Earth to LEO - discuss

SBird · 2004-03-12 03:10:00

There seems to be quite a bit of innovation going on lately with regards to interplanetary drive systems. However, it seems as if the ground to LEO launch systems are still purely chemical in nature. I wanted to start up a discussion about whether we're at the point where we can start talking about alternatives to chemical propulsion in the next 20 years to get cargo to LEO.

If possible, I'd like to try and actually crunch numbers. It's easy to wave hands and talk about how such and such launch technology will make getting to LEO so cheap that everyone will move up there because of the lower housing prices up there but another thing entirely to actually prove it.

Aside from chemical propulsion, I see the following as potential alternatives/augmentations:

space elevator
rail/maglev assisted launch
air-breathing engines for 1st stage
Nuclear thermal rockets
laser/microwave assisted launches

Have I missed any?

Adrian · 2004-03-12 04:39:15

Your list seems pretty comprehensive. However, while nuclear thermal rockets have a great ISP and are very powerful, I find it totally inconceivable that they would ever get the political go-ahead - and with just cause, given the possibility of radioactive exhaust and other saftey risks.

GCNRevenger · 2004-03-12 09:51:11

I think that a nuclear engine would be possible as an upper stage to a conventional rocket, where the fine dispersion of any trace radionucleides would be pretty harmless. Such an engine was considerd as the next step to making a Saturn-V rocket varient powerful enough to go to Mars or launch 200 ton payloads, were actually ground tested in the 1960's, and when made of modern ultra-high-temp ceramics should not produce a massive fallout plume.

Chemical propulsion isn't that bad, the trouble is having to lug along the propellant mass. One solution to this is to use the oxygen in the atmosphere to reduce propellant carriage, as with the X-30 NASP with its SCRAMJET engine. The NASP could reach perhaps as high as Mach 20 today and Mach 25 tomorrow at the edge of space using light hydrogen fuel and not lift a single gram of liquid oxygen.

Even when you do have to carry along the oxidizer for the chemical engines, modern high-ISP engines aren't that bad if you can keep the vehicle mass down. The DC-X rocket's production form for instance could have become a true SSTO vehicle with its liquid hydrogen engines and still carry 10-15 tons to LEO in a perfect world, though I have my doubts if this mass fraction could be achieved.

One possibility to combine the two strategies is to combine the fuel efficency of an advanced conventional turbine (jet) engine to get DC-X off the ground and up to Mach 6 at altitude, then kick in the LOX fueled rockets for the rest of the acent and deorbit. You still couldn't carry a very large payload, but you could carry one pretty often.

Edit: Oh and then of course you could build a "Shuttle-Z" SDV of some sort, basicly Shuttle but without the orbiter, which could perhaps lift 120 tons to orbit and carry very large (size) payloads, but cost estimates vary from $250-750M per flight counting development. Combine the Shuttle main tank with the new Five-Segment heavy boosters, two Boeing RS-68 engines on the base of the tank, and an upper stage powerd by clusterd RL-10's or the new RL-60 for the final push to orbit.

SBird · 2004-03-12 12:40:11

Thanks for the input. I deliberately didn't comment about what I thought about the practicality of the various technologies since I didn't want to bias the discussion from the start.

I agree that chemical still seems to be the way to go.

NTR rockets are nice but the overall performance gain isn't THAT spectacular and the danger of radionucleotide release is significant. What most people forget to mention about the 60's NERVA tests is that all but the last two tests had significant amounts of engine breakup and radioactives release. When I mean radioactives release, I mean chunks of Uranium oxides flying out of the back of the rocket - seriously. Even with newer ceramics, I seriously doubt the ability of an engine to reliably maintain integrity with the hign temperatures, thermal gradient induced thermal shock, vibrations and action of high temperature hydrogen. As for high altitide release, I'm almost more comfortable about doing it near the ground where the radioactivity may be more concentrated but at least it's localized.

The whole space elevator business is a potential cool idea but relies upon the fact that we can actually build the damn thing. Having worked with carbon nanotubes before, I am dubious about the chances of this happening.

