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:
- 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.
- 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.
- 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.
- 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.
- 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
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 the founder and CEO of Altius Space Machines, a space robotics startup that he sold to Voyager Space in 2019. Jonathan is currently the Product Strategy Lead for the space station startup Gravitics. 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.
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- 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.
- I had to rewrite that sentence at least a half dozen times to make it not sound completely dirty.
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.
Personally I think right-sized vehicle is over-rated in the current launch market. The current market is basically divided into many segments from payload mass/launch energy point of view, but each segment only has a small number of payload each year. So if you silo your launcher to a particular segment, it’s not going to get enough flights to support reusability. (Nanosat, smallsat market may be an exception, it remains to be seen whether it has a high enough demand to support a launcher by itself, but if you build a nanosat/smallsat RLV, it’s not going to compete with SpaceX/Blue, its main competitors would be RocketLab, Virgin, etc.)
SpaceX gets around this by building a large enough vehicle to cover as much segments as possible, i.e. one size fits all. People don’t realize how large Falcon 9 is, it’s basically a Proton M, yet it frequently flies payloads that can be launched on Soyuz. Of course now that FH has flew, it will further drive this point home: Next FH will launch a mere 6t commsat, using the most powerful operational launcher in the world by a factor of two. This is a preview of how BFR would work: Size doesn’t matter, at least not for now. If space traffic picks up to the point that the amount of propellant spent in each launch becomes a significant factor in launch cost, then right-sized launcher will be needed, but by then I think the space industry would be developed enough to actually need 150t to LEO.
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.
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?
@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.
@ 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.
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.
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.
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.
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.
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.
“”” 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?
“” 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.
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 !
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.
SECOND STAGE AS AN SSTO?
Musk alluded to this, very briefly.
Solid geometry is the BFR’s friend because of its huge size, so the mass fraction would be less than for a smaller vehicle. BUT, it would have to be a different vehicle in that it would need a different internal configuration — bigger propellant tanks.
And what of the engines? The orbiter has its nozzles optimized for altitude, right? Except for the central one for landings? Would it not makes sense, if an SSTO variant is considered, to leave the altitude nozzles, but fit them with ablative ejectable nozzle inserts for the boost phase.
And would this be worthwhile? What might the payload fraction be for SSTO? How many passengers?
I’m skeptical about the point-to-point travel idea, but what about the orbiter as a standalone cruise ship for space tourism? Its considerable size and passenger capacity would make this technically feasible, I would think.
I goofed re the payload of the BFR to LEO with full Booster recovery to launch site. Although the BFR is indeed derived from Falcon, the upper stage is relatively larger, thus the Booster has a smaller job to do in terms of delta-V, and the slower the ensemble is going at staging, the less propellant is needed to bring the Booster home. A friend with extensive formal training in astronautical engineering estimates the reserve mass in the Booster for full recovery to launch site at a mere 107 tonnes, about what I figured it would need for downrange recovery. With some tweaks in other masses, bringing Booster dry mass down a few tonnes while raising the BFS upper stage propellant reserve up 10 percent to 22, but noting a somewhat greater propellant capacity for both stages, and working with a smaller “mission delta V” target of 9600 m/sec, routine delivery to a low orbit with minimal inclination adjustment should be 154 tonnes payload from Cape Canaveral. Expending the Booster instead of recovery would add just 19 more tonnes and draining the BFS all the way another 20 or so. Adding 10 or so tonnes with downrange recovery scarcely seems worth developing that infrastructure!
So, I was wrong to characterize it as a 50 tonne to LEO system stretchable to around 150; it seems sure that the vast majority of launches would deliver 150 tonnes to LEO, no more, no less, and every launch except maybe one in 200 would strive for booster recovery to launch point.
