Author Topic: Defense Meteorological Support Program (DMSP)  (Read 27627 times)

Offline leovinus

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Re: Defense Meteorological Support Program (DMSP)
« Reply #20 on: 04/07/2022 08:42 pm »
One question is how much lead time they required to re-program shutter opening (or staying closed) opportunities. Somewhere I read that they (the meteorologists?) had to produce punching cards, which were then used to update the shutter opening windows "just in time" (i.e. during the final pass of HEXAGON over a US ground station just ahead of its photographic pass over the area of interest).

Hmmm... I find it hard to believe that it was that clunky. The process that was developed for CORONA by 1960/61 was that they had the ability to send a command up to CORONA to tell it to skip a photographic pass. Of course, that's kinda overkill, because maybe clouds only covered part of an area, and skipping an entire pass would miss viewable area. But it seems to me that there should have been an ability to send up a command to HEXAGON without requiring a lot of prep. But I'm no expert in 1970s computer capabilities.

Emphasis mine. Per discussion in the ANS thread, in 1973/74, ANS was publicly the first on-orbit satellite with reprogrammable computer and core memory on board (which saved the day when inserted in a wrong orbit). So, yeah, would be fun to learn more about the HEXAGON on-board computer.

Offline edzieba

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Re: Defense Meteorological Support Program (DMSP)
« Reply #21 on: 04/08/2022 09:21 am »
If I were trying to program just-in-time behaviour with the minim of on-board computing and with the ability to program only in a communications window immediately before the pass, I would:
- Write imaging schedules many orbits ahead of executing them. We know target prioritisation was used in-orbit, so you would write your schedule with the assumption both that all targets are visible, and with more targets than you actually have time to image. These could be updated on the final CONUS overflight if last-minute targets were added.
- Upload them as soon as the satellite enter visibility, or ideally a few orbits ahead (depending on satellite memory capacity and desire for tolerance to ground system issues)
- Using the DMSP imagery captured the morning of the imaging pass, forecast cloud cover over that passes ground track
- Calculate an 'inhibit list' based purely on ground track distance, or even on mission time (easier to follow in-orbit, but would need dynamic offsetting for imaging ahead/behind direct overhead point)
- Upload this list once ready, which can even be done multiple times over a single CONUS overflight to allow for updated forecasts right up until the satellite exits contact
- As the satellite performs its pass, it follows the imaging schedule, working down the inhibit list alongside it to either release the shutter or inhibit it. If you want to be extra fancy, you look 'one shot ahead' in your imaging schedule so you can skip a frame before even starting to repoint the mirror or roll/slew the satellite.

The advantage of doing it this way is that:
- Preparation of imaging targets is done independently of real-time weather and only based on long term forecasts (e.g. "don't bother even trying to shoot there, it's winter and covered in snow for 5 months")
- Preparation of weather forecasts is done independently of imaging target selection (good for security compartmentalisation, weather forecasting department are only concerned with a single strip of cloud cover at any one time)
- Forecasts can be updated at any point without affecting imaging target schedule
- Imaging target schedule can be updated without affecting inhibit list
- Using an inhibit list rather than a 'permit list' mean the fail-safe condition is to waste film rather than miss intelligence in the event of a ground communications issue

A final wrinkle to the story would be if there was a low-bandwidth relay capable satellite available (possibly even one of the DMSPs themselves) that could talk to HEXAGON after exiting CONUS coverage. The inhibit list could then be updated right up until a particular image was taken, but that capability seems too niche to have really been worth it unless somebody really wanted to try and retrofit a crisis-response capability to HEXAGON in order to command imagery and capsule release ASAP after an imaging pass rather than waiting for a 'once more around' with CONUS commanding, and I can't recall such a capability being mentioned in any documentation released thus far.

Offline Jim

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Re: Defense Meteorological Support Program (DMSP)
« Reply #22 on: 04/08/2022 11:16 am »

- Upload this list once ready, which can even be done multiple times over a single CONUS overflight to allow for updated forecasts right up until the satellite exits contact


There are only two CONUS AFSCN stations and it is in a polar orbit so only one station pass.

