Lanyards And The Pulley
A pair of lanyards are used to launch a near space stack because the
lanyards can take much more strain than the load line can without breaking.
The pair of lanyards also allows greater control of the raising of the
balloon. The balloon can be raised at different rates, brought down, or
translated from side to side. The lanyards consist of two lengths of woven
nylon cord, each 1/8" in diameter. The lanyards pass through a pulley suspended
a couple of feet below the base of the balloon. To keep the weight and cost
low, the pulley consists of a welded metal ring.
This image shows the underside of a stack. One of the lanyards remains in
this image, as the other one has already been released. The lanyard is the
line going from bottom left, to the balloon neck, and back to bottom right.
Winders
Each lanyard is wrapped around a winder, similar in design to a kite string
winder. Two launch crew members control winders. The third member controls
the release mechanism, a short length of PVC pipe. 
In this image you can see KNSP launch crews in the process of raising the
stack with the lanyards. Once the stack is fully raised, one of the
lanyards will be released