How to build a mile wide mirror/dish

[arkain101]

:)

I had this very, um, wild idea and went with it for awhile. I was thinking about how small out telescope dishes are in comparison to the size of the EMR waves that are traveling through space.

 

So how do we build a giant mirror or radio dish without using much for materials. Where are the biggest dish shapes already made?

 

What if we were to use an array of nuclear weapons to build a dish miles across! Nuclear bombs are capable to melt the ground material into a glass like structure.

 

I imagine we wouldnt want to do it on earth, so maybe on the moon.

 

Would it be possible to find a giant crator on the moon, and blast it with a bunch of nuclear bombs and melt the crator into a giant mirror? or dish that can detect some kind of frequency.

 

There is no atmosphere so I am not sure if the energy from the bombs would be capable to melt the moon dust. Maybe on earth it could be possible..

 

:Glasses:

 

Thats as far as I can take it lol.. anyone have any thoughts?

[GAHD]

Well, if you have an array of dishes working in sync you can use them as if they were a single dish with a diameter equil to the distance between the two farthest dishes.

 

I'm pritty shure this method is allready in use.

[InfiniteNow]

It's an interesting thought, but part of the reason mirrors can pick up on such frequencies is because of how precise and accurate they are, often down to micron scales.

 

Blasting with nukes might produce objects with reflective qualities, but I wouldn't presume them to be of much use due to the high likelihood of irregularities.

 

Now, did you mean radio antennae like GAHD referred to? If so, he's right and this is already in use in New Mexico as the VLA.

[arkain101]

Oh just any kind of frequency that works best. Maybe one could fill it with mirror flakes creating all kinds of perfect reflections?

 

Now, did you mean radio antennae like GAHD referred to? If so, he's right and this is already in use in New Mexico as the VLA.

 

Yes I was aware of the many types, but I meant if we wanted to go HUGE, like 10 miles diameter or something nuts like that, and use almost no material.

 

We got some big ones, but, not like super advanced alien race versions :)

 

The likelyhood of such an idea working is pretty far fetched I agree.. since these devices need to quite precise. It was a funny thought, and maybe a good use for a bomb for once?

 

It doesnt have to be a telescope either. we could possibly build a death ray, or maybe shine it back on earth and make a free energy source. I dunno, think big :Glasses:

[Jay-qu]

I doubt it would work due to the shapes you would make. The purpose of having a large dish is that all the incoming rays are focused at one single point. Somehow I dont think a nuke could do this..

[pgrmdave]

Would it be possible to have dishes on the 'north pole' of the moon, and the North Pole of Earth and have an effective dish the size of the distance from the Earth to the Moon?

[InfiniteNow]

Yes, I believe this is possible, just not cheap, but you would likely need a third to triangulate...

[Jay-qu]

but you would likely need a third to triangulate...

perhaps on a satellite? expensive yes, but we would have one massive dish on our hands!

[CraigD]

Would it be possible to have dishes on the 'north pole' of the moon, and the North Pole of Earth and have an effective dish the size of the distance from the Earth to the Moon?

Pgrmdave appears to be proposing a Very Long Baseline Interferometer. These are very cool, though fairly rare instruments.

 

These days, an instrument like Dave describes would almost certainly use high precision clocks to encode time data on digital images, transmit them to Earth, and generate a synthetic high-resolution image.

 

The problem with putting the pieces of such instruments on planets and moons is that such places are rumbly places, with almost constant seismic activity that instruments of such precision would be bothered by. Also, atmospheric disturbances on the Earth-based mirror would be limiting.

 

The wiki article I linked mentions that astronomer Antoine Émile Henry Labeyrie is working on making a “hypertelescope” out of many free-flying spacecraft, using laser interferometry (which works really well outside of an atmosphere) to keep the individual mirror elements aligned. With such a scope, we could potentially see surface features on extra-solar planets.

 

I expect that a spacecraft-based approach like this will be preferred to planet/moon based ones.

 

A VLBI with a baseline of about a light-year (10^16 m) is the subject of an old, very speculative thread of mine, 5823.

 

PS: Why is this in strange claims? It involves some pretty imaginative telescope-making ideas, but it’s not what I’d call “strange”.

