The end of the Cold War has made large-aperture telescope technologies from the U.S. Strategic Defense Initiative program available for non-defense missions. Now, a four-meter aperture space telescope, a seventy percent larger aperture than that of the Hubble space telescope, has been proposed for a dual military and astronomical mission. An important part of the preliminary design work was to determine how to meet the telescope's pointing and jitter criteria. The telescope will be required to maintain an rms pointing accuracy of 24 nrad, preferably over periods of several hours. Vibration was a critical issue in the study because of the stringent pointing requirement, the relatively light structures desirable for spacecraft, thermal transients, the presence of disturbances from many spacecraft mechanisms (solar array drives, momentum wheels, thrusters, antenna steering mechanisms, etc.), and the many external appendages. The four-meter telescope design uses an inertial optical reference system combined with an actively controlled `fast steering mirror' in the target beam path to actively counteract vibration.