Subject:      UCT 81214: Bright and stealthy
From:         [email protected] (Allen Thomson)
Date:         1995/10/11
Message-Id:   <[email protected]>

   A month or so ago we had a brief discussion of the 
feasibility and utility of stealth in LEO.  At the time I opined 
that it might be worthwhile in tactical situations, but wouldn't 
be a good idea if the aim were to protect satellites from 
detection for long periods of time.  The principal reason for 
this, IMO, is the very wide range of sensor types and viewing 
angles encountered by satellites in LEO and the fact that the 
stealth technologies which have been revealed to date apparently 
presuppose a known, fairly restricted set of "threat" sensors 
and engagement geometries.  Thus things designed to be stealthy 
against one set of sensors might be detectable by other sensors 
the designers hadn't known about or couldn't take into account
because of engineering constraints.

   As it happens, a fairly concrete example of this has just come 
to light (so to speak).  Several papers in the proceedings of the 
1995 Space Surveillance Workshop* describe preliminary results of 
a orbital debris campaign sponsored by Space Command in late 
1994.  One of the interesting results concerned an object (UCT 
81214) which was easily detected by a number of optical sensors 
but was basically invisible to radars, some of them highly 
sensitive range instrumentation radars, operating from 217 MHz 
up to ca. 35 GHz.   While 81214 probably wasn't intentionally 
designed to have low rcs  -- I'd guess it's a just a stray 
fiberglass panel or something of the sort -- it nonetheless 
illustrates the point that monostatic-radar-stealthy doesn't mean 
optical-stealthy (and then there's IR, bistatic radar, lidar, etc). 

      "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