5 ms·

Stealth, Countermeasures, and ELINT, 1960-1975

42 points by runlevel1 12y ago

djyaz1200 12y ago
The way to defeat stealth is instead of looking for the size of the object look at speed and trajectory. The B2 famously has the radar cross section of a honeybee. No problem. I would just build filtering software for my radar that said show me all the objects of any size (even Bee size) heading my way at over 300mph. I'm sure this has been done, and it's alluded to in book Skunkworks (good book btw).
- AndrewKemendo 12y ago
  Sounds easy but in practice it's not. There is a surprising amount of high speed things flying around at altitude. Not to mention that RCS reductions aren't always just about reduction, but also obfuscation.
  - djyaz1200 12y ago
    Yeah, acknowledge things are always easier said than done and this is still a very complicated problem but fundamentally it's a pattern recognition puzzle that could be solved IMO.
- crazypyro 12y ago
  Isn't there also the issue of missiles needing an object to look for as well? IIRC, missiles are often measured by the minimum RCS (radar cross section) needed for a successful targeting + hit.
  - djyaz1200 12y ago
    Yes, I'm (conveniently) separating the problem of detection and destruction here.
- theoh 12y ago
  Actually a better approach is to use longer wave radar, getting a reflection from the whole metal airframe as a conductive object rather than just bouncing waves off the surface. Apparently this technique has difficulties with clouds but was successful in shooting down an F117 in the Balkans.
  - djyaz1200 12y ago
    Yep, that would be better. IMO the broader point is that stealth isn't magic. Just like any other tactic it has countermeasures... and pretty cheap ones. IMO this should be discussed more as our country pours billions into stealth aircrafts.
  - teeks99 12y ago
    Another way is bi-static radars. Stealth is generally designed to prevent returns from going back to the sender, with the downside that they get scattered in all other directions. Just setup a (silent and difficult to locate) receiving station(s) and give it a communication channel to the sender (to synchronized), then it will receive the emissions from the sender that bounce off stuff.
    - vonmoltke 12y ago
      Another way of using bistatic radar is to look for holes. Pick a frequency band that has significant background noise and search for places where the background is consistently lower than average. Essentially, invert the detection algorithm. Nice thing about this approach is it can be done non-cooperatively; that is, the EM sources do not need to be controlled by whomever is running the receiver.
  - deleted 12y ago
    [deleted]
  - D4AHNGM 12y ago
    Correct, but long-wave radar suffers terribly from noise, I believe. The difficulty is finding a tiny needle in the proverbial very busy, noisy haystack. The F117 shootdown over Serbia had the advantage of having been able to tap the NATO radio network, and subsequently position their AA batteries according to that information. Even with that they only had a 20 second window or so to fire whilst the F117 had its bomb bay doors open. I wonder if the B2 or F-22's radar profile is similarly expanded noticeably enough to stand out amongst the noise in long-wave radar during bombing runs. I doubt we'll known that with any certainty for 20+ years, if at all.
- nether 12y ago
  You think that radars don't already have extensive filtering for clouds (otherwise it becomes a weather radar), birds and the like? What makes you think a bumble bee signature is readily trackable? Also, do you think radar engineers miss obvious solutions, and that you'd make a good engineer at Raytheon? Maybe you should apply.
  - djyaz1200 12y ago
    I'm simply pointing out that stealth isn't magic. In any battle it's good to spend time thinking about how you would kick your own ass. That makes you better.
- johngalt 12y ago
