Power Limits of Advanced Propulsion

C M Edwards · 2002-05-10 11:59:15

A review of various proposals for advanced propulsion systems quickly reveals a disturbing common characteristic. Although many of these systems appear promising for interplanetary transportation, few or none can even lift their own weight in the surface gravity of Earth or Mars, and most couldn?t even get off of the surface of the moon. This is because, although these advanced propulsion systems are capable of providing far more energy than traditional chemical rockets, they seem incapable of the same level of power output. Getting from Earth orbit to Pluto requires a lot of energy, but the rate at which the power is supplied is ultimately irrelevant. Getting from Earth?s surface to Earth orbit requires a great deal of power as well as energy.

Advanced propulsion systems just don?t seem to have it. Nuclear thermal rockets (the only contender with chemical rockets ? in terms of thrust -- that ever actually had engines on the test stand) must operate close to their melting points to exceed the performance of chemical engines. This gives them a much slimmer safety margin than conventional nuclear power plants, and, given the consequences of a melt-down, that makes them simply too dangerous. I fear even the much touted nuclear fusion rocket (if we should ever get one) is unlikely to be able to both sustain a fusion reaction and provide enough thrust to lift itself at the same time.

Does that leave us stuck with chemical rockets forever? Are there any alternatives for Earth launch?

CME

Canth · 2002-05-10 18:11:17

Nuclear pulse propultion is one. You basically blow up small (very small) nuclear bombs behind your craft which can be fission, fusion or a combination (fission used to make fusion). The only one with acceptable non pollution limits for in atmospheric use is a pure fusion bomb. This is hard but not impossible to make. The actual sanity of this scheme has been tested by several different groups. Look it up under project orion and/or daedelus (don't know if I spelled it right).
Another option is beaming power to a rocket from the ground. You can send microwaves or light waves to a spacecraft and it can use them to power a propulsion system of some kind. You can hit a craft quite accurately with such a system. One system like this under testing uses lasers from the star wars failed missle defense system to bounce off a mirror aboard the craft. The mirror reflects the light to a point behind it superheating the air there and causing an explosion which pushes the craft upwards. These type of systems don't require the craft to lift its fuel (at least for much of the flight) and thus they are very cheap and effecient.
There are many other endeavors for advanced propulsion. I suggest checking out This site which talks about many of the ones nasa is working on.

Phobos · 2002-05-10 19:37:08

The thing to remember with these low power rockets like ion drives is that they build up speed over a long span of time and not all at once like conventional chemical rockets. Sure ion drives or solar sails are hardly going to send you off at the speed of light instantly, but over time they have a cumulative effect in space being that there is no drag there.

Mark S · 2002-05-11 19:16:55

Yes, ion and plasma rockets have very low levels of thrust, but high thrust is not essential for thier mode of operation. Most of them work for propulsion away from earth and into deep space. It does not need to exert a force strong enough to fight the earth's gravity. As for nuclear thermal rockets, I do not share in your concerns about their safety. I feel that a lot of the guesswork in building a safe NTR was taken out by the Kiwi/Nerva program of the 1960's, and new research will make them a viable and safe form of propulsion.

RobS · 2002-05-11 22:47:11

Air breathing chemical launch systems hold out a huge potential for making launches cheaper. A launch from the Earth's surface to low earth orbit requires 8 or 9 times as much fuel as payload (structure plus cargo). Hydrogen-oxygen rockets are usually about 5/6 oxygen and 1/6 hydrogen (that includes extra hydrogen to lower the molecular weight of the exhaust and increase its velocity). The big problem is that after you get to 5,000 mph or so, it takes more energy to slow the air in order to use it to burn the fuel than you get back. Hypersonic burning of fuel is theoretically possible and will probably be developed in the next few decades. Once it comes along, the weight of launch vehicles could be cut to maybe a quarter of what they are now; maybe even less. Once the technology becomes mature, low earth orbit should be reachable for $100 per kilo or less. It's a matter of time and a lot of research and development funding.

-- RobS

C M Edwards · 2002-05-12 08:57:17

Hello All.

