[NASSP 8] [Apollo 7] SPS 3 problem

STS

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Hello all,

I am encountering a difficulty during SPS-3, that is when I press the THRUST ON button as per the checklist, my engine doesn´t fire.

I think that I am doing something wrong but I don´t know what it is.


My SPS line heaters are on A/B but even if I turn them off before the burn my SPS doesn´t fire. Also, I am on the version prior to the ECS update and to the optics update.

Best regards,
 

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indy91

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Oh wow, it's already been 2.5 years since I updated the SPS engine start logic. But what didn't get updated since then is the checklist. The "Thrust On" button actually requires an ullage thrust signal to be present to start the SPS. So just fire the +X RCS thrusters and then press the button. That will start the engine. In future Apollo 7 MCC and checklist updates the ullage burn will play a more important role, as that was done on all Apollo 7 burns in reality.
 

STS

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Oh wow, it's already been 2.5 years since I updated the SPS engine start logic. But what didn't get updated since then is the checklist. The "Thrust On" button actually requires an ullage thrust signal to be present to start the SPS. So just fire the +X RCS thrusters and then press the button. That will start the engine. In future Apollo 7 MCC and checklist updates the ullage burn will play a more important role, as that was done on all Apollo 7 burns in reality.
Thanks again for the quick reply!

So, I should +X 15 seconds before the burn, as per flightplan? And press the button on the last second of the ullage...

Will try that!
 

indy91

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Nominally there is a 1 second overlap between ullage and SPS burn. So 15 second pure ullage burn, then at the ignition time press the THRUST ON button and then stop the ullage one second later. That's how the burn is modelled in the RTCC. Doesn't have to be done super exact of course.
 
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