Offline edzieba

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Re: Defense Meteorological Support Program (DMSP)
« Reply #23 on: 04/08/2022 12:17 pm »

- Upload this list once ready, which can even be done multiple times over a single CONUS overflight to allow for updated forecasts right up until the satellite exits contact


There are only two CONUS AFSCN stations and it is in a polar orbit so only one station pass.
Were none of the RTSs able to forward commands?

Offline LittleBird

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Re: Defense Meteorological Support Program (DMSP)
« Reply #24 on: 04/08/2022 12:55 pm »

A final wrinkle to the story would be if there was a low-bandwidth relay capable satellite available (possibly even one of the DMSPs themselves) that could talk to HEXAGON after exiting CONUS coverage. The inhibit list could then be updated right up until a particular image was taken, but that capability seems too niche to have really been worth it unless somebody really wanted to try and retrofit a crisis-response capability to HEXAGON in order to command imagery and capsule release ASAP after an imaging pass rather than waiting for a 'once more around' with CONUS commanding, and I can't recall such a capability being mentioned in any documentation released thus far.

I have absolutely no knowledge of whether that was possible, but I am intrigued that DMSP was i)  asserted to have another kind of low bandwidth comms ability-essentially that from agents in the field overseas embassies etc (Des Ball's DMSP history in JBIS in 1986), though Ball's article states with no real evidence that the relay system was hosted on the Burner II stages, and ii) asserted in early 70s to be going to carry  an AFSATCOM relay (Ball again, but this time citing the AW&ST article that covered the public announcement of DMSP).  See these two articles below. I've been curious for a while if either assertion was ever substantiated elsewhere.
« Last Edit: 04/09/2022 05:50 pm by LittleBird »

Online Blackstar

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Re: Defense Meteorological Support Program (DMSP)
« Reply #25 on: 04/08/2022 01:21 pm »
Maybe we can try to not derail this thread?

Online Blackstar

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Re: Defense Meteorological Support Program (DMSP)
« Reply #26 on: 04/08/2022 10:02 pm »
The original Tiros had its cameras pointing out the bottom. The first DMSP had its single camera pointing out the side. Later versions of Tiros adopted the DMSP approach.

Offline LittleBird

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Re: Defense Meteorological Support Program (DMSP)
« Reply #27 on: 04/09/2022 06:23 am »
The original Tiros had its cameras pointing out the bottom. The first DMSP had its single camera pointing out the side. Later versions of Tiros adopted the DMSP approach.

I hadn't really appreciated that ESSA was essentially a DMSP, as per Hall history-see grabs below. This may be the only example when an entire NRO spacecraft design has been passed over to civilian use (i.e. even more completely than Lunar Orbiter ) ?

I may of course have misunderstood-how similar were they, in fact ?

[Edit: It does now make me wonder how the design change was explained away at the time.]
« Last Edit: 04/09/2022 01:22 pm by LittleBird »

Offline kevin-rf

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Re: Defense Meteorological Support Program (DMSP)
« Reply #28 on: 04/09/2022 11:27 am »
The original Tiros had its cameras pointing out the bottom. The first DMSP had its single camera pointing out the side. Later versions of Tiros adopted the DMSP approach.

The mechanics of this is the one thing I have never really understood. For a GEO spinner it makes sense to orient the axis of rotation north/south. With Tiros 1 was the axis of rotation aligned straight down? Then a second smaller spin on the axis itself to keep the axis pointed down as it orbited? One full rev per orbit? On later side camera satellites, was the axis of rotation oriented in the direction of the orbit so it was scanning east to west with north at the top of the images?
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Online Blackstar

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Re: Defense Meteorological Support Program (DMSP)
« Reply #29 on: 04/09/2022 11:37 am »

