What are the most difficult challenges SpaceX will face getting astronauts to Mars by about 2025?

Question

SpaceX has been announcing very ambitious goals such as starting to send manned missions to Mars in order to (eventually) create a colony, and recently there has been a substantial release of more technical details about this plan (see links at the the end). As quoted in Spaceflight Now's article SpaceX’s Elon Musk announces vision for colonizing Mars:

SpaceX plans to launch its first mission to Mars, a robotic test flight with a modified Dragon capsule, as soon as May 2018. After that “Red Dragon” flight, Musk said SpaceX’s goal is to send at least one spacecraft to Mars during every interplanetary launch opportunity, which come every 26 months or so.

The concept detailed Tuesday features a huge rocket standing 400 feet (122 meters) tall, and a fleet of passenger-carrying spaceships and refueling tankers.

Musk’s long-term vision is to build a self-sustaining civilization on Mars, complete with “iron foundries and pizza joints.” Eventually, it might have a million residents or more.

“When will we reach that million person threshold? It’s probably between 20 and 50 total Mars rendezvouses,” Musk said, counting Mars launch windows occurring every other year. “It’s probably anywhere from 40 to 100 years to fully achieve a self-sustaining civilization on Mars.”

He counts those numbers from the time of the first crewed flight, which might some as soon as the 2020s.

“We aspire to launch in late 2024 with an arrival in early 2025,” Musk told reporters after his presentation at the International Astronautical Congress in Guadalajara, Mexico. “That’s optimistic, so I would describe that as an aspiration and within the realm of possibility, but a lot of things need to go right. That said, I don’t think it would be significantly beyond that if it did go later.” (emphasis added)

This seems really soon. Has technology advanced enough for this type of mission to be fulfilled - transporting astronauts all the way to Mars, and (presumably) returning them safely home again? And what about the radiation problem in the trip?

Question: Based on the more detailed information available by SpaceX recently, what are the most difficult challenges that SpaceX faces accomplishing this goal by 2025, or not "significantly beyond that"? Are there any obvious technology or logistic "show-stoppers" that could make this goal convincingly untenable?

More about the plan can be found on the SpaceX page http://www.spacex.com/mars and a link to a PDF of Elon Musk's position paper Making Humans a Multi-Planetary Species can be found at http://online.liebertpub.com/doi/full/10.1089/space.2017.29009.emu

Answer 1

Since there have been no answers in over a week, I'll venture a partial answer.

There are of course several challenges. Among them in no particular order:

• Crew selection and training

  Putting together, evaluating, and training the crew would be the first challenge. They need to train together on accurate replicas of the systems to be used in the future. Just as a comparison: astronauts for the ISS train for almost two years. The apollo astronauts trained for at least five years.

• Landing site

  Landing site selection is a difficult process. See for example a summary of the third Mars 2020 Landing Site Workshop held in Monrovia, CA, from February 8-10, 2017 for an example from NASA. And thats just for rovers, not a site that allows for the relaunch of a large space craft.

• Space suits reliable for EVAs and Mars-walks

  What kind of space suit are they going to use? The one they are building now is the "indoor" space suit for use inside the space craft.

• Dust, toxic perchlorates

  On the moon missions, regolith caused a few problems. It stuck to the suits, entered the living space, and it caused a lot of wear and tear. See Air and Space's article Stronger Than Dirt; Lunar explorers will have to battle an insidious enemy—dust. for more. Martian regolith is also known to contain a substantial amount of perchlorate, a nasty, toxic combination of chlorine and oxygen. The Space.com article Toxic Mars: Astronauts Must Deal with Perchlorate on the Red Planet covers this nicely, with a good overview of the challenges.

Devilishly dangerous

The high levels of perchlorate found on Mars would be toxic to humans, Smith said.

"Anybody who is saying they want to go live on the surface of Mars better think about the interaction of perchlorate with the human body," he warned. "At one-half percent, that's a huge amount. Very small amounts are considered toxic. So you'd better have a plan to deal with the poisons on the surface."

The value of one-half percent is mentioned in the abstract of the 2013 paper Perchlorate on Mars: a chemical hazard and a resource for humans, while a lower but significant value of 0.6 g/kg is found in the abstract of the 2017 paper The nitrate/(per)chlorate relationship on Mars at a different location.

Proposed solutions include leaving EVA suits docked on the outside of the spacecraft/habitat, though it's not clear how practical this could be, another proposed there is a water wash down in the airlock.

• Refueling station

  While in theory, the Sabatier process will work, they have to research and develop it at first for a practical and reliable implementation on mars, because nobody currently knows how to really do that. An often overlooked aspect in this regard is, that you are going to need mining equipment to bring the reactants into a proper state for processing. NASA does have a research project on that. See for example the SBIR summary In-Situ Resource Utilization - Mars Atmosphere/Gas Chemical Processing:

State of the art (SOA) technologies for these ISRU processes either do not exist or are too complex, heavy, inefficient, or consume too much power.

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The Mars Exploration Program Analysis Group seems to be a good source for further reading. There should be a risk analysis for a mars mission there, but I was unable to locate it.

As an aside; Buzz Aldrin thinks that the SpaceX plan is unfeasible. More on this can be found in Purdue University's course introduction page Project Aldrin-Purdue, Mission to Mars. The page also links to the nicely produced video Project Aldrin-Purdue, Mission to Mars which includes Aldrin's discussion.

I hope that I was able to at least provide a starting point and encourage more people to answer. This is a very interesting and developing topic and there should be a place to collect current information.