational issues that are a simple function of their size and flight envelope, and which polywell will not help solve.


pB11 has a neutronicity 1/660 that of DD and 1/50 that of DHe3. Color me unconcerned. A few minutes of full power operation on the runway is a non issue. Surround the reactor with boron-doped polyethylene for shielding.

As to the remass, that is REB-heated in both the ARC and CSR modes. No direct contact of reactor products with the working mass.

ANTIcarrot wrote:It also faces thermal problems during reentry because of its shear size. Chemical SSTO use their light structures as an advantage, because it means they can slow down quickly and have light weight/robust thermal protection systems.


The slow speeds and tiny thermal loadings achieved by huge aerobraking ballutes are very impressive. Also, the reentry method used by Rutan on SS1 creates a minuscule thermal loading. Hell, with ARC you can do an all-powered braking reentry.

This is a non-issue.

ANTIcarrot wrote:Lastly, it is blithely assumed that experimental electric rockets that struggle to produce thrust in the Newton range can easily be scaled up to produce thrust in the tons range. This seems unlikely.


Possibly. But 8000 MW-thermal of power (90%+ conversion to MW(e)) from, IIRC, 5000kg of structure offers a LOT of energy to work with.
Vae Victis

93143
Posts: 1131
Joined: Fri Oct 19, 2007 7:51 pm

Postby 93143 » Thu Mar 13, 2008 10:18 pm

ANTIcarrot wrote:
93143 wrote:Surround the reactor with six inches of water (IIRC) and a thin layer of boron-10 and you're good to go. If you use air thrust to get to orbit, there should be no problem with the extra mass.


That's just moving the problem around. And arguably making it worse. With that kind of throughput you will have issues of some kind of neutron activation, and hence the production of radioactive waste and embrittlement.


...wha? Activation isn't a problem in this scenario; water or PET thermalizes the neutrons and boron-10 absorbs them, resulting in helium and lithium ions, which have very short mean free paths in any liquid or solid. The shield is stationary and covers the entire reactor. Problem solved.

Actually, no one today is considering such a proposal. Space X is going to try and hack the EELV market off at it's knees. NASA is aiming for a 'son of apollo' design as a safe bet. Ariane Space is concentrating on slow progressive improvements to their successful family of launchers, as is Russia. All professional studies into launching large amounts of payload have almost universally concluded that VTOL is better.

Absolutely no one is contemplating monster space planes. :) Well, apart from Reaction Engines Ltd, and I'm not sure if they count.


Well, yes, vertical launch is better now, with current technology and flight rates.

People are still researching scramjets and RBCC engines. The biggest reason no one is trying to build a scramjet launcher is that we don't yet know how, or whether or not it would be a good idea - hence the research.

Reaction Engines does too count! Skylon is a good idea; it gets rid of all the reasons the space shuttle is so expensive (vertical takeoff among them). With a higher flight rate it would be very economic; the problem is that without that higher flight rate, no one is willing to fund development of such a vehicle, and as long as we're stuck with ELVs our flight rate won't go up...

How does polywell solve noise/overflight issues? Or the problems that there are only about twenty runways world wide that could land such a large aircraft in an emergency? Or that HTOL vehicles cost 3x or 4x as much as VTOL to develop? They were originally suggested to make up for perceived (nonexistent/illusionary/fictional) shortfalls in rocket technology. But those perceptions are shrinking, while awareness of the problems of hypersonics is growing. How could polywell ever solve *these* problems? :(


Overflight? Launch over deserts or water, like now.

Twenty runways is fine considering that emergencies should be relatively rare. You could use retro-rockets to increase that number (or build more long runways...). If all else fails, just parachute into the ocean - no runway required. Besides, how else do you propose to do a reusable launch vehicle? We can't keep throwing away our rockets forever...

Development costs are nothing compared to operational costs. The Shuttle failed to lower costs not because it was expensive to develop, but because it requires such extensive reprocessing in between flights. Something like Skylon, which requires only basic maintenance and refueling, would solve that and allow the higher flight rate (>60/year, according to multiple studies) that makes RLVs competitive.

Do you really think chemical rockets are the best we can do? Hypersonics has problems, but the field is in its infancy and rockets are maxed out. What we have now isn't good enough.

