Earth to LEO - discuss

GCNRevenger · 2004-03-23 21:34:50

Mmmmm radical monoatomic hydrogen fuel... interesting idea, but definatly would fall under the "metastable" more than the "chemical" fuel section. The hazard of using such fuel would be crazy... and you thought liquid hydrogen was bad. Maybe our children or their children may want to look into it some day.

SBird · 2004-03-24 02:31:27

I agree entirely that the Mars Direct architecture is just cutting too many things too close to the bone for comfort. I'd stick with a 4-6 person crew but try and get the Mars transfer mass to at least double what Zubrin talks about.

I went back through the figure Zubrin gives along with delta V's and I think that I've been able to extract the true numbers since he hides a lot of them in the book. The cargo/ERV module is 140 MT, 54.1 MT are spacecraft, 85.9 MT are fuel. (assuming an Isp of 450) This means that there's an extra 7.9 MT of spaceship unaccounted for in the book which I assume to be engines and fuel tanks not counted in the useful Mars orbital mass.

The crew module is 47.1 MT with 92.9 MT of fuel. The mystery mass is 6.5 MT in this case.

If we do an in orbit refuel with SSTOs, the entire fuel component of the spacecraft mass doen't have to go on the HLV. a 60 ton to LEO HLV is enough to do the original Mars Direct at this point.

The mass that gets to Martian surface is 28.6 and 25.2 MT respectively. It appears Zubrin uses a figure of about 53% of the spacecraft mass to Mars, figureing for an aerobraking shield and parachutes, etc. In those final dry masses, there is also a lot of stuff like consumables, astronauts and H2 that can be loaded up on SSTOs as well.

For the ERV, there's 13.0 MT of stuff like water, O2, H2 and CH4 that can be easily loaded in LEO. That brings our total mass for the ERV down to 41.1 MT. For the crew capsule, you can lose 3.0 MT of water, food and the weight of 4 astronauts with pressure suits. (I'm assuming that the astronauts will do an EVA transfer to the crew module from an SSTO after SSTOs have fueled the crew module.) This brings the crew vehicle mass to 44.1 MT.

We're now down to a 50 MT HLV and regular SSTO service.

Now, let's look at bringing the mission weight up a bit.

I'm assuming H2/O2 chemical thrust with an Isp of 450. NTR would help but lets do worst case scenario for now. (BTW, Mars Direct doesn't subject the crew to 0-g, it has provisions for a rotating tether system to maintain artificial gravity. And to address the issue of reusability, a lot of the Mars Direct stuff is reused in terms of remaining on the surface for potential reuse by later crews.) Let's also assume that the crew to MArs transfer time is 180 days. Any shorter either requires massive fuel expenditures and a very unfavorable Hohmann return trajectory or some more direct route that requires extremely high Isp engines to be practical.

Let's Assume we've got a 100 ton to LEO booster like the Shuttle variants. How much can we land on Mars?

For the cargo module, the dry craft is 100 MT, we need to bring up 31.6 MT of supplies, we end up with an unfuelled mass of 131.6 MT. You'll need to supply 209 MT of fuel via SSTO to the craft bringing the total mass up to 340.62 MT. Assuning the same mass fraction to the Martian surface, we can land 69.74 MT of stuff on Mars. The increase in the surface mass is 2.44 to 1 with a 100 MT to LEO HLV vs the original 140 MT to LEO.

For the crew module, you need 6.78 MT of supplies and 210.60 MT of fuel giving a total mass of 317.38 MT. Your surface mass goes up to 56.59 MT for a total increase of 2.25 to 1.

The problem now is that we've got huge numbers of SSTO flight to get all the fuel up to the spacecraft. Even if they can get cargo to LEO at $500/kg, you're looking at $100 million just to fuel up one of the modules.

I can't think of any ways to make the crew modules less expensive aside from going to NTR or NEP drives. Perhaps VASMIR will come to our rescue but let's not wait on it.

Let's assume that the crew module remains as above and we can expect the total bill to be $500 milion to $1billion per crew module. How can we shave costs for the cargo modules?

I have some ideas.

For one, an a electrotether system can basically provide solar-powered reactionless propulsion to boost an orbit. Based off of a study by Tethers Unlimited, I made a rough design I posted elsewhere here. Such a system could boost 140 tons of cargo to a near-escape orbit in about 4 months. The tether itself would not be trivial, weighing about 70 MT itself and using 384 kW of solar power. I suspect the development and deployment of this tether would run $1-2 billion but it would quickly pay for itself. The tether basically lets you go from LEO to L1 for free.

