SSI-87

SSI-87
Designations	CY-3
Launch date	June 1, 2019, 10:20 PDT
Launch site	Le Grand Elementary School, Le Grand, CA
Launch coordinates	37.226, -120.251
Flight profile	Ballast and vent control
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SSI-87 (project designation CY-3) was the third launch of Project Cycloon on June 1, 2019. It featured a legacy ballast and vent mechanism from ValBal operated by Cycloon avionics and was the first such fully controlled Cycloon flight. The mission was noted for its eventful manual equilibration, early termination, and for being the last latex Cycloon before the project transitioned to polyethylene. The payload was recovered the afternoon of the launch.

The bulk of the avionics work for the two payloads was completed on May 27, followed by demonstration of vent control on May 29. As winds forecasts for favorable for a float-drop profile, a floater was confirmed for the final configuration. The bulk of the mechanics work occurred on May 29, though due to a lack of spare mechanics the second payload was cancelled. Finally, substantial system integration occurred on May 31.

Project context

Before and around the time of the previous flight, CY-2, a reevaluation of project goals for the quarter had been underway. While a full apex vent equipped flight had originally been envisioned for the weekend of June 2, delays on the project prompted a decision to focus more on quick iterations and numerous launches rather than awaiting longer term initiatives. In particular, it was decided that a legacy ValBal vent mechanism, while unlikely to suffice as a long-term solution, was sufficient and necessary for building altitude control expertise within Cycloon in the short term. Therefore, on May 19, the day after CY-2, it was decided that two payloads would be launched on June 1, alongside Spaceshot and onboarding, each with ballast, vent, and (winds permitting) tether and floater mechanism.

The bulk of the avionics work for the two payloads occurred on May 27, and first demonstration of vent motor control was achieved on May 29. The bulk of the mechanics work occurred that same day, although due to a lack of spare mechanics the second payload was cancelled. Due to favorable wind forecasts, a floater was confirmed. Substantial mechanical integration was finalized on May 31, the day before the launch.

Configuration

Balloon: Kaymont 1500g latex.

Mechanics: ValBal-style cylindrical polycarbonate sheeting, ValBal ballast and vent mechanism. Parachute in parachute tube. Total payload mass (without ballast, tether or floater) 1.07 kg.

Ballast: 1.5 kg.

Tether and floater: 30m paracord tether from balloon to payload and 30m paracord tether from balloon to floater. Total tether mass: 0.34kg. Hydrodynamic floater of mass 0.785 kg.

Avionics: BMP280, TinyGPS, Teensy 3.2 reporting all data at regular, fixed intervals via RockBlock modem. 2 solar-charged LED modules. Ballast motor controlled by N-type MOSFET.

Power: 18 L91 lithium AA batteries. In comparison with the standard ValBal complement of 12 L92 batteries, this was thought to be more than sufficient under the most optimistic conditions.

Mass budget: 3.42 kg. Counterweight was designed to balance 3.1 kg of total lift, after which ballast would be removed. In actuality, target fill resulted in nearly perfect buoyancy and no significant ballast was removed.