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.

EDL = Entry/Descent/Landing, for anyone else confused.

Heh, I figured it was ok to use the acronym since it's defined in the article.

Not everyone reads the articles. I usually skim the comments first to find out if the article might be worth reading; defining the abbreviations definitely helps.

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.

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

The biggest problem with a space elevator on Mars is that the orbit of one of its moons is closer than the minimum height of a space elevator to be stable. Eventually the elevator cable will get hit.

Hang the cable from the moon and let the end trail?

Interesting proposal.

You still need a lot of delta vee to get a harpoon+cable from orbit to the surface. You can't just fire it straight down, you have to cancel most of your orbital velocity (which would have to be way out at geostationary). Dunno what the strength requirements of the cable would be either, but I imagine the answer is "not small".

Doing the same trick to Earth probably wouldn't be that much harder than Mars. So maybe, once you've solved the hard problems, you wouldn't have to worry so much about mass-to-orbit anyway.

You don't need to get the entire mass of the elevator down initially. Just the harpoon and cable.

Many of the ideas for visiting other planets could and should be tested on earth first. I think we need to get comfortable with visiting the moon and performing large scale industrial projects in space before we have any chance of visiting remote planetary bodies and returning.

>You don't need to get the entire mass of the elevator down initially. Just the harpoon and cable.

That's what I said. The trouble is there's no "just" about it. A cable long and strong enough is going to be extremely heavy, never mind the "harpoon". In a traditional "harpoon" the cable is a small fraction of the total mass - you can't really afford that kind of design (shoot heavy thing, drag negligible thing behind) so it's not clear how the orbital dynamics would work. You'd be looking more along the lines of little tug rockets spaced along the length of the cable.

>Many of the ideas for visiting other planets could and should be tested on earth first.

Quite. This Mars stuff is completely pie in the sky. Let's see a self-sustaining habitat in a desert on Earth, never mind even the moon. As an incidental benefit of solving this we would be able to perform sustainable agriculture anywhere on Earth.

The harpoon could be a big heavy thing. Perhaps we crash an astroid into Mars that is trailing a cable. That doesn't really jive with the planetary protection principals but it might be the kind of thing we need to consider to get the job done.

> As an incidental benefit of solving this we would be able to perform sustainable agriculture anywhere on Earth.

True. Although sustainable on Earth usually also means economical. I would like to see a sustained habitat on the moon.

I feel like a good first step would be setting up an orbital base/space station that orbits mars. It might be be a little easier than habitation On the planet itself, and more risk for the astronauts involved. However, if we set that up using knowledge gleaned from the ISS, I think its a viable path to take.

The attractive thing about landing on dirt is that the raw materials mean that a closed life support system isn't needed. There are relatively accessible supplies. Space stations anywhere, be that LEO, lunar orbit, Mars orbit, deep space, or floating in Venus' atmosphere, lack that option.

That means building a mining operation and industrial plant on Mars. Big job just for a few explorers.

With robotics, it's no harder than any other pioneering expeditions humans have conducted.

As I told the robotics people at Stanford who were talking about something similar on the moon in the 1980s, "how soon can you do it in Arizona?" The machines sent to Mars so far are very small and wimpy. Because they're semi-teleoperated, and have very limited solar power, they're really slow. If you want to do any high-power activity on Mars, you'll probably have to send a nuclear reactor.

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

Alternatively, send a probe that generates LOX and liquid methane from water ice and CO2 on Mars using solar power to create the fuel needed for ascent.