I almost skipped the videos embedded in this article, but they are well curated gems. A few tidbits I found amazing:
- 800°F (and above) was the temperature of their cooling air
- the engine ran too hot for electronics, so they designed a hydraulic mechanical computer responsible for regulating various inputs
- the roar from the two external 400 cubic inch Buick V8 engines originally used to start the aircraft was so irresistible to the hotrod enthusiasts running them that they sometimes neglected to disconnect in time before the starter engines overran RPM limits and "puked their guts out under the airplane" - they had to buy up so much replacement stock as to deplete every single junkyard across the USA of that particular model (so the story goes - probably hyperbole but a fun tale!)
I remember quite well the day the auctioned off a unique "jet fuel analyzer" that was used to do some of the specialized testing for these exact aircraft.
It was not a benchtop unit, it was a forklift model :\
A handful of the surviving planes are in museums. If you're at all interested in aviation and have the chance to see one, do. There's something special about them that doesn't come across in pictures.
I wonder for such abandoned projects with non existent supply chain/know-how/documentation, whether there is any benefit of trying to revive them instead of starting from scratch.
I think we can look to the SLS [1] for the answer there. It was basically NASA's answer to (amongst other things) get to the Moon in a kind-of-new way. For some historical context we first man a man in orbit in early 1962, so that was just barely starting to appreciate the systems involved in space. Kennedy would give his 'To the Moon' speech in late 1962. We'd then land a man on the Moon less than 7 years later.
The SLS started in 2011. 15 years later, it finally managed a manned flyby. The entire program has generally been an endless series of errors and mishaps, and the Moon flyby probably should never have happened, but was greenlit for political/managerial reasons - highly reminiscent of Columbia and Challenger, but with a better outcome owing purely to good fortune.
Not only has it been an endless series of mishaps over an increasingly absurd timeframe, but the program has already been obsoleted by the Falcon Heavy, to say nothing of the ongoing development of Starship. It has a lift capacity of about 50% more than the Falcon Heavy, but one SLS launch costs as much as 40 Falcon Heavy launches, so it's existence just doesn't make any sense, at least not as a space launch system.
---
It seems likely that NASA would have been much better advised to have simply revived the Space Shuttle or perhaps even further back rather than trying to do something from scratch, simply because when you do it from scratch you end up trying to iterate on top of something that you no longer necessarily have the expertise or human knowledge of how to create.
I think where intuition fails a lot of us (myself included) is that in the software world if you have the code/documentation for something then building it is trivial. But in the hardware world, even if you have all the instructions and knowledge, actually applying that know how to create a working project is still very far away, through certainly nowhere near as far away as if you have started from scratch.
a) Some clearly preposterous order that originated with the demented commander in chief, and they're just going through the motions. Same concept as ordering steam catapults put back on aircraft carriers.
or
b) Intentional misdirect/bait to send various groups of people off in a wrong direction as cover for something else entirely.
I wouldn't leave out: c) The rot has become so pervasive, in the manner of the late Soviet Union, that the people issuing the orders are completely disconnected from the reality on the ground.
This differs from 'a' in that the decision is not humoring the momentary whim of a mad dictator, but an a deliberate decision by a group of professionals (at least in theory), who have destroyed any possible means of connecting themselves with real information.
Up until relatively recently, the Saturn V (and the F1 engine) was the most powerful rocket ever made, even though it's almost 60 years old. Now I believe both SLS and Starship are more powerful.
So this led to the obvious question: why didn't we just recreate the F1 engine and the Saturn V? It turns out there were lots of reasons:
1. Materials science has changed. You can't necessarily make the same materials you made back then. And substituting them might have consequences on certification and testing that would make it much more expensive than a simple recreation;
2. We didn't necessarily know how to. Surprising as it sounds, the Saturn V program was pretty rushed. The engines and rockets were essentially handcrafted. Lots of things were documented but not necessarily everything. Even if it was, has that documentation been lost?
