Paul S. Wilke

Multi-axis whole-spacecraft vibration isolation for small launch vehicles

Small launch vehicles present an economically viable method for placing small satellites into orbit. These launch vehicles would be even more attractive to satellite customers if they could provide a softer ride to orbit. Passive whole-spacecraft vibration isolation systems have been developed for small launch vehicles to greatly reduce the dynamic launch loads. To date, two types of isolation systems have been designed.

Whole-Spacecraft Passive Launch Isolation

Abstract : A spacecraft is subjected to very large dynamic forces from its launch vehicle during its ascent into orbit. These large forces place stringent design requirements on the spacecraft and its components to assure that the trip to orbit will be survived. The severe launch environment accounts for much of the expense of designing, qualifying, and testing satellite components. Reduction of launch loads would allow more sensitive equipment to be included in missions, reduce risk of equipment or component failure, and possibly allow the mass of the spacecraft bus to be reduced. These benefits apply to military as well as commercial satellites. This paper reports the design and testing of a prototype whole-spacecraft isolation system which will replace current payload attach fittings, is passive-only in nature, and provides lateral isolation to a spacecraft which is mounted on it. This isolation system is being designed for a medium launch vehicle and a 6500 lb spacecraft, but the isolation technology is applicable to practically all launch vehicles and spacecraft, small and large. The isolator significantly reduces the launch loads seen by the spacecraft. Follow-on contracts will produce isolating payload attach fittings for commercial and government launches.

Protecting Satellites from the Dynamics of the Launch Environment

Abstract : Reduction of the vibration and shock loads seen by spacecraft during launch would greatly reduce the risk that the spacecraft and its instruments will be damaged during their ascent into orbit, and would also allow more sensitive equipment to be included in missions. As the severe launch environment also accounts for much of the expense of designing, qualifying, and testing spacecraft components, significant cost can also be saved if dynamic responses seen by the spacecraft are reduced. The launch events include low frequency dynamic loads such as liftoff, motor excitation, buffet, motor starts and shutoffs. Spacecraft are also subjected to shock loads in the several thousands of gs level during their trip to orbit. These high shock loads usually result from some separation event, such as staging, spacecraft separation, and fairing separation. Protecting the satellite from these loads by whole-spacecraft vibration and shock isolation systems has now been demonstrated. The basic concept of whole-spacecraft isolation is to isolate the entire spacecraft from the dynamics of the launch vehicle. This paper discusses two different systems: the SoftRide system, which is a lower frequency (10 - 50 Hz) isolation system and the ShockRing system, this is designed to attenuate higher frequency loads (70 Hz and above), including shock. All seven flights of CSAs SoftRide systems have shown excellent loads reductions in the coupled loads analyses and verified in the flight telemetry data Component tests have been performed on the ShockRing using a specially built pneumatic gun that can generate 10,000 gs on the test article. Results from these tests demonstrate substantial reductions of the shock being transmitted to the payload. Results from a system test consisting of a spacecraft simulator, payload attachment fittings, avionics section, and shock plate will be discussed.

Whole-spacecraft shock isolation system

Spacecraft are subjected to shock loads in the several thousands of gs level during their trip to orbit. These high shock loads usually result from some separation event, such as staging, spacecraft separation, and fairing separation. Shock loads are very detrimental to spacecraft components, instruments and electronics. A new type of shock isolation system is discussed. This shock system, referred to as the SoftRide ShockRing, is a whole-spacecraft isolation system, i.e., it shock isolates the complete spacecraft from the launch vehicle. Seven whole-spacecraft vibration isolation systems (SoftRide) have flown to date and flight data confirms large reductions of the dynamic loads on the spacecraft. The standard SoftRide system is a lower frequency isolation system than the ShockRing, vibration isolating the spacecraft starting in the approximately 25 Hz range. The ShockRing is targeted at shock loads and is set to isolate above approximately 75 Hz. Component tests have been performed on the ShockRing using a specially built pneumatic gun that can generate 10,000 gs on the test article. Results from these tests demonstrate substantial reductions of the shock being transmitted to the payload. Results from a system test consisting of a spacecraft simulator, payload attachment fittings, avionics section, and shock plate are discussed. In the system tests, pyrotechnic devices were used to obtain the high levels of shock for the tests.

