The Polar
Satellite Launch Vehicle (PSLV) of Indian Space
Research Organisation (ISRO) is capable of undertaking
planetary missions for direct exploration of the Moon,
Mars and Venus. It can, for example, put a 480 kg
spacecraft in circum-lunar orbit at an altitude of 100
km and can carry about 280 kg and 300 kg respectively,
on Mars and Venus fly-by missions. For a 1000 km
circular orbiter mission to Mars and Venus, the
carrying capacity reduces to about 140 and 100 kg. The
Geosynchronous Satellite Launch Vehicle (GSLV), which
will shortly be commissioned, can significantly
enhance this capacity and can be used for missions to
inner planets (Mercury, Venus and Mars) as well as to
asteroids and comets.
A
mission to the moon is under active study by
ISRO33,34. The best choice for the first mission
appears to be a lunar polar orbiter with a
circular orbit, having an altitude of ~ 100 km.
Considering the weight of the lunar craft and
the fuel required for a nominal life of about
two years, about 60 kg should be available for
science payloads. Discussion of scientific
objectives and choice of payloads within the
weight constraints, scientific priorities and
expertise available indicate that
simultaneousphotogeological and chemical mapping
should provide a good approach to resolve some
of the problems discussed in the foregoing
sections. The following payloads are being
considered34: terrain mapping camera (TMC);
hyperspectral spectral imager (HySI); laser
ranging instrument (LLRI); low energy X-ray
spectrometer covering 0–10 keV region (LEX) and
hard X–g-ray
spectrometer covering 15–200 keV region (HEX).
The TMC uses three-strip imaging configuration
(fore and aft looking at ± 19.4o and the third
at nadir) and is designed to have 5 m spatial
resolution and 40 km swath. It can achieve a
height resolution of about 10 m. The HySI
employing a wedge filter operating in 400–90 0
nm band, will have a ground resolution of 80 m
and 32 channels will select the spectral bands
of interest with a spectral resolution of 15 nm
for mineralogic mapping. It can easily
distinguish anorthosite (highland), basalt
(mare) and some minerals expected to be present
at some depth within the moon. The LEX, using
well-collimated X-ray CCD or swept charge device
is designed to measure the concentration of Mg,
Al, Si, Ca, Fe and Ti, whereas the HEX, using a
CdZnTe solid state detector and CsI
anticoincidence system, would measure the
distribution of 222Rn, Th, U and some rare
earths on the moon. The superior energy
resolution and lower background of these
detectors should enable us to map the abundances
of Fe, Ti, U, Th, K, etc. with reasonable
spatial resolution (< 100 km) using their
de-excitation or decay radiations. An infra red
detector covering wavelengths up to 2.5 mm (for
mineral identification) and gamma-ray
spectrometer based on hyperpure germanium
detector may be suitable for detection of K, H
and other elements of interest. Though
desirable, it may be difficult to include these
instruments in the first lunar mission because
of cooling requirements, power and weight
constraints. This study should enable us to
determine the stratigraphic correlation of
various surface units in selected areas of the
Moon, which include some features in the SPAR
and areas of the north and South poles.
Information
Courtesy:
PRL, India
