All Astronautical Evolution posts in 2017:

Scenario Block Diagram Analysis of the Galactic Evolution of Life (Nov.)

Comments by Alex Tolley (Oct.)

Elon Musk’s “Great Martian” (Oct.)

Elon Musk’s Mars Plans: Highlights from His Second Iteration (Sept.)

What is a Supercivilisation? (Aug.)

Quantifying the Assumptions Behind the METI Debate (July)

Five Principles of a Sustainable Manned Mars Programme (June)

Pale Red Dot: Mars comes to Oxford (May)

Back to 2016:

Elon Musk and Mars: Looking for a Snowball Effect (Oct.)

New in 2020:

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AE posts:

2022: What’s to do on Mars?…

2021: New space company Planetopolis…

2020: Cruising in Space…

2019: The Doomsday Fallacy, SpaceX successes…

2018: I, Starship, atheism versus religion, the Copernican principle…

2017: Mars, Supercivilisations, METI…

2016: Stragegic goal for manned spaceflight…

2015: The Pluto Controversy, Mars, SETI…

2014: Skylon, the Great Space Debate, exponential growth, the Fermi “paradox”…

2013: Manned spaceflight, sustainability, the Singularity, Voyager 1, philosophy, ET…

2012: Bulgakov vs. Clarke, starships, the Doomsday Argument…

2011: Manned spaceflight, evolution, worldships, battle for the future…

2010: Views on progress, the Great Sociology Dust-Up…

Chronological index

Subject index

General essays:

Index to essaysincluding:

Talk presented to students at the International Space University, May 2016

Basic concepts of Astronautical Evolution

Options for Growth and Sustainability

Mars on the Interstellar Roadmap (2015)

The Great Sociology Debate (2011)

Building Selenopolis (2008)


Issue 138, 5 October 2017 – 48th Apollo Anniversary Year

Comments to issue 137

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From Alex Tolley, 1 Oct. 2017

I like that you have used the analogy to air travel.  This is a much-needed update from Clarke’s original air travel analogy.

However, starting from 1960 simply because that was the start (well nearly) of commercial jet aviation and jets fly very high, is not the appropriate starting point.  It would be far more reasonable to start at a point that reflects the same sort of passenger flight rates as the space program.  As flying was mostly for the wealthy in those days, this might make it even more apt.

I do understand that you have also used the size of the vehicle (100 passengers) to make your analogy, and this is where your point really hits home.  When flight rates for passengers were low, only smaller aircraft were made, befitting the number of passengers and their destinations, e.g.:

  1. The Hindenberg could carry 72 passengers (slowly) (1930s)
  2. Ford Tri-Motor – 7-9 passengers (1925)
  3. Lockheed Constellation – 62–95 passengers (1943)
  4. Pan Am Clipper Flying Boat – 77 passengers (1940s)

Assuming exponential growth and starting with 25 passengers in 1910 (no reason for that date) and ending in 1975 with 500,000,000 passengers, growth must have been closer to 35% pa.  Starting with 10,000 passengers – 18% pa.

What this suggests is that your analysis is still correct.  A 100 passenger BFR is too big to introduce so early.  Countering that is Virgin Galactic’s pre-bookings that claim 500 passengers in year one.  If they all took a BFR ride to orbit and returned, that would be 5 BFR flights pa.  Probably not enough to reduce the ticket price sufficiently by amortizing the vehicle cost, but perhaps enough to get started while flying freight.

As Clarke noted, US commercial travel started with airmail.  SpaceX could continue to focus its business on freight, flying passengers as the icing.  If so, I would make the passenger section a module that could be “dropped in” to a payload bay so that a dedicated passenger vehicle was unneeded until flight rates for passengers increased.  The question then becomes: “Is there enough space business at lower prices to increase the demand to meet the needed BFR fleet supply?”

Perhaps he should scale his BFR down further?  Using the Boeing 777 as a reference, passenger capacity of ~300 is about 30% of the aircraft + passengers + luggage.  The F9 can loft 13,000 kg to LEO.  This implies about 20 passengers with luggage sitting in a vehicle comparable to a 777 in comfort and complexity.  The smaller vehicle would allow faster amortization of costs assuming the smaller size still offsets the lower unit launch costs of the BFR.

Keep more analyses of the space tourism business coming.  They help ground us all in reality.

From Alex Tolley, 4 Oct. 2017

Partial second thoughts

On reflection, I realize that Musk’s focus on the suborbital transport business plan might just be the way to justify the 100 seat BFR.  Assuming it is the same ship as the orbital one, the 100 seat BFR taking passengers point-to-point around the planet in very fast times would justify the size of ship.  Concorde carried 90-100 passengers by the 1970s and was a success.  What sank it was the banning of overland flights due to the sonic boom, reducing its role to overseas flights.  The huge development cost could never be recovered with the reduced flight rate.  Given the far larger passenger market today, I would expect a business traveler to be very interested in such a flight as it leapfrogs over the new plans for supersonic aircraft on the drawing boards.

Why this plan might fail

To avoid the noise and security issues, Musk intends to arrange the flights from offshore platforms.  If states refuse to allow this, his plan for this market is a non-starter.  Like Concorde, he may get a few, but with insufficient flight rates to justify the vehicles.

The second issue is passenger comfort.  Spending up to 1.5 hours in near freefall is unpleasant.  Worse, you cannot get to a toilet for any sort of relief.  As Clarke said, half the time the toilet is unreachable, the other half unusable.  Having once experienced a lot of turbulence flying over the Alps with the aircraft dropping rapidly, I was fairly miserable.  At least it was possible to reach a working toilet.  We know that about 30–50% of people will get motion sickness in freefall, so that alone needs to be fixed with suitable drugs before the flight commences.  The flights will also need to ensure that passengers will not need the toilets for any reason during the flight unless some sort of zero-gee toilet can be constructed.  The size of the BFR might make some sort of carousel-located toilet possible, allowing some sort of partial gee to make them usable during the ballistic phase of the flight.  Without that, I am skeptical that business travelers will put up with the discomfort for the flight duration, especially once the novelty wears off.

If Musk can ensure these two obvious problems are not insurmountable obstacles, then the flight rate of today’s business traveler market would justify a fleet of passenger BFRs, some of which would be used for orbital, Lunar, and Martian flights. If so, then the existing air travel market is the relevant metric, not the likely very much smaller hypothetical Martian colonization market.

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