Air breathing engines do help, especially ones that can operate hypersonically. However, that only gives you a discount on oxidizer for the first 100,000 feet or so. I suppose that if you try to maximize your acceleration in that part of the ascent, you might be able to eek some extra mileage out of the atmospheric O2 but you've still got to gain most of your delta V on your own oxidizer. Plus, now you've got to lug this engine around if you're going for an SSTO design.

Personally, SSTO designs are distasteful to me. The whole idea of a reusable spaceship just reminds me too much of the Shuttle. I'm afraid that we'll get another 'reusable' spacecraft that needs major reconstruction with every flight and is a disaster from a performance and safety standpoint.

The maglev rail system has the same flaws - you do cut down on fuel by getting that initial boost but it's really a small part of the total energy requirements to get to LEO. Every little bit helps, though.

Potentially, the microwave/laser assisted systems are very promising but I'm dubious about the ability to pump that much coherent energy through a laser. As it is, these giant, military megawatt lasers can send a spaceship the size of your hand to about 200 ft. I mean, I can do that with a slingshot. Lasers don't scale up very well so I think that lightcraft are going to be impractical. Using microwaves might work better as phased array microwave emitters do scale up fairly well and can have stupidly large power outputs. I have no idea what sort of progress is being made on this front, though.

I'm just wondering if it would be possible to run some rough numbers for the various advantages of these systems vs the investment costs of building the infrastructures involved. For example, if one were to build a maglev going up the side of Killiminjaro (sp?) that gets the rocket to mach 1 at 20,000 feet, kicks on some air-breathing engines that fall off at 100,000 geet and mach 6 before engaging an NTR upper stage, just how much performance increase would we see. Would it actually be enough to justify the investment in R&D and infrastructure for these technologies?

ERRORIST · 2004-03-12 12:47:14

Yes, you missed the pipeline to space.

SBird · 2004-03-12 13:42:43

No, your pipeline idea is a variant of the space elevator which is already on the list.

GCNRevenger · 2004-03-12 13:51:20

NTR engines for Nerva "blew up and stuff" because they meant to do it, they tested the engines all the way to the point of failure intentionally. Today's carbide ceramics can handle temperatures of 4000K or so, and I think would work just fine... as far as dispursion goes, a little tiny amount of radioactive dust spread over hundreds or thousands of miles is preferable to alot of spread in a small area. Small amounts of radiation just aren't dangerous, plenty has been spread around by nuclear testing... And doubling of the efficency of the engine is hardly what I would consider "not spectacular."

For a rocket, alot of the trouble of getting into space is just getting off the ground, where the turbine engines might hold some edge, and Nasa/et al have been playing around with hybrid engines (basicly turning the afterburner into a rocket with onboard LOX).

The really cool thing about the X-30 Scramjet airplane was that it could hit orbital velocities (or close to them) while flying around in the atmosphere using free oxygen, lightening the load geometricly. Though I concede that building a SSTO rocket like the DC-X would be simpler most likly.

Although the Shuttle fiasco is such a pain, the only way we are going to get off this rock as a species is with a single-piece ship of some sort. SSTO should be the ultimate goal of rocket design... DC-X came pretty close, modest payloads to orbit weekly, no boosters or gantry or whatnot required.

ERRORIST · 2004-03-12 14:07:55

Yea but I would not take a 1/100 risk of losing my life, and even less for the shuttle.

GCNRevenger · 2004-03-12 14:12:44

Flying in the Shuttle and flying in another craft aren't really comperable, because the Shuttle is the only manned spaceship ever that doesn't have an escape system. Sure you might lose the vehicle but that doesn't mean the crew is doomed.

