The fourth firing of the propulsion system of the Mars spacecraft on Monday morning was among the six exercises planned by the ISRO and aimed at achieving an apogee of 1.92 lakh by the fifth move, scheduled for November 16.
The craft must leave the Earth orbit on November 30/December 1 if it has to meet Mars as planned for mid-September next year.
The release said the spacecraft was in good health and its apogee had been moved to 78,276 km now.
The other point or perigee remains at nearly 250 km from Earth.
In the latest engine burn, the ISTRAC team managed to impart an incremental velocity of 35 metres/second as against the required 130 m/second.
The ISRO described the performance shortfall as part of ongoing trials that its scientists performed to ensure all systems would be in order later during the orbiter’s long journey to Mars.
‘No reason to panic’
An official involved in the building of the Mars spacecraft said, “Everything is safe and under control. There is no reason for panic.”
ISRO scientists explained to The Hindu that the 440-Newton engine onboard is equipped with a primary and a redundant electrical coil that enable the fuel and the oxidiser to flow through two valves of the spacecraft.
During the firing on Monday morning, the team was trying to use both the primary and the redundant coils together as part of a trial. However, there was no fuel flow in this mode and the orbiter could not pick up the required velocity or reach the desired higher orbit.
Meanwhile, the time slot for firing the engine had expired as the spacecraft had moved away.
A senior engineer involved in the process said, “Both the coils are working independently (but not if they are switched on together.) Tomorrow we will use the primary coil (as they did on November 7, 8 and 9.) It’s a very minor issue. We are confident that we will overcome it.”
He explained: “In the last three firings we operated only the primary coil. Today we wanted to conduct a trial. We first operated the primary coil and the redundant coil later, and both worked independently. We then switched on both together in the test firing today but the system did not work in that mode. So we went back to using them separately and they worked well.”
The release said, “In the fourth orbit-raising operation conducted on November 11, the apogee (the farthest point to Earth) of the Mars Orbiter spacecraft was raised from 71,623 km to 78,276 km by imparting an incremental velocity of 35 metres/second (as against 130 m/second originally planned to raise the apogee to about 1,00,000 km). The spacecraft is in normal health. A supplementary orbit-raising operation is planned tomorrow (November 12) at 0500 hrs.”