Random Thoughts: A Now Rather Cold Take on BFR

When Elon gave his update on BFR at the IAC conference in Australia, I was originally going to post some thoughts right away1. But with Falcon Heavy’s maiden launch attempt coming up tomorrow, I realized I still hadn’t collected my thoughts about BFR into one place, instead of leaving them scattered over two dozen twitter arguments with Chris and others. I’ve had a lot of thoughts since the original announcement, but I wanted to share five thoughts that I had at the time that I still feel pretty strongly about:

  1. More Reasonable Size (Though Still Probably Too Big): I liked that Elon shrunk the size of BFR to something slightly less insane than ITS (a 50% drop from 300mT to 150mT). I still think he’s going way too big for any realistic markets near or medium term markets, but it’s a step in the right direction. I’m not convinced you need anything bigger than ~30-40mT to LEO to do Mars exploration and settlement, and you definitely don’t need anything that big to service near-term and future markets.
  2. Replacing Falcon 9, Falcon Heavy and Dragon with BFR/BFS: This was actually my favorite part of the plan in theory. In theory replacing the semi-expendable Falcon 9 and Falcon Heavy with a fully-reusable, and in-space refuelable launch vehicle would be a great idea. Especially one that was a single-stick, not crazy high aspect-ratio vehicle. And once you have that, and have the upper stage reliability up high enough, having an integral crew/passenger capability without needing a separate capsule could be a really powerful combination. Getting to high flight rate reusability is far more important for affordable deep space transport than getting to gargantuan rocket size. Something more modestly sized (say in the 30-40mT fully reusable range) would’ve been a much smaller leap, and I think would’ve much better taken advantage of the best part of Elon’s updated plan.
  3. BFR Leaves Open Room for Competition:At 150mT, BFR would be flying mostly empty on most flights for the foreseeable future. It would only really replace Falcon 9, Falcon Heavy, and Dragon if nobody else succeeds at doing a fully-reusable vehicle in a more sane scale. While it may be possible that a BFR sized fully-reusable launch vehicle might have much lower $/kg when flying completely full than a smaller sized fully-reusable vehicle using similar design architecture and technology choices, if BFR is flying mostly empty for most realistic near-term missions (satellite launch, ISS crew/cargo, etc), the actual cost to fly a realistic payload will probably be cheaper on a more right-sized vehicle. Personally, I think there’s a huge potential here for someone who wants to make a 1-10mT to LEO full RLV. While the $/kg might not be as good as a fully-loaded BFR or fully-reusable New Glenn/New Armstrong, the $/mission for most realistic near-term missions would likely be lower. I really hope someone else is able to raise money and execute on a small to medium RLV, I really don’t want to have to go back to launch vehicles for my next startup.
  4. Skeptical about Suborbital Point to Point: If you project BFR economics out to the point where it really hits some low multiple of the propellant costs, it theoretically could be competitive for some long-range travel. I just have a hard time seeing a rocket-based system with that high of performance and that razor thin of margins ever getting within spitting distance of the reliability of jet aircraft, especially within the foreseeable future. There are just so many technical and non-technical challenges for this market to make sense, and I think a lot of them are exacerbated by how big BFR is.
  5. What About Space Tourism? While I’m really skeptical about how realistic the suborbital point-to-point market for BFR, I’m kind of surprised Elon didn’t propose space tourism as a market. After all, if BFR can really keep 100+ people comfortable for a 6+ month Mars mission, you’d think they could easily handle 100 people for a 1-2 week stay in LEO. Even without space hotels as a destination, if he can really get down to a $200k/person Mars ticket using 5 launches, he should be able to get down to a $40k/person ticket for a two week space trip. If he was going to a space hotel and could pack people in as tightly as they were suggesting for BFR point-to-point suborbital flights, he could probably get the price for a LEO vacation down below $10k. While there are legitimate questions about how much market there is for space tourism at $20M+ per seat, is there really any doubt that there’d be a market for space tourism if it really cost only $10-20k per person for a 1-2 week LEO cruise?

Those were the five things that hit me the most. While I think BFR is an improvement over the original ITS plan, I think it still leaves a big opening for a serious competitor that didn’t feel the need to get into rocket size competitions with Elon and Jeff2.

