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SBird: Wonderful, that you went right to work on the Kilimanjaro maglev track launching proposal numbers for me, since I would hardly know where to start. My first object was to eliminate the need to lift all that weight just to clear the tower. Next, the mountain's practically on the Equator, as opposed to Canaveral. Then, the rail switchyards to the west of the mountain would allow repeatable launchings of checked-out payloads upon demand, as they "bear" on launch window opportunities. Payload dimensions can vary, e.g., large sized but of low density habitat structures, small sized but of high density water-ice pellets, etc. Increasing the angle up to 45+ degrees after release would be accomplished by vectoring the orbiter engine(s) after reaching full thrust. I would love to get your slant on refueled in orbit retrograde re-entry to geostationary velocity, with vertical rocket-burn letdown until density altitude is reached capable of developing sufficient lift for a commercial-type flyback, landing followed by stepping out to kick the tires. Wouldn't that be great stuff, though?
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I think that any proposal for a maglev track would have to demonstrate that it is actually an advantage. Using any realistic track design, you gain so little actually benefit that it's not worth it as far as I can see.
For example, using the main engines to get an effective 45 degree launch angle doesn't help since you're using your engines and fuel which would be better spent just blasting away straight up.
Also, the engineering challenges of building on ice fields are very significant and not fully worked out yet. Plus, you are subjecting the ice field to massive forces and blasts of heat and vibration. The engineering involved would be mammoth and for what would probably only be a few percent lighter rocket. If you could somehow get to, say mach 3 on the track, get a launch angle > 45 degrees, it's probably worth it but not otherwise.
I think that the money spent on such a design would be much better spent on more and better rockets or things like rotational booster tethers or space elevator research.
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Oh, dear, I was hoping for a more optimistic reply. But, at least you didn't actually fall down laughing, or lol, as they like to express it here. Well, I read that the ice is melting on Kilimanjaro, but (1) I hope not for the sake of the Tanzanians, and (2) if it is inevitable, I wouldn't be prepared to wait that long. I looked at the strato-volcanos at the Equator in South America, and they look a lot steeper. Their "foothills" to the west however are daunting, and the distance from the peaks to the Atlantic stretch a great distance above the Amazon jungle (which has enough problems already, to contend with).
So, what to do, what to do? On the other hand, how about that re-entry scheme that I threw out?
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I think that the prolems of building on the PAcific ocean and dealing with the foothills are child's play compared to building a precision, large structure on a mountain. I've done mountain climing in the past and it is NOT a friendly environment to anything more involved than a hut or a gondola tower. The Andes do seem more promising. I suppose that a 50 degree launch angle might even be possible for some of those peaks.
Assuming that we can build the track in that kind of envorinment and the first avalance doesn't wipe the track away, what sort of numbers are we looking at?
Well, since we've pretty far into the future with being able to build this mega track, lets assume that we can go supersonic. Soem of those Andean peaks can top 23,000 feet. Let's assume you get a launch angle of 50 degrees at a launch velocity of mach 3. You've got a vertical velocity of about 785 m/s which is about 10% of the total delta V needed. I'd say that this might be worth using. You've still got to carry a lot of weight to space but it wil help.
Assuming an H2/O2 launcher and ignoring air drag, this launcher give you about an 23% increase in the cargo capacity of the rocket. Not stupendous but measureable. To double your launcher capacity, you've got to have atotal vertical velocity of 2420 m/s or 5413 mph. At a launch angle of 50 dergrees, you need to lob that rocket at mach 9.5.
I don't think the equations I'm using take things like staging into account properly so you could probably improve those numbers quitea bit.
However, it remains that a maglev launcher is an incremental launch improver. It won't give you 10-fold decrease in launch cost. THe differences will be measure in percent. It may well be a vialbe option someday but I think that we need to have a much more crowded launch schedule to justify the contruction of something like this.
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You've got a vertical velocity of about 785 m/s which is about 10% of the total delta V needed. I'd say that this might be worth using.
I disagree that it is worth it - not for a small 10% benefit. The following drawbacks are major:
- Significant investment and infrastructure needed for the track
- Locked into one orbital inclination
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The situation I was thinking of is the future where we're launching large numbers of rockets off to Mars on a regular basis. That justifies the fixed orbital inclination. If the launcher costs $10 billion to manufacture and $100 million a year to run, saves 20% of the $500 million a launch per rocket costs, it could end up being a net money saver in a decade.
A space elevator would be the best bet but read one of my messages on the boards here to see what I think of the probability of that happening anythine soon...