It cannot go far beyond LEO even with zero payload at launch, not without refueling. With restocked propellants it can go quite a lot of places; I am in the middle of investigating what options it opens up for Lunar travel, and whether it makes sense to try to harvest oxygen from Lunar regolith to supply 80 percent of the propellant mass needed from an extraterrestrial source. The catch is if we have to transport methane from Earth in all phases–if we do, the cost of that, in terms of mass of LOX from Earth needed to enable supplies of Lunar LOX in LEO or at the Lagrange points or Low Lunar Orbit, is what determines whether it is more sensible to derive Lunar LOX or keep shipping it up from Earth.
To refuel the main propellant tanks would require some eight 150 tonne cargo loads. I hope to improve on that with Lunar in situ LOX!
Taking passengers to LEO is not that much harder than point-to-point. So maybe intercontinental travel will be after spending a week in orbit. LEO conference center and luxury hotel, anyone?
With no payload, 85 tonnes of dry structure and 1115 tonnes capacity for propellant, burning itself dry and with the use of Vacuum Raptors only (pretending for the moment these can work at all in the lower atmosphere, which they cannot) theoretical mission delta V is about 9740 m/sec; considering my friend believed 9600 is good enough for orbit, that allows a 3.5 tonne payload. Considering that the dry mass probably can include infrastructure for human life support, that could amount to quite a number of passengers, 4 or 5 anyway, plus a bit more infrastructure and supplies. But it allows nothing for orbital maneuvering and landing reserves, which ought to dwarf this small payload. We’d need an Isp of 400 to achieve zero payload with 22 tonnes of post-orbital launch OM and landing propellant. So clearly aside from thrust issues we cannot rely on the 330 sec sea level, 356 sec vacuum, SL Raptors. The three of them deliver about 500 tonnes thrust so clearly we cannot launch on their thrust alone! We would have to do something that currently is not on the development path, which is to remove the SL Raptors and develop something allowing the Vacuum Raptors to temporarily function with less expansion allowing them to work at sea level. There are practices that might accomplish much along these lines such as the so-called “Thrust Augmented Nozzle” scheme that adds some extra gas flow of some kind to the nozzles, or perhaps developing an airbreathing phase is the way to go–or some kind of ablative nozzle as suggested, or something. But at best that would give us say seven engines, which is not enough. If we redesign the thrust structure completely and ditch the Vacuum engines, there is plenty of room for all the SL engines we might want, since these have much smaller nozzle diameters–after all, the Booster has 31 of them! I think 13, a ring of 12 around a single central one, is about right. The brisker launch acceleration might help offset the lower Isp of 356 in vacuum. (We ignore atmospheric effects in simple mission delta V computations). If we can add 450 tonnes to the 1115 standard tankage, payload is zero. Of course as we add propellant like that at launch we need to add more Raptor engines but we can surely do that; what limits us is how much more tankage the volume will accommodate without stretching the length any.
Just looking at one of Musk’s presentations the volume of the BFS above the propellant section might offer 5/6 more for extended tankage; say that amounts to 75 percent allowing some space for the actual payload, say maybe 800 tonnes more. With 19 SL Raptors installed we might close with 24 tonnes payload though I don’t know what the penalty in dry mass of adding replacing 4 V Raptors with 15 SL Raptors would be nor if the mass penalty could be offset by eliminating other elements of structure while extending the tankage. 24 tonnes is very little margin!
So yes, technically it might close as an SSTO, and if we can keep even half of 24 tonnes as payload then bearing in mind much of the mass of an ordinary capsule is substituted by the fixed dry mass of the bigger ship, that could amount to quite a lot of passengers indeed. A suborbital SS version could carry larger passenger loads although not to every point on Earth; and to avoid radiation hazards in the Van Allen belt ballistic flights beyond a certain range must have depressed trajectories quickly approximating orbital. Since it is a variant on an existing planned design, if the added engine installation to meet the necessary launch thrusts does not eat up the payload then maybe SpaceX might consider developing it if it turns out the masses desired by customers to go to orbit do not grow to fill BFR capacity as they hope; a ballistic transport version holding a couple dozen or so passengers instead of a thousand or more might fit the market better especially for suborbital transport; note that one of several thorny questions left unanswered by Musk’s presentations is how fast an upper stage can be installed on top of a booster; with just one stage point to point we sidestep that whole problem; with sufficient reuse reliability it could be a question of gas and go!