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Jonathan Goff

Jonathan Goff

President/CEO at Altius Space Machines
Jonathan Goff is a space technologist, inventor, and serial space entrepreneur who created the Selenian Boondocks blog. Jon was a co-founder of Masten Space Systems, and is the founder and CEO of Altius Space Machines, a space robotics startup in Broomfield, CO. His family includes his wife, Tiffany, and five boys: Jarom (deceased), Jonathan, James, Peter, and Andrew. Jon has a BS in Manufacturing Engineering (1999) and an MS in Mechanical Engineering (2007) from Brigham Young University, and served an LDS proselytizing mission in Olongapo, Philippines from 2000-2002.
  1. Had I done so at the time, this post might have qualified as a hot take, but now that it’s been over 4 months, I’m not sure I can even count this as a “lukewarm take” on BFR, hence the self-deprecating title.
  2. I had to rewrite that sentence at least a half dozen times to make it not sound completely dirty.
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14 Responses to Random Thoughts: A Now Rather Cold Take on BFR

  1. Dave Salt says:

    Better late than never, Jon 🙂

    I think your Point 3 is the most significant as reusable launcher economics tend to favor systems that fly full and frequently, so smaller vehicles may be more successful at serving existing markets than extremely large ones. Sure, this will likely change as the markets develop but this will not happen instantaneously, so a small RLV may have a reasonable window of opportunity to make serious money.

    It’s a real pity that XCOR failed in their endeavor to do exactly this, so I’d love to see someone like Musk or Bezos funding something in parallel to their ‘big sticks’… and the sight of those two FH cores landing together shows just what can be accomplished with today’s technology.

  2. While BFR+BFS for the point-to-point market is crazy, BFS is really close to being able to haul 5-10 t of payload as a single stage to suborbit vehicle. It needs a bit more T/GLOW, but there’s plenty of room for more engines (especially the under-expanded ones). It’s definitely a different thrust structure, but that might be a small development price to pay to crack open a market that big.

  3. N/A says:

    What’s a LEO delivery taxi capable of 8-10 people (or equivalent pressurized cargo in the empty seat space) weigh if done like a BFS-esqe integrated second stage/lander? 10 metric tons or so as payload? Design to that?

    Gemini capsule was two guys packed like sardines, and that was what, 2mT?

  4. matterbeam says:

    @TheRadicalModerate:

    My own calculations show that while delivering a payload to orbit as an SSTO is possible… you cannot also carry enough propellant in reserve to do a powered landing.

  5. @ matterbeam

    Yeah, I forgot that when I wrote the comment. So I did a little figuring.

    First, a correction: We don’t care about orbit and an SSTO; we care about viable suborbital trajectories and an SSTSO to interesting places.

    The slideware version of the BFS has a structural coefficient of 0.072. Your total delta-v, assuming 5 t of payload (50 passengers with luggage) at about Isp=343, is 8686 m/s. Lop off 650 for landing (a tad more than what the F9 uses) and 1420 for gravity and aero drag, and you’re down to 6616 m/s of point impulse.

    That’s enough for a range of 7115 km with no rotational bonus, 8620 km going due east from New York, and 6004 km going due west. That’s good enough for pretty much all American coast-to-coast flights, JFK to Heathrow and back, but not for the big Pacific hops. Furthermore, to get T/GLOW to 1.4, you need 10 Raptors.

    On the other hand, the BFS has a ludicrous amount of habitable volume for a passenger point-to-point system. If you can chop it down enough to get to a structural coefficient of 0.06, you can now do New York-Baikonur, Baikonur-Shanghai, and Shanghai-LA. That starts to look like a marketable system.

    You can make do with 9 Raptors if you can manage T/GLOW of 1.33. Obviously, adding engines hurts your structural coefficient, so the ultimate viability of the system requires going to the next level of detail. In general, BFS doesn’t do it, but a BFS variant, chopped-down, lighter heat shield, 3-4 more engines, starts to look interesting.

  6. Paul451 says:

    Couple of things about scale. If we are to believe Musk, the numbers don’t work for reusability for the F9 US. And that’s just the US, not a combined US/fairing/crew-capsule. So a fully reusable system would require a launcher larger than F9 in order to hit that sub-10 tonnes to LEO range.

    (And along those lines, New Glenn apparently will have a expendable upper-stage. Suggesting that the numbers don’t even work for a 40t-LEO scale launcher.)

    It might be possible to develop a fully reusable system smaller than BFR, but it’s going to be a similar scale of development as BFR (given that rocket development doesn’t scale linearly, you aren’t saving much by going smaller.)

    That’s a lot of risk if BFR is offering ride-share at half your own launch prices.

    (Remember, BFR doesn’t have to launch 150t or fly empty. The first BFS will be crew+cargo. They can launch say 20 tonnes equivalent to GEO, plus max out of the remaining volume with humans. The payload pays the running costs, the humans are pure profit. A smaller vehicle can only do one or the other, or a much smaller amount of both.)