From L1, you can go to Mars on a 0-energy trajectory. The orbital mechanics are complicated so I don't know the total travel time but I assume it's something like 1-1.5 years. The total approach speed to Mars is low so minimal aerobraking is needed. We need about 0.5 km/s of delta V to get to the surface. Assuming the same sort of mass fractions, our Earth to Mars cargo capacity is still 69.74 MT but we now only need to ferry up 31.63 MT of supplies and 9.3 MT of fuel. That can be done in 4 SSTO flights rather than the previous 25.

If we plan on using an NTR, we can significantly bring the crew capsule fuel requirements down to 76.9 MT from 210.6 MT. Cargo with NTR alone can manage to get the fuel down to 80.3 from 209.0 MT. However, we can do better with the tether propulsion as long as we're not in a hurry. Given the high cost and political difficulties of NTR drives, minimizing their use is probably a good idea.

So, the final rough plan:

Crew modules - use a 100 MT to LEO booster, 9 SSTO flights provide fuel, water and oxygen and the crew. NTR is used to get to Mars in 180 days and the NTR drive goes on a Hohmann return trajectory to Earth for reuse. Total mass to Martian surface = 56.6 MT.

Cargo - slow cargo uses an tether system and slow mars approach. 100 MT to LEO booster and 4 SSTO flights to fuel up. Standard chemical bosters are used. Total transit time = ~ 2 years. Martian surface mass = 69.74 MT.

Cargo - fast cargo for time sensitive material or emergency resupply uses NTR like the crew capsule but a 270 day Mars transit instead. 100 MT to LEO booster and 11 SSTO flights. Martian surface mass = 69.74 MT.

SBird · 2004-03-24 02:36:32

I'll go with GCNRevenger on the monoatomic hydrogen. Great performance but if it heats up past a few degrees above absolute 0, it explodes. The handling difficulties alone are monumental. It also strikes me as being VERY expensive to manufacture.

dicktice · 2004-03-24 09:33:40

SBird: Forgive me for dredging up your appealing digression regarding the Saturn V, expecially since you are going to so much trouble to upgrade Zubrin's estimates.
You wrote: "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."
To me, this shows you have an appreciation for past lost opportunities which drives you, as well as the same frustation I'm feeling right now. The whole thing could have been accomplished so much easier then, before all of the security considerations we have to contend with now--quite aside form the engineering technicalities. Just for fun, imagine how a landing on Mars in the 1980's, and a successful return (or even an unsuccessful return) could have influenced World Affairs today--especially with the discovery of water as an incidental consequence of being there in person--not to mention life, of course, which is still problematical.

Gennaro · 2004-03-24 09:37:25

The great thing with New Mars is that you encounter a lot of people with original and ingenious ideas. I get impressed everyday.

About the plan. The good things I see is that it:

1) Prompts the development of SSTO, which later will be there, demonstrated and ready, for different applications.

2) It more than doubles the mass to Mars surface of Mars Direct. Wow!

The bad things I can see are:

1) It prompts the development of SSTO, which will drain resources, costs and make the entire architecture more complicated.

2) It uses different systems to pull the Transhab and the ERV, which will add to complexity along similar lines as above.

Two considerations: First, the transit times for the unmanned cargo/ERV package and the Transhab package are obviously dissimilar. Is there not a basic sense in having both of these on a 180 day Hohmann trajectory cruise, in order to ensure the rythm of the extended series of missions that Mars Direct entails? To make Mars Direct into a seamless process, organically covering the switch from the exploration phase to the base building phase, there will be a large number of principally identical missions, first to several sites around the planet, then to the decided base building site.
Second: You propose the NTR stage (if used) be circled back to Earth and reused. How's that compatible with using the final stage as a counterweight to the tethered artificial grav system? Will not the NTR stage be identical to the final burnt out counterweight stage (which in the Zubrin's plan is simply dumped)?

This was my take on what's needed to be done with Mars Direct before I read your suggestions:

Develop the gravity tether system and test it full scale in orbit, before settling on exact mission parameters. We need it so let's design it and have it demonstrated.

It would be nice to have a NTR upper stage. Make it a simple NERVA derivative design. I'm sure it will be good enough to fill in eventual blanks in the tight all chemical structure. Remember that Zubrin suggested a 140 tonne Saturn V rocket outline simply as a very conservative baseline. Adding a NTR would be a simple and logical improvement to the plan that the good Dr himself foresaw.