Plus, the majority of cargo flights wouldn't have to be manned at all, computers are better than people at flying in space most of the time, and they are good enough to land on their own now, so the only issue left is docking that the Russians have nearly perfected.

dicktice · 2004-03-12 14:49:51

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

Bill White · 2004-03-12 14:57:25

The really cool thing about the X-30 Scramjet airplane was that it could hit orbital velocities (or close to them) while flying around in the atmosphere using free oxygen, lightening the load geometricly. Though I concede that building a SSTO rocket like the DC-X would be simpler most likly.
Although the Shuttle fiasco is such a pain, the only way we are going to get off this rock as a species is with a single-piece ship of some sort. SSTO should be the ultimate goal of rocket design... DC-X came pretty close, modest payloads to orbit weekly, no boosters or gantry or whatnot required.

Maglev to 0.9 Mach then scramjet or rocket then scramjet seems plausible to me. I recall NASA has looked at maglev as a starting point for launching a scramjet.

About the SSTO, I kinda see it the other way round. Find a really good (persuasive) reason to get off this rock and then people will be motivated to spend the money needed to build SSTO.

Chickens and eggs, again. . .

GCNRevenger · 2004-03-12 15:03:12

Ah but Bill, i'm not writing concerning the why, i'm writing concerning the how... the only way to get people off Earth in any number is with a rocket that you don't have to rebuild or reassemble every time you use it, like the DC-X.

Ah the DC-X, the rocket Nasa loved to hate... offering some possibility of upstaging Shuttle if a giant one could be built, "adopted" by the agency and killed after the one landing accident.

Bill White · 2004-03-12 15:08:27

Ah but Bill, i'm not writing concerning the why, i'm writing concerning the how... the only way to get people off Earth in any number is with a rocket that you don't have to rebuild or reassemble every time you use it, like the DC-X.
Ah the DC-X, the rocket Nasa loved to hate... offering some possibility of upstaging Shuttle if a giant one could be built, "adopted" by the agency and killed after the one landing accident.

I think we may agree on all this stuff more than it may sometimes appear. :;):

SBird · 2004-03-12 15:13:12

I am aware of the test to destruction they did with NERVA. (which incidentally sent a cloud of radioactive material right over LA) I'm referring to the routine testing. If you go through the testing logs, you see that the vast majority of the testruns showed major engine deterioration and fissilbe material coming out in the run. This is more than an enviromental issue, it implies that the engine is prone to failure.

Modern ceramics have gotten a bit better but not drastically so. The big issue is that ceramics are inherently brittle and do not fail gracefully. Since the material strength of a ceramic is largely determined by the microcracks and defects in the surcace, it is pretty much impossible to build a ceramic part that will fail reliably at a certain stress level. The uncertainty forces you to engineer with absurd safety margins. NTR's aren't impossible by any means but I am highly distrustful of them until we've managed to log at least several hundred hours of reliable operation from them.

The doubling of ISP is nothing to sneeze at but I think the question is just how much an actual decrease in actual launch cost you'll see. Remember that much of the launch cost is due to manpower costs. A standard rocket launch requires hundreds or thousands of people who tend to be expensive technicians and engineers. Personally, I'm not certain why this is the case. A commercial jet probably needs fewer than 20 people to complete a trip when you've averaged out all the air traffic controllers, baggage handlers and fuel truck operators. A rocket is much simpler than a plane - why can't you just have an automated launch system?

The Boeing SeaLaunch uses a conventional launcher but manages to get launch costs down tremendously by using a skeleton crew and a robust chemical launcher that is largely maintainance free.

The problem with SSTO and NERVA is that we're going to sink billions into the development costs with a minimal return off of what we're doing now. A modern chemical rocket gets something like 4-5% of it's mass to LEO. Most of the SSTO designs right now realistically get 0-1% of their mass to orbit. I don't know the figures for NERVA but I imagine that the mass fraction is more like 8-10%.

To get launch costs down, we can do two things two things.

1: make the system as trouble free as possible so that you need a minimal number of people. In this regard non-reusable rockets shine since you just throw away the parts. When you analyze the costs of the rocket, the raw materials cost is fairly low. The steel and H2/O2 aren't what make a launch cost so much - it's all the people on your payroll. What worries me about an SSTO is that you will have the same refurbishing problems the Shuttle does now. Heat protective tiles haven't improved substantially since the 70's unless you just use an ablative tile system which will have to be replaced with every trip. (this actually is probably much cheaper than the reusable tile system we use now) If each launch requires 3 months of 50 $200k a year technicians inspecting the spacecraft after every launch, you're spending $2.5 million a launch on your heat-resistant tiles alone.

