The structure is the backbone of every CubeSat. It carries all subsystems, survives the launch loads and forms the interface to the dispenser that releases the satellite into orbit. Because CubeSats share dispensers and rockets with other payloads, the structure has to follow strict rules. These are set out in the CubeSat Design Specification (CDS), maintained by the CubeSat Program at Cal Poly San Luis Obispo. This article summarises the key requirements of Revision 14.1 from February 2022.
Units and mass limits
The CDS defines a 1U CubeSat as a 10 cm cube with a mass of up to 2 kg and covers configurations from 1U to 12U. Its table of typical maximum masses lists 2 kg for 1U, 3 kg for 1.5U, 4 kg for 2U, 6 kg for 3U, 12 kg for 6U and 24 kg for 12U. Heavier satellites may be accepted on a mission by mission basis, depending on the dispenser.
The rails
A CubeSat slides into its dispenser on rails along its edges. The CDS sets several rules for them:
- Rails must be at least 8.5 mm wide, measured from the edge of the rail to the first protrusion.
- Rail surfaces should have a roughness below 1.6 micrometres, typically achieved by proper anodising.
- Rail edges should be rounded with a radius of at least 1 mm.
- The rail ends must provide at least 6.5 mm by 6.5 mm of contact area with neighbouring CubeSats.
- At least 75 percent of the rail should be in contact with the dispenser rails.
- No component on the side faces may protrude more than 6.5 mm from the plane of the rails.
Materials
According to the CDS, the structure should be made from aluminium alloy. Typical alloys for the main structure and the rails are 7075, 6061, 6082, 5005 and 5052. Aluminium surfaces that touch the dispenser rails must be hard anodised to prevent cold welding. Developers who want to use other materials should contact the launch provider or dispenser manufacturer.
Centre of gravity
The CDS limits how far the centre of gravity may lie from the geometric centre. For a 1U CubeSat, it must stay within 2 cm in each axis. For a 3U CubeSat, the allowed range along the long axis grows to 7 cm.
Deployment switches and the remove before flight pin
From delivery until release in orbit, the CubeSat must stay powered off. At least one deployment switch, pressed while the satellite sits in the dispenser, disconnects the power system. If the switch toggles, the satellite must reset to its pre-launch state. A remove before flight (RBF) pin cuts all power during ground handling.
Separation from neighbouring CubeSats
When several CubeSats share a dispenser, each must have a mechanism that encourages separation from its neighbours, typically separation springs.
Frequently asked questions
What is a CubeSat frame made of?
According to the CubeSat Design Specification, the structure should be made from aluminium alloy, typically 7075, 6061, 6082, 5005 or 5052. Surfaces that touch the dispenser rails must be hard anodised.
How heavy can a 3U CubeSat be?
The CDS lists a typical maximum mass of 6 kg for a 3U CubeSat. Heavier satellites may be accepted case by case, depending on the dispenser.
Why do CubeSats have rails?
The rails guide the CubeSat inside its dispenser and form the contact surface with the dispenser and neighbouring CubeSats during launch and deployment.
Related reading
- CubeSats Explained: Sizes, Standards and How They Reach Orbit
- Payload Fairings, Adapters and Separation Systems
- Satellite Environmental Testing
Sources
Cover image: A NASA engineer installs a CubeSat into its dispenser during payload processing for Firefly's Demo-2 mission, April 2024. Credit: NASA/Jacob Nunez-Kearny (KSC-20240424-PH-FRF01_0005), public domain.