  The point of stealth isnt that you are never spotted by radar, but to make it more difficult to target and track on meaningful timeframes. Think of a normal aircraft as an orange road cone with reflectors. Shine a bright light on it and it can be seen for miles. A stealth aircraft is a matte black speedbump just barely above the normal road height. Even with a really bright light you'll have to be extremely close to see where exactly it is on the road. Meanwhile from the speedbumps perspective they can see the guy shining the bright light clearly. When people talk about a small RCS they arent hoping to blend in with other 600mph hummingbirds. They simply want to avoid being spotted until it is too late for the enemy to do anything.
- NoMoreNicksLeft 12y ago
  You'll still get all sorts of micro-meteorites even with that. I'm not saying it's not a smart compromise, but it's still prone to false positives. Better than nothing, I guess.
Theodores 12y ago
This story is 'revised'. The original idea of the OXCART was to fly so fast that it would not be in one place long enough to rise above background noise on the radar screen. Think of those CRT radar screens and the 'mark' corresponding to the plane not being a big green dot, but more something that just would not excite the phosphor and therefore not show. The OXCART contract was won by Lockheed because Convair had little experience of black projects plus Lockheed delivered the U2 under time and under budget. The OXCART A12 was the 12th revision, sure it might have evolved to have stealth as we know it, however, the original idea really was just to be too quick to register on the phosphor. The big problem as far as radar was concerned was the gigantic plume of exhaust out the back. They tried putting stuff in that to hide it from the radar, however there were problems with that too. Anyway, my point, this is revised history.
- Someone1234 12y ago
  > This story is 'revised'. >> Anyway, my point, this is revised history. This person was a radar / signal intelligence geek who's only work on the OXCART project seems to be related to electronic jamming and determining the radar capabilities of the then USSR. So this entire set of anecdotes are from their perspective. They never claimed to be in the initial OXCART development group nor did they make claims as to what OXCART was design to or not to do. All they said was that based on their data the OXCART would have been trackable on the USSR's radar defence systems. That isn't revising history in any meaningful way. However you should take into account that the scope of the anecdote is just a single person's perspective working in a single field. They also allude to the recently launched satellites in addition to the U2's shootdown being contributors to use the Blackbird was never really used over the USSR. Frankly your concept that the whole basis for the OXCART project was that CRT' refresh rate was too low to literally draw the aircraft bizarre. First time I've heard that and Google has no clue about it either ("OXCART CRT" "blackbird crt" no relevant results). Plus CRT displays have very high refresh rates (around 89 Hz), so there's that too...
  - edwhitesell 12y ago
    If you read the Skunkworks book, they openly admit Oxcart was tracked by radar. Just as they admit they were fired on by missles (using aforementioned radar for targeting). They go on to say the missles at the time were unable to reach the speed (mach 3.2) or height of the plane in time to hit it.
jokoon 12y ago
don't forget that even if stealth is worthless when considering radars, it can still greatly reduce the distance that radars can detect stealthier aircrafts.
- vonmoltke 12y ago
  The second clause of your statement contradicts the first. There is a common misconception that stealth is about making things "invisible" to radar. It is really about reducing the radar signature of a vehicle as much as possible when viewed from a conventional, colocated transmitter/receiver type radar. That includes reducing the detection range or making it harder for fire control radars to get and maintain a lock. One end of this spectrum is making the aircraft undetectable by some or all radars, but stealth goes well beyond that.