3. Loss of expertise. There's probably hardly anybody left who made those engines. Any complicated production line relies on reinforcing and building expertise through training and repetition. You'd have to build that from scratch. This is a common problem with any major weapons program. As soon as you stop making a particular weapon, it's almost impossible to restart it very quickly;
4. We don't necessarily have all the machining and secondary processes that existed then;
5. Advances in technology mean we can do better things now. For example, we can 3D print parts that we had no way of making them previously. It simply wasn't possible. This has come up in commercial aviation where modern aircraft (eg 787/A350) and their respective engines make heavy use of 3D printed parts, something the 747 could never have possibly have done;
6. Even if you can make all a complete system, what's your production capacity? The capacity for Saturn V rockets was quite low and because it was essentially bespoke, it couldn't be scaled. One of the impressive things about the Falcon 9 system is just how many of those rockets SpaceX could produce, even before extensive reuse of first-stage boosters. Capacity is something that almost has to be built in from scratch and it impacts everything. For example, a bunch of weapon systems have been depleted by the Iran War (eg Patriot interceptors, Tomahawks). You can't just turn a knob to ramp up production meaningfully. And where you can, it's incredibly expensive.
This is also a big part of China's current manufacturing advantage. There's an awful lot of standardization and regional specialization. You need a part? The factory that makes it is probably down the road. So certain things get made in Shenzhen because everything you need is also made in Shenzhen. This also means you can react very quickly, something a factory in the US could never do because it lacks that ecosystem.
They discovered all sorts of weird things when they made the original Blackbird. For example, titanium is so hard that they had to use special tools to machine parts like the panels. Well, in doing so they discovered that using cadmium in some tools to make them operate at higher temperatures and against harder materials would "poison" the titanium fatally.
So if you built a new hypersonic airframe now, would you use titanium? Do we have better alloys? We've had a lot of advances in single-crystal manufacturing for metals that have, for example, made jet engines incredibly reliable. And this btw is something China has had massive difficulties reproducing, at least for now. And they've spent decades trying.
As a simple example of this, there was a guy who went out of his way to make an electric toaster from scratch [1]. This is a relatively simple device but it shows how many inputs there are, which each have production lines (eg steel, aluminum and/or plastic). Now imagine what goes into a military plane that needs to fly at Mach 3-4.
In the 90s, NASA refurbished and extensively modified a mothballed supersonic Soviet-era Tu-144. The modifications included fitting different (Tupolev) engines. The total cost was $350M. It was used as a flying laboratory.
Guessing this project was also a way to pay Russian engineers while the Soviet Union collapsed with the goal to do "technology transfer" and prevent them from working for NK and the like as a way to make ends meet.
Yep. After the collapse of the USSR, the US Congress and NASA funded the International Space Station program in part to keep Russian rocket scientists gainfully employed. That way they wouldn't be tempted to go work for Iraq / Iran / North Korea / China.
I’m sure it’s been mentioned a few times in the older thread that came up the other day but I can only recommend the book by Ben Rich, Skunk Works, if you want learn more about how this plane came to be.
When I see this, I can only think of modern high-altitude balloons. My gut tells me the SR-71 would be an ideal interceptor for that new threat (despite not being an interceptor itself).
The balloon issue cannot be addressed by any modern US aircraft, and spending expensive missiles on low cost balloons seems like wasting money and resources.
The SR-71 was never designed as an interceptor, and would require extensive modifications to carry and employ weapons. Not going to happen. There was an earlier YF-12 interceptor program but it never proceeded beyond the prototype stage.
High-altitude balloons are hardly a new threat. They have been used for decades, although some recent Chinese models are more capable than before. Regular tactical aircraft already in the US inventory are perfectly capable of shooting them down.
Current aircraft is not capable of reaching those balloons, read my other commentary. Your link points to a Chinese balloon that dropped way below its operational range.
SR-71 or not, there are already contracts for filling this niche:
If money is flowing to counter/develop high-altitude balloons and declared as urgent, it's likely it's flowing in more than one vein.
The frame modifications you mentioned are already specified and tested, part of the YF-12 programme. It can easily carry air-to-air missiles instead of reconnaissance equipment, and the frame has flown with that configuration.
