KH-11 KENNEN

[Blackstar]

At least in terms of pointing, off-nadir capability should be arbitrary: both GAMBIT and KENNEN could conduct sat-squared missions, which have much tougher pointing requirements than any static spot on the Earth's surface.
Have reasonable approximations of the numerical aperture and focal length for KENNEN ever been published (G³ was 4500mm f/4)? At least for Gambit, the ranges are sufficiently long that depth of field even at extreme slant angles would been tens to hundreds of kilometres thick, so atmospheric distortions would likely have been the main driver of effective resolution off-nadir.

Yes to your first point--since they could point into space, it was not a case of what angle they could reach, but what angle would make sense for imaging.

What I have is a list of satellites over a target on a range of days and their nadir angles. I'm trying to figure out based upon those when it would be reasonable to assume that they tried to image the target. (This is just when they could have done it--the target may have been cloudy on those days.)

[LittleBird]

At least in terms of pointing, off-nadir capability should be arbitrary: both GAMBIT and KENNEN could conduct sat-squared missions, which have much tougher pointing requirements than any static spot on the Earth's surface.
Have reasonable approximations of the numerical aperture and focal length for KENNEN ever been published (G³ was 4500mm f/4)? At least for Gambit, the ranges are sufficiently long that depth of field even at extreme slant angles would been tens to hundreds of kilometres thick, so atmospheric distortions would likely have been the main driver of effective resolution off-nadir.

Yes to your first point--since they could point into space, it was not a case of what angle they could reach, but what angle would make sense for imaging.

What I have is a list of satellites over a target on a range of days and their nadir angles. I'm trying to figure out based upon those when it would be reasonable to assume that they tried to image the target. (This is just when they could have done it--the target may have been cloudy on those days.)

A tangential question-but do we know when/what orbit the KH-11 was in that took the Samuel Loring Morrison shipyard pictures? At least one of these was oblique iirc ?

[edzieba]

At least in terms of pointing, off-nadir capability should be arbitrary: both GAMBIT and KENNEN could conduct sat-squared missions, which have much tougher pointing requirements than any static spot on the Earth's surface.
Have reasonable approximations of the numerical aperture and focal length for KENNEN ever been published (G³ was 4500mm f/4)? At least for Gambit, the ranges are sufficiently long that depth of field even at extreme slant angles would been tens to hundreds of kilometres thick, so atmospheric distortions would likely have been the main driver of effective resolution off-nadir.

Yes to your first point--since they could point into space, it was not a case of what angle they could reach, but what angle would make sense for imaging.

What I have is a list of satellites over a target on a range of days and their nadir angles. I'm trying to figure out based upon those when it would be reasonable to assume that they tried to image the target. (This is just when they could have done it--the target may have been cloudy on those days.)

A tangential question-but do we know when/what orbit the KH-11 was in that took the Samuel Loring Morrison shipyard pictures? At least one of these was oblique iirc ?

Whilst writing my post that was exactly what I was trying to figure out as both were quite oblique, didn't have much luck within my lunch hour though.
For those wanting to take a crack at it: the two shots are of Shipyard 444 (now known as the Black Sea Shipyard or sometimes Nikolayev Shipbuilding) Slipway 0, and the gantry cranes in the photos are still present. If you have better luck then me finding their dimensions, that'll be enough to determine the viewing angle.

[zubenelgenubi]

Moderator:
New splinter discussion split/moved here:
https://forum.nasaspaceflight.com/index.php?topic=61727.0

[gosnold]

At least for Gambit, the ranges are sufficiently long that depth of field even at extreme slant angles would been tens to hundreds of kilometres thick, so atmospheric distortions would likely have been the main driver of effective resolution off-nadir.

For sat squared depth of field can become an issue though

[Blackstar]

Moderator:
New splinter discussion split/moved here:
https://forum.nasaspaceflight.com/index.php?topic=61727.0

The two leaked single-page documents from last week are really not that different from declassified intelligence assessments from the early 1980s. If you look at documents in the CREST document archive, you can find cables that report that kind of stuff. Now I'm sure there are important differences. For instance, the new documents include information from both imagery as well as from signals intelligence, and some of the early 1980s stuff that has been released is only imagery assessments (not SIGINT). But it's still essentially the same thing: look at the evidence and write a quick summary.

