Chandrayaan-1 (SARA)

On 22 October 2008 the Indian satellite, Chandrayaan-1, was launched from Srikharikota, India, to fly to the moon with a total of 12 instruments. One of these was SARA (Sub-keV Atom Reflecting Analyzer), developed and built by IRF in Kiruna.

The SARA instrument studied how the plasma around the moon interacts with the moon whose surface is not protected by an atmosphere or a magnetic field. For the first time ever, SARA could investigate energetic atoms that are knocked from the lunar surface when they are hit by the solar wind.

From the measurements carried out by SARA, it appears that the moon is a surprisingly strong source of hydrogen atoms. Scientists have previously believed, because the moon surface is a loose collection of irregular grains of dust, that every particle that hits it bounces between the grains and is absorbed.

In analysing data from SARA, the scientists discovered that every fifth incoming proton from the solar wind bounces off the lunar surface. In the process, the proton joins onto an electron and becomes a hydrogen atom.

Two sensors

SARA consisted of two sensors. One was a detector for energetic neutral atoms, CENA (Chandrayaan-1 Energetic Neutrals Analyzer), and the other, SWIM (Solar Wind Monitor), was an instrument to measure the flow of ions in the solar wind (the charged particles that flow out of the sun). The third part of the instrument SARA, the associated data-processing unit (DPU), was developed by  the Space Physics Laboratory – Vikram Sarabhai Space Center (SPL-VSSC) in India. The SARA experiment was the first collaborative project between IRF in Kiruna and the Indian Space Research Organization (ISRO).

Contact: Martin Wieser, martin.wieser@irf.se, IRF in Kiruna.