Re: Observations: 3 Unknowns

Allen Thomson (
Tue, 17 Jun 1997 09:08:45 -0700 (Robert Sheaffer) reported with some perplexity:
>Observations  15 June 1997    (Sun Eve., 16 June UT)
[observations of three mag 3-4 unidentifiable satellites deleted]
>Either we have a bunch of UFOs flying about, or else there are a
>bunch of objects up there not cataloged in ALLDAT.TLE. The first
>two objects may well be associated with the same launch. New stuff
>that didn't get catalogued yet?
    One possibility is that these are objects with such low radar cross-sections
that SPACECOM, which relies on VHF and UHF radars to conduct surveillance of LEO, 
has simply failed to detect them. Optically bright, very low rcs objects are not
unknown, viz:

      "Of special interest was data collected on object 81214. 
   Initially detected by the ETS [Lincoln Lab optical sensors at 
   White Sands], this object has a bright optical signature but 
   appears very small to radar sensors, and may indicate the 
   presence of many more objects of this type...
      "A considerable amount of data was collected on an interesting 
   object. Satellite 81214 appears moderately bright to optical 
   sensors, suggesting a large physical size. However, radar 
   tracking on this object indicates that it is quite small. 
   Millstone data at L-Band indicates a radar cross section of 
   approximately 0.00003 square meters, suggesting an object with a 
   small physical size. Several highly sensitive UHF radars have 
   been unable to track this object, however. Even the telescope 
   sensor at Anderson Peak, CA, that is normally not involved with 
   satellite tracking had no difficulty tracking this satellite. 
   The existence of this object and the data that has [sic] been 
   obtained lend credence to the theory that there is a population 
   of optically bright objects that appear quite small to a radar. 
   In fact, it is possible that many of the unknown objects 
   detected by optical sensors could fall into this area."

     1994 Space Debris Campaign - Preliminary Results 
     Taft DeVere, SenCom Corp. 
     Tim Payne, SWC/AE 
     Capt. Gary Wilson, HQ AFSPC/DOYY 

      "[Kwajalein Missile Range] sensors participating in the 1994 
   Debris Campaign included ALTAIR (VHF, UHF), TRADEX (L- and S-
   band), ALCOR (C-band) and MMW (Ka-band), and SuperRADOT visible 
   band optics... 
      "The most interesting optical track was on object 81214, which 
   was extremely bright to the SuperRADOTs, but was so small in 
   radar cross section as to be untrackable by the radars at the 
   1756 km point of closest approach."

     Kwajalein Missile Range Contribution to the 1994 Debris Campaign
     A. Gerber, G. Duff, and D. Izatt
     MIT Lincoln Laboratory, Kwajalein Missile Range

*Proceedings of the 1995 Space Surveillance Workshop
 28-30 March 1995
 Lincoln Laboratory
 Massachusetts Institute of Technology
 Lexington, Massachusetts
 K.P. Schwan, Editor
 Project Report STK-235, Vol.1