Earth to LEO - discuss

SBird · 2004-03-29 00:43:51

That turbofan/rocket's a pretty spiffy idea. I also think that the scramjet is about as good as you can get for standard launch tech barring major advances in things like rotovators/space elevators/antigravity. Some further advances in scramjet tech can come from microwave power transmission that can further lighten the fuel load on the plane. Also, a maglev launcher system actually makes sense with a scramjet system.

However, I'm trying to head off the 'scramjets will make spaceflight too cheap to meter' crowd that always seem to crop on on places like Slashdot. I can realistically see scramjets getting orbital costs for things like fuel to LEO down to <$300/kg. However, that's still a substantial cost - lofting me and luggage to orbit would still cost more than my parents' house.

dicktice · 2004-03-29 09:04:41

While my "last resort" scheme for lifeboat re-entry was admittedly off the wall, I still long for a serious discussion concerning ISS staffing requirements of six or more in order to carry out alloted tasks, beyond housekeeping and maintenance. Soyuz style lifeboat capacity of three maximum prevents this for the foreseeable future, so why isn't this a top priority topic, since launches by the Russians are at least feasible to fully crew the ISS right now. Looking further into that "foreseeable future," it seems to me that the U.S., Congress and NASA are flirting with the possibility of losing stretegic control of--or even any meaningful involvement with--the only habitable space platform orbliting Earth, by default!

GCNRevenger · 2004-03-29 09:19:42

Nasa is putting the project on hold for one simple reason: You don't need a reuseable spaceship to get to the Moon and Mars. At least not initially... money is tight enough as it is without sinking the many billions needed to make a Scramjet SSTO airplane. Let the USAF work on it for a while and improve it, the first Liquid Hydrogen engines were actually developed for military spy planes, not the Nasa Apollo rockets' J-2 engine. Which the technology, by the way, eventually made its way to the RL-10 & RS-68 commertial and SSME Shuttle engines.

Also, if Nasa doesn't go anywhere beyond LEO, then it risks its own demise at the hands of an uncaring congress.

Scramjets will be expensive, but eventually the sheer number, efficency, and flight rate may make them cheap enough for occasional civilian space travel. Of course, this is still some distance down the road, but other than a rocket SSTO there aren't many other options.

Giving up control of the ISS by default? Okay. Sounds fine to me. When can we sign the deed transfer? ...The sooner we're rid of the ISS, the better. Worry about a LEO space station down the road, launched by HLLV, and manned by CEV vehicles with 4-6 seats each.

dicktice · 2004-03-29 09:35:22

But, aren't you overlooking (change that to "underlooking") the effect of a Russian controlled ISS, on the American Public (harking back to Sputnik) and the old Soviet's policy of using space platforms for long-term space exploration research and staged development. Especially now, with Putin's changeover in their Space Agency Direction to the military. Does that still sound fine to you?

P.S. I couldn't resist appending this latest from NASA regarding ISS activities:

Expedition 8 Commander Michael Foale and Flight Engineer Alexander Kaleri spent two days last week replacing a liquids unit and a water flow system of the Russian Elektron, in the Zvezda Service Module. The Elektron separates water into oxygen and hydrogen. The oxygen is used in the Station's atmosphere while the hydrogen is vented overboard. In the meantime, the crew used oxygen and air from the Progress cargo vehicle docked at the Station to replenish the atmosphere, as well as Solid Fuel Oxygen Generation (SFOG) canisters. With the Elektron running smoothly, Foale and Kaleri devoted much of the week to science activities. Kaleri tended the Rasteniya experiment, a greenhouse containing peas, designed to see how plants grow in a microgravity environment. Kaleri also did a test of the Russian TORU manual docking system, using the ISS Progress 13 vehicle docked to Zvezda. That Progress is to be undocked and burn up in the Earth's atmosphere in mid-May, the day before a new Progress arrives with about 2½ tons of equipment, supplies, water and fuel.

Note the continued development of the onboard remote manual docking system, the lack of which was the cause of the Progress collision under primitive manual control, which put Mir out of commission for a while, eventually leading to its being decommissioned and deep-sixed in the Pacific (tragically and unnecessarily, in my opinion).

