My Subjective Probabilities on India’s Moon Mission

[Author’s Note December 29 2008: Please see my ‘Chandrayaan adds a little good cheer! Well done ISRO!”  — as a good Bayesian would, I  have had to update my subjective probabilities ex post and gladly so!]

The subjective probability I would place on the odds

of our Moon rocket leaving earth orbit successfully is 20:1 against,
of it reaching the moon’s vicinity about 50:1 against,
of it entering lunar orbit successfully about 100:1 against,
and of it transmitting half the data it is intended to about 200:1 against.

Going to the Moon requires a spacecraft reach an “escape” velocity of some 40,000 km per hour. After some 324,000 km, the craft escapes Earth’s gravity and comes to a “standstill” or “neutral” point, a fictional station on the Earth-Moon axis, still some 32,000 km (about 19 Moon radii) away from the Moon. The Moon’s gravity then gradually takes over, drawing the spacecraft faster and faster towards the Moon, to either land on its surface or go into orbit around it, though to avoid a fatal impact crashing into the Moon, the spacecraft may require retrorockets to slow itself down.

All Indians will be delighted if the Moon-launch  tomorrow is successful. At the same time, all Indians, especially millions of wide-eyed children, will be more than disappointed if ISRO’s plans fail through avoidable error.  It was of the highest national importance to try to ensure beforehand that the Indian mission succeeded if it is going to be tried at all.  That has not taken place.

The numerous sources of possible failure include

(A) launch-failure causing the spacecraft to never reach, let aside exit from, terrestrial space onto a path to the Moon, all through belts of intense heat and radiation;

(B) trajectory-failure causing the spacecraft to move wrongly through cislunar and translunar space, miss the Moon and go into solar orbit like everything else in the solar system;

(C) failing to enter lunar orbit, crashing into the Moon instead;

(D) failing to transmit intended data from lunar orbit.

Only if all these and more are avoided, can ISRO’s Moon mission be considered successful.

Here are some questions the PM and his Government needed to answer before the liftoff but failed to do so:

1. Is there an indigenous rocket powerful enough for a spacecraft to reach 40,000 kmph, the escape-velocity from Earth’s gravity?  If a foreign rocket is being used in whole or in part, what are the terms of collaboration?

2. India’s will be mankind’s 85th mission to the Moon on record and there  was a vast amount of publicly available knowledge already gained in other countries; did ISRO do a survey of all previous Moon missions by other countries, especially the USSR and USA since 1957 to investigate and analyse the numerous errors and failures they made?  If not, why did it not do so ?  If we did absorb all existing lessons available, and there are people at ISRO wholly conversant with what went wrong with every case of launch-failure, trajectory-failure, instrumentation-failure causing spacecraft to fail to reach or leave Earth orbit, or miss the Moon, or fail to communicate etc, what identifiable improvements did this learning cause in our Mission-planning?  The cause of nationalism is not served if we repeat the known mistakes of others;  why were we made to feel so confident we were not headed to be making the same mistakes as had been already made by others?

3. It is a blow to national prestige and self-confidence if there is failure at any stage of this difficult enterprise and it may have been better to do the job in discrete and successful stages or not do it at all than fail at it most spectacularly; was any thought given to breaking down the present aim into several stages – e.g., improving rocketry to aim at a “parking orbit” around Earth permitting ground control to better calculate trajectories to the Moon, then to flyby the Moon, then to attempt to go into lunar orbit? Why are scientific payloads being planned to be carried even before we have gained any experience in successful rocketry through terrestrial, cislunar, translunar and lunar space?

4. Our country has not been a major manufacturer of engines, aircraft bodies, computers or communications and imaging equipment, all vital to this enterprise; did we import the components to be used and if so, which ones?

5. Science is universal, and belongs to all mankind; all mundane international disputes appear petty when seen from selenocentric space which is the one good reason to want to try to reach it; why not release into the public domain for scrutiny by everyone in the country and the world the equations involved in the rocketry, and even whether Newtonian or Einsteinian frames of reference are being used?

Subroto Roy
October 21 2008

Advertisements