Thanks for posting the link. I've also been an active poster over at nasaspaceflight.com, Chris Bergin's show, and the "Newspace" issue gets batted back and forth all the time.

The issue of what is sometimes referred to as "NASA subsidies" is a double edged sword. There are those who want R&D money to complete a vehicle that may supply the Space Station on a contractual basis--thus providing a service that NASA might buy. However, they ask NASA for the R&D money--which strictly speaking isn't really appropriate. They should be seeking investors outside--but since the venture is so risky, nobody wants to front their own money. So almost all of these ventures start out with their own money--usually from the CEO who started the business in the first place.

Even if NASA chooses to buy services from a "contracted service provider" the other entrants will scream that this is an unfair government subsidy--which it is not. Sometimes NASA will even decide to look at its own launch vehicle--and then drop the concept. Meanwhile the millions it has spent on its own 'in house' R&D has so frustrated entrents that they collapse: this is essentially what killed the Kistler K-series vehicle, and Beale also got out of the launch business...

Sad, but true...

The economics of "Space Launch" is an extremely difficult thing to grasp. It involves all the usual things that a normal business must contend with (space rent on offices, labor cost, medical benefits, construction supplies, and utilities,) and then it has the additional problems associated technical preperation (building prototypes, bench testing, assembly testing, breaking things, analysizing data, fixing them, rebuilding things, and retesting them, over and over again.) I vividly remember a very telling, joking quote "The easiest way to make a small fortune in the space business is to start with a large one..." This is literally true! It may take a decade before a space venture even sees income let alone breaking even! And yet, this is what they are up against, and yet there are thoughs willing to try! I applaud them--it takes guts to invest personal fortunes in something that no sane investor would touch!

Yet a "buck" can be made out there--otherwise the big companies wouldn't have jumped in. The economic potential of satellites is growing every year--there is talk of it getting close to the $100 billion mark soon. Weather satellites, spot imagining or contractual "personal spy satellite' imagery, personal communication (sat phones) satellite, micro research satellites. For $5000 colleges can buy a "cube sat kit" and breadboard their own satellites! Due to the variety of global launch services available, the Russians offer a pretty "fair" price for launch services.

So while it is really tough to make a buck--especially if you're a "launch provider"--it can be done. And I personally like to see them try. Space travel is risky, and as long as we must rely on high performance chemical propulsion systems, or any reaction driven system for that matter, space travel will always be a risky endeavour. And space tourists will have to accept some of that risk if they want to try the ultimate vacation travel.




-- Edited by GoogleNaut at 16:49, 2007-06-15

The Earth to orbit problem is major. I've spent a lot of effort on this to basically discover (rediscover since the experts have been there before!) why this is so much trouble. If money is on object the current disposable boosters do the job and NASA is going back to that with the retirement of the space shuttle. I just can see the throwaway spacecraft as an economical solution. Of course reusable systems have to carry extra weight in order to be reusable, i.e. my many friendly arguments with Googlenaut. What would a current technology shuttle designed form scratch would be?

What about just making staged boosters be reusable? It would seem that first stages would be very feasible for this. The final stage would seem hopeless. Yet I'm told that this would not be cost-effective.
 
A single-stage to orbit vehicle such as the X-33 would be able to transport small payloads relative to total gross takeoff weight. But the 6 to 1 ratio just seems to be another from of impractical.

I've been favorable to scramjet type systems such as the NASP was going to be. In an LH2-LOX propellant the LOX is the really heavy part. If the first (or first and a half) stage equivalent used oxygen from the atmosphere the total propellant mass could be greatly reduced so that the final push to orbit would use a limited amount of LOX. We could save more weight by using a rocket sled or a maglev catapult to boost the system to several hundred miles per hour before on board power takes over. I think that this might have great promise. Of course flying scramjets have been limited to a few small prototypes that operated for a few seconds. I think this are could use some money (similar to my views on fusion).

Another version might be to take a vehicle somewhat like the X-33 (with a much more favorable mass to payload ratio) and launch it piggyback from a Mach 3 aircraft similar to the old B-70 bomber that would be specially designed for this mission.

One issue that has caused major maintenance cost for the space shuttle is the use of LH2 and the effect this has on fuel pumps, etc. What if we could use more conventional fuels like kerosene and LOX? System might be built to have less maintenance. Also, going back to Googlenaut basic points on the disadvantages to spaceplanes one of the results of using LH2 is the volume of take up by fuel tanks (and the high ratio of fuel to oxidizer). The could be solved by going back to kerosene and using more light weight materials to get a 3.7 GTOW to EW ratio. Use the old MUSTARD concept with two vehicle transferring fuel and one might have a spaceplane system that could provide a more economical transport to LEO.

