[LINK] "Why we're not going to see sub-orbital airliners"

[rfmcdonald]

Writer Charlie Stross makes the case at his blog that just because something is technologically possible doesn't mean it will come about. In this case, he's talking about sub-orbital passenger flight. Even if it could be afforded, dear God, the security issues!

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.

It's going to be a lot harder to intercept a hypersonic service, to say the least. If nothing else, the reaction time will shrink by an order of magnitude. Today, it takes perhaps 2-5 minutes to get an RAF QRA Typhoon-II into the air. It can then go supersonic and overhaul a subsonic target at relatively high speed. From Coningsby or Leuchars a Typhoon-II can reach just about any spot over the UK in 15-20 minutes, in which time a subsonic airliner can travel perhaps 100-200 miles. The picture is very different for a hypersonic passenger craft. In 20 minutes such an aircraft would travel somewhere between 1000 and 3000 miles. None of today's military aircraft are up to the job of intercepting it, and indeed, active radar can't even track it effectively—for that, you'd need something on the order of a cold war ballistic missile warning radar system, designed to provide advance notice of an ICBM strike.

A hypothetical hijacker interfering with the flight profile of a hypersonic transport wouldn't need to deviate from their flight plan 20 minutes before it crashes into a target; it could be a last-minute gambit. So the security surrounding such flights is going to be intense, they're only going to be allowed to fly on well-established schedules (no short-notice bizjet-equivalents need apply!), and they're going to fly in and out of spaceports some distance from the destination city. For example, there's a proposal to use the former RAF Lossiemouth in Scotland as a spaceport for the UK. It's a good site for polar orbit satellite launches (north of Moscow but with far more clement weather), but it's nearly 600 miles from London. Similarly, the New Mexico spaceport isn't exactly next door to Los Angeles.