AIM-120 range and altitude upgrades have been in the works for many years, and balloon defense is a relatively low priority mission. It will also be supplemented by the new AIM-260 which has greater capabilities. The primary goal of those programs is to achieve greater stand-off range versus near-peer adversary aircraft.
The YF-12 prototypes looked superficially similar to the SR-71 but had substantially different airframes. There is simply no place in an SR-71 to mount the necessary weapons, sensors, and avionics without completely rebuilding the entire aircraft. That would be a stupid waste of resources when existing platforms can already accomplish the mission well enough.
> Current aircraft is not capable of reaching those balloons
Is a missile a form of aircraft? Because there's variants of the Standard Missile which can hit a low earth orbit satellite, with the right timing, fired from effectively zero velocity and at sea level from a frigate.
No it's not. And it's indeed very costly. But on the grand scale of things of what the US DoD spends per day as a fully loaded lifetime cost to operate a single SSN, SSBN or aircraft carrier, it's a drop in the bucket. They spend absurd amounts of funds on all sorts of things.
The service ceiling of the SR-71 is still well beneath the altitude of a modern balloon. The speed isn't necessary, and it's altitude record has been beaten by other modern jets.
If we're spitballing solutions, balloons are slow, fragile and move in relatively predictable paths. An F-15 could reach the same altitude, and launch it's own balloon with a small solid-fuel booster that also corrects the trajectory. If the interceptor balloon could get within 1-2km of the target balloon, then a cheap kinetic weapon firing HEI projectiles might be enough to destroy it.
That is the lower bound of what modern high-altitude balloons can reach. Back in 2023 multiple balloons were observed much higher than that up to 50,000 feet.
This is still in the lower spectrum for such balloons. BS 13-08 reached 176,000 feet back in 2013 (there is reason to believe spy balloons would not go that high though).
So, you're wrong. There is no US aircraft that can reach them (unless they drop low as they did in 2023). The US likely wants to hit them before they go low.
The SR-71 is uniquely suited for this task, having reached up to 90,000 feet during testing. It was specially made for some kind of hybrid space war possibility (not balloons, but something high up there).
Your amounts are off. that wikipedia page lists the f-15 as having a service ceiling of 65,000 feet. Perhaps irrelevant but a f-15 shot a satellite down once(not relevant because that is more the missiles capabilities than the planes, which is probably the relevant point)
Unit mix up?
The f-16 however, does have a surprisingly low ceiling, there are fighter pilot memes about it. https://www.youtube.com/watch?v=koEQp8ImlnI?t=643 something about having small wings, get above 30,000 feet and it's not happy.
You misread your source: the F-15 can climb 30,000 feet in 60 seconds - the service ceiling is closer to 60,000 feet officially, and 90,000 under ideal conditions:
By "same altitude" I was referring to the SR-71. I do not know what the payload capacity was for either aircraft in the 90,000ft testing conditions, but for interception missions there are more important metrics.
Per the first link you provided, the F-15 has the following:
Service ceiling: 65,000 ft (20,000 m)
That's high enough to go 15k feet above the highest ballon mentioned in the second link you provided, which was 50,000 feet.
Also, the SR-71 carried no weapons, only cameras, and re-tooling to support them would be far more expensive than merely shooting a balloon with a missile from the ground (or building an air-to-air missile that can be fired from existing platforms at altitudes like 65k feet).
Fair correction on the altitude (still in the lower bounds of the balloons, as I mentioned).
The SR-71 already flew in the configuration I mentioned. It's the YF-12C (a converted SR-71).
Recovering and converting another sure is more expensive than one missile, but it's a reusable platform.
A ground missile able to reach those balloons is more expensive than a modernized SR-71 sortie. High-altitude, precision missiles are also not allocated for this task. China can launch dozens of balloons for cheap, and spending one multi-million-dollar missile on each is insanity. Even the long range air-to-air ones are too expensive for that.
The SR-71 (as a new YF-12D interceptor) makes more sense. It can take multiple balloons in one flight with cheap shorter range air-to-air missiles (or maybe even cheaper weapons, for a balloon a laser would do), then go home and do that over and over again.
