SSI-93

SSI-93
Designations	CY-7
Launch date	October 26, 2019, 10:14 PDT
Launch site	Brigantino Park, Hollister, CA
Launch coordinates	36.849, -121.433
Flight duration	4h:04m
Flight length	202 km
Flight profile	Folded zero pressure w/ ballast control
Landing time	October 27, 2019, 14:18 PDT
Landing site	9 km SW of Tulare, Tulare County, CA
Landing coordinates	36.164, -119.431
←SSI-92 SSI Balloon Launches SSI-97→

SSI-93 (project designation CY-7) was the seventh launch of Project Cycloon on October 26, 2019. It was the zero pressure balloon equipped with altitude control (ballast mechanism), and launched alongside two other zero-pressure balloons at Onboarding. It was the first balloon in the folded topology as a result of a notably eventful filling, and consequently also experienced a noteable post-landing.

Project context

The launch plan at the beginning of the quarter had called for a fully controlled ZPB flight coincident with onboarding on October 26, 2019. However, the unavailability of a vent mechanism and the surprising endurance of SSI-92 motivated the decision to do a long-endurance ballast-controlled ZPB instead. The analysis of data from that previous flight had suggested a thermal difference of 10% during the day; given this, it seemed possible to aim for a multi-day flight with a reasonable amount of ballast. Briefly, on October 18, a floater was considered as the forecast appeared to show winds going towards the ocean, but this was temporary. The primary upgrades, in addition to the vent mechanism, was a heating mechanism and a GPS reset mechanism, lessons learned from the last flight.

Construction of the payload was a streamlined process by this time. Avionics were produced in an October 15 worksession; on October 18 a large number of balloons were manufactured for Onboarding; and on October 20, the payload was integrated, marking launch readiness a week ahead of time. The integration of the payload was tricky, as no top piece was suitable for the legacy ballast piece, and furthermore thermal insulation was a concern.

Configuration

Balloon: 0.8 mil polyethylene tubing, folded topology, width 2.5 m, length 10 m, volume unknown. Total mass 1 kg with fill tube (PVC of length approximately 12 inches and diameter 1/2 inch).

Avionics: TinyGPS, Teensy 3.2, BMP 280 transmitting at adjustable intervals over Rockblock. SPOT Trace. Ballast control; nichrome cutdown; GPS power reset MOSFET.

Power: 12 L91 lithium AA batteries. 3 L91 lithium AA batteries on resistive heater and cutdown.

Ballast: Legacy valbal mechanism with 500 g ballast, theoretically enough for two nightfalls.

Payload: Half valbal-style polycarbonate cylinder within styrofoam enclosure. Mass 1.25 kg including ballast.

Mass budget: 2.26 kg total.

Flight synopsis

Ascent rates against altitude

Flight profile

October 26 953 PDT: Balloon released after an attempted titration to 0.5 kg of free lift. Moderate winds made this difficult. However, within a few dozen seconds of release the balloon began to descend, and was caught barely within the southwestern boundaries of Brigantino park. A large leak at the top seal was discovered, motivating the decision to fold the envelope over. The balloon was re-filled and observed for 10 minutes for second release.

October 26 1014 PDT: Balloon released at approximate 1.5 m/s ascent with initial motion to the southwest.

Flight trajectory