MIT Reports to the President 1994-95

Haystack Observatory

The Haystack Observatory, located in Westford, MA, is an interdisciplinary research center engaged in radio astronomy, geodesy, atmospheric sciences, and radar applications. The radio astronomy program is conducted under the auspices of the Northeast Radio Observatory Corporation (NEROC), a consortium of 12 educational and research institutions in the northeast. The Observatory receives financial support primarily from federal agencies including the NSF, NASA and the USAF through MIT Lincoln Laboratory.

The Observatory instrumentation consists of the following facilities: a 37m-diameter radio telescope enclosed in a radome that is used for astronomical observations at wavelengths from 2.6 mm to 13 cm, as well as for wideband radar measurements at 3 cm; an 18m-diameter radio telescope involved in geodetic measurements of the earth's plate motions using very long baseline interferometry (VLBI) techniques; a VLBI correlator to process global geodetic experiments and astronomical observations at millimeter-wavelengths; and a high-power radar that utilizes two large antennas, 46 m and 67 m in diameter, to study the earth's upper atmosphere using incoherent backscatter techniques. The radar is operated in conjunction with an optical observatory to monitor airglow emission and measure upper atmospheric winds.

Highlights of the radio astronomy program using the 37m-diameter radio telescope in the past year include the detection of the N2H+ ion in many star-forming gas clouds that had previously revealed the presence of NH3, a tracer of dense molecular cores. This allowed Harvard astronomers (Dr. Philip Myers and colleagues) to study the ionized component of these clouds as well as the neutral gas, and strong correlation was found between the two tracers indicating the dynamic coupling of the plasma to the magnetic field in these stars. The high-resolution spectra obtained for the N2H+ ion, unavailable previously, have been used to correct the molecular constants obtained from laboratory measurements. A search for CO that has been redshifted in frequency towards the 35 GHz band was conducted in a set of 20 candidate galaxies by Haystack astronomers (Dr. Richard Barvainis and collaborators), but no emission above thermal levels was detected. This null result, carefully verified, contradicts observations made elsewhere that were difficult to explain theoretically. The experiment demonstrated the excellent electronic detection and processing capabilities of the radio telescope at low signal-to-noise ratios. Finally, a pilot project has been initiated by MIT astronomers (Prof. Jacqueline Hewitt and her students) to detect radio emission at 22 GHz from gamma-ray bursts. Although no detection was made, an upper bound for the emission was established, and a routine technique was validated to prepare for additional searches when the High Energy Transient Experiment (HETE) satellite is launched and operated later this year by the MIT Center for Space Research.

During the past observing season, a total of 34 observing projects were conducted at Haystack by members of the astronomical community, including 14 graduate students. Most of the observing projects were carried out in the 85-115 GHz frequency range which takes advantage of the newly-upgraded telescope. In the face of constrained budgets in radio astronomy, the telescope was used successfully by the visiting astronomers and students, without the assistance of an experienced Haystack operator crew. Haystack staff provided primary support to the visitors and insured that the hardware and software systems were adequately upgraded to allow this new mode of operation.

In Very Long Baseline Interferometry (VLBI) applied to astronomical observations at 3mm-wavelength, a new Coordinated Millimeter-VLBI Array (CMVA) was organized under MIT Haystack's leadership to provide easy access to this technique by the community at large. A set of 11 radio telescopes distributed globally, including the Haystack telescope, forms the CMVA, and their participation in joint experiments is controlled through the submission and review of proposals at Haystack. In addition, the data processing is conducted at Haystack using the Mark IIIA correlator. The first CMVA experiment was carried out successfully in April 1995 with the conduct of six projects, and the prime achievement in this experiment was the participation of the Hat Creek radio interferometer operated by the University of California, Berkeley, which was equipped with all necessary hardware systems and tested by Haystack prior to the experiment. Both galactic center experiments and polarization observations of quasar structures were part of the first set of experiments, revealing new details at high resolution of the evolution of the cores of these objects.

