[kordless]

There's also the argument for doing things a better way. Our propulsion systems suck, which is why we're having to send robots to comets instead of humans. Humans don't get stuck in cracks. Robots get stuck in cracks because they have no clue how to measure things they've never seen before.

[mikeash]

What exactly is your point? Better propulsion would solve a ton of problems with space flight all at once, but how do you achieve it? This is nearly as bad as saying that gravity sucks, if we could just turn it off then it would all be so much simpler.

[schoen]

> Humans don't get stuck in cracks.

https://duckduckgo.com/?q=trapped+in+a+crevasse

[mturmon]

Come on. Propulsion is far from the first reason we're not sending humans to comets -- safety, risk, mass, need for return, habitability.

[spdegabrielle]

All those things are inseparable from propulsion.

[mturmon]

Again, clearly not true. Crewed implies habitable implies need for O2 implies more complexity. This complexity could not be carried on the budget, schedule, and risk allocated for this asteroid lander.

You could say the same thing about safety, and the need for return.

[johncolanduoni]

How do you figure? One of the biggest safety issues for manned space travel is radiation. Do you plan on outrunning it?

[snowwrestler]

If you have awesome propulsion then you can just bring a shitload of shielding mass.

[mturmon]

But use of such a system requires development, testing, and flight qualification, affecting cost, schedule, and risk. It will also affect other variables, like volume.

Focusing on a point solution like "propulsion" is not even the right kind of question to answer "why not solve this problem with humans?".

[snowwrestler]

> development, testing, and flight qualification, affecting cost, schedule, and risk

These are all a lot easier if you are not worried about mass anymore. Just give all your structures a 3x safety factor like a bridge, and bring extras of anything complicated. Heck bring a mechanic and tools, too.

Of course this is all fantasy, which was the point of this subthread under kordless, in the first place.

EDIT

> Focusing on a point solution like "propulsion" is not even the right kind of question to answer "why not solve this problem with humans?".

To be more clear: I agree with you. I'm just playing the idea of "what if we had much better propulsion." But of course we don't, so in real life, we do need to carefully consider the factors you mention.

[rm_-rf_slash]

That's a fair point. That's like saying "we have the best medical facilities in the world for any treatment imaginable, but the hospital is five miles away. How will we carry you there in time to be treated?"

[mjrbrennan]

Yeah I'm surprised there aren't more humans volunteering to get blasted onto a moving comet with no way to get back off it, seems very safe.

[dfox]

With our current understanding of physics, chemical rockets have one giant engineering advantage: the same mass that is consumed for energy production is also the reaction mass. So anything better for imparting large delta-Vs has to be non-newtonian and our current understanding of physics does not allow existence of any such thing.

[johncolanduoni]

That's a big oversimplification. Project Orion-style propulsion is certainly not ruled out by our current understanding of physics. There's no non-Newtonian mechanics involved, just the substitution of a nuclear reaction instead of a chemical one. Not to mention that we have lots of evidence of non-Newtonian mechanics (e.g. Special and general relativity), even if whether GR can assist in space travel is an open question.

[cben]

If look at it the other way around: burning the reaction mass is the only source of energy you use to accelerate the reaction mass — it doesn't sound obviously optimal.

Nuclear thermal, and nuclear/solar electric (aka ion) rockets achieve better specific impulse despite carrying separate weight for power. Some nuclear designs (e.g. Orion as johncolanduoni said) do have overlap between reaction mass and energy source mass. Solar sails, ground lasers, and gravity assists avoid some of the need for carrying reaction mass. All these are perfectly newtonian.

Chemical does win among currently working designs at accelerating quickly, which is critical for human exploration, and to some degree for getting to orbit. There is no inherent physical reason alternatives can't achieve that.

I must recommend the extremely fun Project Rho site though I'm just started reading it: http://www.projectrho.com/public_html/rocket/enginelist.php It's not always clear where existing science ends and Sci-Fi begins, but that's generally on technology barriers (e.g. we haven't yet managed break-even contained fusion), not mythical "entirely new understanding of physics". And the amount of actual science — detailed papers, prototypes etc — on diverse and bizzare drive designs is way more than I expected!