Lots of people who are interested in going to Mars have been gathering this week at George Washington University for the annual Humans to Mars Summit, and the star attraction this morning was Andy Weir. He's the author of the novel "The Martian," which has sold 3 million copies, been translated into something like 45 languages and served as the basis of the blockbuster movie by the same name, directed by the legendary Ridley Scott and starring Matt Damon. So, yes, that book did well -- remarkably so given that he originally published it in chapters on his website and later as an electronic book that could be downloaded for free.

Weir, whom I interviewed on stage in the summit's opening session (you can probably find the video here), was scheduled to pop by The Post for today's "Transformers" event and then visit Capitol Hill to testify before the House subcommittee on space. Busy day! He said he was going to talk about how an interplanetary spacecraft, such as one going from Earth to Mars, can be designed to spin to create artificial gravity. That's a potential way to moderate the severe physical effects of weightlessness on the human body. Without artificial gravity, the first astronauts on Mars would likely spend many days just trying to recover from all those months in zero-g conditions.

But he's also working on another novel, this one about a city on the Earth's moon that features a female protagonist who is something of a criminal but still lovable, according to Weir. He said he doesn't intend to bring back Mark Watney of "The Martian," essentially because the wisecracking Watney would threaten to steal the show.

I asked him if he's implicitly endorsing a return by NASA and its partners to the moon -- something that has been a politically fraught question in space policy circles. His answer: Yes. Weir thinks it's a great place to test the technology for long-duration off-world missions. The moon is right next door, cosmically speaking; you've got a bailout option with the Earth just four days away. But when you fire your thrusters to go to Mars, you're not coming back for close to three years. As everyone at the H2M Summit will tell you: Mars is hard.

The problem is, we've been to the moon already, a fact cited by President Obama in 2010 when he said we should go to an asteroid and forget about his predecessor's back-to-the-moon plan, called Constellation. In the overused space-policy shorthand, the moon is a red destination and an asteroid is a blue destination.

NASA checked out the asteroid possibilities and winced: Such a trip, involving an asteroid in its natural orbit, would require a mission of several hundred days, as well as construction of a habitation module that could keep a crew of astronauts alive all that time while they traveled around the sun. NASA, as we've reported, went to a convoluted backup plan in which it would capture an asteroid robotically and redirect it to lunar orbit. Astronauts would then go in the new Orion capsule to visit the asteroid and bring home samples. (It's hard to find the right asteroid for such a mission, though, so NASA is now talking about breaking off a boulder from an asteroid and letting that be the redirected object.)

A lot of people find this Asteroid Redirect Mission deeply unsatisfying. Some of them are determined to go to Mars, however hard such a mission might be. SpaceX, for example, and its founder Elon Musk have been clear that they are going straight to Mars with humans rather than doing a practice run anywhere near the moon. Musk and his people have said they could put a human on Mars in the 2020s, an extremely optimistic view, and it’s notable that SpaceX has a limited presence here at the conference. Maybe the H2M conference is too NASA-centric and bureaucratic for those folks.

Robert Zubrin, the founder of the Mars Society, was backstage this morning and shared his own thoughts. He thinks NASA's much-hyped "Journey to Mars" is "fictive" and fundamentally a rationale for a broad assortment of programs that were approved to satisfy provincial interests and don't really knit together into a coherent plan.

"The real question for NASA is, do you really want to go to Mars or don't you?" Zubrin said. I asked him about SpaceX going in the 2020s. "Plausible," he replied. "Not necessarily probable. But not impossible."

In the meantime, SpaceX says it will send an uncrewed Dragon spacecraft to Mars as soon as 2018. The mission will be known as Red Dragon, and NASA will provide technical support under a no-cash-exchanged Space Act Agreement.

Landing anything on Mars is tough, as many countries have learned. NASA is the only space agency on Earth to have succeeded in landing a fully operational spacecraft on Mars. The Curiosity rover, the largest of those payloads, weighs only about one metric ton (at time of launch here), but the SpaceX Dragon would be at least five times heavier and would use the supersonic retro-propulsion technology that the company has used to land the first stage of its rocket boosters.

This could obviously go either way. You could wind up with a new crater on Mars. Or, if it all works, you've opened the way toward the kind of large payloads necessary for a human mission to the surface. And one of these days we'll talk about a nearer-term concept: a Mars Sample Return mission. That's a longer conversation that includes a discussion about planetary protection and whether we should fear Martian microbes.

Zubrin, for one, says no, because chunks of Mars reach the Earth all the time in the form of meteorites that originated as Martian rocks blasted into space by asteroid impacts.

"If we could get the Red Death from Mars, it's already here," Zubrin said.