Offline LittleBird

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Re: Defense Meteorological Support Program (DMSP)
« Reply #30 on: 04/09/2022 01:14 pm »
Some good vintage pics and animations in this short DMSP history:



and also a mid 70s longer feature on DMSP (lots of detail on ground segment):



Latter includes a look at encapsulation of a Block 5-era sat (looks like a 5A?) [Edit: looking at colour pics Blackstar has uploaded above I see this must be a 5B/C as it is more like 7 feet tall than 4 feet.] and a Thor  launch (looks like a Burner 2 but shroud hard to see):

« Last Edit: 04/17/2022 03:17 pm by LittleBird »

Offline Jim

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Re: Defense Meteorological Support Program (DMSP)
« Reply #31 on: 04/09/2022 01:29 pm »

[Edit: It does now make me wonder how the design change was explained away at the time.]

Easy block change.  They came up with a new idea and tested it on TIROS 9.
« Last Edit: 04/09/2022 01:30 pm by Jim »

Offline LittleBird

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Re: Defense Meteorological Support Program (DMSP)
« Reply #32 on: 04/10/2022 09:47 am »

[Edit: It does now make me wonder how the design change was explained away at the time.]

Easy block change.  They came up with a new idea and tested it on TIROS 9.

I am also struck that they moved to polar orbit at the same time. I guess this wouldn't have seemed odd, as Nimbus had already been launched into polar orbit, but what seems remarkable with hindsight is that TIROS 9 and the first 2, and last, of the ESSA series were launched out of the Cape on Thor Deltas, unlike the first 4 Nimbus launches which used  Thor Agenas from Vandenberg. A contemporary writer, Turnill's Observer's Book of Unmanned Spaceflight, in mid 1970s, remarks that TIROS 9 was first polar launch from the Cape but otherwise doesn't discuss this. My first thought was that this a cost-saving measure and/or  avoided drawing attention to possibility of military operational metsats, but then I see from Gunter's excellent list https://space.skyrocket.de/doc_sdat/essa.htm
 that some of the ESSA's did indeed go from VAFB.
« Last Edit: 04/10/2022 01:39 pm by LittleBird »

Offline LittleBird

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Re: Defense Meteorological Support Program (DMSP)
« Reply #33 on: 04/10/2022 05:57 pm »
The original Tiros had its cameras pointing out the bottom. The first DMSP had its single camera pointing out the side. Later versions of Tiros adopted the DMSP approach.

The mechanics of this is the one thing I have never really understood. For a GEO spinner it makes sense to orient the axis of rotation north/south. With Tiros 1 was the axis of rotation aligned straight down? Then a second smaller spin on the axis itself to keep the axis pointed down as it orbited? One full rev per orbit?

You would think so but apparently not, see discussion of "normal point" in first grab below, from AW&ST, Aug 3rd, 1964, page 44. [Edit: This is interesting, if accurate, because the second spin you refer to was identified as early as the late 40s RAND studies and implemented in Agena, for example. Was it perhaps not deemed necessary for the earliest Tiros, perhaps because they were mainly looking at the US, and because it was one less thing to go wrong ?]

Quote
On later side camera satellites, was the axis of rotation oriented in the direction of the orbit so it was scanning east to west with north at the top of the images?

Second grab below is the comparison figure from same issue, has the image Blackstar posted and the comparison with early Tiros.

 
« Last Edit: 04/11/2022 09:04 am by LittleBird »

Offline kevin-rf

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Re: Defense Meteorological Support Program (DMSP)
« Reply #34 on: 04/12/2022 02:15 am »
Quote: "In Tiros 1-8, axially mounted television cameras, aimed downward through the satellites 42-in-dia. baseplate, pointed directly toward the center of the earth at only one point in orbit, called the normal point, the cameras viewed the earth at increasingly oblique angles, finally seeing outer space rather than the earth. "

Well that explains it, it really only looked straight down at one point in it's orbit. Like one expects a spinning top to behave in orbit. I just thought there had to be more to it than looking straight down at only one point in it's order. Hence why DMSP side camera was superior. 

