Thursday, September 24, 2009

What is CHACE ??

CHandra’s Altitudinal Composition Explorer (CHACE) is one of the most sensitive Quadrupole Mass Spectrometer ever to be flown into the space. Developed at Space Physics Laboratory, a R&D center operating under Vikram Sarabhai Space Center (VSSC), ISRO.  CHACE was part of the Moon Impact Probe (MIP) Mission, which was launched in the month of October, 2008. Immediately after its deployment in 100 km orbit,  ISRO took a decision to detach the MIP from the main space craft to be able to have an impact on the southern pole of the moon on 14th November, 2008. While CHACE had a 22-minute observations; all the other instruments of Chandrayaan-I during this period were still under the hibernation period; and hence it can safely be said that the CHACE had opportunity to be part of the FIRST time scientific experiments of Chandrayaan-I project.

CHACE, Flight model
CHACE is a state-of-the-art marvel which is almost 10,000 times more sensitive than the mass spectrometers carried by the Apollo-17 team. Though, the Apollo equipment lived a 8-plus month life; they could never get a reliable data on the day time of the lunar ambiance; it could collect some data as the sun was on horizon. The reason being a very low night particle concentration during the dark part of the moon which could not have been detected; while on the day time the instrument was saturated due to in-appropriate integration times.

On the other hand, CHACE with a capacity to measure 100,000 particles/cc effortlessly measure the lunar ambiance thanks to the latest technology embedded in its detection system. The detector system can measure currents as small as femto-amperes (1.0 X 10(-15) amps). It covers a mass range of 1-100 amu with a resolution of 1-amu.

CHACE was carefully developed to fulfill the demanding conditions of a lunar mission. It weighs just around 3.3 kg while consuming a meager amount of 20 watts of power. Enormous efforts have been gone in preparing a payload which should be robust enough to make a lunar journey. Not only the instrument needs to withstand the vibrations during the lift-off it should also be able to live through the harsh environment of moon.

CHACE got switched on 15-minutes before the separation of MIP from the mother space craft, the actual mission lasted for 22-minutes after the separation. With 4-sec integration time, the instrument collected a total of around 600 spectra during its descend from 100-km orbit. The spectra were clean and rich in elements with a very high signal to noise ratio for few notable peaks. Here is a sample shown..

Published papers:

1. Comprehensive details (Sridharan, Ahmed et al., Planetary Sp. Sc., 1567, 2010)

2. First time measurements of lunar water (Sridharan, Ahmed et al., Planetary Sp. Sc., 947, 2010)

Dr. S.M Ahmed*, Project Manager, Space Physics Laboratory, Vikram Sarabhai Space Center-ISRO

* Presently, Principal Scientific Officer, University of Hyderabad,