This doesn't include engine refurbishing, frame inspection or any of the other stuff. IMO, our ability to create a reusable launcher system hasn't improved in a meaningful way since the 1970's. The engines might have improved a bit but the rest of the system is still about the same. The lack of an escape system isn't what bothers me about the Shuttle. The apollo capsules had an escape system but I seriously doubt that it would have done the astronauts any good if the Saturn V had blown up under them. My concern is that SSTO and reusable spacecraft have inherent reliability issues that outweigh any advantages gained from having a single stage.

Bringing the personnel costs down suggest that we use a simple design. Lifting bodies are difficult to manufacture and to make replacement parts for. The engineering costs go up enormously. Repair and maintainance become more difficult. The big metal tube design works well and and easy to manufacture.

Keep the engine design simple. Assuming that we can get NTR designs to work reliably, this is a big advantage - fewer moving parts.

2: Bring the mass fraction of cargo up higher. This is accomplished by higher ISP engines and NTRs are the best in this regard. A possibility here is the use of microwave powered flight. look here:
[http://monolith.caltech.edu/Papers/ParkinLauncher.pdf]http://monolith.caltech.edu/Papers/ParkinLauncher.pdf
It's basically a NERVA design that uses beamed microwaves instead of a nuclear reactor. The microwave beaming technology is already possible. I wouldn't want to have to pay the power bill though. :;):

Ultimately, though these high ISP technologies are fairly technologically complicated. They also tend to push materials science to the limit which is never a good idea. NTR's and microwave beaming require thermal performance and reliability that I, frankly, find unrealistic.

SSTO's have the same problem. In order to get your spacecraft weight to power rations good enough, your have to trim corners everywhere. This is a guarantee for an unsafe and unreliable vehicle. The mass fraction for an SSTO is pretty awful as well. Plus, any technology that you can use on an SSTO such as scramjets, lifting bodies, advanced propellants, etc can be used on a disposable multistage rocket with better overall performance and lower cost.

Personally, I favor the KISS approach the Russians have taken. Simple chemical rockets that are designed with ease of maintainance and high reliability instead of high performance like we tend to do.

GCNRevenger · 2004-03-12 15:30:39

Yeah and the Russian philosophy is what let us beat them to the Moon, even though they had a head start in manned rocket technology... without the introduction of liquid hydrogen, which Russia rejected that increased Isp's so dramaticly for the Saturn-V, Apollo wouldn't have happend.

And I don't think you give modern materials enough credit... the tile problem has already been essentially solved, we can make big bolt-on pizza box size tiles out of various materials which can handle 2,000K+, which is essentially all the surface area of a lift body.

The use of composits over aluminum and even titanium has also substantially reduced the total vehicle mass, making a SSTO rocket like the DC-X a real current-tech possibility... and it, by the way, was also designed so that a small crew with minimum heavy equipment could launch the rocket weekly. The test demonstrator actually built was able to turn around in twenty four hours... the production model would haul about ten or twelve tons using 1990's technology, or room for 6-8 people in a crewed varient... it can't haul huge amounts, but its within a good stones' throw of Shuttle payload masses.

Cheap to develop no, but you get the entire rocket back for the price of fuel and maintenance, and that can add up... Shuttle was never really intended to be a fly-weekly machine, and before it no engines were ever reused... as it has been said, Shuttle was an experimental and not an operational vehicle. Today, we're better at building rocket engines than we used to be, with a little help from Russia I imagine, should be able to build a cryogenic engine (no soot!) that is sufficently reliable.