Bill White · 2004-03-24 09:44:48

I agree entirely that the Mars Direct architecture is just cutting too many things too close to the bone for comfort. I'd stick with a 4-6 person crew but try and get the Mars transfer mass to at least double what Zubrin talks about.

SSTO is marvelous, of course, but it doesnt exist yet, right?

If the mass budget is too tight, are there cheap and dirty solutions? I am thinking dollars and cents not engineering elegance.

For example, $50 million would buy two Progress supply missions from Kouru, correct? Launch MarsDirect via Ares, circularize the orbit then dock with two Progress and offload food, water and other heavy bulk supplies. Save the Ares mass budget for things Progess cannot carry.

Kistler or ATV or Falcon works also.

Adding $50 million to the MarsDirect financial budget hardly seems like a deal breaker. But then for double the mass you might need two Ares launches, joined in LEO.

GCNRevenger · 2004-03-24 10:36:55

Ummm the Progress cargo capsule simply can't haul that much mass. You would need alot of them, a whole lot, and they take a while to make. A single production DC-X could launch 260 tons per year... I have strong doubts that the little Progress vehicle could move this amount of mass. Each Progress can move about 2-4MT of payload total. Even doubling this figure by using a cryogenic upper stage, I doubt you can launch them fast enough to match a light SSTO RLV.

ATV is severely limited by the low flight rate of the Ariane-V booster rocket, talk is only launching one or two per year to the ISS as a substitute to Shuttle for basic flight supplies and reboosting.

Kistler... doesn't exsist. And it might never exsist.

SBird · 2004-03-24 12:15:23

Dicktice:
It's too bad we don't have the capability to make Saturn V's anymore. They weren't the most effficient vehicle but they worked well and carried huge payloads. OTOH, a Saturn V clone made now would probably have considerably better performance with improved materials.
I try not to think of al the missed opportunities in our history - the loss of the library of Alexandria, the sacking of Baghdad by the Mongols, etc. I just try to remember how much humanity has changed in the last 300 years towards treasuring knowledge and technology as a species and it doesn't bother me quite as much.

Gennaro:
I agree - the SSTO makes me nervous. The potential payoff is huge but the fact remains that the closest thing we've had to an SSTO, the DC-X just hovered a couple of times. It's one thing to hover, it's another to get to LEO and back.
As for the differing mission profiles for the cargo and crew, NTR could be used for both to begin with to start. The 180/270 day crew/cargo transit times are directly from Zubrin's original plan which I think are fairly sound. Once we're established on Mars and we can start moving cargo on a more relaxed schedule, we can start working on a tether scheme. For example, you could move entire bulldozers and backhoes to Mars this way. Time is not essential here and you want the overall cost to be as low as possible on these sorts of purely cargo missions.
As for the gravity generating tether, it still works. Basically, the Mars Direct plan uses a free return trajectory that comes back to Earth if it doesn't enter Mars orbit. You just cut the tether and seperate from the NTR stage before having the crew/cargo do an orbit entry burn. The crew/cargo goes to Mars, the NTR sails home for reuse. (Of course, this has the problem of a nuclear reactor flying up to earth at high speeds. It might be politically untennable - there's probably no way to make an entire reactor core reentry-proof.)
Finally, NTR does appear to be the way to go. Without it, we have to move stupid amounts of mass to LEO via SSTO. With chemical thrust, and 2 10-MT SSTO's operating at 20 flights a year apiece, it would take 6 months to fuel up each module. With NTR, that value drops by over half to about 3 months per module.

Bill and GCNR:
There's no good disposable SSTO alternative. Even looking at Space X's projected Falcon V specs, it would take 23 launches and the cost would be $276 million per module just for fuel transfer. If SSTO can hit $500 per kg, that value drops down to ~$150 million which is much more acceptable.

SBird · 2004-03-24 12:20:31

PS: the Falcon V figures are for an NTR drive module. I don't even want to look at what a chemical staged module would be like.

Gennaro · 2004-03-24 16:06:25

The 180/270 day crew/cargo transit times are directly from Zubrin's original plan which I think are fairly sound.

Is it? In The Case of Mars, p.4 it says quite clearly that "the ERV reaches Mars after a six-month trip" (=180 days).
But it doesn't matter since my entire objection was borne out of flawed logic anyway. If the transit for the ERV's would take longer, you only need to blast them off in a more rapid succession.
Jeez, I must have been awfully tired last night.