There are much thornier questions about ballistic transport of course, starting with the ginormous noise 31 or even 19 SL Raptors will make at launch, how far out sonic booms of launching and landing craft will be a serious problem, etc. 19 SL Raptors will make thrust on a similar scale to the Space Shuttle launches. So, how close to the center of a major city like Paris, London or Los Angeles would you propose to launch a Shuttle from? The full size dual stage version will dwarf the Saturn V at takeoff! Clearly we cannot locate these ports in city centers. Then the question of flight frequency; if a capsule does not launch toward a given port in a brief enough interval then world travelers will realistically find subsonic jets, and anyway even at a somewhat greater launch rate advanced SSTs will compete; frequency must be great enough to give a clear advantage to using the suborbital method.
Launching suborbital from a single stage like this, even one stretched to nearly 2000 tonnes of propellant, surely will cost less than the 150 tonne to orbit capacity full BFR. But it also will have 1/10 or less the payload. It is probably rightsized for the initial very exclusive suborbital travel club but with success if any, that market should grow.
All,
Sorry I didn’t see these replies till just now. For some reason the blog isn’t sending me comment notifications like it used to. I’ll try to reply to a few of these tonight.
~Jon
Dave,
Not only would a smaller RLV have a window of opportunity to make a lot of money, but it would also be cheaper and easier to both iterate on its design, and to improve on its manufacturing. Iterating on something BFR/New Armstrong size is going to take more money and time than something small. And since I’m almost positive that the first attempt at a full-RLV is going to leave something to be desired, having a platform small enough that you can iterate quickly is going to be very important.
~Jon
Spacerfirstclass,
My point is that BFR is way too big for any existing market. By a longshot. Without refueling, and with a LOX/LH2 upper stage, you could address every existing market with a full RLV that is probably 4-5x smaller than BFR. With refueling, you could address 95% of the market with a vehicle 30x smaller than BFR. Anyone who does a smaller full-RLV has a good shot at taking a lot of market share away from SpaceX, IMO. Not sure if anyone will, and if anyone will execute competently, but I think Elon’s ego has left a big opening for a clever competitor.
~Jon
N/A,
A lot of the mass of Gemini was tied up in reuse features that would already be built into a BFS-esque integrated second stage/reentry vehicle. I think you could do 8-10 people for less than 5mT of payload. Especially if you trusted a stage design that didn’t require a separable capsule/launch escape system. To me, 5mT fully reusable seems like the magical sweet spot to meet most of the existing market. Big enough for a decent crew/cargo capability. Big enough to launch most GEO birds (filled to their Beginning of Life prop load), allowing GTO or GEO missions using distributed launch (ala Dave Salt).
That said, I’d still think that going after a 1mT class vehicle first might make sense. That’s big enough to address the megaconstellation market, but small enough to minimize up-front development cost, and enable rapid and affordable iteration and upgrades. Also big enough to at least be able to fly say 1-2ppl to orbit or a small chunk of cargo, which might be a better fit for near-term post-ISS facilities. Make that work, then use the profits to fund a bigger brother version.
~Jon
Paul 451,
I don’t believe for a second that it isn’t possible to do a reusable upper stage on F9 scale. And I don’t believe for a second that making a F9US sized reusable upper stage is going to be in the same development cost range as making a reusable BFS. I really don’t get why people believe this is the case. F9 can put something like 12-15mT into LEO while recovering the first stage. The expendable F9US weighs less than 5mT IIRC. Do we really think a reusable F9US is going to triple or quadruple the weight of that stage? I’m sure there are ways to do reuse that have that high of a penalty, but I’m almost positive there are more effective ways. I seriously think you could make a 1mT to LEO full RLV that closes.