SBird · 2004-03-12 16:38:35

I would counter that the Russsian approach is why they beat us to orbit and to manned space flight and came distressingly close to beating us to the moon despite our enormous technological and engineering workforce head start and the fact that half of our country hadn't been bombed into rubble just a few years earlier. The N-1(?) design was a poor one and crippled their space program. However, aside from that blunder, we didn't surpass their space program until Apollo 8. Also, bugetary constraints and the death of the head of the Russian space program (forget his name right now) also contributed to the decline of the Soviet space program. Despite the loss of the moon, Russia went on to do some truly amazing work on Venus including the design of landers that could operate almost indefinately on the surface.

The Zenit launchers that Boeing uses for SeaLaunch are a perfect example of that philosophy. They can be stored, fueled on their sides for transport and are just moronically simple. I contrast that to the Arianne which IIRC has never had a successful launch with the new first stage. What gets me is that almost all of the rocket failures these days are due to software glitches. Why do you need a million lines of code to point a gimbal mount? We got to the moon with computers that would get the lunch money stolen from them by my watch. The additional performance and capability given by all that software probably gives a minimal impact on the performance and has cost hundreds of millions due to lost reliability.

NASA has been a bit too tech happy for the last few decades. If you read that microwave launcher proposal, there's a diagram of payload mass fractions for various different launchers. Despite having an isp only ~75% of what modern launchers have, the Saturn V managed to deliver a payload mass fraction to orbit that was greater than what either the Titan or Shuttle can do. An earth to LEO launcher needs to do one thing - get mass to orbit as cheaply as possible. Reusability, efficiency, materials, and all that stuff are secondary to that objective.

I don't give modern materials credit precisely because I'm a materials engineer. The shuttle reentry tiles went through a massive development program. (some of which occurred in my department way back when) They were supposed to work fine but have been nothing but problematic in use. Therefore, I look at these grandiose claims of new materials and I take them with a BIG grain of salt. There is areason that commercial airliners took 20 years to start using composite materials widely. It's not because Boeing and Airbus are afraid of new ideas. It's because composite materials come with severe reliability problems. For a Rutan design where you aren't looking at tens of thousands of loading cycles and getting your mass to cargo ratio good as possible, composites weren't a problem. For Boeing, it took a MASSIVE effort to get the stuff working properly.

Yes, the Shuttle was an experimental craft but it was designed to have a short turnaround time. When I see things like estimates of the DC-X having a 24-hour turnaround, I get VERY dubious. When we actually have a full-scale prototype that actually demonstrates that level of reliability, I'll believe it.

Incidentally, the DC-X is pretty close to the sort of approach I've been talking about. No fancy lifting bodies, fairly non-revolutionary engines, no untried scramjets - just an ugly, squat cylinder that yoyos to space and back. Personally, I'd like to see an estimate of the DC-X performance with a breakaway 1st stage. Something made to be as cheap as possible and disposable. I'd bet that you'd be able to get a significant performance increase. As long as the disposable stage is fairly simple, it would probably lower the overall operational cost. If the first stage is a a simple SRB, ther shouldn't be any reason that is should cost more than $1 million.

Any time you use a part that's reusable, it means that you had to design it much more robustly so that it retains top operational performance even after a full launch cycle. You have to then go through an extensive examination process to look for things like cracks and corrosion and fatigue. In composite materials, this is much more difficult and prone to missing dangerous flaws. The end result is heavier and ultimately less reliable that a disposable part.

Here, you have to start doing cost benefit analysis. If the cost of the disposable part exceeds the cost of inspection and occasional component replacement in the reusable part, then reusable is the way to go. Otherwise, just trash the part. Things like crew cabins and avionics and reentry systems are probably good examples of stuff that could be reused. A metal can with solid rocket fuel in it is a good candidate for something that can just get tossed away.

Strict SSTO design is just like Mars In-situ propellant generation before Zubrin changed it. They were so fixed upon living completely off the land that they concluded that it was impractical. Zubrin simply decided to relax the rules and bring the hydrogen along. The result is a practical design.

If you are willing to drop the requirement for pure SSTO, I think that you will find that you can get much better performance for minimal additional cost. That additional performance would have originally come from a larger, heavier design that, despite reusability, would have incurred higher maintainacne costs dues to the greater stresses on the materials involved. My guess is the cost of a disposable stage is much less in the long run.

