NASA's
High
Resolution
Microwave
Survey

Targeted Search and Sky Survey Status
Quarterly Report -- October 12, 1993

Prepared by:
Peter R. Backus, SETI Institute
Edward T. Olsen, Jet Propulsion Laboratory

STATUS

One year ago, after nearly two decades of scientific research and technology development, NASA's High Resolution Microwave Survey (HRMS) began its observational phase. On October 1, 1993, the Congress decided to terminate the program. Minimal termination funds have been provided to try to preserve the advanced signal processing systems for future use. The SETI Institute in Mountain View, CA, is attempting to raise private funds to support continued development and use of the Targeted Search System. The Sky Survey Prototype System will be transferred to NASA's Deep Space Network. Data products from observations during the past year will be made available later this year through the National Space Science Data Center at the NASA Goddard Space Flight Center.

BACKGROUND

The HRMS was part of the Toward Other Planetary Systems (TOPS) program in NASA's Solar System Exploration Division. The HRMS searched for evidence of planets orbiting other stars through radio emissions that may be produced by technological civilizations. The HRMS had two search modes, a Sky Survey and a Targeted Search. The Sky Survey was managed by the Jet Propulsion Laboratory and used 34-meter antennas in NASA's Deep Space Network to sweep the entire sky over a wide range of frequencies for the presence of strong signals. The Targeted Search used the largest available radio telescopes to observe nearby Sun-like stars over a narrower range of frequencies for weak signals. The Targeted Search was managed by NASA's Ames Research Center, which was also the lead center for the HRMS. The combination of the two search modes was potentially millions of times more comprehensive than the sum of all previous search programs. The observational phase of the HRMS was inaugurated at 1900 UT on 12 October 1992 at the NASA Goldstone Deep Space Communications Complex in California and the Arecibo Observatory in Puerto Rico. The Arecibo Observatory is part of the National Astronomy and Ionosphere Center operated by Cornell University for the National Science Foundation. In a coordinated initial observation program, the Arecibo antenna pointed at the star Gliese 615.1A and the Goldstone antenna began to scan the area of sky that included the targeted star. This report presents an overview of the observations, project activities and results during the past year.

SKY SURVEY

Observations used the Sky Survey Prototype System (SSPS) with the new 34-meter antenna and an existing low noise microwave receiver at the Venus Development Station at Goldstone. The SSPS spectrum analyzer divides a single-polarization, 40 MHz wide radio frequency band into slightly more than two million channels of 19 Hz resolution. The SSPS observatory control software drives the antenna very rapidly in a precision scan pattern lasting about 90 minutes. The pattern systematically covers 1.4 degrees high by 30 degrees wide rectangles, called "skyframes," which are fixed on the celestial sphere. The skyframes therefore appear to move across the sky as the Earth rotates. While observing, the SSPS real time signal detection subsystem excises channels contaminated by terrestrial signals and stores data from uncontaminated channels whose power exceeds a specified threshold. The scan pattern is designed so that each point in a skyframe will be scanned by the antenna at least twice (with slightly different position offsets) separated by about eight minutes in time. At the completion of each skyframe, the SSPS post processing subsystem analyzes the stored data and selects 20 candidates for the first level verification tests. The verification tests employ the SSPS in a targeted mode to perform more sensitive and localized reobservations.

Sixty-three single-polarization skyframes were completed (i.e., both the initial skyframe and candidate reobservation phases were performed). Three events have reappeared in a first level verification reobservation, albeit at a much weaker power level than in the original skyframe. These events did not survive additional verification tests, and the appearance of three such false alarm in 63 skyframes is consistent with statistical expectations arising from small fluctuations caused by the thermal noise of the receiver itself. Except for a one month hiatus necessitated by unavailability of the antenna, the SSPS was observing constantly for approximately 30-40 hours per week on the 34-meter Goldstone antenna, while being controlled remotely from JPL.

The SSPS also completed a series of special observations on a nearby 26-meter antenna at lower microwave frequencies. These observations were designed to enhance radio astronomy spinoffs from Sky Survey operations and to improve interference excision algorithms. Three skyframes covering half the galactic plane visible from the northern hemisphere were repeatedly observed in frequency bands that include the natural emission lines produced by hydrogen atoms and hydroxyl radicals (OH). Results of these observations, including maps of the detected emission, will be published later this year.

