All's not well with MOM as fourth orbit-raising manoeuvre hits snag

Glitch minor, won't affect mission as anomaly will be corrected in subsequent operations, says Isro chief

Having completed three orbit-raising manoeuvres successfully, the Mars Orbiter Mission (MOM) faced its first setback on Monday, as the fourth manoeuvre fell short of the targeted apogee (farthest point from Earth) of about 100,000 km;  

According to Indian Space Research Organisation (Isro) officials, the spacecraft could achieve an apogee of only 78,276 km due to a glitch in the fuel flow to the engine.

Speaking to Business Standard, Isro chairman K Radhakrishnan sought to downplay the development saying it will not affect the mission. “Some extra fuel will be consumed but enough cushion is available to address the additional fuel requirement, since we have placed the Mars Orbiter spacecraft very precisely on to an elliptical orbit around the Earth after the launch on November 5.”

A supplementary orbit-raising operation is planned on Tuesday at 5:00 am to raise the apogee to nearly 100,000 km.

In a statement, Isro said: “The redundancies built-in for the propulsion system were exercised, namely, (a) energising the primary and redundant coils of the solenoid flow control valve of 440-Newton liquid engine and (b) logic for thrust augmentation by the attitude control thrusters, when needed. However, when both primary and redundant coils were energised together, as one of the planned modes, the flow to the liquid engine stopped. The thrust level augmentation logic, as expected, came in and the operation continued using the attitude control thrusters. This sequence resulted in reduction of the incremental velocity.”

On Monday, the spacecraft's apogee was increased from 71,623 km to 78,276 km by imparting an incremental velocity of 35 metres a second, against 130 metres a second originally planned to raise apogee to about 100,000 km.

The statement said that health of the orbiter is normal.

In the orbit-raising operations being conducted since November 7, 2013, Isro has been testing and exercising the autonomy functions progressively. The functions are essential for trans-Mars injection and Mars orbit insertion.

“During the first three orbit-raising operations, the prime and redundant chains of gyros, accelerometers, 22-newton attitude control thrusters, attitude and orbit control electronics as well as the associated logics for their fault detection isolation, and reconfiguration have been exercised successfully. The prime and redundant star sensors have been functioning satisfactorily. The primary coil of the solenoid flow control valve was used successfully for the first three orbit-raising operations,” the release noted.