After the engine tests are completed PERSEUS is ready to begin its “second life”. During the Science Phase the satellite will perform astronomical measurements. Since a multi spectral, multi purpose imaging and spectroscopy space telescope (such as the Hubble Space Telescope) is not feasible for a small satellite mission a niche, currently not covered by a space mission, had to be found. This niche was spotted by the Institute for Astronomy and Astrophysics at the Univeritaet Tuebingen. The scientists there proposed a small telescope in combination with a spectrometer and a one mega pixel CCD detector in the vacuum UV (VUV) range. Telescope and spectrometer will be especially designed to work at wavelengths between 120 nm and 180 nm with a resolution of about 0.15 nm (R = 1000) since important spectral lines of hot plasmas are located in this range.
It is planned to observe nova, dwarf nova and supernova explosions as well as active galactic nuclei (AGNs).

• Novae are thermonuclear explosions of hydrogen on white dwarfs. This hydrogen was previously gravitationally drawn off another star accompanying the white dwarf in a binary system.
• Supernovae are explosions of stars that are either collapsing under their own gravity at the end of their life cycle, or the explosion of a white dwarf that crossed the Chandrasekhar limit (about 1.4 solar masses) after drawing mass off its companion star.

• In contrast to the two previous events, dwarf novae occur regularly with a period of several days to some weeks. Previous to a dwarf nova explosion the gas of the accompanying star drawn to the white dwarf forms a disc. This accretion disc is unstable and phases of high accreation rate trigger an outburst due to the release of gravitational energy.