SA's purpose is NOT to reduce the accuracy of the cheap-and-cheerful GPS
receivers of mere mortals.  It is intended to prevent just anybody adapting
accurate GPS to weaponry.


    Both the NAVSTAR and GLONASS systems were
    conceived as military systems, intended to augment military
    weaponry in times of war. However, GPS is a classic example
    of a dual use system. That is, one which has both military and
    civilian uses. In this case, GPS is an extremely expensive
    publiclly funded system which has potentially massive
    civilian benefits.

    Situations In Which Misuse Could Occur

    Attacker vs. Country of Origin
        In this case, the enemy would be directly attacking the
        GPS system's creator by using it's own system against
        it. Example: Iraq using NAVSTAR augmented weapons
        vs. the United States.

    Attacker vs. Ally
        In this case, the enemy would be attacking an ally of the
        GPS system's creator using the GPS system. Example:
        Iraq using NAVSTAR augmented weapons vs. Saudi

    Attacker vs. other nation
        In this case, the attacker would be attacking a nation
        not allied with the GPS system's creator. Example:
        Libya using NAVSTAR augmented weapons vs. Chad.

    Types of Misuse

    Intelligence collection
        GPS combined with laser rangefinding systems permits
        accurate positioning of potential targets from a
        distance. Information resulting from such data
        collection can be attacked at a later time using a variety
        of methods. These would include infantry assault, air
        attack, artilltery, etc.

    Augmentation of existing weapon systems
        Potential for terrorist use in short range mortar attacks.
        Postprocessed mapping grade differential GPS
        combined with commercial laser rangefinders could be
        used to surreptitiously map potential targets with
        respect to potential hiding spots for mortars. This
        would allow for better first shot accuracy with most any
        indirect fire weapon.

        Similarly, military artillery batteries can shorten the
        time needed to survey in guns before they begin
        operation. This is relatively important in modern
        warfare because artillery batteries must move often to
        keep from being hit from counterfire. This principle is
        demonstrated in the U.S. Army's MLRS surface to
        surface missile system. The MLRS vehicle can carry up
        to eight unguided rockets in one tracked vehicle. An
        inertial guidance system in the vehicle is used to
        position the vehicle and aim the launch box at the
        target. A single MLRS vehicle, such as the one shown
        below, can stop, aim, shoot and leave within four
        minutes while providing the firepower of an entire

    Integration into ballistic missile systems
        A RAND study has shown that the accuracy of short
        range ballistic missiles such as the Scud or the No Dong
        I can be improved by 20% to 25% by using the civilian
        SPS GPS signals. The GPS receiver is used to provide
        more accurate boost phase velocity measurements to
        the guidance system. Differential correction provides
        little added benefit because other systemic errors begin
        to dominate. Longer range ballistic missiles benefit
        more because they are more affected by boost velocity

    Integration into cruise missile systems
        Biological weapons can be dispersed more easily and
        more effectively from a cruise missile than from a
        ballistic missile. Even civilian grade GPS provides
        sufficient accuracy for a low cost cruise missile to lay
        down a biological toxin such as anthrax in a desired


    The RAND Corporation is a federally funded research group
    that focuses on national and military issues. The organization
    was formed to be a U.S. Air Force think tank studying
    nuclear weapons targeting issues in the '60s. RAND has
    several papers on GPS, some discussing the use of GPS for
    ballistic missile guidance. These papers may be ordered
    directly from RAND.