China can launch a lot more than a dozen balloons, perhaps thousands if convincing decoy payloads can be made. The A-12 was intended to counter high-value targets in a limited number, not low-value targets en-masse.
I can't rule out that Issacman does have this mission profile in mind, but it seems contrived. Whatever weapon the SR-71 could carry to-altitude could be be done cheaper, more numerously and probably more quickly too with F-15s. Refurbishing a fleet of SR-71s and a fleet of KC-135Qs would be a lot of work for an extremely limited capability.
F-15s are not stealth. You don't want to risk escalation by sending fighter jets towards someone else's airspace. To me, they don't make sense for this kind of mission.
It does sound like a lot of work, but that's the part of the puzzle that is not a mystery. Someone is in fact putting one of those back to work, we just don't know why.
36 comments:
I almost skipped the videos embedded in this article, but they are well curated gems. A few tidbits I found amazing:
- 800°F (and above) was the temperature of their cooling air
- the engine ran too hot for electronics, so they designed a hydraulic mechanical computer responsible for regulating various inputs
- the roar from the two external 400 cubic inch Buick V8 engines originally used to start the aircraft was so irresistible to the hotrod enthusiasts running them that they sometimes neglected to disconnect in time before the starter engines overran RPM limits and "puked their guts out under the airplane" - they had to buy up so much replacement stock as to deplete every single junkyard across the USA of that particular model (so the story goes - probably hyperbole but a fun tale!)
For those that want to know more about the Buick engines and their replacement, here's [0] a writeup about it.
[0] https://www.thesr71blackbird.com/Aircraft/Engines/starting-t...
I remember quite well the day the auctioned off a unique "jet fuel analyzer" that was used to do some of the specialized testing for these exact aircraft.
It was not a benchtop unit, it was a forklift model :\
A handful of the surviving planes are in museums. If you're at all interested in aviation and have the chance to see one, do. There's something special about them that doesn't come across in pictures.
I'd second that. I saw the surviving M-21 in Seattle. The highlight of the visit. If you get the chance, well worth your time
I wonder for such abandoned projects with non existent supply chain/know-how/documentation, whether there is any benefit of trying to revive them instead of starting from scratch.
I think we can look to the SLS [1] for the answer there. It was basically NASA's answer to (amongst other things) get to the Moon in a kind-of-new way. For some historical context we first man a man in orbit in early 1962, so that was just barely starting to appreciate the systems involved in space. Kennedy would give his 'To the Moon' speech in late 1962. We'd then land a man on the Moon less than 7 years later.
The SLS started in 2011. 15 years later, it finally managed a manned flyby. The entire program has generally been an endless series of errors and mishaps, and the Moon flyby probably should never have happened, but was greenlit for political/managerial reasons - highly reminiscent of Columbia and Challenger, but with a better outcome owing purely to good fortune.
Not only has it been an endless series of mishaps over an increasingly absurd timeframe, but the program has already been obsoleted by the Falcon Heavy, to say nothing of the ongoing development of Starship. It has a lift capacity of about 50% more than the Falcon Heavy, but one SLS launch costs as much as 40 Falcon Heavy launches, so it's existence just doesn't make any sense, at least not as a space launch system.
---
It seems likely that NASA would have been much better advised to have simply revived the Space Shuttle or perhaps even further back rather than trying to do something from scratch, simply because when you do it from scratch you end up trying to iterate on top of something that you no longer necessarily have the expertise or human knowledge of how to create.
I think where intuition fails a lot of us (myself included) is that in the software world if you have the code/documentation for something then building it is trivial. But in the hardware world, even if you have all the instructions and knowledge, actually applying that know how to create a working project is still very far away, through certainly nowhere near as far away as if you have started from scratch.
[1] - https://en.wikipedia.org/wiki/Space_Launch_System
I would bet good money it's one of two things:
a) Some clearly preposterous order that originated with the demented commander in chief, and they're just going through the motions. Same concept as ordering steam catapults put back on aircraft carriers.
or
b) Intentional misdirect/bait to send various groups of people off in a wrong direction as cover for something else entirely.
