The Boring Sky (Sun)

[GaryN]

During the EVA they may have stopped the rotation,

Yes, they had stopped the rotation, which had absolutely nothing to do with heat from the Sun, there is none. The rotation was 'spin stabilisation'.

While the moon was at similar crescent stage for both, Apollo 16 10% lit, Apollo 17 2% lit...

You are doing better than I am so far! I need to become more familiar with navigation in Celestia, mostly I have just managed to make my head spin. Do you think you might be able to determine where the Sun should have been at the time and location of the EVA's? There is a forum where there seem to be some people with a good understanding of the missions and are working on simulations:
https://www.orbiter-forum.com/threads/n ... ion.40421/

There is also a project that intends to use A.I. to try and figure out what was being said on the voice recordings that are now just transcribed as *garbled*. The astronauts were a pretty coarse bunch, lots of what must have been inside jokes and comments, much more to be learned still about their voyages. Haven't figured out the metal visor comment from A17 yet, but from other comments it seems space was so deep and black they really were nervous on the EVAs, thought they were going to be sucked into the deep, be devoured as Cargo puts it. Their depth perception circuits went haywire and they couldn't look into it for very long at all, like being in an isolation chamber for a while.

[Holger Isenberg]

Yes, they had stopped the rotation, which had absolutely nothing to do with heat from the Sun, there is none.

Found a reference to the stopping, near page top:
https://history.nasa.gov/afj/ap15fj/22d ... eward.html

They rotated the spacecraft to predefine navigational star alignment to initialize the inertial navigation system. If that alignment included some tilt to point the rear nozzle towards Earth, it could explain roughly the same shadows on all 3 missions. The lunar phase, according to lunar calendars wasn't that different between all 3, varying between 2% and 16% sunlit at mission launch from Earth.

But if there was a 2nd exterior lamp on a pole near the high gain antenna it would also explain the same shadows.

Another interesting detail: The mapping camera of Apollo 15, 16, 17 you brought into the discussion already, had a 2nd film and optics included, pointed away at a fixed angle and exposing on 35mm UV film, to image the stars so a precise registering of the large film mapping photos was possible:
https://www.drewexmachina.com/2017/12/1 ... pace-evas/

[GaryN]

.. had a 2nd film and optics included, pointed away at a fixed angle and exposing on 35mm UV film, to image the stars so a precise registering of the large film mapping photos was possible:

The UV stellar camera was at that angle so the line of sight to the stars would be through the lunar atmosphere (which includes electrons). It is the depth of the column of atmosphere and the composition which makes the stars visible. From lunar orbit they did photograph the stars during A16 using long exposures and the very high speed film in the 35mm Nikon Where the stars can be seen they have long trails. The closer to the lunar surface the line of sight passes through the more visible are the stars.

http://tothemoon.ser.asu.edu/gallery/Ap ... 2035%20mm

The same principle applies even from Earth LEO, which is why the stars can be seen when the line of sight passes through Earths atmosphere (as it always must from the cupola).

Even the FUVC camera of A16 was not pointed directly away from the Moon but at an angle to increase the depth of the column to the objects they imaged.

Even from Saturn it is evident that Cassini was looking through matter in order to see the Earth.
https://www.electronicproducts.com/wp-c ... 0x1080.jpg

There will be no finer view of the stars than we have from Earths surface, and the first civilians to go to the Moon or Mars (if they are ever allowed to) will be very disappointed indeed.

[Cargo]

IRT: Helmets
A quick search
https://www.hq.nasa.gov/alsj/alsj-LEVA.html
The metal shields are side and top(with a central flap). These were the helmets for Lunar surface work.
It does seem odd about the audio saying not the metal shield but the gold shield. According to the design, you couldn't lower the meta shields unless the gold shield lowered as well, since it's on top of it.

http://www.collectspace.com/ubb/Forum29 ... 01284.html
Worden wore Scott's LEVA and OPS on the Apollo 15 transearth EVA.
Mattingly wore Young's LEVA and Duke's OPS on the Apollo 16 transearth EVA.
Evans wore Cernan's LEVA and OPS on the Apollo 17 transearth EVA.

[Holger Isenberg]

The UV stellar camera was at that angle so the line of sight to the stars would be through the lunar atmosphere (which includes electrons).

