In this thread, Tom Davis asked

This raises an interesting possibility. The resolution of a 70cm radar is rather limited for tracking the smaller but still dangerous debris. The Air Force might propose a new higher frequency radar for this job. Will they? If they do, would we support their request in Congress?

Tom

The Air Force (USAF), thru MIT Lincoln Labs (LL), have several higher resolution radars at Millstone Hill, northwest of Boston, near the NH border and at the junction of Westford, Tyngsboro and Groton townships. The facilities there support several DoD radar programs, while the "civilian" side of the house is known as the Haystack Observatory (see http://haystack.edu/ for an overview of the facility). The Haystack Observatory activity on the hill is operated by MIT on behalf of NEROC, a consortium of 8 universities (listed at http://haystack.edu/hay/neroc.html). [For full truth in advertising, I have been a member of Haystack's extended family for many years, and I currently serve as an At-Large member of the NEROC Board of Trustees.]

At Millstone Hill, the USAF/LL has the 85' "Millstone" dish used as a high power surveillance radar at 1295 MHz. Some interesting info on DoD's various radars (including both Millstone & Haystack) can be found at http://www.ll.mit.edu/news/journal/pdf/vol12_no2/12_2detectsatellitiesplanet...; see Figure 26 for an aerial view of the entire facility.

Haystack, Millstone and the smaller 60' "Westford" telescope were originally built ~1960 by LL with USAF funding in order to bounce microwave signals off of a belt of passive, resonant dipole "needles" at a time before there were any active communications satellites.Thousands of fine wire needles were embedded in a block of napthalene (think moth balls) so that they would be slowly and uniformly dispersed throughout the orbit. A prototype of the needle dispenser is near the Oscar-1 model at the Udvar-Hazy museum. Yes, there is an in joke involving "needles in a haystack".

As an aside, after the AO-10 and -13 launches and motor burns, NORAD's radars had troubles finding our satellites. With some quick round-trip transponder & Doppler measurements, KA9Q & I were able to give Millstone enough orbital data so that could see our spacecraft at 10,000+ km and provide Keplerian elements until NORAD got their act together.

At Haystack, there are two antennas. The larger is 37M (120') in diameter and is under a rigid radome (it looks like a HUGE golf ball on top of the hill!). This antenna has been used for a lot of astronomy programs since the early 1960's. Until about 1972, a high-powered 8 GHz transmitter and traveling-wave maser receiver were available for use as a Planetary Radar to obtain spectacular "photos" of the Moon, Mars, Venus and Mercury; Haystack's Lunar images were invaluable to the Apollo astronauts Now it is equipped with a DoD high power 10 GHz radar transmitter with ~1 GHz bandwidth. The 1 GHz bandwidth lets it be used to take a radar "photograph" of satellites with ~20 cm resolution (comparable to a wavelength at the 1 GHz spanned bandwidth).

Beside the "big" golf ball is the smaller HAX (Haystack Auxiliary Radar) housed in a smaller golf ball. HAX operates at Ku-band with its own forty-foot antenna, transmitter, RF hardware and receiver, but it shares control and signal and data processing systems with Haystack. HAX, which began operation in 1993, is the first radar to have a signal bandwidth of 2 GHz, which improves the range resolution to ~12 cm. HAX represents a significant advance in radar imaging capability, producing finer and sharper images of satellites than the Haystack. In addition to its DoD sponsored imaging task, HAX has extremely useful in producing detailed information for NASA on the locations, orbits and characteristics of space debris. For some comments on Haystack & HAX tracking debris see http://www.nasa.gov/home/hqnews/1994/94-136.txt and http://web.mit.edu/newsoffice/1995/needle-0208.html.

The new "big project" at Haystack is the refurbishment (really, nearly a total rebuild) to upgrade the Radar capabilities to a bandwidth ~10 GHz at P-band (90-100 GHz). Information on HUSIR(Haystack Ultra-wide Satellite Imaging Radar) can be found at http://haystack.edu/obs/haystack/LincolnUpgrade.pdf. With this new radar, images can be made with a few cm resolution.

So the answer to Tom's question is definitely YES, it is being done. I leave this question to your own imagination: Why would DoD want cm-level "photos" of stuff in orbit?

73 de Tom, K3IO