    If it were my company, sure I’d be building something on the scale of FH. (Raptor, single stick. Designed, like BFR, to replace the Falcon lines, but merely to replace.) Then, only once the tech is stable, scale up another level. But I have no interest in putting a million people on Mars. BFR is the largest thing Musk thinks he can self-fund. ITS was the largest thing he thought he could develop if externally funded. His goal is clearly not to build the next minimum step up to serve the existing market.

  7. Paul–

    I suspect that the F9 S2’s inability to move the center of pressure back far enough to be stable requires that it reenter nozzles-first, which pretty much dooms it to hypersonic retropropulsion through all the hot stuff. That in turn takes a lot of delta-v off the performance of the stage. So the numbers really don’t work.

    The question is whether you could build a stable lifting body for a second stage that had a structural coefficient that wouldn’t mess things up. I’m pretty sure that BFS transitioning from the CAD package to slideware is a good indicator that that can happen at BFR scale, but things are gonna get weird at the smaller scales. At the very least, you’re going to need hefty fins or winglets near the back, which I doubt is the designer’s first choice for how to give your modestly-sized second stage a low structural coefficient. At larger scales, the extra mass isn’t so bad.

  8. Paul D. says:

    TRM: perhaps a S2 with a plug/aerospike nozzle could more easily do high speed entry. The nozzle throats could have slide-over covers to keep the hot gas out, and the broad area on the base could be cooled using the existing coolant channels and some extra propellant (hydrogen? methane?).

    Reuse of the shroud as a heat shield for the engine end of the stage is also a possibility.

  9. Paul D. says:

    Another point against BFR:

    F9 reusability development benefited hugely from being able to piggyback off expendable launches. Many F9 first stages were lost in experiments to see what worked, and in refining the recovery procedures.

    BFR will not have this internal subsidy. Losing a BFR stage in testing means you’re paying for a new stage.

    SpaceX does benefit from F9’s legacy because no one else will have the same opportunity to double dip off expendable launches. And I anticipate plenty of lost vehicles when Blue Origin starts trying for orbit.

  10. peterh says:

    It’s something of a miracle that the Falcon rocket used a stage that evolved to be reusable for less cost than the established players spend for expendable stages. If they can get similar construction cost figures for BFR, losing stages during the recovery phase won’t break the bank.

  11. Roderick Reilly says:

    “”” I liked that Elon shrunk the size of BFR to something slightly less insane than ITS (a 50% drop from 300mT to 150mT). I still think he’s going way too big for any realistic markets near or medium term markets, but it’s a step in the right direction. I’m not convinced you need anything bigger than ~30-40mT to LEO to do Mars exploration and settlement, and you definitely don’t need anything that big to service near-term and future markets. “””

    Agreed.

    But what drives Musk’s assumptions of how big the BFR needs to be?

    From what I understand, it’s a fixation with making Mars a Second Earth. Big Mistake. His vision is further compounded by a sense of desperation about the state of affairs here on Earth. Also a mistake, as it leads to an exaggerated sense of urgency which skews the process.

    Then again, who’s proposing a more scaled-back, but still ambitious reusable system?

  12. Roderick Reilly says:

    “” Then again, who’s proposing a more scaled-back, but still ambitious reusable system? “”
    To answer my own question, Blue Origin? But I’m not familiar enough with their New Glenn plans.

  13. Archibald says:

    but not for the big Pacific hops.

    Be creative ! Have a stopeover in Anchorage or Hawaii. While it would take far, far too much time for either a 747 or a Concorde, for BFS it is only a matter of minutes…

    A great document that crunched some numbers (page 25)
    https://isulibrary.isunet.edu/opac/doc_num.php?explnum_id=95

    Cheers !

  14. Shevek23 says:

    Admittedly somewhat enthused by Musk’s latest thing, I have taken a look at the numbers, offered and inferred. We’ve been given values for the Raptor vacuum and SL vacuum Isps, dry mass of the upper stage BFS (85 tonnes, a 10 tonne growth margin on the 75 tonne target), maximum propellant load (1100 tonnes for BFS–silent on BFB), been told (see below for my caveats!) the target payload is “150 tonnes” and that all up launch mass is 4400 tonnes. I infer, by proportion with the mass breakdown of the Falcon booster stage (the BFB has essentially the same role after all) that of a strongly inferred 3065 tonnes, 2900 are propellant for a dry mass of 165.