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Gosh! I never thought, SBird, that you'd pick-up on the Andes strato-volcano launch site possibility! Whew, now I can get back to the practicalities. Imagine how often you could loft a lot of different kinds of payloads, with a rail switchyard spread out west of the slope(s). I wouldn't recommend velocities greater than Mach 0.9 (at 20,000 feet, say) in order for the enclosure aerodynamics to accomodate all sorts of stage size/mass combinations to be kept simple and flexible for greatly differing end-uses. For example, s single-stage-to-orbit could deliver a habitat module filled with enough fuel to reach sufficiently high LEO to function as a space platform, with the engine intact for subsequent orbital transistions. Multi-staged crewing , provision and refueling launches, would follow. as often a needed. Granted acceptance of the above, the return transportation means still needs to be addressed.
I would resist capsule re-entry, and parachute/solid rocket grounding "out on the steppes" as a final solution, of course.
So, as I have suggested earlier: What about a rocket-engined lifting body, that comes out of orbit by retrograde braking with a downward vector to prevent re-entry burnup (having no ablation tiles) as the atmospheric density and Mach number are reached where the flyback angle-of-attack permits engine thrust-reduction to whatever is needed, to fly home under squirts of power, and land like the Space Shuttle?
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You've got a vertical velocity of about 785 m/s which is about 10% of the total delta V needed. I'd say that this might be worth using.
I disagree that it is worth it - not for a small 10% benefit. The following drawbacks are major:
- Significant investment and infrastructure needed for the track
- Locked into one orbital inclination
One orbital inclination might actually be a good thing if this is intended as a transit point for destinations beyond LEO for reasons of space debris and traffic control.
If space traffic laws require all cargos leaving Earth LEO to exit from a single inclination (with provisions for special exceptions) then the resulting debris from on orbit assembly errors (lost bolts etc. . .) will be confined to a known orbit or "tube in space" making it far easier to track and clean up or simply avoid.
Also, if most space traffic is travelling the same direction within a narrow band of inclinations, traffic control will be simplified.
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Bringing the maglev speed back to mach 0.9 again puts the whole system back into the whole 'not worth it' regime. The biggest advantage to this system is with an air breathing engine. That would mean a ram/scramjet which needs supersonic speeds to operate. I'd say that if the system can't get the spacecraft up to at least mach 2, it's not worth bothering with.
What I've got envisioned is a NASP-type scramjet launcher that would come in a large and small variety for cargo and crew carrying respectively. Truly massive cargo would probably still be launched on standard boosters but the ability to loft satellites and routine resupply missions will be essential if we want to maintain any sort of significant presence in space.
I'd also avoid retrograde braking since it will require your spacecraft to carry twice as much fuel. The atmospheric reentry is actually a great boon - it lets you avoid having to pay for the massive delta V of getting back to the surface of th Earth without making a big crater. I suspect that a craft with enough fuel to both take off and then land solely with retros will be vastly too heavy to even take off.
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Oh, boy . . . here we are, back to explaining what I/you meant, way back when this forum began.
[I have no objections to any practical means of routine access to and back from LEO-- except the so-called Space Elevator concept, which I think of as a pipe dream on Earth (at least withinin my lifetime, which ain't much longer, dammit) and a threat to Mars's moon-resources if and when it becomes possible.]
I doubt that a mach-plus maglev would be a practical proposition because of shockwave interactions with the surface constructions and terrain: therefore Mach 0.9. Whatever booster power works, including rocket burn to reach mach-plus for air-breathing engines to function. The main object began as a (hopefully practical) means of eliminating the need for that huge amount of Saturn-V type first stage fuel load, just to clear the tower, with the rise up to 20,000 feet, and all that, a bonus, since once-built, it would be avilable for launch-after-launch using already well-known railway switchyard approaches, upgraded but essentially the same as the Japanese have worked out for their highspeed trains.
I've always liked the piggybacked, flyback launching booster aircraft (as Clarke describs, in Prelude to Space--but without his 1950's vintage nuclear ramjet) but no one seems to be able to sell that obvious idea, even now. So, the strato-volcano maglev first-stage-rocket elimination idea depends upon whether or not Mach 0.9 departure from 20,000 feet limitation can be justified by payload flexibility, and launching rates gained, over vertical or horizontal takeoff first-stage alternatives.