I think I posted a document on one of these threads from 1982 reporting about a new warship under construction at a Soviet shipyard in Leningrad--it reported the beam, the fact that it was compartmented like a warship and not a civilian vessel, and differences in how it was mounted on the construction slipway. A few years ago Asif Siddiqi and I did an article on the Soyuz T-10-1 on-pad fire and abort. One of the cool things I had was several declassified documents that were based upon KH-11 images of the Soyuz sitting on the ground nearby, surrounded by recovery forces.

[LittleBird]

Thanks for th up Hoku. I remember Jim saying that HEXAGON didn't use CMGs, and I thought that I'd read in an NRO source that GAMBIT didn't but I'm now wondering if that's true, especially for the later G3 etc.

There is also an interesting comment from Bob O'Dell's oral history interview on HST:
O'Dell:
(...) We had things that we generally didn't expect, like this business about 2.4 meters being just about the largest size you could package with a low moment of inertia, a point I made in the review panel. That was really the driver, on 2.4 meters. That's what kept the costs down. That was the big break on the costs. The uncertainty of cost in making 3 meter optics was great, but very hard to define, whereas the certainty of the difference in cost between reaction wheels and control moment gyros was clear. That was black and white.
https://www.aip.org/history-programs/niels-bohr-library/oral-histories/4802-1

Thanks, yes. Funnily enough when I saw you mention that quote before https://forum.nasaspaceflight.com/index.php?topic=29545.560 I wongly inferred that KH-11 wouldn't have used CMGs either. I couldn't really grok the simple reality that it was apparently OK to use them on about 20 odd KENNENs https://en.wikipedia.org/wiki/KH-11_KENNEN
 yet one for one Hubble it was too pricey ...

Some cost estimates for KENNEN:

<snip>

all from Wikipedia.

KH-11 has/had different pointing and tracking constraints than HST. According to the attached table from the 1999 edition of TRW's "Space Data", CMGs are the preferred choice for "high" maneuvering rates (like frequent acquisition of new ground targets along the orbital track). HST on the other hand, is optimised for long exposures, and slow slew rates.

Thanks hoku, that's fascinating. One feels the author was instructed not to mention anything built by arch rival  Hughes while constructing that table ;-) (Oops: failed to see the Intelsat entry)

So I am now even more curious about the NRO and CMGs, Skylab, and the KENNEN.

Was Skylab thus probably the first LEO s/c to use CMGs, and if so was this experience directly useful to KH-11 designers ? If so they had more than just National prestige incentive to help NASA out by imaging it in its distressed state.

 

Re earlier discussion of Control Moment Gyros I am interested to see that the recently published NRO "Innovators & Innovations" book (large file, uploaded at https://forum.nasaspaceflight.com/index.php?topic=40314.msg2640202#msg2640202 , H/T to hoku) has some material about their use on KENNEN. Appears to have been first NRO spacecraft to do so, making me wonder, as I did above, if indeed Skylab was indeed first ever use of them.

[hoku]

<snip>
Re earlier discussion of Control Moment Gyros I am interested to see that the recently published NRO "Innovators & Innovations" book (large file, uploaded at https://forum.nasaspaceflight.com/index.php?topic=40314.msg2640202#msg2640202 , H/T to hoku) has some material about their use on KENNEN. Appears to have been first NRO spacecraft to do so, making me wonder, as I did above, if indeed Skylab was indeed first ever use of them.

It seems plausible that space stations like Skylab, MIR, and ISS with their large moment of inertia, were the first to employ GMCs (while the Salyut stations apparently were relying primarily on gravity gradient stabilization).

Among (commercial/civil) "high-resolution" satellites, WorldView claims to have been the first user:

"WorldView 2 builds upon many of the technical capabilities of WorldView 1, which was the first high-resolution satellite to operate with Control Motion Gyros, and provides very high agility with large scale collection capabilities and fast point tracking. (...) At this time, there isn't another satellite which combines high resolution with eight-bands and the level of agility that we get from the WorldView-class satellite."

