PicSat was a French observatory nanosatellite, designed to measure the transit of Beta Pictoris b, an exoplanet which orbits the star Beta Pictoris.

PicSat was designed and built by a team of scientists led by Dr. Sylvestre Lacour, astrophysicist and instrumentalist at the High Angular Resolution in Astrophysics group in the LESIA laboratory with Paris Observatory, Paris Sciences et Lettres University and the French National Centre for Scientific Research (CNRS). It was launched on 12 January 2018, and operated for more than 10 weeks before falling silent on 20 March 2018. The cubesat decayed from orbit on 3 October 2023.

With an age of about 23 million years, Beta Pictoris is a very young star. Compared to the Sun, which is 4.5 billion years old, Beta Pictoris is about twice as large in mass and size. Beta Pictoris is relatively close to the Sun: just 63.4 light-years away, making it bright and easy to observe. This makes Beta Pictoris interesting for study as it allows astronomers to learn more about the very early stages of planet formation.

In the early 1980s, a large disk of asteroids, dust, gas, and other debris were found surrounding Beta Pictoris, leftovers from the formation of the star. In 2009, a giant gas planet orbiting Beta Pictoris was discovered by a team of French astronomers led by Anne-Marie Lagrange from Grenoble, France. The planet, named Beta Pictoris b, is about seven times as massive as Jupiter. It orbits Beta Pictoris from a distance at around ten astronomical units: ten times the distance between the Earth and the Sun, and about the same distance between Saturn and the Sun.

In 2016, it was predicted that Beta Pictoris b's Hill sphere or the planet itself would be passing in front of its star as seen from the Earth. The detailed observation of such a transit would reveal detailed information about the planet, such as its exact size, the composition of its atmosphere, its density, and its chemical composition. Because Beta Pictoris b is so young, this information would reveal more about the formation of giant planets and planetary systems.

However, as Beta Pictoris b's orbit is not well known, the moment of transit could only be estimated roughly. The transit was predicted to occur between the summer of 2017 and the summer of 2018. A transit of the planet would have lasted only a few hours; a transit of the planet's Hill sphere would have lasted anywhere from days to months. Continuous monitoring would have been the only way to capture the phenomenon. Since Earth-based observatories would not be able to accurately capture the transit, as long-term continuous monitoring was unlikely to work with Earth's atmosphere, day-night cycle changes, and scheduling conflicts, only a satellite could accurately capture the transit.

The purpose of PicSat was to continually observe Beta Pictoris' brightness in order to capture the change in brightness when Beta Pictoris b transited over the star and partially blocked some light.

PicSat, a contraction of "Beta Pictoris" and "satellite", was a CubeSat. PicSat was composed of three standard cubic units, called a "3U", each 10x10x10cm in size.