by Prasad Ganti
Millions of people across India watched the live coverage of the intended soft landing of the Vikram lander near the South pole of the moon on 7th September. It was past midnight. Things really went very well until the last minute or two. The trajectory appearing on the screen showed the spacecraft right on the target. Then there was a slight deviation from the planned trajectory. And then the dot stopped, signifying that the spacecraft stopped sending any signals to the Earth. The mission control went silent. All the news channels came to a standstill. Expecting some good news, hoping against hope, hopes do not die that easily after all. After a while it became obvious that something had really gone wrong.
Vikram Lander was part of the Chandrayaan 2 mission to the moon. The launch took place on July 21st atop GSLV Mark III (Geostationary Space Launch Vehicle). This model of GSLV is India’s most powerful launch vehicle capable of putting 4 tonnes of payload into space. But not powerful enough like the Saturn V rocket to hurl the spacecraft to travel towards the moon in three days. Getting a little boost at a time, the orbit around the Earth became increasingly elliptical over a few weeks. With a little more boost it went into orbit around the moon. After stabilizing its orbit around the moon, the Vikram lander separated itself from the orbiter. The lander contained a rover and some scientific instruments, while orbiter contained some more scientific instruments. The picture below shows the trajectory Chandrayaan 2 took.
Soft landing a spacecraft is the most difficult maneuver. More difficult than the launch, or putting it in an orbit around the moon. From such great speeds of thousands of miles per hour, it has to be slowed down in a very controlled manner to a standstill by the time it reaches the surface. The final moments are the most difficult ones. What Dr. Sivan the ISRO (Indian Space Research Organization) Chief called as fifteen minutes of terror. The complete landing sequence had to be programmed into the Vikram lander ahead of time. There is no scope for Mission Control from the Earth to alter the trajectory in real time.
Although officially not confirmed, I read in India Today magazine that the Vikram lander did a maneuver to orient itself to point the camera towards the ground to get a better estimate of the landing site. In the process, a somersault occurred and the speed increased and the Vikram lander spun out of control. It is presumed to have crash landed. The orbiter took a picture a few days later. The picture showed that the lander is still in one piece and is lying on the surface at a tilted angle. NASA’s LRO (Lunar Reconnaissance Orbiter) failed to find the Vikram lander when it tried to picture the vicinity of the intended landing site. Presumably because the shadows were lengthening as the days approached the lunar dusk (a lunar day lasts 14 days). Also the landing site was closer to the south pole where the Sun appears at a slanted angle. This increases the amount of shadows in the cratered surface closer to the pole.
The radio contact with the Vikram lander was lost just as it spun out of control. Either the hard landing damaged the radio equipment or the tilted angle is pointing the antenna in the wrong direction. In any case, the chances of making contact is slim to none. The lunar night is so cold and dark that the batteries and the equipment would have died permanently.
Space is a tough game. It is dangerous and unforgiving. US, Russia, Europeans, Israel, Japan and China have all experienced space disasters. Apollo 1 caught fire on the launch pad in 1967 and all the three astronauts died. Apollo 13 nearly perished and with great difficulty and some luck NASA was able to bring the crew home. Space shuttle Challenger perished soon after takeoff while Columbia was destroyed during reentry into the Earth’s atmosphere. Space-X, the private company pioneered by Elon Musk faced several failures before starting ferrying supplies to the International Space Station. More recently, Israel lost a spacecraft while trying to soft land on the moon.
Regardless of the crash landing, it has been a tremendous achievement by the Indian scientists. The orbiter is still going around the moon. The orbiter with ever sophisticated instruments consisting of cameras (to capture high resolution pictures), spectrometers (to analyze light and other forms of radiation), radar (Synthetic Aperture Radar to analyze the ground surface up to a certain depth), and various detectors of X-rays, electrons etc. The trajectory of the orbiter is inclined to the equatorial plane, since the Vikram lander was supposed to land closer to the south pole of the moon. From this trajectory, these instruments will reveal a lot about our natural satellite.
Congratulations to the entire ISRO team who made it possible to get the spacecraft to this point. Prime Minister Modi’s presence in the Mission Control in Bangalore was praiseworthy. Modi consoled a tearful Sivan and was a pillar of strength for the disheartened scientists.
India’s mission to Mars a few years ago being a success on the very first try was a statistical outlier. No other country did it. Against all odds, as well captured in the recent Bollywood movie “Mission Mangal”, with a low powered rocket PSLV (Polar Space Launch Vehicle), India made it. GSLV, it’s more powerful cousin, was not ready at that time. But expecting to stretch that luck all the time is not realistic. We should in all humility feel a sense of gratitude that things really went well on the road to Mars.
I am sure data analysis of the flight parameters and the pictures will come up with the root cause. And the lessons will be learnt. Chandrayaan 3 may be launched in due course which will hopefully reach its goal.
Amateur Astronomers Association of Princeton 