Highlights From Musk’s Ask Me Anything Session on Reddit

Elon Musk (Credit: SpaceX)

Elon Musk conducted an Ask Me Anything session on Reddit on Saturday. Below are selected responses to questions. A full list of questions and answers is located here.

BFR Development

Will be starting with a full-scale Ship doing short hops of a few hundred kilometers altitude and lateral distance. Those are fairly easy on the vehicle, as no heat shield is needed, we can have a large amount of reserve propellant and don’t need the high area ratio, deep space Raptor engines.

Next step will be doing orbital velocity Ship flights, which will need all of the above. 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.

Raptor Thrust Reduction From ~300 Tons-force to ~170 Tons-force

We chickened out

The engine thrust dropped roughly in proportion to the vehicle mass reduction from the first IAC talk. In order to be able to land the BF Ship with an engine failure at the worst possible moment, you have to have multiple engines. The difficulty of deep throttling an engine increases in a non-linear way, so 2:1 is fairly easy, but a deep 5:1 is very hard. Granularity is also a big factor.

If you just have two engines that do everything, the engine complexity is much higher and, if one fails, you’ve lost half your power. Btw, we modified the BFS design since IAC to add a third medium area ratio Raptor engine partly for that reason (lose only 1/3 thrust in engine out) and allow landings with higher payload mass for the Earth to Earth transport function.

Scaling Up Sub-scale Raptor Engine

Thrust scaling is the easy part. Very simple to scale the dev Raptor to 170 tons.

The flight engine design is much lighter and tighter, and is extremely focused on reliability. The objective is to meet or exceed passenger airline levels of safety. If our engine is even close to a jet engine in reliability, has a flak shield to protect against a rapid unscheduled disassembly and we have more engines than the typical two of most airliners, then exceeding airline safety should be possible.

That will be especially important for point to point journeys on Earth. The advantage of getting somewhere in 30 mins by rocket instead of 15 hours by plane will be negatively affected if “but also, you might die” is on the ticket.

Production of the Raptor Engines

Some parts of Raptor will be printed, but most of it will be machined forgings. We developed a new metal alloy for the oxygen pump that has both high strength at temperature and won’t burn. Pretty much anything will burn in high pressure, hot, almost pure oxygen.

Details on Fuel Tanker

At first, the tanker will just be a ship with no payload. Down the road, we will build a dedicated tanker that will have an extremely high full to empty mass ratio (warning: it will look kinda weird).

Landing Sites on Mars

Landing site needs to be low altitude to maximize aero braking, be close to ice for propellant production and not have giant boulders. Closer to the equator is better too for solar power production and not freezing your ass off.

In-situ Resource Utilization System Development

Design is pretty far along. It’s a key part of the whole system.

Plans for Developing Colony on Mars

Our goal is get you there and ensure the basic infrastructure for propellant production and survival is in place. A rough analogy is that we are trying to build the equivalent of the transcontinental railway. A vast amount of industry will need to be built on Mars by many other companies and millions of people

  • Terry Stetler

    “Will be starting with a full-scale Ship doing short hops of a few hundred kilometers altitude and lateral distance. Those are fairly easy on the vehicle”

    This alone could kill most all suborbital joyride business models, if SpaceX chose to pursue it. Longer, higher, and it looks like a futuristic spaceship – which it is.

  • savuporo

    IMO he confirmed again that all he has is a bunch of handwaving, not a specific plan to go and build a service and product from this. By IAC next year, it’ll be a new story and more outrageous hype

  • Michael Vaicaitis

    Strange, I got exactly the opposite impression: Raptor testing is proceeding well, the carbon fibre tank technology has been proven beyond the pressure requirements, the tooling for tank/hull manufacture HAS BEEN ORDERED, SpaceX has a $2-3 BILLION contract for carbon fibre supply. If all of this is just “hand-waving”, what then would you consider to be a firm commitment to proceed with a development program?.

  • ThomasLMatula

    Probably NASA giving him money to produce pretty viewgraphs as with they did with their real RLV efforts, X-33 and X-34 πŸ™‚

  • Douglas Messier

    The Air Force just issued a RFP for new launch vehicles that I imagine could help fund development of this program. Either this or an uprated Falcon 9 with Raptor second stage.

