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Comment by hinkley | Hacker News Reader

The SR-71's actual top speed was classified, and the 'official' top speed was faster than anything else in production.

At several points growing up someone would come up with a new plane that encroached on the SR-71's speed record. Then a couple weeks later there would be an announcement about the SR-71 setting a new top speed.

I suspect someone in Intelligence had to decide that being officially the fastest was important, but exactly how fast being a secret made the plane and pilot a little bit safer. So they had to nudge the fiction a little bit closer to the truth any time there was a pretender. Or, manufacturing improvements nudged the maximum safe speed up over time, and they only bothered updating the public about this when a dick measuring contest was held in their honor. Or maybe both.

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That said, we both know the shape of the SR-71, and the Compressor Inlet Temperature limit. The shape determines the smallest Mach angle that the entire plane fits inside, which gives a value for the maximum speed. The CIT limit gives a value for the maximum speed, which is roughly the same as the Mach angle value, at approximately Mach 3.3. To go faster, the plane would have to be skinnier, or the wing tips would poke beyond the Mach cone, and the entire tip would generate it's own set of shockwaves, which would most likely result in a sharp increase in temperature for the part outside the cone (which can be read as: the wing tips melt off).

It's just nuts to think about people on Concorde sipping champagne at Mach 2.04. I wonder if that's something which will be possible again in my lifetime.

It's likely there will be Starship-based passenger transport from point to point on Earth within 10-15 years.

The biggest hurdle will be getting countries to allow an ICBM filled with humans to approach their mainland.

Highly doubt. The Concorde's problem was economics not science and a rocket based solution is even less economical - even a reusable one.

For normal people sure, but for VIPs and especially military it will happen.

Imagine being able to drop Seal Team Six into Taipei, the Red Square, or literally any other piece of earth with a ~50ft clearing on ~30 minutes notice? That's a capability which is very hard to put a price on.

I'd like to not imagine a boots-on-the-ground shooting war, where you are launching a craft that is indistinguishable from an ICBM at a nuclear power's capital.

I'd like anyone at the DOD who is imagining it to either be fired or shot, before they drag the rest of us into their geno-suicidal fantasies.

Starship is worse than an ICBM. ICBM carries a handful of MIRV warheads. Starship potentially carries hundreds of warheads. It is a single rocket first strike. Nobody would put that many warheads on one rocket, but the target needs to act like it could.

In real life adetachment of a couple of hundred soldiers with very limited support dropped into the middle of enemy territory, with their destination known 30 minutes in advance to anyone with tracking satellites will be very quickly overrun. Said adversary will also be thankful for the gift of the vehicle delivered to them with now way to get it out.

You sir, have clearly never met us special forces. A “couple hundred” with combat load would be an absolute force to be reckoned with.

Is there any reason this would be more possible with a rocket than with, say, a plane? It has to land slow enough that the passengers survive, and during that process it can be spotted and shot down, or surrounded.

I mean I’m definitely in favor of getting some sci-fi style orbital drop troops, but I think it will require some development beyond the rockets; we’ll need to figure out how to get people who can survive a bunch of extra G’s.

A human being can withstand ~8g's for medium short duration with minimal accommodation, say tens of minutes - see fighter pilots. I would imagine that would be enough to get someone on the ground pretty quickly. 30 minutes door-to-door is also incredibly fast, how much of the world could be covered by AA or a fighter plane in time?

As a for instance, imagine if in the initial invasion of Ukraine Russia had the capability to drop a starship heavy's worth of men and supplies onto Antonov airport as soon as it was secure, instead of waiting for transport planes that didn't arrive in time.

You don't need the whole world to be covered. There is no point dropping special forces into the middle of nowhere. The air force can certainly respond within minutes to threats to major cities and strategic targets.

A starship wouldn't have made that much difference in the invasion of Ukraine. You're talking maybe two additional MBTs.

>There is no point dropping special forces into the middle of nowhere

Most of everywhere is the middle of nowhere and almost everything behind the lines is poorly guarded[0]. The vast vast majority of military strategy relies on two basic facts: things are far apart from each other[1] and one needs to move through another place to get to where one is going[2]. Ballistic transport gets around both of these limitations, which is why it is going to happen, costs be damned. Maybe it'll be drones getting dropped, or bombs, instead of people, but it'll be done nonetheless.

I don't know if you've ever played bughouse - but the timely application of even small amounts of resources can have a drastically outsized effect. A starship could have easily doubled the resources the Russians had to take that airport, a few more could have taken another while everyone was busy with the first.

[0]Because those resources are better spend on/near the line.

[1]Lines vs. back-lines vs. civilian areas, conventional logistics and its demands

[2]Walls, trenches, emplacements, AA defenses

If they have a predictable landing in a big clearing they are gonna be in a tough spot regardless of how capable they are.

Drop them with armored transport near a supply line and it could work if you have already done SEAD.

It's a preposterous scenario. China would blow the thing out of the sky long before it could land. And even if it did, they'd simply use armor and helicopters to decimate the forces.

