Boom Selection

The mechanical booms are used to extend the sensor heads past the plasma sheath in order to take ambient plasma density measurements.  The original design for the hybrid plasma probe required four sensor heads.  Two sensors were located on the ends of the two booms (one sensor head per boom) for the ambient plasma density measurements.  The other two sensor heads were located on the sides of the satellite for ram and wake plasma density measurements.  Two different boom designs were under consideration; the first was a hinge-mounted, swinging boom and the second was a telescoping boom.

            For the single-hinge, mounted boom some constraints arose in the placement of the boom on the satellite due to issues with balance and stabilization.  In order to balance the satellite, the single-hinge would be mounted to the center (vertically and horizontally) of the side panel of the satellite.  The boom would be constrained by a time-release device, which is located at the end of the boom, opposite of the hinge.  At the time of deployment, the time-release device would free the boom.  The force provided with a kick off spring deploys the boom.  The boom swings out 90˚, perpendicular to the side panel of the satellite.  The boom is secured in its deployed position by a locking device located in the hinge.  Once secured, the boom would be considered a single, rigid body. 

The second design is a telescoping boom, which is located within the base of the satellite.  A picture of a telescoping boom used in a sounding rocket can be seen in Figure 3.  The two outer plates of the boom are attached to the inner structure of the satellite.  The third plate, or sliding plate, is located between the outer plates.  It is free to slide on the two rods between these outer plates.  The boom is attached in the center of the base of the sliding plate.  Before the deployment of the boom, the sliding plate is restrained next to the rightmost outer plate as seen in Figure 3.

 
Figure 6: Telescoping Boom

   The boom in Figure 3 is a two part, telescoping boom.  There is a thinner boom located within the outer boom, which attaches to the sliding plate.  Before deployment, the thinner boom is moved within the outer boom.  In Figure 3, the thinner boom has been pulled out of the outer boom for illustrative purposes only.  Externally, the only part of the telescoping design that is visible would be a small portion of the end of the boom.  A small hole is cut out of the solar panels on the side panel to allow the boom to slide in and out of the satellite’s structure without any interference. 

Upon deployment, the time-release device would free the sliding plate.  A kick off spring, located within the housing of the endplate, would provide the force necessary to completely deploy the telescoping boom, as seen in Figure 4.   

Figure 7:  View of the tube housing the kick off spring

 When the sliding plate is deployed by the kickoff spring, it moves along the two guide rails until it reaches the leftmost, outer plate of Figure 3.  There is a hole in the left, outer plate to allow the boom to slide through.  A conical shaped holder on the sliding plate attaches the boom to the sliding plate, as seen in Figure 5.   

Figure 8:  Conical Shaped Boom Attachment

  When the sliding plate reaches this hole, the conical shaped holder of the sliding plate becomes wedged in the hole.  This locks the boom in its final position; and the boom is considered to be a rigid body.  In the situation of a two part, telescoping boom, a smaller kickoff spring is located within the outer boom at the base of the sliding plate.  There is a second, smaller kick off spring located at the base of the thinner boom to drive the thin boom out of the outer boom.  The thinner boom locks into place by a method similar to the conical mount wedging into a hole, used for the outer boom and outer plate.  The outer boom wedges the thinner boom when it has fully deployed, thus locking it into place.

The single, hinge-mounted boom would be simpler to design and construct than the telescoping boom.  Hinge-mounted booms have been used frequently in space before and they have proven to be a qualified choice for our needs.  The hinge-mounted boom would be designed with the guidance of an experienced sponsor, Walter Holemans, of Planetary Systems Corporation.  The hinge-mounted boom design would also be lighter than the telescoping boom.  However, the length of the boom in the hinge-mounted design is limited by the position of its attachment to the satellite.  Since it is required to attach the hinge at the center of the satellite’s side panel, the length of the boom would be at most, half the height of the satellite, or 22.5 cm.  Also, all the components of the single, hinge-mounted boom design are located externally on the satellite.  This requires a significant amount of surface area on the outside panels, and thus would decrease the number of active solar cells on the outer panels.  This decrease in solar panel affects the amount of power generated to charge the batteries, hence limiting the amount of available power to the other components of the satellite.

            On the other hand, the telescoping boom is primarily located within the satellite.  The only area of the solar panels that would be needed for the telescoping boom would be a small hole for the boom to move through.  This design greatly reduces the amount of solar cells sacrificed, thus allowing more power to be produced by the solar cells for the other components of the satellite.  The nature of the design of the telescoping boom allows for a longer boom than that of the hinge-mounted model.  Since the sliding plate is located at one extreme of the satellite and a small portion of the boom extends through the side panel in the restrained position, a single boom could be as long as 40 cm.  However, a pyro-wire cutter device was used to deploy the boom in the telescoping model.  This would be a safety issue with NASA/AFRL, as the use of pyrotechnic devices is not allowed.  Therefore, an appropriate substitute would be needed.  The telescoping boom design would be heavier, with most of its mass located in the center of the satellite.  This interferes with the Attitude/Orbit Control group’s goal of achieving a spinning-oblate stabilization method for the satellite, in which the satellite approximates a short and fat object by extending mass away from the center.

The length required of the boom was determined to be 40 cm during LionSat’s Safety Review, on Monday April 14, 2003.  Since the maximum length of the boom in the hinge-mounted design is 22.5 cm, the telescoping boom model is the only option.  Therefore, the two booms for the satellite will be based on the telescoping design in Figure 6.