  • duheagle

    About the new engine alloy: It probably has a very high nickel content. The Monel and Inconel families of high-nickel superalloys have been around for a long time. Perhaps this new SpaceX Raptor engine alloy should be dubbed Elonel.

  • Mr Snarky Answer

    “viewgraphs” how the frack old are you?

  • Mr Snarky Answer

    Your detachment from reality seems to be approaching clinical levels.

  • Michael Vaicaitis

    Air Force money would help, but launching Falcons and Starlink should be enough. I could be wrong, but I’d say that an uprated Falcon with Raptor second stage would not be entertained, as it would distract resources from the BFR effort. Similarly, we all naively assumed that Dragon 2 was not being qualified for powered landing because of NASA related costs or issues. But looks like it was a SpaceX led decision, to divert funds and resources to BFR. I reckon SpaceX’s achievements have bought them a huge amount of trust and respect from the Air Force and NASA – who both have detailed access to data. They may not wish to contribute to BFR funding early on due to their own political pressures, but I wouldn’t take that as a sign of their lack of confidence in SpaceX’s ability to succeed with BFR; or as a sign that SpaceX won’t be able to finance at least the early development independently of government money. Once they build and fly a BFS demonstrator, further investment capital shouldn’t be much of a problem if needed. We don’t have access to their financial details, but seems unlikely Elon would steer this course now if he hadn’t already crunched the numbers quite thoroughly.

  • windbourne

    Why do u say this?
    One thing about musk is that when he sets his mind to something, he accomplishes it. The only that he differs with, is timelines.

    SX is the lowest priced launch system and is only going to be cheaper in.the near (stage 2 reuse ) and medium future( BFR/BFS ).
    Tesla is going gangbusters, though model 3 is still coming up to speed. Tesla has forced car makers to move from the last 5 years of THEIR hype, and are now starting to produce real EVs, and not their current jokes.

    Boring company, along with hyperloop, are making headway.

    All in all, I’ve never understood why ppl rip on HIM when he is busy changing the world.
    Even look at Doug. He does not rip on musk, but some the companies actions. Big difference.

  • Mr Snarky Answer

    Could be just a optimization on Mondaloy 200.


  • savuporo

    That part setting his mind at something and accomplishing it is obviously false, if you pay even slightest bit of attention. Many examples, Dragon powered landings, Red Dragon, F9H crossfeed, Tesla battery swaps, Falcon 1 achieving cost savings, Model S turning a profit etc etc.

    And this isn’t a critique: when things don’t work, the plan obviously needs to be changed. As they say, planning is everything, but the plans are worthless. I take more issue with the tunnel visioned hyperventilating fan club that praises everything that Musk utters without any rational thought, than the man himself.

  • Mr Snarky Answer

    Those aren’t goals, they are paths to goals. And if path doesn’t pan out, he uses another one.

    For instance, why cross-feed if you F9 baseline performance increased over time to not require it? No one is demanding performance above what FH can do at the moment.

    The propulsive landing and Red Dragon are the same so you are double accounting there. That is pretty straight forward, rather spend resources on BFR than spend time on qualifying Dragon 2 for prop landing.

    F1 did achieve cost savings the problem was market at the time wasn’t well developed for the payload class.

    You are in such denial, it’s sad.

  • Jimmy S. Overly

    Yeah, a nickel-based allow is a good bet.

  • Jimmy S. Overly

    I know, right? Blue Origin barely breaks 100 km with NS…and Elon’s talking about *a few hundred km* altitude? I wonder if the emphasis was supposed to be on lateral distance and we’re just reading too much into it.

  • Paul_Scutts

    To be fair to Musk/SpaceX, savuporo, they have a lot more than the usual Boeing/LM/etc. PowerPoint/Excel Spreadsheet presentations. At the time that Musk declared the putting on hold of Dragon 2 propulsive landing development, I thought, big mistake, but, when they released plans of the BFR, then I understood their reasoning that PLD2 was redundant and small potatoes. They are producing hardware and I wish them well with their plans, as, IMO, all HSF supporters should. Regards, Paul.

  • Bernardo Senna

    Right, but at least BO has plenty of time to operate before the BFR is even tested and offer a reliable time and price schedule to the public. If it happens, it’s the end of NS indeed. Virgin although is algready doomed even by BO which looks that will start to operate earlier, unless Virgin offers a survival trainning (yacht weekend in Bali) and other things included on the SST ticket.

