Lunar Observatories and Orbital Mechanics

[Superewza]

...and probably one other thing that i've just completely forgotten.

Basically i've had a few questions on my mind that have been bugging me for a bit, thought i might as well ask:

1) Lunar Observatories/Telescopes:

What would be the advantages and disadvantages to a Lunar Telescope as opposed to a Space Telescope (ala Hubble/JWST)? Advantages seem to be sparse (only one i can think of it being easier to deal with excess heat), so lets consider it a theoretical study.

For starters, what axis(es?) would the stars move on? They would appear to spin around the poles, as they do on Earth, but surely only about 30 times as slow? How would the orbit around the Earth effect them? And the pair's orbit around the sun?

Then you might say that the ability to use it only every other month (while it's in darkness) would make it hugely inconvenient, but would that be the case. At first i thought you could put it near the North Pole, which is perpetually in darkness - but then i realized that you would only be able to view half (less than?) of the sky in that position. So then i thought 'why can't it image when it's lunar daytime'? As long as the mirror, lens or whatever is in shadow then it shouldn't matter, since while the area around it would be a lot brighter because of it - like it is on Earth - the lack of atmosphere would mean that the light had nothing to bounce off and then back into the telescope. So you could image as long as you had a shade, would that be correct?

Lastly, a bit of blue sky thinking Could you use the craters to your advantage. How perfect a parabola do they get? Would it be possible to simply clear one of dust then cover it with mirrors? Of course, this wouldn't move - but then how does the Arecibo Observatory aim? You could use it as a sort of portabowl-esque mount - fill it with ball bearings and put a mirror of the same shape in it

2) Orbital Mechanics:

I understand the basics of how you change your orbit in terms of altitude and circularization (fire forwards at the apogee to raise, backwards at the perigee to lower), but i've never been able to get my head around how you would (or if it would be possible to) change it in terms of left/right (port/starboard?).

For example, say i launched from my back yard, 55° North, 1.5° West at an angle of 135° (South East), putting me in an orbit something like this (yes, yes i know - but i couldn't find any way of freely rotating shapes and after half an hour i gave up ):

And i wanted to meet up with the ISS, which is in an orbit similar to this:

How would i do it? Assuming, of course, that the fuel we're using here is fairy dust

And while we're at it - is it apogee and perigee or apoapsis and periapsis? Or anything else, i have heard helions mentioned when talking about the sun, why so many different words for the same thing?

Oh, and i just remembered the third - radio waves. Simple one this, i should remember from GCSE Physics, but what wavelength(s) do they use to penetrate the Earth's atmosphere for communicating with spacecraft and satellites? Because i've heard of people using the 10m band, but i thought that something that long had a tendency to bounce of the atmosphere (known as skip)...

Thanks for reading the ramblings of a bored 16 year old, if you feel like you want to reply then that would be grand

PS: I might ad more questions as and when i remember them

[Space Bat]

Getting access to Area 51 to install a telescope where they faked the moon landings would be somewhat tricky

In all seriousness - although would have some serious advantages - can't see how it would improve on Hubble - and the cost of such a venture would be Astronomic *Groan*

It would make more sense to make larger versions of Hubble - as unmanned launches are far and a way cheaper than the costs to construct something on the moon.

Money was no object in the race to the moon...its been done so costs of going again can't be justified....let alone to build a scope on it

Good Idea though.

[JulianO]

I think the advantages of a moon based site are quite significant. Yes it would be very expensive, but it would be hugely beneficial.

I'd say the advantages are:

• Size - you can build something much bigger on the moon. You can anchor it to the bedrock. Getting an 80m mirror into a satellite is very difficult, because you have to basically send it up in one go. Complex folding which might not unfold and so on. Look how complex the James Webb is. Aligning mirrors with nothing solid to fix them to would very tricky. It could be done I'm sure, but we know how to construct things under gravity. Whereas building something on the moon could be done stage by stage as it is on earth, although more complex.
  
• All the benefits of being outside the atmosphere - access to all wavebands, not light pollution, no moving atmosphere.
  
• Another issue with satellites in orbit is that they are subject to hot and cold periods which distort them and have to be compensated for. I know hubble shakes and wobbles as it moves from earths shadow to sunlight and vice versa. On the moon you could have a conventional dome.
  
• If you put the satellite outside the orbit somewhere stable, like the Webb is going to be, it means it can't be serviced, upgraded or fixed. On the moon you can service it, and probably have a team maintaining it. There are a few unmanned robot telescopes now working on earth, but most of them have some servicing at some point. The Hubble needed to be fixed, and has been serviced a few times. The Webb is on its own after launch.
  
• Radio silence on the far side of the moon would be ideal.
  

It needs really to have going to the moon be a little more routine than it is right now however.

[Superewza]

Building on the vast success of this thread (), i'd like to add another question - to do with the position of a satellite in orbit, and what it's relative to. Logically, i would think that if you launch into orbit and the Earth is, say, to your left (assuming it's not a spin-stabilized satellite ) then the Earth will be to your left for the entirety of the orbit. I did consider an alternative however, that the satellite would stay in the same orientation relative to how it was when it was released from the launch vehicle, but i think the first is correct since the Earth is effectively bending it's path. Always best to make sure though

Cheers and thanks for the replies as well you two