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Time for humans to start thinking about moving says Hawking

For many years humans have dreamed of one day colonizing other planets and moons.  Although research would be an important reason for the foreign bases, could the survival of the human race depend on whether or not we can colonize other planets?  World-renowned astrophysicist Stephen Hawking recently said that humans need to colonize a planet or moon because the Earth might face destruction -- A man made disaster -- global warming being a good example -- or natural disaster could potentially destroy the planet. 

Although he believes humans can colonize the moon within 20 years, and establish a sufficient base on Mars within 40 years, humans "won't find anywhere as nice as Earth," unless we visit another solar system.  The moon looks to be like an ideal place for a potential new colony.  Not only does it appear to have everything needed to sustain humans, ice has also been found at its poles.

Nations have been thinking about colonizing other planets for years.  DailyTech earlier reported that NASA is working towards a permanent moon base that would be a stepping stone to allow astronauts to explore Mars firsthand.  Swedish researchers are also studying different ways to have a self-sustaining colony on the moon.


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RE: moon base
By masher2 (blog) on 6/15/2006 2:48:24 PM , Rating: 2
quote:
> "actually that wouldnt work cause you would have the moon in the way to get any signal back to the earth. so since you would already need more then 1 to make it work, why not just put 4 in place for complete 360 coverage?"


You've forgotten elementary astrodynamics. The moon is tidal-locked with the earth...meaning it only rotates once every 27.something days. Meaning despite its lower mass, a synchronous satellite would be at an height of 85,000 km or so (assuming I did the math right). Such an orbit certainly wouldn't be stable on the Earthside, due to Terran gravitational perturbations. On the nightside, however, it would not only be stable, but would be far enough from the moon so that it could transmit directly to Earth.

To provide GPS-level satellite coverage of the entire lunar surface, you therefore couldn't use just four synchronous satellites. You'd need a much larger network, based much lower...probably on "orange-slice" polar orbits.


RE: moon base
By kattanna on 6/15/2006 4:29:06 PM , Rating: 2
quote:
but would be far enough from the moon so that it could transmit directly to Earth


actually no.

a satellite directly opposite the earth 85km out from the moon by the time the signal reaches the moon the signal already has a diameter of 3.4km, the diameter of the moon.

now it needs to travel another 384km to the earth. Thats 4.5 times the distance it as already traveled making the signal diameter by the time it reaches earth 15.3km. But since the earth only has a diameter of 12.7km, the moon is still totaly blocking the signal.

now it could get a signal to/from a earth geostationary sat, but you would need to send up 3 of those that are designed to talk inbound and outbound. all the ones up there now are all earth facing, and you would need 3 to have at least 1 sat "visible" to the moon sat at any given time.

so, we are back to the need for more then 1 comm sat, and with earth geostationary orbit getting full, it makes more sense to have them orbiting the moon itself. that allows for lower power comm systems in orbit, and on the ground, and for local "real time" transmissions.


RE: moon base
By masher2 (blog) on 6/15/2006 6:33:20 PM , Rating: 2
> " But since the earth only has a diameter of 12.7km, the moon is still totaly blocking the signal."

Kattana, I applaud you. You solved that problem in a very elegant manner. You're still wrong...but only because your premise was incorrect.

Yes, if you base the satellite directly on the earth-moon axis, it's going to be occulted no matter at what distance you base it. However, a single satellite-- if offset a few degrees from this baseline, can not only cover the entire lunar darkside (sans a small fringe due to libration), but still have line of sight to the earth. Draw a picture...it'll become obvious.


RE: moon base
By kattanna on 6/16/2006 9:35:43 AM , Rating: 2
LOL the one here who is missing the point my friend, is you.

i'm talking about total coverage 360 degrees, north, east, south, west coverage.

your talking about partial coverage.

when you want to talk about the same thing i am, let me know.



RE: moon base
By masher2 (blog) on 6/16/2006 9:49:17 AM , Rating: 2
Now you're just being silly. The libration fringe is very small...the approach I detailed covers some 96% of the lunar surface. With ONE satellite. How long before more than 96% of the lunar surface is occupied? Ten thousand years?

Fact is, for the forseable future, there would be NOTHING whatsoever Darkside, save for a research outpost. Easily coverage with one satellite. All the industrial and commercial activity would be done Nearside, where they need ZERO lunar satellite coverage...they can use Terran ones directly.

Now, do you have any idea how many orange-slice orbiters you'd need to provide full coverage of the lunar surface? For stable orbits, they have to be based much lower than they would be on Earth, which means much less coverage. At a bare minimum, you're talking a 48-satellite constellation...probably more.

Your notion of "total coverage" with just four satellites is wholly unworkable. As I explained...a Nearside synchronous orbit isn't stable. And the idea we'd want to launch several dozen satellites for no gain whatsoever is even less tenable.


RE: moon base
By kattanna on 6/16/2006 12:25:03 PM , Rating: 2
quote:
since we have such a short sighted vision we will object to the larger upfront cost and will instead spend massively more in the long run to get things setup as cheaply upfront as possible


thank you for continuing to prove my original closing point.

does any starting moon base NEED such a complete setup..no, but thats not my point, thats yours.

im talking about designing such a system that would provide such services without relying upon anything earth based/orbiting to make it function. why? because we will be going to other bodies where trying to use comm resources from earth get to be very impractical/impossible.

also people arent the only ones that will need to be using the comm system. robotic rovers will be roaming and exploring for "interesting" geological areas, that will then want to be followed up by actual people.

