This is the Solar System Mapping Project control room.
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Voyager spacecraft interstellar record,1977 |
Bracewell , Von Neuman and others have suggested the possibility that alien civilizations might send space probes to explore the galaxy, much as we are just learning to do ourselves. Duncan Lunan has even suggested that the presence of such a probe in our solar system is a plausible explanation for the mystery of Long Delayed Echoes, known as LDEs. Attempting contact with such a probe seems to be a reasonable alternative to seeking ET in deep space and requires solution of far simpler technical problems.
To facilitate the search for a such a probe,I would like to suggest the possibility of the ..
Imagine if you will, a network of amateur radio receivers located around the Earth. For simplicity we can imagine that each antenna is pointed in a fixed direction and since it is not possible to know the nature of the anticipated signal we can further imagine that the frequencies and signal detection schemes have been left to the discretion of individual experimenters.The simplest scheme that comes to my mind is the detection of returned TV signals, which I will discuss in greater detail below.
Ideally, the antennas should "nod" up and down on a daily cycle to follow the plane of the ecliptic as the Earth turns, but for those unprepared to do this, a simple broad beam antenna would be a reasonable compromise.
In the system just described, each antenna would scan the entire solar system every 24 hrs, and over a six month period would do so from opposite sides of the Earths orbit, a baseline of roughly 200,000,000 miles.
It has been suggested that an interstellar probe in our solar system might try to get our attention by returning our own signals to us.Since TV signals are among the most powerful and numerous on Earth they would be obvious candidates for such a scenario.
If we were looking for returned TV signals the receiver need only be a TV and the antenna an old "bowtie" type TV antenna at the focus of a 10 ft satellite dish. The old style dishes are pretty much free for the asking these days. As for signal detection we need only run a tap from the sync seperator stage of the TV. The presence of a sync signal is a dead giveaway that a TV signal is present.A FFT examining the output of a more sophisticated receiver would produce the same result.
If we use the sync signal to trigger a VCR to record the signal and notify a computer to record the time, the system is ready to go.It is also possible to record an entire 12 or 24 hr run of the system and process the data at a later time. In either case the time of arrival is determined.
The information gathered in this fashion is useful in the following ways.
It is worth mentioning at this point that if such a probe actually exists and is presently responding in precisely this fashion it would remain undetected for the simple reason that no one is looking. In fact anyone accidently receiving such a signal would almost certainly consider it interference and take steps to eliminate it!
A larger dish and a good preamp would certainly improve the signal strength and multiple receivers reporting the same signal at the same time from widely seperated locations would greatly reduce the false alarm problem.
Once operational, this system can and should be improved upon. Getting several such systems up and running in a coordinated search is a worthwhile goal.
A few points before moving on
The system as described here suffers from severe limiations, but once functional it can be improved upon.
My suggestion that the system be used to look for returned TV signals is intended to make this project feasable for inexperienced amateurs on a tight budget.Too many interested people are already shut out of SETI because of financial limitations and lack of technical expertise.
Searching for returned commercial broadcast signals a perfectly reasonable thing to consider, but it is not the only possibility and it certainly is not the best. We are only guessing that such a probe might return our own broadcast signals, in fact it could transmit almost anything. Any of the currently fashionable SETI schemes could be applied here to great advantage. Microwave, UHF, VHF, optical, and infrared are all worth considering.
Modes of communications that would never work at interstellar distances become perfectly feasable for "local" transmissions. The possibilities are wide open. There is plenty of room for innovation.
I am in the process of constructing the system described here and will update this page as progress is made.
This is the Solar System Mapping Project control room.
Please notice the TV and VCR on the left. The output of the TV,(the low frequency video and audio) is fed to the sound card of the computer on the desk. Several FFT packages are currently being evaluated.
At the moment we are planning to run the VGA computer output through a VGA to TV converter while running spectrogram software and a Sideral clock and then recording the VGA and the raw signal on a VCR for future examination.The resulting tape will be a spectrogram display of the data and Local Sidereal time with the actual data on the audio channel.
It is expected that in the event of an actual detection that doppler shifted horizontal sync would be one of the most obvious characteristics to identify, in that sync pulses are the most powerful portion of the TV signal and are transmitted at a standard frequency of 15750 pulses per second. While it is not impossible that the doppler shift could be precompensated, if you are trying to get my attention leaving it uncompensated would be a great way to accomplish it. There aren't very many tranmitters on Earth that are moving at several miles per second!
We also need to give further thought to the processing of the remainder of the video signal,in that original picture information could easily be included in a re-broadcast.There would be no reason to include the picture that went with the broadcast in the first place as the rebroadcasting in our own standard TV format would be sufficient to identify the signal as being ours and doppler shift combined with antenna direction would pretty much say it all about the origin of the rebroadcast. The picture (high frequency video) would be an ideal place to put a reply.
In my opinion it would almost certainly be designed for easy detection and might easily be a stationary image not unlike the Pioneer plaque,(shown at left). In fact, if we give a little thought to the video frequencies needed to convey an image of the Pioneer plaque, it might suggest a good place to start guessing what kind of spectrum to look for in a probe reply.A convential computer controlled AM receiver scanned across the video frequencies might be all that is needed to produce fairly reasonable spectrum analysis.