Chandrayaan-I : For beginners

What does it take to go to moon? Why now? What is in it for us?

Moon is one object that catches fascination of humans like no other celestial body. “Chandamama Rave, jabilli raave..” is probably one of the first words Telugu kid would hear. This children’s song is a desperate effort by a mother to feed the kid, while distracting the kid by asking the moon to come and serve the food. For a kid, it almost seems to be within reach, as if an extended hand could grab it. From imagining that Moon would sail through the clouds to realizing Moon is a 385,000Kms away and not coming down any time, is a revealing journey for a kid. Chandrayaan-I is the first baby step to making this object of our fascination closer than it ever was.

After the second successful launch of the Polar satellite Launch Vehicle (PSLV-C2) in 1999, which lofted Indian satellite OCEANSAT along with Korean and German satellites, Dr. Kasturirangan, then ISRO chair, proposed going beyond the earth’s orbit. Here is one effort to delve into the mission and timeline.

What does it take to reach moon?

I used to wonder what the big deal is about going to the moon. Didn’t we send couple of launch vehicles every year! Here is an analogy to better explain the finer details.

Imagine a hunter trying to hit a flying bird with a stone, analogy being moon is the bird and stone is Chandrayaan-I. And simply put, hunter has to make sure flight paths of the bird and the stone meet. For this,

• First, shooter has to assess the flight path of the bird.


• Secondly, shooter has to assess where in the flight path, stone should hit the bird.


• Third, hunter has to throw the stone in the right direction with enough velocity and angle, such that it will be at the right place and right time to hit the bird, not early not later. For this, one has to take into account velocity of the stone, earth’s gravity and other factors like wind.

The above is a gross oversimplification for our case. As one can imagine, the skill needed to replicate that with moon is incomparably high.

• First, we have to assess the flight path of the moon, easiest task of all.


• Second, we need to identify where Chandrayaan should meet the moon. Unlike the hunter in earlier example, Earth is rotating and revolving around the Sun while the Moon is revolving around Earth. So, relative positions of Earth and Moon need to taken into account. From earlier analogy, imagine trying to assess bird's flight path from a moving jeep, or for more fun, from rotating chair in a moving jeep.


• Finally, its all about throwing the satellite in the right direction with the right velocity and making corrections on the way, if needed.

Easy? Lets see :

Hunter-Stone-Bird :The first picture shows initial plan for Chandrayaan.

• Chandrayaan-I is first made to circle around the earth in increasingly large elliptical orbits (diagram below), nudging them into higher orbits requires switching on board thrusters at precisely the right place (Perigee-Point in orbit that is closest to earth). At various points while it is orbiting Earth, Chandrayaan-I goes through gravitational pulls of other celestial bodies including Sun and Moon. This needs to be closely accounted for.


• The distance the probe has to travel to meet moon is 385000 Kms, while moon’s diameter is approximately 3,774 Kms. Just like the bird, Chandrayaan should be at the desired point 3,85,000 Kms away at the precise time, not early, not later. And unlike our hunter-bird analogy, there little margin for error. After travelling 3,85,000 Kms, if the velocity of the craft is too low, it will crash into the moon or miss it all together. If the velocity is too high, it may just zoom past the Moon, without giving moon's gravity a chance to "catch" Chandrayaan.

So, it has to fall within moon’s gravity cleanly. Achieving this requires delicate maneuvering of the probe using on board rockets/boosters for course correction. In this plan, as it begins a third orbit, Chandrayaan would have been thrusted towards the moon. From above picture, it seems like if it misses the moon, then we pretty much loose the craft as it continues into infinity. This is closer to hunter-stone-bird analogy : If hunter misses the bird, he will loose the stone as well.

Hunter-Boomerang-Bird

Shortly before launching, new trajectory plan with more orbits was adopted. In this plan, Chandrayaan's orbit will be gradually raised, until it reaches an orbit that intersects with the moon. It is my interpretation that this is analogous to a boomerang. If the hunter uses boomerang to hit the bird and misses, boomerang still comes back to him. He has another chance to hit the bird.

Why now?

While we wait for Chandrayaan to reach its destination, it would help to understand the steps that finally led to this mission. While the end result catches our attention, we fail to appreciate the time and perseverence that is needed to get there. Here is the timeline from when the idea of moon travel started to get traction in the Indian scientific community.

May 1999 - Sriharikota : Second operational launch of PSLV vehicle. For the first time India has launched three satellites on one launch.

Oct 1999 – IAS 1999, Lucknow : The micro symposium on “An Indian case for going to the moon” was oranized under the aegis of Dr. Kasturirangan. This set the ball rolling for Chandrayaan-I. [1]

Feb 2000 – ASI meeting, Ahmedabad : Astronomical Society of India joined the discussions.

National Lunar Mission Task Force was constituted by the Indian Space Research Organisation (ISRO) under the leadership of Dr. George Joseph. [2]

April 2003 : Peer group of scientists discussed the Study Report of the Task Team and unanimously recommended mission to moon. [2]

August 15 2003 : India’s Prime Minister Atal Bihari Vajpayee announced. “Our country is now ready to fly high in the field of science. I am pleased to announce that India will send her own spacecraft to the moon by 2008. It is being named Chandrayaan-1″.

Nov 2003 : Government of India approved the Indian mission to moon called Chandrayaan-I.[3]

March 2004 : Announcement of Opportunity : ISRO Inviting proposals for scientific payloads on Chandrayaan-I [4]

June 2005 : Agreement for including European instruments on Chandrayaan-I signed (3 instruments)[6]

May 2006 : ISRO and NASA sign MOU for Chandrayaan-I (for 2 instruments) [7]

Oct 22, 2008 : Liftoff, Chandrayaan-I launched from Sriharikota, Andhra Pradesh. India is sixth country to send mission to moon.

Oct 26, 2008 : Chandrayaan-I enters deep space as it enters EBN3.

What is in it for us?

This mission to moon is of great significance in terms of pushing the limits of Indian Space Research and understanding the dynamics of deep space. This revives the same sense of exploration and curiosity that has led our ancestors thousands of years back to establish trade links with Europe and spread the Indian region of influence throughout South East Asia. Though this civilization has lost its way in the past few centuries, it is time to set our home in order and look beyond tomorrow.

But above all, it makes us relevant in the new world order that is on the horizon.