SBird · 2004-03-24 17:23:08

Wierd, it must be a typo, the figures for transit time and cargo capacities later in the book clearly show that the ERV would have a 270 day transit to Mars. However, the way that the ERVs and crew modules are staggered (the ERV going up a full 2 years before the first crew module), this isn't a problem.

Gennaro · 2004-03-24 21:13:20

Well, you're absolutely right. It's just me not having read the book in a while. The reason for the 250 day journey of the ERV apart from pushing more payload mass, is obviously related to the fact that aero-braking is made easier at a minimum departure velocity (3.34 km/s), while on the other hand the optional return to Earth if the mission has to be aborted is cut from 3 to 2 years if using the 5.08 km/s departure velocity for a conjunction transit of 180 days.
In other words the 180 day journey is good for the crew in both in order to get to Mars and in case of an abort, but is had at a certain increase of risk in terms of succesful Mars aero-entry.

Moreover, it's the ERV transit times (and in situ fuel operation) which sets the mission sequence to two years for every new Transhab, not the other way around.

Note: in my book the transit for the ERV is 250 days, not 270 days.

Bill White · 2004-03-24 22:31:59

Well, shall we have a go at the XCOR guys testimony?

NASA can position itself to grow with the private sector very simply – by buying space transportation services available on the open market. That is a simple rule with profound implications – for I mean that NASA should use commercial providers as its sole means of transportation to Earth orbit. That means that if they cannot find a commercial provider for a given launch capability, THEY MUST DO WITHOUT IT. Off-the-shelf transportation settled the New World, explored the American West, and built the Antarctic stations. Surely, it can carry us into the future. Almost every bridge and building in the world was built with parts that come on trucks in 25 ton pieces. The Space Station is built from 25ton pieces. The South Pole station is built from 20 ton pieces that fit into an airplane. We can go to the Moon and Mars this way.
And if we are going to go, we have no choice but to do it this way. NASA will never see the limitless budgets of the Apollo program – we must work within the budget we have. The inescapable truth is that current funding will not support both a NASA-unique launch vehicle and a series of payloads to put on top of it. While estimates vary, it is clear that sustaining a NASA-unique launch vehicle has a cost of several billion dollars per year; that is not affordable. That is not surprising; Delta-IV and Atlas-V take at least a billion dollars per year to sustain – but vehicles already on the market can spread their costs over many customers – which NASA cannot do. A simple economic analysis shows that a new NASA-unique vehicle would never pay for itself in launch costs – even if that vehicle were on schedule and on budget. The recent history of NASA suggests it will be neither.
Existing Delta IV launcher capable of lifting 25 tons to orbit
If NASA buys launch services on the commercial market, they will also be able to continue the program during future budget rises and falls. Once you launch on commercial vehicles, you buy more or fewer launches depending on your budget. We need never find ourselves in the position we now have with ISS, where the failure of the transportation system imperils the enterprise. By using only launch capabilities available from multiple providers, we get a sustainable program, which can rise and fall with budget cycles, and keep flying regardless of vehicle failures. Coincidentally, Delta-IV, Atlas-5, and Ariane 5 all have similar payload capacity, roughly 25 tons, so this is not a difficult choice. And in the case of Delta and Atlas, they were designed for launch rates more than adequate to support an exploration mission.

Link: [http://www.xcor.com/jeff-aldridge-full.html]http://www.xcor.com/jeff-aldridge-full.html

= = =

PS - - Today, the Russians are cheapest, correct?

Does he mean private sector, just not the Russians? How free market is that?

GCNRevenger · 2004-03-24 22:54:21

Okay time for some poking of holes... Its not very efficent to build ocean-going ships out of bundles of lumber and big dinghies when you are already at sea.

Forcing Nasa to do without a launch mode that is required is not a reasonable thing, space travel is hard enough as it is, and "they must do without it" is a recipie for disaster, fiscally and engineering wise.

Furthremore, there is not now nor was there ever "off the shelf" operational hardware capable of doing what Nasa needs to do for exploration. Saturn-V and Shuttle are/were speciality vehicles, and no other hardware in the world can deliver a large mass to orbit - either through a single throw or multiple rendevous. And to be frank, the ISS as a project has been a monumental disaster considering its supposed mission and costs both monetary and human.

