On Sub-Orbital airlines and feasability

Charlie Stross has an article up exploring Why we’re not going to see sub-orbital airliners. It is an interesting exploration of why a technology that might be feasible will never really be practical and certainly would never be profitable. Some good food for thought for authors seeking to extrapolate into the future a bit.

One of the failure modes of extrapolative SF is to assume that just because something is technologically feasible, it will happen: I’m picking on sub-orbital passenger travel as an example of this panglossian optimism because I got sucked into a thread on twitter the other day and I think it’s worth explaining my objection to it in a format that permits me to write more than 140 characters at a time.

Let’s start with a simple normative assumption; that sub-orbital spaceplanes are going to obey the laws of physics. One consequence of this is that the amount of energy it takes to get from A to B via hypersonic airliner is going to exceed the energy input it takes to cover the same distance using a subsonic jet, by quite a margin. Yes, we can save some fuel by travelling above the atmosphere and cutting air resistance, but it’s not a free lunch: you expend energy getting up to altitude and speed, and the fuel burn for going faster rises nonlinearly with speed. Concorde, flying trans-Atlantic at Mach 2.0, burned about the same amount of fuel as a Boeing 747 of similar vintage flying trans-Atlantic at Mach 0.85 … while carrying less than a quarter as many passengers.

Rockets aren’t a magic technology. Neither are hybrid hypersonic air-breathing gadgets like Reaction Engines’ Sabre engine. It’s going to be a wee bit expensive. But let’s suppose we can get the price down far enough that a seat in a Mach 5 to Mach 10 hypersonic or sub-orbital passenger aircraft is cost-competitive with a high-end first class seat on a subsonic jet. Surely the super-rich will all switch to hypersonic services in a shot, just as they used Concorde to commute between New York and London back before Airbus killed it off by cancelling support after the 30-year operational milestone?

Well, no.

Firstly, this is the post-9/11 age. Obviously security is a consideration for all civil aviation, right? Well, no: business jets are largely exempt, thanks to lobbying by their operators, backed up by their billionaire owners. But those of us who travel by civil airliners open to the general ticket-buying public are all suspects. If something goes wrong with a scheduled service, fighters are scrambled to intercept it, lest some fruitcake tries to fly it into a skyscraper.

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