  • Tom Billings

    Some of us are old enough to remember when viewgraphs were the new way to present ideas. πŸ™‚

  • ThomasLMatula

    Remember NS is merely serving as a test vehicle for the New Glenn. And market revenue it earns from space tourism or research flight is secondary to the experience gained. You need to breakout of the Ansari X-Prize mind set in looking at NS.

  • ThomasLMatula

    Old enough to know how to write Fortran IV on punch cards πŸ™‚

  • Bernardo Senna

    Yes, but I was saying in Thethe sense that BO has a business plan beyond tourism, through NG and N. Armstrong. NS will build a reputation to BO like F9 did to Spacex. Virgin has nothing competitive in the long haul.

  • ThomasLMatula

    Yes, VG is basically a dead end, both for space tourism and their small sat system – Launcher One.

  • Bernardo Senna

    Remembering the SSO, it broke the mental resistance for the very idea of space tourism, it’s a great merrit. But at the end it became one “how not to do” case. Not entirely predictable but it shows the diference the vision, focus and passion do, besides money and previous prestige in Branson’s case.

  • MzUnGu

    Nxt time someone go ask him… If 1 or 2 BFR can basically launch all the satellites that people can build in a year, what on earth is it going to do 4 the rest of the year? Waiting a few decades for the big payload to come like the Saturn V?

  • duheagle

    We ain’t done big reusable rockets before.

  • Aerospike

    Let us assume for a moment, that your scenario is realistic* and “1 or 2 BFR can basically launch all the satellites that people can build in a year”.

    What are they going to do the rest of the year?
    Well flying payloads to the moon, mars and the rest of solar system of course! πŸ˜‰

    * = I’m pretty sure your assumption is wrong. Even if all the satellites in one year could be launched by mass in one or two BFR launches, they sure can’t cope with all the different target orbits at once. And then there is the thing about schedules: not every bird is ready at the same time and I doubt anybody want’s their finished satellite collecting dust on a shelf for up to a year until the next launch.

    “Aggregated launch” is not how the future will look like, not even with BFR, New Glenn and other (super) heavy launchers.

  • windbourne

    Let’s see;
    Powered dragan landing/red dragon are pretty much the same thing. And yeah, I am still not happy that he is not doing that, but his choice.
    FH Xfeed not needed. He was looking at 54 tonnes with that and now will have 64-70 tonnes with block 5.
    Tesla battery swap works, and a site setup but nobody wanted it. Otoh, it appears that it will be used for semi.
    F1 was much cheaper than other launchers that size, but still more expensive than F9 on per kg basis.
    Turning profits with Tesla is easy. Just quit building out network, showroom, rtc. Of course, that would be the kiss of death. And once M3 is in full production, they will likely be profitable.

    All in all, he has done what he has said he would do.

  • windbourne

    Let’s leave personal attacks out.
    Savuporo has his beliefs and that is fine.
    And he does not attack you for your beliefs.

  • windbourne

    The fact that it’s supposed to cost less than FH or F9 to launch, will mean that they can launch weekly or monthly, and ppl can add last minute loads.
    But it also means that BFR will go up light for some time.

  • ThomasLMatula

    Same was true with the first FedEx flights, which was why they used converted business jets. It took a while for business to realize that next day delivery was worth it and adapt. And now FedEx uses jumbo jets and has competitors in the rapid package delivery business.

  • ThomasLMatula

    Especially big reusable rockets so cheap as to make point to point on Earth feasible…

  • windbourne

    I was thinking that one possibility for SX, is to set up up landing spot in Australia, and another off England.
    At the same time, that they are launching sats, they could land in a different area and simply take 100+ tonnes of cargo there.

  • Mr Snarky Answer

    There is a term when one’s beliefs don’t comport with reality…i’m looking for it….

  • ThomasLMatula

    Not really, as Dennis Tito did that.

    VG did make it seem possible for a while but the delays of VG has almost turned it into a joke again. FYI


    Time’s up for Spaceport America
    By D.Dowd Muska | October14, 2017

    “Virgin Galactic once hoped to launch their first customers as soon as 2008. Almost a decade later, no tourists have soared into the wild black yonder from New Mexico. And despite regular promises that other firms will soon make use of the spaceport, activity there remains essentially nil.”

