Earth to LEO - discuss

mboeller · 2004-12-18 13:36:38

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.

No problem

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.

OK, so you talk about the far future. I'm more concerned with the near future, cause NASA and ESA always seem to seek to master the problems of the far future and overlook the problems of the near future and so finally we have to stick to the same old V4-style rockets for ever.

So I try to figure out how to get into orbit ("LEO") now using available or nearly available technology. Therefore I reject fancy technology like scramjets which need; as I have heard after the last X43a flight " a hundred years to develop".

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.

Ouch!
Well yes, this would improve the ISP but IMHO on the other side the vehicle would have to withstand even greater stress due to the depressed trajectory to get most of the acceleration within the atmosphere.

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.

Well; IMHO your 1/4 - 1/3 more density seems to be a little bit much for Slush-Hydrogen. I have heard only two figures here, one being 10% from an NASA PDF and the other being more in line with your figures indicates AFAIR 85kg/m³ instead of the normal 70kg/m³, which translates to an improvement of ~21% in density.

Or do you mean "gelled Hydrogen"; using CH4 or even Al in the H2 to densify the fuel. Here the best seems to be up to 60% Al within the H2 to reach an density of ~170Kg/m³. Unfortunately the overall performance seems to be the same or even worse than with pure H2/O2, which I cannot understand but that's the conclusion of the http://gltrs.grc.nasa.gov/reports/1998/ … 206306.pdf from the NASA.

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.

Have you a link for this. I don't know much about ceramics.

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 separation.

OK, you are basically talking about the MIPCC system as an pure plug on for existing turbojet engines. Well RTA will/wants to improve this even further and will/should result in turbojets being able to work at up to M4 - M4.5.
Other's like ESA-SART in Germany have studied the MIPCC approach too (but only PDF's so far) using water, LOX or CH4 to augment the turbojets used in the first stage.

Maybe this PDF is something for you: http://hypersonic2002.aaaf.asso.fr/pape … 7_5148.PDF

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.

So finally we are not so far apart. Well I don't like Sänger too much. It's an Highend-System with a lot of failure modes built in by design. The M6.8 ramjet/turbojet Booster is really complex and the Orbiter is far too small to have any useful payload (manned only ~3to) so every small weight gain during development would have wiped out large chunks of payload.
Because of that I "fell in love" with the SpaceJet study from the 1970's. The booster is rather simple and very small with only (then) off the self SST-derived turbojets, and the Orbiter/Shuttle would only use available technology already developed for the Space Shuttle. All this technology resulted in an remarkable system with an TOW incl. Booster of around 2.600.000Ib and an payload of 65.000Ib.
Well today such an big system is no longer possible due to the missing link, the SST. So we would have to do it with only fighter type engines with "only" 35000Ib. But despite this, IMHO CFK and advanced technology already in use would result in an fairly good shuttle with maybe 10000-20000Ib payload. So with present day technology using the "correct" system approach you could build an HTHL TSTO shuttle with an very good payload fraction. IMHO even with scramjets you cannot produce an better system with an higher payload fraction.

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.

NASA needs always a lot of money to do an simple job...unfortunately. This is not because the people are stupid or something like that, but because of the "system". So I don't expect something from NASA at all. The last and final clue for that was the Venture-Star-debacle. NASA back then didn't choose the "best" system for the job but the most complex system for the job. So the failure was built in from the beginning. This was IMHO an political decision and so technology were on the backseat.
So you will ask how I define the "best" system. Well for me the "http://www.spacefuture.com/archive/single_stage_to_orbit_vertical_takeoff_and_landing_concept_technology_challenges.shtml]Millennium Express" from General Dynamics would have been the best system cause it was the simplest system to do the job. VTVL + base first reentry + axis-symmetrical body would have resulted in the lightest vehicle with the highest payload.
But NASA decided otherwise. They wanted an Shuttle II and they got an Shuttle II. If you compare the old articles about the SSTO Shuttle II from the 90's with the final Venture Star then you can see that it is an close copy ( The Venture Star has only a more pronounced conic/wedge shape ). They even demanded that the Venture Star was man-rated with the capability to dock to the ISS....tsss and this from an first-gen SSTO barely able to even reach orbit. What about OMV? What about escape-rockets? How about using the rocket at first only as an "freight liner"?

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.

