Recently, Elon Musk’s SpaceX launched its Falcon Heavy spacecraft on its third mission, and the most complex one yet by the company. Among the various reasons which make the mission important, one is its huge payload — 24 satellites from various organisations, including government agencies. These will be launched in three different orbits. What are these satellites for?

* Deep Space Atomic Clock- Sent by NASA, DSAC is incredibly precise and compact, and has the size of a toaster. Accurate timekeeping is crucial to the performance of GPS, and atomic clocks work by observing the behaviour of atoms as precisely as possible. The NASA website says DSAC is expected to be stable to better than one microsecond per decade (one second per 10 million years), which would be about 50 times more accurate than atomic clocks already abroad GPS satellites.

At present, satellites rely on an exchange of signals with Earth, where atomic clocks calculate the time it takes for the signals to arrive. The new technology targets aims at helping spacecraft navigate by themselves, relying on the new atomic clock in space. The DSAC project will perform a year-long demonstration in space.

* ASCENT green fuel- One of the satellites will be a test spacecraft for a safer rocket fuel. The traditional fuel used in satellites is hydrazine, which is extremely toxic to humans as well as the environment. The new alternative is called ASCENT (Advanced Spacecraft Energetic Non-toxic Propellant), formerly called AF-M315E, which is a hydroxyl ammonium nitrate fuel/oxidiser blend. First developed by the US Air Force and now launched as part of a NASA-led collaboration, ASCENT is described as a fuel with significantly reduced toxicity levels compared to hydrazine, and potentially shorter launch processing times, resulting in lower costs.

* Solar-powered sail- LightSail 2 is a crowd-funded solar sail project from the Planetary Society. It seeks to become the first orbiting spacecraft to be propelled solely by sunlight. In 2005, the Planetary Society launched the world’s first solar sailing spacecraft, Cosmos 1, which was lost due to a rocket failure. In 2015, LightSail 1 spacecraft successfully completed a test flight. LightSail 2, which is aimed to go into orbit, is enclosed within Prox-1, a small satellite built by Georgia Tech students, which is scheduled to deploy the sail on July 2, the Planetary Society website says.

* Ashes of the dead- Falcon Heavy’s payload includes the ashes of over 150 deceased persons, one of those being astronaut Bill Pogue, who flew on Skylab in the 1970s and died in 2014. Among other items aboard, the US Air Force Research Laboratory had space weather experiments, while the National Oceanic and Atmospheric Administration has six small atmospheric experimental satellites for weather forecasting.