Doubts Raised About Elon Musk’s Point-to-Point by Rocket Plan

BFR crew vehicle propulsion (Credit: SpaceX)

John Logsdon has spotted a potentially showstopping problem with Elon Musk’s plans to fly people point-to-point using his humongous rocket.

“It is a very attractive prospect, but I think extremely unrealistic in any relevant time frame,” Logsdon told CNBC in an interview….

Passengers on a spacecraft are subject to forces that are as much as five times the force of gravity as they accelerate into space, then are in microgravity or zero gravity for the duration of the flight. They get hit with the G-force again on landing, he said.

“The idea that a typical airline passenger would be able to go through the experience just doesn’t compute,” he said. “Musk calls all of this ‘aspirational,’ which is a nice code word for more than likely not achievable.”

However, Logsdon did say Musk’s presence and his work is healthy for the industry overall.

“I think the phenomenon called Elon Musk is fascinating and serves as a kind of beacon of hope that there is a better space future ahead of us,” he said, “and the transition from that beacon to reality will almost certainly take longer than Elon and his supporters hope.”

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  • Mr Snarky Answer

    When looking at this plan, G loading of passengers is not in the top 10.

  • ThomasLMatula

    Dr. Logsdon may understand space policy but has no clue about transportation economics. The market will not be humans but very high priority cargo that must get somewhere immediately.

    Imagine Fed-Ex or DHL matching this with fast drone delivery and offering same day delivery anywhere on Earth, for a price. Or the military using it for its fast logistic needs.

  • newpapyrus

    Commercial ballistic passenger transport is a concept that goes back to the 1960s. With average ballistic speed around 27,000 km/hr, passengers should not be subject to accelerations of more than 3 g.

    Marcel

  • brightlight

    When the Concorde retired, there was talk by a delivery company, it might have been FedEx, about buying a couple for rapid deliveries.. Nothing more than talk though.

  • passinglurker

    What could you possibly deliver that will also tolerate these G forces and bring in routine business to support global launch and landing pads?

  • Nuclear warheads.

  • Since the rocket isn’t going for orbital speeds it doesn’t need to pull high gs.

  • Nickolai

    For military responsiveness, I think it would be important to take into account prep time of the rocket as opposed to just flight time. Since it would have to be prepped/fueled, it would probably take a couple hours for deployment. Still pretty fast, but depending on the location it might be faster to chopper in some forces from a nearby base.

  • Nickolai

    I’m really curious as to how economical this would be at economy class pricing. A 747 costs a couple hundred million, seats ~400 in multiple classes, and lasts for decades. A BFR would probably cost more, maybe close to $1 billion if you take a look at Saturn V/Shuttle costs, and seating capacity/longevity is unclear. Not to mention that there’s all sorts of support infrastructure for 747’s today, i.e. long runways, big passenger terminals, etc.

    I thought this might be a secondary revenue stream in addition to the primary revenue stream of launching satellites, but the math there didn’t really work out. Assuming 60 launches per year with an average payload of 15 tons (probably an overestimate), that’s 900 tons/year launched, which could be launched with 6 BFR flights. Not much of that primary revenue stream to go around, and that assumes 100% market capture, which is also probably unrealistic for reasons of national security for non-US countries and question of reliability in the early stages.

  • therealdmt

    Every party has a pooper, and we have John Logsdon

  • Mr Snarky Answer

    Less than a billion, far less.

  • Andrew Tubbiolo

    I hope the passenger global transport has landing legs. I was out flying today and part of my scan of the flight sequence as well as my visual scan was … “where will I land if something goes wrong?”. … This landing on the launch ring bit is fair game to play when you’re talking cargo, or professional crew who can understand the risk they are taking. But 500 odd paying customers on their way from Shanghai to Port Canaveral for a trip to Disney World and the Fla sun? Uhhhhh, no. Landing on the launch ring has darn near zero fault tolerance. At least with landing legs any clear horizontal surface is a place to call home should things go south, but a landing ring? I’m not sure Grandma Ho and fluffy the shitzu can really understand what they are signing up for. I would think we might see a return to the 80’s in accident rate with most of the disasters focusing on failure to make the landing ring. And then you have to consider the now empty tanks filled to the gills with gaseous CH4 and O2 vapors. When you miss the landing ring, a lot of passengers who survived the tip over and the breaching of the pressure vessel won’t survive the conflagration that will occur when all the gaseous CH4 and GOX mix.