First, I must point out that I am uninterested in advanced propulsion systems that are incapable of lifting themselves. They have a place, but that place is in outer space, and I'm only interested in getting to orbit. Thus, my main concern is thrust and raw power. (Insert big Tim Allen grunt here. )

The NERVA research does indeed look promising, and could, conceivably, work just fine. It certainly produces sufficient thrust to compete with conventional chemical rockets. But I fear they are pushing too close to their safety margins. Nothing new there -- most rocket engines do that. But if a nuclear thermal rocket has a catastrophic failure, more can fall off than just the engine bell. Still, a nuclear thermal rocket is not _supposed_ to leak.

Nuclear fission pulse rockets, however, _are_ supposed to leak. Everything I'm leary of nuclear thermal rockets because there's even a slight risk they might do, nuclear fission pulse rockets do as an integral part of their operation. I could stand some convincing about NERVA. But if anyone ever proposed using a nuclear Orion system for Earth launches, you would find me among the protestors chained to the launch pad.

Rockets with pulsed operation -- a la Orion -- look promising as long as there's no fission product exhaust. A chemical pulse rocket engine could readily exceed the average thrust of a conventional chemical engine. However, I suspect it would need it, because I know of no reason they would get better specific impulse that a conventional chemical engine employing the same propellant. One might as well just employ a conventional engine unless you had to move an exceptionally large payload, like, say, a building on the NASA campus.

Fusion, theoretically, could give us a lot of power to play with. Unfortunately, to the best of my knowledge, an adequate fusion drive does not exist, even on a drawing board. (I ignore all otherwise detailed plans with large blank boxes labelled "insert fusion drive here". )

Air-breathing systems are a good bet, as are balloons. If nothing else, they can give you a lot of potential energy of position. But jets have low ISP, so some of the advantage they get from abandoning oxidizer is eaten up by the extra fuel they need.

A version of the Lightcraft looks promising, though remotely powered craft using masers will suffer from the inverse square law in a big way. Any remotely powered system will require huge dedicated power plants, probably in excess of 100MW capacity for a liftoff weight of just 1T. That sounds like a lot of power plant for a little bit of lightcraft, but mobile diesel generator sets of that size do exist.

Any form of electric/laser/non-chemical propulsion suffers from similar power requirements. And most 100MW powerplants are not lightweight. However, it is conceivable that one could be built at a fraction of the mass of a typical municipal power plant, provided some pretty severe constraints were placed on its operation. A 100MW powerplant able to fit inside a 1T craft (or a 1000MW powerplant in a 10T craft) could provide the power to lift itself into space. Then it would have to be rebuilt.

So, ultimately, if you want to get off of the planet, it comes down to: Conventional Chemical, NERVA, Rockoons and air-breathers (i.e., _reliable_ conventional chemical), remote beam power, and some fervent mutterings about tethers and nuclear fusion.

That about sums it up for advanced propulsion off of the planet.

CME

Canth · 2002-05-12 17:26:01

I would also chain myself to an orion style launch pad, if it produced the bi-products of a fission weapon. However one using laser heated pulsed fusion bombs are feasable. You can make a short fusion burst if you whack a dueterium pellet with powerful lasers from several sides. This really isn't that high tech and is much more plausable and do-able than a lot of propulsion methods. This is not as controlled or high tech as a controlled plasma fusion reactor, and thus it is much easier. We don't even demand it produce more power than it consumes, an onboard nuclear reactor could probobly cover the difference. Any way it produces little to no radioactive waste and it is extremely high powered, it just requires time, talent, money, and not to much protester interference.

Tom Jolly · 2002-05-12 22:40:25

I rather like Myrabo's Lightcraft, partly because he's actually tested a model of it and proves it works, and evidently started his own company based on the research he did at Rensellear (sp?) Institute. Myrabo and Ing's book the Future of Flight goes into a lot of leading-edge propulsion concepts, is good reading, and has an awesome Bibliography on just about everything (including laser-blasting of nuclear pellets). A second book that's also very interesting is Robert Forward's Indistinguishable from Magic (aka Future Magic). He talks about an awful lot of unique propulsion systems, including oddities like magnetically riding a stream of iron pellets that are being continuously shot up into the air from a mag-rail, caught and reused on their way down. Equally bizarre is the slingatron concept (big, expensive, and the g's would kill you, but a nifty idea). However, despite how nifty all the ideas might be, one of the only guys that's doing hardware in the field is Myrabo, for now. Space Studies Institute did a lot of research on the mag-rail gun concept (they didn't call it that), but I haven't heard that anything has come of that.