I imagine that this basically also describes the CMG use case for KH-11.

https://spaceflightnow.com/delta/d345/d345status.html

[JetProp]

<snip>
Re earlier discussion of Control Moment Gyros I am interested to see that the recently published NRO "Innovators & Innovations" book (large file, uploaded at https://forum.nasaspaceflight.com/index.php?topic=40314.msg2640202#msg2640202 , H/T to hoku) has some material about their use on KENNEN. Appears to have been first NRO spacecraft to do so, making me wonder, as I did above, if indeed Skylab was indeed first ever use of them.

It seems plausible that space stations like Skylab, MIR, and ISS with their large moment of inertia, were the first to employ GMCs (while the Salyut stations apparently were relying primarily on gravity gradient stabilization).

Among (commercial/civil) "high-resolution" satellites, WorldView claims to have been the first user:

"WorldView 2 builds upon many of the technical capabilities of WorldView 1, which was the first high-resolution satellite to operate with Control Motion Gyros, and provides very high agility with large scale collection capabilities and fast point tracking. (...) At this time, there isn't another satellite which combines high resolution with eight-bands and the level of agility that we get from the WorldView-class satellite."

I imagine that this basically also describes the CMG use case for KH-11.

https://spaceflightnow.com/delta/d345/d345status.html

I think, that Moliniya satellite use CMG. First launch 1965 year.

На спутнике впервые была применено управление движением объекта вокруг центра масс по трем осям с помощью одного гироскопа.

The satellite was the first to use a single gyroscope to control the motion of an object around the center of mass along three axes.

https://web.archive.org/web/20190305184307/http://kik-sssr.ru/Hist_3_Molnia.htm

[LittleBird]

<snip>
Re earlier discussion of Control Moment Gyros I am interested to see that the recently published NRO "Innovators & Innovations" book (large file, uploaded at https://forum.nasaspaceflight.com/index.php?topic=40314.msg2640202#msg2640202 , H/T to hoku) has some material about their use on KENNEN. Appears to have been first NRO spacecraft to do so, making me wonder, as I did above, if indeed Skylab was indeed first ever use of them.

It seems plausible that space stations like Skylab, MIR, and ISS with their large moment of inertia, were the first to employ GMCs (while the Salyut stations apparently were relying primarily on gravity gradient stabilization).

Among (commercial/civil) "high-resolution" satellites, WorldView claims to have been the first user:

"WorldView 2 builds upon many of the technical capabilities of WorldView 1, which was the first high-resolution satellite to operate with Control Motion Gyros, and provides very high agility with large scale collection capabilities and fast point tracking. (...) At this time, there isn't another satellite which combines high resolution with eight-bands and the level of agility that we get from the WorldView-class satellite."

I imagine that this basically also describes the CMG use case for KH-11.

https://spaceflightnow.com/delta/d345/d345status.html

I think, that Moliniya satellite use CMG. First launch 1965 year.

На спутнике впервые была применено управление движением объекта вокруг центра масс по трем осям с помощью одного гироскопа.

The satellite was the first to use a single gyroscope to control the motion of an object around the center of mass along three axes.

https://web.archive.org/web/20190305184307/http://kik-sssr.ru/Hist_3_Molnia.htm

Thanks, I’d forgotten that, see also a 1971 paper https://www.sciencedirect.com/science/article/abs/pii/0005109871900744

Attitude control of the Molniya I communication satellite which moves in a high eccentric, periodically corrected orbit, and is continuously facing the Sun with its solar panels and the Earth with its antenna, is a difficult problem. It is shown that this problem may be solved by means of the multi-purpose usage of a speed modulated double-gimballed control moment gyro.

[Blackstar]

The section of the NRO history on relay satellites. This is disappointing. Set aside the poor copy editing (several problems in that last column), most of this is about communications, and then when it gets to the actual relay satellite topic, it really misses an opportunity to say something useful.

It does say something interesting, although it is not clear if this is meaningful--it mentions TRW's Intelsat III satellites as a useful baseline. (I wrote an article for Spaceflight on the Intelsat III satellites, but cannot find the citation.) The Intelsat III satellites were flying when the relay satellite program was first discussed, so it makes sense that the NRO looked at them and thought that they could use something similar. But Hughes won the contract with a proposal based upon the Intelsat IV design. It's too bad they mention Hughes but not the Intelsat IV.

