How will the 'Yo-Yo' be used to despin the IMAGE spacecraft?

The Third Stage and spacecraft will have a typiocal spin rate of about 60 rpm after launch, and this has to be reduced to less than 2 rpm after the Third Stage is jetisoned. Two equal weights, sized to achieve the final spin rate are attached to kevlar cables wrapped about three times around the Payload Attach Fitting...a short cylindrical collar that connects the spacecraft to the top of the Third Stage. The weights are held in place by lanyards which are severed by cable cutters just before Third Stage separation. Like a figure scater spining and unfurling their arms, the weights will spin out and slow down the spin of the spacecraft. The whole process will take about 3-5 seconds. It will happen about 3270 seconds after launch just after Third Stage burnout and 5 seconds before spacecraft separation. It is a crucil maneuver, because if it doesnt work the IMAGE satellite will be spinning too fast for its experiments to work, and for the RPI antennas to be deployed.


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