Let me put it this way: Space planes = ITER. Or a 'self licking lollipop' as someone else described it. If you want Cheap Access To Space, you can spend money on building a real CATS vehicle, or you can use it to push another agenda, like material/technology R&D, or polywell. There was until recently a page that listed every rocket proposal since 1960, and it made very damning reading for anything with wings.


[cough]Pegasus[/cough]...

We CAN'T make ELVs cheap - SpaceX is probably as good as it gets. Skylon is significantly cheaper than Falcon once the development cost has amortized, but it's limited to 12 tonnes of payload, or less for unfavourable orbits. To get any better than that, we probably have to develop new technology. Like Polywell - which BTW doesn't really need space planes as an excuse to exist...

Besides, I don't think a pure Polywell-powered spacecraft COULD take off vertically. You'd need to use the reactor power to augment combustion heating in a conventional rocket to get enough thrust, at least with first-generation reactors. This makes SSTO almost as marginal as it is now. If we ever figure out how to shrink the reactor and still protect the coils from overheating, thrust-to-weight of 3:1 or better may be possible...

I think everyone's just gun-shy from the Shuttle. It's the only orbital space plane that has ever been put into service, and its development was severely cramped by Nixon's budgets, so we don't have a very good sample.

Before seriously proposing a 4GW version of Engine X, you might want to build a 1kW version first. Or point to someone else who has, or someone completely independent of the polywell community and reputable who thinks it can be done.


Aren't you forgetting VASIMR? I don't know if it scales to GW range, but it certainly scales to MW range...

No one has tried to build a GW-range electrical engine for the simple reason that Polywell is the only power source that's even on the horizon that has the capability to power one. If Polywell fails, the research is wasted.

Barring Dr. Minovsky coming out of the woodwork and turning the Standard Model on its ear, of course...

Once in space, this would be a preferred engine for things like a trip to Mars. Or indeed, somewhere that's actually worth going to. But that airframe will cost tens of billions and take years to develop. A well designed chemical rocket will out compete it economically despite flight costs being ten times higher, simply because purchase costs will probably be several orders of magnitude lower. Just like Concorde.


IIRC, British Airways managed to operate the Concorde at a profit despite its aged, inefficient engines and lack of upgrades over the aircraft's lifetime. This despite the fact that a number of factors combined to ensure that only a very few planes were ever built, which hopefully a good spaceplane design won't have to contend with.

Also note that for an ELV, purchase price and launch cost are the same figure. Tens of millions at best. The key is to get the flight rate up. With a high enough flight rate, the development and purchase costs of a spaceplane - particularly one with the mass fraction of an airbreathing BFR-powered SSTO - will eventually be made up for by the low operating costs. You just have to make sure the operating costs actually are low...

...I guess there are two ideas I've been mixing and matching bits of in this thread. One is a proposal to use air as reaction mass over most or all of the boost regime to increase the mass fraction of Bussard's SSTO space plane. There are many advantages to having a very high mass fraction, including the possibility of carrying fuel for a retro burn, a huge ballute as mentioned by djolds1, unusually large payloads, remote manipulator systems, etc. This space plane would be designed like Skylon, with a minimum of reprocessing required between flights.

The second idea (which is much more of a pipe dream) is to use the high mass fraction gained by airbreathing ascent to maximize the design for SSTA with continuously-variable specific impulse. This would probably not be cheap, but it would certainly be versatile. In theory, it could be designed to radiate waste heat from selected parts of its structure, reducing or eliminating the expenditure of propellant for cooling during atmospheric flight and obviating the need for deployable radiators in space. It could use the atmosphere of any planet as propellant, and even take it on board and liquefy it for use in space. In theory it could operate indefinitely with only fusion fuel resupply, since it can refill its propellant tanks on any planet with an atmosphere without even landing. Reliability for long-term operation would of course be a major concern in the design of such a vehicle.

ANTIcarrot
Posts: 62
Joined: Wed Aug 15, 2007 11:47 pm
Contact:

Postby ANTIcarrot » Fri Mar 14, 2008 10:02 pm

93143 wrote:Surround the reactor with six inches of water (IIRC) and a thin layer of boron-10 and you're good to go.


And all the material inside the shielding?

Well, yes, vertical launch is better now, with current technology and flight rates.


Judging from this you're confusing two concepts:
EELVs - which we currently use now
VTOL RLV SSTO or TSTO - which is what I've been talking about.