Beijing is defended by two guards divisions. Who get woken up once it is determined that Beijing is the target and move into position.

Special forces are not very good against good regular troops. Special forces are really good light infantry. Regular troops have heavy weapons. Armored regiments have tanks. Mechanized infantry shows up with IFVs and troops.

The whole scenario would be like black hawk down ... but with less survivors.

Special Forces aren't great in head-to-head combat against well-equipped and well-supplied soldiers who know they're coming. They lose their advantage. Plus they would need a whole lot of resupply.

Starship is insanely vulnerable for landings. It starts fast but has to slow down for landing. Which means that is vulnerable to every SAM in Beijing region.

I guess it could be done as drop of pods or something. The problem is that target can’t know the pods are troops and has to assume that they are nukes and this is first strike. China has no choice but to launch ICBMs immediately.

Plus, this risks the Starship itself. It might be possible to drop pods, now space and recently capable, and change directions. But is more likely that get in range of anti-ballistic missile.

Concorde was profitable. Accidents + 9/11 pullback killed it. The major factor against supersonic is actually the fact that sonic booms are not allowed over the continental United states. Companies like Boom Supersonic are focussed on eliminating those.

https://simpleflying.com/did-british-airways-make-a-profit-f...

> If British Airways and Air France were looking for more profit, these issues would have to be addressed. And that was the plan. British and French aerospace divisions were looking to create a brand new supersonic aircraft before plans to take the Concorde out of service in 2000 were realized.

> Of course, that never happened. With a plethora of odds stacked against it, the 2000 crash in France, 9/11 affecting interest, and Airbus scrapping Concorde part replacements, the Concorde was shelved before its time.

The prohibition on sonic booms mysteriously appeared when it came out neither the Lockheed nor Boeing SST would ever become a reality, leading to the embarrassing situation of the only supersonic airliner being a British-French collaboration.

NASA's X-59 project is aiming for a very low sonic boom

> The major factor against supersonic is actually the fact that sonic booms are not allowed over the continental United states.

How do military pilots train then I wonder?

Only civil aviation above Mach 1 is prohibited by the FAA. Rulemaking to certify quieter supersonic planes is underway. [1]

1. https://www.faa.gov/newsroom/supersonic-flight

There are explicit supersonic-permitted areas used by military, but you can actually do supersonic flight as civilian too if you arrange their use (mainly a thing of scheduling so you don't collide with military/state aircraft).

The big rarity of that is that there are very low numbers of supersonic planes in civilian hands, and outside of Concorde and some Tu-144 models (not all of them), all are ridiculous fuel guzzlers in supersonic flight. I know there's one near Palo Alto, a civilian owned MiG-21.

Who the fuck owns a MiG-21?

Well, there's one guy in Palo Alto who had instructor permit on it even, and was looking for partner in its ownership (quite common solution for more expensive planes in civilian hands).

According to wikipedia: 44 people in the US and one big company that owns 30:

https://en.wikipedia.org/wiki/Mikoyan-Gurevich_MiG-21#Civili...

Numbers from 2012 tho... But probably won't be too different now.

More than 11.000 were made, wow.

Two quotes from the link you provided.

> In total, both the French and UK governments put in $1.44bn to get Concorde off the ground. $2.8bn went into realizing the world's first mass supersonic transport.

> At the end of it all, British Airways had gained £1.75bn in revenue with the Concorde against an operating cost of £1bn.

Making some money doesn't mean it was necessarily profitable enough to be worth flying. Typically you have a rate of return across the company that an investment needs to clear to be worthwhile. Especially when considering the aircraft almost certainly required specialized maintenance crews and parts, the bar was probably fairly high.

It was also limited in where it could operate out of. I'm guessing that landing Starship at SFO or JFK or Dulles is not going to happen, ever.

Ever is a long time! In 50 years when travel via rocket between cities on Earth is common, why wouldn't airports build rocket pads for it? When you can fly New York to Singapore in less than an hour, JFK isn't going to just give up that market, they're going to want to capture some of that money.

Probably because the blast radius during lift off is close to the entire JFK property size? Of course, let's not forget the blast radius of a Starship undergoing unscheduled rapid disassembly.

I mean, I like roller coasters, but I think the biggest challenge might be getting hundreds of humans on that ICBM with the current flight profiles.

That seems to be mostly scrapped, they sold off the offshore platforms they'd purchased. It also wouldn't be nearly as fast as the point to point numbers suggested because the trips out to the platforms would have been rather slow on either end.

Fifteen years is a long time in software but a blink of an eye in the world of infrastructure. A decade of Starship development has created a missile that blows up when launched. I'm sure they'll eventually get to orbit, but they're a loooooong way away from anything that the FAA will allow to operate for regular passenger flights near cities. And that's ignoring all the logistics involved in creating a profitable passenger service.

My aunt once rode the concord from Paris back home to NYC as an indulgence. She ended up sitting next to Jacque Cousteau of all people and had a fantastic time. It's one of her favorite stories.