  • Andrew Tubbiolo

    Intercontinental ballistic trajectories require delta V’s from .85 to .98 LEO circular orbital velocities. It’s the reason why ICBMs were the basis for the first set of orbital launch vehicles. Look at the changes needed to make orbit for the Titan II ICBM vs the changes needed for Thor (The IRBM) to become a orbital launch vehicle.

  • ThomasLMatula

    Paper and spare parts are pretty G force resistant compared to humans.

  • ThomasLMatula

    I am not thinking of troops necessarily, but critical spare parts or supplies.

  • ThomasLMatula

    Or conventional ones.

  • True, but Prompt Global Strike has never gone anywhere so the idea that it would support passinglurker’s “global launch and landing pads” probably wouldn’t do. Nukes are a PROVEN business case. 🙂

  • passinglurker

    Paper doesn’t sound that valuable.

    Neither do durable spare parts

  • Nickolai

    Same logic applies.

  • Duncan Law-Green

    “Assuming max acceleration of 2 to 3 g’s, but in a comfortable direction. Will feel like a mild to moderate amusement park ride on ascent and then smooth, peaceful & silent in zero gravity for most of the trip until landing.” — Twitter @elonmusk. https://twitter.com/elonmusk/status/913775198423408640

    “Musk calls all of this ‘aspirational,’ which is a nice code word for more than likely not achievable.”

    He called the Mars-landing-by-2022 target “aspirational”, not the entire design concept.

  • Duncan Law-Green

    The (unmanned) first stage lands back on the launch mount. The second stage/passenger vehicle has legs, lands on a pad, and is then craned back onto the first stage and refuelled for turnaround.

  • Andrew Tubbiolo

    Pfhhht … Silly me! You’re so right! Thanks for pointing out that simple reality. 🙂

  • ThomasLMatula

    You are assuming that the supplies are available at a nearby base. Which is where this rocket would land anyway. You aren’t going to risk it where the danger of enemy fire is high. Think of a very fast, expensive replacement for B787, not a C-130 or C-17.

  • ThomasLMatula

    True, but no one wanted to invest in building a prototype. Now that you have a commercial vehicle capable of accomplishing it available off the shelf you will be able to test the idea. Big difference.

    The best historical case is the Boeing 880. The USAF wasn’t that interested in a jet tanker until they saw what the Boeing 880 could do, then it decided they were a good idea.

  • ThomasLMatula

    Depends on the paper and it’s importance. FedEx built its business case on rapid transportation of paper and still makes money on it. And if you are losing a million dollars a day because you don’t have a critical spare you would be glad paying for same day delivery.

  • savuporo

    The g-loads are the least of the problems for this. Infrastructure, regulation, air traffic control, noise, cost .. just not happening as a commercial service.

  • Paul451

    Any object which can’t handle a continuous 3 or 4g is going to be too fragile to handle 90% of freight options anyway.

    It’s the same with people. Astronauts have higher demands because of their duties, but theme parks and zero-g “vomit comet” rides deal with regular passengers. They don’t require medical teams to screen each rider.

    People (including the OP) are being hysterical about this. The issues that would prevent p2p transport are not g-load, but noise, safety, and probably restrictions of trajectories due to similarity of the launch profile to an IC or IRBM.

  • Paul451

    Fuel requirements scale with the square of delta-v. So 85% of delta-v means ~70% of the fuel demand. That allows you to lower the rate of acceleration during launch.

    Additionally, if BFR is rated at 150t to LEO, a cargo-bay even filled to standing-room-only with people/seats/bags is going to mass less than that, freeing up more fuel, allowing you to waste that fuel on a lower-g launch.

    And your grandmother can handle 3g.

  • Tom Billings

    Nickolai, over 60 years ago, the ABMA Huntsville team had figured out how to load propellant into a Jupiter missile fast enough that its launch time from a cold start was driven by the 20 minute spin-up time for its gyroscopic inertial guidance system, not loading the LOx. The loading time for Kero/Lox is quite short, and Methane is not a big imposition on top of that. Multiple load points make short work.

    BFR could fly within an hour of getting word to load propellant. That makes a maximum prep/trip time of 2 hours probable, with 75 minutes more likely in most cases.

  • Tom Billings

    Also note that the Army has announced its new program to use 3d-printing of metals at battalion and brigade level for as many parts in its inventory as it can wiggle to do, and that future inventory will be designed to use this capability specifically. This will make whatever *still* has to be brought from the States that much more valuable as a “get it now!” item.

  • Paul451

    if you take a look at Saturn V/Shuttle costs

    Then you’re doing space wrong. If the unit cost of BFR is $1b, SpaceX can’t afford it.