In anticipation of reduced support for radio astronomy at Haystack in the future, a set of studies have been undertaken to further modernize the radio telescope and enhance its sensitivity, thus improve its competitive edge relative to other telescopes. A new antenna surface is being considered using light-weight panels that can be actuated based on a laser-ranging measurement system. Design studies that examine the various alternatives for such an upgrade are presently underway to develop the most effective approach for such a project. The primary advantage is that such an upgrade would allow radar imaging to be made at 95 GHz with much finer resolution than presently possible, and would allow the radio astronomy observations in the 100 GHz band to be made with shorter integration times on faint sources. The possibility of including radiometers in the radar equipment box to simplify the logistics of changing operational modes on the antenna is also being examined in order to improve the operational efficiency. Finally, efforts are being made to further automate the radio telescope so as to allow remote monitoring of the data collected.

Work has continued during the past year on VLBI technological developments, both in high data rate recording (exceeding 1 Gbit/s) and in high speed data processing. The advanced correlator, the Mark IV system, has met its first goal of developing a VLSI chip that operates at 64 MHz, and despite some problems in the testing and packaging of this prototype chip, the design was successfully verified. A second iteration of the chip is presently underway, prior to the production of the large lot of chips needed to construct six correlators worldwide. The prototype board for the processor was also completed and its design tested successfully. Several national and international programs are collaborating and supporting the development of the Mark IV system at Haystack, including NASA and the US Naval Observatory for geodetic and time services applications, the Smithsonian Institution for submillimeter-array processing, the Joint Institute for European VLBI for its planned large correlator, the Netherlands Foundation for Radio Astronomy for the Westerbork array at Dwingeloo, and the Institute for Applied Geodesy in Germany for geodetic data processing at the Max Planck Institute. In high-speed data recording, we have arranged for strong industrial collaborations to develop a thin-film head array jointly with Seagate Tape Technology Inc., and expect to complete our first array in the next year. This will allow a vastly enhanced recording rate exceeding 2 Gbits/s at relatively one-third of the cost of current ferrite headstacks. The new head-array will serve both the astronomical and geodetic research communities, as well as provide industry with new commercial application opportunities such as in high volume data archiving and information storage.

A spin-off from our VLBI research has resulted in the past year in our first industry contract, with Associated Communications Corporation, to develop and test the design of a cellular phone location system. This is driven primarily by the need to locate cellular phones that request 911 emergency service. The design involves the application of precise ranging using the time delay of signals received at various cellular sites, and the use of correlation techniques to determine the location of the phone signal. Prototype hardware and processing systems have been developed and tested in the field in collaboration with industrial partners, and further development is underway towards an operational system in the next year. The project illustrates the benefits of our research to an application in the national interest.

In our radar programs, the atmospheric sciences group has led efforts to analyze and interpret measurements collected during major geomagnetic storms in the earth's ionosphere, revealing vastly decreased electron densities and greatly enhanced ionospheric plasma drifts to the south of the auroral region. Such data are critically needed to allow the community to assess the impact of "space weather" phenomena caused by solar coronal events which propagate in the solar wind and perturb the earth's upper atmosphere. These effects result in communication problems, satellite electronic upsets and orbit changes - problems whose solution is now being sought in a national program. The Millstone Hill incoherent scatter radar is well suited to collect data for this application. In addition, the atmospheric sciences group is developing a collaboration with other groups to consider the construction of an ionospheric radar in the northern polar cap region where the effects of energetic particle precipitation effects due to solar disturbances are most readily observed.

Finally, Haystack's educational programs have continued successfully during the past year. These have included post-doctoral researchers, graduate and undergraduate students who utilized the Haystack instrumentation for research projects, and an undergraduate summer internship program involving 18 students this year who are mentored by our various staff to gain research experiences. In addition, our Young Scholars program, aimed at pre-college level students, involved 25 students and four science teachers from the local area in a three-week summer program followed by an academic year project and special mentorship by our staff. Special efforts are made to use the Observatory instrumentation to highlight research in our discipline to the public in our nearby communities.

Joseph E. Salah

MIT Reports to the President 1994-95