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I assume this was a case of "we're sending a probe to the moon, what else can we put on it?" rather than "we want to put a telescope on the moon, let's send it
by privong 11y ago
I assume this was a case of "we're sending a probe to the moon, what else can we put on it?" rather than "we want to put a telescope on the moon, let's send it on a probe".
In principle having a telescope on the Moon gives you a longer continuous period of observation (and a longer period of inability to observe) for a single object, when compared to a telescope in geosynchronous orbit. Roughly speaking, the continuously obserable stretches for an object on the celestial equator would be ~28x longer for a telescope on the far side of the moon (of course, this particular telescope+probe is on the near side). This is just that the Moon takes ~28x longer to go around the Earth's center of mass, compared to a satellite in geosynchronous orbit.
Thinking about future applicatoins, if humans ever put a base on the Moon, a telescope on the surface would be far easier to maintain/upgrade than one in orbit. So, it is potentially worth testing small telescopes there now to determine their performance in that environment/location.
- paulmd 11y agoI agree with this (see: my post below). It's probably a case of "we're sending a probe, would you like to put a telescope on it or have nothing at all". I edited that I mean geosynchronous lunar orbit in particular. If the target is in the plane of the ecliptic then the period of observation is probably not a full 28 days - for roughly half of that period a target would be eclipsed by the moon, plus some change for the Earth. I have no idea the precise time this would be better or worse than the Earth given the Moon's lack of magnetosphere or atmosphere pushing the drag down and decreasing the orbital radius vs the smaller angular view of the moon and so on. It's still probably longer than the Earth's when comparing the radii equivalently, I'd think. It's 28x and change for sure, but with significant confounding factors. Counterpoint: the Moon has near-trivial gravity, so getting to lunar orbit isn't much of a problem. Assuming we had a moonbase, we could service lunar-orbital telescopes very easily. Remember, lunar orbit was attained by the Apollo LEM, compared to a S-V to get off the terrestrial surface. The rocket equation is a bitch, and strong gravity wells suck ass.
- nitrogen 11y agoWhat is a "geosynchronous lunar orbit"? I can't find that term on the interwebs and I'd like to know more. What body is being orbited, and at what distance and period?
- privong 11y agoI think they mean a lunar orbit which is synchronized with the Moon's rotational period[0]. The Hill radius[1] for the Earth-Moon system is only 24,000 km. The orbital period for a satellite at this distance from the moon should be about 90 minutes. Increasing the distance to increase the period would put the object outside the Hill Radius, causing the satellite to eventually go into orbit around the Earth, rather than the Moon. So, it seems that lunar synchronous orbits do not exist, except at some lagrange stability points of the Earth-Moon system. [0] https://en.wikipedia.org/wiki/Geosynchronous_orbit#Other_synchronous_orbits https://en.wikipedia.org/wiki/Geosynchronous_orbit#Other_syn... [1] https://en.wikipedia.org/wiki/Hill_sphere https://en.wikipedia.org/wiki/Hill_sphere