Changes

| landing coordinates = 37.6634, -121.3217

| landing coordinates = 37.6634, -121.3217

| last = 90

| last = 90

| next =  

| next = 92

}}

}}

'''SSI-91''' (project designation '''CY-5''') was the fifth launch of [[Cycloon|Project Cycloon]] on August 5, 2019. It was the second launch of an in-house manufactured polyethylene envelope and the first SSI zero-pressure balloon to report telemetry throughout the flight since [[SSI-20]]. It was also a rare sunset launch, a weekday launch, and featured an even lighter payload than its predecessor, [[SSI-90]].

'''SSI-91''' (project designation '''CY-5''') was the fifth launch of [[Cycloon|Project Cycloon]] on August 5, 2019. It was the second launch of an in-house manufactured polyethylene envelope and the first SSI zero-pressure balloon to report telemetry throughout the flight since [[SSI-20]]. It was also a rare sunset launch, a weekday launch, and featured an even lighter payload than its predecessor, [[SSI-90]]. The payload was recovered on August 31, 2019.

==Project context==

==Project context==

'''Balloon''': 0.3 mil polyethylene, paper bag topology, width 1.8 m, length 7 m, volume approximately 6 cubic meters. Total mass 0.26 kg with fill tube (PVC of length approximately 12 inches and diameter 1/2 inch).

'''Balloon''': 0.3 mil polyethylene, paper bag topology, width 1.8 m, length 7 m, volume approximately 6 cubic meters. Total mass 0.26 kg with fill tube (PVC of length approximately 12 inches and diameter 1/2 inch).

'''Avionics''': TinyGPS, Teensy 3.2 transmitting at adjustable intervals over Rockblock. SPOT Trace.

'''Avionics''': TinyGPS, Teensy 3.2 transmitting at adjustable intervals over Rockblock. SPOT Trace. Attempts to interface this Teensy with a BMP 280 were universally unsuccessful. This set of avionics was finished from the incomplete second set made for [[SSI-87|CY-3]].

'''Power''': 9 L91 lithium AA batteries. Resistive heater running on single L91 battery.

'''Power''': 9 L91 lithium AA batteries. Resistive heater running on single L91 battery.

'''August 5 2059 PDT:''' After almost an hour of steady ascent, balloon reaches a maximum altitude of 10.298 km over (37.1502, -121.4077). Ascent rate had fluctuated above and below the initial rate of 3.8 m/s. In theory, a slight acceleration in ascent was expected. By this time the balloon was in the jet stream layer travelling north at nearly 30 m/s.

'''August 5 2059 PDT:''' After almost an hour of steady ascent, balloon reaches a maximum altitude of 10.298 km over (37.1502, -121.4077). Ascent rate had fluctuated above and below the initial rate of 3.8 m/s. In theory, a slight acceleration in ascent was expected. By this time the balloon was in the jet stream layer travelling north at nearly 30 m/s.

'''August 5 2103 PDT:''' Balloon reported an altitude of 10.291 km, a highly unexpected measurement. In retrospect, it is believed that venting began at this altitude, but the vent hole was far too small to vent the necessary volume, leading to envelope rupture. The resulting leakage resulting in the balloon never reaching the calculated equilibrium altitude of 14-15km and following what more resembles a latex profile than a zero-pressure balloon profile.

'''August 5 2103 PDT:''' Balloon reported an altitude of 10.291 km, a highly unexpected measurement. In retrospect, it is believed that venting began at this altitude, but the vent hole was far too small to vent the necessary volume, leading to envelope rupture. The resulting leakage prevented the balloon from reaching the calculated equilibrium altitude of 14-15km and caused what more resembles a latex profile than a zero-pressure balloon profile.

'''August 5 2055 PDT:''' Balloon reported first definitive descent at an altitude of 9.905 km.

'''August 5 2055 PDT:''' Balloon reported first definitive descent at an altitude of 9.905 km.