[Qfwfq]

Also, atmospheric disturbances on the Earth-based mirror would be limiting.

Which is the reason for Hubble. Earthbound efforts for increasing baseline make sense for longer wavelengths.

 

PS: Why is this in strange claims? It involves some pretty imaginative telescope-making ideas, but it’s not what I’d call strange”.

What's outlandish is to use a nuke. Try making a good rotation paraboloid and you'll find out why. The nuke would only do the initial digging but in a very unpredictable way, far cheaper to use quarrying techniques. I've seen pictures of a huge radiotelescope on a mountain top, hundreds of metres but I couldn't say exactly.

[TheBigDog]

Why not take something like Meteor Crater in Arizona as the starting point?

 

Bill

[CraigD]

Why not take something like Meteor Crater in Arizona as the starting point?

That’s essentially what Cornel did to make Arecibo, though on a smaller (“only” 305 m) scale.

 

Still, any single dish built on the surface of Earth, the Moon, or any other body, are dwarfs compared to proposed free-flying space “hypertelescopes”. They also can’t use that neat nulling interferometry trick that movable multi-dish systems can.

 

Though really huge baseline (> 10^10 m) telescopes seem a long way in the future, several space-based interferometers are scheduled for the next decade. These are exciting times for astronomy enthusiasts.

[InfiniteNow]

I don't recall exactly where, but I read once that if were ever truly to find gravitational waves, we'd need a gravitational interferometer that extended from the Earth to Jupiter... That's a spicy meatball... :cup:

[stamarama]

;)

 

(I imagine we wouldnt want to do it on earth, so maybe on the moon.)

 

Interesting thought, but I would imagine trying to sufficiently smooth out a big reflective dish on the moon would be very, uh, expensive.

 

I wonder if setting off a bunch of nukes on the moon would change it's orbit enough to affect tides here on earth.

[CraigD]

I wonder if setting off a bunch of nukes on the moon would change it's orbit enough to affect tides here on earth.

I think not.

 

Simply exploding a nuke on the surface of the moon isn’t going to much effect it’s motion – with nothing to push against, most of the energy will go into light and heat, making a big flash and heating the nearby lunar surface.

 

For the explosives to have the greatest effect on the moon’s velocity, they need to just barely eject a mass of lunar stuff – that is, accelerate it to greater than the moon’s escape velocity of 2380 m/s. A 1 mega-ton bomb – about the largest common size – produces about 4*10^15 J of energy. Doing the math,

[math]Energy = 0.5 * Mass_{ejected} * Velocity_{ejected}^2[/math]

[math]4.185e15 J = 0.5 * Mass_{ejected} * (2380 m/s)^2[/math]

[math]Mass_{ejected} = 1.4*10^9 kg[/math]

 

[math]Mass_{moon} * Velocity_{moon} = Mass_{ejected} * Velocity_{ejected}[/math]

[math]7.348e22 kg * Velocity_{moon} = 1.4*10^9 kg * 2380 m/s[/math]

[math]Velocity_{moon} = 4.53 *10^-11 m/s[/math]

 

So each nuke would change the moon’s speed by a tiny 0.0000000000453 m/s (compare to its orbital speed of about 1000 m/s). We’d run out of nukes before making a noticeable change in the moon’s orbit.

 

If you’re old enough, or watch TV series reruns, you might remember that the moon being propelled completely out of the solar system by accidental nuclear explosions was the foundation plot of Space: 1999. While this show had some pretty nifty models and special effects, it’s physics were terrible.

[Jay-qu]

In the new movie "Time machine" (not sure if the old movie and book had the same thing happen) they blew apart the moon with nukes that where supposed to be demolition for construction purposes :Waldo: they must have been some pretty strong nukes!

[stamarama]

Helluva post up there CraigD - nice analysis. I suppose that if getting whacked by meteors doesn't make the moon budge neither would a nuke. Besides, it would not be neccessary to make another hole on the moon since there's lots of craters up there already. And if one were able to line a crater with mirrors how would you aim the thing? A crater, it seems, is always pointed the same direction.

 

Stam