Haystack LRIR

The Haystack radar is large dish radar at the Lincoln Space Surveillance Center near Boston, and a contributing sensor to the U.S. Space Surveillance Network.[1]  From 1978 until April 2010, when it was shut down for a major upgrade to add a W-Band capability (which will be discussed in a future post), Haystack operated part-time as the X-Band Long-Range Imaging Radar (LRIR).  The LRIR was reportedly the only U.S. radar capable of imaging satellites out to geosynchronous orbit range.  The upgrade involved installing a new antenna and was due to be completed by about 2013, after which the radar will be known as the Haystack Ultrawideband Space Imaging Radar (HUSIR).  Under the upgrade, the LRIR’s X-band capability will be retained and is expected to return to operation in 2012.

September 2010: The top portion of the Haystack’s radome about to be reinstalled after the installation of the new antenna.  Photograph from MIT Lincoln Laboratory, 2010 Annual Report, p. 13.[2]

Background

The Haystack radar system became operational in 1964 with a 36.6 m diameter antenna dish.  It was originally built by Lincoln Laboratory and was used for space communications and radio propagation experiments, as a tracking radar and for radar research, and as a radio telescope.  In 1970, ownership of the radar was transferred to MIT, which operated it under an agreement with NEROC (the North East Radio Observatory Consortium), a consortium of research and educational institutions.

In the 1970s, a wideband X-band radar imaging capability was added to the existing system.  This new capability, known as the Long-Range Imaging Radar (LRIR), became operational in 1978, and was supported by the U.S. Air Force.  However, for the majority of its time, Haystack continued to be used for scientific research. 

Initially U.S. Air Force contracted to use the Haystack LRIR for 1,000 hours per year for satellite tracking and imaging. However, this time was limited primarily to only about eight pre-scheduled weeks per year. Eventually the USAF decided that these limits were too restrictive, particularly for short-notice needs, and this led to the construction of the smaller, adjacent Haystack Auxiliary (HAX) radar.  Although HAX has a shorter range than the Haystack LRIR, it had better resolution, and thus could produce sharper images of near-earth satellites. 

Technical Characteristics

The Haystack LRIR had a 120 foot (36.6 m) antenna in a 150 foot radome.  The antenna structural tolerances were capable of supporting operations up to 50 GHz.  It produced a beam width is 0.058 degrees. At X-band its gain was 63.6 dB (= 2.3×10⁶).[3]  The newly installed new HUSIR antenna has the same dimensions, but with much more closely controlled tolerances.

In wideband mode, the LRIR operated at 10 GHz with a bandwidth 1.024 GHz, giving a range resolution of 0.25.  The single wideband waveform (at least as of about 2000) is 256 μs long and is linear-frequency modulated.  Its typical pulse repetition frequency is 1200 Hz.  It can obtain a cross-range resolution equal to its range resolution of 0.25 m with a target rotation of 3.44˚.

Narrowband waveforms, with a bandwidth of up to 10 MHz, are used for non-imaging applications, such as for acquiring and tracking targets and for space debris measurements.

Initially, the LRIR had a peak power of 400 kW and an average power of 200 kW.  However, modifications to the transmitter to make it more reliable have reduced the average power to about 140 kW, with a maximum pulse length of 5 ms.  The transmitter uses four Varian TWTs in parallel, each of which produces 100 kW peak and 50 kW average power at X-band.

As of 2000, Haystack’s maximum duty cycle was about 35%, and its maximum pulse repetition frequency was 1,367 Hz.[4] At that time an upgrade to Haystack’s processing and control system  was planned, and since has apparently been completed, that would have enabled  variable-length wideband  pulses and higher pulse repetition frequencies.  As of February 2012, initial X-band operating capability was expected in 2012 with W-band operations to begin in 2013.[5]

Operations and Capabilities

As of 2000, Haystack operated as the LRIR for 13 weeks per year (in one or two week blocks, seven days per week, 16 hours per day).[6]  The rest of the time Haystack was operated by NEROC (North East Radio Observatory Consortium) for radio astronomy research.  Haystack is also used for research on space debris.

Within a few years of becoming operational, the Haystack LRIR was capable of producing satellite images in near real time (within one hour).  Haystack is capable of imaging satellites out to geostationary orbit distances.

According to a 1997 paper Haystack could achieve a sensitivity of S = 58 dB with a 1.024 ms pulse.[7]

A 2005 paper stated that Haystack could achieve a sensitivity of (1 m², 1,000 km) of S = 56.8 dB (480,000) with a 1.024 ms pulse and S = 62.1 dB (1,600,000) with a 3.457 ms (narrowband) pulse.[8]  Operating in this way, it could detect objects as small as about 0.5 mm (at an altitude of about 1,000 km — this was done using non-coherent integration of 12 pulses).   This corresponds to S = 50.8 db (120,000) for a single 0.256 ms wideband pulse.