[collinf]

Posting this here hoping that someone with more knowledge can enlighten me about this. After going down a bit of the rabbit hole, I see that the SR-71's first flight was in 1964. It has held the record for fastest air-breathing manned aircraft[0] since 1976. What is the reason that given all of the technological advances that record hasn't been broken?

[0] https://en.wikipedia.org/wiki/Flight_airspeed_record

[VLM]

No one has answered why; only answers have been "no marketable product".

There are several technical reasons why, none of which have been been subject to any technological advances in half a century.

1) There's a buffer factor where burning fuel adds a thousand degrees (or whatever) to temp of the air in the engine and steel / titanium / classified will melt several hundreds of degrees above that. Most all jet engines can only work with subsonic airflow. Supersonic aircraft use exotic inlet designs that are inefficient but can convert fast air into very hot compressed air. Somewhere around mach 2 to mach 4 the inlet air temp plus the heat of burning fuel will melt any metal turbine blade. You can pay a lot of money to get a couple mach numbers but fundamentally cheap steel gets you mach 2 and price is no object aerospace material tops out in the mid mach 3 range. True lab experimental materials might survive mach 4 temps, maybe. You just can't get a usable thrust to weight ratio inlet design that works above mach 4 or so.

2) Second aerodynamic problem is if you define "fly" as a lift to drag ratio better than a lawn dart, optimizing wing sweep etc for mach 3+ means its a truly awful performer below 5000 feet or so. Its hard to make an aircraft that actually "flies" above mach 4. Space shuttle L/D ratio was around or below 1:1. Essentially things flying thru the air above mach 4 don't fly in the sense of wings producing lift, they're ballistic trajectory like a missile or bullet, don't bother slapping wings on them.

None of the above can be solved with faster computer cycles. Titanium still melts at the same temp, etc.

[Gravityloss]

There are relatively simple ramjets that fly at around Mach 4 speeds. They are unmanned and are accelerated to speed by solid rockets. Probably the ramjet can't even start below Mach 1 or so.

Designing an air breathing propulsion system for a wide speed range is difficult.

Rockets are much easier after a certain point. McDonnell Douglas and Paul Czysz had interesting projects. If you want manned reconnaissance, a Mach 6 air launched liquid rocket powered lifting body would probably be the next logical step from the Blackbird and would not even be super hard. With rockets you don't have the inlet problem at all and they have excellent thrust to weight ratio.

[gavindean90]

Basically, satellites took over They are cheaper to operate and less vulnerable to defensive countermeasures and other failure conditions. From a Los Angeles Times article from '89 [0]:

> "The Air Force decision to retire the Blackbirds in 1990 is based on several factors. In congressional testimony, Air Force Chief of Staff Gen. Larry D. Welch identified the increased survivability of reconnaissance satellites, SR-71 vulnerability to the Soviet SAM-5 surface-to-air missile and the cost of maintaining the SR-71 fleet."

[0] https://www.latimes.com/archives/la-xpm-1989-04-09-op-1582-s...

[village-idiot]

They took over, but there’s still an argument for spy planes; satellites arrive on their own schedule in predictable orbits. This makes it very hard to get timely photographs, and it makes them easier to defend against. A spy plane could get in and out of a trouble spot within an hour, all before the enemy can hide the nukes or whatever.

A modern spy plane however would have to be faster than the SR-71, which I don’t believe would be safe against modern SAMs.

[walrus01]

Based on the totally amateur knowledge level of someone that once spent a few hours researching stealth satellites (MISTY, etc), there's obviously a demand within the NRO for satellites that can be launched into a known orbit, with published two line elements, and then go stealthy and change their orbit into something which cannot be predicted by enemy nation-state ground forces.

I don't believe anything worthwhile about current capabilities has been declassified, it's all conjecture by people looking at the X-37 and similar systems.

[nradov]

There's no way to really "go stealthy" in space. If a satellite is operational then it has to emit enough heat to be clearly visible to IR sensors.

http://www.projectrho.com/public_html/rocket/spacewardetect....

[handedness]

The X-37B is likely a test platform for exactly that scenario (and more).

[knute]

There are faster air-breathing aircraft (e.g. [0]), but none of them are manned because with modern technology there's no need to put a person in them, and the people funding these developments aren't interested in spending lots of money just to chase records.

There's also the outside possibility that faster manned aircraft exist, but remain classified [1].

[0] https://en.wikipedia.org/wiki/Boeing_X-51_Waverider [1] https://en.wikipedia.org/wiki/Aurora_(aircraft)

[golergka]

I just love how this super-hightech, experimental military aircraft has parts secured with duct tape in this Wikipedia photo: https://upload.wikimedia.org/wikipedia/commons/thumb/e/e5/X-...

[JohnBooty]

There's just never been a need. The SR-71 could already outfly missiles.

And in general, now that we have the technology, the SR-71's role is much better filled by unmanned craft like satellites anyway.

Stuffing a man inside one of these deathtraps and getting him home safely adds orders of magnitudes of difficulty. A better question might be, why would you want to send a person up in something like this, if you could possibly avoid it? It would most definitely be awesome, but it would come at the cost of billions of dollars and possibly human lives.

Also physics is a real bastard. Air resistance increases with the square of velocity. Even small gains over the SR-71's speed would come at a very, very high cost in terms of fuel burn rate, etc.

[lb1lf]

-Wholly uneducated guess: many of the tasks handled by the SR-71 is adequately handled by satellites today.

Additionally, if someone had indeed broken the record in some black project or the other, chances are they would keep mum about it rather than calling Guinness Book of Records.

[iscrewyou]

I want to go out on a limb and say two things: (i) It probably is broken. (ii) That table doesn't show when the data was listed as public. The reference on the top speed is "Taylor 1988, p. [51]."