I'm not very optimistic about using nuclear systems for Earth to LEO. Classic Orion (not the CEV) could be made to work but I can imagine that will be allowed. Maybe rouge Chinese government in the future might do that. Nuclear thermal on board usually doesnt have enough thrust to weight to work in that application. The Laser concept might work. It seems to have its on problems, i.e. keeping the laser focused through out the whole launch. I'm going to withhold my opinion on this one.

-- Edited by John at 16:12, 2007-06-16

Fusion on the other hand is also very interesting, but rather pointless to discuss without a demo plant running.
I wasn't suggesting that fusion had anything to do with Earth to LEO.  I was just saying research on scramjet was being under funded just like research on fusion.

I'm well away of the value of specific impluse.  But there are all sort of issues with using nuclear thermal propulsion in the atmosphere.  A lot of them are political.

I also heard something about airships using ion engines. Does anybody know anything about that?
Ion propulsion is a high Isp low thrust system that uses ionized xenon or cesium as a reaction mass and accelerates it electrostatically.  But since you mention "airships" perhaps you are referring to something else.

-- Edited by John at 07:02, 2007-06-17

Andrew wrote:

---

I also heard something about airships using ion engines. Does anybody know anything about that?

You heard right Andrew.
See JP Aerospace's ATO (Airship To Orbit) at http://www.newmars.com/wiki/index.php/Airship_to_Orbit

During the NERVA program there was some problems with radioactive material from the core being eroded away by the propellant flow.  I agree on the issue of hydrogen becoming radioactive by exposure to the neutron flux. 

The only problem I see is nuclear-hysteria.
That is a very real problem perhaps the most critical.  Some of these concerns would be real and most just hysteria.  The orginal NERVA system was going to be a 75,000 lb thrust stage that could replace the S-IVB stage on a Saturn V.  I just don't see enough gain to overcome all of the political problem that it would raise in the area of going to LEO. 

Another great thing about NTR is that you can use a variety of fuels, including water.
Water is interesting.  If you use hydrogen in a solid core nuclear thermal system you might be Isp of 900 sec.  When you substitute water you would get about 300 sec which is on the same level as kerosene-LOX or storable liquids plus you have the extra weight of the reactor and the shielding.  So you have to use LH2 or its really not worth it for assent to LEO.  I've here some arguments for use say on Mars using local CO2 (even worse Isp) but the propellant doesn't have to be shipped to Mars.

This way I tend to think of nuclear for LEO to the Moon or other planets.  It seem that nuclear-electric systems such as VASIMR or Ion would be the first applications.  Here the Isp is so great that its give enough advantage to be worth the political battle.

Where did you get the Isp of 300? For a NTR-solid system, it would be around 400, max. Higher if you use NGC-CC (Nuclear gas core - closed cycle). There is also the interesting advantage, is that if you can heat the water high enough, water will break down, giving you hydrogen.

There is also ammonia and methane. Methane tends to clog, but there is no such problem with ammonia that gives you the ISP of 500.

Not using liquid hydrogen saves you allot of costs, at the expense of mass.

Regarding reactors cores, the NERVA tests were done in the 50's and 60's. Since then, we discovered more materials and learned more about neutron radiation. I'm certain that the problem can be solved, even if you have to change the core between flights.

Where did you get the Isp of 300?
Basically starting with Isp = 900 sec for a solid core NTP system with H2. Given that you have the same amount of energy per particle at a given temperature and the atomic weight of H2O is 18 and H2 is 2 then the velocities will be the square root of the ratio of the masses.  So H2O will move at one third the velocity of H2.  Since the Isp is proportional to the exhaust velocity hence I get 300 sec for H2O.

What would you do with the NTR after it was done with the 'boost burn?' Is it jettisoned?

Depending upon the destination and the orbital alignment parameters, an NTR might be a good choice for transportation to and from near earth orbit comet cores...

An NTR using water as reaction mass has always interested me, especially if thousands of tons of reaction mass may be available on a comet or comet remanant. This could be the key to the Near Solar System.