Unfortunately, this entry doesn't really state anything new about the subject, and it seems to avoid certain topics. For instance, the SDS satellites used a Molniya orbit, and I believe that the NRO has acknowledged that before, but doesn't say so here. It hints that the relay task was not as simple as expected, but doesn't say why. A big reason why was the use of a frequency that could not penetrate the atmosphere. And the traveling wave tubes apparently burned out early. Also, apparently there was a problem early in the program with lining up the satellites (as somebody put it to me, the satellites were not where they were supposed to be when the KH-11 was transmitting to them, although I don't know what that means). My assumption is that this book is only based upon previously declassified information (in other words, no information declassified specifically for the book), but they didn't even use what they could have used.

We're coming up on the 50th anniversary of the first KH-11 launch and the first SDS launch, and it's a shame that they still dance around the subject so lightly.

[LittleBird]

The section of the NRO history on relay satellites. This is disappointing. Set aside the poor copy editing (several problems in that last column), most of this is about communications, and then when it gets to the actual relay satellite topic, it really misses an opportunity to say something useful.

It does say something interesting, although it is not clear if this is meaningful--it mentions TRW's Intelsat III satellites as a useful baseline. (I wrote an article for Spaceflight on the Intelsat III satellites, but cannot find the citation.) The Intelsat III satellites were flying when the relay satellite program was first discussed, so it makes sense that the NRO looked at them and thought that they could use something similar. But Hughes won the contract with a proposal based upon the Intelsat IV design. It's too bad they mention Hughes but not the Intelsat IV.

It's meaningful, in that it is quoting the Dirks Blue Book, see first grab below. I'd need to check dates but I think that may have been written before the award of Intelsat IV. More intriguingly, as I have remarked before, the same page of the Blue Book mentions an alternative, a body stabilised TRW bus capable of carrying a larger antenna than SDS would need. This sounds like development work on RHYOLITE, as per my post here https://forum.nasaspaceflight.com/index.php?topic=37169.msg2294863#msg2294863

Unfortunately, this entry doesn't really state anything new about the subject, and it seems to avoid certain topics. For instance, the SDS satellites used a Molniya orbit, and I believe that the NRO has acknowledged that before, but doesn't say so here.

More than acknowledged, they have
i) included a line drawing in a released doc that shows the rabbit ears configuration of the 2 satellite orbits (third grab)
ii) drawn the satellite, with a clear Hughes family appearance (second grab),
and iii) issued a YouTube video that features same type of design (last grab), though with a more generic looking Kennen  and with a vaguer orbit,

[Edit: Looking at the video I see it could actually be representing a later Hughes satellite, Shuttle optimised, in GEO-as per some released info about the second generation SDS.] We have an SDS thread if anyone finds any new info, btw.

It hints that the relay task was not as simple as expected, but doesn't say why. A big reason why was the use of a frequency that could not penetrate the atmosphere. And the traveling wave tubes apparently burned out early. Also, apparently there was a problem early in the program with lining up the satellites (as somebody put it to me, the satellites were not where they were supposed to be when the KH-11 was transmitting to them, although I don't know what that means). My assumption is that this book is only based upon previously declassified information (in other words, no information declassified specifically for the book), but they didn't even use what they could have used.

We're coming up on the 50th anniversary of the first KH-11 launch and the first SDS launch, and it's a shame that they still dance around the subject so lightly.

It's unfortunate because the downplaying of the info about the HEO orbit here, and the reference to Arthur C Clarke, makes it read as if the relay satellite was in GEO.

One thing they do emphasise is the role of Tony Iorillo, though he is named at the end, not in the relay section. I get the feeling that the editing task defeated them.

[Blackstar]

I have not bothered to put together a simple chronology, but that might be helpful:

-1968 first Intelsat III satellite launched (failed soon after launch)
-1968 second Intelsat III satellite launched (operated until 1971, planned lifetime was 5 years)
-last Intelsat III satellite launched
-Tacsat
-awarding of SDS satellite contract to Hughes
-1971 first Intelsat IV satellite launched
-1976 first SDS satellite launched

A useful point would be when Intelsat IV's design was first started. But the obvious conclusion is that Intelsat III was operating around 1968-1970 when the SDS work was first starting, so it was an obvious baseline.

