During the Apollo missions the astronauts of the Apollo 15,16,and 17 performed cislunar space EVAs to check on experiments located in an external bay but said they could see no stars: Transcript from A16:
219 00 33 Mattingly (EVA): It is that, all right. I don't even see any stars.
219 33 44 Duke (onboard): Okay. Can you see the sunsight?
219 33 46 Young (onboard): On this - on this event timer, Charlie, I got 04:16. Is that right?
219 33 50 Duke (onboard): That thing ain't working. No. Can you see the sunsight, Ken?
219 33 57 Mattingly (EVA): No, sir.
219 36 48 Mattingly (EVA): You get a good look at the Earth, Charlie?
219 36 49 Duke (onboard): Oh, yeah. And I spun around and looked at the Moon, too. The thing that impresses me, though, is how black it is, Ken. Yeah, is it black!
219 37 05 Mattingly (EVA): I'm really surprised I don't see any stars.
219 37 07 Young (onboard): Charlie's only said 25 times it's black out there.
219 37 11 Duke (onboard): What?
219 37 12 Young (onboard): You've only said that 25 times. (Laughter)
219 37 14 Duke (onboard): (Garble) see (garble) (laughter).
219 37 15 Young (onboard): It really must be black out there! (Laughter)
219 37 17 Duke (onboard): It's really black! (Laughter)
What possible reason is there for them not being able to see the stars?