The trouble with using an NTR style reactor as a main power reactor (as an auxiliary power unit) for electric propulsion is two fold:

1) the NTR-style reactor is designed more for short duration operations at very high thermal power (clost to 1000 MWt.) Trying to get the reactor to operate in a second mode can be done, but it is hard. Pratt and Whitney's TriTON (Tri-modal Thermal, Oxygen augmented, Nuclear) engine could generate about 20-40 KWe with an independent closed loop Brayton Cycle turboalternator which also acted to remove decay heat after primary thrust shut down. However, 20-40 KWe, as substantial as that is, is insignificant as far as electric propulsion goes. We need hundreds of kilowatts minimum, and a lot closer to hundreds of megawatts of electric power to run a substantial Nuclear Electric Propulsion system.

2) It is absolutely the heaviest of both options, because the NTR engine and reactor system must have additional coolant lines, power conversion steps, etc. There was a proposal to use an NTR engine directly with a movable plug that would block the nozzle throat and divert working fluid through a turboalternator. This is possible, however the force needed to get a good seal with little or no leaks is substantial, and may damage the liner of the nozzle throat. Also, because the movable plug would necessarily retract into the core, it is susceptible to prolonged neutron radiation exposure, which compounds any attempt to using anything by carbon as the sealing material--and RCC tends to be very brittle, so stress cracks are to be expected.

Gas core is an interesting possibility, although I suspect the vapor-core will be tried first. The reason, is that vapor core (UF4 at 3000-6000 K) is between one and two orders of magnitude cooler than the the all gas core (fissioning uranium plasma at 250,000 K.) The vapor core ought to be easier to control, and should have excellent power conversion abilities if an easily ionizable seed material is introduced (like KF potassium flouride,) and an MHD unit is used for primary power conversion with a possible helium gas Brayton Cycle gas turbine secondary. It is still very heavy, and such a vehicle will mass quite a bit. But it is doable I think.

Relativistic electrons? Electron beam welders use them every day. Infact, there is a nice patent listing for a device that can cut through concrete and metal fairly easily. In 1971 patent 3556600 entitled "Distribution and Cutting of Rocks, Glass and the Like." It describes a high powered 10KW+ electron beam system that could be used to slice through just about anything.

High energy electrons can be used to excite gas to a plasma, but application of radio frequency energy can do the same thing. This is the premise behind the VASIMR engine in which a gas is introduced into a chamber and is ionized by electron cyclotron resonance heating (in the tens of Gigahertz typically) and the resultant cool plasma is then subjected to Ion Cyclotron Resonance Heating (typically in the MegaHertz range) where most of the power is transmitted--this will heat the plasma to millions of degrees in a magentic field, and can generate a high speed plasma jet that can give 30,000 seconds of specific impulse using hydrogen gas as reaction mass.

Actually you wouldn't want to use NTP system to go to LEO because you have a hot reactor flying around in earth orbit that is going to eventually fall on someone!  Anti-nuke idiots would go absolutely ape!  Even I would be slightly concerned.  This might would if it was the propulsion system for a reusable shuttle since the reactor would be coming back with the vehicle (this doesn't deal with any of the problems of powering a shuttle this way).

NTR might be most effect as propusion system for Earth orbit to Lunar orbit and back.  It might also be usable as a launch stage to eject spacecraft for interplanetary trips.  The trip would either be a long minimum energy trajectory or a seperate nuclear electric system would take over.

Andrew, I think you're thinking of the containment building for modern nuclear power plants. They are the 'armored' concrete dome that is designed to hold radioactive gasses in the event that there is some kind of coolant leak or some other failure of the primary coolant system/ pressure vessel combination. This structure is also designed to protect the core from a direct hit from a large aircraft--the reinforced concrete and steel 'low pressure' shell comprising the containment structure is several feet thick.

Space reactors can be designed with an integral entry heat shield--and most are, which gives them the pronounced conical shape. They are mostly designed to survive entry and to impact the ground for instant burial in the event of a land fall. The burial is to provide local containment of radiation to help protect people who may 'stumble' across the wreck in the bottom of a crater. Hopefully, nuclear emergency response crews would arrive immediately or soon after land fall to begin recovery and cleanup operations...

An NTR however is an integral nozzle, gas plenum, and turbopump package--making it particularly difficult to package into an aeroshell. It is also physically much larger than the typical power reactor being studied, and its peak power output would be approximately atleast two orders of magnitude greater than the smaller power reactor.

