Iīm thinking about a possible relaunch of NERWA and ROVER projects,because technology is going forward to make it more efficient and reliable and safer of course.Bruce Berhorst had spoken about tungsten ceram technique by NTRīs.When I understand right is the exhaust plume of a tungsten ceram in comparisation with a graphite NTR core non or very less contamined,is that right or not?A further advance wuld be the non corrosion fact with the possibiltity to use other gases like hydrogen.So it would be possible to use also martian atmosphere (liquid carbon monoxide) as well.How is the official and political attitude about this theme in USAīs responsible politicians,NASA headquarter and manufactors aerospace like Lockheed-Marten,Boeing,P & W...but also trade industry like Westinghouse or General Electric?Which project would you favorite?Classic rocket propusion with Nuke as Auxillary Power Unit,Orion/Daedalus,Nuclear powered magneto electric drive/plasma,or NTR derrivates like mentioned,what would be the best choice?
Tungsten based Cermet seems to offer pretty low erosion which adds to longevity of operation and decreases emission of radioactive particles (by this I mean fission products, nuclear fuel, or neutron activated species.) By carefully choosing materials that have low activation cross sections, it is possible to improve but not completely eliminate radioactivation of structures within and surrounding the engine.
I would add that an NTR engine such as the Pratt and Whitney Triton with its LOX afterburning can significantly augment the thrust produced by the engine over a pure NTR, but since the thrust to weight ratio is still faiirly low, I do not see this engine being used as a 'first stage' engine, even if operated in a cluster. The reason being, it simply cannot produce enough thrust to lift a vehicle with a usable payload off the ground.
However, if used as a second stage, with a first stage using a chemical booster burning a fairly energetic propellant combination like LOX/RP-1 (kerosene,) then we can have a vehicle with a significant payload fraction.
The orginal NERVA project was intended to fly a nuclear thermal rocket stage as a second stage payload lofted by a Saturn 1 and later a Saturn 5. As an upper stage or deepspace propulsion system, the NTR really shines. But as a booster, it sucks!
Orion (the nuclear pulse vehicle) is a pretty inefficient but startlingly brutal way to launch an enourmous amount of payload all in one shot. It is deceptively simple because the basic idea of lobbing a nuclear explosive underneath a steel plate to make it move can, in principle work. However, as the saying goes: "...the Devil is in the details..." Setting the radioactive pollution arguments aside and looking only at the trajectory and attitude control of such a vehicle leads me to believe that a ground launch is a nontrivial task and not for the faint hearted. Attitude and roll control will be extremely difficult because of the sheer mass of the vehicle. The conclusion I came up with is that almost all of the payload would have to be RCS (reaction control system) propellant, despite the fact that Orion could in principle loft thousands of tons of mass into orbit. So the actual payload fraction would still be insignificant despite the Herculean power of nuclear pulse propulsion! If Orion were built in space, then it may be more practical, but then why use such an inefficient propulsion system if you now don't need 200,000 tons of thrust?!!!
Yes,thatīs a real problem,NTRīs haveīnt recently not enough energy density for using as lounch stage and the use in parallel is problematic due the interaction with the closest NTRīs neutron fux.Maybe solid rockets could give extra thrust,lke Space Shuttle or Ariane5,because H2/LOX engines have the same weak performance.Our recent dilemma is the medium power by nuclear propulsion is missing.NTR is not powerfull enough Orion pulses are wery much to strong.I think this problem will stay for a longer periode of time to obtain a medium range thrust system like nano fission or fusion pulses.
Well, I just don't see NTR useful in the boost phase. It has more to do with safety than with operation performance. An NTR core is practically inert until the safing rods are withdrawn and the control drums rotated. A virgin reactor will have only the native radioactivity associated with the nuclear fuel material because there will be practically no fission products within the fuel matrix. It's probably best to keep it in that condition until the reactors are well on their way.
It's just that during launch and boost, this is the most dynamic and dangerous time for a rocket. The dynamics of trajectory adjustment, atmospheric drag, and mechanical stresses are all at a maximum during this time. So, generally, if anything bad is going to happen, it will be during this phase.
There is also the reliability of the booster's engines. If each engine is 99% reliable then a cluster of 5 engines will have an aggregate reliability of (0.99)^5 = 95%. A cluster of 20 engines could have a reliability of (0.99)^20 = 81% This is one of those inescapable statistical realizations that possibly helped kill the original Saturn-NOVA super booster. The more engines you add, the more likely something bad will happen. Of course, if you go the way of the SSME (Space Shuttle Main Engine) with its smart engine controller, then it is possible to have an engine health monitoring system that can shut down an engine before it blows up--possibly. And then you have to have enough reserve thrust of the remaining engines to keep the vehicle flying so you need inflight spares for really big vehicles...it's a vicious cycle.
I think NTR is best as an upper stage or better yet, a deep space propulsion system.
I have often pondered the idea of safely ferrying up the NTR engines, or atleast the reactor cores up to an orbital assembly point, seperate from the main vehicle launches. A separate flight could be done on a stripped down CEV with a pressure shell, heatshield, parachutes, and launch escape system, but no life support. The idea is that if an inflight abort occurs, the LES could pull a reactor core payload away from the impending explosion, and safely return it back to earth or the ocean for intact recovery. I think this should alleviate some of the fears regarding transporting nuclear fuels to orbit onboard launch vehicles. Of course, this also increases orbital operations complexity by requiring an additional core insertion step, or engine mating on orbit, which has never been done before...