Bill White · 2004-03-29 16:19:34

Interesting link with various mission architecures including LaGrange to lunar surface.

[http://fti.neep.wisc.edu/neep602/FALL97/lecture30.pdf]http://fti.neep.wisc.edu/neep602/FALL97/lecture30.pdf

One minor problem with Earth orbit assembly appears to be rare launch windows for lunar landing.

dicktice · 2004-03-29 16:50:37

Headline from today's Google Newsweek magazine column:

Engineer and entrepreneur Gregory Olson could soon become the third civilian in history to visit Russia's International Space Station

I sure hope this erroroneous assignation isn't an indication of how the magazine's editor sees the ISS ownership. If the Letters to the Editor next week don't call attention to this goof, future "wish fulfillment" could begin to set in and, before you know it, make it all come true!

showtime17 · 2004-12-09 23:32:41

Headline from today's Google Newsweek magazine column:
Engineer and entrepreneur Gregory Olson could soon become the third civilian in history to visit Russia's International Space Station
I sure hope this erroroneous assignation isn't an indication of how the magazine's editor sees the ISS ownership. If the Letters to the Editor next week don't call attention to this goof, future "wish fulfillment" could begin to set in and, before you know it, make it all come true!

haha... but it's true that it's only the russians and their ability to get into space that are keeping the iss alive right now

however the food is running low
http://story.news.yahoo.com/news?tmpl=s … ...station

Austin Stanley · 2004-12-11 04:46:12

I think one of the big problems with reusable rockets is that they focus to much on re-using the upper stage and not enough on re-using the lower stages. The lower stages are much more massive and thussly genearly more expensive, if anything it makes more sense to reuse them then it does the upper stages. Likewise the lower stages genearly undergo much less stress then the upper stages, they never go into space and thus they never have to deal with re-entery. The problem with this is that the vertical geometry of space-flight has always made designing the lower stages to be recapturable more difficult. I don't have an easy answer to this, but I think it is something that should seriously looked at. It makes no sense to waste all the engines and tankage on a lower stage which never realy leaves earth in the firstplace.

As for scramjets, I am hopefull, but I think it is still way to early to start placing any bets on these. We are relay only just getting started here. There max velocity is only Mach 12 or so anyways so certianly it will have to switch into some other mode of opperation or be augmented somehow to achive orbit. You also have the problem (as someone else pointed out) that you are generating all this horizontal velocity inside the atmosphere and so making alot of drag to go with it. I still hold the hope that a scramjet might be usable as some sort of reusable upper stage though.

NTR were discussed earlier, and I am with GCN on this one. It may not be possible to generate the necessary thrust for a lower stage, but they should definetly work fine for an upper stage, and they will certianly be deployable before scramjets ever will. Making them reusable would be tricky however, as you have to service a nuclear reactor. I am optimistic about the material concurns though. Materials are something you can test reliability for pretty succesfully, unlike complete launch systems which have a tendency to fail in new and unusualy ways. In terms of the cermaic designs one of the things I know they have been working is making them with regular microfactures already built in so that they fail less often and in a more regular way.

As for maglevs and railguns, I just don't think they are going to work. You might be able to set up some sort of railgun-scramjet-rocket system that would get small satilites into orbit, but you would never deliver people or other large cargos that way.

GCNRevenger · 2004-12-11 11:48:47

Nuclear thermal is best suited to rockets that are leaving Earth entirely. Having an NTR second stage reenter the atmosphere isn't acceptable most likly, and the shielding would be very heavy may as well stick with chemical.

The trick to make a Scramjet spaceplane is to use the drag, by preheating the fuel using atmospheric heating before injecting it into the engine. The faster you go, the more powerful the engine would become.

I don't think any reuseable space vehicle that isn't essentially 100% reuseable, all the stages, is worth the trouble.

mboeller · 2004-12-15 04:48:23

Well,

After reading most of the thread, I want to give you my opinion about the subject too.