The retrograde rocket, of course, depends on refueling in LEO (I thought i made that clear), assuming water-ice launchings on a regular basis, for multiple purposes in orbit--as the ideal way of storing potential H2/O2, prior to the refueling. I admit that this is my real hobby-horse, since until your comments, no one has replied regarding the idea. My main incentive is the bypassing of ablative means of braking from LEV, deadweight, inspections on Earth, and now in orbit, ad nauseum. I've envisioned (to borrow your handy expression): de-orbiting inverted, until relatively geostationary, gradually going vertical until pointing straight up, employing throttled burns for controlling the descent into the atmosphere to avoid excessive bottom surface heat buildup while braking at the 90-degree angle of attack, until further gradual pitch-over is possible to bring about angles of attack below stall, and lifting forces can take over.
So, what's wrong with that scheme for bringing back crews from LEO on a routine basis, once refueling in orbit is possible?
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To point out one big safety concern, is that if the landing system fails, then you are in for a several hundred mile fall... capsules and to a lesser extent lifting bodies can in theory come back surviveably without any active landing method at all.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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Well, here's a laundry list:
Problems with the maglev:
1: unless you get a large delta V from the maglev, it really gives a minimal improvement in the launcher performance. The Saturn V 1st stage got the rocket to 200,000 feet and mach 5. The relative amout of fuel and energy spent getting past the launch gantry were fairly minimal. At most, you could reduce the launch mass of a 1st stage by maybe 20-30% with a subsonic launch platform. You also have to add lots of weight for a rocket that is structurally capable of handling the stresses of accelerating both on a rail car and under its own power.
2: The reduction in cost by using a slow maglev is going to be negative. Less than 5% of the cost of a rocket launch is in the fuel. Most of the cost is in personnel and facilities maintainance. Using 10% less overall fuel and then adding the cost of designing, building and maintaining a maglev will result in a massive *increase* in your launch costs overall.
3: You add a whole new failure element in your launcher system. You maglev is in a very hostile environment of avalanches and rockfall as well as horrendous thermal variations. The rock on high mountain slopes is notoriously unstable because of freeze thaw cycles chewing it up.
Unless you can get a LARGE seperation speed with your maglev launcher, you actually make the launch more expensive. By my very rough guesstimate, it needs to be something like mach 4 - perhaps as low as mach 3. This also requires some sort of NASP type hypersonic air-breathing plane to take advantage of the large horizontal velocity.
Problems with retrobraking reentry:
1: your retro braking reentry requires an *absurd* amount of fuel. In order to skip the whole aerobraking step, you have to lose ALL of your horizontal momentum and then lower yourself back down through Earth's gravity well. This takes the same amount of energy as getting up into orbit. To illustrate, imagine an Apollo comand capsule in LEO. It would take a SATURN V attached to the back of it to do the retroreentry you are talking about. To get it to orbit, you would need a booster capable of lunching an entire fueled Saturn V to orbit. An SSTO is barely possible as it is - it's patently impossible if you try your braking scheme.
In contrast, standard aerobraking reentry is relatively safe (one failure in the history of manned spaceflight) and very cheap if done correctly. Correctly means forgetting the reusable reentry tiles and just using cheap ablative tiles. You don't have to worry about extensive inspections or refurbishing - you just pull off the old tiles and slap on some new ones. The Chinese are using resin treated wood as an ablative reentry shield. Heck the Apollo capsules used the equivalent of bathroom caulk for a reentry shield. Spaceflight materials don't get much cheaper than THAT.
2: As GCNRevenger pointed out, you have an enormous safety issue - a single engine failure dooms the spacecraft to burning up or making a crater without a viable rescue or escape route.
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In defense of tiles though, the technology has progressed from the insane Shuttle "glass foam" tiles quite a bit, and if the heating can be held low enough current metal alloys are not out of the question, and foot-square bolt on metal tiles have been tested beyond 2000C. Small metal tiles have actually been tested on low-heating areas of Shuttle's underside if memory serves. They might do just fine for a Mars lander/aerobrake and small advances in them or modern ceramics could make a very robust reuseable shield for Earth reentry practical.
As far as low-cost access to orbit with a small payload (4-6 people or 10 tons of cargo) that is near-term practical, my money is on the DC-X SSTO rocket. No boosters. No throw away tanks. No ablative heat shield... just inspect, refuel, and roll to the pad.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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Please excuse me if this has already been discussed. (I just skimmed the previous posts.)
Why are people so caught up in creating a SSTO vehicle? I know a single stage is nice looking and all, but can't we just use reusable stages? All rocket designers know that stages get more bang for the buck. So let's just reuse them.
