MadSci Network: Astronomy |
Hi, Kevin,
Without an atmosphere for protection, conditions in space can get pretty
harsh. The temperature varies a lot from shade to sunlight, and cosmic
rays represent a pretty strong radiation environment. The spacecraft also
shakes violently during launch, and has limited resources, such as
electrical power, and limited amount of room for instruments. If you just
bought a high-quality digital camera at the store and tried to operate it
in space, it would probably fail for one of several reasons
Break due to the severe vibrations experienced during the launch,
Freeze up when it got too cold (in the shade),
Fail when it got too hot (in the sunlight),
Have problems with cloudy lenses or failed electronics due to the radiation environment,
Weigh more than necessary (which makes it expensive to launch), or
Use more power than the limited amount available on a spacecraft.
In addition to all of these potential problems, remember that the camera has to operate on its own for several years without failing. If you buy a good quality camera at the store, it comes with a warranty. Perhaps a few percent of the cameras have a problem, but if anything goes wrong, you can get it fixed, and the warranty covers the cost so you're not too inconvenienced. If your camera is several hundred million miles away, the warranty doesn't help much, and anything that breaks is pretty hard to fix. When you also consider that a mission costing several hundred million dollars could be badly compromised if the camera were to fail, you realize you need a very reliable camera. As with anything else, 100% reliability is impossible, and extreme reliability is very expensive.
The specific camera you were asking about was made by Malin Space Science Systems, and their website gives some information about it. I don't know why that particular camera was designed for monochrome, but often the reason is that you can get better performance in one area (resolution, size, power, etc.) by sacrificing in another area, such as color. The camera design is normally based on what kind of science you want to do with it, and color isn't always the most important thing.
Your other question ("At what point do images created this way not reflect reality?") is very interesting. Clearly, these and other "reconstructed" images represent some kind of reality, but how close is it to what you'd see with your own eyes if you were really there? Even the best camera doesn't behave the same as your eyes. Your eyes are sensitive to a particular range of wavelengths of light. (There are lots of descriptions of human vision on the Web. ) A camera typically is sensitive to fewer colors, and the filters used will necessarily not be the same as the response of a human eye. Most of the time, the camera is actually also sensitive to some wavelengths which the human eye cannot even see. We can try to adjust the images to compensate for differences between the camera and human eye. Furthermore, the reason for taking pictures from space is usually not just to get a pretty picture, but to try to help answer a scientific question. Often the best solution for solving the scientific puzzle is to combine the colors in a way which is very different from what a human eye would do. These pictures certainly reflect one aspect of reality, but no picture is ever enough to reflect the full reality of the object.
[A philospher might also ask why you consider what our eyes see to be "reality." Moderator]
Thanks for the interesting question.
-Steve Levin
Try the links in the MadSci Library for more information on Astronomy.