I am a little bit nervous about proposing an NTR powered launcher--although from a strictly energetics point of view it looks great. However, when I look at the history of launch vehicle failures, I realize that there is a significant, non-vanishing chance (say optimistically 1/50) of a LOV (Loss of Vehicle) failure. In the case of an NTR booster, this also means loss of reactor. Depending upon the exact scenarios imagined, it may be possible to fit an aeroshell around an NTR and eject it safely from the vehicle to have it parachute to the ground (with visual, radio, and acoustical locator beacons operating.) Such a protective shell may even be able to keep the reactor a float on the open ocean in the case of a likely sea ditching. But such systems are complex, expensive, and add significant dead weight to the vehicle, robbing it of payload. However, in the case of a catastrophic turbopump failure (total disintrigration of impeller and/or turbine) the probable destruction of the pump case and release of high-velocity fragments, that coupled with an uncontrolled loss of coolant and emergency shutdown of a reactor operating at GW levels of thermal power, leads me to believe that such a failure will result in complete loss of both vehicle, and reactor, not to mention loss of payload and possibly any crew going along for the ride.

A conventional chemical booster for flight to LEO makes more sense to me, in that the 1/50 LOV is not compounded significantly by a LOR incident and subsequent release of radioactive materials in the atmosphere.

What I have looked at is using a man-rated booster using a stripped down but otherwise man-rated aeroshell (like a stripped down CEV) to ferry up a fueled NTR core to an orbital assembly site. The nozzle can then be attached, and the NTR can then be bolted onto the vehicle. This process may even be able to be automated so thatteleoperated robotic vehicles can actually do the assembly.

The reason for this otherwise more expensive option is that in the event of a LOV incident, the stripped down CEV (let's call it a UCV for Unpressurized Cargo Vehicle) can fire its launch escape motor to pull it safely away from the booster, where it can then reenter Earth's atmospher on its own and parachute to a land or water landing. This allows an intact, fueled reactor to be returned safely to Earth with no risk of contamination. And the other benefit will be: no damage to reactor so a 'quick' reflight may be possible...

This more expensive option allows the safe and responsible use of nuclear thermal propulsion systems to be used on orbital transports and deep space vehicles. It however does require a EOR (Earth Orbit Rendezvous,) docking and assembly menuver (which is not a trivial operation at all!)

Eventually at End of Life, a nearly spent NTR stage may be flown into a sunward disposal orbit, or even shot into the sun itself (using a Jupiter Slingshot Trajectory.)

The space elevator is a future possibility, but this will require vast space industrial infrastructure, which necessarily must include NTRs.


-- Edited by GoogleNaut at 20:42, 2007-06-22

That sounds like a good idea is we were using a closed cycle system. I'm still not impressed with the idea of using it the earth to orbit regime. Unless you are using a pure nuclear system (except for launch assistance, i.e. SRBs or jet engines) I dont see much advantage in go nuclear below orbit. It the LEO onto TLI or TMI, etc. that these systems come into their own. In leaving earth orbit for manned flight the is the issue of how fast you can get through the Van Allen belts with nuclear-electric systems. This is where NTP could set in to solve the problem.On the other hand the progress in nuclear systems like the MITEE described on this site could possibly be scaled up to thrust levels that would make a SSTO nuclear system interesting. With Isp in the 900 to 1000 sec region (again with sum limited launch assist) this vehicle could easily achieve orbit without going to extreme GTOW to Empty Wt. ratios. This would have all of the negatives cited above but it should be workable. I dont think the U.S. would ever to this but China might 40 or 50 years from now.

Simple, because they don't have the same type of legal system we have in the west.  Also, they don't have all of the environmetalists that we have either.

I think the Chinese will make slow steady progress--I don't see them dumping billions into an NTR system now, atleast not yet. The reason is that they are still making 'baby steps' so to speak. They have publically stated their intention to orbit their own space station and they have publically stated a long term intention to go to the moon. But then, so have the Russians in the past.

The Chinese will develop NTR when it is in their national interest to do so. Once they realize or are able to physically achieve manned missions to the moon and beyond, NTR will become a natural propulsion solution then. They simply are not ready for it right now, but in twenty years they might be ready.

On the other hand, if the US pushed hard and devloped and flight tested NTR hardware, acceleration development of a heavy lift launch vehicle, and really set about to build an orbital staging and assembly area for big ships--then you can bet money that the Chinese will dump billions into their program and accelerate their own efforts. Because then, it would be in their national interest to do so.

Pessimistically enough, my own personal observations of the pace of Chinese space development is that their apparent 'slow' progress is infact an indication of their own confidence in their own methods...in otherwords, they don't consider our program a 'threat' or even 'competition,' i.e., they don't want the systems we have beause they are too expensive...