IMHO SSTO is not possible due to the needed high fuel:structure ratio of around 10:1. Even then the payload is rather small, so you need a really large SSTO to overcome the problems and have an useful payload using the favorable scaling factors.

At the moment I prefer more than one approach:

1; pure rocket TSTO
2; Turbojet assisted SSTO
3; Tether assisted SSTO.

1; Pure rocket TSTO’s are well known so I will only briefly mention it here. Most people tend to think that “the highest ISP wins” and so they favor only H2/O2 as an fuel. IMHO this is not true for TSTO’s. Here Kerosin or other denser fuels (see http://www.dunnspace.com/alternate_ssto … lants.htm) work far better despite the far lower ISP.

If you need to stick to H2/O2 then use the engine which gives the most for the bang….PDE’s.
According to an older paper from http://www.ssdl.gatech.edu/main/publica … lications/ (sorry no direct link) which compared an RBCC-SSTO with an PDE-SSTO; PDE’S have an higher efficiency than normal rockets and can reach around 492.5 sec! Well AFAIR that’s the figure they used in the comparison. By the way, the pure rocket PDE proved to be superior to the RBCC-based SSTO regarding payload fraction and TOW. :)

2; At the moment this is my favourite cause in the last APR V5N5 ( http://www.up-ship.com/apr/v5n5.htm ) I have read an article about the “SpaceJet” developed in the lat 1970`s at Langley.
The HTHL-Spacejet uses an Turbojet-Booster stage together with an large Shuttle on top. The Booster accelerates the Shuttle to M3.5 and 50-60.000 feet (not sure at the moment). Due to this the Shuttle can have an mass fraction of around 0.20 cause it needs only around 7400m/s instead of the ~9350m/sec for an pure SSTO (based on the mass-calculations in the article).

I like this system cause with this approach you can get rid of the large booster aircrafts used for other HTHL-TSTO’s. The booster here is very small as can be seen in the link above.

Advantage:
nearly SSTO operations with only an small and “simple” Booster.
Shuttle with only one type of engine
Booster with commercial Turbojets possible (military engines)
High performance ( 65000Ib payload with only 2.600.000Ib TOW including booster)

Disadvantage:
The Shuttle needs large and heavy wings to lift itself and the booster from the Runway, but as an small bonus this reduces the reentry heating .
IMHO only suitable for H2/O2, otherwise the mass fraction would be too low.
Needs a large amount of Turbojets if the Shuttle is heavy. For an small shuttle with around 180to you need already 4 35000 Ib turbojets found in modern combat aircraft. If your shuttle is as large as the one in the Langley-study then you need 8 turbojets with 85000 Ib each!

IMHO this system can be improved very easily compared to the old study done at Langley.
The Turbojets could be improved with the MIPCC-system in development for RASCAL and the SSME-engines could be replaced with rocket engines with an higher ISP ( 465-475 sec) and maybe use an aerospike nozzle (if this is needed at all); or even with the high performance PDE-engines in development today.

The structure could be improved also cause they used pure 1970’s style systems and materials in the study (according to the article). So an heavy dose of CFK should lower the empty weight quite a lot.

3; tether augmented rocket.

Well I will not cover this at all, cause you can find a lot of information’s about this system on the web an it was already discussed here :

http://www.affordablespaceflight.com/ho … /home.html
http://www.spacetethers.com/]http://www … thers.com/
http://members.aol.com/Nathan2go/SPELEV … SPELEV.HTM

4; well you can also combine 2 and 3 to improve the system further. :)

Hope you like it.

Manfred

GCNRevenger · 2004-12-15 09:29:35

SSTO is possible with Scramjets, a vehicle like the proposed X-30 is entirely possible... its just not easy. Such a vehicle would be ideal because it could turn around quickly without even a reassembly hanger and with a minimum of personel. That said, barring a breakthrough, TSTO does seem to be preferable for the flight rates needed.

The idea of an all-rocket TSTO doesn't strike me all that favorably with the riskier takeoff (engine failure on the runway? boom!) and because of one factor about PDE that you forget mboeller... that the superhigh listed is vacuum Isp. Its actual Isp, like the SSME and RS-68, is likly around 20-25% less at sea level air pressure. This would also require a large first stage due to LH2 tankage.

