An apparatus called a "pneumatic stinger" has been developed to enable a first spacecraft, operating under remote control, to grasp a second spacecraft that is in orbit or other unpowered flight. The pneumatic stinger, which is mounted on the first spacecraft, is inserted in a rocket-engine nozzle of the second spacecraft, then actuated to grasp the nozzle from the inside, as explained below. Both NASA and the Department of Defense could use this apparatus for servicing satellites. The design of the pneumatic stinger might also be adaptable to soft-docking mechanisms or grappling mechanisms for use on Earth.
The pneumatic stinger offers advantages over an older stinger-type apparatus used to attach a first spacecraft to a rocket nozzle on a second spacecraft. In operation of the older apparatus, an astronaut on the first spacecraft had to position the stinger mechanism in alignment with the nozzle on the second spacecraft, then actuate a trigger mechanism to initiate attachment. In addition, it was necessary for the second spacecraft to be equipped with a structural surface, adjacent to the nozzle, that mated with an interface ring on the stinger and that carried loads. Often, it was not possible to equip a satellite-type spacecraft with a structural surface of this type. In the cases of satellite-type spacecraft that could be equipped with such structural surfaces, the surfaces were required to be of specific shapes and designs. In contrast, the pneumatic stinger is fully automated in that it can be operated without intervention by an astronaut, functions without need for precise initial alignment, and can be used without expensive structural modification of the spacecraft to be grasped.
Figure 1 shows the pneumatic stinger in its preactivation state. A soft bumper on the insertion end of the stinger prevents damage to the combustion chamber associated with the nozzle. A pair of bladders (two are used for protective redundancy) is located near the insertion end. After insertion of the stinger in the nozzle and combustion chamber, these bladders are inflated into contact with the interior wall of the combustion chamber, thereby capturing the second spacecraft. Two larger bladders are located about midway along the stinger (the exact location depending on the size of the nozzle); these bladders are inflated (see Figure 2) to center the stinger and react loads through the nozzle to the structure that attaches the nozzle to the second spacecraft. The gas for inflation is supplied from redundant pressurization cartridges through valves and regulators controlled by electronic circuits.
The inflated inner and outer bladders trap the throat between them. The axial reaction of the inner (combustion-chamber) bladders is balanced by the opposite reaction of the outer (nozzle) bladders; this balance serves to preload the stinger into controllable contact with the nozzle. The contact between the bladders and the nozzle is soft; it does not damage the nozzle because the bladders hold the nozzle at relatively uniform pressure, which the nozzle is designed to withstand. Moreover, the preload is applied in all directions, so that axial loads and moments can be applied to and through the stinger and nozzle to control the orientation of the second spacecraft.
In addition to the advantages mentioned above, the pneumatic stinger offers two other advantages over the stinger in the older docking apparatus:
- After insertion of the stinger, the only action required is opening of pressurization valves. Consequently, it is easy to fully automate the operation of the pneumatic stinger.
- Use of the pneumatic stinger is relatively inexpensive.
This work was done by William C. Schneider of Johnson Space Center.
This invention has been patented by NASA (U.S. Patent No. 5,735,488). Inquiries concerning nonexclusive or exclusive license for its commercial development should be addressed to
the Patent Counsel
Johnson Space Center
Refer to MSC-22745