A solar sail is a propellant-free propulsion system that converts photon momentum into thrust. By deploying a large reflective membrane and continuously reflecting sunlight, the sail experiences a small pressure. Although the force is extremely weak, it can act continuously in space (without atmospheric drag), enabling long-duration acceleration without fuel. Accordingly, maximizing the deployed sail area is essential for practical performance. As a key reference, LightSail 2 (2019) demonstrated on-orbit deployment of a ~32 m² sail from a 3U CubeSat, where ~2U was allocated to the solar-sail system. The system used four TRAC booms that extended outward and tensioned a thin membrane to form a square sail.

My personal impression is that the launch of this NRF(National Research Foundation of Korea) project in 2020 may have been influenced by LightSail 2. At the time, Korea had relatively limited experience and research base in solar-sail systems, so our goal was not to immediately surpass LightSail 2, but to follow up enabling technologies and build a domestic technical foundation while exploring distinctive concepts.

Accordingly, we targeted a 12U-class CubeSat and aimed to package the deployable sail system within an 8U stowed volume, pursuing two tracks: (i) a self-deploying sail module concept and (ii) a deployable boom system to support sail-module deployment and positioning. My team focused on the boom-system track, exploring origami-inspired deployable boom concepts through prototyping and deployment testing.

We built multiple origami-inspired deployable boom prototypes, including (1) Sarrus-linkage designs with spring-assisted deployment and self-locking, (2) hybrid concepts that combine a tape-measure boom with a Sarrus linkage to improve both bending and torsional stiffness, and (3) a boom that stiffens by folding upon release. We ultimately selected the folding-to-stiffen boom concept for the final prototype. The system was tested under launch-environment vibration*, and successful deployment was confirmed after the vibration test.

* Launch-environment vibration test conditions

a) Resonance (sweep rate 2 oct/min): 5~2000Hz, 0.5 g

b) Sinusoidal (sweep rate 2 oct/min): 5~21 Hz(11mm), 20~60 Hz(20g), 60~100 Hz(6g)

c) Random vibration (2.5 min per axis): 20~100 Hz(+3 dB/oct)

d) Shock test (duration 0.5ms): 50 g

Video at 2× speed