Full Scale Venture Star w/ Unique Configuration...

[john_316]

Ok X-33 folks...<br /><br />What if a full scale version of Venture Star was built and used hydrogen to fuel the Gas Core Nuclear Rockets as a SSTO vehicle?<br /><br />I know the saftey ramifications here but do you think even Area 51 could pull something like this off in secret?<br /><br />What weight classification do you think we would have? 20 to 40 tons?<br /><br />Just to see if anyone proposed a X-33 or VS-3 idea with nuclear rockets and or if anyone is awake at 5:15am on a sunday morning... LOL<br /><br /><img src="/images/icons/smile.gif" /><br />

 

[henryhallam]

Gas-cored NTR is some way off, but even a modest solid-core NTR with ~800s Isp could easily manage SSTO. Politically, not going to happen. I think effort with NTRs should be concentrated on relatively low-cost, low-thrust engines for in-space operation as "earth departure stage" and for entering/leaving lunar and martian orbit.

 

[gunsandrockets]

a nuclear rocket SSTO manned spacecraft isn't practical<br /><br />The spacecraft would be weighed down with too much radiation shielding. The problem is the atmosphere.<br /><br />Out in the vacuum of space shadow shielding is enough to protect the crew from the radiation emitted from the nuclear rocket engine. That is, a small shield placed on the forward end of the rocket engine provides a narrow cone of protection (the shadow) for the crew.<br /><br />But operating in the soup of the Earth's atmosphere shadow shielding isn't good enough. Some of the radiation from the engine will reflect off of the air surrounding the spacecraft thereby bypassing the shadow shield. The crew would need a full sphere of heavy shielding to protect them from the radiation.<br /><br />You might be able to bypass this problem with a dual engine system. Conventional rockets to boost the spacecraft to a very high altitude, say 100,000 feet, then the nuclear rocket to give the spacecraft orbital velocity. The biggest problem here is I don't know how quickly a nuclear rocket engine could be 'warmed up' (the nuclear pile turned on) to begin thrusting.<br /><br />An unmanned SSTO nuclear rocket at least wouldn't have the radiation problem. I don't think you would want to use liquid hydrogen as your propellent though. ammonia might be a better choice. It's true that with ammonia the ISP would only be about half of what you could get with hydrogen, but the engine thrust would be greater and propellent tanks could carry ten times the mass of propellent.<br /><br />I don't think you would want to use a gas core nuclear reactor either. I'm not sure but I think the gas core designs are all low pressure very low thrust to weight designs. I'm not sure even the solid core rocket has good enough thrust to weight for a vertical take off. <br /><br />[another possible solution to the radiation problem: bury the crew compartment of the spacecraft inside the propellent tank, using the mass of the propellen

 

[henryhallam]

<font color="yellow"><br />But operating in the soup of the Earth's atmosphere shadow shielding isn't good enough. Some of the radiation from the engine will reflect off of the air surrounding the spacecraft thereby bypassing the shadow shield. The crew would need a full sphere of heavy shielding to protect them from the radiation.<br /></font><br /><br />Are you really sure about this? I have some practical experience with x-ray and neutron shielding techniques, nothing like the same intensity of course. As I understand it, gamma rays do <b>not</b> reflect off anything to much extent, certainly not anything as thin as the atmosphere. Neutrons do bounce around a bit - again the atmosphere isn't thick enough for them to bounce around very much within a short enough distance that a lot of them would return to the spacecraft - but it's easy enough to shield neutrons anyway, in fact a hydrogen tank combined with a little boron is ideal for this.<br /><br />Certainly radiation shielding must be considered but I don't think it's a show-stopper, and I don't think the atmosphere makes it any worse. If I'm wrong I'd love to know more about this reflection phenomenon! <br /><br /><br />Edit: Crap, gunsandrockets, I just noticed your private message... sorry, I've been away for the last few weeks. Haven't done much further work on that NEP tug study either, apologies for my laziness. Things are pretty tight for the next few days but I'll try to at least put together what work I have done into something presentable, and send it to you.

 

[bushuser]

What radioactive debris would be expected in the exhaust plume of a nuclear-gas engine? I'm not expecting tritium to come out of this thing, but wouldn't some small part of the radioactive core shed debris?

