Marlin (Ben) Schuetz, Director of Boquete Optical SETI Observatory
Development work at the Boquete Observatory has always been a high priority. It is the principal activity during the rainy season when good observing nights are few in number. When gains have been made the efforts always began with a broadened viewpoint. During the past year or so, and in close collaboration with Bruce Howard (Owl Observatory in Michigan), our two observatories have made significant improvements in methods and practices for SETI searches.
To put things in perspective, we should first discuss a thing called parameter space after which I’ll bring you up to date on our doings. An appreciation of parameter space is key in understanding the flow of change that takes place in all SETI activities. For example, if one wanted to design a family car, the criteria for design would include: the maximum speed, seating capacity, cargo space, cost, road conditions, weather factors and so on. Each of these items has a span of practical values. That is, a family car needs more than two seats, but less than 8. If it is meant to operate in primitive areas it needs a minimum road clearance, but not more than a practical limit. Once the items, (parameters) are considered, they are generally interrelated and most often self defining. If parameter space could be limited to three dimensions it might be seen as a box within which a design can be satisfied.
The same is true for optical SETI. If one chooses pulsed over continuous wave signaling then the list of primary parameters includes only: signal amplitude, pulse duration, optical wavelength and periodicity. However, the problem is a bit more complicated since each of the primary parameters must be considered for their currently perceived and interrelated transmission and reception limiting properties. Given this and a few assumptions we can try to make a case for the expected range of each of these toward the design of a practical detection scheme. To keep this reasonably simple, we’ll consider the problems of transmission and reception separately.
Transmission. Without going into much detail, there are seeming practical and economic reasons for setting the various limits of pulsed transmission. For example, any ETI transmitting pulses would want sufficient pulse energy to be detectable at the target without the need of extraordinary means, i.e., extreme telescope systems of which there may be few or none. As is currently understood, this defines the approximate minimum transmission energy.
The presumed pulse width, periodicity and optical wavelength ranges are also self defining for practical and economic reasons, For instance, there is no known advantage and many disadvantages for pulse lengths less than ~1 nanosecond. The other extreme of this parameter is examined in the case for reception. Similar arguments exist for each of the other transmission parameters
Reception. As alluded to above, ETI transmissions would have the greatest likelihood of being received if only modest (perhaps numerous) telescopes were required. Among other disadvantages, large telescopes collect too much starlight which can result in detector overload. There are various means of overcoming that particular problem, but each solution requires significant compromises. Consequently telescopes having apertures less than about 1 meter appear to be ideal for SETI searches and help define the minimum pulse transmission energy.
The pulse width extreme also mentioned above is, at this time, limited to less than 100 nanoseconds because competing stellar noise impedes signal detection. To better appreciate the problem consider that a pulsed signal may occur only once in every 100 seconds against a stellar background signal count of 500,000 pulses per second. If the detector is tuned to detect long pulses there can be too much competing stellar noise. It may be possible to overcome this with advance techniques, but that only reduces the “market” of receiving stations. It is more likely that pulse lengths will be limited to less than 100 nanoseconds. Thus, and for each of the parameters, there are competing transmission and reception needs that define the limits.
Recent observatories’ upgrades. Bruce and I communicate frequently and have yearly meetings to work out problems and plan for the future. In the last year we have greatly expanded our operational parameter space by the following.
Abandoned fft (fast Fourier transform) analysis in favor of custom software to detect signals with periodicities as low as 1 pulse in 200 seconds; a factor of 5 improvement.
Upgraded the photometers with photomultipliers having larger spectral sensitivity (200- 850 nm) and greater quantum efficiency; a factor of ~2 improvement.
Improved the LED pulser test timing stability to allow for very long pulse periodicities.
All “hit” detections are time stamped and stored. The hit rates are adjustable and typically less than 2 per second. Higher hit rates can yield improved sensitivity. The custom “periodicity” software allows for this.
A photometer modification was made to enable the detection of pulse widths from <5ns (coincident photons) to >50ns in length; a factor of 2 improvement.
Telescope targeting error was reduced from 1.5 arc minutes to <20 arc seconds.
At Owl Observatory:
Telescope operations are now remotely controlled.
A new photometer has been built to accommodate the photomultiplier upgrade.
Work on the near horizon. The Owl Observatory has time stamp accuracy of ~15 nanoseconds while Boquete is currently limited to one millisecond timing accuracy. The Boquete deficiency will be corrected soon with the addition of a GPS timing signal.
The dry season is still a few months off, but every so often there will be a clear night for observations.
Special note: Each time the parameter space is expanded we must go back and check all stars previously observed. So, although the Boquete star count was well over 4000, we have begun anew. A list of the stellar observations (Objects Observed) and other information is frequently updated at the website: optical-seti.org
Once again (and for the nth time) I’m at the point of suggesting the systems have been, within reason and our capability, optimized. Each time that comes to mind, a new crop of ideas emerges. It is an exciting time to do optical SETI research and expectations grow with capabilities.
I have a note posted on the wall at the observatory. It reads, “Any Moment Now”. While it helps perk me up in the wee hours, it isn’t just a trick. I really mean it.