Well, all the scramjet TSTO's studied at the moment have an max. payload of around 10MT, not more. This vehicles already approach the practical TOW-limit for HTHL-vehicles. For example look at this study: http://www.ssdl.gatech.edu/main/ssdl_pa … .pdf]Aztec: A TSTO Hypersonic Vehicle Concept

The TOW of this study is already at 314to this early in the development cycle. So you can expect that finally it will come in at maybe 380-450to (pure guess) and this is already close to the max. possible with HTHL-vehicles.
You can also see how slow the acceleration of the scramjet is compared to the ramjet. From M2.5-M6 =80sec ; From M6-M8 =180sec. Also the ISP of the scramjet is not really great compared with the rocket(!). Only twice that of the rocket at M8. The thrust is even worse at M8 (maybe 1/8 of the rocket engine).

Also, only an 5x-10x reduction in payload prices per Ib. Why not more? If SpaceX can bring the FalconV to market this kerosene-LOX TSTO with simple rocket engines will bring down the cost toward US $900/Ib and this is already at least 5x lower than the cost of the Shuttle.

So I don't think that we have to wait for exotic technology like scramjets to bring us "the future" but we can make it today with clever engineering and the "best" system.

PS.: here is the link to the comparison between PDE-rocket and air augmented systems. The weight of the pure-PDE-system was the lowest!:

http://www.ssdl.gatech.edu/main/ssdl_pa … 9-2354.pdf

GCNRevenger · 2004-12-18 23:17:40

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.

Simple: high flight rate

I am thinking about a 20MT capacity vehicle capable of weekly flights with two one-week overhauls per year. If 4/5ths of these flights are tankers, then three RLVs would be able to ship 2,400MT of fuel a year... Which would require two dozen Shuttle-C+ or about a hundred Thiokol launchers to match.

Payloads would become like shipping containers, in standardized 20MT packages. Its the only way to move beyond the "McMurdro" phase of space travel to/from Earth without a space elevator.

BWhite · 2004-12-23 21:56:05

When sending low value fuel http://www.astronautical.org/pubs/vol40i3Feat.htm]to LEO - - failure is an option.

Using your Rolls Royce RLV 80% of the time for slogging fuel will increase capital costs significantly.

Since this proposed launch vehicle would carry fluids, including water to re-supply the International Space Station, it is named for Aquarius, the water carrier. Twenty percent, or perhaps even one-third of all Aquarius launches would be expected to fail. This is roughly the fraction of electric power lost during transmission from power plants to consumers, and roughly the fraction of water lost while flowing through aqueducts, as Figure 1 illustrates. Loss factors of these magnitudes were doubtless known from the beginning for these systems, and were permitted in the early development of the Atlas missile later developed into a launch vehicle. Reducing the losses in these systems might be possible through the use of superconductors for power transmission or by constructing covers for the aqueducts, but these improvements are too expensive to implement at present. Improvements were, of course, made to launch vehicles to improve reliability, but costs increased considerably along with success rates. On the other hand, for a payload of low intrinsic value, like water or fuel, it is cost-effective to accept certain losses.

Edited By BWhite on 1103860633

GCNRevenger · 2004-12-23 22:03:42

Ehhh I've heard of this idea, I don't think they can do it.

The minimum absolute complexity needed for payload delivery is such its still not cheap enough to compete with an RLV fleet.

Numerous pad failures might not be acceptable either.

Fledi · 2005-03-31 13:01:01

Hello, just wanted to tell you about another way to go to LEO using an orbiting spinning cable made of carbon fibres. Actually it is a downscaled version of the space elevator. I'm working on it's simulation in my spare time and it looks quite promising yet, although the docking part might be difficult.
There is a company researching this concept at http://www.tethers.com/MXTethers2.html]Tethers

I also had some discussion about it at
http://www.halfbakery.com/idea/Space_20 … Halfbakery

dicktice · 2005-05-20 15:44:53

And now, for something a little different:
Starting at the South Pole, launch straight up through the atmosphere, a single-stage rocket with a detachable payload, to rendezvous with one end of a bolo-tether rotating about a polar-orbiting space platform. The payload is captured by one end of the bolo, at relative zero-velocity, and accelerated to orbital speed and then some, above the North Pole. Meanwhile, the launcher returns to Earth, straight down to a rocket assisted landing just where it started. What happens to the captured payload, depends upon the mission objective (e.g., transportation of crew to the space platform, ditto fuel and components, microgravity laboratory experiment support, acceleration to cis-lunar velocity for delivery to the Moon, interplanetary vehicle assembly and checkout.
such a scheme, utilizing a polar orbit over Anarctica, seems too simple and obvious if feasible to have been overlooked. Where's the flaw?