Whole-spacecraft vibration isolation for broadband attenuation

Launch vehicles impart high levels of vibration to spacecraft during launch. The vibration environments are defined over several frequency bands: (1) transient vibration <80 Hz, (2) random vibration 20 to 2000 Hz, and (3) pyrotechnic shock 100 to 10000 Hz. Loads from transient vibration define spacecraft design of primary structures such as spacecraft bus, solar panel and antenna supports, instrument mounts, etc. Loads from random vibration define the design for spacecraft light structures such as antennas and solar panels, and shock loads define the design of electronic components and instruments. The spacecraft must survive the combination of all vibration environments. This requires spacecraft structures, instruments, and components to be designed to minimize vibration across a broad frequency range. Spacecraft are designed for the short launch to orbit, which is well beyond the requirements for on-orbit performance. A better choice is to reduce the magnitude of the high launch loads across all frequency bands and design smaller and less costly spacecraft. SoftRide systems are under development for the first and second OrbitaVSuborbital Program (OSP) launches and for the TaurusNTI 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.

Whole-spacecraft vibration isolation system for the GFO/Taurus mission

A whole-spacecraft isolation system for the GFO/Taurus mission was designed, fabricated, tested, and subsequently flown on February 10, 1998. This isolation system was designed to reduce dynamic responses on the GFO spacecraft caused by the resonant burn dynamic load introduced by the Castor 120 solid rocket motor. Longitudinal (flight direction) response of the GFO spacecraft center of gravity, due to the resonant burn load, was reduced by a factor of seven. The isolation system design was very nonintrusive to existing hardware, lightweight, and effective. Flight data indicates that the isolation system performed as designed. The GFO spacecraft had a successful launch and is currently operational on-orbit. A second flight of this type of isolation system occurred in October 1998. Similar isolation systems are planned for other flights in 1999 and 2000. This whole-spacecraft isolation technology was highly successful for the GFO/Taurus mission.

Payload isolation system for launch vehicles

A spacecraft is subjected to very large dynamic forces from its launch vehicle during its ascent into orbit. These large forces place stringent design requirements on the spacecraft and its components to assure that the trip to orbit will be survived. The severe launch environment accounts for much of the expense of designing, qualifying, and testing satellite components. Reduction of launch loads would allow more sensitive equipment to be included in missions, reduce risk of equipment or component failure, and possibly allow the mass of the spacecraft bus to be reduced. These benefits apply to military as well as commercial satellites. This paper reports the design and testing of a prototype whole-spacecraft isolation system which will replace current payload attach fittings, is passive-only in nature, and provides lateral isolation to a spacecraft which is mounted on it. This isolation system is being designed for a medium launch vehicle and a 6500 lb spacecraft, but the isolation technology is applicable to practically all launch vehicles and spacecraft, small and large. The feasibility of such a system on a small launch vehicle has been demonstrated with a system-level analysis which shows great improvements. The isolator significantly reduces the launch loads seen by the spacecraft. Follow-on contracts will produce isolating payload attach fittings for commercial and government launches.

Whole-spacecraft vibration isolation on small launch vehicles

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.

Passive and active launch vibration studies in the LVIS program

A U.S. Air Force-sponsored team consisting of Boeing (formerly McDonnell Douglas), Honeywell Satellite Systems, and CSA Engineering has developed technology to reduce the vibration felt by an isolated payload during launch. Spacecraft designers indicate that a launch vibration isolation system (LVIS) could provide significant cost benefits in payload design, testing, launch, and lifetime. This paper contains developments occurring since those reported previously. Simulations, which included models of a 6,500 pound spacecraft, an isolating payload attach fitting (PAF) to replace an existing PAF, and the Boeing Delta II launch vehicle, were used to generate PAF performance requirements for the desired levels of attenuation. Hardware was designed to meet the requirements. The isolating PAF concept replaces portions of a conventional metallic fitting with hydraulic- pneumatic struts featuring a unique hydraulic cross-link feature that stiffens under rotation to meet rocking restrictions. The pneumatics provide low-stiffness longitudinal support. Two demonstration isolating PAF struts were designed, fabricated and tested to determine their stiffness and damping characteristics and to verify the performance of the hydraulic crosslink concept. Measurements matched analytical predictions closely. An active closed-loop control system was simulated to assess its potential isolation performance. A factor of 100 performance increase over the passive case was achieved with minor weight addition and minimal power consumption.

Passive Isolation Systems for Launch Vehicles

One of the most severe environment that a satellite will be subjected to during its lifetime will occur during qualification testing and launch. This paper summarizes the results and status of research efforts in the area of satellite isolation from the launch environment. The objective of this effort was to reduce the launch induced-dynamic acceleration of the satellite by insertion of a passive isolator. Isolation issues involving the use of passive elements and launch vehicle system-level requirements will be discussed.