C M Edwards · 2002-05-13 11:19:45

A laser primed fusion engine running on beamed power offers little thrust advantage over the typical lightcraft scheme.

If a laser-primed fusion engine does not achieve breakeven (produce more power than is required to keep it running in the first place), then the best it can do in terms of efficiency is less than double what you would expect of a lightcraft using the same power input, and its power output can be treated in the same way. That?s assuming it didn?t actually require ten times the power input of a lightcraft for the same thrust, which is a distinct possibility. Plus, what size are the required engines likely to be, even with remote beamed power? If it weighs too much more than a lightcraft, it may not be able to lift itself.

Without breakeven and self-sustained fusion to give an advantage over any other form of beamed power, one would do just as well to forgo fusion and build a larger lightcraft with a bigger ground station. Now, fusion does yield higher exhaust velocities, which allow smaller mass ratios. However, you could just make a lightcraft run hotter for the same power and get nearly the same advantage. Without breakeven, fusion requires greater complexity without yielding any dramatic improvement in performance.

If you don?t have breakeven with beamed power, all you?re doing is running a hotter lightcraft.

Now, if a fusion engine with power plant could be self-contained aboard the craft and still lift itself, that would confer operational flexibility, making it worthwhile even if it couldn?t achieve breakeven. It?s also important to note that any beamed power engines become more complex past a certain range of operating temperatures, because then you?re dealing with plasma exhausts.

CME

Mark S · 2002-05-14 14:05:06

Lars, what is your source on the "Chernobyl levels of radiation at every launch" if we went ahead with nuclear thermal rockets? I find it hard to believe that a small (100,000 pound thrust) nuclear thermal rocket would be equivalent to the worst peacetime nuclear disaster in history. No matter how much radiation is released by an NTR, it will all happen either high in the earth's atmosphere or in orbit, above the atmosphere.

Nuclear thermal rockets were the first non-chemical rockets, but politics have prevented us from using them. I don't want to see mankind fail to achieve its destiny in space because we are afraid of nuclear power. If NERVA continued through the 1960's, it is possible that humans would have been to Mars by 1986. Right now, the Bush administration and NASA's chief administrator both support applications of nuclear power in space. Let's seize the opportunity and venture to Mars before this window of opportunity closes.

Mark S · 2002-05-15 10:24:38

I was thinking about an argument that was made against NTR's, namely that they run much hotter than commercial reactors so they can get the highest possible ISp. I then looked in NASA's report for the 1998 Design Reference Mission. It turns out that the NTR proposed for the mission would run at an incredible 3100 K ! In order to do so, the reactor would use a tri-carbide material that would resist the extreme temperature. This type of reactor had been tested during the Russian NTR program and had run successfully for over an hour before the test was halted.

C M Edwards · 2002-05-15 11:57:37

Hello Lars.

I concur that various schemes using chemical power offer the most promise of any alternative, on or off the drawing board, although I haven?t said so explicitly until now. Thanks for drawing me out.

I suspect that insisting on a single ?point? to this discussion would stifle it a bit. But here?s an important one to consider.

The thrust provided by a rocket engine is F = m? v.e, where m? is the rocket?s reaction mass (in kg/s) and v.e is its exhaust velocity. So, to increase the thrust of a rocket engine, you can either increase its reaction mass or increase its exhaust velocity. However, the kinetic power of the rocket exhaust is P = ? m? v.e^2. This means P/F = ? v.e. So, if a rocket has twice the ISP of another rocket engine using the same reaction mass, that rocket has half the thrust or less. Thus, an advanced propulsion system, such as NERVA, that expects to operate at double the ISP of conventional chemical systems but still produce the same thrust must either double its rate of propellant use or double the rate at which it can put thermal power into the propellant.

All rockets labor under the same rule. What?s more, the loss of performance becomes nearly insurmountable beyond some upper limit of ISP. I suspect this upper limit is around 10 km/s, or just over double what can be done today with chemical rockets. All of the best contenders to replace them ? NERVA, lightcraft, etc. ? operate below this threshold.

Fusion rockets and nuclear Orion-style concepts, with their exhaust velocities of 250000m/s or more, may be a possible exception, but only because the incredible energy available to them allows them to put out the kind of power that they would need just to compete. Perhaps they cannot, even so.