To underline the difference:
The S-IVB stage from the Saturn V was built with 1960s materials and engineering, and was capable of getting into orbit by itself with zero payload. It's a matter of record that the engine was very reusable, and that we've done even better than that. (the RL10 springs to mind.) It's a fairly simple matter to prove that with modern materials that are X times lighter, a variant on the S-IVB stage could carry a useful payload and reentry system. (You can even make a good argument that it was also possible back in the 1970s.) Google SASSTO.

Meanwhile, the space shuttle is the closest we've ever gotten to a space plane, and it don't work so good. Every other time people have looked into it theoretically, or tried to actually build one (NASP, X-33, Hermes, etc) the outcome has been the depressing familar sounding phrase, "We're not there yet, but we're sure we can get it to work in another thirty years!" It's not just the shuttle they're gun shy of but lots and lots of trade offf studies that show Skylon style vehicles are usually marginal and often require two or three times the R&D costs of VTOL rockets.

In other news, SCRAM jets are good at *maintaining* a hypersonic speed, but are appalling at accelerating up to that speed, or beyond it. This is diametrically opposite of what you want in rocket or any kind. SCRAM has military and civilian use, but not as any kind of launch vehicle.

Making paper airplanes doesn't maker you an aerospace company. :P

Skylon might work, but it relies on imaginary materials which do not exist yet. It's also rather unambitious, since the DC-Y has similar development costs, and promises cheaper cargo, and use beyond low earth orbit. Proposals like the DH-1 require 1/10th of the development cost and promise even lower launch costs; albeit for significantly smaller payloads.

Overflight? Launch over deserts or water, like now.


you seem to be missing the point: The purpose of low cost launch vehicles is not to save the government money, but to open up space for EVERYONE. So if your vehicle similar can't launch from everywhere, or at least every country, it's going to lose out to chemical competitors, which aren't so picky.

Twenty runways is fine considering that emergencies should be relatively rare. You could use retro-rockets to increase that number (or build more long runways...).


Yes. Yes. Retro rockets and pixie dust. It's not that easy, and it makes no sense to impose such a crippling problem on your customers when there is no need.

Development costs are nothing compared to operational costs.


<sigh> And where does your knowledge of aerospace come from? Operational costs are proportional to development costs and fleet size, so yes they do matter.

And Skylon only requires basic maintenance *in theory*. The TPS or those fancy engines could go wrong in all sorts of ways. The TPS might be fixable, but the entire system simply wouldn't work if the engines didn't perform as advertised.

<ELV stuff deleted>

No one has tried to build a GW-range electrical engine for the simple reason that Polywell


don't change the subject. You've proposed a *specific* type of electric engine for polywell. You might want to test that at *any* power level before magically assuming it'll work.

IIRC, British Airways managed to operate the Concorde at a profit


Only because the UK and France wrote off it's costs. And it still proved vulnerable to NotInventedHereitus when American forced an unwarranted grounding due to single technician's screwup.

which hopefully a good spaceplane design won't have to contend with.


A good RLV could operate anywhere. By your own admission, a ploywell space plane couldn't do this.
Some light reading material: Half Way To Anywhere, The Rocket Company, Space Technology, The High Fronter, Of Wolves And Men, Light On Shattered Water, The Ultimate Weapon, any Janes Guide, GURPS Bio-Tech, ALIENS Technical Manual, The God Delusion.

JoeStrout
Site Admin
Posts: 271
Joined: Tue Jun 26, 2007 7:40 pm
Location: Fort Collins, CO, USA
Contact:

Postby JoeStrout » Fri Mar 14, 2008 10:45 pm

ANTIcarrot wrote:It also faces thermal problems during reentry because of its shear size. Chemical SSTO use their light structures as an advantage, because it means they can slow down quickly and have light weight/robust thermal protection systems.

Just to stick two cents in here, the thermal problem on reentry only occurs because we're reentering the atmosphere at orbital speed. It would not occur if you entered at a much lower (even zero) groundspeed; this could be accomplished by transferring momentum to something else in orbit (e.g. a rotovator), or via good old-fashioned rocketry.