The option I favor is somthing closer to pure-jet assisted launchers, but uses RBCC engines or turbines with a kerosense rocket for kick with an onboard LOX supply to achieve higher speeds and altitudes to reduce the size of the upper stage. This may also solve the problem of low required thrusts from contemporary turbine engines... Bigger airplane, smaller rocket.

The upper stage would probobly be powerd by LOX/LH2 and use only 2-3 (hopefully) of the COBRA engine or similar high-thrust cyrogenic engine tailored to be reuseable for 100 flights. It would come in an unmanned cargo model and a 10-12 seat (or 6 with some payload) manned version in a reentry-capable crew cabin with an airlock/docking collar to the rear.

Tether augmentation is a bad joke or somthing

Grypd · 2004-12-15 13:58:51

There has been many proposals for TSTO which use the efficiency of normal jet engines until they are much higher then either boost the jet engine through various fuel or afterburner effects or to actually have a rocket aboard that pushes the carrier plane to the required speed and height for seperation. Then the upper stage will use its rocket engine to enter LEO. Advantages to this is the carrier stage is completely reusable and only has to use its rocket or boosted engine for a short while. And the seperation of the two craft happens at a point where there is a reduced atmosphere to impact dangerously on the seperation operation.

Seperation of TSTO aircraft was always the most dangerous part of the launch. The saanger aircraft designed by Germany had real problems with this issue.

mboeller · 2004-12-16 06:22:40

SSTO is possible with Scramjets, a vehicle like the proposed X-30 is entirely possible... its just not easy. Such a vehicle would be ideal because it could turn around quickly without even a reassembly hanger and with a minimum of personel. That said, barring a breakthrough, TSTO does seem to be preferable for the flight rates needed.

Scramjets are useless for any orbital vehicle. Get over it. I have seen only one (!) scramjet based SSTO study which made sense compared to an pure rocket based SSTO and this vehicle used AFAIR acetylene instead of H2 and used the atmospheric heating to break the acetylene into H2+CO. This cooled the vehicle as good as pure H2 but due to the far higher density of acetylene and rather good ISP of the broken down acetylene the payload was reasonable.

Otherwise scramjet are useless for SSTO's.

How do you come to the conclusion that scramjet vehicles are easier to maintain? The opposite is true cause this vehicles have an far higher complexity than simpler rocket vehicles. Also the development costs are higher cause the empty weight is higher (which is an clear indicator for development cost) and the complexity of the structure and the systems is far higher compared to an rocket RLV.

The idea of an all-rocket TSTO doesn't strike me all that favorably with the riskier takeoff (engine failure on the runway? boom!) and because of one factor about PDE that you forget mboeller... that the superhigh listed is vacuum Isp. Its actual Isp, like the SSME and RS-68, is likly around 20-25% less at sea level air pressure. This would also require a large first stage due to LH2 tankage.

Yes...and? I said above that I prefer other fuels than H2 for TSTO's cause here the ISP of H2 is not needed and using fuels with higher density reduces the vehicle size, weight and therefore development cost.
The all-rocket TSTO would be an pure VTVL-vehicle too, cause here wings are for wimps.

The option I favor is somthing closer to pure-jet assisted launchers, but uses RBCC engines or turbines with a kerosense rocket for kick with an onboard LOX supply to achieve higher speeds and altitudes to reduce the size of the upper stage. This may also solve the problem of low required thrusts from contemporary turbine engines... Bigger airplane, smaller rocket.

This is the option everyone tries. But than you increase the empty weight of both stages ( booster >>; shuttle > ) due to the higher complexity and therefore the development costs are higher. Also with more complex systems the development costs increase as well. If you increase the staging speed you will have to streamline the shuttle even more too and so the structure will weigh more too.

IMHO the SpaceJet-study is rather nice cause here you have two rather simple vehicles. A very compact booster using off the shelf turbojet engines and an pure rocket shuttle on top. The only drawback I see is that the available turbojet engines restrict the weight of the shuttle and so the shuttle has to use H2.

