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On many pictures (maybe on most of the pictures) part of nose looks hammered or slightly smashed, or bent. Please note these 2 symmetric dents just behind nose spike:

enter image description here source

enter image description here source

On other pictures these dents are missing:

enter image description here source

Why? Is this a feature or damage?

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    $\begingroup$ You don't normally see perfectly symmetrical damage. They look like fairings that are installed over sensors that have to be mounted in the chines, or, it was decided to put a step along the edge of the chine for an aerodynamic reason, and the shapes are transition fairings. $\endgroup$ – John K Oct 18 at 11:35
  • $\begingroup$ Good info here:flightglobal.com/pdfarchive/view/1973/1973%20-%202291.html $\endgroup$ – Mark Jones Jr. Oct 19 at 17:24
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    $\begingroup$ Micrometeorites and bits of smashed satellite? $\endgroup$ – Harper - Reinstate Monica Oct 19 at 17:51
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    $\begingroup$ High-speed mosquito strikes. $\endgroup$ – Mark Oct 20 at 20:09
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The SR-71 had a detachable nose (photo #2), and could change between three different nose cones depending on the mission. I haven't found a lot of information on the three, other than what this site and this site mentions:

  • Training nose with dead weights
  • Radar nose containing a Side Looking Radar. This is probably the bulge you saw on the photos.
  • Photo nose containing the optical bar camera, taking very wide photos of the ground.
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    $\begingroup$ The linked sites are good references, but they don't explain the leading edge bulges. As those links explain, the sensors are located elsewhere. $\endgroup$ – mike Oct 19 at 8:28
  • $\begingroup$ From SR-71.us: "The antenna assembly/motion sensing unit, transmitter, receiver and related equipment are installed in a specially-configured detachable nose." $\endgroup$ – bjelleklang Oct 19 at 18:03
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    $\begingroup$ TIL the mission payload is in the nose of SR71. $\endgroup$ – user3528438 Oct 20 at 2:25
  • $\begingroup$ This info is pretty on the nose, thanks! $\endgroup$ – Anoplexian - Reinstate Monica Oct 21 at 15:27
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Got it. Those indents are cut-outs for the "DEF A2" radar warning and ECM system.

Text from pdf of (purported) SR-71 Flight Manual describing components of the DEF A2 defensive electronics system

Relevant quote:

The receive antennas are located aft of cut-outs on the left and right nose chines.

The transmit antennas may also be visible in the OP's picture on the underside of the A/C, but hard to say.

This manual is linked from the wikipedia article on the SR-71 as refs 72-75. Direct link to the imaged page from the manual: https://www.sr-71.org/blackbird/manual/4/4-124.php

Note that the manual is silent on rear-facing sensors. This is consistent with the SR-71's primary defense characteristic, that being speed to outrun all threats. To the SR-71, a threat not already in the forward cone is simply not a threat. Also alluded to in this article about a one-off SR-71 development for countering an eventual hole in the defense strategy:

There was also the possible threat that future ground defenses would someday have the ability to reach the SR-71 from behind since it carried no aft facing defensive countermeasures.

There's an illustration without explanation on a reddit thread:

The picture there is not attributed, and at any rate, is too large to upload here. As mentioned in the reddit thread, the SR-71 itself did not carry the large radar illustrated -- the picture is actually of a YF-12, but close enough for our purposes here, as the other element in the picture is clearly identifiable as lying within the cut-out, and consistent with the manual's description of the DEF A2 system receive antenna. It shows the fairing removed from the area in question, revealing a light/off-white/silvery disc positioned at the aft end of the cutout.

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    $\begingroup$ Does it seem like there are two different sets of chine indentations available? I think the photo shows indents that are further forward than the DEF A2 referenced in the manul. Or maybe the position was changed for some installs. $\endgroup$ – user2298 Oct 20 at 12:32
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    $\begingroup$ Nice find !!!!! $\endgroup$ – Fattie Oct 20 at 18:32
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Bjelleklang is right, the nose is detachable and would be switched out according to the mission's needs. The bulges are a key component of the (for that time) very sophisticated radar imaging system, ASARS-1. There's more information here.

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    $\begingroup$ Welcome, Mitch! IMHO, the link provided does not identify the "notches" referred to in the OP as specific to ASARS. Your link shows ASARS components to be in the L and C bays, which are not in the location mentioned by the OP. There is a sensor described as in the "detachable ASARS nose", but its location is not indicated beyond that. I'm no expert -- just working to improve your answer, which so far is the only one to propose a specific answer which is not just plain wrong, i.e., there is no way that this is deformation or damage. $\endgroup$ – user2298 Oct 20 at 7:02
  • $\begingroup$ As it turns out, the notches have nothing to do with the ASARS, see Haakon Dahl's answer. $\endgroup$ – Jpe61 Oct 21 at 9:52
  • $\begingroup$ The indentations have nothing to do with ASARS-1, based upon first hand knowledge. $\endgroup$ – mongo Oct 22 at 3:16
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When looking at a picture of a Blackbird, you might be looking at either of 2 different aircraft - the YF12 and the SR71. One of the differences between them is the nose - the SR71 has a smooth continuous chine, whereas the YF12 has the indentations that you've spotted but with usually a forward-looking sensor there (possibly IR?).

So it depends which aircraft you're looking at.

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  • $\begingroup$ SR-71 and YF-12 have disdinctly differend noses, the aircraft in the pictures of this question definitely are not of an YF-12. It might be possible, even easy, to confuse SR-71 and its predecessor A-12: migflug.com/jetflights/a-12_oxcart-vs-sr-71_blackbird $\endgroup$ – Jpe61 Oct 22 at 15:00
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I don't have a copy with me right now, but the book Skunk Works is Ben Rich's account of taking over the Lockheed special-projects group from Kelly Johnson, and includes quite a lot of description of the SR-71 development and operation.

As I recall, he described that the SR-71 nose would often soften and deform in flight from the heat of very high speeds. I suspect that the bulges are a product of that.

As to why they are so symmetrical, I especially notice on your second picture, where the bulges appear to be propagating back from the join in sections.

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    $\begingroup$ If a nosecone would deform like this from heat, you'd have a serious problem. $\endgroup$ – Mast Oct 19 at 17:42
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    $\begingroup$ @Mast According to this site about the SR-71 the "Temperatures ranged from 450 degrees F (232 C) near the back part of the aircraft to 950 degrees F (510 C) near the engine exhaust. The cockpit had special heat-resistant glass to withstand surface temperatures of 640 degrees F (338 C).". Dunno if that's enough to deform a nosecone. Probably not. $\endgroup$ – PerlDuck Oct 19 at 18:25
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    $\begingroup$ @PerlDuck Considering the entire thing is built to withstand that heat, yea, don't think deformation is the answer here. The other answer(s) look(s) much better. $\endgroup$ – Mast Oct 19 at 19:01

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