The CubeSat standard (10 × 10 × 10 cm and weighing 1kg) has evolved into one of the most widely accepted families of picosatellite designs. A CubeSat can package a universe of payload possibilities for launch into space at a fraction of the cost of traditional multimillion- dollar satellites. The success of any CubeSat project will owe much to how closely participants adhere to unforgiving timelines linked to launches scheduled far in advance. Serving to jumpstart projects and keep them on track within the typical 24 months from inception to launch, Pumpkin, Inc. created an off-the-shelf CubeSat Kit™ offering all the advantages of a standardized assembly. Conforming fully to the recognized CubeSat specification, the kit’s structure, electronics, and software are intended to save time and money.
The kit’s finished, ready-for-launch flight-module structure forms a unique sheet-metal solution, which is predesigned, pre-fabricated, and in stark contrast to how structures usually are produced. Historically, CubeSats have been machined from aluminum blocks carrying the worries over machining error and lost time and resources. Machined blocks further require thick cross-sections to accommodate threaded bosses for fasteners, which limits internal volume and adds bulk in a chassis where every millimeter and every gram will count. Precision sheet-metal construction instead of machining mitigates these issues and facilitates the thinnest possible chassis walls (0.0560" in thickness) without infringing on the overall dimensional tolerances (100 ±0.1mm on a side) demanded in the CubeSat specifications.
Envisioning a very thin 5052-H32 aluminum chassis, designers at Pumpkin turned to threaded fastening hardware for attachment functions. (Much thicker sheet metal can be tapped for threads, but, in this case, the necessarily thicker walls would constrain internal dimensions.) The need for reliable metal threads was fulfilled by installing self clinching fasteners permanently in the sheet-metal assembly.
The newest-generation CubeSat Kit integrates various types of self-clinching fasteners in the base plate (six threaded nuts, four thru-hole threaded standoffs, and one unthreaded thru-hole standoff) and cover plate (four threaded nuts). The nuts (thread size M3) serve to attach the base and cover plates to the chassis wall assembly; threaded standoffs support internal PCBs; and the single nonthreaded standoff acts as a guide bushing for the Remove-Before-Flight pin.
A reduced parts count and lower weight attributable to less fastening related hardware represent an added bonus. With the clinch fasteners requiring only a mating screw to complete final attachment, ten flat head stainless screws (M3) do the job. Overall, the total hardware tally in the CubeSat Kit is less than half the amount (and weight) encountered in similar conventional structures.
Taking advantage of thinner aluminum construction and the enabling threaded fasteners, the CubeSat Kit chassis boasts the largest possible internal volume (97 × 97-mm section width). Even after incorporating a processor, radio, and power supply boards, roughly 40 × 97 × 97 mm of volume (almost half a liter) remains available to place a payload.
The fasteners in the CubeSat are stainless (specified for their non-magnetic properties and resistance to corrosion) and their installation occurs during fabrication after the structure has been applied with a combination of conductive and hard-anodized coatings. Final assembly for a project team is made simple, streamlined, and mistake-free.
At the sheet-metal shop, the fasteners are inserted into drilled holes and a squeezing force is applied to embed the clinching ring completely in the aluminum panel. Permanently installed and exhibiting high torque out and push out resistances, the fasteners allay any concerns about potential loosening or failing when subjected to the extreme vibration of a rocket launch.
At launch, CubeSats (three at a time) are safely tucked away inside a P-POD until they are deployed. Once in space, missions can last from a few days to one or two years. Then, the CubeSat will deorbit naturally or via an onboard mechanism (such as deployable conductive tether).
The first space-bound CubeSat Kit was assembled by a small university team from Bogota, Colombia, and was successfully launched into orbit earlier this year from the Baikonur Cosmodrome in Kazakhstan. Dozens of other projects are in progress and will follow.