The moon is indeed a piece of cheese, a coveted one at that with India getting her historic moments of fame right in space. India’s unmanned mission to the moon worked with clockwork precision, from the word ‘lift off’, the ISRO (Indian Space Research Organisation) team tasting success in the very first attempt which is again, a pioneering feat. Sanmar Engineering’s BS&B (India) lived up to ISRO’s expectations. Mission accomplished, it is time to lie on the laurels at least till the call of the next mission.
10, 9, 8……lift off. PSLV-C11, Chandrayaan - 1’s launch vehicle prepares the spacecraft for the day flight to the moon at Sriharikota. After a few orbits around the earth, the closest point (perigee) of 256 kms and an apogee (point on the orbit furthest from earth) of 22,866 kms, comes the toughest part - orbit hopping. This requires several manoeuvres to pull out of the earth’s gravitational field and on to the moon’s orbit. The orbits around the moon implies circling the moon, over its polar caps with a periselene (nearest point from the moon’s surface) of 504 kms and an aposelene (farthest point) of 7,502 kms. Then again, after a series of manoeuvres the satellite is brought closer to moon at a 100 km circular orbit. Once the spacecraft gets to this orbit, the Moon Impact Probe (MIP) is ejected from the mother craft to impact the moon’s surface.
This was Chandrayaan - 1’s space path.
The skill and precision required by ISRO’s ground station crew to conduct the manoeuvres was more than shooting in the dark at a moving target. The first crucial move was orbit-hopping, in space language – Lunar Transfer Trajectory. Chandrayaan-1 had to change course from an elliptical orbit round the earth and propel the spacecraft in a perpendicular angle to orbit the moon. of 7,502 kms.
Then again, after a series of manoeuvres the satellite is brought closer to moon at a 100 km circular orbit. Once the spacecraft gets to this orbit, the Moon Impact Probe (MIP) is ejected from the mother craft to impact the moon’s surface. This was Chandrayaan - 1’s space path. At this time the velocity was reduced so that the spacecraft moves into the lunar gravitational field.
To achieve this, this elliptical orbit was gradually increased in four manoeuvres to 265,000 kms as apogee and 465 kms as perigee. Then finally when it went to the Lunar Transfer Trajectory the retro rockets were fired to reduce the velocity of the spacecraft by 366.8 meters per second, to be captured by the moon’s gravity and ensconced safely in the lunar orbit. The spacecraft started circling the moon, over its polar regions with a periselene (nearest point from the moon’s surface) of 504 kms and an aposelene (farthest point) of 7,502 kms. ISRO flawlessly executed this highly complex manoeuvres.
Shackleton crater in the south polar region of the moon
The most crucial part of the mission was the separation of the Moon Impact Probe (MIP) from the mother ship and impacting the surface of the moon. With Chandrayaan - 1 still in orbit, the MIP was detached, propelled into a designated path using a de-orbit motor to reduce velocity and assigning a 25-minute time frame to finally crash-land on the moon. These 25 minutes were power-packed minutes when instruments on board the MIP captured and sent out data to the mother craft which was beamed back to the ground station. As the MIP weighing about 35 kgs, was detached from the spacecraft, two spin motors got ignited. This set the MIP into a spinning rotation ensuring directional stability to the MIP, giving a gyroscopic action to the probe. The MIP, spinning like a top was headed for the surface of the moon.
The MIP
At this point, the de-orbit motor was fired to reduce its speed so the trajectory could be controlled before it impacted the moon’s surface. During the action packed 25 minutes, the key instruments that swung into action were the mass spectrometer to analyse the available medium of the moon’s atmosphere, the altitude meter to know the descent, and an on board camera to take pictures of the moon’s surface as it descended. The polar region so far unexplored, would provide valuable data on the composition of soil, and the Altitude measuring meter to measure the rate of descent to enable future missions for soft landing.
The MIP, with the Indian tricolour painted on all its sides, finally impacted the moon surface at a place called the Shackleton crater in the south polar region of the moon. This is the first Indian probe-print on the moon.
The spin motor diaphragm disks were manufactured by Sanmar Engineering’s BS&B (India), as per the design given by ISRO. The diaphragms were fitted in the spin motors which were positioned in the diagonally opposite direction on the sides of MIP. The spin motors got activated after it got detached from the mother-craft and once sufficient pressure got developed inside both the motors, the diaphragms ruptured simultaneously, imparting a spinning motion to the MIP. The criticality in the process is the bursting of diaphragm precisely simultaneously to create the required spin motion as planned.
Rupture disk fitted to the spin motor
The product went through repeated trials and testing to ensure consistent opening of the diaphragm at a particular pressure to create the required thrust when the motors were fired. The diaphragm made of silver was micro-plasma-welded to the titanium base. This critical welding of two dissimilar materials was a great technical challenge as the physical properties of the base material of the disk had to be maintained.
The fast-spinning MIP’s velocity had to be reduced and its path controlled as it impacted the moon. The de-orbit motor, fitted with the BS&B diaphragm made of inconel material and plasma-welded to the nozzle, provided the required thrust to slow down the velocity of the MIP and control the descent time before its impact. These two applications had helped make the MIP mission a success. This success goes to prove that creative application engineering using unique metallic membrane as a disk material is a fail-safe product and many more new applications can be thought of for similar applications.
Rupture disk fitted to the de-orbit motor
The Sanmar Engineering team thanks ISRO for powering their imagination in application and design engineering and guiding through precision manufacturing process. They look forward to more such success stories, adding many more moments to the chronicles of Indian space history.