Microsats and picosats are miniature satellites. Although there is no formal classification, they are generally referred to as a follows:
Satellites with a wet mass (including fuel) between 100–500 kg (220–1100 lb), are sometimes called minisatellites, but more often just "small satellites." A minisatellite has a size somewhere between a small refrigerator and a small car. Oftentimes, minisatellites (and anything smaller) are released as part of a package of more than one, where a payload releases multiple sub-units upon reaching orbit. Despite being relatively small, minisatellites generally use the same technology as larger satellites.
Microsatellites have a wet mass between 10 and 100 kg (22–220 lb): roughly between the size of a small refrigerator and a microwave. Abbreviated "microsats," microsatellites in space are not to be confused with the same term in genetics, which means something entirely different. Microsats are popular with universities and companies who want to perform experiments into space but lack the funding to launch a conventionally-sized satellite. As the current cost to launch something into space is about $5,000 per kg, launching a microsat still costs between $50,000 and $500,000.
Nanosatellites, or "nanosats," are the next stage smaller than microsats. These have a wet mass between 1 and 10 kg (2.2–22 lb). Nanosatellites have a size roughly between that of a toaster and a microwave. These are sufficiently small that many can be deployed, making "swarms". Sometimes these swarms coordinate with a central, larger satellite, which sends data to the ground using a more powerful antennae. Complex docking procedures are also possible. Microsats and nanosats are small enough that innovative propulsion, attitude control, communication and computation systems are required.
Picosatellites are the smallest, with a wet mass between 0.1 and 1 kg (0.22–2.2 lb), between the size of a toaster and a tennis ball. These are the smallest satellites and some of the most interesting. CubeSat is a standardized version of a picosatellite, with dimensions of 10 cm x 10 cm x 10 cm. These are especially popular in academia. Its dimensions are chosen because the agency responsible for tracking satellites and space junk only tracks objects of this size or larger.
