18 THE WEEK • JULY 21, 2019
COVER STORY
CHANDRAYAAN-WHILE INDIA HAS PROVEN
TECHNOLOGY WITH
CHANDRAYAAN-1 AND THE
MARS ORBITER MISSION
FOR MOST OF THE STEPS,
THE SOFT LANDING IS A
NEW GAME ALTOGETHER.Moon journeys are tricky busi-
ness. The distance of about 3,
lakh km requires great trajectory
accuracy, as even a minor veering
off course could result in the craft
wandering in space, far from its
intended destination. Space envi-
ronments are hostile, and the risk
of losing communication with the
ground station (India’s is the Indian
Deep Space Network antenna at By-
alalu, Karnataka) is high. The moon
is not a static body; it rotates on its
axis and revolves around the earth,
which itself is revolving around the
sun. The lunar capture (getting into
the moon’s orbit) requires some
mind-boggling calculations. The
moon has a lumpy gravity, because
of its uneven mass and extreme
temperature variation. In the desti-
nation desired for, this ranges from
-157°C to 121°C, which is harsh on
the hardware.
Finally, the landing itself has to
be finely calibrated, kicking up as
little dust as possible. Even a grain
of dust is enough to disrupt the
lander’s functions and render it use-
less. ISRO is not taking its chances.
It chose this particular landing site
because, from what we know of the
moon, the terrain at this spot is not
too pockmarked or rocky. ISRO also
plans to do more imaging of the site
to minimise a rocky landing. Since the probe will enter the
lunar orbit 27 days before the landing, there will be time
enough to do better mapping with the probe.
While India has proven technology with Chandrayaan-
and the Mars Orbiter Mission (MOM) for most of the steps,
the soft landing is a new game altogether. Chandrayaan-
had an orbiter and a lander, which was an impact probe.
The lander’s job was to take rapid images of the moon as it
detached from the orbiter and fell on the surface. Once it
crashed onto the moon, it became inert. Chandrayaan-2,
however, will have an orbiter, as well as a lander (Vikram)
and rover (Pragyan). The latter two have to land intact on the
moon, because they have a full lunar day’s work (14 earth
days) ahead of them. To achieve this, they will first be low-
ered from a 100km orbit around the moon to a 30km one.
Then, they will descend, very slowly, to minimise impact