BFR Point To Point

Sam Dinkin looks at the business case.

There’s not currently a ferry terminal in the South Bay, so they’d have to build one somewhere, maybe by the Marina or King Harbor to make it more convenient to LAX.

15 comments on this post.
  1. DarkstarSF:

    By “Marina,” you mean “Marina del Rey”?

  2. Rand Simberg:

    Sorry, yes.

  3. DarkstarSF:

    Thanks!

    I read it, and I’m still skeptical. My biggest concern is the health of the passengers from launch and reentry.

    As for the selection of foreign cities, I’m more agreeable with adding Shanghai, Hong Kong, and Mumbai, but not Dubai. Europe would be a problem. I’d be against the English Channel and maybe the Irish Sea for political concerns. How close do you need to be to London? Would the North Sea work?

  4. wodun:

    $774,000 seems like a pretty lean cost for a single flight… Assuming $774,000 revenue per flight

    This is a little confusing. Is he referencing a cost to SpaceX of $774,000 a flight or the revenue from sales? There are a lot of unknowns but it is a certainty they wont be doing this at cost.

    The ptp analysis was interesting. Essentially speed has to be worth paying a premium. What would conditions be like for someone flying first class, would it be a first class experience?

    The most interesting was the passenger counts of 258 and 437. What does this mean for the orbital version in terms of seats?

  5. Sam Dinkin:

    The orbital version is designed to have state rooms for 100, but to LEO they could use the suborbital version. The Moon and Mars, staterooms are probably best. $774k is 3000 each way for 258 passengers based on the Tokyo flight from LAX I picked out of a hat at fully refundable coach with a few days notice.

  6. wodun:

    The orbital version is designed to have state rooms for 100, but to LEO they could use the suborbital version.

    They really need someone to make a Mars/Earth cycler because that would make the numbers much better. Putting 258 people a pop onto an actual spaceship would allow for many reuses of the BFS and drive ticket prices fairly low.

    Will the confluence of technological innovations take advantage of SpaceX just as SpaceX took advantage of the confluence?

  7. Edward M. Grant:

    “Putting 258 people a pop onto an actual spaceship would allow for many reuses of the BFS and drive ticket prices fairly low.”

    Only if it can carry enough fuel to get to the cycler, then turn around, return to Earth and land. Otherwise, it’s still going all the way to Mars to refuel, and the passengers just get better accommodation for the trip.

    I guess maybe whatever launches them from Mars at the other end could bring up enough extra fuel to load onto the cycler to refuel the next ship from Earth. But the ship from Mars is also going to need extra fuel to return to Mars, so that seems unlikely (though I haven’t actually looked at the numbers at all).

    The other problem with cyclers is that your ship still has to be able to survive not managing to rendezvous with the cycler for whatever reason. Though in that case, I’d presume you could use the Mars landing fuel to do a course correction and catch up.

  8. wodun:

    Only if it can carry enough fuel to get to the cycler, then turn around, return to Earth and land.

    I assume they wouldn’t do it if they knew it was impossible before spending so much time and money. The article points to the possibility that more than 100 people could be sent to LEO, so there is a sweet spot there that could allow more passengers and reusability.

    A cycler could also be fueled by the BFS.

    I guess maybe whatever launches them from Mars at the other end could bring up enough extra fuel to load

    They would use the BFS. Having some sort of cycler doesn’t mean Mars wouldn’t get the BFS, just that the BFS wouldn’t be the primary means of transport between Earth/Mars.

    The other problem with cyclers is that your ship still has to be able to survive not managing to rendezvous with the cycler for whatever reason.

    That is the tricky part but a BFS that only goes to Mars every couple of years isn’t going to have a very high number of reuses unless they use a refurbished ptp version. More launches means more sharing of costs and if they could use their ptp version to get to a cycler, they can get a lot of launches and send tens of thousands of people to Mars instead of hundreds every season possibly for a ticket price that regular people can afford.

  9. David:

    I’m confused by his inclusion of the booster into the cost and scheduling. Nothing I’ve read indicates that a booster would be necessary for PTP suborbital passenger flights.

  10. Sam Dinkin:

    Well, no booster would save money, but to go half way around the world on a ballistic trajectory, you almost need to be in orbit. Escape velocity is 11km/s, but ICBMs go 7km/s. I am guessing the drag of getting out of the atmosphere is more important than the 2.5 times as much energy needed to go 11 km/s vs. 7km/s, but maybe enough to get the fuel cost down to something reasonable.

    If they do not use the booster, they might need more engines than for the 2nd stage version because the ship is optimized for vacuum with only enough atmospheric thrust for landing, but maybe not enough for launching full in full gravity.

    It’s not clear what the payload mass will be. A 35 kg seat, 100 kg passenger and 65 kg of baggage for 400 people is only 80,000 kg which is much less than the 130,000 rated maximum launch payload for BFR if they do not carry any mail, but bulkheads, life support, cockpit, and so on also weigh something.

  11. Sam Dinkin:

    This analysis indicates the 2nd stage could launch partially fueled and achieve a delta v of 7.9 km/s so you might be right. http://lilibots.blogspot.com/2017/09/bfr-upper-stage-as-booster.html

  12. Paul D.:

    ICBM velocity is misleading as they don’t need to reenter with survivable deceleration.

  13. David Spain:

    FWIW the P2P animation used during Elon’s talk last year shows a two stage configuration with the BFR first stage doing an RTLS.

  14. Brad:

    After a suborbital passenger BFR was proposed, I thought of the Ithacus troop transport. Hello DoD!

    http://www.astronautix.com/i/ithacus.html

  15. gbaikie:

    It seems a important aspect of suborbital travel is reducing rocket fuel used, related to gravity loss of suborbital trajectory.
    Or using a zero stage or assisted launch, so things like motherships or maglev track to get a rocket going at some speed.
    With mothership, the starting point for rocket burn is the high elevation and something like speed of mach 1.
    Though inherent problem is limitation size of the rocket launched from a mothership. And I guess, are saving much in terms rocket fuel used.

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