Mars Orbiter Anomaly

An anomaly or malfunction has occurred yesterday during the Mars orbiter's attempt to raise its orbit above Earth. The orbit was only raised to 78,000 km instead of the targeted 100,000 km:

http://www.bbc.co.uk/news/science-environment-24900271

http://isro.gov.in/pressrelease/scripts/pressreleasein.aspx?Nov11_2013



ISRO reports that the spacecraft is in good health, and that only a small amount of fuel was wasted. Tonight they will again re-attempt to raise the orbit to the required height. Then after that there will be one more planned orbit-raising after a few days, and then the planned final engine burn on Dec 1 to fling the orbiter towards Mars.

The problem seems to have resulted from their attempt to perform various equipment checks as part of the orbit-raising maneuver. The spacecraft's main rocket motor has 2 fuel lines - a primary one and an extra one for backup - and the fuel flow through each is regulated by their respective solenoid valve. So to do a systems check while the rocket was operating, they opened the main fuel line / flow valve and this worked, then they switched to the backup fuel line / flow valve and this also worked, but when they tried to use both fuel lines / flow valves together at the same time, then this resulted in a stoppage of the fuel flow to the rocket motor and its shutoff.
The software's automatic thrust augmentation logic then triggered on its own to fire additional thrusters to compensate, however their weaker strength meant the resulting orbit achieved was only 78K km instead of 100K km.

So what they've then learned from this is that they cannot use both valves / fuel lines together at the same time. This may be due to a tank pressure limitation. Perhaps it can't supply the required pressure to push enough fuel through if both valves are open, instead of just either one alone.

If that's the case, then it's something that should have been tested and discovered on the ground first. I recall reading that ISRO did not build a duplicate mockup of the spacecraft for testing on the ground, but only tested using software simulations in order to save costs. Maybe this is something which would have turned up had they tested on a physical duplicate of the spacecraft. Being able to use both the main and backup fuel lines together is not absolutely essential, however it's what traditionally gets done during the deceleration at Mars, in order to guard against stoppage of fuel flow which would be fatal during this critical maneuver. At least by discovering the problem now, they can reconfigure a software workaround to switch to backup in the event of a fuel line problem.