PratikDas wrote:If this theory is true then either:
a) Mangalyaan no longer has a 440 N rated LAM but a lesser rating for all intents and purposes, or
b) the 440 N rated LAM can be turbocharged so to speak with extra fuel to get more than 440 N when operating both solenoids
The mission couldn't possibly have relied on option (b) because it is too risky. Either the LAM is rated for 440 N and used at that thrust or it is rated for a higher thrust. One doesn't mess around. At least I hope the engineers aren't this cavalier.
If option (b) is ruled out then let us try to understand option (a). If both the primary and redundant solenoid are required for 440 N, then one has to ask why the primary fuel flow wasn't designed to be sufficient for delivering the maximum 440 N thrust by itself. Also, the 440 N rating was proven through Chandrayaan so I don't see how anything less than 440 N could have been used to plan the trajectory to Mars, which implies that option (a) would set back the Mangalyaan mission significantly, but ISRO says the spacecraft is in Normal condition.
In summary, nothing about this theory of extra thrust makes sense to me.
Oh sorry! I made a mistake in the comprehension of ISRO's press release. I somehow felt that they were trying to fire both the LAM and the attitude correction motors simultaneously. There is logic to that. The closer you are to the perigee while you are imparting incremental velocity, the more efficient you are in raising the orbit. Hence the higher the thrust, the higher is the rate of imparting incremental velocity and more efficient is your orbit raising operation. That is why I concurred with Lilo sir's post. However a question remains in my mind. Why don't they actually fire the LAM motor and the attitude control motors (those which can work the same direction) together for maximum efficiency during the orbit raising operation?
Anyways, I understand ISROs press release completely now. This is obviously a failure of a test point. Both solenoid valves for fuel supply should have worked in parallel, but they did not. It is okay, because they work independently.
Also many in the press (and here) have got the emboldened part wrong. The thrust attitude control thrusters did not lead to the reduction of velocity. The key is the word "incremental".
During the fourth orbit-raising operations held today (November 11, 2013), 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.
The attitude control thrusters are much weaker than the LAM and hence the orbit raising would be much less efficient (same logic as I discussed in the beginning of this post). Hence even if they kept them firing for the same units of time as they had planned before, there was a reduction in the incremental velocity
I like what they are doing through FB. They respond to questions immediately. And people are hooked. Never seen such great following of a space mission. This is good.