After his introduction of the ITS at the IAC talk, Elon Musk honored /r/spacex with a question and answer session, also called "Ask me anything" (AMA).
Here presented are the questions of the Reddit users and Elon Musk's answers, together the occasional comment that was useful or entertaining. I also added the linked pictures from redditors into the article.
For more information have a look at the original [thread here.](https://www.reddit.com/r/spacex/comments/590wi9/i_am_elon_musk_ask_me_anything_about_becoming_a/)
Let's start:
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# Introduction
### I am Elon Musk, ask me anything about becoming a spacefaring civ!
This AMA is meant to be supplemental to my IAC talk: http://www.spacex.com/mars
Proof: https://twitter.com/elonmusk/status/790267936258666496
Thanks everyone. Have to sign off now. *(note from engineercampus: Elon edited his post here after his time for the AMA was over)*
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# Question 1
### El-Psy-Kangaroo
What equipment and procedures will be required for refueling operations on Mars? Will they be designed to function autonomously for the initial unmanned test flight?
Also, are there any plans to introduce a third variant of the ITS with just a large shuttle-like payload bay to allow for transporting bulkier cargo?
### ElonMuskOfficial CEO of SpaceX
We are still far from figuring this out in detail, but the current plan is:
1. Send Dragon scouting missions, initially just to make sure we know how to land without adding a crater and then to figure out the best way to get water for the CH4/O2 Sabatier Reaction.
2. Heart of Gold spaceship flies to Mars loaded only with equipment to build the propellant plant.
3. First crewed mission with equipment to build rudimentary base and complete the propellant plant.
4. Try to double the number of flights with each Earth-Mars orbital rendezvous, which is every 26 months, until the city can grow by itself.
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# Question 2
### Ulysius
As a follow-up, considering the synodal reuse of the ITS spaceships, what form of permanent habitation do you foresee? Shipped modules or an (eventual) shift to in-situ resource utilization such as Martian rigolith/plastic-reinforced concrete structures?
Thank you for your time.
### ElonMuskOfficial CEO of SpaceX
Initially, glass panes with carbon fiber frames to build geodesic domes on the surface, plus a lot of miner/tunneling droids. With latter, you can build out a huge amount of pressurized space for industrial operations and leave the glass domes for green living space.
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# Question 3
### FoxhoundBat
- Overall is the landing architecture of ITS booster and distances needed to be covered to be same as Falcon 9’s? Boostback, re-entry burn, landing burn?
- Could you give us nuggets on what changes the ”final” Falcon 9 version (”v1.3”) you mentioned will have? Uprated engines obviously from 170k to 190k lbf, but what else? Is it mostly geared towards reusabilty over performance?
- Gwynne mentioned 2 weeks ago that F9 v1.2 will be reused only once or twice while ”v1.3” should be reused up to 10 times. Can you talk about what are the limiting factors for Falcon 9 reuse?
### ElonMuskOfficial CEO of SpaceX
The big booster will have an easier time of things than Falcon, as the mass ratio of the stages is lower and it will have lower density. Net result is that it won't come in quite as hot and fast as Falcon, so Falcon should be a bounding case on the big booster.
Final Falcon 9 has a lot of minor refinements that collectively are important, but uprated thrust and improved legs are the most significant.
Actually, I think the F9 boosters could be used almost indefinitely, so long as there is scheduled maintenance and careful inspections. Falcon 9 Block 5 -- the final version in the series -- is the one that has the most performance and is designed for easy reuse, so it just makes sense to focus on that long term and retire the earlier versions. Block 5 starts production in about 3 months and initial flight is in 6 to 8 months, so there isn't much point in ground testing Block 3 or 4 much beyond a few reflights.
### Comment 1: secondlamp
> Falcon 9 Block 5
Falcon 9 naming scheme everybody
### Comment 2: Destructor1701
> Falcon 9 Block 5
Alright, now I know you're taking the piss with the names, man!
Falcon 9 (retconned to v1.0)
Falcon 9 v1.1
Falcon 9r v1.1
Falcon 9 Full Thrust (which then had fuller, fullerer, and fullerest thrust upgrades iirc)
and now "Falcon 9 Block 5"!?
Do you have something against consistent naming schemes!?
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# Question 3
### MINDMOLESTER
Hi Elon,
ITS question:
What SpaceX technology/material still requires the most development for ITS to be a success?
Thank you!
### ElonMuskOfficial CEO of SpaceX
It used to be developing a new metal alloy that is extremely resistant to oxidation for the hot oxygen-rich turbopump, which is operating at insane pressure to feed a 300 bar main chamber. Anything that can burn, will burn. We seem to have that under control, as the Raptor turbopump didn't show erosion in the test firings, but there is still room for optimization.
