Patent Application
20080111031
1. Field of the Invention
This invention relates generally to a deployable truss structure for a spacecraft and, more particularly, to a deployable truss structure for maintaining a membrane sufficiently flat in a space environment.
2. Discussion of the Related Art
Spacecrafts sometimes employ various types of devices, such as reflectors, antenna arrays, sensors, etc., that must be deployed from the spacecraft on a boom and associated truss when the spacecraft is on orbit or in space. These booms and trusses typically employ support rods coupled together by hinges that allow the boom and the truss to be folded or stowed in the spacecraft envelope or fairing during launch, and then be unfolded in space to the deployed position. Various devices and techniques are known in the art for unfolding or deploying a boom and truss, including the use of motors, preloaded springs and various types of actuators.
For certain spacecraft missions, there is a need to deploy a flat membrane on a truss at the end of a boom, such as a Fresnel lens that is part of a telescope, where the lens is a thin plastic sheet. It is necessary that the lens be folded in the fairing for launch, and then be deployed in space on the truss, where the truss maintains the lens in tension so as to keep it flat for effective operation. The truss must be stowed in a small volume, be lightweight and have a high bending and torsional stiffness. If the membrane does not have uniform tension, then some areas of the membrane will have greater tension than other areas of the membrane, possibly causing wrinkles that adversely affect the membrane's performance.
In accordance with the teachings of the present invention, a truss structure for supporting a membrane is disclosed that is able to be deployed in space and maintain the membrane sufficiently flat with uniform tension. The truss structure includes a circular perimeter truss and a transitional truss. The transitional truss includes a series of ties that are coupled to the perimeter truss and the membrane. When the truss structure is deployed, telescoping parts of the perimeter truss that are stowed in expansion cause the transitional truss to expand and pull the membrane into the flat configuration.
Additional features of the present invention will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings.
The following discussion of the embodiments of the invention directed to a truss structure for deploying a membrane in a flat configuration under uniform tension is merely exemplary in nature, and is in no way intended to limit the invention or its applications or uses.
As will be discussed in detail below, the truss structure 18 has a configuration that when deployed spreads the lens 28 in a flat configuration having uniform tension, according to the invention. The Fresnel lens 28 is provided by way of a non-limiting example in that the truss structure 18 of the invention has application for supporting any type of membrane in a flat configuration with uniform tension.
The transitional truss 32 includes a plurality of transitional truss sections 52, each including a pair of ties 54 and 56. One end of each tie 54 and 56 is coupled to a common location of the lens 28, and the other end of each tie 54 and 56 is coupled to opposing ends of a batten 44 or 46. Some of the transitional truss sections 52 are angled and some are straight, where every one of either the batten 44 or 46 includes three transitional truss sections 52 coupled to it and every other of the batten 44 or 46 includes a single transitional truss 52 coupled to it in an alternating sequence, as shown. A prime batten 58 including a truss 50 couple the telescopic boom 16 to the perimeter truss 30 with the appropriate rigidity and pointing stiffness. It is noted that the transitional truss 32 can have other configurations within the scope of the present invention.
The lens 28 includes an inner membrane 60 and a perimeter catenary 62. The membrane 60 is made of a suitable plastic, such as Kapton, for the Fresnel lens 28, and has a desired thickness. The catenary 62 provides a transitional region between the membrane 60 and the ties 54 and 56 to provide a robust enough structure for supporting the membrane 60 with uniform tension in a flat configuration. In this configuration, the lens 28 is positioned at a central location of the truss structure 18 in that it aligns midway along the length of the battens 44 and 46 as provided by the ties 54 and 56.
The structural components of the truss structure 18 can be made of any suitable material for the purposes described herein. In one non-limiting embodiment, the longerons 40 and 42, the battens 44 and 46 and the diagonals 48 are made of a graphite composite and have a tubular shape. The ties 54 and 56 are foldable members and can be tapes or cables that provide tension, but not compression. Suitable materials for the ties 54 and 56 include graphite, Kevlar and fiberglass. The longerons 40 and 42, the battens 44 and 46, the diagonals 48 and the ties 54 and 56 are coupled together in the configuration as shown using any suitable coupling device, such as metal or graphite fittings, glue, etc, which would be well understood to those skilled in the art. When the truss structure 18 is deployed, as shown, the lens 28 and the transitional truss 32 will be in tension, and the perimeter truss 30 will be in compression. In order to provide such a compression, the longerons 40 and 42, the battens 44 and 46 and the diagonals 48 must be relatively stiff.
In one non-limiting embodiment, the lens 28 has a diameter of about two meters and a thickness of about 0.001 inches. The perimeter truss 30 has a diameter of about three meters and the telescopic boom 16 has a deployed length of about eight meters. In another embodiment, the lens 28 has a diameter of about three meters, the perimeter truss 32 has a diameter of about four meters and the telescopic boom 16 has a deployed length of about sixteen meters. Further, the satellite body 14 has a width of about twenty-four inches, a height of about twenty-four inches and a length of about forty inches. It is noted, however, that there is no limit for the diameter of the perimeter truss 30, and can be as large as it needs to be, such as 10, 20 or 50 meters.
The truss structure 18 is compressed or folded into a cylinder when it is in the stowed configuration. A strap (not shown) is wrapped around the outside of the perimeter truss 30 to hold it in the stowed configuration. Once the spacecraft body 12 is on orbit, and the lens 28 is to be deployed, the boom 16 is first extended from the spacecraft body 12 in a manner that is well understood in the art. The strap is then released by a suitable device (not shown). The diagonals 48 are telescopic members that are stowed in expansion, where they may have static energy. When the strap is released, the static energy stored in the diagonals 48 is released causing the diagonals 48 to reduce in length, which causes the perimeter truss 30 to expand and open, pulling the transitional truss 32 and the lens 28 into tension and providing the configuration shown in
The foregoing discussion discloses and describes merely exemplary embodiments of the present invention. One skilled in the art will readily recognize from such discussion, and from the accompanying drawings and claims, that various changes, modifications and variations can be made therein without departing from the spirit and scope of the invention as defined in the following claims.
