Engineers at Johnson Space Center have invented a relatively inexpensive, lightweight device that provides vibrational and thermal isolation for low-power electronic equipment. The device was developed for use in outer space, where it has already proven successful in connection with the Inter-Mars tissue-equivalent proportional counter on shuttle flights and in a gas proportional counter flown aboard the satellite of the TRW Small Spacecraft Technology Initiative. The device could also be used on Earth to isolate sensitive items from extremes of temperature and vibration.
Until now, vibration and thermal isolation have been provided, in general, by means specific to each electronic component, electronic circuit, or other item for which the need has occurred. Vibration isolation has been effected by use of little more than adjustable spring devices. Moreover, it has been necessary to consider a vibrationally isolated item to be surrounded by a dynamic envelope in which it can move, making it difficult to insulate or thermally isolate the item from any structure in its vicinity. Worse, for purposes of spaceflight, the prior art does not necessarily provide thermal control, electrical isolation, or protection against electromagnetic interference.
The present device (see figure) does provide thermal control, electrical isolation, and protection against electromagnetic interference. An item to be isolated is placed inside a boxlike shroud, wherein it is floated on pads made of Nomex (or equivalent) aramid felt that have been bonded to inside surfaces of the shroud. The shroud is hard-mounted on a spacecraft structure through four attachment feet.
During the intense vibrations associated with the spacecraft launch, the felt pads provide dynamic damping of the vibrational loads, keeping these loads to a level at or below that allowed by the design of the item to be isolated. In outer space, the felt pads provide thermal isolation for experiments. Inasmuch as the shroud is unpressurized, the only means of transfer of heat to or from the item to be isolated are conduction through the felt pads and radiation between the item and the inner shroud surfaces. Radiative heat transfer is controlled via judicious selection of the thermo-optical properties of both the interior and exterior surfaces of the shroud so that the net thermal effect is to satisfy the thermal requirements for the item to be isolated. The operation of the device, with and without external multilayer insulation (MLI), has been demonstrated in tests and in flight. The need to add MLI is determined for each application.
This device contains no mechanisms and is very inexpensive, in comparison with prior devices developed for the same purpose. Unlike in similar products, the dynamic envelope of the item to be isolated is contained within the shroud. Its versatile design has been demonstrated during operations in a variety of thermal and vibrational environments. The combination of the shroud and felt provides electrical isolation in addition to vibrational and thermal isolation. The felt is easily tailored: the number, initial compression, and density of the pads can all be varied to obtain the desired thermal and vibrational response.
This work was done by Steven L. Rickman, John P. McManamen, Sharon K. Whitcomb, Christopher P. Hansen, William C. Schneider, and Gautam D. Badhwar of Johnson Space Center and Robert P. Dunn of Lockheed Martin.