And honestly I don’t care what Elon’s goal is. If he goes too big, he’s leaving an opening for someone with more realistic goals. His call. He might get lucky that nobody competent gets the resources to challenge him.
~Jon
TRM,
People have looked at things like this, and AIUI a high-alpha reentry is typically possible even with a back-heavy stage. If you’re having to do hypersonic retropropulsion you’re doing something wrong.
~Jon
Peterh,
Even at their most optimistic, SpaceX was claiming stage costs >$200M for BFR and BFS. A loss, especially a loss of both stages, would cost more than losing several Falcon 9s. And I’m skeptical they’re going to make an all carbon-fiber stage as cheaply as they think. Especially when their fairings are already one of the most expensive pieces on Falcon 9. No, I think Paul D has a point–BFR development has the potential to be a lot more expensive than they think, especially if they have the number of failures/iteration cycles as they did for Falcon 9.
~Jon
Rod,
I think Elon’s banking on nobody else even trying. He might be right, but if not…
~Jon
Shevek23:
“” (pretending for the moment these can work at all in the lower atmosphere, which they cannot) “”
That is why I suggested the ejectable ablative nozzle inserts that would reconfigure the Raptor altitude/vacuum nozzles for off-the-pad to the altitude where the primary nozzles are optimized for.
Jonathan Goff:
“” Not sure if anyone will, and if anyone will execute competently, but I think Elon’s ego has left a big opening for a clever competitor. “”
I think so too. I’m concerned because SpaceX has created a new and important paradigm for space launch. By not going for an interim, and scaled-down, concept first, BFR may sabotage private space.
Musk’s motivator, to me, is the biggest flaw: turning Mars into a second home for humanity. No humans have been there yet, and he wants to start populating it. That skews his calculations and goals. Instead of trying to be “Moses,” I think he should try to be Cornelius Vanderbilt.
Jon: “My point is that BFR is way too big for any existing market.”
I get that, but building vehicles too big for existing market is what SpaceX does. F9 is too big for the Delta II market, FH is too big for the GTO market. The thing is, if you just build vehicles to fit the existing market, then the existing market will never change, which is bad since the existing market doesn’t support RLV very well and in general is preventing us from having a vibrant space economy.
Jon: “I think Elon’s ego has left a big opening for a clever competitor.”
This assumes he haven’t already changed the market when the competitor appears. Also ignores the potential for BFS to do SSTO.
You seem to be assuming that all payloads under 5 tons will disappear with the advent of BFS/BFR. That’s along the lines of pickups disappearing with the arrival of semis. For smaller loads that need responsive attention, semis can’t compete.
Check your numbers on SSTO as it is second cousin to useless when it comes to actual work.
Here’s a question: How many commercial payloads can a F9 class launcher based in US can reasonable get every year in today’s market, excluding the mega constellations?
I bet it’s less than 20 (~10 GTO payloads, ~5 LEO payloads). You think you can support a new fully reusable vehicle with just 20 potential launches per year, with SpaceX (and Blue Origin) competing with you for all of the 20? I doubt it.
Even SpaceX couldn’t do it, that’s why they want to get DoD launches plus NASA launches. And that’s why I said “the existing market doesn’t support RLV very well”. You need to expand the market, building a cheap fully reusable SHLV is one way of doing it, it opens up all sorts of potential commercial applications (space based solar power, space manufacturing, tourism in LEO and on the Moon, trading mass for cost to build super cheap satellites, etc), plus interesting possibilities in government market (kill SLS instantly and get $1B NASA contract, how about that? Plus what kind of mega payloads DoD can come up with). And of course SpaceX themselves will also need it if they want to beef up their constellation so that it can go toe to toe with terrestrial fiber networks.
