What helped Vikram lander to soft-land on the moon

Subject: Science and tech

Section: Space technology

Introduction

India’s Chandrayaan-2 mission aimed to soft-land the Vikram lander on the moon but encountered a crash during its descent.
ISRO learned from the Chandrayaan-2 failure and implemented several corrections for the Chandrayaan-3 mission.

Phases of Landing

Before reaching the moon’s surface, there are four critical phases in the landing process:

Cause of Crash

Rough Braking Phase: During this phase, the lander successfully reduced its velocity.
Attitude-Hold Phase: Problem emerged. In this phase, the thrust should have been maintained at half the level, but a malfunction in the guidance system resulted in the thrust exceeding the expected level.
Fine Braking Phase: With large errors in velocity and altitude due to the guidance system malfunction, the system attempted to make corrections in the fine braking phase.
However, the control system was not designed to produce large orientation changes quickly, Leading to a crash.
The crash was a result of three cumulative errors:
- excessive thrust due to dispersion,
- guidance system malfunction, and
- limitations in the control system’s ability to make large orientation corrections.

Correcting Mistakes for Chandrayaan-3

Dispersion Control: Measures were taken to prevent excessive thrust dispersion.
Guidance System: The guidance system was improved to avoid malfunctions.
Control System: Restrictions on orientation changes in the control system were removed.
To enhance safety, Chandrayaan-3 incorporated several additional precautions:
- Redundancy: Extra sensors and propellant were added to enable the lander to reach an alternate landing site if necessary.
- Expanded Landing Area: The landing area was expanded from 500m x 500m to 4km x 2.4km.
- Increased Weight: The lander’s weight increased by approximately 250 kg.
- It was equipped with two engines instead of one.