Embedded Files
Design of a Daksha satellite. The gold dome carries the detector packages. Credit: Daksha team.
Three kinds of eyes, on one dome
Three kinds of eyes, on one dome
Each Daksha satellite carries three types of detectors, each tuned to a different band of X-ray and gamma-ray energies. Mounted on a dome that faces every direction at once, they let Daksha see most of the sky without ever needing to turn.
For astronomers: technical details
For astronomers: technical details
Per satellite: 13 Low Energy Packages (LEPs; five SDDs each, 1–30 keV), 17 Medium Energy Packages (MEPs; twenty CZT detectors each, 20–200 keV; 13 on the dome and 4 facing the Sun) and 4 High Energy Packages (HEPs; 20×20×2 cm NaI(Tl) read out by SiPMs, 0.1 to >1 MeV). All photons are time-tagged with microsecond precision. Design, effective areas, background and sensitivity: Bhalerao et al. 2024, Daksha: On Alert for High Energy Transients (Experimental Astronomy 57, 24; arXiv). Coded-mask options for the LEPs: Mandal, Vadawale & Bhalerao 2026 (Experimental Astronomy 62, 1). All Daksha papers are listed on our Publications page.
An early mechanical model of the Daksha dome, with one Medium Energy Package mounted. Credit: Daksha team.
The shape of Daksha
The shape of Daksha
The heart of each satellite is a dome with 13 square faces, approximating half a sphere. Every face carries two detector packages — one for low energies and one for medium energies — so the dome looks out in all directions at once. Four more medium-energy packages sit under the satellite, facing the Sun, to cover the rest of the sky. Tucked inside the dome are four high-energy packages: at their energies the dome is nearly transparent, so they can see straight through it.
Because the faces point in different directions, a burst shines more brightly on the faces turned towards it. Comparing how many X-rays each face records tells Daksha roughly where in the sky the burst came from.
Low Energy Packages (LEP): 1–30 keV
Low Energy Packages (LEP): 1–30 keV
For the softest X-rays, Daksha uses silicon drift detectors: small, electronically cooled silicon sensors that measure the energy of each X-ray very precisely. Each LEP holds five of them. The same type of detector has already flown to the Moon on India’s Chandrayaan-2 mission. The Sun is extremely bright in soft X-rays and would blind these detectors, so no LEPs are placed on the side of the satellite that faces the Sun.
Technical: 450 µm active thickness, 1.5 cm² per SDD, thin beryllium window, ~2.5% energy resolution at 5.9 keV, 10 µs timing; median all-sky effective area ~26 cm² per satellite.
Medium Energy Packages (MEP): 20–200 keV
Medium Energy Packages (MEP): 20–200 keV
The workhorses of Daksha are cadmium zinc telluride (CZT) detectors — crystals that turn each incoming X-ray directly into a tiny electrical pulse. Each detector is divided into a grid of 256 pixels, and each MEP carries twenty detectors. These detectors have a long track record in space, including on the CZT Imager of India’s AstroSat, where they have been used to measure the polarisation of gamma-ray bursts. The team has built and tested a fully populated laboratory model of the MEP.
Technical: 5 mm thick CZT, 3.9 × 3.9 cm, 16 × 16 pixels, ~12% energy resolution at 60 keV; 304 cm² per MEP on-axis; median all-sky effective area ~1300 cm² at 100 keV; passive cooling through a radiator plate.
Laboratory model of a Daksha Medium Energy Package, with all twenty CZT detectors mounted. Credit: Daksha team.
Close-up of a CZT detector on the MEP electronics board. Credit: Daksha team.
High Energy Packages (HEP): 100 keV to beyond 1 MeV
High Energy Packages (HEP): 100 keV to beyond 1 MeV
At the highest energies, Daksha uses large crystals of sodium iodide, which give off a tiny flash of light whenever they absorb a gamma ray. An array of silicon photomultipliers — very sensitive light detectors — records each flash and works out where in the crystal it happened. The four HEPs sit inside the dome, where they can also catch gamma rays that first bounce off a medium-energy detector; tracking such bounces helps work out where the gamma ray came from.
Technical: one 20 × 20 × 2 cm NaI(Tl) crystal per HEP, sparse SiPM array at ~40 V, ~1 cm position resolution; median all-sky effective area ~760 cm²; MEP–HEP Compton events usable for localisation and Compton imaging.
How Daksha finds where a burst came from
How Daksha finds where a burst came from
Daksha’s detectors don’t form images like an ordinary camera. Instead, Daksha works out a burst’s direction from how brightly it lights up the different faces of the dome. For a typical faint burst this gives a position to within about 10 degrees; for bright bursts, to about a degree. When both satellites see the same burst, comparing the two improves the position further.
Many optical telescopes can only see a patch of sky about a degree across, so the team is studying ways to do better. One promising idea is to place a coded mask — a plate with a carefully designed pattern of holes that casts a shadow on the detectors — in front of the low-energy detectors. Studies show this could pin bursts down to between one and two degrees, and better than a degree in the best case.
Technical: projection-method localisation ~10° for a 1 s burst of fluence 10⁻⁷ erg cm⁻², ≈1° for 10⁻⁶ erg cm⁻² s⁻¹; joint two-satellite triangulation 1–2°. A coded-mask telescope with position-sensitive SDDs or X-ray CCDs could reach ~0.7°–1.8° (Mandal, Vadawale & Bhalerao 2026 (Experimental Astronomy 62, 1)).
From detection to alert in a minute
From detection to alert in a minute
Software on board each satellite constantly watches for sudden rises in the number of X-rays and gamma rays. When it spots a burst, it works out the burst’s position, brightness and duration, and sends a short message to the ground within about a minute, to be shared publicly with astronomers worldwide. Every X-ray and gamma ray that the detectors record is also stored and sent down on each pass over a ground station, so scientists can later analyse every event in full detail.
Technical: ~2 kB alert packets, distributed through the General Coordinates Network (GCN); full time-tagged event data downlinked every ground-station pass; data made public after a limited proprietary period, in standard FITS formats.
Where the satellites will fly
Where the satellites will fly
Both satellites will orbit about 650 km above the Earth, close to the equator, on opposite sides of the planet. From that height the Earth blocks a little under a third of the sky, and satellites must also switch off their detectors while passing through a region of intense radiation over the South Atlantic. With two satellites, each covers what the other cannot see: each one sees about 71% of the sky at any moment, and together they cover about 86% of the sky averaged over time. For comparison, the Burst Alert Telescope on NASA’s Swift sees about 11% of the sky at a time.
Support Daksha
Support Daksha
If you would like to see Daksha fly, please take a minute to fill in our short support form. Every response helps show the scientific community’s interest in the mission.
Page updated
Google Sites
Report abuse