Here's my idea for an evolving Reusable Launch system:
1. Use a launch stack similar to Zubrin's Ares -- 3 stages.
2. Start by designing only a resusable first stage -- 2 flyback boosters. They won't get as much wear and tear as the others, so it's a good place to start.
3. Then, work on getting the main booster to land DC-X style.
4. Who cares about the third stage. It will take the biggest beating from reentry and is the smallest piece of equipment, so it doesn't have to be reusable any time soon. Hopefully, it would be sent to the Moon or Mars anyway.
5. Upgrades can be incorporated into any stage at any time.
What do ya think?
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SSTO has a number of advantages...
First and biggest is the simplicity of operations: no expensive & slow (re)assembly procedure (even the Delta-IV HLV is alot of trouble, and thats automated), ship goes up and comes back down as one piece.
No reuseable stage recovery operation - the whole thing returns to the landing site as one piece - and soft returns are easier on stages than parachute landing.
Only one set of engines required, reducing nonfuel weight, reducing operations/construction expense & complexity, and lowering the chance of fatal engine failure (less stuff to go wrong).
...and as with all RLVs, many payloads - one rocket. Harder? Yes. Expensive to build? Probably. Smaller payloads? Likly. But if it can be pulled off without requiring too much maintenance, then its certainly more efficent per-pound than throwing your rockets away. Say they could build the big brother to the DC-X, able to haul 10 tons or four people to orbit every two weeks... Then you could have a REAL space station, with 200+ tons of cargo and 24 people moved a year for each ship. For exploration, have two or three ships serving as fuel tankers, and move 600+ tons of fuel a year for the price of operations. I shouldn't have to mention how much cheaper this would be than "big dumb boosters".
As far as modifying the Ares "Shuttle Z" concept to be a quasi-RLV, that ain't gonna happen. You could in theory replace the boosters with liquid flyback ones, but the solid boosters aren't that horribly expensive, and you aren't going to be flying often enough to justify the flybacks. Also, the Energia-style 2nd stage would simply be too hard to make reuseable, you just can't make it come back down DC-X style. And the 3rd stage isn't a trivial cost, since it would use multiple expensive cryogenic engines, would be fairly large, and would contain much of the guideance hardware for the rest of the rocket.
I'm all for a Shuttle-Z HLLV to launch large cargo, but a SSTO vehicle for smaller ones has substantial merit and is technologicly achieveable.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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SBird: Harking back to the composite-, or strato-volcanos of Ecuador post--I just just now stumbled upon one of the finer points--Mt. Chimborazo (20,561 ft) south-east of Quito, is actually farther away from Earth's centre than Mt. Everest (29,000 plus ft). For the record, then--
Translations of Chimborazo, Ecuador's highest peak at 6310m are a few. "Woman in Ice" or "Icy Home of the Gods" or "Sacred Winds of the Moon" are some and nowadays it is also called the "Nation's Roof". Till the early 19th century, Chimborazo was thought to be the earth's highest mountain and if measured from the earth's center, it still holds true as the Himalayas are farther away from the equator and lose therefore due to earth's equatorial bulge. The German naturalist Alexander von Humboldt tried to climb it unsuccessfully in 1802, reaching a height of 5900m. Finally in 1880, Edward Whymper and the Carrel brothers reached the top for the first time.
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To point out one big safety concern, is that if the landing system fails, then you are in for a several hundred mile fall... capsules and to a lesser extent lifting bodies can in theory come back surviveably without any active landing method at all.
GCNRevenger: How great, to be discussing the return from orbit phase, at last! I'm curious: How does the SSTO return from orbit differ from the return I was proposing--aren't the risks the same?
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SSTO vs disposable rockets: I see SSTO's becoming important for regular satellite launches, crew transport and station resupply. The problem is that an SSTO is always going to have less cargo to LEO than a disposable rocket. First, you lose the performance advantage of staging. Then, you've got to have a reentry shield, enough fuel to deorbit and the not inconsiderable weight of your landing systems. Any technological improvement in material weight in an SSTO can also be applied to a disposable launcher. I imagine that SSTO performance will eventually approach disposable launchers but are inherently limited in being able to surpass them.
Also, I've still got reservations about the reusability of an SSTO. If you're carrying people or expensive crew, you have to go through some sort of inspection/refurbishing process no matter how good your materials are. While materials might have improved, things like the DC-X have never been operationally tested to LEO and back. When a DC-X is capable of getting to LEO and returning a few times, we'll be able to see how well the materials hold up. Until then, the reliability of those materials is based off of laboratory tests which are never 100% accurate.