 

[henryhallam]

As I understand it there are two major ideas for nuclear-gas engines:<br /><br />For those who don't know, specific impulse and therefore rocket efficiency is directly proportional to the exhaust velocity of the gas, and hence to the temperature of the propellant in the chamber. With a solid NTR this temperature is limited because you have to make sure the structure of reactor, and the fuel elements, do not melt. In theory gas-core NTRs allow considerably higher temperatures, and correspondingly higher Isp.<br /><br />(1) A reactant such as UF6 is actually present in the same chamber as the propellant gas (the propellant will usually act as moderator). Clever hydrodynamics may be used to try to keep the UF6 in a vortex that mostly doesn't escape the engine, so you don't lose all your reactant immediately. The heat from the reaction is transferred by conduction and convection to the propellant gas which then exits through a nozzle. Because there is no real separation between reactant and propellant, fission products escape into the atmosphere. Nasty!!!<br /><br />(2) "light-bulb" design. UF6 or similar is reacted inside a quartz envelope, outside of which flows the propellant gas. Heat is transferred through the quartz by radiation. Here you can avoid releasing fission products, and therefore drastically reduce the radioactive pollution.<br /><font color="yellow"> "I'm not expecting tritium to come out of this thing" </font><br />Actually that's a sizeable fraction of the nasty stuff that you -do- get with a "lightbulb" NTR! Tritium produced by neutron activation of the hydrogen propellant. The cross-section for this is fairly low since you need to go H- />D->T.<br />There will also be some more neutron activation products formed in the air due to neutrons escaping the reactor. But this is much less nasty than option (1).<br /><br />To say the least, either of these ideas is much more technically difficult than a solid NTR. Don't expect to see them in

 

[gunsandrockets]

"Are you really sure about this? [radiation reflection]"<br /><br />No. I don't even remember where or when I read about it. I would be delighted if I were wrong too, because that would make a nuclear rocket so much more practical.

 

[john_316]

I dont know where I came up with that wild idea of a VS-3 with nuclear propulsion...<br /><br />I was thinking of the VS-3 shell with 2 gas core or even solid core nuclear thermal rockets. The hydrogen tanks sizes would be reduced and the foward section from the cargo bay foward would be lightly protected with a light graphite mix and possible water mix for radiation protection. I thought about engine protection surrounding the rocket engines themselves but thats alot of shielding there.<br /><br />But anyways as far as chemical means I thought about 2 or 4 J-2S in tandem (outboard each port/starboard) with 2 NERVA (centerline) like main engines in case of abort or to ensure on orbit capability...<br /><br />I initially thought of a 30 to 40 ton capacity suffient for LEO I would imagine.<br /><br />Now a VS-4 (VS-3 Upscaled) which could be used for a Mars Trajectory flight. That would mean a rocket that could do it in on shot but the VS-4 idea would be very large indeed with 4 NTR's and perhaps 4 to 6 J2S's for abort capacity. <br /><br />Any feasibilty here if we could use NTR's?<br /><br /><img src="/images/icons/smile.gif" /><br /><br />

 

[dwightlooi]

I think the easiest way to make the venture star viable is to stop making it an SSTO vehicle. Stick six two segment shuttle SRBs up its ass and fly it. It'll make orbit with a good payload and not need super lightening and breakthrough structural technology.

 

[najab]

><i>Stick six two segment shuttle SRBs up its ass and fly it. It'll make orbit with a good payload and not need super lightening and breakthrough structural technology.</i><p>Stick two 6-segment SRBs on it and it'll never make orbit - it will suffer structural failure and fall apart the moment they light - ~8-9 million pounds of thrust on a million pound vehicle? Yeah, that'll work out <b>real</b> good.</p>

 

[spacefire]

is a fusion powered craft clean enough to fly through the atmosphere? We've been eharin of some advances in the field of cold fusion lately, if this technology takes off thes ame waya s computers, in 20 years it'd be omnipresent. <div class="Discussion_UserSignature"> <p>http://asteroid-invasion.blogspot.com</p><p>http://www.solvengineer.com/asteroid-invasion.html </p><p> </p> </div>

 

[najab]

Cold fusion isn't what you'd want for rocket propulsion - at least not for a surface-to-orbit vehicle. Cold fusion (if it is perfected) is best suited to in-space nuclear-electric propulsion. Hot fusion, on the other hand, would work well for a launch vehicle - all you do is make your fusion chamber "leaky" on one side and the vehicle will go the other direction with great haste!

 

[spacefire]

sorry I jumbled the concepts in the post. Once again I posted without thinking much >:-( Yes I meant hot fusion for propulsion and cold fusion came into play to illustrate the advances we're making in the science and technology of fusing atoms. <div class="Discussion_UserSignature"> <p>http://asteroid-invasion.blogspot.com</p><p>http://www.solvengineer.com/asteroid-invasion.html </p><p> </p> </div>