Six-unit (6U) CubeSats are recognized as the next nanosatellite to be considered for standardization. The CubeSat standard established by California Polytechnic University (Cal Poly), which applies to 1U–3U sizes, has proven to be a valuable asset to the community. It has both provided design guidelines to CubeSat developers and a consistent, low-risk interface to launch service providers. This has ultimately led to more flight opportunities for CubeSats. A similar path is desired for the 6U CubeSat. Through this process of standardization, a consistent, low-risk interface for the 6U needs to be established.
Two design concepts for this interface have been developed and presented to the community. One design approach is similar to the current approach taken by Cal Poly through their 3U Poly Picosatellite Orbital Deployer (P-POD). This design relies on four corner rails to guide and constrain the satellite with little preload in the axial direction. This approach allows movement of the satellite under load and makes it difficult to predict the satellite’s response to the loading conditions. The other design approach utilizes a clamping action on two rails along the length of the satellite. This improves predictability, but does rely on friction to hold the satellite in the axial direction.
In an effort to create a safe, more predictable satellite constraint method while providing a guided ejection, an alternative 6U interface design was developed. The first innovation is to separate the constraint and guide features on the ejector, leading to a reduction of guiding rails from four to two. This directly increases the amount of ejector internal packaging volume. The second innovation is to fully constrain the satellite in all directions. Lateral directions are constrained by using two tapered pins in the bottom and two tapered pins at the top. The tapered feature allows for ease of separation after launch. At the door side, the loads are transferred from the satellite to the ejector using a “shear plate.” This shear plate, along with the pins, is retracted from the satellite’s path by attaching them to the ejector door. To constrain the axial direction, a floating clamp-like interface is used at the door, while the satellite seats are flush at the bottom with the ejector. A two-stage deployment is to be executed mechanically. The satellite is held at the top of one of its guide rails with a lever. When the door rotates open to a certain position, the lever rotates away from the satellite and allows it to proceed with ejection via a compression spring and pusher plate. The door will be completely open prior to the satellite exiting the ejector.
This work was done by John D. Hudeck and Luis H. Santos of Goddard Space Flight Center. GSC-16795-1