I'd check into Reaction Engines, and the concept of precooled jet engines in general. The math says they should be capable of efficient cruising at speeds up to mach 5. The question is if anyone can make the engineering practical and affordable. But in terms of pure possibility, there's wide open possibilities.

Isn’t the temperature on the body surface the big factor here? The sr-71 would heat up tremendously and it barely had any air pressure to contend with.

It's difficult but not a show stopper. Materials have come a long way. Also, a pre-cooled engine will be using cryogenic fuels so active cooling is an option, even desirable (some of these engines harvest energy from the precooler using turbines on the hot side). SpaceX thinks they can handle the thermal loads of Starship re-entry with ceramic tiles and stainless steel.

Recently got inside the Concorde used for testing, now at Duxford. That plane is much cozier than I thought, even with no seats. And the number of fuses is slightly crazy.

The example at the Museum of Flight in Seattle (somewhat ironically resting at a Boeing factory...) still has original seating and the interior is open to the public - it's really cramped. What got me most though is the tiny portal of a window you got, due to the design constraints of supersonic flight etc. All that cost and prestige, but a cramped seat and no view.

Honestly, if I'm spending that much money for a ticket, I'd prefer luxury over speed. I don't know how many people would prefer a cramped supersonic aircraft over a trip that takes slightly longer and gives you a lay-down bed.

> I wonder if that's something which will be possible again in my lifetime.

Is there a historical situation where a form of travel was long forgotten only to be brought back decades or centuries later?

My thought goes to the Viking Colonies in Newfoundland.

Not really forgotten, but trams/streetcars definitely went out of fashion in many places and have been making a comeback in the form of modern LRT systems.

Many tram lines were built by developers at a time before cars were affordable. Otherwise there would have been no way for the homeowners to commute to work.

Yes, except I don't think developers have built tramlines anywhere but the US (and also the expansion to the suburbs didn't quite happen that way). I'm talking about the period of time that in Europe started in the 60s, and in the US earlier due to the earlier rise of the personal car, when many cities abolished their tram systems due to being "old-fashioned".

Region dependent on exact dates but common bicycle ownership predates common car ownership by 40 years or so.

So a lot of existing cities that are introducing dedicated bicycle infrastructure likely fit.

My toddler loves the movie Moana. Turns out part of the movie is based on a real historical time period where Polynesian people stopped sailing long distances to colonize new areas.

https://historydaily.org/disneys-moana-depicts-an-actual-eve...

I was sitting at JFK back in the day waiting for my flight back to London.

Over the speakers came an announcement: "if anyone is prepared to give up their seat on [my London flight] we'll fly them back tomorrow on Concorde and put them up in [a ritzy hotel] tonight".

I bolted for the service desk to take up the offer and got there in seconds but there were already several people ahead of me. Never got to fly Concorde.

I had a professor who said that in the early days of priceline he used to book fully refundable flights from London or Paris to NYC on the concorde then cancel them - just to pick them back up on priceline for a few hundred bucks at the last minute. Never knew if it was bullshit but certainly made a good story when I heard it in 2008. The context of the global financial crisis made the .com boom/bust look quaint.

That is (a reason) why airlines overbook

Blake Scholl and Boom Supersonic are trying to make that possible again.

https://boomsupersonic.com/

This might be a dumb question, but isn’t that the maximum sustained speed for the plane, and higher speeds would be possible for short bursts? (as in, before the wing tips get hot enough to melt off)

Yes, that is correct, though I guess an issue would be that the drag would increase sharply if parts of the plane is sticking out of the shockwave, necessating even more thrust.

My understanding of bomber height was 1) fighters and ground cannons cannot attack them directly, and 2) SAM missiles have to climb to meet them while matching velocity, and the bomber can shed altitude to increase ground velocity and outpace the missile long enough that it runs out of fuel.

That puts a big gap between top cruising speed and top speed.

> Compressor Inlet Temperature limit

How do we know this is also not part of an official/unofficial limit?

I guess the point is you can make an estimate of the CIT based on the geometry of the plane, and the speed and altitude it's traveling at. And similarly the CIT limit can be estimated from published data about the engine plus knowledge of the limits of the materials used when it was designed.

This is actually an engine limitation. It's to keep the turbine blades from melting. Unfortunately, you can't measure the turbine inlet temperature very well, because of the whole melting thing. So they determine what the limit should be, and then back calculate it to somewhere they actually can measure it (which is the front of the compressor). So, you could exceed the CIT limit, but you would run the chance of damaging the engines. The MiG-25 has famously destroyed it's engines by running to fast.

It’s like the lawyer attitude during a deposition: provide as little info as necessary. Classified by default.

A related quote from the same pilot on how fast the SR-71 could fly: “There really isn’t one number to give, as the jet would always give you a little more speed if you wanted it to.”

https://www.thesr71blackbird.com/Aircraft/Stories/sr-71-blac...

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