Dishing out more blows... What customers? There aren't any NGO customers for HLV type rockets. There aren't any even enough NGO customers for Delta-IV Medium rockets. When's the last time you heard of a NGO Atlas-V launch? The government will be paying for the flights one way or the other, let the government use a better rocket.

It is also quite questionable if the Delta-IV HLV can sustain the launch rate required for extended and nontrivial exploration work, Ariane-V not being able to launch often at all, and its questionable if an Atlas-V HLV will be built since the USAF has the Delta-IV already. The tripple-barrel Atlas-V is already scrapped... Oh and Angara won't be able to provide launch services from Plestek in Russia either due to orbital inclination.

Building a SDV-HLLV will not be as big a task as making a new rocket alltogether, we already have Pad 39/VAB, we already have the SRBs and their infrastructure, we already have Michoud for the ET, already got LH2 engines... thats half the thing right there, infrastructure and all. Though I will admit that its a valid question if its operational costs can be held low enough.

Gennaro · 2004-03-25 09:15:53

Right! If government is the sole customer, you don't need private enterprise, they'll only end up making things ridiculously more expensive than need be (profit maximising, see).
Free market competition doesn't work in a small, high investment sector. The companies will merge or set up functional trusts in no time.

This is true in America, Europe and everywhere else. And if state operations are inherently inefficient, how come NASA in the 60's could accomplish magnitudes more with about the same amount of dollars real value?

Also consider this. Just say you wanted a real space station. It means heavy launchers (in fact, I'd like to blast up the entire centre structure in one Orion or NSWR launch). If you want something specific done, form a small group of committed experts on a state budget and they'll deliver for you. If nothing else because at last they're able to do what they really want.

For a space agency on Earth, cutting pork barrel is key and in space it's socialism, strange as it may sound in respect to accepted wisdom down here.
A high degree of planned economy in space is the solution to the Gordian knot of eggs and chickens. You'll only have to maintain a free market as an outlet for your merchandise, not for producing it.

dicktice · 2004-03-27 18:01:34

I'm still hung up on the re-entry problem of ablative coating avoidance, for liftbody crew-return vehicles. Here's a variation on my theme of 90-degree angle of attack initial braking: The vehicle undocks from the ISS, deploys a tether downwards to de-orbit, while maintaining a nose-up attitude with the underside facing the direction of orbital rotation. As the height decreases, atmospheric drag heats up the undersurfaces which comprise a water jacket, producing high pressure steam which is jetted downwards to modulate the rate of descent into the atmosphere. Eventually, as geostationary atmospheric velocity is approached, nose-over to aerodynamic lift producing angle of attack enables powerless flyback to a conventional landing.

GCNRevenger · 2004-03-27 21:30:14

Why would a lift body need an ablative coating? It has a much higher surface area per-mass than Shuttle does, it could get away with an all-metal shield. The X-33? Its heat shield was going to be made from steel.

Water also is pretty heavy for a given phase transition and gas heating, too heavy most likly. I'm not thrilled with any kind of active cooling reentry mechanism in general... if somthing goes wrong and coolant leaks, your goose is cooked.

Also much more fond of using conventional rockets for deorbiting. Tethers would probably be pretty slow, they are quite unprove in this role, and a deorbit burn requires only a small Delta-V anyway.

dicktice · 2004-03-28 09:27:40

Wonderful! to get a reply to my off-the-wall suggestion. My responses to GCNR's points:
Re. ablative coating, IF such was required, a water jacket might be the way to prevent hotspots from developing leading to possible melting.
Re. water used for preventing overheating (sans ablative coatings) might be in the form of surplus condensates and (ugh) urine at first, and later when surplus H2O in the form of consumables via Progress shipments.
Re. something going wrong, I thought the built-in relationship between superheating vs. steamjet thrust tendency to modulate re-entry rate rather clever (ahem)--something like dihedral used by airplane designers to provide hands-off roll stability--as a fail-safe feature.
Re. cooked goose, I prefer to ignore that unfortunate expression in this context.
Re. tethered de-orbiting used as a default mechanism, just in case, to avoid being stranded in case the deorbit burn fails. Maybe the scheme represents the ultimate stripped-down lifeboat means of excape. After all, the main reason stated for limiting ISS crew numbers is "lack of lifeboat capacity."

GCNRevenger · 2004-03-28 11:35:07

There shouldn't be any serious hot spots except the leading edges, since the vehicle will have a pretty uniform shape on the underside. The leading edges can be shielded with improved X-37 carbon surfaces since the thing wouldn't have foam to fall off from above and hit it.