Tether augmentation is a bad joke or somthing

Not at all! Read the links and maybe the PDF's of the HASTOL-study see:

http://www.niac.usra.edu]www.niac.usra.edu/

http://www.niac.usra.edu/studies/study. … 0.0]HASTOL Phase I

http://www.niac.usra.edu/studies/study. … 0.0]HASTOL Phase II

GCNRevenger · 2004-12-16 13:39:34

"I have seen only one (!) scramjet based SSTO study..."

Yeah whatever. Then you must not have looked very hard. The Air Force has done quite a bit of work in this field. Considering how much work was put into the X-30 project, for you to claim this is unthinkable.

Anyway, the Scramjet need not power the vehicle all the way to orbit, getting to a high enough fraction of orbital velocity should be sufficent for a small rocket injection burn. I suppose you will also discount the practicality of slush hydrogen fuel or using cyrogenic hydrogen as coolant out of hand as well.

I came to the conclusion that such a vehicle would be easier to turn around between flights because it would be only one vehicle, that there would be no delicate assembly procedure involved, and that the Scramjet engines are mechanically speaking quite simple, and with modest improvements in materials should be mostly trouble free.

You also apparently aren't aware of some work that has been done on rocket/jet hybrid engines and the low level of advancement needed to yeild high payoffs. Modified production fighter jet engines with modified LOX injectors have been ground tested with the capability of pushing a vehicle into the Mach 5 or 6 speed region and U-2 like altitudes.

Using these on the carrier plane able to operate at these conditions would increase its size and increase its development costs, but the payoff of requiring a substantially smaller and lighter upper stage would be well worth it. Your notion that "streamlining would increase weight" and such is just blather, the higher altitudes achieved will make seperation easier since the air is so thin, not that streamlining is a problem anyway.

Overall the idea is to intentionally spend big on development costs to save on launch costs down the road. If it costs a few tens of billions of dollars, then thats just fine if it reduces launch costs by an order of magnetude and permits weekly flights of the same vehicle.

I also find your notion that system weight will unavoidably increase development cost as unfounded, especially today with advanced materials available. Technology has advanced signifigantly and the old "big simple rocket = better then fancy ones" is not longer true either.

And please, a study from the NASA advanced concept people? Come now... tether space plane indeed, a fairy tale if there is one.

Austin Stanley · 2004-12-16 14:39:09

A while back we discussed the use of H-F rockets for use on a terrestrial HLLV. While I dismissed it's use at low altitudes due to hydroflouric acids toxicity and corrosivness, it occurs to me that it might have some use as an upper stage or a TMI/TEI stage. Flourine could probably be stored in the same tanks that we currently use for liquid oxygen, as the two gasses are realitivly similar, a teflon coating might be necessary on the inside, to help deal residual HF in the tank.

Of course, that's not to say aren't still problems:
- spreading HF around in the upper atmosphere is still probably not to great an idea
- Fluorine is MUCH more expensive than oxygen.
- HF is highly corrosive. While only a weak acid, F- ions are highly reactive and will dissolve pretty much any oxide from rust to glass. This may be a problem for the engines, depending upon their exact makeup.
- HF is very toxic. The stuff easily penetrates through your skin and the F- ions eat up the Calcium in your bloodstream and bones. Therefore testing a modified engine might be difficult.

But since the H-F reaction is more exothermic than H-O you do get improved ISP (~550), flourine is the best oxidizer you could possibly find. It might also be possible to easily covert existing engines and tanks over to a H-F system, the oxidizer-fuel ratio should be the same, and the tanks might not require any modification. Also, the concurns about toxicity aren't such a big deal at high altitudes and in space.

Alternativly, you could mix some Flourine in with your oxygen for improved efficency as well.

GCNRevenger · 2004-12-16 15:08:01

I think it would be easier to build a larger LOX rocket then it would be a liquid fluorine rocket really... think of the disaster if there was a pad "incident." The marginally higher efficency isn't worthwhile.

