Ballistic Missile Defense: Radars Proposed for Midcourse Discrimination by National Academy of Sciences Report Are Far too Small. (September 20, 2012)

George Lewis and Theodore Postol

The September 11, 2012 National Academy of Sciences (NAS) Report “Making Sense of Ballistic Missile Defense,” calls for deploying new “stacked” X-band radars alongside four existing early warning radars in order to provide a discrimination capability for the current U.S. Ground-Based Midcourse (GMD) national missile defense (NMD) system.  The report also calls for abandoning plans to mothball the Sea-Based X-band (SBX) radar and to replace the 30 currently deployed Ground-Based Interceptors with fifty new high acceleration interceptors, including some at a site in the northeastern United States.


Figure 1.  The drawings in the upper left of the figure show the relative physical sizes of the Clinton Administration’s proposed GBR x-band discrimination and the stacked x-band radar proposed by the NAS Report.  The lower rectangles compare the physical size and modules of the current TPY-2 X-band radar, the NAS’s proposed stacked X-band radar, Clinton’s proposed GBR.

These new stacked X-band radars would basically consist of two of the current AN/TPY-2 X-band radar antennas, one stacked on top of the other, mounted on a rotating turntable.   Thus these new radars would have twice the aperture, gain, and output power of the current TPY-2 radars.

Our detailed calculations (coming soon to this blog) show that the NAS’s proposed new radars are far too small to carry out the discrimination mission the NAS Report proposes for them.  However, it is possible to arrive at the same conclusion simply by comparing the proposed “stacked” radars to earlier radars proposed by the Clinton Administration for exactly the same mission.

The 3+3 National Missile Defense System developed (but never deployed) by the Clinton Administration, like the current GMD NMD system, would have upgraded existing early warning radars to allow them to be used as part of the NMD system.  However, the designers of the Clinton system correctly recognized that these early warning radars lacked the bandwidth to be useful for discrimination.   To at least attempt to address this problem, they thus planned to deploy a number of very large X-Band Ground-Based Radars (GBRs) alongside the upgraded early warning radars and at a few other locations.  Specifically, these large X-band radars would have been deployed alongside the upgraded early warning radars in California, Cape Cod, central Alaska, Thule (Greenland), Fylingdales (Great Britain), next to the former Safeguard Radar in North Dakota (now used primarily as an early warning radar), and in Hawaii, Shemya Island in the Aleutians, and possibly in South Korea.  For a discussion of these GBRs, see the 2000 Countermeasures Report.

The NAS Report calls for using their proposed stacked TPY-2 radars for exactly the same purpose, and would put them alongside the upgraded early warning radars in Thule, Fylingdales, Cape Cod and central Alaska as well as at the Safeguard site in North Dakota.  However, as the illustration above shows, these radars are much smaller than the GBRs that the Clinton plan would have put at these sites. 

Since the GBRs and the NAS’s stacked X-band radar use essentially the same technology (they are both members of the “family” of X-Band radars from the Raytheon Company), we can make a simple and direct numerical comparison between them.  The GBRs would have had an antenna aperture of about 384 m2 populated with 69,632 transmit receive modules.  A stacked TPY-2 would have an antenna aperture of 18.4 m2 populated by 50,688 modules.  The modules used in the GBR would have had an average power of about 2.0 Watts.  The TPY-2 uses a later version of the modules, which we estimate to have an average power about 60% higher, or about 3.2 Watts. 

The relative tracking range of each radar will then be roughly proportional to the fourth root of the product of each radar’s average power (P), antenna aperture (A) and gain (G).  Since both radars operate at the same wavelength, their gain will be proportional to their antenna area, and so their relative tracking ranges will be proportional to the fourth root of the product of their average power P and the square of their antenna area A.  Then we get


That is, the tracking range of the NAS’s proposed stacked X-band radar is only 1/4.4 = 23% of the radars proposed for exactly the same purpose by the Clinton Administration.


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  1. Allen THomson

     /  September 20, 2012

    > That is, the tracking range of the NAS’s proposed stacked X-band radar is only 1/4.4 = 23% of the radars proposed for exactly the same purpose by the Clinton Administration.

    But how do their mid-course discrimination/imaging capabilities compare?

  2. They have the same bandwidth, so resolution will be the same. Thus they could form equally sharp images on a given target as long as there is enough signal-to-noise in each range cell or imaging range-Doppler cell. Another way to state the result in the post is for any resolution cell, whether just a range cell or an imaging range-Doppler cell, the GBX will get the same signal-to-noise ratio as the GBR for the same observing time when the range for the GBX is 0.23 that of the range for the GBR. Or, if they are at the same range, the GBX would have to integrate for about 374 times longer to get the same signal to noise, which in any real situation would be useless. So they have the same limiting resolution, but the target must much be much closer to the GBX (by a factor of about 4.4) than the GBR to be either detected or imaged in the same amount of time.
    George Lewis


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