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Former SR-71 engineer talks NASA's Blackbird revival program

110 points · 76 comments · rkagerer

gaigalas · 1791086277 · focus · HN ↗
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.
1. bigyabai · 1791087911 · focus · HN ↗
  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.
  1. gaigalas · 1791092723 · focus · HN ↗
    The F-15 can climb 30,000 feet.
    <a href="https://en.wikipedia.org/wiki/McDonnell_Douglas_F-15_Eagle" rel="nofollow">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.
    <a href="https://en.wikipedia.org/wiki/List_of_high-altitude_object_events_in_2023" rel="nofollow">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).
    <a href="https://en.wikipedia.org/wiki/High-altitude_balloon" rel="nofollow">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).
    lelandbatey · 1791094771 · focus · HN ↗
    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).
    gaigalas · 1791095645 · focus · HN ↗
    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.
    bigyabai · 1791096402 · focus · HN ↗
    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.
    gaigalas · 1791105533 · focus · HN ↗
    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.
    mrec · 1791117410 · focus · HN ↗
    I'm missing something - why would you be wanting to intercept balloons over someone else's airspace? The 2023 incident was in US (and Canadian) airspace.
    gaigalas · 1791118203 · focus · HN ↗
    Sorry, I should have explained it: you want to intercept a spy balloon before it enters your airspace, not after it has already entered and possibly gathered any information.
    morkalork · 1791129756 · focus · HN ↗
    Well there's a whole lot of ocean one doesn't need to be stealth to fly over but really, your comments read like endless goal-post shifting from someone who has a preferred solution in mind and is working backwards to justify it. Also the SR-71 was never stealth, only reduced observability. The USSR was very aware of the overflights taking place.
    gaigalas · 1791130974 · focus · HN ↗
    It seems no one else offered any other concrete uses that would justify the efforts that went public regarding the frame reuse.
    That likely concentrated the discussions towards this single idea I presented. However, I'm not actually that committed to it. If you have any other, I would very much would like to hear about it.
    bigyabai · 1791135930 · focus · HN ↗
    It's boring, but "aerial hypersonic testbed" is almost certainly NASA's intention, just like they did in the 1990s: <a href="https://en.wikipedia.org/wiki/Linear_Aerospike_SR-71_Experiment" rel="nofollow">https://en.wikipedia.org/wiki/Linear_Aerospike_SR-71_Experim...
    This is a NASA/JPL project; there are a limited number of airworthy SR-71s, they are not modernized for combat, and they cannot scramble to intercept. The M-21 variant has a well-documented conversion to a mothership[0] that can ferry payloads externally to-altitude and at high speed. This is incredibly ideal for testing captive ramjet/scramjet technology, since they require Mach 3+ speeds to attain ram pressure through the engine.
    Sending the SR-71 into denied or uncontrolled airspace seems like a terrible idea, in 2026. Chinese and Russian naval interceptor missiles could shoot down the plane at it's maximum speed and altitude; it's not going up against 1980s missiles anymore. The risk is absurd, and there's not enough SR-71s to treat them like they're expendable.
    [0] <a href="https://en.wikipedia.org/wiki/Lockheed_D-21" rel="nofollow">https://en.wikipedia.org/wiki/Lockheed_D-21
    gaigalas · 1791137537 · focus · HN ↗
    Thanks, that is a little bit more elaborate than the information on the interview and actually makes sense.
    There has been some speculation about this outside this thread though:
    <a href="https://theaviationist.com/2026/09/23/nasa-chief-teases-mysterious-aircraft/" rel="nofollow">https://theaviationist.com/2026/09/23/nasa-chief-teases-myst...
    I don't know how credible those reports are, but Jared Isaacman's comments do suggest more than just a testbed. Do you have any comment on that?
    bigyabai · 1791140537 · focus · HN ↗
    I don't have access to any privileged information, here. My best bet is that DARPA is lighting a fire under JPL's ass to explore variable-cycle engine technology: <a href="https://en.wikipedia.org/wiki/Variable_cycle_engine" rel="nofollow">https://en.wikipedia.org/wiki/Variable_cycle_engine
    The US has tested ramjets before, but mostly in the context of missiles and boost-glide vehicles. The "holy grail" of efficient propulsion would be to taxi/accelerate with a turbofan engine, bypass into a ramjet for Mach 3-to-6ish, and then transition to a liquid-fuel rocket motor for the last Mach 6-10 climb. An engine like that could escape the Earth's atmosphere without sacrificing efficiency at lower altitudes. I realize that "space fighter engine" is also a longshot, but China has ramped up investment in variable-cycle technology quite a bit in the past 2 years. Simply solving the turbofan-to-ramjet transition would be a huge boon for high and fast flight.
