Reddit AMA — “I am Elon Musk, CEO/CTO of a rocket company” (r/IAmA, 2015)

u/prettypenny42: Hi Elon, I'll leave the technical questions to the experts. 1) Do you plan on getting any sleep tonight and 2) how will you celebrate if the test is successful? Best of luck!

Elon Musk: Yes, but probably only a few hours Party at Cocoa Beach!

u/salty914: Has the Raptor engine changed in its target thrust since the last number we have officially heard of 1.55 Mlbf sea-level thrust?

Elon Musk: Thrust to weight is optimizing for a surprisingly low thrust level, even when accounting for the added mass of plumbing and structure for many engines. Looks like a little over 230 metric tons (~500 klbf) of thrust per engine, but we will have a lot of them :)

u/[deleted]: [question deleted by its author — it asked about the Falcon Heavy centre core recovery, the Mars transport system, and the SpaceX spacesuit]

Elon Musk: 1. Yes, the Falcon Heavy center core is seriously hauling a** at stage separation. We can bring it back to the launch site, but the boost back penalty is significant. If we also have to do the plane change for geo missions from Cape inclination (28.5 deg) to equatorial, then a downrange platform landing is needed. 2. The Mars transport system will be a completely new architecture. Am hoping to present that towards the end of this year. Good thing we didn't do it sooner, as we have learned a huge amount from Falcon and Dragon. 3. Our spacesuit design is finally coming together and will also be unveiled later this year. We are putting a lot of effort into design esthetics, not just utility. It needs to both look like a 21st century spacesuit and work well. Really difficult to achieve both.

u/salty914: Question about the Mars Colonial Transporter: there has been a lot of speculation over exactly how much mass you are hoping to send to the Martian surface with the MCT. Can you tell us how much cargo you would like to be able to land on Mars with MCT, not including the mass of the MCT itself?

Elon Musk: Goal is 100 metric tons of useful payload to the surface of Mars. This obviously requires a very big spaceship and booster system.

u/FoxhoundBat: In order to use the full MCT design (100 passengers), will BFR be one core or 3 cores?

Elon Musk: At first, I was thinking we would just scale up Falcon Heavy, but it looks like it probably makes more sense just to have a single monster boost stage.

u/awests: Hello Mr. Musk, I sold you a pair of hiking boots at the Sports Authority Elite in Corte Madera. I just wanted to know how your walk through the forest (as you described it) went? Also did you like the boots?

Elon Musk: Yeah, they were great

u/salty914: Emily Shanklin indicated in late 2013 that the Raptor would be the first of a “family of engines” designed for the exploration and colonization of Mars. Could you elaborate on her wording — was she simply referring to a vacuum version and a standard version, or do you plan on building multiple methane-based engines with significantly different thrust and size specifications?

Elon Musk: Default plan is to have a sea level and vacuum version of Raptor, much like Merlin. Since the booster and spaceship will both have multiple engines, we don't have to have fundamentally different designs. This plan might change.

u/StapleGun: Hi Elon, I'm already saving up for my Model 3. Can you share anything about the Model 3 that we don't already know?

Elon Musk: It won't look like other cars

u/1201alarm: Mr Musk, how will you secure the first stage of the Falcon 9 to the barge when it lands? Gravity or some mechanism?

Elon Musk: Mostly gravity. The center of gravity is pretty low for the booster, as all the engines and residual propellant is at the bottom. We are going to weld steel shoes over the landing feet as a precautionary measure.

u/AvenueEvergreen: Previously, you've stated that you estimate a 50% probability of success with the attempted landing on the automated spaceport drone ship tomorrow. Can you discuss the factors that were considered to make that estimation? In addition, can you talk more about the grid fins that will be flying tomorrow? How do they compare to maneuvering with cold-gas thrusters?

Elon Musk: I pretty much made that up. I have no idea :) The grid fins are super important for landing with precision. The aerodynamic forces are way too strong for the nitrogen thrusters. In particular, achieving pitch trim is hopeless. Our atmosphere is like molasses at Mach 4!

u/Forrestal: SpaceX's current strategy revolves mostly around old style rockets, even if they are now approaching complete reusability (Grasshopper rocks). Has SpaceX looked into hybrid craft like the SABRE programme happening in the UK, or looked into the possibility of a space elevator (even at a thought-experiment stage) in the way that Google and NASA have done?

Elon Musk: If you want to get to orbit or beyond, go with pure rockets. It is not like Von Braun and Korolev didn't know about airplanes and they were really smart dudes.

u/usa_dublin: Hi Elon. A friend of mine is all paranoid about the computer singularity, and used your name as a source of his paranoia. Don't you think it could all be a bunch of hype?

