Given the choice, do ISS astronauts prefer to schedule EVA tasks on the “day light” side of the ISS, the “shadow" side of the ISS or in the shadow of Earth’s night side?

I suspect the intense, direct solar illumination of full sunlight would produce very deep shadows, while reflected Earthlight would produce very diffuse, even, (dare I say, “pleasant”?) lighting.

I would guess that harsh artificial lighting in Earth’s night time shadow would make tasks more challenging.

enter image description here Day light Gemini

enter image description here

Shadow side ISS

enter image description here Earth nightside

The same question of lighting is likely even more applicable to robotic operations.

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    $\begingroup$ The first photo is actually Ed White on Gemini 4 in 1965, the first U.S. spacewalk. You can even make out the capsule reflected in his visor if you zoom in. Of course that doesn't change the fact that it's a representation of a daylight EVA, I just wanted to point out the historical significance of the photo. $\endgroup$ Commented Nov 15, 2023 at 0:38
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    $\begingroup$ @StevePemberton ... good catch ! $\endgroup$
    – Woody
    Commented Nov 15, 2023 at 1:07
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    $\begingroup$ @StevePemberton ... edited to conform with your comment. $\endgroup$
    – Woody
    Commented Nov 15, 2023 at 2:53

2 Answers 2


---Note that this answer was invalidated by an edit to the question after the answer was posted---

Frame challenge: Any such "preference" for EVA scheduling would be irrelevant, because most ISS EVAs take 6-8 hours or more. (Due to the extensive prep time required for any EVA, tasks are accumulated until they fill a full work day. No one's popping out to tighten a screw and then coming right back in).

What with the ISS taking ~90 minutes to complete an orbit, that means they fit in lots of both day and night on every EVA.

This page from the flight plan of STS-127 (an ISS assembly mission) shows EVA-1 lasting over 6 hours with 7+ sunrise/sunsets during the EVA.

Reference STS-127 Flight Plan - (Highlighting mine) enter image description here

  • $\begingroup$ Do the astronauts have a preference for lighting conditions? If there are multiple "screws to be tightened" in different locations on ISS, tasks could be scheduled so that lighting is optimal, since orbits provide lots of day and night. $\endgroup$
    – Woody
    Commented Nov 15, 2023 at 1:06
  • $\begingroup$ Again, preference irrelevant, if lighting is available at night (often it wasn't space.stackexchange.com/a/17175/6944) they work, otherwise they wait for the sun. EVA time is precious. $\endgroup$ Commented Nov 15, 2023 at 1:08
  • $\begingroup$ Interesting the variability in "post sleep" time slots on that schedule. Is that a euphemism for "unstructured self time"? $\endgroup$
    – Woody
    Commented Nov 15, 2023 at 1:15
  • $\begingroup$ @Woody and/or catch-up time, housekeeping, eating breakfast, etc. $\endgroup$ Commented Nov 15, 2023 at 1:16
  • $\begingroup$ And I notice meal scheduling is inconsistent. I suppose meals happen during scheduled "prebreathe time", "post sleep", etc? I wouldn't look forward to a 6 hour EVA on an empty stomach. $\endgroup$
    – Woody
    Commented Nov 15, 2023 at 1:19

I can't answer the question from the astronaut's perspective, but astronaut preference for working in sunlight/shadow doesn't really matter anyway.

EVAs are scheduled months in advance to complete critical station repairs or equipment installation. The timelines are developed by the EVA planning team and generally are broken down into a series of tasks based on priority. The tasks are location dependent, therefore they just have to deal with the lighting conditions at the work site.

Every little detail is planned out in advance, including the route and handholds the crew members will use when getting to the work site. Since the duration of an EVA is generally between 6-8 hours, the crew members will experience between 4-5 complete day/night cycles during the EVA.

That being said, NASA is aware that direct sunlight in the astronaut's FOV is a problem. They have an evaluation of issues for the Artemis missions here: https://ntrs.nasa.gov/api/citations/20230006313/downloads/IAASS%202023%20Paper_Final_24apr23.pdf


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