srmeaney · 2005-05-20 17:32:02

There is always antigravity. Yes I know, bugger off with that Sci fi stuff. But String theory describes gravity as the result of strings twisted in opposite directions as a sum of the total strings. Our planet has gravity and most of the strings making it up are twisted in a single direction of dominance (say for the sake of argument clockwise), but is also has a certain aspect of antigravity (gravity in opposition to the inherent gravity) Even though they are both gravity, they are of opposite twist and therefor repel.
An anti gravity engine would require of us the ability to take a very great mass and alter the twist of it's strings so that they are in opposition to what is dominant in our gravity well.

The complexity of even knowing how to do this is at least a hundred years away and the best you can hope for is a couple of very expensive orbital lift tugs designed to lift a cruise ship sized space vehicle out of a gravity well and into space where it's big nuclear motors can push it (and it's ten thousand passengers) around the solar system. That means space vehicles launching out into the ocean from a sea port and going up and comming back with the use of the orbital lift tugs. It also means that a cruise ship in space can generate its own local (earth like) gravity with a small "gravity motor" if you will.

reddragon · 2005-05-20 17:54:16

I read a book on antigravity once The Hunt for Zero Point by Nick Cook) that talked about some research that has been done on the subject. I'm not sure how much of it to believe though; some of the things it described, such as possible top-secret military work on antigravity, seemed a bit far fetched. There were some interesting and perhaps more plausible parts though. For instance, it talked about a Polish (or was it Russian? not sure) scientist named Podkletnov (or something like that) who supposedly produced antigravity with a spinning superconductor disk. Interesting, although I don't have any idea why such an effect would be created.

As for the physics of antigravity, if it exists at all, I really can't comment on your string theory description as I haven't really studied string theory. Looking at it from the general relativity standpoint, I would think that antigravity would have to be created by some sort of warping of space time that is inverse to the normal warping caused by mass which causes gravity. It is also interesting to note that the time dilation effects of anti-gravity would probably be the reverse of those of gravity (i.e. anti-gravity would speed up the passage of time). One more thought: if gravity and acceleration are essentially the same thing, how would anti-gravity fit into that picture? Of course, I've heard that anti-gravity is impossible based on our current understanding of the laws of physics, although i'm not sure why that is.

srmeaney · 2005-05-20 18:26:45

I read a book on antigravity once The Hunt for Zero Point by Nick Cook) that talked about some research that has been done on the subject. I'm not sure how much of it to believe though; some of the things it described, such as possible top-secret military work on antigravity, seemed a bit far fetched. There were some interesting and perhaps more plausible parts though. For instance, it talked about a Polish (or was it Russian? not sure) scientist named Podkletnov (or something like that) who supposedly produced antigravity with a spinning superconductor disk. Interesting, although I don't have any idea why such an effect would be created.

It comes from a time when they considered antigravity to be associated with the reduction of earth magnetic field above a superconductor. Real gravity is created by the strings that make us up.

As to the whole space cable at the south pole, That would require a small city to provide system support. There goes another UN sponsored treaty.
I suppose the idiots in Japan who are attempting to stake a claim on Commonwealth Antarctic territory for the purpose of "further research of Whales" (aka sushi slaughterfest 2006) will be the tip of the iceberg as every plunderer in the northern hemisphere heads south for exploitable resources.

Hello, just wanted to tell you about another way to go to LEO using an orbiting spinning cable made of carbon fibres. Actually it is a downscaled version of the space elevator. I'm working on it's simulation in my spare time and it looks quite promising yet, although the docking part might be difficult.

Not realy fledi, A cargo block or passenger transport on a space cable does not need to dock "on cable". It simply needs to ride a carry-all into orbit and detach so it's robotic arms can crawl along the orbiting superstructure like a spider and dock in elsewhere.