However, let's assume that a DC-X vehicle is economically workable and works without too many problems. Let's assume that it can carry about 3% of its mass in cargo to LEO vs a disposable launcher's 5%.
It's basically a cost/benefit analysis of the amount of money you save from not throwing away a rocket per launch vs the additional costs of being able to carry less mass to orbit. I'm guessing that for <10 MT loads to LEO like sattelites and crew AND a large number of lights per year (>10) the SSTO comes out ahead.
However, for Mars Direct, you need > 100 MT to LEO. Furthermore, you're only averaging something like 1 launch per year. If you amortize the huge cost of developing a heavy lift SSTO, I seriously doubt that you can gain back any cost savings in a reasonable amount of time.
Also, a large SSTO suffers from problems with reentry. Reentry thermal stress goes up linearly with vehicle weight - twice as heavy and you have twice the Joules/m^2 to deal with. Your heat shield is going to seriously start eating into your cargo mass if you try to make a 100 MT to LEO SSTO to the point where it probably isn't feasible.
OK, what about your suggestion about in-orbit assembly. Here, we've got to maintain a crew of people in orbit to assemble a spaceship. Our experience with the ISS is that in-orbit assembly is very laborious. It also contrains your spacecraft design to what can be lofted in 10 MT parcels. That's at least 10 SSTO flights. Then you have to maintain a space station crew to do the in-orbit assembly where you can't assemble things to the same tolerances or with the same sort of safeguards as on the ground. Things like aerobraking and reentry shields would have to be assembled from parts. This is a formula for massive cost overruns and potential problems arising in the final Mars spacecraft. You're now relying upon at least 10 launches, an orbital assembly area and a highly compromised Mars spacecraft design for a modest reduction in initial launch costs. These cost reductions are probably going to get eaten alive and then some by the orbital assembly costs alone.
I agree that eventually, we will develop the necessary experience to reliably build a spacecraft in orbit. That won't happen for a while, though. In the meantime, why are we developing all new launcher technologies, space assembly stations and all this other stuff for what could have been launched with a 1960's Saturn V with little fuss or muss? If we're going to go to Mars, we should just get to Mars. Later, the more advanced methods will catch up.
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GCNRevenger,
I agree with much of your argument about SSTOs. One assumption I always have is that I wouldn't be launching stuff into orbit just to service some existing market. My idea is that these vehicles will be developed for a company/country that has its own agenda/market, like agressive settlement of Mars.
If you just want to make money in today's market, definitely keep that SSTO small.
I still don't see why it is so hard to couple three stages of a rocket together. Why isn't it as easy as clipping an extenal fuel tank to the bottom of a bomber?
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Did I say that a SSTO light cargo hauler should be scaled up to rediculus proportions able to haul Shuttle sized stuff? Or that it should be used to build any space station or Mars ship? Not to my memory... an SSTO would be great for hauling of light cargo like ISS-sized racks of supplies, crew transfers, or fuel. Make a version with a side-hatch MPLM instead of a cargo bay, one with an insulated Liquid Hydrogen tank, and one with a crew module. Leave launching the space station or Mars ship to a HLLV.
Jet engines are pretty complex and high-RPM beasts, and maintaining them safely hasn't killed the airline industry, so I think its quite possible if the engines are designed for maintenance unlike Shuttle's SSMEs. The production model of the DC-X was slated to use a radial areospike setup with engine out capability and even higher efficency than regular bell nozzle engines.
The amount of heat that the vehicle will experience on reentry is dependant on the surface area, angle of the surface to the airflow, and of course the weight of the vehicle. Since the DC-X would have a wide, large nose, not be terribly heavy, and not be flat as a pancake as Shuttle i'm confidant that a metal heat shield would suffice, and that certainly would be low maintenance.
Such a vehicle is not needed for exploration. However, if private money can put up for part, then I think Nasa ought to chip in to make it happen. Build a cargo-only model at the moment, and when the kinks are worked out down the road use it as a LEO replacement for CEV.
Edit: It is alot of trouble to glue together rocket parts that wern't intended to from the start. Flight control hardware has to be redone almost from scratch, and with the extreme dynamic stresses most often requires structural redesign, the aerodynamics have to be done from scratch, that sort of thing. Putting a tank on a bomber is not a huge deal because it isn't under the incredible stress that a rocket is under.
Its a marvel of mankind that we can get anything into space!