[LittleBird]

I have not bothered to put together a simple chronology, but that might be helpful:

I am assembling one that includes this era for a longer project which I hope to get written up by next spring.

-1968 first Intelsat III satellite launched (failed soon after launch)
-1968 second Intelsat III satellite launched (operated until 1971, planned lifetime was 5 years)
-last Intelsat III satellite launched
-Tacsat
-awarding of SDS satellite contract to Hughes
-1971 first Intelsat IV satellite launched
-1976 first SDS satellite launched

A useful point would be when Intelsat IV's design was first started. But the obvious conclusion is that Intelsat III was operating around 1968-1970 when the SDS work was first starting, so it was an obvious baseline.

Intelsat IV design process evolved in parallel with  pilot domestic comsat studies, and had started by mid '66, with Hughes and Lockheed doing more serious studies by early '67.  TRW had already been awarded Intelsat III by early '66, much to Hughes' chagrin  (https://www.thespacereview.com/article/4096/1) . Tacsat was awarded to Hughes in January '67, and Intelsat IV sometime in the summer of 68.

The Dirks blue book is dated May 68 so indeed Intelsat III is the known quantity, see first grab. Interestingly, at that time, GEO seems to be favoured over HEO, see other grabs, I haven't dug into when HEO first made an appearance in the SDS story. As you'll recall you (and others) uploaded some of the key docs in the SDS thread: https://forum.nasaspaceflight.com/index.php?topic=59168.0 thanks all.

[Blackstar]

I should continue this over in the SDS thread (I guess I should cross-post my earlier post), but wanted to mention this image.

I almost certainly saw this before, but it did not completely register. This may in fact depict the second block of SDS satellites, which I learned were based on the Leasat series. This looks like Leasat with a deployable skirt--something that was done for other Hughes satellites, but was not done for Leasat.

I will hold a certain amount of skepticism, because usually these graphics are not based on reality but are notional. But this one is intriguing.

[LittleBird]

I should continue this over in the SDS thread (I guess I should cross-post my earlier post), but wanted to mention this image.

I almost certainly saw this before, but it did not completely register. This may in fact depict the second block of SDS satellites, which I learned were based on the Leasat series. This looks like Leasat with a deployable skirt--something that was done for other Hughes satellites, but was not done for Leasat.

I will hold a certain amount of skepticism, because usually these graphics are not based on reality but are notional. But this one is intriguing.

I'll move over there but won't move my posts above as I think they were also relevant here-I'll just point to them as needed.

[Blackstar]

https://thespacereview.com/article/4899/1

National Reconnaissance Program crisis photography concepts, part 4: FASTBACK and FASTBACK-B
by Joseph T. Page II
Monday, November 25, 2024

The fourth system introduced in this series on National Reconnaissance Program crisis photography concepts is an intriguing—yet fundamentally dangerous—way to send a reconnaissance satellite system into orbit. As presented to the NRO in the early 1970s by Martin Marietta, the FASTBACK system concept envisioned a refurbished LGM-30 Minuteman intercontinental ballistic missile (ICBM) placing a relatively small, quick-reaction photographic satellite into low earth orbit (LEO) within 24-hours of launch decision.

Rapid reaction via ICBM
Established in the early 1960s, the National Reconnaissance Program (NRP) was the single, national program dedicated to the collection of intelligence, through overflight, to meet the needs and objectives of the United States government. The NRP consisted of overt and covert overflight projects for intelligence, geodesy, and mapping photography and electronic signal collection based upon intelligence collection requirements and priorities established by the United States Intelligence Board. Based upon documentation detailing earlier series installments, NRP analysts estimated the number of “critical situations” desiring a quick-reaction reconnaissance capability hovered between three and five a year, with two situations occurring simultaneously. Considerations on likely crisis locations, launch capabilities, and film/data delivery all drove system concept designs.

