Confronting the Credibility Gap for Crewed Exploration of Mars • Hacker News Board

Re: Confronting the Credibility Gap for Crewed Exploration of Mars

#31

Post by jack9 » Wed, Dec 21, 2016, 8:38 AM UTC

daveguy wrote: post #14

fapjacks wrote: post #13

Earlier quoted context omitted.

But that's not what he's saying, now is it? He is dismissing it entirely as "impossible". Care to point me to the part of the scientific method which says "Feel free to dismiss outright things that don't make sense to you"?

Everything in science starts out impossible. It doesn't even get considered in science unless it has a chance of being impossible. Then it is up to the scientist to demonstrate that it is possible and explain how it is possible. Edit: The 1) demonstrate and 2) explain parts are critical and it's not science unless you have 1). Preferably 2) also. EM has neither to match the magnitude of the claims until they can push…

> EM has neither to match the magnitude of the claims until they can push something across the solar system and back

That is hyperbolic. Pushing something around in orbit is sufficient to move forward (pardon the pun).

Re: Confronting the Credibility Gap for Crewed Exploration of Mars

#32

Post by chandmer » Wed, Dec 21, 2016, 8:52 AM UTC

Animats wrote: post #26

Landing is really hard. Not enough atmosphere for aerobraking, and too far from home to have enough fuel for a powered landing. It's a fuel problem. There's the expensive approach. Send multiple unmanned tanker ships into Mars orbit and have them rendezvous into an orbital supply depot. Send landing tanker ship to rendezvous with them and refuel with enough fuel for a powered landing. Landing ship descends. Repeat to…

All kinds of problems! The ITS gets around a lot of them - the trick is to have a lifting body. But there's still a lot of problems.

Re: Confronting the Credibility Gap for Crewed Exploration of Mars

#33

Post by aedron » Wed, Dec 21, 2016, 9:22 AM UTC

nickparker wrote: post #17

There's a very enjoyable discussion in the comment section with my (brilliant) former colleague Max Fagin. He points out that Casey's first draft of this post neglects the curvature of Mars, and when you account for it Casey's model predicts the craft punching out the other side of the atmosphere.

Can't see those comments. Were they deleted?

Re: Confronting the Credibility Gap for Crewed Exploration of Mars

#34

Post by james-watson » Wed, Dec 21, 2016, 9:35 AM UTC

What gets forgotten here, and something that I keep bringing up, is the lack of a Martian magnetosphere. This means long term human settlements have to be artificially shielded.

This means living underground, which defeats the point of going to Mars in my opinion. Elon mentioned using a local magnetosphere generator, which is one of those ideas that is theoretically possible but whose practicality seems questionable. How powerful a magnetosphere generator is required to deflect ionizing radiation? How much power generation capacity will a Martian colony have to spare? Will this require a Fusion reactor?

The only hope I have for Martian settlement is that Musk and his engineers are some of the most audacious and brilliant people on the planet. I will never bet against their success, and I wish them the best of luck.

I have been a space exploration fan since as long as I can remember, I just worry that humans have a tendency to focus on the wrong goals when ideals and emotion cloud our judgement (e.g. the Space Shuttle).

Re: Confronting the Credibility Gap for Crewed Exploration of Mars

#35

Post by james-watson » Wed, Dec 21, 2016, 9:42 AM UTC

chandmer wrote: post #24

fapjacks wrote: post #2

"And then you have the EM/reactionless drive, which is less efficient than a Hall effect thruster, and also impossible." I could sense this was coming, and I stopped reading here.

Sorry to come across as grumpy. It wasn't really the venue or topic to argue about exotic propulsion. There are many excellent resources online explaining why EM cavities are reactionless. You can write down the Poynting vector and then use Green's theorem, it's a neat result. With dire consequences for wish-powered spacecraft. -C

Don't be sorry. We need scientists to be skeptics when it comes to absurd assertions which violate the most fundamental principles of physics.