Lars_J · 2004-03-12 17:25:19

Yes, the KISS (keep it simple stupid) rule is certainly one rule that ought to be followed more frequenctly in aerospace. Here are my general thoughts:

Capsule vs. Lifting body - I'd pick a capsule every time. Just build a capsule that is simple, robust, and perhaps even refurbishable. (expendable ablative heatshield)

HTOHL (Aerospike) vs. VTOVL (rocket) - VTOVL all the way. Somtimes the brute force method is the simplest and cheapest.

SSTO vs. TSTO - One day we will (hopefully) have economical SSTO's, but I'd prefer not to wait for cheap space access until then. We'll have to work incrementally towards that goal.

-------------

I'm definately paying close attention to the progress of [http://www.spacex.com]Space-X. The seem to be making some good progress, and hopefully we'll see a launch soon.

GCNRevenger · 2004-03-12 18:35:42

I suppose it matters alot about the flight rate and the cargo... if you are shooting satelites then TSTO would probably be okay, but i'm thinking more along the lines of the "post/late Bush initiative" world, with hopefully twice or thrice monthly flights I would have to say "no" to TSTO. That upper stage is still on the expensive side (the good ol' RL-10 engine runs about $3M a pop) and that it adds sufficent complexity that it would cut into the efficency advantage of SSTO flight... and it would be another set of engines and control systems to lug.

Trouble with TSTO on the DC-X style rocket, that its center of mass is arranged such that the payload has to go in the middle of the rocket, and its a little on the cramped side, i'm not sure a second stage will fit.

It did take a big effort to get carbon/polymer composits to be flight-reliable, but now they are, and its practical to build rockets like the DC-X or with high-temp metal alloys make airplanes out of them.

The DC-X demonstrator did indeed fly twice in two days, same vehicle and engines... the nice thing about LH2 fuel for reuseability is no residue in the engines, just purge with dry gas after use if need be, and the DC-X's engines are theoreticly rated for multiple firings even though they are designed as disposeables.

I think that its possible to pull off a "Soyuz-sized" DC-X VTOL rocket today or a Scramjet+Rocket light spaceplane of similar payload in the near future, and Nasa was trying to save its precious Golden Goose by axing the DC-X.

dicktice · 2004-03-13 09:26:11

Once the solid rocket boosters are out of the picture. . . .

SBird · 2004-03-15 16:26:59

I can see how the center of mass might be a problem. However, the solid booster stage I was thinking of was something along the lines of looking like a flat tuna can on the bottom of the DC-X. Alternately, I suppose that you could strap a set of SRBs to the outside of a DC-X so that the denter of gravity is minimally disturbed.

The advantages to solid rocket boosters is the extremely low failure rate and low cost of manufacture. The more complex reusable rocket engines would be in the DC-X upper stage. Basically, you throw away an empty metal can when you jettison the 1st stage.

The primary disadvantages to the solid rocket booster is that the geometry involved would require multiple engines. This adds the danger that there will be a thrust differential that would send the rocket off course. However, given that 6 SRBs are used in the Delta IV which has the highest success rate of any booster in history, this is probably a moot concern.

However, regardless of TSTO or SSTO, I'm more interested in hammering out just how adventageous it is to employ the sort of low level boosting schemes that have been mentioned. For example, just how much of an advantage do you have by setting up a maglev train booster?

I'm personally dubious about the maglev booster since it can realistically only achieve about mach 1 and imparts mostly horizontal velocity rather than vertical velocity. Gaining horizontal velicoty that low in the atmosphere might even be counterproductive since it means fighting much more atmospheric drag. The only way I see this being advantageous is with some sort of scramjet boosted orbiter.

