Changes

The same day that [[SSI-87|CY-3]] failed to reach the Pacific Ocean due to an unexpected flight termination at relatively low altitudes, [[Spaceshot|Spaceshot's]] [[SSI-88]], flying a Raven 50k cubic foot polyethylene ZPB, experienced ''increased'' flight endurance thanks to equipment failure, surviving into the Pacific Ocean and floating on its surface for two days despite a conscious objective to avoid doing so. It was remarked by many that Spaceshot had achieved Cycloon's mission profile more successfully than Cycloon. This was almost entirely attributable to the characteristics of Spaceshot's polyethylene envelope --- unlike a latex envelope, it was capable of passive venting and equilibration, was impossible to pop, and was significantly more water-resistant. Upon reflection, it became clear that the only reason Cycloon had defaulted to latex was that no low-cost polyethylene envelopes could be purchased at a size suitable for Cycloon-type missions. However, thanks to the obvious low cost of the raw materials and relative simplicity of manufacture, an initiative was launched to look into manufacturing polyethylene in house. As an additional benefit, active venting would be highly simplified in a zero-pressure envelope, as an apex vent could be mechanically identical to a latex bottom vent.

The same day that [[SSI-87|CY-3]] failed to reach the Pacific Ocean due to an unexpected flight termination at relatively low altitudes, [[Spaceshot|Spaceshot's]] [[SSI-88]], flying a Raven 50k cubic foot polyethylene ZPB, experienced ''increased'' flight endurance thanks to equipment failure, surviving into the Pacific Ocean and floating on its surface for two days despite a conscious objective to avoid doing so. It was remarked by many that Spaceshot had achieved Cycloon's mission profile more successfully than Cycloon. This was almost entirely attributable to the characteristics of Spaceshot's polyethylene envelope --- unlike a latex envelope, it was capable of passive venting and equilibration, was impossible to pop, and was significantly more water-resistant. Upon reflection, it became clear that the only reason Cycloon had defaulted to latex was that no low-cost polyethylene envelopes could be purchased at a size suitable for Cycloon-type missions. However, thanks to the obvious low cost of the raw materials and relative simplicity of manufacture, an initiative was launched to look into manufacturing polyethylene in house. As an additional benefit, active venting would be highly simplified in a zero-pressure envelope, as an apex vent could be mechanically identical to a latex bottom vent.

On June 6, 2019, summer goals were formally codified. It was determined that writing an altitude control algorithm, improving simulations, manufacture of an platform PCB, manufacturing polyethylene envelopes, and mass producing ballast and vent mechanisms were the top priorities. After a summer recess, work began in earnest following a meeting on July 9. A launch schedule was set, featuring a test launch of an in-house manufactured ZPB on '''July 21, 2019''', and an altitude-controlled ZPB on '''August 18, 2019''', with other goals and deadlines left unspecified.

On June 6, 2019, summer goals were formally codified. It was determined that writing an altitude control algorithm, improving simulations, manufacture of a platform PCB, manufacturing polyethylene envelopes, and mass producing ballast and vent mechanisms were the top priorities. After a summer recess, work began in earnest following a meeting on July 9. A launch schedule was set, featuring a test launch of an in-house manufactured ZPB on '''July 21, 2019''', and an altitude-controlled ZPB on '''August 18, 2019''', with other goals and deadlines left unspecified.

Significant work was done on simulations in preparation for the eventually need for trajectory search and optimization, forcing the launch to be delayed to '''July 21, 2019''', but efforts quickly turned to the ZPB. Raw materials, namely 0.3 mil painter's plastic, a slab of acrylic, a 500 W strip heater, and a current regulator were purchased. On July 17, the heating assembly was assembled, and on July 20 mechanisms of polyethylene sealing were explored. After discovering an effective routine, a single 22 ft length, half-width (6 ft) polyethylene envelope was constructed that day. A 18 inch length of a 1 inch PVC tube was affixed to the bottom of the envelope as a fill tube and payload anchor point.

Significant work was done on simulations in preparation for the eventual need for trajectory search and optimization, forcing the launch to be delayed to '''July 21, 2019''', but efforts quickly turned to the ZPB. Raw materials, namely 0.3 mil painter's plastic, a slab of acrylic, a 500 W strip heater, and a current regulator were purchased. On July 17, the heating assembly was assembled, and on July 20 mechanisms of polyethylene sealing were explored. After discovering an effective routine, a single 22 ft length, half-width (6 ft) polyethylene envelope was constructed that day. A length of a 1 inch PVC tube was affixed to the bottom of the envelope as a fill tube and payload anchor point.

The recovered avionics from CY-3 were detached from the mechanical assembly and the motor control components removed. Final integration occurred on July 23, and no further avionics work was required. Due to a miscalculation, it was thought at launchtime that the equilibrium altitude would be around 24 km, making a trajectory into the Pacific Ocean highly likely.

The recovered avionics from CY-3 were detached from the mechanical assembly and the motor control components removed. Final integration occurred on July 23, and no further avionics work was required. Due to a miscalculation, it was thought at launchtime that the equilibrium altitude would be around 24 km, making a trajectory into the Pacific Ocean highly likely.

==Configuration==

==Configuration==

'''Balloon''': 0.3 mil polyethylene, paper bag topology, width 1.8 m, length 7.5 m, volume approximately 6.9 cubic meters. Total mass 0.23 kg with fill tube.

'''Balloon''': 0.3 mil polyethylene, paper bag topology, width 1.8 m, length 7.5 m, volume approximately 6.9 cubic meters. Total mass 0.23 kg with fill tube (PVC of length approximately 18 inches and diameter 1 inch).

'''Avionics''': CY-3 avionics: BMP 280, TinyGPS, Teensy 3.2 transmitting at adjustable intervals over Rockblock. At the last minute, it was decided to ''not'' include a SPOT Trace. Although communications were perfect leading up to the launch, no transmissions were received after launch.

'''Avionics''': CY-3 avionics: BMP 280, TinyGPS, Teensy 3.2 transmitting at adjustable intervals over Rockblock. At the last minute, it was decided to ''not'' include a SPOT Trace. Although communications were perfect leading up to the launch, no transmissions were received after launch.