Spacecraft Design

RAX-1 and RAX-2 are standard 3U CubeSats with physical dimensions of approximately 10 cm x 10 cm x 34 cm and approximate mass of 3 kg. The satellites conform to the 3U CubeSat standard such that they can be launched from the Cal Poly P-POD, a specialized container and deployment mechanism by engineers at Cal Poly San Luis Obispo that many launch providers are able to attach as secondary payloads to their launch vehicles. While smaller and lighter than traditional spacecraft, designing a nanosatellite for a science mission is no small task. The constraints on component size and weight present formidable design and operational planning challenges. These challenges were overcome by the ingenuity of engineers at SRI and the students, professors, and staff at the University of Michigan. The RAX-1 spacecraft was developed by over 40 students (undergraduate through graduate), six professional engineers, and one Michigan professor in just two years time. RAX-2, built to correct a solar panel failure on RAX-1 and continue the scientific mission, was launched less than one year after the RAX-1 launch.

Design Strategy

The general design strategy for RAX was to make use of commercial off-the-shelf (COTS) components to reduce development time and cost. Several of RAX’s subsystems are comprised of a central commercial component with support electronics (power, bus communication, switches, etc) built around it. However, there were many instances where subsystems needed to be designed from the ground up because COTS solutions did not meet mission requirements. While these instances cost the team a great deal of time and funds, the benefit was the development of in-house expertise for building customizable systems for future Michigan missions. Please see the subsystems section below for specific design details.

Design Implementation

RAX is comprised of seven subsystems, one payload, 15 total circuit boards, 7 microprocessors, and two FPGAs. The subsystem boards are designed around the PC-104 standard so that each board plugs into another at the 104-pin header from the base of the satellite up to the payload. From there, individual interconnects run from the electronics stack to the payload receiver. Aluminum rails run through each corner of the board, and threaded standoffs are located above and below to lock each board in place. The four long sides of the satellite are covered with eight solar cells each, leaving the top and bottom panels open for the communication and GPS antennas.

RAX-1 CAD Model Exterior
(click to image enlarge)
RAX CAD Interior Cutaway
(click to image enlarge)

Subsystem Design Information

Journal papers have been published on the RAX attitude determination system as well as the GPS system, an publications on the other subsystems are in work. The attitude determination and GPS papers are:

  • J.C. Springmann, A.J. Sloboda, A.T. Klesh, M.W. Bennett, J.W. Cutler, The attitude determination system of the RAX satellite, Acta Astronautica, Volume 75, June–July 2012, Pages 120-135, ISSN 0094-5765, 10.1016/j.actaastro.2012.02.001
  • S.C. Spangelo, M.W. Bennett, D.C. Meinzer, A.T. Klesh, J.A. Arlas, J. W. Cutler, Design and Implementation of the GPS Subsystem for the Radio Aurora ExplorerActa Astronautica, Volume 87, June-July 2013, Pages 127-138, ISSN 0094-5765, 10.1016/j.actaastro.2012.12.009

In addition to subsystem design papers, a full list of conference and journal papers can be found on the MXL publications page.

Weighing the RAX-1 CubeSat

We also have specification sheets for these subsystems:

Electric Power System
Spacecraft Specifications and Operations Summary

Please contact us with any questions you may have.

(Images © RAX Team)

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