I’m not saying 5t payload would disappear, but if you just count on 5t payloads in today’s market, then you’ll have very low flight rate and couldn’t compete with launchers that have a high flight rate due to their ability to launch heavy/high energy payloads, see Antares for an example. This goes back to my point above: RLV in today’s market makes no economical sense, that’s why no major aerospace companies were doing it before SpaceX. SpaceX (and Blue Origin) is doing it because they’re not interested in serving today’s market, they want to reshape the market to another one where our orbital traffic increases by orders of magnitude. Only in this vastly bigger market would your pickup makes sense, since there would much more payloads to launch, and the price of launch would be reduced low enough such that the fuel cost difference between a pickup and semi is not a rounding error. Of course in this market there would also be a place for semi’s, both can co-exist just like in the road transportation market.
For doing actual work with SSTO, Skylon already has a design that solves the issue, you just need a small reusable orbital tug.
Okay you got me. I thought you were serious until you brought in Skylon.
I thought you were serious until you brought in Skylon.
I don’t recall seeing your post evaluating Skylon. I’m looking forward to it if it’s on your to do list.
My understanding is that Skylon is effectively dead and that all RE’s efforts/funds are now focused upon developing SABRE for application to hypersonic missiles – their work with Lockheed tends to support this conclusion.
Having worked on HoTol back in the late 1980s and followed closely the subsequent efforts of RE since then, you may not be surprised that I find this situation rather depressing. Nevertheless, I do believe that a pure rocket solution is probably the best way forward, though I also think there’s a role for airbreathers… ideally as the zero-stage of an air-launch system.
I’ve never done a post on Skylon. It just has the same problems as many airbreathing SSTOs. From the time the airbreathing engine shuts down on Skylon until it reaches LEO, the mass ratio is about 5 with LH2/LOX. So a complex engine and airframe optimized for supersonic flight rather than mass ratio is dead weight through most of the mission. However much mass penalty from the extra engine and airframe one assumes, it must have 5 times that much propellant to reach LEO, and larger tanks and rockets to carry it. Even given a fully functional engine and airframe, that mass is one for one loss against payload. I don’t believe the technical number will close on Skylon as SSTO. I might buy it as first stage at some point, which brings it back to direct comparison to the F9.
One of my big concerns with Skylon / Sabre is how much attention the vehicle and engine will need between flights, and associated costs. Get those down and a Sabre based booster could be very attractive. More so if you’re already using LOX/LH2 on the upper stage.
Dave Salt: I’m not surprised they’re focusing on cruise applications, for which airbreathing is better suited.
John,
“For smaller loads that need responsive attention, semis can’t compete.”
However, BFR will be the more responsive launcher than small expendables. And if Musk is even close to right about launch costs, it will be cheaper too.
Why on earth would the customer care if the vehicle is 90% empty?
Jon,
“I don’t care what Elon’s goal is. If he goes too big, he’s leaving an opening for someone with more realistic goals.”
The development cost of a “realistic” HLV will be on a similar scale to BFR. Rocket development doesn’t scale linearly — three times the payload isn’t three times the dev cost — because larger rockets have more generous structural margins. (The old Sea Dragon concept was going to be made of ship steel.) Manufacturing costs should be more reasonable, but again, not linearly so.
And the operating cost of a “realistic” HLV won’t be much cheaper compared to BFR. It’d use less fuel, but man-power and systems costs will be roughly equivalent.
So the launch price of a “reasonable” HLV will not be much less than BFR. Certainly not a third of BFR, probably not a half.
And, when launching a few current scale large payloads (so, small tiny by BFR standards), you’ve got the rest of the capacity to carry a hundred paying passengers.
I can’t see how a rival company could compete unless they match the scale & price.
Blue Origin can’t compete, because NG is partly expendable. ULA can’t compete, because even if built, Vulcan is fully expendable (and almost fully expendable even if they develop their ridiculous engine-recovery scheme.) And no foreign nation/group seems even close to understanding the rules of this new game.
