Thruster malfunction could have doomed lander

Vikram descent trajectory.

Hitting the lunar surface much faster than planned, the Chandrayaan-2 Lander could have ‘crash-landed’, ending a 47-day, 3.84 lakh km space journey in disaster in the wee hours of Saturday.

But beyond the ‘high-velocity’ factor that jeopardised an otherwise flawless mission, the end-stage thrusters could have also malfunctioned.

Isro sources indicated that the thrusters (engines) could have over-performed, severely affecting the Lander Vikram’s stability. This occurred just before the mission’s Fine-Breaking phase.

Vikram was programmed to take a 90-degree shift in trajectory at this point, preparing for a vertical descent. Instead, the Lander began rotating uncontrollably. The central engine with a stabilising gimbal was critical to keep it steady and change direction if required.

But, as an Isro scientist pointed out, the central engine could have malfunctioned. Since Isro lost its communication link with Vikram at a height of 2.1 km, taking over control was out of question. The Lander was on autonomous mode.

Till the spacecraft reached an altitude of 2.1 km from the surface, the Mission Team had achieved a controlled reduction of the Lander’s orbital velocity. Through a Rough Breaking Phase at 30km height, the velocity was reduced from 1,680 metres per second to 210 mps.

Preliminary analysis pointed to a Lander impact at a velocity in excess of 60 mps, which could have been disastrous. “Its stability severely compromised, the Lander could have crash-landed,” a scientist said, preferring anonymity.

Isro keeps dialling lander

Isro Chairman K Sivan said all efforts were on to re-establish the lost communication link with the Lander. This implied the space agency still harboured a hope to revive the mission, although there was no concrete evidence to support it.

In a televised interview, Sivan said, “Right now, the communication is lost. But the efforts to contact will be made over the next 14 days. If successful, we will try to operate the payload.”

If the mission had gone as per plan, the Rover Pragyan would have rolled out three hours and 15 minutes after Vikram's soft-landing. But this mandated a flat landing site with a gradient not exceeding 12 degrees. The Rover was designed to probe the lunar surface for an entire lunar day, equivalent to 14 Earth days.