Fledi · 2005-05-20 18:33:57

The problem with doing the full zero speed to orbital acceleration with the tether is that with present material strenghts the relative tip velocity of about 8 km/sec leads to a very large center diameter for the tether. The factor which decides all about the speed limit is tensile strength/density of the tether. 8km/sec would be doable with nanotubes if they become aviable for some hundred meters length and get cheap enough. For carbon fibres the limit is somewhere around 3 to 4km/sec which would require your rocket to achieve half the orbital speed by its own engines. This is not that bad because it already needs more than 2km/sec delta v to go to 100km altitude and the speed vectors are at 90 degree angles. So you'll need about 5km/sec delta v on the rocket, which allows for 10 times as much effective payload considering less structure mass for tanks and heat shielding.
It is really possible that the suborbital spacecraft will evolve to that degree relatively fast. Setting new altitude records, for exampe first spaceship that can go up to 1000km (much easier to achieve than going orbital, delta v for that one about 4km/sec) should help this process.
Also the tip acceleration after docking depends on relative tip speed an lenght of tether. For example you have 3g for a tether extending outward 500km from the center of rotation and moving at relative tip speed to the center of 3.8km/sec.
(Should really get some webspace and put up the programs I did for that so far, but better wait until they are somewhat finished)
By the way looks somewhat tricky to simulate a rope consisting of many segments which all can move freely in 3D, but will solve that sooner or later

Yes you can use a tether to get payloads to Moon, even to Mars which should be fine for cargo transports, where you can think of the tether like of a mother ship launching off small capsules, with all the advanced engines placed on the tether station.
Also you have that tether station as "ballast" at the tip of the shorter side of the cable with very high quality artifical gravity from the spin.
There is some good stuff about all kinds of tethers at
http://spacetethers.com/]spacetethers and http://en.wikipedia.org/wiki/Space_tether]wikipedia

For antigravity it might be that many things about gravity are somewhat different from what the traditional Einstein approach is. Don't know really much about it but have heard some interesting stuff in conjuction with the zero-point-energy theory with gravity being suggested of being the result of masses shielding a portion of that energy from space.
But then we have the measurement that the expansion of the known universe is accelerating which is a strong evidence of there not only being something like antigravity out there but it being the stronger force compared with gravity.

But let's just stick to the tether first as long as no physicist comes and totally messes up our understanding of the world again (which should statistically happen soon, if you go with one genius at every 100 years)
For my part it's still easier to comprehend a turning rope.

Fledi · 2005-05-20 18:51:42

Oops looks like I took too much time with this last post so reddragon already talked about the zero point stuff. Will try to write faster next time

Not realy fledi, A cargo block or passenger transport on a space cable does not need to dock "on cable". It simply needs to ride a carry-all into orbit and detach so it's robotic arms can crawl along the orbiting superstructure like a spider and dock in elsewhere.

Not just that, but the cargo block should have its own harpoon like rope launching gun, so that it rapidly gets a kilometres long rope across the orbital path of the spinning tether. You have a kilometer of maneuvering tolerance in every direction that way which is pretty important given the small timeframe you have for the docking.
Also the meeting and connection of the two ropes would ensure a "soft" docking with the additional acceleration stress building up as the ship swings to the tip instead of an abrupt change.
This also allows for some 10s of m/sec difference in the speed of the two tethers.
I wouldn't want the cargo block to separate from the launcher (if that is a winged or some otherwise landing capable craft) until it is safely catched by the orbiting tether, so if the attempt fails you simply let launcher+cargo fall back into the atmosphere and try again next day (or week or wathever it takes to re-ready the craft). If only every second attempt succeeds (but I expect every one to succeed in the long run) you're still much better off than with a full orbital rocket.

Chazbro38 · 2005-05-20 22:01:23

Chemical propulsion in the form of a SSTO or maybe a two stage to orbit vehicle is definitely the future STS to LEO. With an air breathing 1st stage, the vehicle can use oxygen in the atmosphere to fly to sufficient altitude to get beyond most of the atmospheric drag before the vehicle begins its rocket powered acceleration and ascent to LEO. An NTR that is ignited at ground level will never get approved in a million years with the radioactive exaust issues, and at our current state of the art a space elevator is a pipe dream at best.

Charlie

Fledi · 2005-05-21 05:36:22

For conventional air breathing engines you still have the problem of the atmosphere being 80% nitrogen, which doesn't contribute to the reaction but causes additional drag and has to be warmed together with the other components further lowering ISP.
There is another possibility with silicium-hydrogen mulecules with a structure of conventional hydrocarbons with Si in the place of C, that uses N2 for the reaction. There have been some advances made recently in this field as far as I know.
But that tether is still possible to do with current tech, I'm not talking about a full-scale space elevator here.