Having a true "global" independant comm system for any body we choose to get serious about going to, aka lots of rovers..a settlement..etc not just a pop shot for some intriging study like Galileo, has many positives. it allows for local real-time traffic, usefull only really for people, but if they are there..then its usefull. it also allows for much more science to be done and returned. done by the fact that they can count on not having to spend weight/power/space on comm resources that need to "phone home" like they do now. but instead can count on sending the info up to an orbiting sat, that then can send the info off to earth at MUCH higher bandwidths then is now possible, and therefore allowing more science data to be returned. another plus to that is that once a comm system is in place, all following missions can be done cheaper to boot. Also such a system allows for continous contact of all craft on the surface and in orbit at all times. great for when new craft are coming into that zone.

lets treat the moon as if it wasnt so close, and design systems accordingly that way when we do parts 2 & 3 of "moon, mars & beyond"...we have designed and build systems and know how best to implement them already. having had time to get some of the bugs worked out here "locally" where they are easier and faster to correct.

THATS..been my point.

Does such a complete system need to be built before anything else..no. of course it will be built in stages, but each piece should be designed to be part of the overall design. not some happy chance of luck.


RE: moon base
By masher2 (blog) on 6/16/2006 12:36:49 PM , Rating: 2
> "does any starting moon base NEED such a complete setup..no, but thats not my point"

Your remarks were, and I quote, "I, for one, can't wait till we have a viable moon base...but before we can do it...we need some other items in place first...once in place then a small network of GPS/comm sats need to be but into orbit around the moon

Emphasis mine. Now you're saying something totally different. It seems clear you've realized your error, though, so lets put that behind us. Let's also forget the errors that we can't provide full coverage of the moon via synchronous satellites, and that we *can* communicate with the earth via a Darkside satellite.

That just leaves this final point of yours:

lets treat the moon as if it wasnt so close, and design systems accordingly that way when we do parts 2 & 3 of "moon, mars & beyond"...we have designed and build systems and know how best to implement them already

But we already know how to build such systems. We've done so on the Earth. Building non-needed satellites and launching them into lunar orbit doesn't give us any additional experience, to putting such a system on Mars or elsewhere. Its just a waste of money. Far better to spend those dollars designing more efficient, reliable satellites on EARTH...then launch them only when they're actually needed.





RE: moon base
By kattanna on 6/16/2006 2:46:57 PM , Rating: 2
hmmm..why the fixation on synchronous orbits? we wouldnt need them to be in the exact same spot at all times, just at least one within line of sight to make a comm connection. Dont need synchronous orbits for that, they only need to be far enough away to see their "half" of the body, a few thousand km for the moon.

as for "need", yes we would need at least part of the system to be in place first before we start sending people. 1 sat for total

ecliptical orbitable coverage and rotating surface areas, 2 for decent global surface coverage and polar orbital coverage, 3 for maximum

surface coverage, and a 4th for redundancy for when one fails.

so 2 to start would be optimal so you have orbital and surface coverage, and in case one fails you still have ecliptical orbit coverage, till the remaining ones can be placed.


no..we in fact do not have any such system of its kind built and operating now. most of the sats in earth orbit are 2 way systems

only..ground to sat to ground systems. some have 3 ways systems..ground to sat to ground with ability to go also from sat to sat. But

what we need is a 4 way system..ground to sat to ground/ sat to sat/ and sat to earth. about the closet we have now is the mars orbitor

which can relay back..but..thats far from a "global" working system.



RE: moon base
By masher2 (blog) on 6/16/2006 3:51:30 PM , Rating: 2
> "hmmm..why the fixation on synchronous orbits?"

For the same reason they're so useful on earth. You can cover a larger area with a smaller number of satellites. Furthermore, a nonsychronous satellite requires the ground station to track a rapidly moving body...or else to broadcast (and receive) a far more powerful signal.

Certainly still possible, but you're talking about a much larger number of much higher power satellites. Much costlier. And again-- whats the point? You've already admitted such a system isn't needed on the moon...just to prove we can do it for some other planet?

> "Dont need synchronous orbits for that, they only need to be far enough away to see their "half" of the body"

I've explained this earlier. High lunar orbits are not stable, unless they're darkside only (which means they must be synchronous). The mass of the earth is 80 times that of the moon, meaning Terran gravity causes severe perturbations.

An orbit only a thousand or two km high would be stable, but that provides very little coverage. Remember, the moon is not perfectly smooth. Even on Earth, a satellite 35,000 km up is often occluded by terrain. Furthermore, the lower a satellite is, the faster it moves...complicating tracking tremendously.

> "yes we would need at least part of the system to be in place first before we start sending people"

No, you need no satellite whatsoever for a Nearside colony. They communicate directly with Earth.

> "2 for decent global surface coverage and polar orbital coverage, 3 for maximum"

Heh, no. Honestly, look up some basic orbital dynamics. Failing that, look up how many satellites the earth's GPS constellation requires (24, plus a few spares) which ARE at Geosynch height, and STILL don't provide perfect 100% global coverage, due to terrain occlusion. Hell, Sirius uses 3 satellites (also at geosynch height, though with a elliptical plane) just to cover the North American continent.


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