    Issacman's quotes in that article suggest, to me, that he wants to reboot the SR-72 program (or something similar) with cleansheet propulsion as a feature. The SR-71 could be the engine testbed, and a future airframe could be designed around the requirements of the engine. Just my $0.02 though.
    gaigalas · 1791161548 · focus · HN ↗
    Don't worry about being precise, this is an informal speculation thread with low stakes. I don't expect anyone (especially me) to nail it.
    Thanks for the insights!
    bigyabai · 1791095090 · focus · HN ↗
    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:
    <a href="https://theaviationgeekclub.com/how-the-f-15-streak-eagle-broke-eight-time-to-climb-world-records/" rel="nofollow">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.
    somat · 1791095120 · focus · HN ↗
    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. <a href="https://www.youtube.com/watch?v=koEQp8ImlnI?t=643" rel="nofollow">https://www.youtube.com/watch?v=koEQp8ImlnI?t=643 something about having small wings, get above 30,000 feet and it's not happy.
2. nradov · 1791092151 · focus · HN ↗
  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.
  <a href="https://www.af.mil/News/Article-Display/Article/3288579/f-22-safely-shoots-down-chinese-spy-balloon-off-south-carolina-coast/" rel="nofollow">https://www.af.mil/News/Article-Display/Article/3288579/f-22...
  1. gaigalas · 1791093268 · focus · HN ↗
    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:
    <a href="https://www.war.gov/News/Contracts/Contract/Article/4613098/contracts-for-sept-28-2026/" rel="nofollow">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.
    <a href="https://en.wikipedia.org/wiki/Lockheed_YF-12" rel="nofollow">https://en.wikipedia.org/wiki/Lockheed_YF-12
    nradov · 1791094017 · focus · HN ↗
    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.
    gaigalas · 1791094638 · focus · HN ↗
    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.
    nradov · 1791134985 · focus · HN ↗
    What are you talking about? The "YF-12C" designation was not a combat aircraft. It was a fake designation slapped on a regular SR-71 that NASA used for flight testing in order to hide the secret origins of the program. There was never a real YF-12C.
    You might be confusing the fake YF-12C with the real YF-12A. Both designs were derived from the original A-12 and look superficially similar but are internally quite different. There is no practical way to modify an SR-71 to carry and employ weapons. I mean it would be like trying to convert an F/A-18F into an F/A-18G: not technically impossible but so complex and expensive as to be utterly pointless. If the SR-71 ever actually flies again it will be used for nothing more than aerodynamic tests.
    gaigalas · 1791135398 · focus · HN ↗
    <a href="https://www.nasa.gov/image-article/yf-12a-yf-12c-flight-formation-dawn/" rel="nofollow">https://www.nasa.gov/image-article/yf-12a-yf-12c-flight-form...
    > Ultimately, 935 became the workhorse of the program, with 146 flights between 11 December 1969 and 7 November 1979. The second YF-12A, 936, made 62 flights. It was lost in a non-fatal crash on 24 June 1971. It was replaced by the so-called YF-12C (SR-71A 61-7951, modified with YF-12A inlets and engines and a bogus tail number 06937).
    nradov · 1791135994 · focus · HN ↗
    Right, the YF-12C was a fake designation for one SR-71 and not capable of carrying or employing any weapons.
    walrus01 · 1791097446 · focus · HN ↗
    > 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.
    gaigalas · 1791098089 · focus · HN ↗
    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.
    walrus01 · 1791098588 · focus · HN ↗
    > 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.
    gaigalas · 1791105640 · focus · HN ↗
    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.
    numpad0 · 1791114013 · focus · HN ↗
    missiles shot from fighter jets aren't reusable either, and ships that fire those missiles are as reusable as jets
    gaigalas · 1791116443 · focus · HN ↗
    I don't know which weapon would be used. A laser or a machine gun can take out a balloon if you're close enough. Even if missiles are used, closer range air-to-air are cheaper.
    Also, approaching the balloon in stealth with a plane that has its own radar system is considerably less paraphernalia than ships chasing balloons.
    I could be wrong about how the SR-71 will be used, but I'm very sure using expensive missiles designed for much more advanced threats to take out balloons is insanity.
    nradov · 1791123062 · focus · HN ↗
    You seem to be confused about basic aerodynamics. At those altitudes, attempting to shoot a balloon with a machine gun would be insanity. The high wing loading limits maneuverability so severely that the shooting platform would risk running into target debris.