The unique capabilities of the SSPS were employed for a week at the end of August to search for weak signals from the lost Mars Observer spacecraft. Small areas of the sky centered upon Mars and along the projected hyperbolic fly-by trajectory were observed utilizing a modified candidate reobservation strategy. The limiting sensitivity achieved by the strategy would have detected an intermittent 17 watt EIRP signal from the spacecraft if it lasted for at least 16 seconds. This would have detected a signal from the spacecraft low gain antenna, even if Mars Observer was tumbling. No signal was detected. In September a similar set of observations were made in an unsuccessful attempt to locate the Landsat satellite.

Work continued at JPL on the development of the Sky Survey Operational System (with sixteen times the bandwidth of the SSPS) and of the wide band receiver systems for both search modes.

TARGETED SEARCH

The Targeted Search System (TSS) used the Arecibo 305-meter antenna, the world's largest radio telescope, during its initial campaign to observe 25 stars within 100 light years of the Earth. Receivers provided by the observatory allowed observations in four frequency bands covering a total of about 300 MHz within the range from 1300 MHz to 2400 MHz. The TSS processed a dual-polarization 10 MHz wide radio frequency band into more than 14 million channels, each only 1 Hz wide. It simultaneously processed the same band into channels with 7 Hz and 28 Hz resolution. Real time signal detectors scrutinized the data for the presence of continuous wave and pulsed signals that might drift in frequency by as much as 1 Hz per second.

An "observation" of a star in a 10 MHz frequency band consisted of three steps: pointing the antenna at the star, then away from the star, and then back at the star. Each step lasted either 92 seconds or 299 seconds. Signals that were present only when the telescope was pointed at the star (and not previously seen in other observations) were selected as candidates for further verification tests. Signals that were present both "on" and "off" the star were rejected as terrestrial interference. During the 200 hours of assigned telescope time the TSS made 436 observations of the target stars and a variety of test observations. Many interference signals were detected and cataloged. Fifteen signals satisfied the basic candidate selection criteria. These candidates were immediately subjected to further verification tests, but all proved to be intermittent terrestrial interference. Off-line analysis of the data collected at Arecibo focused on developing better techniques for quickly identifying, classifying, and perhaps even avoiding interference signals.

After returning from Arecibo, the TSS was moved to the development laboratory at NASA Ames for a planned system expansion timed to coincide with major upgrade activities at the Arecibo Observatory. The "lessons learned" through operational experience were being implemented as modifications to several circuit boards and improvements in the software. These activities planned to expand the TSS to process two dual-polarization 10 MHz radio frequency bands with additional resolutions. The Mobile Research Facility that houses the TSS for transportation to and operation at observatories has received additional cabling and electronics racks needed for the 20 MHz system. The expanded TSS was being developed for the 1994 Targeted Search Campaign, during which nearby Sun-like stars in the Southern Hemisphere were to be observed using the 64-meter antenna of the Parkes Observatory in Australia. Parkes is part of the Australian Telescope National Facility operated by the Commonwealth Scientific Industrial Research Organization. A Memorandum of Agreement has been negotiated between NASA and CSIRO through the Australian Space Office for the use of this facility. NASA has already paid for some modifications to the Australian facilities.

RESULTS

No signals of extraterrestrial intelligent origin were detected. It was encouraging that most of the terrestrial interference signals encountered were immediately recognized as such by the Sky Survey and Targeted Search Systems. A few signals required additional verification tests to determine that they were of human origin or due to thermal noise. Both the Targeted Search and the Sky Survey components were using the lessons learned in the initial observations to improve their hardware, software, and observation techniques as they expanded their systems by stages to the final configurations required to pursue the full-scale search. Data collected during observations remains proprietary for a period of one year. During that time, members of the HRMS Investigators Working Group have exclusive use of the data sets. Initial data products are now being prepared for release to the scientific community later this year.

In summary, the HRMS successfully inaugurated its observational phase on time and within budget. Seven members of the HRMS team received individual awards and the entire team received a Group Achievement Award from NASA. Scientific papers reporting the results of one year of observations will be published later this year. The signal processing systems developed by the HRMS are now being prepared for possible future use by the science community.

Note updated October 1995:
The equipment developed for the HRMS Targeted Search was completed and expanded with private funding by the SETI Institute under Project Phoenix. The Targeted Search System, now with a 20 MHz bandwidth, was deployed for observations at the Parkes Observatory from February through June 1995. It is now being upgraded for deployment to the National Radio Astronomy Observatory in Green Bank, West Virginia in the summer of 1996.

Other Information

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