Fledi · 2005-05-21 05:39:39

An NTR that is ignited at ground level will never get approved in a million years with the radioactive exaust issues

I bet it would in that timeframe anyways

dicktice · 2005-05-21 14:40:38

Single-stage to altitude (SSTA) medium lifters, launched from the South Pole, comprised of LH2/LOX-fueled multiple gymbal-steered engines, basically cylinder structural envelope containing tanks, launched at 90 minute intervals (minimum polar orbit period) or more (bolo tether rotation period dependent) delivering detachable payloads for synchronized orbiting tether capture--would have some features of a space elevator, with the advantage it would appear from the preceding posts, of being currently feasible, as opposed to the not yet feasible actual space elevator. In other words, repetitive launchings and landings of a fleet of utterly simple, reuseable rockets (refueled from a water-ice derived wind-powered/stored electricity, electrolysis plant) would represent a kind of stationary "tower" sticking up through the atmosphere from the Soth Pole.

Fledi · 2005-05-21 17:49:47

What I don't understand in that scheme is that the center of mass of the tether still has to move at orbital speed if it is on a polar LEO . Then the tip speed of it relative to the center of mass still has to be something between 7 and 8km/sec to be able to catch the payloads launched on a simple straight up path.
That speed is not practically doable without nanotubes.

dicktice · 2005-05-21 21:01:48

First of all, is the scheme even feasible? It would seem to be, since there have been no objections to it in principle. Okay, let's say the bolo tether has some rotational period that's a whole number multiple of the polar orbital period (1, 2, 3 ... n) of, say, 90 minutes. Since only one end of the tether would be used for pickup, the centre of mass being the space platform about which it rotates, the length and tension for given payload masses can be calculated. What do we get? (Don't expect me to do it, because I'm error prone.)

Fledi · 2005-05-22 06:44:18

Just looked at some scenarios in me tether designing program. Good carbon fibres have a tensile strength of about 4GPa and more than 1kg/litre density. Unfortunately the program goes beyond its variable limits for these values and zero speed to 7.5km/sec.
Luckily it still works for 5GPa, 1kg/litre and same speed difference, which is slightly better than most of todays fibres.
Then we get about 40,000 tons of tether mass for a cargo to the tip of 10 tons. Sounds still quite impractical to me.
With normal carbon fibres this figure is about 1,000 tons of tether+station mass for a 10 ton payload at tip speeds of 3 to 4km/sec.

dicktice · 2005-05-22 08:20:16

I'm not surprised at the impractically of the scheme, otherwise it would have been proposed before this, even if imaginable in principle. Let's leave it on file, so to speak, for future dreamers to stumble upon. The main thing is to consider any means of routinely transitioning from Earth to orbit and back again, until a generally acceptable solution is agreed upon internationally.
My main worry, just now, is the threat to private space initiatives of government imposed safety, and military security regulations. What Burt Rutan, et al, are currently experiencing bears close watching.
Meanwhile, let the ideas proliferate however impractical, so long as they aren't certifiably impossible.

Fledi · 2005-05-22 15:20:48

I was really surprised just how unknown rotating tether schemes are generally. Didn't hear anything of them until three months ago.
By the way, these tethers were impractical too before high strength plastics came up. The practical tip speed limit is somewhere at 700m/sec with high stregth steel cables.
A polar launching station is not a bad idea anyways, it is no big difference if you launch the cargo ships staight up or sideways with a higher speed. Another good orbit is the equatorial one where you have an additional 500m/sec "for free" from the Earth rotation. And sycronizing the rotation with orbital periods is a good idea, too, but it looks like there will be several complete rotations within one orbital turn.

srmeaney · 2005-05-25 01:14:06

I'm not surprised at the impractically of the scheme, otherwise it would have been proposed before this, even if imaginable in principle. Let's leave it on file, so to speak, for future dreamers to stumble upon. The main thing is to consider any means of routinely transitioning from Earth to orbit and back again, until a generally acceptable solution is agreed upon internationally.
My main worry, just now, is the threat to private space initiatives of government imposed safety, and military security regulations. What Burt Rutan, et al, are currently experiencing bears close watching.
Meanwhile, let the ideas proliferate however impractical, so long as they aren't certifiably impossible.