    Assuming 60 launches per year with an average payload of 15 tons (probably an overestimate), that’s 900 tons/year launched, which could be launched with 6 BFR flights.

    a) You can’t 60 different payloads into the same 6 orbits. That’s not how the market works.

    b) SpaceX’s intention is that BFR will cost less per launch than F9, hell, less than F1. F9 already pwns the launch industry. So if BFR can merely match the per-launch cost of the semi-reusable F9, then it doesn’t matter if it is only carrying a single 5 tonne payload. (A lot of people get fixated on this. “It’s too big! There’s no market for big payloads!”)

    c) Either the satellite industry starts to use that mass capacity to lower its own costs, or SpaceX will combine cargo flights with passenger tourism. If the payload pays for the launch, the passenger tickets are gravy.

    (Weight saving materials and design increases your costs. Being able to use bulk off-the-shelf materials, without special mass shaving processing, drastically reduces costs. Look at the number of people playing with cubesats, because the launch costs for a cubesat are so low, therefore you can throw off-the-shelf components at the problem and not really care if it doesn’t work. That brings in small companies, universities, self-funded researchers and general enthusiasts.)

    (People currently pay $5000 for “zero-g” flights on vomit comets, 15 runs of max 30sec weightlessness. $5000 for 7 minutes of intermittent zero-g. How much would they pay for half a day in orbit? I said tourism, but many technologies intended for space are tested on vomit-comet flights, in spite of the ridiculous limitations. Low cost manned orbital flights will revolutionise system development.)

    d) The ESA wants to develop a “lunar village”. Lowering the transport costs by an order of magnitude will make that much more affordable for them, it will also increase the number of flights.

  • Tom Billings

    And if you are losing a kilometer of ground every hour, because you lack X, at the front line 30 kilometers from the landing zone, you really don’t want that spare computer/whatever in your hands “in just 36 hours”.

  • Andrew Tubbiolo

    I was only brining up the point that velocity requirements are close. I was not trying to say it could not be technically done. Yes, this can be done.

    As far as passenger g tolerance. I take folks up on rides in a nice comfortable Grob 103 glider on a regular basis. It has a nice spacious cabin with reclined seating. A lot of people unaccustomed to pulling g start to lose it at 2. I’ve never had a non-pilot passenger not ask me to stop when I’ve taken it to 3 and held it there for 10 sec or so. About half the folks I take up can take protracted 2, but the only folks who could take 3 or more were other pilots. So my experience makes me doubt that a lot of folks will be ready for 3g for minutes at a time. You’ll need a cabin that can be hosed down rather quickly. If you have a full cabin of 500 people, I’d fully expect 200 or so to blow chunks every flight. That’s IF you keep them in their seats. If you allow them to float to the windows …. 🙂 I won’t do zero g pop overs with new passengers, because that makes almost everyone new at it very unsettled. It’s going to be some really interesting crowd dynamics when the engine cuts out and the passengers inner ear tells them they’re heavy one sec and falling the next.

  • ThomasLMatula

    Actually Robert Heinlien wrote about it in “The Man who Sold the Moon” in 1941.

  • ThomasLMatula

    Yes, it’s a niche market, but a very profitable one.

  • WhoAmI

    I’d puke, but then again they have anti-nausea medications you can take such as Zofran. Maybe everyone would be required to take an anti-nausea medication ahead of time or have to wear a bag over their head for the duration of the flight. 😉

  • ThomasLMatula

    Yep, and if they do have extra room and mass it enable the satellite owners to add more Solar Panels or propellant for station keeping.

  • duheagle

    Cost is a non-issue. Sub-orbital BFR’s will cost a fraction of what a new 747 or A-380 goes for. Rockets don’t have most of the expensive complexities of aircraft.

    Infrastructure will be offshore floating or fixed platforms – no revolutionary technology required and something SpaceX already has some small-scale (relative to BFR) experience with.

    Noise will be limited by putting the infrastructure at least a few miles offshore or maybe more than a few miles. The excursion-type craft shown for surface transport of passengers over water in the point-to-point BFR video was cute and cuddly, but hydrofoils or hovercraft would be a lot faster and more practical. Again, decades old technology.

    Air traffic control will be a minor issue at best. BFR’s won’t be taking off and landing at airports. Uncontrolled airspace starts surprisingly close to even major airports, especially to seaward of coastal airports. Just don’t put the platform under a major glide path.

    Regulation? Once upon a time there was no regulatory framework for aircraft either. Contra the apparent opinions of some, government regulations have not been with us since the Dawn of Time and are not actually laws of nature.