What this means is that there is a strong possibility that we have, _today_, the strongest heavy lift rocket engines that mankind will see for the next hundred years.

CME

PS. NERVA's too darn hot only if you run it at the kind of temperatures required to push the 10km/s threshold. If you were to try it at a lower exhaust velocity, the temperature range would be a lot closer to safe.

RobS · 2002-05-15 23:07:40

Most of the articles I have read about nuclear thermal engines propose to use them from low earth orbit up, not for launch to earth orbit. Most people are assuming that chemical engines will be used for the foreseeable future to get things to low earth orbit.

Another nuclear engine worth remembering is the gaseous core nuclear engine. Apparently the uranium or plutonium fuel is maintained as a gas inside the engine and is separated from the hydrogen propellant by keeping the former inside a spinning vortex. There are computer simulations indicating gaseous core engines are possible, but no one has built one yet. The Isp, if I remember right, is 2,000 to 3,000 seconds; in other words, 40,000 to 60,000 mph. Now THAT'S fast! I don't know what thrusts are contemplated, but nuclear engines are capable of fairly high thrusts compared to other engines because of the compact nature of the energy source and the fact we are using heat, not electricity (and thus are able to use the entire power output of the engine).

I have seen articles about these engines on the web, but I don't remember where.

-- RobS

C M Edwards · 2002-05-17 14:30:19

What is the largest cargo a modern jet aircraft can carry to higher than 20km (65000ft)? It seems to me, if you were going to make a small RLV, it would be wise to start with a size that would could lift today.

CME

Canth · 2002-05-18 11:38:16

Robert Zubrin of Mars Society fame was involved in designing a vehicle which used jet power to get a payload to space. The vehicle took off like a plane with some fuel (for wieght reasons) and then was fueled by a tanker in mid air. The jet then accelerated to maximum speed and at it's peak altitude released a rocket which got the payload to space. It was a really facinating concept, I beleive he talked about it in entering space. Speed is more important that lifting capacity, if you need to you can fuel it once it has taken off like Zubrin proposed, but if it can only go as fast as a 747 it actually isn't much use. Speed is more important than altitude, that is why launch sites aren't high in the mountains. Starting a rocket 2 miles up at only three hundred miles an hour reduces the distance it still has to go and the additional speed it needs by less than a percent. The problem with going into orbit is simply reaching the necisary speed to continue circling the earth, the speed needed to go up a hundred miles looks relativly small in comparison to the speed needed to maintain that altitude. Look at how much more power the Atlas which carried John Glenn into orbit had than the Redstone which put Alan Shepard up a hundred miles. It just isn't worth using a jet plane if you can't reach sevral times the speed of sound, and a 747 won't. I beleived Zubrins vehicle used modifeid F-16 engines, like six or eight of them.

Tom Jolly · 2002-05-19 09:56:57

Response to CM;
You said;

?The thrust provided by a rocket engine is F = m? v.e, where m? is the rocket?s reaction mass (in kg/s) and v.e is its exhaust velocity. So, to increase the thrust of a rocket engine, you can either increase its reaction mass or increase its exhaust velocity. However, the kinetic power of the rocket exhaust is P = ? m? v.e^2. This means P/F = ? v.e. So, if a rocket has twice the ISP of another rocket engine using the same reaction mass, that rocket has half the thrust or less. Thus, an advanced propulsion system, such as NERVA, that expects to operate at double the ISP of conventional chemical systems but still produce the same thrust must either double its rate of propellant use or double the rate at which it can put thermal power into the propellant.?

It seems to me, just using F=m?v.e, that if you double the Isp with the same mass-flow rate, you double the thrust, since F is thrust, not P/F. The interpretation of P/F = 1/2 v.e can be better understood as P= 1/2 Fv.e, which according to my Sutton means the POWER TRANSMITTED TO THE VEHICLE (Sutton actually uses P = Fv.e, dropping the 1/2, which we argued about extensively in class years ago). The Power transmitted to the vehicle is actually a function of the square of the exhaust velocity, which makes sense, since you?re increasing the kinetic energy of the vehicle with respect to Earth.