Austin Stanley · 2004-12-16 15:46:14

Hmm, I had not considered the possiblity of pad accident. That could be bad, very bad. Liquid F2 would burn with, well pretty much anything, even traditional exstinguisher gases like CO2, Halon (a chloroflurocarbon), and chemical salts would burn. It would be pretty much unextingusihable, because Flourine is such a strong oxidizer. And of course, you wouldn't want to breath flourine either, and all the burn products would of course also be very toxic (just about everything associated with flourine is toxic).

But it still might be worthwhile on Mars. Flourine shouldn't be that (flourspar should exist on Mars) hard to find, and you would need it for other purpouses any ways. And it's toxicity/reactivity wouldn't be as dangerous in Mar's cold low-pressure atmosphere. Just something to think about.

GCNRevenger · 2004-12-16 15:49:18

On Mars, the higher Isp isn't such an advantage, and Methane/LOX engines can give you mass ratios around 0.20 to orbit, perhaps more with careful staging.

Have you ever looked up the treatment for HF exposure? Its... unpleasent.

Austin Stanley · 2004-12-16 15:59:18

Yeah, we were dealing with it at one of the places I have been doing some interning at, and so I went over the MSDS. Like I said, the stuff is pretty toxic. For a serious industrial accident involving HF, treatment isn't much of an issue, you are dead.

H-F might not be as necessary for getting to orbit, but an improved ISP would still be nice for getting about the solar system/getting home. I was just pointing out that the materials can be more safely handled in the Martian enviroment, and might not be that hard to come across.

Euler · 2004-12-16 19:41:28

But since the H-F reaction is more exothermic than H-O you do get improved ISP (~550), flourine is the best oxidizer you could possibly find. It might also be possible to easily covert existing engines and tanks over to a H-F system, the oxidizer-fuel ratio should be the same, and the tanks might not require any modification. Also, the concurns about toxicity aren't such a big deal at high altitudes and in space.

Actually, the oxidizer/fuel ratio for F2/H2 is double the ratio for O2/H2. F2 is also a bit denser than O2, which ends up giving the F2/H2 combination an overall density that is about 65% higher than the density of the O2/H2 combination.

If you want to get fancy, you could also ad some Li and have a tripropellant reaction. That would give you an even higher Isp, but it would also introduce some extra difficulties.

Alternativly, you could mix some Flourine in with your oxygen for improved efficency as well.

There have been some studies using Flox (F2/O2 mixture) and various hydrocarbon fuels. It turns out that Flox can actually achieve a higher isp than either F2 of O2. A 70% F2+30% O2 mixture has the highest Isp for use with Kerosene (it seems that the O reacts better with the C, and the F reacts better with the H).

I have also seen an idea for mixing Li metal powder into a hydrocarbon base and then reacting it with Flox. That should be capable of some pretty good performance if it works properly.

Hop · 2004-12-17 01:29:42

My hobbyhorse: The maglev tracked launch up the mountain to 20,,000 feet and Mach 0.9, is not at all trivial since it eliminates that huge first stage, entirely. Two stages to orbit, and by refueling, a vertical return at geostationary re-entry velocity.

Yeah! I'd like to see one on Mount Chimborazo, Ecuador. By the time you fire your rocket engines, you'd already be going mach .9 and be above much of the troposphere.

And at the equator you're already going .5 km/sec

mboeller · 2004-12-17 07:20:59

Then you must not have looked very hard. The Air Force has done quite a bit of work in this field. Considering how much work was put into the X-30 project, for you to claim this is unthinkable.

Why unthinkable….only unworkable. All the different tests and studies have gone nowhere. So for me scramjets are death…purely technically. IMHO X30 showed this beyond doubt.

Why is the Air force then still working on scramjets? Simply because they have different requirements. They want to launch a hydrocarbon fuelled scramjet missile from aircrafts (fighters, bombers) and strike something hundreds of miles away within a few seconds.

For this mission, scramjets are the only way to do the job. But the requirements are far different from an SSTO.

