Why not lunar communications satellites?
lardom
Posts: 1,659
I have developed Martian fever and I will rush home to watch streaming video of Martian rocks being vaporized.
My imagination has caused me to wonder why we don't have any communication satellites on the lunar surface? It's got to be tough to lock communications satellites into a stable position above the equator.
I think surface based devices would be simpler to locate and help manage the problem of 'space junk'. What am I missing?
My imagination has caused me to wonder why we don't have any communication satellites on the lunar surface? It's got to be tough to lock communications satellites into a stable position above the equator.
I think surface based devices would be simpler to locate and help manage the problem of 'space junk'. What am I missing?
Comments
http://en.wikipedia.org/wiki/Geostationary_orbit
The transmitters would need to be much more powerful.
The lunar based "satellite" would have sunlight only half the time.
Landing on the Moon is more difficult than parking in geostationary orbit.
The moon sets and rises, so you can only see it for half a day at a time.
The receiver dish would probably need to be 30 feet in diameter.
The goals would be to create a "Moon Craft" with an artificial Van Allen belt to protect against solar radiation (asteroids, etc...) and artificial gravity on the inside surface. The inside surface would have moon-dust-proof bubble enclosures for maintaining atmosphere and astronomic traveller comfort. Some of the shields would have solar panels on them and spin so that they are always facing the sun.
So the Moon Craft could serve as a communications base using an LED TV for all of earth's people rich or poor to watch Fox news. Could serve as a permanent viable space station, and then eventually a star ship. It would suck all of earth's resources, but that's ok because as the sun gets hotter in a billion years, we could launch the moon into a Mars orbit (and beyond). When the sun goes supernova, the Moon Craft could be launched into interstellar space with a sail toward another solar system that we can abuse.
And we could probably connect a few million Propellers to it so that it can achieve self-awareness .....
All the conversations would be loony
I see the point of having a geostationary satellite at 22k mi from the earth. I think there is a possible role for a lunar rover to transmit data that's not as time sensitive. I read that the orbiting satellites require fuel to correct for drift which means they have a limited lifetime. A solar powered lunar rover should have a relatively long lifetime.
We don't have much need for moon rocks but it could play a role as a mobile communication device.
Moon people. There's no one on the Moon to communicate with. :thumb:
They do this using the moon as a "passive repeater", it's called moon bounce.
Where there are several satellites in a line, some of those are for services like Dish TV. (One satellite dish can point to one direction and receive from several satellites at the same position.)
http://www.boeing.com/defense-space/space/bss/launch/980031_001.pdf
Did you say looney repeaters?
I emplore every one to read the Apollo lunar surface journal .. you will be in awe the deatails that happen .
Latency is higher.
Expense of deployment / low returns in general. The current plan to put a telescope at L2, for example, makes a lot more sense. Way more good science to get at from there than from around the moon.
High availability requires complexity compared to geosynchronous sats here. Would need complex hand-offs to be always on. Seems to me just putting stuff on the moon itself would be better in this respect. One or both of the Google founders has talked up using the moon as a data center. (Brin and Page) I like that idea more than I do a satellite system. Kind of cool too. If we were to ever really botch it here, the data would be there waiting for us to boot strap ourselves up to the point of being able to make use of it, assuming the engineering worked on those time scales. As an idea, it's pretty out there, but strangly plausible and compelling to me.
Moon is close enough to observe in high detail here, or from our orbiting sats. True, we don't get a good look at the dark side. Seems to me, that's a possible case for a lunar observation type satellite. Not sure what there is to look at though. In any case, it could just queue it's data, sending when it's possible to do.
I've discovered that geostationary sats require fuel to adjust for drift which means they have a limited lifetime. That could be an issue in a bad economy.
In another thread erco suggested a solar powered robot-base from which smaller more agile robots could recharge and get their marching orders. I think that's a great idea.
More specifically, a mobile robot base. IIRC the Sojourner rover used its stationary base as a relay station, but that meant it couldn't stray too far away from home base.
If I remember correctly, GPS satellites' time difference is sped up by the effects of less gravity and slowed down by their higher velocity. The velocity effect is much greater than the gravity. If these differences in time weren't accounted for then GPS fixes would drift by a few miles each day.
I would guess that the time dilation for the Moon is much, much smaller than for GPS satellites. Its velocity relative to Earth is quite slow. Since mass and velocity have opposite effects on time, and the Moon is slow (3,500 km/hr) yet 1/6 the mass of Earth, my gut says that they would come close to canceling each other out.
The rule of thumb is 2.5 S round trip.
Relativistic time dilation due to gravity is vanishingly small.
The signals travel at very very close to the speed of light.
So, distance variations are by far the most significant factor in the delay time.
(Ok, there is some delay in the transmitter and receiver but that should be fixed.)
(Also, though not called time dilation there are significant Doppler frequency shifts
caused by the motions of both the Moon and Earth, mostly the Earth.)
Duane J
An interesting wrinkle is that anything on the surface of the Moon is in the dark two weeks at a time, so the lunokhods had lids that could hinge shut and nuclear heat sources -- not power, but just to keep the electronics within temperature spec during the long cold lunar night.
I'm sure we'd be living on the moon at least by now in spite of those that put financial obstacles in the way.
Had all that money not been wasted on the cold war.
BTW NASA has a Lunar Reconnaissance Orbiter that has capabilities for an RF communications link for future lunar missions. It is pretty cool, gathering images and other data and sending It back to terrestrial receivers.
http://www.nasa.gov/mission_pages/LRO/main/index.html
As for Beau's question, it was asked in this physicsforums' thread, and although the thread doesn't contain the actual numeric answer it does contain the equations.
-Tor
Could almost touch it! If we speak metric here you should add another 3 zeros to the numbers. But I'm sure you knew that.
Boy, that would fill the night sky wouldn't it? ... yes and additional 3 zeros - lol