So the angle between the main mapping optics and the 35mm star tracker optics was around 90degrees? Do we have any images in public of that star tracker film? The reason they used UV here could be reusing an existing mapping camera designed for high altitude reconnaissance airplanes as there we learned UV was needed for star based navigation to be feasible during daylight. In space, using UV for a star tracker wouldn't make sense for someone following standard model science. Sure, we now know why, but would be interesting to look up the public official reasoning for that UV choice for the Apollo stat tracker camera.

[Holger Isenberg]

Found more details about the stellar camera on the mapping camera even with a few digitized images. Search for the following text on
http://onebigmonkey.com/apollo/stars/ap16bstars.html

The images from this camera are no doubt buried in a long forgotten archive somewhere having served their purpose, but a request to the data collection organiser for NASA did turn up a couple of low resolution second or third generation copies from the Apollo 16, namely these two.

Those stellar camera frames show how stressed the film was to barely capture some stars. Pretty bad for a specialized camera only tasked to capture the bright typical 57 navigation stars of 1st and 2nd magnitude. The stellar camera was indeed pointed at 90° away from the mapping camera's optical axis, towards the lunar limb.

In case it wasn't listed here in the thread yet, high quality 5000 dpi scans of all mapping camera images from Apollo 15, 16, 17, though no stellar camera images there:
https://astrogeology.usgs.gov/search/ma ... amera-Data
https://wms.lroc.asu.edu/apollo/browse

[Holger Isenberg]

Correction: angle between mapping and stellar camera was 96°

All the details about the Fairchild Lunar Mapping Camera and its included 35mm stellar camera: https://history.nasa.gov/afj/simbaycam/ ... amera.html

[Holger Isenberg]

Short movie from a GoPro Hero 7 camera on a cube sat: https://nanoavionics.com/news/nanoavion ... -in-space/

So far only with the Earth in view and the Moon. Looking forward to the night side and hopefully they "look up".

[GaryN]

Looking forward to the night side and hopefully they "look up".

Looking up I think all they would get, with long enough exposure, are hot pixels. The GoPro is prone to this with astrophotography though for such a small sensor they do pretty well. Elon Musk used a GoPro on the SpaceMan mission, can't figure out what the little white lights specs are that show up here:
https://youtu.be/aBr2kKAHN6M?t=5344

Do you remember EchoStar's Satellite Earth camera? It was at high orbit and it saw the Moon pass by but I say that is only because it was looking through Earths atmosphere. NASA usurped the channel allocation to use for its ISS livestream views after the Earth Camera had shown quite clearly a couple of obviously artificial objects passing close by. Unfortunately those vids were removed from Dish networks web site soon afterwards.
https://www.youtube.com/watch?v=4hWJ-SHfqk4&t=52s

[Holger Isenberg]

GoPro on the SpaceMan mission, can't figure out what the little white lights specs are that show up here:
https://youtu.be/aBr2kKAHN6M?t=5344

Do you remember EchoStar's Satellite Earth camera?

The Starman camera without stars was strange. The small moving lights in the video are just floating small debris particles from the spacecraft itself lit by sunlight. But at 2h 6min the Starman recording shows an interesting detail:
https://youtu.be/aBr2kKAHN6M?t=7594

First it looks like moving into Earth's shadow and everyone is expecting to see stars soon...
But then a lamp is switched on and illuminating the car's front hood and windscreen. The light on the hood is too diffuse to be sunlight and it starts at a low color temperature in red until the camera's whitebalancing adapts or the lamp reaches its normal operation temperature and went into sunlight colors temperatures. Sure, if you want to make sure to avoid a black video feed, then switching on the lamp makes sense.

The light switches on at 2h 11min.

About the EchoStar live feed I was't aware. But looks like it was fixed on Earth without the ability to move away from it into the star field.

[GaryN]

But then a lamp is switched on and illuminating the car's front hood and windscreen.

There were no lamps on the Starman mission. Lighting is tricky as we don't know the geometry, the position of the Sun and what density of atmosphere it is being seen through. The furtter out from earth horizon the less intense, but Starman at the time was only at 100 miles altitude so lots of matter above it still.
The GoPro with never show stars running at 24 FPS, though from Earth using an image intensifier you can see stars in real time. Here is a Sony video camera running 60 FPS through an intensifier:
https://www.youtube.com/watch?v=rZfSDF9mdQs
They have never used an image intensifier in deep space because they wont work, if they did you wouldn't need a fancy expensive Star Tracker camera for navigation! Atmosphere makes the difference.

