### Summary: Factors Affecting Vikram Lander's Failed Soft-Landing in Chandrayaan-2 Mission
The Chandrayaan-2 mission, which was launched by India on July 22, 2019, aimed for a soft landing on the moon. Unfortunately, the Vikram lander crash-landed due to a series of three critical errors. A national-level failure analysis committee led by Dr. V. Narayanan of the Liquid Propulsion Systems Centre (LPSC) identified these errors to help make necessary corrections for future missions.
#### Four Key Phases of Lunar Descent
1. **Rough Braking Phase**: The lander’s velocity was successfully reduced.
2. **Attitude-Hold Phase**: Problems started here with higher than expected thrust levels.
3. **Fine Braking Phase**: The system failed to correct large errors in altitude and velocity.
4. **Landing Phase**: Lander crashed due to cumulative errors.
##### Example
During the Attitude-Hold Phase, the thrust was supposed to be half. However, the actual thrust was more than half, causing the guidance system to malfunction.
#### Three Critical Errors
1. **Higher-than-Expected Thrust**: The engines produced more thrust than what was simulated before the flight.
**Example**: The actual thrust during the Attitude-Hold Phase exceeded the planned half thrust.
2. **Guidance System Malfunction**: The system was not designed to handle large dispersions.
**Example**: The malfunction led to full thrust being given to the lander instead of half.
3. **Rate Restriction in Control System**: Failed to make large-scale orientation changes.
**Example**: The control system took too much time to correct the orientation, causing the lander to reach the moon’s surface before corrections could be made.
#### Learnings for Chandrayaan-3
ISRO addressed all three errors in the Chandrayaan-3 mission. They corrected the system to prevent extra dispersion, modified the guidance system, and removed the rate restriction in the control system. Additional improvements were also made, such as adding extra fuel, sensors, and stronger lander legs.
##### Example
In Chandrayaan-3, two engines replaced the single central engine to manage the increased weight of the lander, a lesson learned from the failed Chandrayaan-2 mission.
#### Conclusion
The Chandrayaan-2 mission would have succeeded if even one of the three critical errors was avoided. Learnings from this mission have been crucial for planning and executing subsequent missions like Chandrayaan-3.
