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The Vikram lander, who was carrying a small rover called Pragya, was ready to launch earlier this year. ISRO lost contact with the LG during its descent to the lunar surface earlier this month. (credit: ISRO) |
by Ajey Lele
Monday September 16, 2019
By the time this article is published, no change has occurred in the status of Chandrayaan 2, the second Indian mission on Moon. The latest update took place on September 10 when the website of the Indian Space Research Organization (ISRO) stated that "Vikram Lander was located in the orbit of Chandrayaan-2, but that no again took place with him. Every effort is made to establish communication with a landing gear. (Vikram owes its name to Vikram Sarabhai, the father of India's space program.) India's second mission to the moon began cautiously and only achieved limited success. The Chandrayaan 2 voyage for 48 days was difficult and demanding and ISRO successfully ensured that the craft safely reached the Moon's surface in accordance with the plan.
The trip
Initially, ISRO was to launch the Chandrayaan 2 mission on July 15th. To this end, a 20-hour countdown began on July 14th. However, the launch was canceled due to a technical problem one hour before the launch. Subsequently, an expert committee appointed by ISRO analyzed the cause of the problem and corrective measures were taken. Finally, the launch of Chandrayaan 2 took place on July 22nd.
| It is safe to conclude that a hard landing of the undercarriage has taken place. Only ISRO can correctly identify the reasons for this failure. |
This mission has two main parts: the orbiter and an LG system. The orbiter is a 2,379-kilogram satellite, while the undercarriage weighs 1,471 kilograms and the mobile weighs 27 kilograms. The expected lifetime for the orbiter is one year. However, ISRO saved a significant amount of fuel on its journey to Moon and expects the orbiter to operate for seven years. This would study the lunar surface of an approximate distance of 100 kilometers. The LG system was to be positioned on the surface of the Moon and operate for 14 days on Earth, from sunrise to sunset on the Moon.
The mission was launched with orbiter and lander as a coherent system. On September 2, the undercarriage, with the rover inside, separated from the orbiter to get to the surface of the moon. A soft landing was attempted on September 7th. However, the communication was interrupted at an altitude of 2.1 km above the Moon's surface and, as shown in the orbiter image, it is reasonable to conclude that a hard landing took place. Only ISRO can correctly identify the reasons for this failure.
About 50 years ago, Apollo 11 had reached the lunar orbit in just 51 hours and 49 minutes using a very powerful Saturn V rocket. However, the Indian mission took 48 days, mainly because the l '. India does not have a powerful rocket.
Chandrayaan 2, from launch to August 6, underwent five orbiting maneuvers that peaked at about 150,000 kilometers. Subsequently, on August 14, the observation of the Trans Lunar Insertion (TLI) interface, followed by the Lunar Orbit Insertion (LOI) of August 20. Once in orbit around the Moon, five maneuvers lowered its orbit. After the landing of the LG on 2 September, the aircraft successfully performed de-orbiting maneuvers on 3 and 4 September and the final landing was attempted on 7 September. Some details available on this trip (open source) are presented in the form of: a table below:
| Dated | Orbit climb maneuver | Offers | Real | Deviation |
| July 24 | first | 230 x 45162 km | 230 X 45.163 km | 1 km |
| July 26 | Second | 250 x 54,689 km | 251 X 54,829 km | 1 x 140 km |
| July 29 | Third | 268 x 71,558 km | 276 x 71,792 km | 8 x 234 km |
| August 02 | Fourth | 248 x 90,229 km | 276 x 71,792 km | 29 x 757 km |
| August 06 | Fifth (final) | 221 x 143,585 km | 276 x 142,975 km | 55 x 610 km |
| August 14 | Trans | Lunar | Insertion | (TLI) |
| 20 August | Entry of the moon | 118 x 18,078 km | 114 x 18,072 km | 4 x 6 km |
| 21st of August | Second lunar orbit maneuver | 121x 4303 km | 118 x 4412 km | 3×109 km |
| August 28 | Third | 178 x 1,411 km | 179 x 1412 km | 1 x 1 km |
| August 30 | Fourth | 126×164 km | 124 x 164 km | 2 km |
| 01 Sep | Fifth | 114x 128 km | 119 x 127 km | -5 x 1 km |
| 02 Sep | Lander | separate | of | orbiter |
| 02 Sep | 119 x 127 km | |||
| Désorbitant | maneuver | |||
| 03 sept. | first | 109 x 120 km | 104 x 128 km | 5 x-8 km |
| Sept. 04 | second | 36 x 110 km | 35 x 101 km | -1x 9 km |
| 07 Sep | Hard | Landing | Occurred |
This table indicates that, on a few occasions, there were significant differences between the proposed and actual orbits. But they could be considered less significant from the point of view of the health of the mission, taking into account the distance traveled by the orbiter.
Is it a failure of autonomy?
For any planetary exploration, landing on the surface of a planet is the hardest part of the mission. The president of ISRO had indeed repeatedly stated that the last part of the mission that involves the controlled landing (motorized) was going to be terrifying! This involved the LG trip for the last 35 kilometers. This trip was to take 15 minutes and became known as "15 minutes of terror".
| In the near future, after undertaking the detailed failure assessment, ISRO may consider repeating the assignment. |
Everything was supposed to happen in autonomous mode during these 15 minutes of descent. The president of ISRO said: "We can not do anything … We can not interrupt. It's a total autonomy. We do it for the first time. A deviation from the trajectory after 12 minutes of descent was visible. Obviously, the system malfunctioned during standalone mode. The speed was perhaps higher than necessary at this height. It is also believed that the problem could have involved a kind of glitch in the operation of the engines used in the descent. Overall, regardless of the problem, the system did not go into secure mode to anticipate problems. Did this happen because the landing gear was very close to the landing site for the system to take corrective action?
The goal here is not to undertake a detailed failure assessment. In general, it can be concluded that the system was not designed to identify the defect and take corrective action. The strength of autonomy of any system would depend on the basic design factors. The design would be mainly based on what scientists and technologists anticipate as possible anomalies and introduce them into the system. Normally, autonomous systems operate in complex and evolving environments with a high degree of independence. They are supposed to learn and reason with themselves. In addition, they are designed to identify unforeseen changes over time and react accordingly. What is not publicly known is the nature and quality of artificial intelligence (AI) involved in the entire landing process of the LG Vikram. The rover was supposed to be a product totally based on AI. However, since it did not have the opportunity to function, no judgment could be rendered in this regard. It could be very difficult to quantify the possible role played by the AI during the last minutes of the mission. AI is working on data entry and for these unique missions it is unlikely that the required data has been available in abundance. As such, some limitations of AI are broadly debated. It seems that space, which is a rare region in data, might not be an appropriate area to keep a blind trust in AI.
The path to follow
Overall, it could be said that ISRO has conducted a very busy moon campaign, but has not managed to manage a soft landing for its Vikram lander. In the near future, after undertaking the detailed failure assessment, ISRO may consider repeating the mission (eg, Chandrayaan 2R) by making the required corrections. They already have an operational orbiter around the moon. They know how to handle communications in the deep space. Normally, space agencies develop two models of equipment (a main and a spare). ISRO could also have an extra pair of lander-rover systems to try again.
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