Is it possible to receive an echo from a radio signal in space?

Question

I'm looking for creative people with knowledge of radio waves and space flight to help me out.

I'm currently writing a screenplay about a spacecraft that is basically a radio antenna in space. The story I made up is about a radio telescope that was launched after the earth received something that resembled an alien transmission. To further investigate this signal, mankind sent a spacecraft to the end of our solar system where the reception would be optimal. After sixteen years of tracking this signal the message still isn't deciphered. The thing they overlooked was that the solar wind at the end of the heliosphere interrupted the transmission, which made it impossible to collect all the data.

It's only at the end of the movie that they suddenly discover that the transmission becomes audible when the spacecraft itself sends larger amounts of information back to earth. Suddenly it's clear that this "alien message" is some form of a long delayed echo. All this time they were receiving their own broadcast and listening to a reflection of themselves.

I did a lot of research, but I'm afraid I'm still a nobody on the issue of radio waves. So I'm not only looking for someone to disprove the whole idea, but it would be of great help if that someone could help me find a more scientifically correct version of the essentials (namely: a spacecraft receives an vague echo of their own radio transmissions and mistook it for an alien message).

There are a lot of things I'm uncertain about here:

• Is there any way that it would be logical to launch a radio telescope into space to receive a signal?

• Is it possible that the antenna of the spacecraft has to be adjusted all the time to "track" the signal? (something I felt was needed in the script)

• Can a radio message from aliens be very faint and distorted (for example by solar winds at the end of the heliosphere)?

• Can we in any plausible way confuse our own broadcast with a message from outer space? (I read about long delayed echoes and such...)

And most importantly:

• Would you buy this premise for a scifi-movie? If not: any thoughts on how you would reprocess the poetics of this idea in a more realistic way?

Answer 1

-Is there any way that it would be logical to launch a radio telescope into space to receive a signal?

We launch telescopes so we can "see" stuff we can't see from here. However, we can already observe radio waves from here using instruments like SETI. In most cases, no, we wouldn't launch for this.

There might be some exceptions, though! Maybe the sun has been active lately so our signals on Earth are hazy, but we can definitely tell that something's not right - so we send a satellite intended to do something else, maybe a flyby of another planet, out to get that signal before it's gone.

-Is it possible that the antenna of the spacecraft has to be adjusted all the time to "track" the signal? (something I felt was needed in the script)

Sure, this sounds reasonable. If the signal gets weaker, it adjusts its position or orientation, if it's stronger it follows. Sounds good, and a robot could do it.

-Can a radio message from aliens be very faint and distorted (for example by solar winds at the end of the heliosphere)?

As far as I know, the heliosphere doesn't have a huge impact on EM waves themselves, but it could mess up the recording instruments on the satellite during a solar storm.

-Can we in any plausible way confuse our own broadcast with a message from outer space? (I read about long delayed echoes and such...)

This is not likely - we will recognize that it's the way we send signals, and interpret it quickly - but if the signal is really so distorted or there are multiple signals it might be plausible for scientists not to recognize it at first.

And most importantly:

-Would you buy this premisse for a scifi-movie? If not: any thoughts on how you would reprocess the poetics of this idea in a more realistic way?

I would buy this, but keep in mind - the audience will expect to see aliens, or see more evidence of them, or something - and they may be disappointed by the ending when it turns out to be nothing.

You could solve this problem by connecting the story to a deeper meaning - that we don't truly know ourselves, or that we expect others to be the same as us and we need to open our minds, etc

In addition to that you could fast forward at the end to twenty years in the future, with the same main characters, and show a scene where they actually do detect something - or they find the first real evidence of alien life -etc

My apology if my English is somewhat incorrect and a very big thanks in advance to only consider responding!

Your English is great, and of course :)

Answer 2

This has already been done using the dish of the Arecibo Observatory. The dish has been used to send high powered radar signals to image the various planets and moons of the Solar System (for example, discovering the rotational period of Mercury. In terms of receiving extremely giant signals and processing them for information, one of the uses of the dish was to study the characteristics of Soviet radar systems by examining signals from Soviet radars reflected off the Moon!

Of course the inverse square law comes into play, the greater the distance of the object you want to image, the greater to drop-off of radiated power. The other issue is the speed of light. Imaging something the distance from the Earth to the Mars can take from 4 to 24 minutes, depending on the positions between the planets in their orbits around the sun.

In order to image distant object, you will need a very powerful beam emitter (to overcome the inverse square law), and an extremely large dish to have the collecting area to pick up the faint return pulses. Accurate pointing of the dish and the ability to hold it on target for several hours is also a requirement if the target is known or suspected to be several light hours distant (for example, looking for a target in the Kruiper belt from Earth).

Luckily, in space there is abundant energy to power the beam emitter, and very large singular sites can be built in zero g. A "virtual dish" consisting of dozens to hundreds of elements or more is also possible, working like an interferometer or the VLA dishes (featured in the book and movie Contact).

Obviously a large array of dishes is more robust and redundant than a single dish, however the user needs a very intricate control mechanism to coordinate large numbers of dishes.

So using radar or radio telescopes in space is entirely possible, both as active transmitting elements and as sensitive receivers. The more important issues in gathering and decoding signals from deep space is the ability to use sensitive filters and algorithms to detect faint signals among the noise of natural and other artificial signals propagating through space.