    Given all these figures, and noting that an expendable Falcon 9 delivering the maximum payload to the lowest easiest orbit from Cape Canaveral (22,800 kg to 28.5 deg inclination, 185 km circular orbit) I infer from the Falcon’s mass breakdown a “virtual” or “mission” delta V of 9760 m/sec achieved by full consumption of all propellant. Assuming the same conceptual vacuum/free fall delta-V requirement holds for BFR to deliver to the same orbit (not likely to be strictly identical–in particular I suspect BFR will often be held to lower G stresses for the benefit of passenger safety and as with the Shuttle being able to deliver more delicate cargoes; this would raise mission delta V requirements) allows me to set up an equation to trade off payloads with variable reserve masses in the BFB for return to launch point stage recovery.

    That is a particularly weak point in my estimate because I have to guess as to propellant reserve requirements for the Falcon, and then assume the same proportions apply–perhaps modified with the superior Isp of the sea level Raptors versus Merlins, but that is a small factor. Examining how payload delivered masses of full launch site recovered launches compare with expendable and downrange drone ship recovery, I figure a BFB must retain 1000 tonnes (!) of its 2900 tonne propellant supply to ensure recovery to launch site. I frankly am staggered by that but it is proportional to what a Falcon seems to do for the payloads to be as limited for launch site recovery Falcon launches as shown. Perhaps better data would correct me rather drastically. However I do have confidence in the maximum payload to orbit possible with expenditure of the BFB–around 164 tonnes! This assumes a 20 tonne reserve of propellant in the BFS for deorbiting and landing and some possibility of retro-propulsive speed reduction prior to final landing.

    Thus even with total expenditure of both stages (well, the BFS stage could be refueled in orbit instead of abandoned to be sure) we cannot go above 184 tonnes of payload. Another 10 would result from getting BFS dry mass down to the initial 75 tonne target to be sure. But these extremes are reached by expending at least the BFB and requiring a second BFS version to dock and refuel the first, so now we require additional launches to complete a mission or the BFS is lost too–a 20 tonne reserve for descent to Earth might not be adequate but if not, the payloads come down even more. For various reasons I think 20 tonnes is about right.

    But of course the goal in BFR operations is to make each launch autonomous and fully recoverable. Drone ship recoveries I believe involve an order of magnitude less propellant reserve–100 tonnes for BFB versus 1000–which means performance comes close to expendable but the stage is still recovered. It does subjectively seem that success with downrange drone ship recovery is less probable than with return to launch site which is to say an intended recovery turns into an unintended and lower performance expendable mission some of the time! If 100 tonnes is the reserve requirement for drone ship recovery, payload falls to 145 tonnes assuming 20 tonne landing reserve for the BFS. But drone ship recovery is not even mentioned by SpaceX presentations, and I suspect they will either be rare or development of the option might be omitted completely; if super heavy masses beyond what BFR can deliver with complete recovery are desired, the company will pay the cost of full expendability rather than develop a sunk cost liability of a recovery mode rarely used and to an uncertain extent. Assuming the system is successful enough, the company will accumulate an inventory of BFBs that have been used to the estimated safe limit of times and should not be relied on for more than two or five or whatever safety margin is determined–these will be retired from recovery missions and stockpiled for expendable launches, and with success the company can offer a tremendous number of these once the pipeline has filled.

    So, what is the payload capability of a fully recoverable launch, with the BFBs returning to their launch sites precisely, typically requiring little more than fast cursory inspection, topping with a new BFS stage and fueling of both, which might conceivably happen in a matter of hours or less? My best though somewhat dubious looking guess is this requires a thousand tonnes of propellant reserve; anyone with a better estimate is quite encouraged to share it! At that reserve level I estimate the system to be capable of putting 50 tonnes into that very low parking orbit.

    Now, in itself that is pretty impressive, considering that the entire system is going to be recovered in full. This is at least twice what the STS could accomplish and STS’s alleged “reusability” was far less of an economy; many argue, no economy at all versus ELVs.