Yang Liwei Rocket · 2004-03-15 17:32:53

The Europeans have created an Ion drive system to be used in their next probes, they are now trying to enhance their ion thrusters, Ion Engines are very weak compared to rocket fuel but Ion thrusts are verry good, they have many advantages, such as needing less propellant, having greater payload capacity and being capable of much more precise spacecraft pointing. They deliver about ten times as much thrust per kilogram of propellant used than a chemical rocket, making them very 'fuel-efficient', and maybe could be used for cheaper long distance transport of minerals and materials in the future, Ion engine link here
[http://www.esa.int/export/esaSC/SEM3JQX … ing_0.html]http://www.esa.int/export/esaSC/SEM3JQX … ing_0.html
There is also Project Daedalus to send an robotic, nuclear-powered spacecraft to Barnard's Star, a very dim red
dwarf that may contain two Jupiter-class planets. Accelerating to 12-13 percent of light speed using a deuterium powered probe.
NASA spent lots of time doing the planning fopr a replacement rocket shaped X-33 was being developed NASA . It was to travel at 16 times the speed of sound and replace the older Space Shuttle. The funding was cut for NASA and military took over the projcets like Lockheed Martin, Russian and Chinese have looked at NASAs old project and might design an X33 of their own. After the recent space disaster NASA might re-open this old project.
Russians, European ESA, China and USAs NASA are all lokking at better ways to fly, cheaper fuel and increased power. Even if we could travel at 10% the speed of light it would take us almost 50 years to reach Alpha Centauri, and maybe another 50 to return home?
Using particle accelerators we have discovered many anti-matter and anti-energy particles in this giant atom smashing tunnels. One german Eugen Sanger had proposed its use for spacecraft propulsion because antimatter has the highest energy density of any material currently found on Earth. It could be used to push mankind to the near the light speed barrier. Under current proposals, the annihilation of matter with antimatter is 10 billion times more efficient than the oxygen-hydrogen combustion in the Space Shuttle's main engines, and about 100 times more than fission or fusion reactions. If we were to use this raw pure nati matter power we could have probes that reach pluto in a few hours, but instead today it takes us months sometimes years to go and travel and send robotic stuff to mars and other planets.
We have many great ideas for the future, I hope NASA can make something great like it has done in the past.

dicktice · 2004-03-15 21:01:15

SBird wrote: I'm personally dubious about the maglev booster since it can realistically only achieve about mach 1 and imparts mostly horizontal velocity rather than vertical velocity. Gaining horizontal velicoty that low in the atmosphere might even be counterproductive since it means fighting much more atmospheric drag. The only way I see this being advantageous is with some sort of scramjet boosted orbiter.
My reply: The strato-volcano mag-lev rail launching sled (which returns back down the mountain regeneratively on wheels) essentially replaces any Stage One requirement, braking near 20,000 feet altitude to automatically release tandem Stages Two and Three at Mach 0.9, in excess of 45-degrees above the horizon.

SBird · 2004-03-16 11:03:27

Re: ion engines:
There has been a tremendous amount of progress on ion drives lately. The new VASMIR design that NASA has been working on is similar to ion engines but has a number of significant advantages.

However, ion drives are useless for getting to LEO because of their low thrust. I was planning on starting a second thread about interplanetary drives once this one winds down.

Re: Maglev launcher:
When considering the maglev launcher, I made the following assumptions:
Maglev going up the side of Mt. Killimenjaro (sp) to the summit.
The maglev is capable of reaching a top velocity of mach 1.
The slope of the mountain is approximately 20 degrees.

While it is possible to cant the maglev tracks upward at the end to get a larger vertical launch angle. However, construction at high altitudes and upon ice fields is very technically challenging. I am very dubious about our ability to engineer such a large structure. (the final, curved portion of track would have to be large to avoid putting excessive G-forces upon the rocket or train.)

So, assuming mach 1 and a final launch angle of 30 degrees, I get the following numbers:
(simplifying mach 1 at that altitude to 700 mph)
Vertical velocity: 350 mph
Horizontal velocity: 606 mph
Total altitude 19,000 feet
At that altutude, atmospheric pressure is approximately 50% of sea level.

In contrast, the Saturn V 1st stage, IIRC, achieved something like Mach 5 and 200,000 feet before being depleted. This maglev partially replaces a 1st stage but only a portion of it, you will have to seriously beef up your 2nd and 3rd stages to compensate. Furthermore, even if you can get a final launch angle of 45 degrees (which I am highly dubious of) your total vertical and horizontal velocity components are something like 490 mph. That's about 312 m/s total velocity which is about 4% of the total velocity needed.