[Holger Isenberg]

Starman at the time was only at 100 miles altitude so lots of matter above it still.
The GoPro with never show stars running at 24 FPS

Ok, that explains. I remembered having seen some stars in Earth-based GoPro videos, but those were apparently timelapse animations with 30s exposure time.

About Startrackers I'm now wondering what type of startracker this probe to that metal asteroid has and why the navigation software couldn't be created in time:

In a briefing held June 24 on just a few hours’ notice, agency officials said the mission did not have enough time to test guidance, navigation and control (GNC) software on the spacecraft before its launch window closes Oct. 11. NASA had already delayed the launch from Aug. 1 because of the software testing issue.

https://spacenews.com/software-testing- ... he-launch/

[fixed: I confused the Psyche mission with the other asteroid mission, there it's a cube sat]

[Holger Isenberg]

Camera: Stellar

Features:
Part of mapping-camera sub-system; 7.6-cm lens; viewing angle at 96° to map square array of 25 reseau crosses, 4 edge fiducial marks, and the lens serial number recorded on each frame with binary-coded time and altitude.

Film Type and Size:
155.4 m of 35-mm film type 3401

Remarks:
A 3.2-cm circular image with 2.4-cm flats records the star field at a fixed point in space relative to the mapping-camera view; Reduction of the stellar data permits accurate determination of camera orientation for each mapping-camera frame.

https://an.rsl.wustl.edu/apollo/data/A1 ... ry_psr.pdf

That film type 3401 was "high speed b&w". The hint to UV I found somewhere was most likely some misunderstanding with other stellar UV photography done at times from Apollo.

The stellar camera, on the other hand, has a 3-inch (76-mm) focal length, f/2.8 lens. The format is 1¼ inches x 1 inch on 35-mm film and the stellar coverage is a 24° cone with flats. Exposure time for the stellar camera is 1.5 seconds fixed. Film capacity for the stellar camera is 510 feet (155.4 metres) compared to the 1,500 feet (460 m) capacity for the metric camera. The critical interlock angle between the metric and stellar cameras is 96°. Correspondingly, the laser altimeter is mounted with transmission and receiving optical axes parallel to those of the metric camera.

https://history.nasa.gov/afj/simbaycam/ ... amera.html

Type 3401 Film (Stellar Camera Cassette, 35mm; Magazines G, H,
I, J, K, L, M, UU - 70mm):
Plus-X'Aerial Film is a panchromatic negative camera film with high
contrast, medium speed, high acutance, fine grain, and extended red
sensitivity. It is coated on a 2.5 mil Estar base with dyed gel
backing. On the Apollo 16 mission, this emulsion was used for
stellar mapping, topographic, and geological survey photography.

https://ntrs.nasa.gov/api/citations/197 ... 007872.pdf

3401 film (MBW).
a. Plus-X, medium-speed black and white, ASA 64 (with filter).
b. Resolution: 105 lines/mm for 1OOO:l test object contrast.
c. Use: terrain photography.

https://tothemoon.ser.asu.edu/files/apo ... ssions.pdf

[GaryN]

Searching 3401 I came by this Apollo 12 report:
Apollo 12 Multispectral photography experiment.
https://books.google.ca/books?id=JFct93 ... 01&f=false

Infrared was most useful in lunar imaging and still is, as it is for Mercury too. So little visible wavelength light out there that they don't even bother with filters, anything below the IR would constitute just very low level noise.

[Holger Isenberg]

But with the stellar camera only pointing away from the surface why would IR help there to see stars? The decision to have the stellar camera pointing 6 degrees above the lunar limb is strange as you pointed out. What other reasons than those we discussed here would speak against pointing it straight into the zenith, like stellar cameras in reconnaissance aircrafts would do?

The 3401 stellar camera film was most likely around 125 ISO only. Look up the Plus-X Kodak film as that additional term is used in the documents above. The Kodak 2401 film was the same except for the base material being of normal thickness.