#Doubts about burns

1 messages · Page 1 of 1 (latest)

granite crystal
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Hello, I have a doubt concerning the planning of the burns. in the academy, it says that we shall use P30 for setup, P52 for IMU alignment and P40 for burn execution. Then it goes to the burn planner, and I input phase, dV and direction. I am asked to input a dv of 100 (by the way, in a free mission, how can I know which is the right number?).

When I do so, the message from mission control gives me the burn attitude (19.62, 81.07, 333.51), and tells me I have TWO options: 1) To use P30 and then V49 to maneuver automatically to that attitude, and 2) To use P30 and P52 to align the IMU so the direction of the burn is (0,0,0).

But the tutorial directs me automatically to the second option, why? Wouldn't it be more natural to simply tell the computer to maneuver to (19.62, 81.07, 333.51) with V49, and then to execute P40 for the burn? I had the idea that aligning the IMU so the burn direction is (0,0,0) is used if you need to MANUALLY set the attitude, as (0,0,0) is much easier to handle than (19.62, 81.07, 333.51) on the FDAI, but to add to my confusion, we are asked to set the computer so it aligns AUTOMATICALLY to (0,0,0), although it can be "helped" manually, why??

This is counter-intuitive for me; either I let the computer handle the whole thing with P30-V49-P40 or I do it manually (pointing to (0,0,0)) with P30-P52-P40, may someone clarify please?

slow escarp
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But the tutorial directs me automatically to the second option, why? Wouldn't it be more natural to simply tell the computer to maneuver to (19.62, 81.07, 333.51) with V49, and then to execute P40 for the burn?

This is how almost all burns were done in reality actually

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unless a new REFSMMAT was needed for an upcoming phase of flight or the burn attitude would be close to gimbal lock, generally the current REFSMMAT was used

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I think reentry asks you to realign for simplicity

true viper
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Yeah simplicity and also until recently the IMU wasn’t robust enough to be able to support accurate maneuvers to non-0,0,0 so it was best to realign

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I doubt the academy has been updated since then so at the time it was best practice

granite crystal
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ok thanks

granite crystal
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Another doubt related to this: I have run P52 and set 0,0,0 as the burn direction; when then I perform V49, after setting the attitude (to 0,0,0), in the same very V49 procedure, I am asked for an automatic maneuver to 0,0,0 (the V50 N18 - V06 N18 - V50 N18). Ok, I do it. But when I move afterwards to P40, it guides me to automaneuver AGAIN. Why the redundancy? Haven't I done it already in V49?
Also, I often find a curious problem, not in a consistent way; in the tutorials for burns, I often find myself with a very short time to the ignition, leaving me no time to go through the procedure (for example, the automaneuver, which in many cases is too long). How can I control this?

granite crystal
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Maybe I let time pass until the burner planner gives me more time?

slow escarp
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so you maneuver to your urn attitude and then P40 is used as a verification and final trim of the attitude