    The problem is that the SpaceX presentations have been bandying about “150 tonnes” as the -nominal- payloads and suggesting that as much as 250 tonnes would be the expendable red line limit. All of the variables in my formulas can be tweaked, but tweaking any combination of them to raise the fully expendable payload that high, and make a 150 tonne payload with full component recovery with BFB returning to launch site, which is clearly the nominal, routine mode of operation envisioned, seem like excursions into Fairy Tale Land to me, unfortunately. Maybe the Isp of the Raptor versions can be improved–but I think they are already near theoretical limits. Maybe the dry masses can be shaved–but they are already small fractions of the total and for the BFS in particular, the model clearly depends on a phase of hypersonic aerodynamic lifting and braking to minimize rocket braking–they don’t spell it out for Earth but they do for Mars entry, and I think if a partially eroded ablative coating (presumably renewed every 10 or 20 uses, I would hope, or else the coating thickness determines the reuses possible of the BFS stage) is good for Mars entry as described starting at 7500 m/sec, it is clearly good for Earth reentry as well. Given this, it is already pretty amazing to assert the dry mass can be as low as 85 tonnes! Going lower seems pretty unrealistic, as does achieving a radically lower dry mass fraction in the BFB–besides that does not help much since the 1255-1370 inert mass of the BFS upper stage dominates the equation at that point anyway. Actually raising the dry mass of the BFB would only hurt performance by lowering propellant–and by raising the mass reserve necessary to bring it back to launch point to be sure, further costing propellant available for payload launch. I could have overestimated the “mission delta-V” target to meet, but again I suspect it is underestimated instead, since it is still under 10,000, the round number figure in my head for “typical” launches–probably over-influenced by Shuttle, but this after all points the way to the gentler, lower max G models we’d want for a mass transportation system.

    What I conclude from all this that
    1) Unless my more pessimistic than SpaceX materials imply presentation is still not pessimistic enough, BFR can indeed as they most often claim deliver as much as 150 tonnes to LEO, beating out even the Saturn V and closely competitive with SLS–but in doing so they must either shave off a bit of it to enable a perhaps too marginal drone ship recovery option that takes the BFB involved out of the routine fast paced relaunch loop for a while, an additional opportunity cost along with the opportunity cost of the risk of losing the booster completely by accident, or for full capability that somewhat exceeds the promise, expend the BFB at least. At least they can meet the promise of 150 tonnes without sacrificing the BFS as well, and that right there is superior economy to the Shuttle for six times the payload! Even if dollar costs of launching a tonne of rocket were exactly the same as the Shuttle’s, which is to say a BFR launch would cost 440/208 or 55/26, about 2.1 times a Shuttle launch, by delivering 6 times the payload the per tonne of cargo cost is still reduced by a factor of three in this mode, and I think it is well understood that SpaceX even with recoverable operations achieves considerably better economy per tonne on the pad than STS ever could. Of course as the main post emphasizes, what are the chances of having a legitimate need for 150 tonnes of payload to orbit in any case? Well, obviously one thing SpaceX counts on is that the market will expand as per tonne to orbit prices fall.

    But anyone paying attention to offhand promises of 250 tonnes to LEO with BFR is going to be disappointed.

    2) Maximum reduction of per tonne on the launch pad launch costs come from total reuse, and the more rapid the pace the better, so clearly most BFR launches will aim for to-pad booster recovery, which constrains the payload down to a mere third of the “nominal” 150 tonne figure the company bandies about. We should be realistic and recognize that actually BFR is a system for launching not 150, but merely 50, tonnes into LEO and this should be regarded as the -nominal- capability.

    Mr Goff and others, I think if you reconsider BFR as a 50 tonne launching system, then the economics of it all seem much more reasonable, especially if we compare to the range of capabilities offered by Falcon Heavy, an option only the most inveterate Musk haters deplore. By and large FH is considered a big step forward and no one is saying, meh, what is the use of this oversized system anyway? Clearly BFR is only an incremental improvement over FH, if we assume most missions will seek booster recovery direct to launch site. In that case, the notion of filling out cargo launches of any size between zero and 50 tonnes opportunistically by offering both ride-along launch deals for other orbital cargo and then topping off with offering space-available space tourism flights to paying passengers seems much more workable than for 150 tonnes, does it not? Meanwhile the Falcons can be totally retired; conceivably Falcon 9 operated in maximum reuse made might remain to take the low mass end of the market but that competes with persuading small payload customers to use BFR ride-along instead. And, by developing downrange drone ship recovery or simply resolving to expend the oldest BRBs as they near nominal end of service life, Musk can use the same BFS stages already earning revenue to “Charter” them for his ambitious personal Mars program–or offer to any other customer (US regulations permitting) a 150 tonne in LEO ride, for little more cost total than a routine 50 tonne mission.

    When we look at it this way then, I suspect that overall the system is a lot closer to being rightsized even for the existing launch market, and quite a good fit to the sort of order of magnitude larger orbital and beyond market Musk hopes can emerge. He may indeed suffer serious competition, but only because he has opened up the market wider, offering opportunity to competitors who will cut down any margin between SpaceX operating costs and existing opportunity to reap superprofits. But to do that, each competitor will have to reduce their own overall operational costs per tonne of payload orbited to the same levels SpaceX has. It must be possible, but it will not be easy for them, and if they can manage it the upshot is SpaceX is merely making an honest profit rather than a superprofit.

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