The discussion revolves around the potential use of the Pratt and Whitney TRITON engine, a nuclear thermal rocket design, for missions to Mars from low Earth orbit. Participants explore the implications of using such an engine on transit times, payload capacity, and the engineering challenges involved.
Participants express a range of views on the capabilities and challenges of the TRITON engine and nuclear propulsion in general. There is no consensus on the effectiveness of the TRITON engine for reducing transit times or on the feasibility of alternative propulsion methods.
Participants highlight limitations related to energy efficiency, the complexities of interplanetary flight paths, and the unresolved engineering challenges associated with advanced nuclear propulsion systems.
etudiant said:nuclear boost engines have a specific impulse 2-3 times that of conventional rockets. They won't cut the transfer time much at all, just improve your payload materially as well as the launch window size.
Triton is written up here: http://www.pwrengineering.com/dataresources/AIAA-2004-3863.pdf
The new wrinkle is the reactor also drives an electric generator, so there is plenty of power for the mission even during transit or at destination.
Substantial engineering work will be needed to make that work reliably.
aquitaine said:So is there anything that would both increase your payload AND greatly improve transit time?
Look up " Project Rover nuclear rocket " on the web. Read http://en.wikipedia.org/wiki/Specific_impulse
In theory, a sufficiently efficient engine could slash transfer times, at the cost of using enormously more energy.
Almost all interplanetary flights are designed to use as little energy as possible, to use barely enough to get out of Earth orbit into a transfer orbit (around the sun) that will eventually intersect the orbit of the target planet at a time that planet is there. Much more complex paths are often used to help boost the spacecraft into a different direction or to hike its speed via a gravitational assist from a planetary fly by or two or many.
If instead a much larger braking burn was possible at the destination, the transit time could be much less, but of course every pound of fuel spent is a pound less payload.
Unfortunately, there is no space equivalent of air, so there we only know to do acceleration or deceleration by throwing away mass, very inefficiently in case of rockets, even nuclear ones.
aquitaine said:Good suggestion.
For probes this doesn't matter as much, but when it comes to actually having people in there (exploring or exploiting the vast riches of our beloved Sol) that quickly becomes a serious issue, after all it's taking new horizons years to get to the asteroid belt, who would want to wait that long?
Actually when I looked up the Rover Project as per Bob's suggestion I ended up running into this, an actual potentially feasible solution to this problem. According to their estimates on page 6 of the pdf that was http://www.rbsp.info/rbs/RbS/PDF/aiaa05.pdf a 10 year mission to 550 AU would use 180kg of fuel. Not only would it be able to travel 1 AU every 6.63 days, but do so with relatively cheap energy. With today's Uranium Hexafluoride price at ~160 USD per kilo, that comes out to using only 28,800 USD plus 1.8 million USD to launch that much (assuming $10,000 USD per kilo). Given the insane distance that covers, I would say that's pretty good. Next question, why the heck isn't this thing being seriously pursued?
Always the warp drive... :)
For serious manned interplanetary travel, first consider the food requirement problem, roughly 1 Kg of food per capita per day. Is it carried on board, or grown (hydroponic?). Do you use natural light, or artificial lighting for photosynthesis? (Photocells are about 20% efficient in converting solar radiation to electricity). Do plants grow well in zero gravity? Do you need insects for fertilization?aquitaine said:For probes this doesn't matter as much, but when it comes to actually having people in there (exploring or exploiting the vast riches of our beloved Sol) that quickly becomes a serious issue, after all it's taking new horizons years to get to the asteroid belt, who would want to wait that long?
1) If the propellant is charged particles, then the spacecraft charges up. and eventually all the emitted charged particles come back and form a halo around (or stick to) the spacecraft .etudiant said:Mind that it is possible to dream up deuterium or tritium fusion reactors that only emit charged particles, which abound in space anyways, so there is a potential for super efficient nuclear engines with ISPs in the range of 1,000,000.
Unfortunately, there are a few engineering obstacles...
Bob S said:1) If the propellant is charged particles, then the spacecraft charges up. and eventually all the emitted charged particles come back and form a halo around (or stick to) the spacecraft .
2) The density of particles in interplanetary space is less than about 10 per cubic cm. So about 60 million cubic kilometers of interplanetary space contains about 1 gram of hydrogen atoms. Not a good source of matter.
Bob S
The deal killer however is that the exhaust, much like that of Project Orion, would be seriously dirty.
We are only starting to recognize what a mess we have made of the near Earth environment with all the space junk. Adding a whiff of long lived fissionables to it is a political non starte