The leading edges of the X43a were molten after the test lasting a few seconds for example. So going from this crude test vehicle toward an SSTO will take quite a lot of time an effort. IMHO it’s not worth it to follow this route when other simpler and better systems are possible.

Anyway, the Scramjet need not power the vehicle all the way to orbit, getting to a high enough fraction of orbital velocity should be sufficient for a small rocket injection burn. I suppose you will also discount the practicality of slush hydrogen fuel or using cryogenic hydrogen as coolant out of hand as well.

How fast do you want to go? M8? M15?
If you want to go only to M8 well then maybe M6.5 is also good enough for you and a far simpler and well understood ramjet is all you need. IMHO with M8 in mind scramjets are not worth it. The Air Force thinks different, but they have something quite different in mind too, so it could work for them.
If you want to go to M15 then all the problems with scramjets are yours. The IMHO biggest problem with scramjets is the low trust:drag ratio so the acceleration is rather slow and basically you turn most of your trust into heat due to the friction.
But even M15 is roughly only 40-50% toward orbit, so your heavy structure (due to the streamlining and very large H2-tankage) and your scramjet engine is only death weight for the other 50-60% to orbit. So even when you take all of the burden you get only so much for it.

I don’t dismiss the practicality to use hydrogen or slush hydrogen as propellant and for the cooling of the vehicle. But all this cooling requirements make your vehicle very delicate cause you have to make 100% sure that the cooling works. With all this cooling canals within the structure of the scramjet SSTO I’m very sure that NASA would turn this into an complete X-Ray job for the vehicle to avoid any burn-up during launch.

I came to the conclusion that such a vehicle would be easier to turn around between flights because it would be only one vehicle, that there would be no delicate assembly procedure involved, and that the Scramjet engines are mechanically speaking quite simple, and with modest improvements in materials should be mostly trouble free.

IMO scramjets are only theoretically simple. In reality they are quite complex with all the different requirements. Also you have to take the systems of the scramjet SSTO into account. IMHO this will increase the requirement to maintain the SSTO to a very large extent.

You also apparently aren't aware of some work that has been done on rocket/jet hybrid engines and the low level of advancement needed to yeild high payoffs. Modified production fighter jet engines with modified LOX injectors have been ground tested with the capability of pushing a vehicle into the Mach 5 or 6 speed region and U-2 like altitudes.

No I’m not aware of this work, except for the MIPCC using in the Rascal vehicle and the TBCC-RTA project. Do you have an link or two?

If you mean the RTA-technology then this engine would work perfectly in an updated booster for the Spacejet system.

Using these on the carrier plane able to operate at these conditions would increase its size and increase its development costs, but the payoff of requiring a substantially smaller and lighter upper stage would be well worth it. Your notion that "streamlining would increase weight" and such is just blather, the higher altitudes achieved will make seperation easier since the air is so thin, not that streamlining is a problem anyway.

OK taking back the "streamlining would increase weight”. That was bad worded.
I don’t think that separation will be easy for any vehicle except when you use the Spacebus – approach and separate out of the atmosphere at >60°. I, for example think that the Sänger would have had big problems with the separation at 38km(?) and M6.8. AFAIR this was one of the big points in the development process of the Sänger.

Overall the idea is to intentionally spend big on development costs to save on launch costs down the road. If it costs a few tens of billions of dollars, then thats just fine if it reduces launch costs by an order of magnetude and permits weekly flights of the same vehicle.

I don’t think so. Spending ~ 50 billion dollar for development (using the latest estimate) would mean that the SSTO would have to fly very often to overcome this Hugh burden. Even when you have 4 vehicles and each vehicle flies 1000 times then each flight would cost you US $12.5 Mio without even getting of the ground. This together with the rather small payload of most scramjet proposals ( 10000-20000 Ib ) means that the per-pound cost of the payload will remain rather high. When I take into account the IMHO high maintenance costs too then scramjet SSTO’s are IMHO a waste of money.

I also find your notion that system weight will unavoidably increase development cost as unfounded, especially today with advanced materials available. Technology has advanced signifigantly and the old "big simple rocket = better then fancy ones" is not longer true either.

