A lot of this is pretty universal material for nuclear thermal rockets. I was surprised by some of the temperatures the USSR program was said to get to. I think he mentioned something like 3700 K. Yikes.It's interesting to hear him come out in favor of a Phobos mission. With a nuclear thermal rocket, is aerobraking in the Martian atmosphere out of the question? It seems like the obvious implication, but no one states this directly.The video was from June 2013. But NextBigFuture just picked it up. Maybe it had just been in the author's watch queue.
Aerobraking with an NTR? Not likely. You'd need to slow WAY down before the Martian atmosphere would have enough effect for an aerobraking maneuver.
You probably wouldn't NEED to, (most NTR missions I've seen have plenty of Delta-V for propulsive breaking) but there is no real reason you couldn't if you wanted to. Some of your short-transit chemical missions have about the same un-breaked Delta-V's incoming as your averge NTR mission and they HAVE to use aerobreaking. You usually need more than one pass though.
A lot of this is pretty universal material for nuclear thermal rockets. I was surprised by some of the temperatures the USSR program was said to get to. I think he mentioned something like 3700 K. Yikes.
Quote from: AlanSE on 03/12/2014 05:24 pmA lot of this is pretty universal material for nuclear thermal rockets. I was surprised by some of the temperatures the USSR program was said to get to. I think he mentioned something like 3700 K. Yikes.That's actually 3100K, right around where a lot of high-temperature materials (like carbon) start to melt. As it happens, that's also just a tad above where hydrogen dissociates, which means a big increase in Isp.
Quote from: JasonAW3 on 03/12/2014 05:49 pmAerobraking with an NTR? Not likely. You'd need to slow WAY down before the Martian atmosphere would have enough effect for an aerobraking maneuver.You probably wouldn't NEED to, (most NTR missions I've seen have plenty of Delta-V for propulsive breaking) but there is no real reason you couldn't if you wanted to. Some of your short-transit chemical missions have about the same un-breaked Delta-V's incoming as your averge NTR mission and they HAVE to use aerobreaking. You usually need more than one pass though.Randy
As a primary developer of SEP, Landis points out something that's very important and frequently gets dropped in discussions of NTRs in these forums. High-Isp, low-impulse rockets are great for transporting almost everything around the solar system except humans. When humans are involved, high thrust is important, to minimize radiation exposure, to save mass on logistical supplies, and because we humans have finite lifetimes. 1960's-vintage NTRs could open the solar system out to roughly Martian orbits for humans; 1990's-vintage NTRs would get us to the asteroids, and we need something more advanced to get beyond that. But if we're willing to wait, i.e. humans aren't going, we can do most missions with low-thrust rockets.
There's room between aerocapture and typical slow aerobraking. Aerocapture is merely aerobraking in a single pass and with an initially hyperbolic "orbit."
Most of the cost involved in BLEO exploration missions won't be hauling freight into orbit, it'll be development costs. The cost of sending the hardware into orbit will be small in comparison, assuming you use already available launchers. This won't change untill a fairly late stage of colonization is reached.
I don't agree. If you have cheap access to orbit, the things like fuel depots become a no brainer and many problems that drive up cost can be easily solved by throwing more weight at it (which currently drives up cost also).