So who exactly is this hypothetical competitor?
Isn’t the BFR design locked into the need for seven Raptors in the orbiter? While a smaller BFR would be desirable to a number of us posting here, the nature of how it returns and lands pretty much requires that many engines. 3 SL, and 4 vacuum.
Could a five-engine configuration work? 2 sl + 3 vacuum? That roughly translates to a BFR stack 70% the size of the configuration proposed. That would also mean 22 Raptors in the booster, if we just do a “linear” scaling of the concept. That’s a vehicle that could put 100+ tons into LEO, I believe.
“Okay you got me. I thought you were serious until you brought in Skylon.”
I am serious, if you don’t want to use Skylon as an example, then re-read the paragraph about space tugs in Jon’s blog post http://selenianboondocks.com/2008/01/orbital-access-methodologies-part-i-air-launched-ssto/. All SSTO’s face the same problem you described, and you can use the same solution, it doesn’t matter how exactly the SSTO works.
You brought up Skylon as having the technical answer to SSTO when it clearly doesn’t. It does matter exactly how a technology works, being the difference between feasible and not. The Skylon tech may eventually be useful for high supersonic cruise which is a totally different application from a space launch vehicle.
On “Skylon.”
A fly-back booster, maybe?
As to airbreather 2-stage or SSTO? It seems to me that the best use of air-breather is in the boost phase where most of the propellant is used. A ramjet would, I think, suffice for that. Integrated rocket/ramjet to MACH 5-6, then all rocket.
Composites issues for BFR
From a NASA forum:
https://forum.nasaspaceflight.com/index.php?topic=42826.0
As for BFR being too big. So was R-7. Good. I’m glad the Russians didn’t think Vanguard small.
My problem is this:
When I hear the word “composites” used with the word “flaps” or “winglets” I have no reaction. When I hear “composites” used with words like “wing-boxes” I squirm a bit.
But use “composite” and “cryogenic tank” in the same sentence–and the fangs come out and I hiss like a vampire hit with holy water.
Jeff Wright says:
“As for BFR being too big. So was R-7. Good. I’m glad the Russians didn’t think Vanguard small.”
Ha, ha. Funny, that has occurred to me in the past. The same basic launcher that put up beach-ball-sized Sputnik now puts up three people at a time to the ISS.
As to the BFR, and my contention that “it’s too big?” Back when we space enthusiasts insisted that going back to the Moon first was a better idea than going on to Mars, the powers-that-be had another surge of enthusiasm for Mars. Someone told us “Moonies” to look at it this way: let the Mars thing happen. The technological advances will then benefit any return-to-the-Moon efforts. Musk has a Mars fixation. Let him and SpaceX succeed in building and launching the BFR, and let the chips fall where they may. I mean, who else we got?
Bezos and Blue Origin seems to want to go on a more varied, and I think, rational path, with space settlement in general. But even Bezos has signed onto the fantasy that humans will populate the Solar System in vast numbers. No matter. He has the bucks, and he’s the other guy building private space on a grand scale.
“” But use “composite” and “cryogenic tank” in the same sentence–and the fangs come out and I hiss like a vampire hit with holy water. “”
I’m not well-versed on the issues of composites with cryogenic propellants. But wasn’t this one of the issues with X-33?
My understanding is the X-33 composite tanks had problems with both the LH2 and the multi-lobed geometry. The anisotropic strength profile of fiber reinforced composites makes them very sensitive to structural geometry. They really don’t like sharp corners.
peterh:
” My understanding is the X-33 composite tanks had problems with both the LH2 and the multi-lobed geometry ”
That’s what I thought. The BFR doesn’t have those “geometry issues” as far as I can tell, but if the tanks on the BFR are containing densified propellants (both LOX and methane), might they also have a cryogenic issue, I wonder? Or have advances in composites negated those issues?