I'm not sure that there is a way to engineer something that would "prevent it being weaponised".

Nation states are likely prohibited by treaty from putting one in orbit, not sure why a private company should be allowed to do so.

In terms of using it for lunar colonisation the same problems arise but there's no treaties preventing it.

In terms of environmental benefit... all the power you lose forcing the microwave transmission through the atmosphere is energy that would not have been added to the Earth's budget otherwise. Attenuation in the air is drastically increased by water content, so cloudy / rainy areas are not great for receiving stations.

It's not a bad idea in principle and it's well within our capabilities from an engineering perspective but there is no world leader / private individual / council of wise pacifists I would trust with control.

There is a small advantage for solar collectors in geosynchronous orbit in terms of time in sunlight.

There is a small disadvantage in the sense that a high power microwave transmitter in geosych orbit can be used as a weapon of mass destruction.

A significantly shorter commute time as well.

OK, so you want to receive a signal from alpha centauri.

There is a tiny red shift for light between here and there due to relative motion of the stars.

The sender would need a pretty powerful laser with a wavelength known to the receiver. They point the laser at the earth and send the message. In astronomical terms, this is not a long distance, the red shift is minimal and the receiver knows the red shift involved and the transmission wavelength of the light. The transmission is also consists of billions of photons all in the same wavelength. Sneding signals over interstellar distances would also involve repeating the message over the course of days with error correction bits.

It would not be a problem to filter out background noise over that range and correct for the minimal red shift.

As long as you are using a highly directional transmitter and know where your receiver is going to be when the signal should arrive, this works fine for distances of many thousands of lightyears. The transmitter power has to be increased to overcome signal attenuation over the distance. The next big problem would be stuff getting in the way. That's unlikely to be a problem under ranges of 100 light years, maybe up to thousands because space is big and mostly empty.

When a signal is redshifted, the redshift will only become problematic for reception if the transmitter is accelerating away from the receiver at a (currently) unachievable rate or varying rate. (as long as your receiving antenna is capable of picking up the redshifted wavelength of the signal).

Varying rate / high acceleration could be factored in to reception with a wide enough spectrum receiving array.

A more significant problem is signal attentuation over the large distance, where the signal strength at the receiver is around the same magnitude of the background noise picked up.

Red shift is "not that strong" for the velocities we've achieved so far.

An admirable sentiment. Would you like to propose this to Vladimir Putin or Xi Jinping?

Well it's an admirable sentiment but we cannot permit our enemies to control space resources because we want those resources.

You sparked my curiosity.

This is what I found.

https://www.reddit.com/r/space/comments/1r22wr/will_the_mars_rover_go_anywhere_near_olympus_mons/

An experimental test was proposed.

Let's see whether the experimental results match the new theory.

Seems like the dataset for the experiment may exist in the cosmic background radiation observations we already have.

The rovers on mars are quite far from olympus mons. Pretty sure it would take a really long time to get there, like years or decades.

It's technically possible to send a new rover to climb that mountain but the scientific justification for that expenditure is lacking.

Landing on an inclined surface is more difficult / dangerous than a nice flat level area, so the risk may also be a problem.

Mars has killed a few probes. Bear in mind that if anything goes wrong with the multimillion dollar rover at any stage it can lead to politicians cutting funding for future exploration.

While it's a spectacular thing, it's not diverse in its' geology or at least not as diverse as the sites selected for robot exploration.

Probably best to start with what you think these terms describe in terms of observed phenomena.

Bacteria would constitute life.

Having bodies of water does not.

A 15% to 30% oxygen atmospheric content would be a pretty good indicator of some sort of life.

good point, well made.

RASER sounds pretty cool too.

Tricky and energy intensive to produce.

Laser light would be more efficient but you would have to know where to point the laser.

Probably something that would need to be "negotiated" with radio communication first to convey specifics of wavelength though.

>How close would an Earth-like planet need to be to detect our signals, and what signals would be easiest to detect at this distance?

The wave front of our radio broadcasts are around 100 light years away. TV broadcasts are just radio signals. With a large enough radio telescope, someone could in principle detect those signals. The signal attenuation over that distance would make it very difficult to seperate signal from background noise.

>How does this distance compare to the observable universe, and what does this mean for the search for extraterrestrial life?

100 light years / 13.8 billion light years. Identifying a technosignature would answer the "are we alone in the universe" question but the further away the origin of the signal, the less chance of engaging in meaninfgul dialogue with any discovered species.

>Is it theoretically possible that there are signals from developed civilizations that we haven't detected yet because it hasn't reached us here on earth, because of speed of light limitations?

Yes. There also may be centuries millenia worth of signals we didn't detect because we weren't even capable of looking for them more than 100 years ago.

Did you read the last line of my post? The one in brackets?

The speed limit is the speed of light.

With that in mind the universe is infinite because the "edge", if there is such a thing, is moving away from us faster than that.

If you enjoy being anxious about things you can't prevent or even detect then how's this:

It's possible that our local presentation of the universe is just local, somewhere out there are other "big bangs" which occupy the same spacetime but at immense distances and their "edges" are approaching us at the speed of light.

We wouldn't even see them coming. We'd just be hit with an overwhelming amount of radiation before we know it.

(this is likely "not even wrong" in how wrong it is, but I do like a cheery thought)

It may be better / cheaper to do some other form of geoengineering.

Dig a really big hole in the middle of a desert, cover it with a highly reflective geodesic dome / tent and use canals to funnel "surplus" seawater into it. Use solar power to refrigerate the inside of the tent and harvest the (slightly) desalinated water for something useful.

Cover all the deserts with solar panels... cheaper.

Launch a big venetian blind in the earth sun lagrange point to reduce insolation by a percent or two.

We may need that water at some point, throwing it away seems silly.

So is that 40 mega-RiceKrispies or is the scale logarithmic?

Melted concrete....

Yes, definitely NASA's fault, not the contractor who provided the concrete. /s

It's not irrational to fear an all devouring, insatiable gravitational pit.

Unless you are safely thousands of lightyears from any of them.

I prefer that someone makes space exploration / travel a reality than not.

I'm fairly convinced that Mr Musk is going through some sort of mid life crisis or breakdown. The rockets still fly though.

He's said he wants to die on Mars. If he can manage that trick then people will live on Mars. If only to provide funeral services.

The twitter nonsense won't impact SpaceX very much because SpaceX is providing services to the US government.

"colonisation", nope....

"expansion" ?