Elon Musk: The timeframe is not immediate, but we should be concerned. There needs to be a lot more work on AI safety. And, with all due respect to the Roomba dude, that is not a concern https://www.youtube.com/watch?v=Of2HU3LGdbo

u/MarsColony_in10years: In your recent MIT talk, you mentioned that you didn't think second-stage recovery was possible for the Falcon 9 — due to the low fuel efficiency of kerosene and the high velocities needed for many payloads. However, you also said that full reusability would be possible for the Mars Colonial Transporter launch vehicle. What have you learned from flights of Falcon 9 that taught you (a) that reuse of its second stage won't be possible and (b) what you'll need to do differently with MCT to reuse its second stage?

Elon Musk: Actually, we could make the 2nd stage of Falcon reusable and still have significant payload on Falcon Heavy, but I think our engineering resources are better spent moving on to the Mars system. MCT will have meaningfully higher specific impulse engines: 380 vs 345 vac Isp. For those unfamiliar, in the rocket world, that is a super gigantic difference for stages of roughly equivalent mass ratio (mass full to mass empty).

u/aerovistae: [The asker later replaced the text of this question. It originally asked how Elon had been able to learn enough to run both Tesla and SpaceX, two engineering-intensive companies, at the same time.]

Elon Musk: I do kinda feel like my head is full! My context switching penalty is high and my process isolation is not what it used to be. Frankly, though, I think most people can learn a lot more than they think they can. They sell themselves short without trying. One bit of advice: it is important to view knowledge as sort of a semantic tree -- make sure you understand the fundamental principles, ie the trunk and big branches, before you get into the leaves/details or there is nothing for them to hang on to.

u/[deleted]: Follow-up question: how much do you sleep per night, on average?

Elon Musk: I actually measured this with my phone! Almost exactly 6 hours on average.

u/Skov: Nice to see you are doing things the Kerbal way.

Elon Musk: Kerbal is awesome!

u/ken27238: Have you played Kerbal Space Program? What do you think SpaceX uses for testing software?

Elon Musk: Kerbal Space Program!

u/danielle_miller: I'm a teacher, and I always wonder what I can do to help my students achieve big things. What's something your teachers did for you while you were in school that helped to encourage your ideas and thinking? Or, if they didn't, what's something they could have done better?

Elon Musk: The best teacher I ever had was my elementary school principal. Our math teacher quit for some reason and he decided to sub in himself for math and accelerate the syllabus by a year. We had to work like the house was on fire for the first half of the lesson and do extra homework, but then we got to hear stories of when he was a soldier in WWII. If you didn't do the work, you didn't get to hear the stories. Everybody did the work.

u/FoxhoundBat: The design life of the Merlin 1D has been mentioned to be 40 “cycles”. Could you expand on what a “cycle” is? Is it just a start of the engine?

Elon Musk: There is no meaningful limit. We would have to replace a few parts that experience thermal stress after 40 cycles, but the rest of the engine would be fine.

u/chasbecht: What kind of mass ratio do your upper stages have?

Elon Musk: With sub-cooled propellant, I think we can get the Falcon 9 upper stage mass ratio (excluding payload) to somewhere between 25 and 30. Another way of saying that is the upper stage would be close to 97% propellant by mass.

u/TCEchicago: What daily habit do you believe has the largest positive impact on your life?

Elon Musk: Showering

u/ghostrider176: 1) What is your favorite airplane? 2) What is your favorite video game? 3) What is your favorite food? 4) If you consume alcohol, what is your favorite alcoholic drink?

Elon Musk: SR-71 Hard to pick a favorite. I tend to like FPS with a story, like Bioshock, Fallout or Mass Effect, but was also a big fan of Civ and Warcraft. French and BBQ Whiskey

u/[deleted]: [question deleted by its author]

Elon Musk: Good school

u/[deleted]: Europa: attempt no landing there. True or false?

Elon Musk: There should definitely be a science mission to Europa

u/catsx3: Hi Elon, I currently work for Toyota Tsusho in Fremont doing the wheel assembly for Tesla. My question: you seem to have had to deal with a tremendous amount of adversity in a few of your ventures. Do you have any advice for those dealing with seemingly insurmountable adversity?

Elon Musk: There is a great quote by Churchill: "If you're going through hell, keep going."

u/[deleted]: Would you ever consider becoming a politician?

Elon Musk: Unlikely