The latter is completely impractical for chemical rockets because they can only barely carry enough fuel to reach orbital velocity in the first place. But if a polywell rocket had a specific impulse 1000X higher, as Bussard proposed, then you seriously could consider carrying enough fuel both to get up to speed and then to slow down again. (Or, perhaps more sensibly, refuel in orbit for the return trip.)
Joe Strout
Talk-Polywell.org site administrator

MSimon
Posts: 14331
Joined: Mon Jul 16, 2007 7:37 pm
Location: Rockford, Illinois
Contact:

Postby MSimon » Sat Mar 15, 2008 5:00 am

Shielding:

Activation is dependent on total flux. n/sq cm It is also material dependent. Not a problem. At worst it would mean a 10 day wait for minor service of the engine (probably much less due to the low total flux) and 100 days for major service. And that is with burning D-D. pBj would probably not require anything other than monitoring the workers. No time delay.

The shielding is strictly for crew protection.

My plan for earth to orbit:

Mag Lev track to get up to Mach .8.

H2 as reaction mass. IIRC a 700 ton vehicle would have a 50 ton payload.
Engineering is the art of making what you want from what you can get at a profit.

hanelyp
Posts: 2255
Joined: Fri Oct 26, 2007 8:50 pm

Postby hanelyp » Mon Mar 17, 2008 2:41 am

ANTIcarrot wrote:
Development costs are nothing compared to operational costs.


<sigh> And where does your knowledge of aerospace come from? Operational costs are proportional to development costs and fleet size, so yes they do matter.

Hogwash. 'Penny wise' decisions made to cut development and building costs may come back to bite you in pound foolish operational costs. Such as the space shuttle with:

- solid fuel boosters. The boosters themselves are less expensive than a liquid fueled counterpart, but the fuel burned in them is more expensive, requires the boosters be shipped elsewhere for refilling, and extensive safety procedures and equipment for the mixed fuel being cast. Adding to the cost, the boosters are fished out of the ocean, which costs a large fraction of the costs to build new casings.

- tiles. perhaps less expensive to develop than other options, but a massive maintenance cost.

- disposable external tank.

TallDave
Posts: 3114
Joined: Wed Jul 25, 2007 7:12 pm
Contact:

Postby TallDave » Mon Mar 17, 2008 4:11 am

JoeStrout wrote:The latter is completely impractical for chemical rockets because they can only barely carry enough fuel to reach orbital velocity in the first place. But if a polywell rocket had a specific impulse 1000X higher, as Bussard proposed, then you seriously could consider carrying enough fuel both to get up to speed and then to slow down again. (Or, perhaps more sensibly, refuel in orbit for the return trip.)


Good point, the specific impulse in a fusion drive is a real game-changer in that regard.

93143
Posts: 1131
Joined: Fri Oct 19, 2007 7:51 pm

Postby 93143 » Tue Mar 18, 2008 2:58 am

ANTIcarrot wrote:Judging from this you're confusing two concepts:
EELVs - which we currently use now
VTOL RLV SSTO or TSTO - which is what I've been talking about.


I apologize - I started to suspect this partway through my last post, but I kept going because I wanted to very thoroughly dispense with the idea that an ELV would be any sort of long-term competition for a fusion-powered spaceplane.

We agree on that, I trust...

I know about vertical takeoff and landing SSTOs; I mentioned SASSTO myself upthread. The DC-1 looks like it would have been a very nice spacecraft, although much larger and heavier than Skylon, and some people were dubious about the safety of a vertical-landing rocket. I don't have sufficient knowledge to judge between them - as in many fields, the devil is in the details, and first impressions can be misleading.

But we're not talking about SASSTO versus HOTOL. Polywell makes a space plane a lot less marginal due to the potential for high Isp, but is incapable (without significant technological advances in other areas) of powering a vertical all-rocket SSTO at all due to the required combination of Isp and thrust-to-weight ratio. This probably tips the balance in favour of a spaceplane.

(Speaking of tipping the balance, that was apparently what was wrong with HOTOL - the heavy part was at the back. Skylon solves this.)

Granted, it is possible that chemical will just turn out to be optimal for cheap space access. But I don't think it will. Also, augmented chemical could turn out to work well for a fusion-powered VTVL SSTO - you know, LOX/LH2 augmented with Polywell power? This could give you sea-level Isp in the 500-600 range or better - or not, depending on how heavy the Polywell and associated systems are. Or you could take in ram air at the top of your VTVL SSTO. That might work...

In other news, SCRAM jets are good at *maintaining* a hypersonic speed, but are appalling at accelerating up to that speed, or beyond it. This is diametrically opposite of what you want in rocket or any kind. SCRAM has military and civilian use, but not as any kind of launch vehicle.


