A CubeSat is a class of miniaturised satellite based around a form factor consisting of 10 cm cubes. CubeSats have a mass of no more than 2 kg per unit, and often use commercial off-the-shelf components for their electronics and structure. CubeSats are a class of nanosatellites that use a standard size and form factor.

The standard CubeSat size uses a “one unit” or “1U” measuring 10x10x10 cms and is extendable to larger sizes; 1.5, 2, 3, 6, and even 12U. Originally developed in 1999 by California Polytechnic State University at San Luis Obispo and Stanford University to provide a platform for education and space exploration.

The development of CubeSats has advanced into it’s own industry with government, industry and academia collaborating for ever increasing capabilities. CubeSats now provide a cost effective platform for science investigations, new technology demonstrations and advanced mission concepts using constellations, swarms disaggregated systems.

With the current SLS and Artemis mission, once Orion had drifted a safe distance away from the SLS upper stage, this stage was able to deploy small satellites that were hiding inside, these were CubeSats.

One of the CubeSats made a slow flyby of an asteroid which measures just 18 metres across. The solar sail spacecraft captured humanity’s first up-close images of an asteroid this small.

The other CubeSats had different jobs to do, including four aimed at studying the Moon.

Have a look at this NASA paper : What are SmallSats and CubeSats?