I wouldn't leave out: c) The rot has become so pervasive, in the manner of the late Soviet Union, that the people issuing the orders are completely disconnected from the reality on the ground.
This differs from 'a' in that the decision is not humoring the momentary whim of a mad dictator, but an a deliberate decision by a group of professionals (at least in theory), who have destroyed any possible means of connecting themselves with real information.
Up until relatively recently, the Saturn V (and the F1 engine) was the most powerful rocket ever made, even though it's almost 60 years old. Now I believe both SLS and Starship are more powerful.
So this led to the obvious question: why didn't we just recreate the F1 engine and the Saturn V? It turns out there were lots of reasons:
1. Materials science has changed. You can't necessarily make the same materials you made back then. And substituting them might have consequences on certification and testing that would make it much more expensive than a simple recreation;
2. We didn't necessarily know how to. Surprising as it sounds, the Saturn V program was pretty rushed. The engines and rockets were essentially handcrafted. Lots of things were documented but not necessarily everything. Even if it was, has that documentation been lost?
3. Loss of expertise. There's probably hardly anybody left who made those engines. Any complicated production line relies on reinforcing and building expertise through training and repetition. You'd have to build that from scratch. This is a common problem with any major weapons program. As soon as you stop making a particular weapon, it's almost impossible to restart it very quickly;
4. We don't necessarily have all the machining and secondary processes that existed then;
5. Advances in technology mean we can do better things now. For example, we can 3D print parts that we had no way of making them previously. It simply wasn't possible. This has come up in commercial aviation where modern aircraft (eg 787/A350) and their respective engines make heavy use of 3D printed parts, something the 747 could never have possibly have done;
6. Even if you can make all a complete system, what's your production capacity? The capacity for Saturn V rockets was quite low and because it was essentially bespoke, it couldn't be scaled. One of the impressive things about the Falcon 9 system is just how many of those rockets SpaceX could produce, even before extensive reuse of first-stage boosters. Capacity is something that almost has to be built in from scratch and it impacts everything. For example, a bunch of weapon systems have been depleted by the Iran War (eg Patriot interceptors, Tomahawks). You can't just turn a knob to ramp up production meaningfully. And where you can, it's incredibly expensive.
This is also a big part of China's current manufacturing advantage. There's an awful lot of standardization and regional specialization. You need a part? The factory that makes it is probably down the road. So certain things get made in Shenzhen because everything you need is also made in Shenzhen. This also means you can react very quickly, something a factory in the US could never do because it lacks that ecosystem.
They discovered all sorts of weird things when they made the original Blackbird. For example, titanium is so hard that they had to use special tools to machine parts like the panels. Well, in doing so they discovered that using cadmium in some tools to make them operate at higher temperatures and against harder materials would "poison" the titanium fatally.
So if you built a new hypersonic airframe now, would you use titanium? Do we have better alloys? We've had a lot of advances in single-crystal manufacturing for metals that have, for example, made jet engines incredibly reliable. And this btw is something China has had massive difficulties reproducing, at least for now. And they've spent decades trying.
As a simple example of this, there was a guy who went out of his way to make an electric toaster from scratch [1]. This is a relatively simple device but it shows how many inputs there are, which each have production lines (eg steel, aluminum and/or plastic). Now imagine what goes into a military plane that needs to fly at Mach 3-4.
[1]: https://www.ted.com/talks/thomas_thwaites_how_i_built_a_toas...
In the 90s, NASA refurbished and extensively modified a mothballed supersonic Soviet-era Tu-144. The modifications included fitting different (Tupolev) engines. The total cost was $350M. It was used as a flying laboratory.
Guessing this project was also a way to pay Russian engineers while the Soviet Union collapsed with the goal to do "technology transfer" and prevent them from working for NK and the like as a way to make ends meet.
Yep. After the collapse of the USSR, the US Congress and NASA funded the International Space Station program in part to keep Russian rocket scientists gainfully employed. That way they wouldn't be tempted to go work for Iraq / Iran / North Korea / China.