First off, I never advocated using supersonic combustion ramjets. I advocated a combined-cycle electric engine with either turbojet or rocket-based ejector jet mode at low speed, ramjet mode at medium speed, supersonic ramjet mode at high speed, and rocket for space (thus giving the advantage at low speed to the ejector jet, which requires a rocket anyway).

Note that with electric heating, you don't need to mix a fuel stream with the air, thus removing the biggest single challenge related to hypersonic engines. Magnetically shielding the engine wall mitigates the heating problem (and, I think, introduces the possibility of using a magnetic nozzle instead of a solid one in the low-speed regime).

Even chemically fueled scramjets can generate net thrust and accelerate. They have done so in flight tests. Without the combustion-imposed restrictions on design, an electric scramjet with magnetic shielding should be able to take a vehicle from Mach 5 to as fast as you want it.

Skylon might work, but it relies on imaginary materials which do not exist yet.


Like?

The TPS is known technology, as is the structure. The precooler for the engine has been successfully manufactured and a frost control system developed for it; everything else is fairly well understood.

you seem to be missing the point: The purpose of low cost launch vehicles is not to save the government money, but to open up space for EVERYONE. So if your vehicle similar can't launch from everywhere, or at least every country, it's going to lose out to chemical competitors, which aren't so picky.


That's true. But an interesting feature of a spaceplane with Isp this high is that it doesn't need to go hypersonic right away. You could take off from just outside Munich (say) and use ramjet mode at high subsonic speed (running the reactor in pulse mode maybe?) until you got high enough and/or far enough from civilization to start the acceleration phase. If the payload mass fraction is as high as I think it could be, this method could still outperform a chemical competitor cost-wise. Maximally quick response is only necessary for military needs or in-space emergencies, in which case who cares about a few sonic booms?

Yes. Yes. Retro rockets and pixie dust. It's not that easy, and it makes no sense to impose such a crippling problem on your customers when there is no need.


What's this? I thought we were having an argument, not a patronizing contest.

Explain to me why you couldn't use retros on the runway to reduce braking distance. Remember that they can fire slightly upwards (still through the C of G) to avoid damaging the surface.

And where does your knowledge of aerospace come from?


I'm working on my PhD in aerospace engineering right now.

Actually most of my knowledge is quite new; I've been looking stuff up as fast as I can think of it, and there will be gaps in my knowledge. But my handle on basic engineering principles is much better (MSc in Mec E), and I do know something of the history of the Shuttle. Besides, you're the one who said (on nasaspaceflight) that it was for budgetary reasons that we got a shuttle that was cheap to develop and expensive to run, rather than the reverse.

The original Shuttle design was for a fully-reusable TSTO with flyback first stage (much easier to deal with than the SRBs). The orbiter would have been much fluffier due to integral tanks, possibly leading to a more robust TPS, and there would have been no foam shedding problem. Von Braun felt he had to push the current shuttle design because if he had held out for the original there would simply have been no shuttle at all.

Interestingly, there was a paper at the 2008 AIAA conference in Reno that detailed some design studies for a quick-response, quick-turnaround low-cost TSTO launch system with a fully reusable flyback first stage...

No one has tried to build a GW-range electrical engine for the simple reason that Polywell


don't change the subject. You've proposed a *specific* type of electric engine for polywell. You might want to test that at *any* power level before magically assuming it'll work.


I didn't change the subject. My engine concept is basically an extension of stuff that HAS been tested - some of it flight-tested - with the addition that heating/enthalpy addition is electric rather than by combustion. QED is just a 'most-probable' placeholder for the electric portion. I'm not rigidly attached to the REB idea, but I do think Bussard (who has actually designed nuclear thermal rockets that worked) probably knew what he was talking about. If the 6 GW space Polywell proves workable, there WILL be engine tests.

You, by contrast, were criticizing the idea that you could scale up Deep Space One's ion engine or a Hall effect thruster or something like that to make it into a first-stage booster engine - which no one is advocating.

The point of this subforum is not to discourse on existing technology, but to speculate on what might be possible IF the Polywell works - which in itself is a much much bigger gamble than "blithely assuming" that there is SOME way to generate high thrust given 6 GW of continuous high-voltage electricity.


Return to “Implications”

Who is online

Users browsing this forum: No registered users and 7 guests