  • Bernardo Senna

    Agree, but he and others paid millions to fly on expensive proven technology. I was refering to new, of “affordable” technology.

  • windbourne

    yeah, that would be my ex.
    That is not savuporo.

  • MzUnGu

    Don’t you need a few decades for the moon hardware development to catch-up? While the BFR is launching 1 or 2 6-tonne sats at a time with , with all the extra rooms/capacity/lifting mass/fuel wasted? Do this a few years, the company coffer will be dry up real quick.

  • Jeff2Space

    When I earned my B.S. in Aerospace Engineering, our required programming class was FORTRAN 77 and our senior design project presentations were all done on overhead viewgraphs. This was right when the DC-X program was well underway, but had not yet flown (graduated in 1992). After I graduated, it successfully flew about a year later proving VTVL was a viable mode of operation for a liquid fueled rocket powered vehicle.

  • Paul451

    While the BFR is launching 1 or 2 6-tonne sats at a time with , with all the extra rooms/capacity/lifting mass/fuel wasted? […] Do this a few years, the company coffer will be dry up real quick.

    That’s retarded. The launch price they are aiming for is lower than Falcon 1. Even if they end up only matching F9’s launch price (including profit margin), then there’s no more “waste” in BFR than an F9 launch.

    Who cares if half the truck is empty if the driver is making money?

    (Literal example, since I’ve “dogged” for a family member who owned/drove a freight truck, you typically did trips with just a quarter or even an eighth of the truck’s volume capacity, and very often less than a tenth the weight capacity. If the client is willing to pay for the trip, the owner didn’t care. It was rare that the truck was at volume capacity, even rarer than it was at weight capacity. And we seriously had trips where the only cargo was a package that we carried inside the cab.)

    In the case of BFR, if they find they are mostly launching light, they can add pressurised compartments and carry tourists. If a launch is paid for by the payload owner, any passenger tickets are pure gravy.

    (People currently pay $5000 for a single vomit-comet flight, which is less than ten minutes total of intermittent bursts of up to 30 seconds of zero-g. What would they pay for half a day in orbit?)

  • Aerospike

    Or – depending what exactly means “BFS can reach LEO with a low payload” – some light payloads could even be launched on BFS alone.

  • duheagle

    So Tuesdaloy 200, then? πŸ™‚

  • duheagle

    Generally agree. I differ, though, anent the Dragon 2 propulsive landing thing. I think that was a last-gasp attempt by anti-SpaceX types within NASA to spite SpaceX. I think the Adelaide BFR proposal owes, at a minimum, its accelerated timeline to it being a strategic response to this sort of NASA obstructionism. I think SpaceX will take USAF money to cover part of BFR’s remaining development and prototype construction expenses if it becomes available, but I don’t think SpaceX is likely to take any more NASA development money for awhile. And even the USAF money would just be a nice-to-have, not a necessity.

    USAF money would, in my view, be vastly less likely to be accompanied by the sort of inimical buttinsky-ism we saw from NASA anent Dragon 2 propulsive landing. USAF is facing a genuine threat to its space domain role in the form of Rep. Rogers’s Space Corps proposal. I think USAF is finally aware that it can’t keep treating space as a piggy bank it can use to bail out aircraft programs. Thus, anything that makes it economical to finally discharge its too-long-neglected space responsibilities is going to massively appeal to a USAF now very interested in saving as much as possible on standing up long-overdue real space war-fighting capabilities. That would be SpaceX in general and BFR in particular. Elon has made a lot of blue-suited friends the last two or three years.

  • Michael Vaicaitis

    You could be right about Dragon propulsive landing. Either way, an earlier and more achievable/realistic BFR is a positive and welcome outcome.
    Whatever the USAF space remit, I’d guess they’d welcome being able to get more things done at an “affordable” cost, after years of being price gouged by the ULA monopoly. The lure of further decreased cost and increased capability from BFR, must be as tantalising to USAF as it is to the rest of us.

  • publiusr

    Medaris at the ABMA wanted Phil Bono’s troop Rockets.

    Sadly, Medaris and Musk missed each other by decades. Both had their troubles with the Air Farce.

    Here is an idea. Don’t put the Space Corp under the USAF–as it stands.

    Bring back the ABMA. BFS is their baby now.