    As of today it's not possible to mount a laser on a tactical aircraft (or SR-71) capable of destroying a balloon. There isn't enough space or power available. Perhaps that will change soon but for now it remains science fiction.
    gaigalas · 1791125897 · focus · HN ↗
    The conversation goes as follows:
    - Reusable/non-reusable
    - Cost/range
    The machine gun and laser are illustrative examples. I offered a cheaper short range missile as an option too, if those two bother you.
    At some point, I believed you got carried away by specific details about aerodynamics and laser payload (you are probably right!), but are ultimately irrelevant for the progression of the conversation: if you are closer, you can use a cheaper weapon.
    It's normal to get carried away (I do it all the time), and I'm fine with having my comments broken down and dissected. However, there are aspects of what I said that weren't answered, so they still stand.
    nradov · 1791135170 · focus · HN ↗
    When regular F-22s were already used to shoot down Chinese spy balloons they employed AIM-9 missiles, which are cheaper than AIM-120. But there's no need to get particularly close: in fact for safety they want to remain well separated from the target and never get on a collision course.
    But in general all of your comments here have been deeply uninformed about how this stuff actually works.
    gaigalas · 1791136446 · focus · HN ↗
    I appreciate the heads up.
    This is a low stakes brainstorming conversation, I presented my ideas as hypotheticals and shared my sources.
    Honestly, I was hoping someone more knowledgeable would share any better insight on what the recently work on the SR-71 frame would be used for in practice. That hasn't happened so far, but that's fine.
    "Your guess is bad because using the SR-71 for _____ in missions such as ______ would make more sense" would be stellar brainstorming about this beloved fan favorite.
    numpad0 · 1791129935 · focus · HN ↗
    You can't gun kill a balloon floating at 60k feet. That's not going to work. It has to be with an active or semi-active radar homing missile.
    The loadout will be like an F-15 with just one or two AIM-7 type missiles of appropriate generation and maybe the center tank. You configure and fly the plane to the altitude as usual, then when instructed, push the throttle all the way forward, do a shallow dive, then pull up to the precise absurd angle as you were briefed and keep it there. The number on the right go crazy and the number on the left goes down slightly less faster. At some point, you will see an angled rectangle with a dot in the center, itself in the center of a large circle on the HUD, and it says SHOOT, so you pull the trigger. You here the thunk of missile leaving, then nothing happens for 30 seconds, and the radio says target radar contact lost as expected, you do a 180 roll into a shallow dive and go home.
    I mean, that's how I as an armchair flightsim pilot think it'll go, but I'm sure this wouldn't be way off. Attempting the same with a gun installed on a Blackbird? That's just waste of everything from time of everyone involved to your own life.
    gaigalas · 1791131965 · focus · HN ↗
    Makes sense. You seem to know a lot of stuff! What do you believe the SR-71 frame is going to be used for?
    speed_spread · 1791150325 · focus · HN ↗
    The only thing it was designed for: recon. It's a spy plane. It has cameras and electronics up the wazoo. You fly it high and fast over a target, collect the info you need, refuel it and change target. Unlike a satellite, you can do that many times per day.
    Against the USSR it had become risky because missiles could reach it? And satellites worked great during the cold war. But in a scenario where things got hotter and you wanted regular fresh intel from deep within enemy territory, the SR-71 could be irreplaceable.
    numpad0 · 1791169146 · focus · HN ↗
    Militarily, it's the lowest-flying and the most maneuverable spy satellite with a turning radius comparable to the size of an European mini/microstate. That's it.
    Just speaking from a couch, maybe it's a simple 50:50 between the NASA administrator just wanting it flying and Boom Supersonic not doing fantastically. Anduril's mini F-16 drone having its air intake painted out in photos also comes to mind. Lessons learned by NASA from an SR-71 engine project is going to be invaluable for new entrants to supersonic planes and engines.
    nradov · 1791135877 · focus · HN ↗
    Yes, certain variants of the SM-3 (RIM-161) have a limited anti-satellite capability. And in general any current Standard missile could potentially be employed against a spy balloon depending on the exact engagement parameters. The problem is that they have limited range and it can be tough to get a launch platform to the right place at the right time to generate an intercept. The Navy surface fleet is already over committed, and ground based launchers have limited mobility. Hence it's more practical to use tactical aircraft like the F-22 or F-15EX for this type of homeland defense mission.
    morkalork · 1791128182 · focus · HN ↗
    What about U-2?
    <a href="https://www.theguardian.com/world/2023/feb/22/pentagon-pilot-selfie-chinese-spy-balloon" rel="nofollow">https://www.theguardian.com/world/2023/feb/22/pentagon-pilot...
3. [deleted] · 1791126992 · focus · HN ↗
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