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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GCNRevenger - I actually think that we're both looking at the problem in the same way - just from different perspectives.
If you go back and read my last message, you'll note that I look at both the huge SSTO single lift and small SSTO multiple trip options. I assert that trying to assemble the Mars spacecraft in orbit, as your earlier message implied, is impractical. However, using a disposable HLV to loft a no-fuel spacecraft and then proceeding to use an SSTO to move fuel up to is in LEO would be fairly straightforward. I've got no problem with that sort of scheme at all - in fact if makes a lot of sense.
I'm just concerned that we get Mars Direct moving ASAP. If we can get the old DC-X program up and running again - we can probably have a fully functional launcher in 10 years. The same time scale also applies to a disposable HLV. Together, the two of them can get significant advantages to Zubrin's original Mars Direct plans. For one thing, the initial HLV doesn't have to carry crew, oxygen, liquid H2 or the orbital transfer fuel mass. Without crunching numbers, I'm guessing that would allow at least 50% more mass to the surface of Mars without the use of nuclear propulsion, electrodynamic tethers or other speculative technologies.
What I don't want is to wait for heavy lift SSTO or advanced orbital assembly experience to be built up before going to Mars - that's a guarantee that we'll spend another 20 years in LEO.
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Dicktice, interesting info on Mt. Chimborazo. I find it rather remarkable that it was climbed in 1880, a nearly 20,000 foot peak back then was quite an accomplishment with the equipment they had.
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Oh yeah, and GCNRevenger, I also find it amazing that we can get into space at all. As it is, with chemical propulsion and even with advanced materials science, we can just barely get into space with a payload. If Earth's gravity well were just a little bit deeper, manned space travel would basically be impossible. The same thing applies to the space elevator - if we can get the theoretical maximum strength for nanotube ropes, we can just barely make it work. Sometimes, I wonder at how the universe seems to almost be set up so that we can just barely do stuff.
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Anathema though it may be, I don't like MarsDirect. Too small (small mass margins, small habitable volume, small payload masses, etc), too slow (zero-G, radiation, psychology), too expendable (nothing really comes back for reuse). I would much prefer we spend a few years reviving the NERVA rocket project so we could get there more than "just barely." Aerobraking also makes me nervous.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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Right, SSTO all the way!!!
One have to keep focus on what it's supposed to do. It's supposed to haul fuel or cargo or passengers to a space station awaiting interplanetary ships; it's not supposed to launch the space station or the interplanetary ships!
Construction and ship deployment is what you have expendable launchers for, but of course, then they're used up.
So actually, the advantage of SSTO goes further than just the fact that you won’t lose your investment after a single flight or that turn around times are unparalleled. Interplanetary ships sent off by an expendable will have to refuel sooner or later too and how are you supposed to do that without a space station and SSTO’s, provided you don’t want your cycler to turn out as an expendable as well?
So if we ever want to become a space faring civilization, not just some nitwits sending out a probe every five years, we'll have to develop these things, sooner or later. At least without a space elevator, SSTO is an indispensible link for regular space flight, although even then we'd probably need them.
Personally I don’t believe in multi-staged hybrid reusables more than as an intermediate solution at best. Think about it. Dropped off parts need to be retrieved and then reassemblied, which I can well imagine might easily become a servicing and security nightmare in its own right. Of course you’ll lose most of the rapid turn around potential as well.
Considering the rapid multiple launches you can make and the appropriate uses for SSTO (which more than incidentally neither is satellite deployment!) I don’t find the terrible mass ratio actually such a big problem.
But, granted, it’s still terrible. Then it might be reassuring to find out that perhaps we’re not stuck with hydrogen/oxygene as the optimal thrust source for all eternity, after all. Check this link for instance:
[http://www.space.com/news/hydrogen_helium.html]http://www.space.com/news/hydrogen_helium.html
Or visit the man in person:
[http://www.aiaa.org/sections/cl/who/bryanp.htm]http://www.aiaa.org/sections/cl/who/bryanp.htm
Yes, I can see difficulties, but hey, even a slight increase in exhaust velocity will have substantial impact on mass ratio. This guy proves at least that the ceiling for chemical performance is not yet in principle reached.
(Hum, it took me so long to write this message so I see the discussion has already went beyond it in some regards... oh, well...)
Hm, I like Mars Direct. Just use till we get to the stage when we really need cyclers, regular space flight, NTR's and SSTO's and then simply switch over to the new track...
Seems to me we might need to begin settling Mars first.
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