Response to Canth; While orbital speed is somewhere in the neighborhood of 7.5 kps, total delta-V for a launch is about 9.1 kps to get there. This is due to two factors; atmospheric drag,
and the fact you have to lift your vehicle vertically out of the atmosphere, which doesn't contribute at all to your orbital vector. Thanks to mass ratio, you're using far more fuel-mass in that initial 2 miles than you use in the next 4 miles (too lazy to do calcs right now), since you are lifting all that propellant. I'm guessing that 300 mph at 2 miles altitude contributes quite a lot more than 1%, probably closer to 10%.
Tom

Canth · 2002-05-19 11:38:01

Your right, I think. However the more effecient your engine the less good altitude does for you.

C M Edwards · 2002-05-19 15:36:21

Hello Tom and Canth.

Tom, you wrote, discussing my earlier equations:

"It seems to me, just using F=m?v.e, that if you double the Isp with the same mass-flow rate, you double the thrust, since F is thrust, not P/F."

In this case, variable F represents thrust and variable P represents power. Thus, the ratio P/F represents Power devided by Thrust. I'm sorry if I did not make that clear. The ratio, however, is independent of the mass-flow rate.

As you point out, doubling the mass-flow rate doubles the power. However, it also doubles the amount of power required. (It has to. P/F = constant if v.e = constant.) Now, chemical rockets do this readily. Doubling the mass-flow rate in a chemical rocket _is_ doubling the power by definition. That's where their power comes from. On the other hand, a thermal rocket or some other design that requires an outside power source (solar panels, a nuclear reactor, etc.) suffers from increasing the mass flow rate because it has no inherent extra power to put in with it. Doubling the mass-flow requires doubling the power source. Otherwise, the exhaust velocity drops.

So, an ion rocket with an ISP of 25500s needs 60 times more power per Newton of thrust than a nuclear thermal rocket with a 410s ISP. Increasing the mass-flow rate won't change that.

Canth, it occurs to me that if a jet aircraft can't lift more than a certain amount, aerial refueling would have similar mass limits. The maximum amount a jet aircraft can keep airborne is pretty much the same regardless of when the weight gets added. I also suspect Zubrin's old Black Horse idea would decrease reliability compared to a straight shot. Launch from altitude does save a little energy and the Black Horse/Pioneer system allows for smaller tanks, so there is some advantage to it. I just don't know if it's enough to make it competitive with a fully fuelled launcher towed to altitude.

CME

Tom Jolly · 2002-05-19 22:17:53

All that is true, and I didn't realize you were speaking only of rocket systems requiring an external source of power, such as nuclear. Still, this statement confuses me; "So, if a rocket has twice the ISP of another rocket engine using the same reaction mass, that rocket has half the thrust or less." I assume when you say "reaction mass" you mean the mass-flow rate through the nozzle, and by ISP you mean thrust force divided by mass flow rate, i.e., seconds, as it's usually defined in rocket design texts. Regardless of what the energy source is, this would imply that 2xISP with the same mass flow rate will give you twice the thrust.

Forgive me for harping on this, but this point bugs me.

C M Edwards · 2002-05-20 10:17:31

(* My previous message -- about how I'm always right about everything in the universe -- has been moved to a more appropriate forum. *)

Actually, Tom, the statement "If a rocket has twice the ISP of another rocket engine using the same reaction mass, that rocket has half the thrust or less" simplifies to

v.1 = 2 * v.2

m'.1 = m'.2

m'.1 * v.1 = 1/2 m'.2 * v.2

= 1/4 m'.1 * v.1

which is a false statement.

Oops!

CME

PS: I still stand by the rest of my rant... I think.

???

John_Frazer · 2002-06-25 13:44:39

> Getting from Earth?s surface to Earth orbit requires
a great deal of power as well as energy.
>...
> Does that leave us stuck with chemical rockets
forever? Are there any alternatives for Earth launch?

Lightcraft are one. Up to the old ideas for flocks of 2 ton pods to a given LEO spot every 90 minutes or so. With a little bit of rocketry to circularize, they'd be a wonder.
Further advancement is offered by tethers.
They'd make a great upper stage either for a payload tossed up by something like a rocketplane or laser-thermal, or to lift the entire craft to LEO, as in the Hypersonic Skyhook. (Neither of these options is to be mistaken for the magic Beanstalk or synchronous skyhook. Momentum exchange and the

space elevator

are obtainable with today's materials.)

Frankly, I'm not too dismayed to be stuck with chemical rockets.

