4 ms·
Thrust to weight still will matter. NTR and NERs still have to drag all that dead mass of engine, radiators and shielding wherever they go.
by valuearb 6y ago
Thrust to weight still will matter. NTR and NERs still have to drag all that dead mass of engine, radiators and shielding wherever they go.
- m4rtink 6y agoNot to forget NTR dumping most of the heat during the burn kinda by definition while NER has to radiate lots of heat continuously to power the engine. Also without high trust you can't really make use of the Oberth effect: https://en.m.wikipedia.org/wiki/Oberth_effect https://en.m.wikipedia.org/wiki/Oberth_effect
- lmilcin 6y agoOberth effect is for long term missions where you have time to swing by other planets or moons just to get some free velocity. This is fantastic, but costs huge amount of mission time. The nuclear engine is about getting so much delta v that you can cut the crap and power directly to your destination.
- laverya 6y agoOberth effect is useful for every reasonable trip - since every reasonable trip either originates or ends deep within a gravity well. (And being in orbit deep within a gravity well implies being at high velocity) It's why you make an escape burn at periapsis and not apoapsis.
- valuearb 6y agoNot really. An 85 ton Starship fueled in LEO can use Oberth effect, get to Mars just as fast, and land directly on Mars. Your deep space NTR has engines that weigh way at least ten times more, while providing only a fraction of the thrust, and also has to push not only hundreds of tons of radiators, shielding and heavier tanks, but also a lander since NTR doesn’t have the thrust to climb out of any significant gravity well. And also is going to have substantial propellant evaporation by the time it reaches Mars since it can only achieve that ISP with hydrogen.