ISRO Chairman K. Radhakrishnan said: "All is well and operations completed as planned."
The ISRO chief had said Monday that a failure analysis committee would examine the glitch the spacecraft had hit, but added that crucially, not much fuel was wasted in the failed attempt.
Reason for firing both together could be..
too many things are currently being relied upon based on simulation confidence
Pratyush wrote:The drawback means the planned simultaneous operation of two coils would not be possible anymore, but if the rest of the operations happen as planned, the spacecraft will reach the Martian orbit on September 24.
Can some one tell this lay man what is the meaning of the portion in bold.
Lilo wrote:Reason for firing both together could be..
Greater the thrust and lesser the time the thrusters are on fire as near to perigee - better the efficiency of the orbit raising maneuver(in terms of kilometers elongated) vis a vis propellant usage - is how I understand.
So 2 firing simultaneously == more thrust
With Impulse constant near perigee and corresponding lesser time of firing.
NRao wrote:Seems to me that they had three options: either of the solenoids are individually or both simultaneously are energized. The last one failed (for whatever reason). Under the circumstances it really does not matter that it failed. The first two options are sufficient for the success of the mission.
juvva wrote:NRao wrote:Seems to me that they had three options: either of the solenoids are individually or both simultaneously are energized. The last one failed (for whatever reason). Under the circumstances it really does not matter that it failed. The first two options are sufficient for the success of the mission.
But they do need to know the root cause of the failure, so that they can mitigate risks of additional failures down the line.
indranilroy wrote:Lilo wrote:Reason for firing both together could be..
Greater the thrust and lesser the time the thrusters are on fire as near to perigee - better the efficiency of the orbit raising maneuver(in terms of kilometers elongated) vis a vis propellant usage - is how I understand.
So 2 firing simultaneously == more thrust
With Impulse constant near perigee and corresponding lesser time of firing.
Exactly my thoughts.
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.
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.
Lilo wrote:Reason for firing both together could be..
Greater the thrust and lesser the time the thrusters are on fire as near to perigee - better the efficiency of the orbit raising maneuver(in terms of kilometers elongated) vis a vis propellant usage - is how I understand.
So 2 firing simultaneously == more thrust
With Impulse constant near perigee and corresponding lesser time of firing.
Kanson wrote:Lilo wrote:Reason for firing both together could be..
Greater the thrust and lesser the time the thrusters are on fire as near to perigee - better the efficiency of the orbit raising maneuver(in terms of kilometers elongated) vis a vis propellant usage - is how I understand.
So 2 firing simultaneously == more thrust
With Impulse constant near perigee and corresponding lesser time of firing.
Sirji, you give the impression that there are two LAM engines of 440 N thrust. But from ISRO, the craft has only one LAM 440 N engine.
Indranilroy wrote: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.
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.
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.
Neela wrote:Indranilroy wrote: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.
Indranilji
Pl have a look at this press release.
Neela wrote:Everything is under control, says ISROISRO 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.
Two valves. One for fuel and one for oxidiser. Flow control is through solenoid valves. The solenoid valves themselves have a primary coil and a secondary coil as back up. Could it be that when both primary and secondary are switched on, the resultant magnetic flux ( possibly working against each other ) is not large enough to open the valve? Possible explanation?
Neela wrote:What you wrote now confuses me: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.
can you elaborate what you mean here?
indranilroy wrote: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.
The two thrusters (LAM at 440 Newtons, and attitude control, at 22 Newtons) were not fired together. As I understand it, they happened in sequence (though the control logic is set up to fire them together). Initially, the LAM motor was activated to put the craft in a higher orbit. But this did not work and the LAM motor did not come on (since it was done with 2 solenoid coils instead of one). Then, the craft's automatic decision-making came online and automatically activated the attitude control thrusters (much smaller, at 22 Newtons). See bolded below from press release. http://www.isro.gov.in/pressrelease/scr ... Nov11_2013Lilo wrote:Reason for firing both together could be..
I read this to mean that the control logic is designed to automatically augment a loss in thrust from LAM with attitude control thrusters.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.
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.
Greetings ISRO team,
I have a question. Due to Oberth effect, the faster the acceleration during the orbit transfer operation, the more efficient the transfer. Is my understanding correct? Or is there something I am missing here because the acceleration is not constant here.
If my understanding is correct, why not use the LAM and the Attitude correction motors (those which can produce thrust in the same direction as the LAM) in unison during the orbit transfer operations?
And by the way thank you for providing prompt updates and answers to our questions. I think your prompt updates and answers are going a long distance in piquing the interest of Indian youths towards science and engineering.
ISRO's Mars Orbiter Mission wrote:Generally, Isp of Attitude Control Thrusters is less as compared to LAM. Comparatively, it will result in more fuel consumption to achieve same delta V. Have a look at this random example: http://www.apfc.com/UK/products_1.php
Due to the Oberth effect and starting from a nonzero speed, the required potential energy needed from the propellant may be less than the increase in energy in the vehicle and payload. This can be the case when the reaction mass has a lower speed after being expelled than before – rockets are able to liberate some or all of the initial kinetic energy of the propellant.
Also, for a given objective such as moving from one orbit to another, the required \Delta v may depend greatly on the rate at which the engine can produce \Delta v and maneuvers may even be impossible if that rate is too low. For example, a launch to LEO normally requires a \Delta v of ca. 9.5 km/s (mostly for the speed to be acquired), but if the engine could produce \Delta v at a rate of only slightly more than g, it would be a slow launch requiring altogether a very large \Delta v (think of hovering without making any progress in speed or altitude, it would cost a \Delta v of 9.8 m/s each second). If the possible rate is only g or less, the maneuver can not be carried out at all with this engine.
negi wrote:^ I was specifically talking about the original question i.e. how is high thrust applied over a shorter duration different from low thrust over a much longer duration.
juvva wrote:^negi: For orientation one would expect selective and pulsed firing of the attitude control thrusters.
In this case it looks like the avionics fired the thrusters continuosly to either augument the LAM, or as a redundant thrust source because the LAM failed to fire.
Second coil is not to give additional velocity boost. Rather, it is a redundancy feature. Hence there is no question of engine doing double work. Note that, both the coils are perfectly functional.
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