<title>Whole-spacecraft vibration isolation on small launch vehicles</title>

Abstract

Small launch vehicles historically provide a very rough ride to spacecraft during launch. This is particularly true of solid-fueled launch vehicles. In order for the spacecraft to survive such a trip to orbit, one of two choices must be made: (1) design all structure, payloads, and systems on the spacecraft to be strong enough to survive the high launch loads, or (2) reduce the magnitude of the high launch loads. The former is not a good choice because it typically requires additional cost, schedule, and weight. The latter is the preferred choice because it allows the focus of the spacecraft design to be primarily for on-orbit performance rather that for launch survival. Under a number of contrasts from the Air Force Research Laboratory, Space Vehicles Directorate, whole- spacecraft vibration isolation systems have been in development since 1993. This work has resulted in two whole- spacecraft isolation systems (SoftRide) that have been flown on Taurus launch vehicles, the first in February 1998 with the GFO spacecraft and the second in October 1998 with the STEX spacecraft. Both of these isolation systems were designed primarily to reduce axial dynamic responses on the spacecraft due to resonant burn excitations from the motors of the solid- fueled booster. Full coupled-loads analyses were used to predict the performance of the SoftRide systems. Using the isolation requirements derived from these analyses, hardware having the correct damping and stiffness was designed to implement the isolation system. All isolation system components were extensively tested and characterized. Typical results show 85% attenuation (i.e., only 15% of original) for the worst case resonant burn condition and 59% attenuation for a combination of static plus worst case resonant burn condition in the axial spacecraft c.g. location. No detrimental effects from the SoftRide system were observed. Limited flight data from the two flights agree with the predictions. SoftRide systems are now under development for the first and second OSP launches and for the Taurus/MTI launch. Additionally, isolation systems are being designed for larger liquid-fueled launch vehicles. This isolation system technology will greatly further the goal of better, faster, cheaper, and lighter spacecraft.