Elon Musk on Reddit AMA

By Kent Nebergall / October 15, 2017

Elon Musk recently did a Reddit Q&A with members (Ask Me Anything).   This mostly focuses on details of the Mars vehicle update.  Here are some highlights.

Mars Settlement

  • The Mars city design from the video was mostly artistic (“I wouldn’t read too much into that illustration”.  There are no specific plans beyond propellant production, power, and life support.  He wants to enable other industries to go to Mars.
  • The landing sites need to be low altitude for maximum aerobraking.  Close to ice for propellant production and free of giant boulders.  Closer to equator is better for solar power.
  • SpaceX is building the ISRU (propellant production system) in house, and it’s pretty far along.
  • They plan to put communications satellites around Mars at some point.

Technical Details of the BFR and Spaceship

  • The vehicle would burn all the fuel in the main tanks getting to Mars (or the moon or Singapore or whatever).  It would then use the secondary tanks for landing.  In the case of Mars, it would turn the nose of the ship toward the sun and vent the outer tanks.  This would basically make the inner tanks super-cold for the trip.  (Editor note – it would also eliminate the possibility of spinning two spacecraft with a tether for artificial gravity).
    • They eventually will add a cryocooler (which would allow it to spin).
  • The newest Raptor engines being tested are actually sub-scale.  The final production version is being designed for reliability, not performance.
  • the small delta wing is to “balance out” the load on reentry, to keep the ship from entering engines-first.  It can also provide some pitch and yaw control during reentry.
  • The RCS system will be methane/oxygen and pressure fed.
  • Early versions of the tanker will be just a fully-loaded propellant tank ship with no payload.  Later versions will look “kinda weird”.
  • Heat shield tanks are mounted directly to the tank walls.
  • The development will start with a full-scale ship doing short hops of a few hundred kilometers up and across.  They don’t need the deep-space Raptor engines for that.
  • VERY INTERESTING – “Worth noting that BFS is capable of reaching orbit by itself with low payload, but having the BF Booster increases payload by more than an order of magnitude. Earth is the wrong planet for single stage to orbit. No problemo on Mars.”
    • Traditionally, methane doesn’t have the specific impulse to do single stage to orbit.
    • A BFS without the booster would be economical for domestic flights, in theory. They could also return themselves from interior destinations like Chicago to coastal launch facilities with the BFR stage.

Anyway, you can read it in detail if you like from the link above.  I simply gleaned what I could from the stream in the notes here.

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