vehicles and also functions to isolate higher frequency shock loads. Whole-spacecraft shock isolation  systems, on the other hand, are being designed to attenuate launch shock loads from about 70 Hz and  upward. Most damaging shock loads have their most significant magnitude in the 1000 Hz and upward  frequency range, however dynamic loads between 100 Hz and 1000 Hz are still considered to be shock  loads and this frequency range has been known to be a real source of problems for some launch vehicles.  So the logical question is: Why not always use a vibration isolation system, as opposed to a shock  isolation system, and get the isolation benefit from the lowest possible frequency? The answer lies in the  relationship between the isolation system, the launch vehicle guidance, navigation, and control (GNC)  system, and coupled loads analysis. The whole-spacecraft vibration isolation system is lower in frequency  and stiffness than a shock isolation system and is carefully sized, for each mission, using coupled loads  analysis. The first bending modes of the satellite are typically reduced by the introduction of a vibration  isolation system and therefore must be designed in concert with the GNC system such that control  instabilities are not introduced. Again, this is possible, and has been done successfully on several flights.  The whole-spacecraft shock isolation system, on the other hand, is relatively high in frequency and  stiffness and has little or no effect on the GNC system or on coupled loads analysis. For missions that do  not anticipate any problems with lower frequency vibration loads, a shock isolation system will be easier to  include with only minimal effort.  Under a number of contracts from the Air Force Research Laboratory, Space Vehicles Directorate, CSA  Engineering has been working on the concept of whole-spacecraft vibration isolation and shock systems  (hereinafter referred as the SoftRide system) since 1993. A number of design and performance analyses  were performed on a variety of liquid-fueled and solid-fueled launch vehicles, all of which showed great  promise. However, it was not until the launch of the GFO spacecraft on Orbital Science’s Taurus launch  vehicle in February 1998 did an isolation system designed to vibration-isolate the complete spacecraft  actually fly. Since that time, two different types of systems have flown, and design work has been  performed on several additional !aunch vehicle/spacecraft combinations. The following sections discuss  each type of system, show hardware pictures, and present flight results.  SoftRide Vibration Isolation Systems  Typical vibration isolation systems work by connecting the isolated structure (payload) to the base  structure (launch vehicle) by means of a resilient mount or mounts. The resilient mounts have low relative  stiffness as compared to the base and payload, and some degree of structural damping. The stiffness of  the resilient mounts is tuned so that the frequency of vibration of the supported payload on the resilient  mounts is a specified value (isolation frequency). Damping in the resilient mounts reduces the amplitude  of response of the payload at the isolation frequency when the system is under external excitation. The  resilient mounts must allow relative motion between the vibrating base structure and the payload at the  isolation frequency, which is referred to as the isolator stroke.  Because the spacecraft is a major structural component of the launch vehicle/spacecraft dynamic system,  variations in the isolation frequencies greatly effect the dynamics of the launch vehicle/spacecraft system.  Any unpredicted changes in the dynamics could have an adverse effect on the control system of the  launch vehicle and cause instability and thereby loss of the mission. Therefore, the stiffness properties of  the isolation system must be predictable for the duration of the flight. This requires a linear isolation  system under all load cases, including preloads from -2g’s to +6g’s accelerations of the launch vehicle.  This eliminates using an elastomeric material (Le., rubber mounts) as the stiffness component of the  isolation system. Owners of spacecraft, which costs tens to hundreds of millions of dollars, demand a  metallic connection between the spacecraft and the launch vehicle. This connection, which is the SoftRide  system, must also provide a fail-safe connection, must be able to handle, without overstressing, the  deflections due to the sum of the dynamic and quasi-static acceleration loads of the spacecraft, and must  be of minimal height (reduces payload volume) and weight (reduces payload weight).  On expendable launch vehicles, spacecraft are attached to the launch vehicle at their base either at  discrete points or by a band clamp. If the attachment stiffness is made soft in the axial or thrust axis, then  we refer to that type of isolation system as an axial system. Axial systems can provide isolation in the axial  and two rocking directions and therefore can isolate against both axial and bending modes of the launch  vehicle. If the attachment stiffness is made soft in the in-plane directions at the attachment points, then  90