Extraordinary claims require extraordinary evidence.

Re: Confronting the Credibility Gap for Crewed Exploration of Mars

#36

Post by DiabloD3 » Wed, Dec 21, 2016, 11:17 AM UTC

techdragon wrote: post #8

XorNot wrote: post #6

Earlier quoted context omitted.

It violates conservation of momentum (i.e. why solar sails work). This is a pretty big problem with any evidence purporting that it does work because it requires a massive reinterpretation of our understanding of existing physical laws: i.e. it's mechanism of operation has to simplify to existing theory in such a way as to also explain why the effect is undetectable at the staggeringly high resolutions of measurement…

There is a big difference between "does violate" and "appears to violate". The orbital motion of Mercury "violates" Newtonian gravity. There are other examples but I'm not trying to make a history lesson. I just want to point out, that science moves forward by impartial investigation of EVERYTHING. It's misguided to assume we know all and that there cannot be some thing we don't understand. I'm as sceptical as anyone…

It only "violates" Newtonian gravity if you ignore large electromagnetic differences between the planet body and the Sun itself.

NASA also does the same thing, so don't feel bad.

Re: Confronting the Credibility Gap for Crewed Exploration of Mars

#37

Post by jcoffland » Wed, Dec 21, 2016, 11:21 AM UTC

Animats wrote: post #26

Landing is really hard. Not enough atmosphere for aerobraking, and too far from home to have enough fuel for a powered landing. It's a fuel problem. There's the expensive approach. Send multiple unmanned tanker ships into Mars orbit and have them rendezvous into an orbital supply depot. Send landing tanker ship to rendezvous with them and refuel with enough fuel for a powered landing. Landing ship descends. Repeat to…

How about we harpoon Mars and pull down one end of a space elevator?

Re: Confronting the Credibility Gap for Crewed Exploration of Mars

#38

Post by kolinko » Wed, Dec 21, 2016, 11:28 AM UTC

Animats wrote: post #26

Landing is really hard. Not enough atmosphere for aerobraking, and too far from home to have enough fuel for a powered landing. It's a fuel problem. There's the expensive approach. Send multiple unmanned tanker ships into Mars orbit and have them rendezvous into an orbital supply depot. Send landing tanker ship to rendezvous with them and refuel with enough fuel for a powered landing. Landing ship descends. Repeat to…

Well, you can retank the ship on Earth's orbit - that's Musk's plan (once he's done with the tunnels)

Re: Confronting the Credibility Gap for Crewed Exploration of Mars

#39

Post by jcoffland » Wed, Dec 21, 2016, 11:44 AM UTC

Radiation is a huge problem. Both en route and on Mars.

A lot of these problems beg the question. Is Mars really the best target? Sure it's close but there are moons around Saturn that are interesting as well. Titan for example. Sure it's cold but it has a lot of atmosphere. Presumably landing would be easier. If we could learn to live underwater we could possibly visit Ganymede or Europa.

Re: Confronting the Credibility Gap for Crewed Exploration of Mars

#40

Post by lmm » Wed, Dec 21, 2016, 11:51 AM UTC

Animats wrote: post #26

Landing is really hard. Not enough atmosphere for aerobraking, and too far from home to have enough fuel for a powered landing. It's a fuel problem. There's the expensive approach. Send multiple unmanned tanker ships into Mars orbit and have them rendezvous into an orbital supply depot. Send landing tanker ship to rendezvous with them and refuel with enough fuel for a powered landing. Landing ship descends. Repeat to…

The "Red Dragon" missions are planning on the cheap approach, using a flattish (indeed rising in places) trajectory to extend the aerobraking long enough to be effective, combined with supersonic retropropulsion. We've got a lot better at fluid dynamics and lifting-body physics in the last few years, and SpaceX in particular is cleverly developing a lot of experience using the same "EDL technology stack" for their booster landings on Earth.