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The title says it all. Why did the astronauts leave a mirror but not a camera on the Moon? Also, is there a reason why the Hubble telescope was built to orbit the Earth and not built to be on the Moon?

Fred
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BЈовић
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    They did leave a camera on the moon. It took video of the LEM taking off. https://youtu.be/sj6a0Wrrh1g?t=169 – Organic Marble Jul 22 '21 at 15:37
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    @PcMan You had a nice answer. Why did you delete it? – David Hammen Jul 22 '21 at 17:12
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    Are you referring to the LLR retroreflectors? And I think the Hubble question should be a separate question. – Fred Larson Jul 22 '21 at 17:27
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    Your question about a telescope on the moon has an answer here – Carl Kevinson Jul 22 '21 at 19:52
  • future optical telescope on Moon and radio telescope – uhoh Jul 23 '21 at 00:07
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    I agree these are two unrelated questions and should not be posted in one Stack Exchange question. But even "Why... a mirror but not a camera?" should contain a little bit of research or explanation. It was an array of retroreflectors and was totally passive; you set it down, align the bubble level and Sun-compass and it just sits there and reflects laser pulses for the next fifty years until eventually too much lunar dust settles on it. – uhoh Jul 23 '21 at 00:23
  • For more on that see this summary. For a camera, what pictures could be taken that would have scientific value; that would produce new information? A "Why didn't they X?" question needs to at least explain why "X" will have some value that outweighs the problems. There were ALSEP systems that [transmitted data to Earth mostly until 1977 but some still transmitted after that! – uhoh Jul 23 '21 at 00:28
  • That data was valuable, but what would a camera be used to image that would produce useful data? – uhoh Jul 23 '21 at 00:29
  • @uhoh The ALSEP data were orders of magnitude smaller than would be the data from a simple camera, and many, many orders of magnitude smaller than would be the data from a useful telescope. – David Hammen Jul 23 '21 at 03:25
  • @DavidHammen 1) there's nothing in my comments that says otherwise, but 2) the ALSEP data transmissions were slow because the data was slow not the other way around; there's nothing about the technology of the era that wouldn't have allowed for slowly-scanned images to be sent had they decided they wanted to, after all, Mariners had been doing that for years from a lot farther. 3) I think what's most important to consider is that there wasn't really scientifically valuable photography work that would have justified the trouble. – uhoh Jul 23 '21 at 05:12

1 Answers1

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Why did the astronauts leave a mirror but not a camera on the Moon?

The Apollo astronauts did leave a camera on the Moon. They left several cameras on the Moon. Most of those cameras were absolutely worthless after being left behind. Every kilogram of camera taken back to Earth represented a kilogram of Moon rocks that could not be taken back to Earth.

It's important to remember how low tech things were in the late 1960s / early 1970s. All of the high resolution imagery was captured on film. The astronauts took the film back to Earth but left behind the very expensive Hasselblad cameras used to take those pictures. Even though those cameras were extremely expensive, Moon rocks were even more valuable.

There were some ridiculously low grade cameras (low grade by current standards) on the Apollo missions that used broadcast technology rather than film. The most successful was the video camera left behind by the Apollo 17 mission. It captured the liftoff of the ascent module and then it lasted another another 27 hours before being overcome by high temperatures at lunar noon. The resolution was 320 lines by 200 pixels. In contrast, a modern cellphone has a resolution of 4032 x 3024 pixels.

Regarding the mirrors, the astronauts did not leave mirrors behind. They left behind something much more valuable to science. What they behind on the surface of the Moon were retroreflectors. There's a huge difference between mirrors and retroreflectors. When you shine a light on a mirror at an oblique angle, the light will reflect off of the mirror at the same oblique angle -- in the other way. You won't see the reflection. When you shine a light on a retroreflector at an oblique angle, the light will be reflected back to you.

Cameras are active devices. Cameras need power to point the camera, to capture imagery, and to transmit the captured imagery back to Earth. The low resolution video camera on Apollo 17 lasted for 27 hours after the ascent module left the surface of the Moon.

In contrast, retroreflectors are completely passive devices. The Apollo astronauts simply needed to place the retroreflectors on the surface of the Moon, with no power supply needed. Those lunar retroreflectors are still functioning to this day, albeit at a highly degraded capacity. The combination of high temperature ranges, solar radiation unfiltered by an atmosphere, and lunar dust have taken a high toll on those retroreflectors. But they are still working.

David Hammen
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