The trouble with using water is, as stated, thats its really heavy for a given amount of cooling power. The thrust produced, given the extreme amount of inertia that the vehicle would have, is pretty small too. I don't like relying on it... if it freezes in shadow, it will expand and possibly crack the heat shield. If it gets in the sun, it might boil off before you want to come back down, etc.

Sorry for the avian euphimism of mistrust in the system

Deorbit engines are pretty reliable, the Shuttle's OMS engines are extremely simple and have proven 100% reliable over the years. Tethers on the other hand, have not been tried once as an orbital maneuvering system, and it would have to be a pretty big tether to get out of orbit quickly. If you want a backup deorbit system, pack a small X-38 style solid rocket booster.

SBird · 2004-03-28 14:40:47

I'll have to agree about the tether deorbit idea. Tethers look like a great idea for satellites where mass and volume is at a premium but you're not in any particular hurry to deorbit. The projected deorbit time for the Terminator Tether ™ system from Tethers Unlimited is on the order of weeks to months for a standard satellites.

John Creighton · 2004-03-28 16:08:34

NASA successfully tested the scram jet at Mach 7. It is only a matter of time before: military fighters can go to the moon, flights from Canada to Australia only take 1 and a half hours and people start flying to space hotels. The world is changing.

GCNRevenger · 2004-03-28 22:34:36

We're still a ways off from the holy grail, the X-30 NASP. Right now, it would still be too heavy and would get too hot to reach orbit, but they're working on it. The technology is today capable of making a hypersonic bomber like the USAF wants, but needs to top Mach 20 to make a practical spaceplane.

Technologies that need to be developed or refined:
~Scramjets themselves need to be made that can handle near-orbital velocities and still provide useful thrust. We're only half way there.
~Must develop hydrogen slush fuel technology; finely devided solid hydrogen in liquid hydrogen is about 25% denser than regular LH2.
~Must develop active cooling for the hull, running fuel through it to keep it cool and preheat the fuel itself for combustion.
~Must develop high-temperature ceramics which are more durable than current day ones and able to handle reentry.
~Should develop dual-mode turbine/rocket engines for takeoff and orbital insertion burns.

etc etc... these things are possible and will eventually be practical, but they aren't today and probably won't be soon.

SBird · 2004-03-28 22:37:57

A scramjet isn't the end-all-be-all of spaceflight. It does help a lot, though. From what I've read, the Isp of a scramjet is close to 1000. While that's great, you have to deal with a fairly heavy scranjet not to mention the turbofans/ramjets that get you up to mach 4/5 where the scramjet takes over. Also, there's no guarantee that a scramjet can take you all the way to mach 25. If not, you've still got to have rocket engines. All of that eats up your LEO weight allowance so that you're lofting space jet rather than cargo. For example the Shuttle is a 100 ton to LEO booster that spends 80 tons of that lofting a kind of crappy space plane. A scramjet powered plane will do better but the same sort of problem is still inherent.

The scramjet will eventually change LEO boosters but it's probably going to be at least a decade or two and the difference will be evolutionary rather than revolutionary.

GCNRevenger · 2004-03-28 23:17:16

The Isp i've seen quoted for the Mach 25 version is in the 1,500 region... I think that barring a space elevator, they ARE the zenith technology for spaceflight for this century.

Nasa actually is way ahead of you, they are working (well, were working) on an turbine engine that can be switched to "rocket mode" and have LOX pumped into it, saving the need for a seperate rocket engine for orbital insertion.

The same "dead weight" issue also applies to conventional multistage rockets somewhat, though it is less a factor. With a Scramjet airplane's massively efficent engine then this problem is not quite as severe as you might think.

The Scramjet is the future ultimatly in my opinion, and will eventually replace all but the heaviest and lightest of launchers, it will just take a while for it to achieve maturity.

Rxke · 2004-03-29 00:30:54

The Scramjet is the future ultimatly in my opinion, and will eventually replace all but the heaviest and lightest of launchers, it will just take a while for it to achieve maturity.

And yet NASA is to scrap the project. Isn't that ... I thought the major part of NASA's 'duties' was in particular to do just such kind of developement? I can imagine the Chinese will be very glad: "Thank you NASA for showing us it's feasible, and has a huge potential... now we can start thinking to build prototypes ourself, otherwise we wouldn't have bothered!"

I know: the military will continue the tests, but will that give non-military people advantages?

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