42 points by runlevel1 12y ago

The way to defeat stealth is instead of looking for the size of the object look at speed and trajectory. The B2 famously has the radar cross section of a honeybee. No problem. I would just build filtering software for my radar that said show me all the objects of any size (even Bee size) heading my way at over 300mph. I'm sure this has been done, and it's alluded to in book Skunkworks (good book btw).

AndrewKemendo 12y ago
Sounds easy but in practice it's not. There is a surprising amount of high speed things flying around at altitude. Not to mention that RCS reductions aren't always just about reduction, but also obfuscation.
- djyaz1200 12y ago
  Yeah, acknowledge things are always easier said than done and this is still a very complicated problem but fundamentally it's a pattern recognition puzzle that could be solved IMO.
crazypyro 12y ago
Isn't there also the issue of missiles needing an object to look for as well? IIRC, missiles are often measured by the minimum RCS (radar cross section) needed for a successful targeting + hit.
- djyaz1200 12y ago
  Yes, I'm (conveniently) separating the problem of detection and destruction here.
theoh 12y ago
Actually a better approach is to use longer wave radar, getting a reflection from the whole metal airframe as a conductive object rather than just bouncing waves off the surface. Apparently this technique has difficulties with clouds but was successful in shooting down an F117 in the Balkans.
- djyaz1200 12y ago
  Yep, that would be better. IMO the broader point is that stealth isn't magic. Just like any other tactic it has countermeasures... and pretty cheap ones. IMO this should be discussed more as our country pours billions into stealth aircrafts.
- teeks99 12y ago
  Another way is bi-static radars. Stealth is generally designed to prevent returns from going back to the sender, with the downside that they get scattered in all other directions. Just setup a (silent and difficult to locate) receiving station(s) and give it a communication channel to the sender (to synchronized), then it will receive the emissions from the sender that bounce off stuff.
  - vonmoltke 12y ago
    Another way of using bistatic radar is to look for holes. Pick a frequency band that has significant background noise and search for places where the background is consistently lower than average. Essentially, invert the detection algorithm. Nice thing about this approach is it can be done non-cooperatively; that is, the EM sources do not need to be controlled by whomever is running the receiver.
- deleted 12y ago
  [deleted]
- D4AHNGM 12y ago
  Correct, but long-wave radar suffers terribly from noise, I believe. The difficulty is finding a tiny needle in the proverbial very busy, noisy haystack. The F117 shootdown over Serbia had the advantage of having been able to tap the NATO radio network, and subsequently position their AA batteries according to that information. Even with that they only had a 20 second window or so to fire whilst the F117 had its bomb bay doors open. I wonder if the B2 or F-22's radar profile is similarly expanded noticeably enough to stand out amongst the noise in long-wave radar during bombing runs. I doubt we'll known that with any certainty for 20+ years, if at all.
nether 12y ago
You think that radars don't already have extensive filtering for clouds (otherwise it becomes a weather radar), birds and the like? What makes you think a bumble bee signature is readily trackable? Also, do you think radar engineers miss obvious solutions, and that you'd make a good engineer at Raytheon? Maybe you should apply.
- djyaz1200 12y ago
  I'm simply pointing out that stealth isn't magic. In any battle it's good to spend time thinking about how you would kick your own ass. That makes you better.
johngalt 12y ago
The point of stealth isnt that you are never spotted by radar, but to make it more difficult to target and track on meaningful timeframes. Think of a normal aircraft as an orange road cone with reflectors. Shine a bright light on it and it can be seen for miles. A stealth aircraft is a matte black speedbump just barely above the normal road height. Even with a really bright light you'll have to be extremely close to see where exactly it is on the road. Meanwhile from the speedbumps perspective they can see the guy shining the bright light clearly. When people talk about a small RCS they arent hoping to blend in with other 600mph hummingbirds. They simply want to avoid being spotted until it is too late for the enemy to do anything.
NoMoreNicksLeft 12y ago
You'll still get all sorts of micro-meteorites even with that. I'm not saying it's not a smart compromise, but it's still prone to false positives. Better than nothing, I guess.

Theodores 12y ago

This story is 'revised'. The original idea of the OXCART was to fly so fast that it would not be in one place long enough to rise above background noise on the radar screen. Think of those CRT radar screens and the 'mark' corresponding to the plane not being a big green dot, but more something that just would not excite the phosphor and therefore not show. The OXCART contract was won by Lockheed because Convair had little experience of black projects plus Lockheed delivered the U2 under time and under budget. The OXCART A12 was the 12th revision, sure it might have evolved to have stealth as we know it, however, the original idea really was just to be too quick to register on the phosphor. The big problem as far as radar was concerned was the gigantic plume of exhaust out the back. They tried putting stuff in that to hide it from the radar, however there were problems with that too. Anyway, my point, this is revised history.

Someone1234 12y ago
> This story is 'revised'. >> Anyway, my point, this is revised history. This person was a radar / signal intelligence geek who's only work on the OXCART project seems to be related to electronic jamming and determining the radar capabilities of the then USSR. So this entire set of anecdotes are from their perspective. They never claimed to be in the initial OXCART development group nor did they make claims as to what OXCART was design to or not to do. All they said was that based on their data the OXCART would have been trackable on the USSR's radar defence systems. That isn't revising history in any meaningful way. However you should take into account that the scope of the anecdote is just a single person's perspective working in a single field. They also allude to the recently launched satellites in addition to the U2's shootdown being contributors to use the Blackbird was never really used over the USSR. Frankly your concept that the whole basis for the OXCART project was that CRT' refresh rate was too low to literally draw the aircraft bizarre. First time I've heard that and Google has no clue about it either ("OXCART CRT" "blackbird crt" no relevant results). Plus CRT displays have very high refresh rates (around 89 Hz), so there's that too...
- edwhitesell 12y ago
  If you read the Skunkworks book, they openly admit Oxcart was tracked by radar. Just as they admit they were fired on by missles (using aforementioned radar for targeting). They go on to say the missles at the time were unable to reach the speed (mach 3.2) or height of the plane in time to hit it.

jokoon 12y ago

don't forget that even if stealth is worthless when considering radars, it can still greatly reduce the distance that radars can detect stealthier aircrafts.

vonmoltke 12y ago
The second clause of your statement contradicts the first. There is a common misconception that stealth is about making things "invisible" to radar. It is really about reducing the radar signature of a vehicle as much as possible when viewed from a conventional, colocated transmitter/receiver type radar. That includes reducing the detection range or making it harder for fire control radars to get and maintain a lock. One end of this spectrum is making the aircraft undetectable by some or all radars, but stealth goes well beyond that.