Government saftey regulations are a good thing. As to Military control of technology transfer issues. It's OK up to a point but One day it will stop a company from expanding because it must employ an increasing number of people in diverse nations to achieve a profit.
Considering it is cheaper to build a launch facility in North Australia and launch from there than Cape Canaveral, That whole technology transfer issue is going to hit the fan sooner than later.

C M Edwards · 2005-05-25 12:53:05

Don't expect me to do it, because I'm error prone.

As a side note:

Dick, everyone posting to this list is error prone. We post entire threads to the New Mars forum that are nothing but brainstorming sessions. In most cases, those ideas can be checked by simply comparing them to previous work by other people.

However, some (a rare few) are sufficiently new or unexplored that nobody else has done the math yet.

If you really believe that your proposed tether configuration has never been examined before, then odds are nobody has done the math on it before, either. If nobody has done the math, chances are that nobody has written a computer program for it.

So, why are we certain that Fledi's result is accurate for this case?

RobertDyck · 2005-05-25 14:54:25

This is a long thread. Should I pipe in with my favourite? I'm sure everyone knows already. Earth to LEO is such a obvious requirement and the first step for any manned exploration of space that it requires a low cost frequent flyer. To me that means reusable, but small. Yea, I think the short term is a lifting body space taxi. I might as well post the link to the picture again: http://chapters.marssociety.org/winnipe … e.gif]here. This is what I consider the short term solution. It could lift 4 astronauts from Earth to LEO and back, but no cargo. You could replace one or more seats with a duffle bag for cargo, or a frame to hold science drawers from ISS.

There are many here who don't see any value to ISS, but I attended the 14th IAA Humans In Space conference in 2003 where I heard presentations from many researchers with Ph.D.s who were doing analogue studies in their lab: bed rest or centrifuge, and trying to extrapolate human response to microgravity. But we have a space station, why are we messing around with toys? Mercury started to explore humans in space in 1958 and launched on May 5, 1961. If a researcher wants to research human response in zero-G then do it in zero-G. We have a space station, use it.

This space taxi would be launched from the back of a 747, one of the two that NASA already owns. It's small enough that the empty tank could be lifted onto the 747 with a mobile construction crane, and the orbiter could also be lifted with that crane. You don't need the dedicated crane structure used for the current Shuttle. Fuel could be delivered with semi-trucks (tractor/trailer) and pumped through hoses directly from the truck tanks to the spacecraft fuel tank on the 747's back. Fuelling would have to be done at a safeing area, but that's just a piece of airport tarmac away from any buildings. The tank could be delivered by a flat bed semi-truck, and the orbiter could be delivered by a flat bed medium truck with dual rear axle. This means the space taxi could take off and land from any airport capable of servicing a 747.

Technology for this would be the same graphite/epoxy body used for X-38 and SS1, as well as the skin of OMS pods on the current Shuttle and the fairing used for commercial launches of Titan 4B, Ariane 5, Atlas V, and Delta IV. Heat shield would use existing technology: RCC, FRCI, DurAFRSI. OMS and manoeuvring thrusters would be the same as Shuttle but smaller. There are a lot of MMH/N2O4 thrusters available. Life support would be oxygen/LiOH, but the O2 tank would be a Carbon Overwrapped Pressure Vessel to reduce weight. OMS/RCS fuel tanks would also be COPV. Main engine would be a single reusable tri-propellant engine similar to RD-701 but single chamber and smaller. Use fibrous Carbon/Silicon Carbide ceramic regenerative exhaust cone and solid Carbon/Silicon Carbide turbo pumps. The Glenn Research Center is already developing this composite engine technology. Main engine fuel would be LOX/LH2/RP1. Use the HL-20 body shape, developed by Langley. The external tank would be expendable, but everything else would be reusable. This is a semi-reusable Two-Stage-To-Orbit (TSTO) design; the first stage is the 747 which uses jet fuel. It can be built today.

