The Columbus Optical SETI Observatory

STUART A. KINGSLEY

ETI Photonics
545 Northview Drive
Columbus, Ohio 43209-1051
United States

This paper addresses the design for a prototype observatory that will Search for Extraterrestrial Intelligence (SETI) in the optical spectrum.^1-9,11-17 In October 1992, to celebrate NASA's official switch-on of the High Resolution Microwave Survey (HRMS)¹⁰, the author commenced the construction of his own Optical SETI Observatory that will operate in the visible and near-infrared spectrum. The design and construction of what has been named The Columbus Optical SETI Observatory has so far been a self-funded activity. This is the first Visible Optical SETI (OSETI) Observatory in the United States, and when it comes on-line, will be only one of three on this planet. A second Visible SETI Observatory based on the former Soviet MANIA (Multichannel Analyzer of Nanosecond Intensity Alterations)^4,9 system is presently under construction in San Juan province, Argentina¹⁴. By early 1995, The Columbus Optical SETI Observatory should be in a state to commence the optical targeted search of the sky.

The optical approach to searching for ETI technologies touches on a subject which for various reasons has yet to be accepted by the majority of the SETI community.¹² This paper deals primarily with the superiority of interstellar optical (laser) beamed communications over their microwave counterparts.

The author has defined three types of Optical SETI:

(a) Professional Optical SETI employing large telescopes and coherent heterodyne detection.¹⁵

(b) Professional Optical SETI employing large telescopes and incoherent direct-detection/photon-counting.¹⁵

(c) Amateur Optical SETI employing small telescopes and incoherent direct-detection/photon-counting.^15,16

 

In this paper we consider the subject of SETI in the optical spectrum using systems (b) or (c). The word Amateur is a bit of a misnomer, for there is nothing amateurish about what will be described herein. Rather, it is a reflection of the size of the receiving telescope aperture that warrants the use of the term. Indeed, the aperture size in the author's prototype Optical SETI Observatory or Optical Earth Receiving Station is 25.4 cm (10"); a little larger than the near-infrared (1.06 m m) ETI Uplinks proposed in NASA's 1971/73 Project Cyclops design study!³

This Optical SETI research is thus applicable to both categories (b) and (c); the degree of sophistication that the "amateur" wishes to employ being dependent on funds available. What is very exciting about Amateur Optical SETI (AMOSETI) is that there is a rare opportunity for amateur optical astronomers to participate in a field with virtually no competition at this time from professional organizations. Of course, one of the aims of the author's OSETI activities is to develop the techniques and procedures which will allow HRMS to be extended into the optical regime, early in the next century. For it is his strong contention, that successful detection of ETI signals will not occur in the microwave regime, rather as every sensible ETI knows, "lasers are far more effective for interstellar and SETI communications"!

Note that the word "Optical" is used here according to its modern definition as employed by photonics (optoelectronic) engineers and scientists throughout the world. It covers that part of the electromagnetic spectrum from the far-infrared to the ultra-violet. However, as with normal optical telescopes, The Columbus Optical SETI Observatory is restricted to operation in the visible and near-infrared regime. Thus, for the purposes of this study, "Optical SETI" means "Visible & Near-Infrared SETI".

This is not the first time, nor will it be the last, that the scientific community may have gone in the wrong direction because of mistaken assumptions. At first glance, the three decades-old idea that ETI signals will be found in the quietest region of the electromagnetic spectrum seems reasonable. Thus, the 21-centimeter hydrogen (H) line and the region of the microwave spectrum between the H and lowest OH resonance lines (1.420 to 1.662 GHz), which has come to be known as the "waterhole", has become a favored "magic frequency".¹⁰ The over-emphasis on the microwave approach to SETI is illustrated by the SETI Lore Time Pyramid of Figure 1.

Besides the issue of quantum noise at optical frequencies, the real reason that the SETI community has largely ignored the optical approach to detecting ETI signals and have generally claimed that lasers were poorer for SETI interstellar communications than the microwave counterpart, can be laid squarely at the process of derating and crippling the ETI transmitter uplink performance. The famous Cyclops Report³ must bear considerable blame for this. Unfortunately, the SETI community has attributed to ETIs the technical prowess of late 20th Century Earth. Just because we do not presently have precise peculiar proper motion data on nearby stars and don't know how to aim (point-ahead target) our lasers on such stars, is not a reason for suggesting that ETIs cannot do this. ETI civilizations may be millions of years ahead of us. However, even within the next 50 years we are likely to acquire the skills to respond to such signals with higher EIRP diffraction-limited beams that are a better match for the zones of life around nearby stars.