With only limited advances, we could revolutionise space access -if we revolutionise our book-keeping and procuring practices: Do NOT buy parts through government graft & contractor lobbying. Day-to-day space access should be privatised, and we'd see a marked decrease in cost.

If the Mars Society gets a mission going, then they'd provide this: Opening production lines and procurement practises for business and private interests without paying government overhead would be one of the greatest gifts the Mars Society could give to humankind!

To nuts & bolts, we all know about the Ares.

The Shuttle-C
is even more near-term, because the ET is unchanged; the only change is to toss the orbiter over to the side of a hangar somewhere. Next, get rid of the roman candles, in favor of

liquid strap-ons.

The Shuttle Orbiter isn't very good for crew launch anyway (it's manifestly unsuited for heavy lifting) Use Soyuz, or evolve to using something like the old HL-
http://www.astronautix.com/craft/hl20.htm]20
http://www.astronautix.com/craft/hl42.htm]42

Notice that one of Grumman/orbital Sciences' proposals for the new NASA SLI is this older spaceplane. (Scroll down to the N-G/OSI section).

Costs would drop, but safety & assured crewed access to space are paramount. (One of my problems with the Mars Direct is launching the crews on top of the booster, without even the Shuttle's unlikely possibility for escape.)

For another idea, there's the old Truax Sea Dragon proposal. 500+tons to LEO in one shot, cheaper than a Shuttle by far.
Just to show that re-usability isn't necessarily the way to lower costs.

Of Course, it would be nice to have an airplane you step into, it rolls down the runway, and takes you to orbit. (The old dream...) The Devil is in the details, of course.
Airbreathing is about the only way, which for now means jets of some sort. Eventually, they'll learn to make SCramjets, which will help, but for now, it's multiple engines for different regimes of flight.
Work on something like the Russian tripropellant rocket engines would be a step in the right direction, too.

For the true spaceplane, we almost need nuclear thermal for the upper stage portions of flight -where rockets would kick in. It may someday be possible to make a NTR airbreather (and make it safe enough that there wouldn't be hysterical fears of a "Chernobyl-like disaster"), but that's way out there.
For that matter, O2 afterburner NTRs would help, too. Increase the thrust, at the expense of some loss of EV, exhaust temperature, and ISP for the O2 being thrown out. Does that change the outlook for NTR spaceplanes?

John_Frazer · 2002-06-26 13:33:05

(C M Edwards @ May 12 2002)

Nuclear fission pulse rockets, however, _are_ supposed to leak. Everything I'm leary of nuclear thermal rockets because there's even a slight risk they might do, nuclear fission pulse rockets do as an integral part of their operation.

Pretty much correct. NPR was designed to get around the materials limitations on NTR, posed by the melting point of the engine's structure. No effort is made to continually confine the plasma of a nuclear pulse engine, thus much more of the energy of nuclear fuels can be used. At this, only a tiny fraction is actually used. The horrendous efficiency can be excused by the fact that they're using nuclear fuel in the most energetic way possible -a runaway chain reaction blast.

I could stand some convincing about NERVA. But if anyone ever proposed using a nuclear Orion system for Earth launches, you would find me among the protestors chained to the launch pad.

Briefly exciting, but they won't find much of you -or the launch pad!

Let's look at this: What are the problems with it?

They figured that their full interplanetary exploration program (not just one ~10,000 ton ship launch, but several) would add a few percent to what we were already adding to the atmosphere with weapons testing.
Still, we don't want to do even this.

Somebody mentioned fusion only. We've got to convince the DOD to declassify some of their new R&D for such things. If we could guarantee that there are no long-lived isotopes -or short lived but highly radioactive ones which may be worse-, would it be such a problem? Launch from an expendable floating platform at sea, where there's no surface dust, and we've got thousands of tons to orbit in one shot.

Another option is the "second generation" Orion: what they designed for an upper stage for a Saturn S1-C booster.

Freeman Dyson is reported to have felt that this restriction lost much of Orion's appeal -the Saturn booster would have been over 50% of the cost. (Now this probably meant the currently selling government graft system costs for the chemical rockets, versus the cheaper, reasonable, zero-graft costs for the Orion stage.)