What I now find interesting is the magnetic coils built into the drum once they switched to the side camera. This let them keep the axis of rotation perpendicular to the orbital path by tilting it left and right. If you ask me, DMSP was very sophisticated for such a "simple" satellite.
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Offline LittleBird

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Re: Defense Meteorological Support Program (DMSP)
« Reply #35 on: 04/12/2022 09:19 am »
Quote: "In Tiros 1-8, axially mounted television cameras, aimed downward through the satellites 42-in-dia. baseplate, pointed directly toward the center of the earth at only one point in orbit, called the normal point, the cameras viewed the earth at increasingly oblique angles, finally seeing outer space rather than the earth. "

Well that explains it, it really only looked straight down at one point in it's orbit. Like one expects a spinning top to behave in orbit. I just thought there had to be more to it than looking straight down at only one point in it's order. Hence why DMSP side camera was superior. 

It does explain it but I do share your surprise. I can only surmise that TIROS was meant to give way to something 3 axis stabilised more like like Nimbus in order to give a world wide system. I'd be surprised if the AW&ST piece was wrong but another source would be nice to have.

Quote
What I now find interesting is the magnetic coils built into the drum once they switched to the side camera. This let them keep the axis of rotation perpendicular to the orbital path by tilting it left and right. If you ask me, DMSP was very sophisticated for such a "simple" satellite.

Yes. I had thought that magnetorquers showed up later than that, so it is very impressive to me.

Offline kevin-rf

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Re: Defense Meteorological Support Program (DMSP)
« Reply #36 on: 04/12/2022 02:08 pm »
Quote
It does explain it but I do share your surprise. I can only surmise that TIROS was meant to give way to something 3 axis stabilised more like like Nimbus in order to give a world wide system. I'd be surprised if the AW&ST piece was wrong but another source would be nice to have.

Remember, one of the early pre-Corona designs was also a spinner. Sounds like it would have had similar issues, and thus been very localized with what it could image ( Say maybe being only able to image between 60 and 70 degrees North Latitude).

Does make one wonder if a gravity gradient stabilized boom might have worked better. Especially with some of the planned rockets. (I know, alternate history with them needing to understand the concept at that point in time)   
« Last Edit: 04/12/2022 02:10 pm by kevin-rf »
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Offline Jim

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Re: Defense Meteorological Support Program (DMSP)
« Reply #37 on: 04/12/2022 02:21 pm »
And another difference, the "wheel" made it easier to find North in the photos vs the axial.
« Last Edit: 04/12/2022 02:21 pm by Jim »

Online Blackstar

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Re: Defense Meteorological Support Program (DMSP)
« Reply #38 on: 04/12/2022 03:13 pm »
It does explain it but I do share your surprise. I can only surmise that TIROS was meant to give way to something 3 axis stabilised more like like Nimbus in order to give a world wide system.

The question is when. They did form a plan to replace Tiros with something more capable. I don't know when that started. But at least early on, they were going with the first thing that they could, which was a limited spin-stabilized system.

Offline LittleBird

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Re: Defense Meteorological Support Program (DMSP)
« Reply #39 on: 04/12/2022 04:38 pm »
Quote
It does explain it but I do share your surprise. I can only surmise that TIROS was meant to give way to something 3 axis stabilised more like like Nimbus in order to give a world wide system. I'd be surprised if the AW&ST piece was wrong but another source would be nice to have.

Remember, one of the early pre-Corona designs was also a spinner. Sounds like it would have had similar issues, and thus been very localized with what it could image ( Say maybe being only able to image between 60 and 70 degrees North Latitude).


Indeed, and yet as early as 1951 for example RAND in the grab below and the attached study are proposing doing the 1 rev/orbit pitch manoeuvre that you mentioned, and which it seems TIROS didn't do.  Description is for a pencil-like satellite such as the Agena, rather than a TIROS-like drum.


So as Blackstar suggests I guess there was some cost/risk/coverage tradeoff going on.

« Last Edit: 04/12/2022 04:45 pm by LittleBird »

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