Recent and related:
NASA asked several former SR-71A staffers to help secret restart - https://news.ycombinator.com/item?id=49890733 - Sept 2026 (401 comments)
I’m sure it’s been mentioned a few times in the older thread that came up the other day but I can only recommend the book by Ben Rich, Skunk Works, if you want learn more about how this plane came to be.
This is probably one of the coolest planes and it's SOP is to leak fuel until it gets going enough that the heat seals it's seams due to expansion
The engine cores alone expand 6” when they heat up.
Neither the SR-71 nor F-14 will fly again without significant funding, and not for any economically-viable use.
The SR-71 won't because there's no JP-7 supplier, no flyable KC-135T, and no parts.
No Top Gun movie series then. :)
When I see this, I can only think of modern high-altitude balloons. My gut tells me the SR-71 would be an ideal interceptor for that new threat (despite not being an interceptor itself).
The balloon issue cannot be addressed by any modern US aircraft, and spending expensive missiles on low cost balloons seems like wasting money and resources.
We'll know soon.
The SR-71 was never designed as an interceptor, and would require extensive modifications to carry and employ weapons. Not going to happen. There was an earlier YF-12 interceptor program but it never proceeded beyond the prototype stage.
High-altitude balloons are hardly a new threat. They have been used for decades, although some recent Chinese models are more capable than before. Regular tactical aircraft already in the US inventory are perfectly capable of shooting them down.
https://www.af.mil/News/Article-Display/Article/3288579/f-22...
Current aircraft is not capable of reaching those balloons, read my other commentary. Your link points to a Chinese balloon that dropped way below its operational range.
SR-71 or not, there are already contracts for filling this niche:
https://www.war.gov/News/Contracts/Contract/Article/4613098/... (search for "swamp gas").
If money is flowing to counter/develop high-altitude balloons and declared as urgent, it's likely it's flowing in more than one vein.
The frame modifications you mentioned are already specified and tested, part of the YF-12 programme. It can easily carry air-to-air missiles instead of reconnaissance equipment, and the frame has flown with that configuration.
https://en.wikipedia.org/wiki/Lockheed_YF-12
AIM-120 range and altitude upgrades have been in the works for many years, and balloon defense is a relatively low priority mission. It will also be supplemented by the new AIM-260 which has greater capabilities. The primary goal of those programs is to achieve greater stand-off range versus near-peer adversary aircraft.
The YF-12 prototypes looked superficially similar to the SR-71 but had substantially different airframes. There is simply no place in an SR-71 to mount the necessary weapons, sensors, and avionics without completely rebuilding the entire aircraft. That would be a stupid waste of resources when existing platforms can already accomplish the mission well enough.
What are you talking about? The YF-12C was a converted SR-71. It flew exactly as I'm describing. All of this has already been done before.
You might be confusing the YF-12 with the A-12, which is related but a significantly different airframe.
I won't engage in discussing whether balloons are high priority or not. Let the 2023 events and the funding towards those areas speak for themselves.
> Current aircraft is not capable of reaching those balloons
Is a missile a form of aircraft? Because there's variants of the Standard Missile which can hit a low earth orbit satellite, with the right timing, fired from effectively zero velocity and at sea level from a frigate.
Well, it's not reusable. You're wasting a resource destined for hypersonic deterrence on some sheets of mylar that float around.
I mean, you can do that, but it would be a tremendous embarrassment.
> Well, it's not reusable
No it's not. And it's indeed very costly. But on the grand scale of things of what the US DoD spends per day as a fully loaded lifetime cost to operate a single SSN, SSBN or aircraft carrier, it's a drop in the bucket. They spend absurd amounts of funds on all sorts of things.
Perhaps the issue is not money, but production capacity? Those take some time to build, and you don't want to deplete your stockpile on spy balloons.
The service ceiling of the SR-71 is still well beneath the altitude of a modern balloon. The speed isn't necessary, and it's altitude record has been beaten by other modern jets.
