Comment by GlenTheMachine | Hacker News Reader

Comment by GlenTheMachine | Hacker News Reader

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Rockets do actually heat in flight. But their launch profile is carefully chosen to keep the heating to managable levels. Liquid fuel rockets typically throttle down somewhere around a minute after launch, at a point called "max-Q", which is the point of maximum aerodynamic pressure. They throttle back up again once they have gotten above enough of the atmosphere.

As a point of reference, the SR-71 was one of the first major aircraft programs to use titanium extensively, the reason being that at the speeds the SR-71 flew, aluminum couldn't maintain structural stability due to the heat. And the SR-71 was "only" a Mach 3 airplane, flying at "only" 60,000 to 80,000 feet. It's fuselage would reach nearly 600 degrees.

An orbital launch vehicle typically reaches Mach 3 very roughly that same altitude, or somewhat higher (the figure I can find is Mach 4.5 at 28 nautical miles, which by interpolation I'm guessing is Mach 3 at between ten to twenty nautical miles; ten nautical miles is roughly 60,000 feet).

Another bit about the SR-71 (and supposedly concordes) is that their structures are designed with tolerances based around the forces they experience at speed. The effect of which is that when sitting on the ground not going anywhere there are gaps between some parts, and others are tightly compressed together (and then separate while traveling at speed). I don't remember if it was the last concorde, or one of the SR-71s, but there's a story out there about the pilot on its final flight sticking his hat into a gap in the cockpit, which on landing promptly closed up permanently sealing his hat in place inside of the cockpit (he did it on purpose to commemorate the last flight). Similarly there are stories out there that claim the SR-71 leaked fuel like a sieve while sitting on the ground because it needed the atmospheric heating from going supersonic to seal up all the various fittings in its fuel system.

I do recall seeing an image of an SR-71 on the ground with pans under it in various places, supposedly to catch leaking fluids.

Ironically there's a series of Russian dive watches that does approximately the same thing.

Instead of attempting to overengineer a high-depth tolerant system that's still sealed in open air, it's sealed more tightly as pressure increases.

An elegant weapon from a less civilized age.

https://en.m.wikipedia.org/wiki/Amfibia#Design

Here's the reference to the pilot's cap:

http://www.seattlepi.com/business/article/Concorde-s-arrival...

Any SR-71 story usually comes with the obligatory story about the Cessna v navy ground speed check. I'm replacing that story with the story of the time an SR-71 went very slowly.

https://www.google.co.nz/amp/foxtrotalpha.jalopnik.com/the-s...

Thanks! Tyler Rogoway can certainly relate a story.

IIRC they would refuel mid-air shortly after take off for long range missions.

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