The FASTBACK design consisted of a relatively small, quick reaction photo-satellite system, launched on-call from Johnson Island in the Pacific. An example mission would have one or two accesses (prime orbital paths) over a target area depending on location and selected inclination. After the photographic mission was complete, the satellite recovery vehicle would splash down in the Atlantic. Hard copy photographic processing would commence in the Washington DC area within 24 hours from launch decision.

[LittleBird]

So I'm going to keep musing on this...

I have some nice images of artwork showing the 3-meter version of the Large Space Telescope. Probably date from around 1973. Unfortunately, they are film slides and I need to figure out how to scan them. I have not found them on the internet.

I know that books have been written about the development of Hubble. I suspect that new stuff could be written now that we're getting more info on the development of large optics in the 1970s.

Would a 3 meter mirror on HST fit in the shuttle cargo bay?

It would surely fit the 15 foot bay that was flown, but I'd be curious about some of the smaller bays that iirc were discussed in the era when final shuttle commitment  was still not quite made (71-72 ish). Not a lot in print about details of this iirc except for "Spies and Shuttles" https://archive.org/details/spiesshuttlesnas0000davi and John Logsdon's Post-Apollo book.

The fact that KENNEN go-ahead preceded the Shuttle go ahead by a good fraction of a year means there is an interesting period when the Shuttle bay diameter (as opposed to length) could no longer be justified by size of committed future NRO imint birds. That's not to say that other likely NRO missions wouldn't have wanted the extra width. What I don't know is how many in government would have known this-or indeed cared.

[Edit: Will upload details when time permits but checked above two references and found that i) only payload in 1973 DoD mission model greater than 10 feet diameter was a polar orbit ocean surveillance satellite [David book], and ii) that David Packard made Fletcher aware in Oct 1971 that DoD payload restrictions were probably more flexible than NASA knew. Fletcher reassured him that 15 foot diameter was more NASA than DoD, while 60 foot length was vice versa. Interestingly designs as short as 45 feet were considered, whereas diameter was not less than 14 feet from my quick reading [Logsdon book] ]

Realised I'd never got round to uploading some grabs from Logsdon's "After Apollo?" re the more interesting of the two references here, the October 1971 conversation between David Packard, then the Deputy Secretary of Defense, and NASA Administrator James Fletcher. I find this convesation very interesting, because, as I said above, it seems that

i) Packard made Fletcher aware during the last lap of pre-approval negotiations that DoD payload restrictions on both cross-range and size were (by then, several months after the KH-11 go-ahead) probably more flexible than NASA realised,

ii) Fletcher reassured him that 15 foot diameter was more NASA than DoD (suggesting to me that as well as a 15 foot telescope,  NASA's long term aspirations about space stations, and even moon/mars modules might have played a role),

and also apparently said that the

iii) 60 foot length was more DoD than NASA.

Two things are interesting here imho, one relevant to this thread, and the other to the mythology of the Shuttle (threads here on Hersch book "Dark Star" and  the ongoing podcast "16 Sunsets"). The latter topic, on who  by late '71, actually wanted the largest possible payload bay is thus one to take elsewhere, but the former, of why Packard and/or Fletcher knew that 60 feet was no longer essential, is relevant here.

It seems certain to me that Packard knew about the KH-11 go ahead,  as he was a party to discussions and a member of ExCom iirc, and it seems quite likely that Fletcher might also know something, as he had had very high clearances in the late 60s (e.g. the Fletcher committee on RHYOLITE options). Perhaps they both already knew that the "Stubby Hubble" was more like the length (~45 feet?) that is now ascribed to it, see e.g. ArchiPeppe's lovely pictures below, from Blackstar's TSR articles  ?

[Edit: I should add that John Logsdon thought that Fletcher didn't know, and that Packard's apparent flexibility was not initially welcome-I should look back at both issues-see last 3 grabs].

[Blackstar]

Two things are interesting here imho, one relevant to this thread, and the other to the mythology of the Shuttle (threads here on Hersch book "Dark Star" and  the ongoing podcast "16 Sunsets"). The latter topic, on who  by late '71, actually wanted the largest possible payload bay is thus one to take elsewhere, but the former, of why Packard and/or Fletcher knew that 60 feet was no longer essential, is relevant here.