Figure 2 illustrates the range of microwave and optical transmitter gains that have been conjectured for ETIs by SETI researchers over the years. Figure 3 indicates the corresponding EIRPs. The graph of Figure 4 illustrates the expected sensitivity of a 32" aperture telescope as a function of the optical bandwidth, This assumes the use of continuous wave laser beacon signals at very high EIRP levels, and noise levels being set by the background stellar radiation of the targeted star.

Monte Ross¹³ has suggested that ETIs would find pulsed beacons and Pulse Position Modulation (PPM) data-streams for far more efficient for interstellar communications. Under this rationale, the peak EIRP may be so high as to make it possible to use incoherent photon-counting receivers, and/or smaller receiving telescopes, with little optical filtering.

Figure 5 shows a schematic of an observatory for both Professional and Amateur Optical SETI. The purpose of the conventional CCD is just to display the star-field on a TV or PC monitor and for precision star tracking. In this preferred design, it does not detect the ETI signal; that job is performed by the relatively fast single solid-state APD or PMT. APDs have the advantage of high quantum efficiency but usually have the disadvantage of higher dark-current; the converse being the case for photomultipliers. Though the imaging CCD can itself be used as the ETI detector, this approach would compromise detection sensitivity and bandwidth.

The Meade LX200 is state-of-the-art in small computer-controlled Schmidt-Cassegrain Telescopes (SCTs). Figure 6 shows a photograph of the f/10 25.4 cm (10") Meade SCT that is employed at The Columbus Optical SETI Observatory. Interfacing and mains power (110 V) for the Meade LX200 is provided at the foot of the pole supporting the satellite dish. For the present time, a 2.3 m (9 ft.) square plinth consisting of concrete patio squares has been constructed in front of the dish to provide a level surface for the tripod. It takes about twenty minutes to set up the system for an observing session, but plans are in hand to either deploy a small permanent dome on the plinth, such as the HOME-DOME, or to relocate the observatory and new dome to the garage roof.

The picture shows the telescope head with its dew-shield extension section, attached to the equatorial mount (Superwedge) on a fully-extended tripod. In practice, for Optical SETI observations, there is no need to use the equatorial mount, since field rotation is not a problem as it would be for astrophotography. Setting up the system as shown is a two-man job because of the weight of the telescope head (61 lbs). However, since the SCT can be used in the altazimuth-mode and the tripod legs do not have to be fully extended, it is possible for one person to set up the system.

Today, the Personal Computer (PC) has become ubiquitous in both the office and laboratory environments. Software and hardware for application in both professional and amateur photon-counting OSETI receivers will be the subject of future investigations. This is not to preclude the use of a scaled-down version of the MCSA (Multi-Channel Spectrum Analyzer) systems being employed for the HRMS project.^10,12

In October 1991, the author set up a BBS for coordinating future world-wide AMOSETI activities. The idea is that when eventually the efficacy of the optical approach to SETI catches on with amateur optical astronomy societies and clubs, there will arise the opportunity to apply a "divide and conquer" approach to the targeted star search. In this way, different groups in the northern and southern hemispheres can be allocated stars and optical wavelength bands to search, that will allow for the most rapid and effective visible search of the stars that appear in the HRMS Targeted Star List. This BBS may one day be employed to allow users to download live Optical SETI data from The Columbus Optical SETI Observatory's control and signal processing computer.

When The Columbus Optical SETI Observatory becomes fully operational, it will be employing a high-speed photometer to analyze starlight. It is almost inevitable that serendipity will apply to Optical SETI, where natural fast phenomenon will be discovered in the visible and near-infrared spectrum that have hitherto not been predicted by astrophysicists.

Future work will involve installing the telescope in an astronomical dome, building a dedicated control room, and devising means to efficiently extract the would-be ETI signals from the background and internal noise of the receiver. In many ways, The Columbus Optical SETI Observatory or AMOSETI Observatory is a small version of the late Shvartsman's "MANIA" system that is now being duplicated in Argentina.^4,9,14 When this observatory comes on-line in 1995, will be simultaneously the only Amateur OSETI Observatory in the world, the only Visible OSETI Observatory in North America, and only the second (or third) Visible Optical SETI Observatory of any description, anywhere on this planet!

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