Biggest question right now is sealing the carbon fiber tanks against cryo propellant with hot autogenous pressurization. The oxygen tank also has an oxidation risk problem as it is pressurized with pure, hot oxygen. Will almost certainly need to apply an inert layer of some kind. Hopefully, something that can be sprayed. If need be, will use thin sheets of invar welded together on the inside.
### Comment: jerobrine
for anyone wondering what Invar is
> Invar, also known generically as FeNi36 (64FeNi in the US), is a nickel–iron alloy notable for its uniquely low coefficient of thermal expansion (CTE or α). The name Invar comes from the word invariable, referring to its relative lack of expansion or contraction with temperature changes.
[wiki link](https://en.wikipedia.org/wiki/Invar)
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# Question 4
### rohishimoto
In addition, what technology (if any) do you think you have nailed down/mastered at this point?
### ElonMuskOfficial CEO of SpaceX
Not sure that we've really mastered anything yet. Maybe starting engines...
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# Question 5
### termderd Everyday Astronaut
We got a pretty good idea of what a Mars EDL looks like, but can you explain how the ITS and the Tanker plan to do an Earth EDL? Having talked with you at IAC about the Mars entry, we learned that there's very powerful thrusters that can handle attitude control. These work great for the Martian atmosphere, but what about on earth? There doesn't appear to be grid fins and the thrusters obviously have less authority here on earth, so what's the trick?
Thanks for your time!
- Tim Dodd, [The Everyday Astronaut](http://instagram.com/everydayastronaut)
### ElonMuskOfficial CEO of SpaceX
Good question -- that wasn't shown at IAC. The spaceship and tanker would have split body flaps for pitch and roll. Probably just use the attitude control thrusters for yaw.
### Comment: Arthur233
Split body flaps might [look like this](http://spaceflightnow.com/wp-content/uploads/2015/02/IXV.jpg) if anyone was curious
*Engineercampus Note:*
http://spaceflightnow.com/wp-content/uploads/2015/02/IXV.jpg
*What split body flaps on the IAC might look like. [Source](http://spaceflightnow.com/wp-content/uploads/2015/02/IXV.jpg)*
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# Question 6
### __Rocket__
**ITS Spaceship design question II.:**
The ITS Spaceship has [two mystical spherical tanks, marked green in this slightly edited image](http://imgur.com/a/UT4ny). The whole tank design looks very exciting, and there's rampant speculation on this sub about the purpose of those spherical tanks:
- are they for landing fuel?
- ... or are they storing 'hot' gaseous propellants as part of the autogenous propellant pressurization system?
- ... or are they used for on-orbit propellant densification to store vapor before it's liquefied again?
All of the above perhaps?
*Engineercampus Note:*
http://i.imgur.com/m1TEWWW.png
*The position of the mysthical spherical tanks. [Source](http://imgur.com/a/UT4ny)*
### ElonMuskOfficial CEO of SpaceX
Those are the header tanks that contain the landing propellant. They are separate in order to have greater insulation and minimize boil-off, avoid sloshing on entry and not have to press up the whole main tank.
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# Question 7
### _rocketboy
Also, why does the booster only have one in 1 tank?
### ElonMuskOfficial CEO of SpaceX
The liquid oxygen transfer tube serves as the header tank for ox
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# Question 8
### TheVehicleDestroyer Flight Club (#IAC2016 Attendee)
Hi Elon. I’ve got 3 questions on the ITS vehicle specs:
- Can you divulge what the Vacuum Thrust+Isp figures are for the Sea-Level Raptor variant?
- The ITS booster is able to hover. Will it ever use this capability to better ensure a successful landing at the expense of some small gravity losses, or is it hoverslams all the way?
- What is the expected maximum acceleration that the ITS booster can withstand during entry/landing?
Thanks for everything.
### ElonMuskOfficial CEO of SpaceX
- Approx 360 sec vacuum Isp and 290 metric tons of thrust
- A high acceleration landing is a lot more efficient, so there wouldn't be any hovering unless it encountered a problem or unexpected wind conditions. A rocket that lands slowly is wasting a lot of fuel.
- Aiming for 20 g's
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# Question 9
### Tesla_X_City
If I recall correctly on one of the slides it mentioned that there it will be 4-6 G's upon reentry. It does not specify, however, whether that will be during the landing burn or aerobreaking. It would be nice if that is clarified as well.
### ElonMuskOfficial CEO of SpaceX
The spaceship would be limited to around 5 g's nominal, but able to take peak loads 2 to 3 times higher without breaking up.
Booster would be nominal of 20 and maybe 30 to 40 without breaking up.
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# Question 10
### __Rocket__
**ITS Booster engine placement design question:**
The tight cluster of 42 engines of the ITS Booster (cool number!! 😉) has created speculation on this sub that maybe they are packed so tighty because that way there's a "virtual nozzle" or "virtual aerospike" effect they can take advantage of: they can have shorter nozzles while most of the exhaust momentum of the inner engines is still axial.
