Chandrayan reaches the final orbital home

India's maiden unmanned lunar spacecraft Chandrayaan-1 on wednesday reached its final orbital home, about 100 kms over the moon surface after ISRO scientists successfully carried out the last critical orbit lowering operation. The satellite will remain in the present operational orbit for about two years carrying a range of experiments. The final 60-second manouvere carried out from a ground station in Bangalore put the satellite into the intended orbit, exactly three weeks after it began its voyage to the outer space after it blasted off atop a polar rocket from Sriharikota spaceport. "The journey part to the Moon is complete," Project Director M Annadurai said signalling the successful completion of the mission to take Chandrayaan-1 to its intended orbit. "We are eagerly awaiting the start of the experiments." ISRO said the next major event of Chandrayaan-1 is the release of Moon Impact Probe (MIP) from the spacecraft and its eventual hitting of the Moon's surface. This is expected to happen on Friday and scientists hope to get the first signals in about 20 minutes after the MIP hits the lunar surface. The entry of Chandrayaan-I into the final lunar orbit followed a series of three orbit reduction manoeuvres conducted during the past three days by repeatedly firing the spacecraft's 440 Newton liquid engine, the Bangalore-headquarted space agency said in a statement. As part of these manoeuvres, the engine was fired for a cumulative duration of about 16 minutes. With this, ISRO said, the carefully planned complex sequence of operations to carrry Chandrayaan-1 from its initial Earth orbit to its intended operational lunar orbit with the use of its liquid engine has been successfully completed. "As a result of the manoeuvres, the farthest point of Chandrayaan-1 orbit (aposelene) from the moon's surface was first reduced from 7,502 km to 255 km and finally to 100 km while the nearest point (periselene) was reduced from 200 km to 182 km and finally to 100 km", ISRO said. During these operations, Chandrayaan-1's liquid engine built by Liquid Propulsion Systems Centre, Thiruvananthapuram, has been fired a total of ten times successfully.
In its present operational orbit, the Chandrayaan-1 spacecraft takes about two hours to go round the moon once. From this operational circular orbit of about 100 km height passing over the polar regions of the moon, it is intended to conduct chemical, minerological and photo geological mapping of the moon with Chandrayaan-1's 11 scientific instruments (payloads).
Two of those 11 payloads -- Terrain Mapping Camera (TMC) and Radiation Dose Monitor (RADOM) - have already been switched on. TMC has successfully taken the pictures of the Earth and the Moon. After its successful launch by PSLV-C11 on October 22 into an initial Earth orbit, the Chandrayaan-1 spacecraft proceeded towards the Moon and successfully entered into an elliptical orbit around that celestial body on November eight. Since its launch, the spacecraft's health and orbit have been continuously monitored from the Spacecraft Control Centre of ISRO Telemetry, Tracking and Command Network with critical support from antennas of Indian Deep Space Network (IDSN) at Byalalu on the outskirts of Bangalore
Moon probe ejection on November 14 or 15
ISRO will study Chandrayaan-1’s orbit for a day or two before commanding to eject on November 14 or 15 the 29-kg Moon Impact Probe (MIP), a box-like instrument on top of the spacecraft. The probe will crash-land on the Moon’s surface. Since the MIP is painted with the Indian flag on its sides, it will symbolically register the Indian presence on the Moon.On Saturday (November 8), ISRO accomplished with aplomb the most crucial and critical manoeuvre of safely inserting Chandrayaan-1 into the lunar orbit with an aposelene of 7,502 km and a periselene of 504 km. This was achieved by retro-firing the engine for 817 seconds, which pushed the spacecraft in the opposite direction of its journey, reduced its velocity and inserted it into the lunar orbit.
S. Satish, Director, Publications and Public Relations, ISRO, said: “The ISRO team was very cautious in executing this critical manoeuvre because we did not want to jeopardise the mission. This is a precious mission for us. Contingency plans were in place in case the liquid apogee motor (LAM) engine on board Chandrayaan-1 did not fire. Then, we would have used other thrusters on board the spacecraft to fire… There have been dynamic changes in our manoeuvres to reach the Moon.”S. Ramakrishnan, Director (Projects), Vikram Sarabhai Space Centre, Thiruvananthapuram, said the orbit reduction under way now was the reverse of what ISRO did in approaching the Moon.After the Polar Satellite Launch Vehicle (PSLV-C11) put Chandrayaan-1 in an elliptical orbit with an apogee of 22,866 km and a perigee of 256 km around the earth on October 22, ISRO performed four manoeuvres by firing the LAM to keep increasing this ellipticity.
On November 4, the spacecraft reached the vicinity of the Moon with an apogee of 3,80,000 km. The Moon is 3,84,000 km away from the earth. Then the crucial manoeuvre of inserting the spacecraft into the lunar orbit of 7,502 km by 504 km took place on November 8 and it was captured by the Moon’s gravity.
“We are now reducing the Chandrayaan’s orbit to come closer to the Moon,” Mr. Ramakrishnan said. On November 9, the LAM was fired and the spacecraft’s orbit around the Moon was further reduced to 7,502 km by 200 km. “The Moon’s gravity is not well characterised. It is not symmetrical like that of the earth. The Moon’s gravity is not well understood. So there will be uncertainties. When we fire the engine to reduce the spacecraft’s orbit, depending on the response, we have to do further corrections,” he said.Mr. Ramakrishnan was confident that the remaining two manoeuvres would succeed because Chandrayaan-1 was already “in a stable orbit and it cannot vanish anywhere.”