Quora Question: What Will it Take to Get to Mars?

The planet Mars in an undated NASA image. Six people have just completed a successful NASA-funded simulation of a year-long mission to the red planet. NASA/Greg Shirah/Handout/Reuters

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Answer from Josh Boehm, former SpaceX Employee:

We have the technology to send people to Mars—the bottleneck at the moment is the cost, which stems from a few issues mainly relating to reusability and fueling.

These graphics from Elon Musk's presentation do a pretty good job of illustrating the problem:

Venn diagram of people who want to go to Mars and those who can afford to based on traditional methods - Source: SpaceX

The same venn diagram updated to show where the price point needs to be - Source: SpaceX

What's needed for the Mars mission?

  • Get the cost down to that of the median cost of a home in the U.S.
    • Full rocket reusability: No transportation method would be affordable if you threw out the vehicle at the end of the journey.
    • Fueling: Using the right propellent (one that is cost effective and can be easily produced on Mars); refueling in orbit; manufacturing a propellant plant on Mars.

Notes on Reusability

  • This is where the "technological breakthroughs" need to be.
    • SpaceX is the only company making considerable efforts and progress toward rocket reusability with their many successful F9R landings. They've come a long way, but there is much further to go.
  • Currently only the first stage of the rocket is partially reusable.
    • It would still need to be refurbished before flight as-is, not just refuel and launch.
    • The second stage isn't recoverable at this point.
  • Rockets and spacecraft take an enormous amount of stress in flight; even when they're reusable, components will have different projected lifetimes.
    • Targeted number of reuses per vehicle:
      • Booster:1,000
      • Tanker: 100
      • Ship: 12

Overall architecture of the Mars mission with targeted reusability stats for each vehicle - Source: SpaceX

Projected costs of Mars transport over time - Source: SpaceX

  • The initial flights will be expensive, but the more you can reuse a vehicle, naturally the average flight cost gets cheaper.

Notes on Propellent and Re-fueling

  • No "technological breakthroughs" are really needed here. Everything has been done in some fashion before.
  • Since there's only a launch window to Mars about once every two years, the colonial fleets will be assembled, fueled and loaded in orbit, à la Battlestar Galactica. (See "System Architecture" graphic under Notes on Reusability.)
    • This is much more efficient than trying to do one large rocket launch anyway. Not refueling in orbit would require a three-stage vehicle at five to 10 times the size and cost.
    • With the context of the two-year window, a projection of 12 uses per ship is much more reasonable.

Chart comparing the options for propellent for the Mars mission - Source: SpaceX

  • As demonstrated by the chart, deep-cryo methalox (CH₄/O₂), is the most viable option, due to the energy density, cost and ability to produce it easily on Mars
  • Water (in the form of ice) and CO₂ are abundant on Mars, which allows us to fairly easily produce methane and oxygen.

Synthesizing oxygen and methane from water and carbon dioxide on Mars - Source: SpaceX

Disclaimer: I am a former SpaceX employee, representing my own opinion. Nothing I've written should be interpreted as a statement from SpaceX. For an official statement please contact the SpaceX Press Center.

What technological breakthroughs are still needed to make Elon Musk's vision for Mars travel possible? originally appeared on Quora—the knowledge-sharing network where compelling questions are answered by people with unique insights. You can follow Quora on Twitter, Facebook, and Google+. More questions:

Quora Question: What Will it Take to Get to Mars? | Tech & Science