Is there any truth to this speculation or is the tight packing done purely to scale up liftoff TWR?
(Members of this sub are torn and conflicted: some suggest it's possible - some think it's physically impossible to have any such thrust increase effect with an exhaust that has hipersonic velocities.)
### ElonMuskOfficial CEO of SpaceX
It had to be 42 for important scientific and fictional reasons!
The dense packing is just to max out thrust to weight, but it would be cool if there was a virtual nozzle side effect.
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# Question 11
### nalyd8991
I think one of the most shocking things in your ITS presentation for many people was the full size carbon fiber tank SpaceX built. [Here](http://i.imgur.com/MtHQM5g.jpg) it is for those who haven't seen it. Can you tell us a little bit more about the design, construction, and role of that particular test article?
*Engineercampus Note:*
http://i.imgur.com/MtHQM5g.jpg
*The full size carbon tank for the cryogenic propellant. [Source](http://i.imgur.com/MtHQM5g.jpg)*
### ElonMuskOfficial CEO of SpaceX
Yeah, for those that know their stuff, that was really the big news :)
The flight tank will actually be slightly longer than the development tank shown, but the same diameter.
That was built with latest and greatest carbon fiber prepreg. In theory, it should hold cryogenic propellant without leaking and without a sealing linker. Early tests are promising.
Will take it up to 2/3 of burst pressure on an ocean barge in the coming weeks.
### Comment 1: ChateauErin
Not only does that sound exciting, it reminds me of a passage from Skunkworks:
> ...We got Dr. Scott of the Bureau of Standards cleared to work with us as an adviser. The Fort Robertson complex was located less than a thousand yards from the Municipal Airport's in-bound runway. And the first time Dr. Scott paid us a visit and saw the three tanks of liquid hydrogen holding hundreds of gallons under storage, his knees began to shake. "My God in heaven," he exclaimed, "you're gonna blow up Burbank."
Interesting that your tanks will be on a barge. :) Good luck, and I hope to help out someday.
### Comment 2: johnkphotos AmericaSpace.com Photographer
> Will take it up to 2/3 of burst pressure on an ocean barge in the coming weeks.
On behalf of all of us, lots and lots of video and camera angles, *please* :)
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# Question 12
### Zucal
Hi Elon, and many thanks for doing this today!
What level of completion is the interior habitable area layout of ITS at, and when might we expect to see renderings of it?
### ElonMuskOfficial CEO of SpaceX
I think we need a new name. ITS just isn't working. I'm using BFR and BFS for the rocket and spaceship, which is fine internally, but...
Will aim to release details of the habitation section when we have actual live mockups. Maybe in a year or two.
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# Question 13
### theZcuber
As an add-on, how differently will the ITS be configured internally for a smaller crew (such as the first one) vs. a full 100-man crew?
### ElonMuskOfficial CEO of SpaceX
Probably just pack the pressurized space with cargo. Early missions will be heavily weighted towards cargo. First crewed mission would have about a dozen people, as the goal will be to build out and troubleshoot the propellant plant and Mars Base Alpha power system.
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# Question 14
### __Rocket__
**ITS Spaceship capabilities question II.:**
[According to your IAC presentation](http://i.imgur.com/fN23l6C.png) the ITS Spaceship has a Δv budget of 7.5 km/s when returning from Mars to Earth, with 150 tons of payload. With a much smaller payload it has a Δv budget in excess of 9.0 km/s - which is amazing!
Could this unprecedented amount of Δv be used to fly between Mars and Earth even outside the launch windows enforced by the synodic period, when payload mass is not a primary factor? It could be used for emergency purposes such as medical supplies/instruments and experts, or for other high priority but low mass cargo like critical replacements.
### ElonMuskOfficial CEO of SpaceX
yes
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# Closing note from Engineercampus
Hi it is me again! I hope you enjoyed this little, but imformative, Q&A as much as I did. It is very interesting to have such a close contact to someone working so far forward in the field. As a personal note, he also confirmed what I see as his intention: Building the bridge to space and making it more possible to go to Mars, but not attemting to build the whole colony himself.
It is litterally an invitation from Elon Musk not to stand on the side and watch him do his magic, but come up with ideas: He wants you to take part and help build this colony, come up with products that makes the lives of future martians easier and the future of humanity on Mars possible.
If you happen to have an idea for a product, you might want to head over to my engineering series. There I layed out the [13 Steps to your Product](https://steemit.com/engineering/@engineercampus/13-steps-to-develop-your-product-an-overview) that will bring an idea into reality and in a few years maybe:
## to Mars
Thank you for reading!
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