The horizontal and vertical components are both 220 m/s at that point. For a standard rocket, that 220 m/s of horizontal velocity is wasted. Really, a rocket should go vertical until it leaves the atmosphere and then start burning horizontally to get the necessary velocity now that it is free of atmospheric drag. The total vertical velocity component that we are looking at here is only 220 m/s which is only about 2.8% of the total velocity required. That assumes a 45 degree launch. If we go with a 30 degree launch, you velocity fraction drops to 1.6%. Plus, you now are fighting a lot of extra air drag because of your horizontal velocity component though the still rather dense air. The maglev will help to get additional payload but not by that much.

The only exception would be an X-33 type hypersonic lifting body. The problem here is that AFAIK, no one has ever demonstrated the operation of a full scale ram/scramjet in real world conditions. It would take years to get an operational vehicle working and we would have to deal with all the teething problems of new technology. Such a vehicle would probably not be terribly useful until at least the second iteration. For longterm space plans, this is a viable option but for something like a Mars Direct before 2020, I think that it is not a viable option.

GCNRevenger · 2004-03-16 13:32:36

The hypersonic airplane you are thinking of Sbird is the X-30 NASP, not the X-33 VentureStar subscale prototype, which was going to be an aerospike SSTO VTO-HL ship and probably the biggest of the "shuttle replacement" fiascos. The point about using the maglev with such a vehicle is to get it going fast enough for the Scramjet engine to kick in, which only works in supersonic flight regiemes.

On paper, such a craft could theoreticly take off horizontally either from the maglev or on conventional turbine engines from a runway and accelerate above Mach 20 and reach the edge of space, requiring little or no rocket power for the final push to LEO. Such a vehicle would be ideal, the proverbial Pan Am spaceliner seen in 2001 Space Odessy, but its still a little ways over the horizon. The Mach 15 hypersonic bomber the USAF wants is almost viable today though.

Ah yeah and about other engines...

Although the Europeans are just now starting to piddle around with small ion engines, Nasa is building giant ones that consume >10kW quantities of power and could reach fuel efficencies of 20 times that of conventional rockets.

VASIMR however is pretty esoteric... it would require megawatts of power to operate a large one efficently, which not even a nuclear system could dream of providing at the moment (vapor core reactions plus MHD generators may do it), and relies on the finicky and mysterious realm of plasma behavior to operate.

SBird · 2004-03-16 15:29:44

You're right, all those X-numbers start getting mixed up in my head after a while. I now vaugely recall something about the X-33 being started *before* the X-30 or something wierd like that.

I realize that you have to be going supersonic for a ram/scramjet to operate. However, maglev or not, you have to get that velocity somehow (rockets or standard turbofans) and in that case, the horizontal velocity component of a maglev launcher wouldn't be wasted as it would with a standard rocket.

I was just reading last night about seismograph readings of the Aurora planes being tracked at mach 6. Perhaps the DOD is further along with high speed aircraft than it is letting on? If so, stuff like the X-30 might be realistic on a shorter time frame.

I agree that VASMIR is still a ways out but it does have some promise. A multimegawatt reactor is theoretically possible. Normal nuclear generators on Earth are in the gigawatt+ range. Therefore, it is possible to think of a space nuclear reactor that operates in the 100 MW regime being possible. It would have to be lofted piecemeal on heavy boosters, though. Such a beast would have to be used in a reusable capacity, though. Sort of a high speed cargo interplanetary freight hauler.

In lieu of that, there's always standard ion engines. I was browsing a Boeing site (don't remember the URL now) that was talking about tests of the new next-gen ion engines. It didn't mention thrust but the engine mouth was 30 cm which gives womething like a 10-fold increase over what Deep Space 1 had for thrust, assuming no increase in thrust per emitter area. Also, the ISP is topping 8000 and the projected engine lifetime is something like 15,000 hours.

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