Everyone is using TOW or empty weight to judge the development costs upfront. So don’t complain to me here. This is a normal way of doing business and it has not changed in the last 20-40 years.

And please, a study from the NASA advanced concept people? Come now... tether space plane indeed, a fairy tale if there is one.

You don’t like tethers? I do! For me this system or comparable ones (using an rocket SSTT) are far better than an scramjet SSTO. I think we will have vehicles using this systems far earlier than scramjet SSTO’s even when we invest 10 times more money in scramjet SSTO’s than into tether applications.

GCNRevenger · 2004-12-17 20:14:07

I must appologize for being a little curt with you, I have had a similar argument over this subject that became rather... heated. Thank you for your demeanor.

I agree that a TSTO vehicle would be preferred for "Shuttle-II" type operations which require a few hundred flights a year and paying modest sums per flight would be acceptable.

Beyond that though, I think that an advanced Scramjet + Rocket vehicle would be needed to access flight rates of many hundreds per year or more and per flight costs that would enable "almost-everyman" space travel. This would obviously be a next-generation "Shuttle-III". The high turn-around rates would dictate a single-piece vehicle where a Scramjet would be the only option.

"The IMHO biggest problem with scramjets is the low trust:drag ratio so the acceleration is rather slow and basically you turn most of your trust into heat due to the friction."

This limitation can be partially overcome by pumping the Hydrogen fuel through the vehicle's skin to cool it and then injecting that into the engine. As friction would increase, so would the thrust, and permit access to near orbital velocities... close enough that a rocket injection burn would be small.

Liquid hydrogen tankage isn't such a problem because it won't be a liquid: the hydrogen would be made into a partially solid slurry, which is about 1/4th to 1/3rd denser roughly, and can draw even more heat away from the vehicles' skin. The USAF is also exploring the addition of additives and processing techniques which would increase specific impulse even further, probobly enabling fuel volume reduction by almost half over regular LH2.

Advances in materials will have to be made for "airline like" reliability of such a "Regenerative" arrangement, fortunatly rare Earth ceramics have been making improving fairly rapidly, with materials that can resist 4000K and even 5000K out at Sandia, with accompanying improvements in mechanical properties also being worked on right now.

I think my use of the term "rocket combined cycle" might be a little too broad. I'm thinking somthing fairly simple, a twist on current jet engines, where LOX would be injected to give the vehicle higher speed and altitude then would be practical for turbines/ramjets alone over the short sprint to seperation.

Ultimatly I guess I am thinking of a vehicle not unlike the German Sanger-II, but without the complex hybrid jet engines... Something a little more brute force and a little less finese'. The seperation problem could probobly be overcome I think.

I don't think that building either type of vehicle would cost NASA fifty billion to build, or at least it shouldn't. The TSTO vehicle could probobly be built for under half that kind of money.

In any event, the vehicle ought to be powerful enough to deliver 45,000-50,000 pounds of payload per trip, preferably 55,000lbs, or a fully armored escape-pod-equipped crew vehicle with room for a dozen astronauts. If it can't haul at least 20MT, then we shouldn't bother... In that case, launch costs of 5-10X lower should be realistic.

BWhite · 2004-12-17 22:14:32

GCNRevenger, how cost effective will an RLV be for slogging fuel to LEO?

If a nice nuclear powered ship were riding "at anchor" then to ferry up crew in an RLV seems great, but if we are lifting LH2 and LOX in 20 MT and 30 MT tanks, how can we go anywhere?

It still seems to me that an expendable that had a very high fuel to dry weight mass fraction (Thiokol SRM tweaked to 95/5 for example) would be cheaper for lifting LH2 and LOX tanks. Being ultra-expendable, its NOT man-rated, ever.

Edited By BWhite on 1103343911

John Creighton · 2004-12-17 22:22:40

I am wondering this too. If you had a refuelable ITV with a condenser or if your RLV had a very fast turn around time weeks or days, you wouldn’t have the boil off problem. Still this only gets you fuel to orbit. For actually building a ship or hab I would hope it is in bigger pieces then 20MT.

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