It seems certain to me that Packard knew about the KH-11 go ahead,  as he was a party to discussions and a member of ExCom iirc, and it seems quite likely that Fletcher might also know something, as he had had very high clearances in the late 60s (e.g. the Fletcher committee on RHYOLITE options). Perhaps they both already knew that the "Stubby Hubble" was more like the length (~45 feet?) that is now ascribed to it, see e.g. ArchiPeppe's lovely pictures below, from Blackstar's TSR articles  ?

I'll toss in a bit of a non-sequitur here that there was a 1973 study of alternative HEXAGONs that also looked at redesigning it for shuttle. That's 2 years too late, but there was certainly the possibility that NRO could have come up with a shorter version of HEXAGON than 60 feet.

Now you have to set the dimensions somewhere, and it seems pretty clear by now, even if we don't have a letter or memo that explicitly states it, that the DoD picked the longest payload they had which in 1971 was brand spanking new, and they said "it has to be able to carry this." Had they told NASA something less than 60 feet was acceptable, they were going to have to redesign HEXAGON to fit in the shuttle, and they were not about to let NASA dictate that to them.

I wish I knew the dimensions for the KH-11. I don't know if I know anybody who would tell me. It is kinda silly that the first launch was 48 years ago and we still don't know the basics about the vehicle.

[LittleBird]

Two things are interesting here imho, one relevant to this thread, and the other to the mythology of the Shuttle (threads here on Hersch book "Dark Star" and  the ongoing podcast "16 Sunsets"). The latter topic, on who  by late '71, actually wanted the largest possible payload bay is thus one to take elsewhere, but the former, of why Packard and/or Fletcher knew that 60 feet was no longer essential, is relevant here.

It seems certain to me that Packard knew about the KH-11 go ahead,  as he was a party to discussions and a member of ExCom iirc, and it seems quite likely that Fletcher might also know something, as he had had very high clearances in the late 60s (e.g. the Fletcher committee on RHYOLITE options). Perhaps they both already knew that the "Stubby Hubble" was more like the length (~45 feet?) that is now ascribed to it, see e.g. ArchiPeppe's lovely pictures below, from Blackstar's TSR articles  ?

I'll toss in a bit of a non-sequitur here that there was a 1973 study of alternative HEXAGONs that also looked at redesigning it for shuttle. That's 2 years too late, but there was certainly the possibility that NRO could have come up with a shorter version of HEXAGON than 60 feet.

I should, btw, have added the citation for the memo from Fletcher to Low reporting the Packard/Fletcher lunch, memo  is
""Eyes Only" Memorandum from J.C.F. to Dr. Low, "Luncheon Conversation with Dave Packard", October 20, 1971, LSN/LHRC where LSN/NHRC means "John Logsdon Source Notes,NASA Historical Reference Collection, NASA HQ, Washington, DC".

The full text of the (presumably short) memo would be fascinating. I think Hersch's is the only book I've seen so far that mentions it apart from Logsdon's own.

Now you have to set the dimensions somewhere, and it seems pretty clear by now, even if we don't have a letter or memo that explicitly states it, that the DoD picked the longest payload they had which in 1971 was brand spanking new, and they said "it has to be able to carry this." Had they told NASA something less than 60 feet was acceptable, they were going to have to redesign HEXAGON to fit in the shuttle, and they were not about to let NASA dictate that to them.

This is why I am so intrigued that  by October 1971 Packard was indicating any flexibility at all-with the reported phrase "something could be done" (grab below). John L, writing in 2015 has interpreted the "program [which] caused the length difficulty" as the "successor to ... Hexagon". This either could mean a future shuttle-tailored HEXAGON variant, which didn't materialise, but which could indeed in principle to be shrunk down somewhat from 60 ft, as per the studies  you mention above, or it could mean the KH-11 which seems certain to have  been shorter, and which had only just become an approved programme.

It could of course have been something else (radar, GEO SIGINT, etc) though that seems much less likely at this stage.

I wish I knew the dimensions for the KH-11. I don't know if I know anybody who would tell me. It is kinda silly that the first launch was 48 years ago and we still don't know the basics about the vehicle.

Indeed, but  remember we do have one, intriguing, official line drawing-admittedly tiny-in the "rabbit ears" image declassified with the main KENNEN release.