Nevertheless, This puts 500 tons into LEO. If cleaner bursts can be made for the lower portions of the flight, where some exhaust products (a few grams maybe?) might enter the atmosphere, then we've got a tremendous lift capability for each Energia or Shuttle derived launch stack.
There is arguably nothing else we can design -even today- that's as near-term, and any where near as capable as Orion.

This single-HLV mission was for an 8 person crew, with a 6 week trajectory! ~45% of the mass in LEO is cargo bound for the destination!

This capability removes every major stumbling block on the way to Mars, or indeed the rest of the solar system.
Long duration spaceflight dangers will be a thing of the past.

If you can't accept the possibility of making clean bombs, or even the acceptabillity of such zero-impact launches politically (if possible), then there's always the hard way. 5-6 Ares or Energia launches does it.

Most "traditional" Mars missions call for some hundreds of tons in LEO. The difference is that with this one, the cargo is the bulk of it, while with chemicals, 90% is fuel.

Send the Pu pits for the pulse units (bombs) up in a separate launch, with tremendous care taken to preserve & protect the Pu in case of a launch accident. This is as much to satisfy people against the preachers of fear of such nonsense as "vaporising the Pu and spreading billions of doses of cancer across the entire planet", as it is to safegard the valuable resource. If the booster malfunctions, the Pu itself is preserved as well as a crew would be!

(the propellant to be vaporised by the blast and directed at the ship's pusher plate is ~90% of the mass of the pulse units. This makes for maybe ~20 tons of Pu itself)

Another idea is the Truax Sea Dragon: the entire 500 tons ship into LEO in one shot. Use ED tethers or something to lift the apogee above the Van Allen belts before the NPR engine is fired.

Long term, Nuclear pulse is arguably the solution for interplanetary travel. If inertial confinement-type fusion engines can be made, then fine, but we know that there's U in asteroids. Any metal mine on an NEA will uncover it, and we know that there must be planetary masses of asteroids out there. Industry in space will allow for huge rapid travel ships (The bigger you make Orion, the better).

Weeks to Mars or the asteroids, months to Jupiter and its moons & trojans, with robust, comfortable & safe ships and massive cargoes.

10 meter upper stage module for S-1-C launch
http://www.astronautix.com/graphics/o/orisatv1.gif]

configured as Mars expedition
http://www.astronautix.com/graphics/o/orimars2.gif]

Launch profile

http://www.astronautix.com/graphics/o/orisatv2.gif]

Visited by moderator 2022/02/02

New Mars Forums

Announcement

#1 2002-05-10 11:59:15

Re: Power Limits of Advanced Propulsion

#2 2002-05-10 18:11:17

Re: Power Limits of Advanced Propulsion

#3 2002-05-10 19:37:08

Re: Power Limits of Advanced Propulsion

#4 2002-05-11 19:16:55

Re: Power Limits of Advanced Propulsion

#5 2002-05-11 22:47:11

Re: Power Limits of Advanced Propulsion

#6 2002-05-12 08:57:17

Re: Power Limits of Advanced Propulsion

#7 2002-05-12 17:26:01

Re: Power Limits of Advanced Propulsion

#8 2002-05-12 22:40:25

Re: Power Limits of Advanced Propulsion

#9 2002-05-13 11:19:45

Re: Power Limits of Advanced Propulsion

#10 2002-05-14 14:05:06

Re: Power Limits of Advanced Propulsion

#11 2002-05-15 10:24:38

Re: Power Limits of Advanced Propulsion

#12 2002-05-15 11:57:37

Re: Power Limits of Advanced Propulsion

#13 2002-05-15 23:07:40

Re: Power Limits of Advanced Propulsion

#14 2002-05-17 14:30:19

Re: Power Limits of Advanced Propulsion

#15 2002-05-18 11:38:16

Re: Power Limits of Advanced Propulsion

#16 2002-05-19 09:56:57

Re: Power Limits of Advanced Propulsion

#17 2002-05-19 11:38:01

Re: Power Limits of Advanced Propulsion

#18 2002-05-19 15:36:21

Re: Power Limits of Advanced Propulsion

#19 2002-05-19 22:17:53

Re: Power Limits of Advanced Propulsion

#20 2002-05-20 10:17:31

Re: Power Limits of Advanced Propulsion

#21 2002-06-25 13:44:39

Re: Power Limits of Advanced Propulsion

#22 2002-06-26 13:33:05

Re: Power Limits of Advanced Propulsion

Board footer