THESEUS (satellite)


Mission typeSpace observatory
OperatorEuropean Space Agency
Spacecraft properties
Power115 W[1]
Start of mission
Launch date2032 (proposed[2])
RocketVega-C[1] (baseline)
Orbital parameters
RegimeLow Earth orbit
Altitude600 km[1]
Inclination5° (equatorial)[1]
DiameterInfrared: 70 cm; Cassegrain type[1]
WavelengthsInfrared, Gamma-rays and X-rays

Transient High-Energy Sky and Early Universe Surveyor (THESEUS) is a space telescope mission proposal by the European Space Agency that would study gamma-ray bursts and X-rays for investigating the early universe.[1][3] If developed, the mission would investigate star formation rates and metallicity evolution, as well as studying the sources and physics of reionization.


THESEUS is a mission concept that would monitor transient events in the high-energy Universe across the whole sky and over the entirety of cosmic history. In particular, it expects to make a complete census of gamma-ray bursts (GRBs) from the Universe's first billion years, to help understand the life cycle of the first stars.[4] THESEUS would provide real-time triggers and accurate locations of the sources, which could also be followed up by other space- or ground-based telescopes operating at complementary wavelengths.

The concept was selected in May 2018 as a finalist to become the fifth Medium-class mission (M5) of the Cosmic Vision programme by the European Space Agency (ESA). The other finalist is EnVision, a Venus orbiter. The winner will be selected in 2021 and it would launch in 2032.[2][5]

The space observatory would study gamma-ray bursts (GRBs) and X-rays and their association with the explosive death of massive stars, supernova shock break-outs, black hole tidal disruption events, and magnetar flares. This can provide fundamental information on the cosmic star formation rate, the number density and properties of low-mass galaxies, the neutral hydrogen fraction, and the escape fraction of ultraviolet photons from galaxies.[1]

Science payload

The conceptual payload of THESEUS includes:[1]

  • Soft X-ray Imager (SXI), sensitive to 0.3-6 keV is a set of 4 lobster-eye telescopes units, covering a total field of view (FOV) of 1 sr with source location accuracy <1-2 arcmin.
  • InfraRed Telescope (IRT), sensitive to 0.7-1.8 μm is a 0.7 m NIR telescope with 15x15 arcmin FOV, for fast response, with both imaging and moderate spectroscopic capabilities (R~400). Mass: 112.6 kg.
  • X-Gamma ray Imaging Spectrometer (XGIS), sensitive to 2 keV-20 MeV, is a set of coded-mask cameras using monolithic X-gamma ray detectors based on bars of silicon diodes coupled with CsI crystal scintillator, granting a 1.5 sr FOV, a source location accuracy of 5 arcmin in 2-30 keV and an unprecedentedly broad energy band. Mass: 37.3 kg.

See also


  1. ^ a b c d e f g h The THESEUS space mission concept: science case, design and expected performances. (PDF). Lorenzo Amati, et al. March 2018. doi:10.1142/9789813226609_0421
  2. ^ a b ESA names space mission concepts in running for Cosmic Vision mission slot. David Szondy, New Atlas. 7 May 2018.
  3. ^ The Transient High Energy Sky and Early Universe Surveyor (THESEUS). Lorenzo Amati, Paul T. O'Brien, Diego Götz. Proceedings Volume 9905, Space Telescopes and Instrumentation 2016: Ultraviolet to Gamma Ray; 18 July 2016. doi:10.1117/12.2231525
  4. ^ ESA selects three new mission concepts for study. European Space Agency. Published by PhysOrg. 8 May 2018.
  5. ^ New ESA Orbiter Might Explain Why Venus Went So Wrong. Bruce Dorminey, Forbes. 8 May 2018.