The ultimate Earth to LEO design would be a SCRAM jet hypersonic space plane. Single-Stage-To-Orbit (SSTO) Reusable-Launch-Vehicle (RLV). Use jet fuel with supersonic combustion turbine engines to mach 5-6, then ignite a SCRAM jet engine fuelled by liquid hydrogen. Fly to mach 17-25, optimum would be about mach 20. Then transition to LOX fed, which would convert the SCRAM jet engine to a LOX/LH2 rocket engine. Once in orbit you can use the same MMH/N2O4 engines for OMS and RCS. When landing just glide until subsonic, then air-start the turbine engine for a powered landing. This requires an extension of the X-43 program.

Fledi · 2005-05-25 16:53:34

In most cases, those ideas can be checked by simply comparing them to previous work by other people.

There is some work already done on the net about space tethers, even a http://spacetethers.com/spacetethers.html]free java simulator. There are still some important details that I haven't seen so far yet. And the best way to really understand them is to do the basics again and incorporate these details into it.

So, why are we certain that Fledi's result is accurate for this case?

I can't give any guarantees of course. It might surprise you, but I don't consider myself to be impeccable, either

Interesting design you propose RobertDyck, somewhat similar to the once proposed spacecraft launched from the top of an AN225. Of course you still have all the structure to fuel weight and reentry issues to cope with as with any full orbital flight, but it might be a possible way to bring people to orbit. It would still have to be very light and small hoever, to fit on a 747.
About the scram jets, question is what ISP you can achieve in the actual scram phase and what additional drag would be caused by staying longer in the atmosphere.

RobertDyck · 2005-05-26 00:51:33

Yup, I ripped-off the design concept of the Russian MAKS. That was a delta wing with fuselage orbiter launched from an AN225.

The external tank used aluminum-lithium alloy 1460. I strongly prefer this to alloy 2195 used by Lockheed Martin because 1460 consists of aluminum lithium and copper, while 2195 consists of those same three metals plus magnesium and silver. Alloy 2195 may only be 0.4% silver but at the size of the Shuttle's external tank that's 264 pounds of silver or 3,850 troy ounces. That's a lot of precious metal to throw away with every flight. If you look at the specifications, at liquid hydrogen temperature alloy 1460 is 3.33% stronger permitting a very slightly thinner wall, and slightly lower density: 2.59g/ml instead of 2.60g/ml. That means alloy 1460 is not only cheaper, it makes a lighter tank. Molniya designed the MAKS tank to be made of alloy 1460, I prefer to stick with that. One aerospace engineer pointed out that alloy 1460 isn't as strong when it's warmer so may not be as dramatically better at LOX temperatures, but I would prefer to use something like alloy 1441 rather than an alloy with a precious metal.
::Edit:: DC-XA used alloy 1460 for its LOX tank.

To reduce weight from the 275 tonne air launch capacity of AN225 to the 109 tonne air launch capacity of NASA's 747 we have to reduce a lot of weight. I did that by first getting rid of the cargo bay and air lock. It only needs a docking adapter; any EVA can be accomplished by depressurizing the cabin like Apollo. Next replace the fuselage and delta wing with a lifting body. The obvious lifting body design is HL-20, but that was designed for 10 astronauts plus 540kg of cargo. Reducing to 4 astronauts and no cargo permits scaling it down, but not too far since you have to add a main engine. The RD-701 engine was designed specifically for MAKS, but this one will be less than half the launch weight. HL-20 can be further reduced by shrinking the pressure hull diameter. A central isle is absolutely necessary for 10 seats, but with only 4 seats you can position the hatch over the central point between the 4 seats. Lower the seats to the floor: HL-20 had high seats like a van, replace that with low seats like a sports car. Lower seats and no central isle permits reduced diameter pressure hull, which permits reducing all dimensions of the HL-20 body while maintaining relative dimensions. Replacing the metal hull with graphite/epoxy and the ribs with foamed aluminum will also reduce weight. I did a spread sheet calculation of the weight and found launch weight is very sensitive to main engine weight. That's why I calculated replacing the double chamber engine of MAKS with a single chamber, and the titanium engine with new ceramics.

I have contact with the company that designed RD-701, and I would suggest hiring them as consultants. CEV cannot be built by foreign contractors, but Atlas V uses RD-180 engines that have an American manufacturer as backup, so CEV engines could be built by an American manufacturer such as Rocketdyne with Russian consultation. Rocketdyne made the SSME so they know how to make reusable cryogenic engines.

I still recommend separating cargo from crew. This is a dedicated 4 crew space taxi. Cargo would be lifted by an EELV or SDV.

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