If we're spitballing solutions, balloons are slow, fragile and move in relatively predictable paths. An F-15 could reach the same altitude, and launch it's own balloon with a small solid-fuel booster that also corrects the trajectory. If the interceptor balloon could get within 1-2km of the target balloon, then a cheap kinetic weapon firing HEI projectiles might be enough to destroy it.
The F-15 can climb 30,000 feet.
https://en.wikipedia.org/wiki/McDonnell_Douglas_F-15_Eagle
That is the lower bound of what modern high-altitude balloons can reach. Back in 2023 multiple balloons were observed much higher than that up to 50,000 feet.
https://en.wikipedia.org/wiki/List_of_high-altitude_object_e...
This is still in the lower spectrum for such balloons. BS 13-08 reached 176,000 feet back in 2013 (there is reason to believe spy balloons would not go that high though).
https://en.wikipedia.org/wiki/High-altitude_balloon
So, you're wrong. There is no US aircraft that can reach them (unless they drop low as they did in 2023). The US likely wants to hit them before they go low.
The SR-71 is uniquely suited for this task, having reached up to 90,000 feet during testing. It was specially made for some kind of hybrid space war possibility (not balloons, but something high up there).
Your amounts are off. that wikipedia page lists the f-15 as having a service ceiling of 65,000 feet. Perhaps irrelevant but a f-15 shot a satellite down once(not relevant because that is more the missiles capabilities than the planes, which is probably the relevant point)
Unit mix up?
The f-16 however, does have a surprisingly low ceiling, there are fighter pilot memes about it. https://www.youtube.com/watch?v=koEQp8ImlnI?t=643 something about having small wings, get above 30,000 feet and it's not happy.
You misread your source: the F-15 can climb 30,000 feet in 60 seconds - the service ceiling is closer to 60,000 feet officially, and 90,000 under ideal conditions:
https://theaviationgeekclub.com/how-the-f-15-streak-eagle-br...
By "same altitude" I was referring to the SR-71. I do not know what the payload capacity was for either aircraft in the 90,000ft testing conditions, but for interception missions there are more important metrics.
Per the first link you provided, the F-15 has the following:
Service ceiling: 65,000 ft (20,000 m)
That's high enough to go 15k feet above the highest ballon mentioned in the second link you provided, which was 50,000 feet.
Also, the SR-71 carried no weapons, only cameras, and re-tooling to support them would be far more expensive than merely shooting a balloon with a missile from the ground (or building an air-to-air missile that can be fired from existing platforms at altitudes like 65k feet).
Fair correction on the altitude (still in the lower bounds of the balloons, as I mentioned).
The SR-71 already flew in the configuration I mentioned. It's the YF-12C (a converted SR-71).
Recovering and converting another sure is more expensive than one missile, but it's a reusable platform.
A ground missile able to reach those balloons is more expensive than a modernized SR-71 sortie. High-altitude, precision missiles are also not allocated for this task. China can launch dozens of balloons for cheap, and spending one multi-million-dollar missile on each is insanity. Even the long range air-to-air ones are too expensive for that.
The SR-71 (as a new YF-12D interceptor) makes more sense. It can take multiple balloons in one flight with cheap shorter range air-to-air missiles (or maybe even cheaper weapons, for a balloon a laser would do), then go home and do that over and over again.
China can launch a lot more than a dozen balloons, perhaps thousands if convincing decoy payloads can be made. The A-12 was intended to counter high-value targets in a limited number, not low-value targets en-masse.
I can't rule out that Issacman does have this mission profile in mind, but it seems contrived. Whatever weapon the SR-71 could carry to-altitude could be be done cheaper, more numerously and probably more quickly too with F-15s. Refurbishing a fleet of SR-71s and a fleet of KC-135Qs would be a lot of work for an extremely limited capability.
F-15s are not stealth. You don't want to risk escalation by sending fighter jets towards someone else's airspace. To me, they don't make sense for this kind of mission.
It does sound like a lot of work, but that's the part of the puzzle that is not a mystery. Someone is in fact putting one of those back to work, we just don't know why.