Deployable Solar Arrays (ISS)

Every experiment, life-support system, and radio aboard the International Space Station runs on sunlight. The hardware that captures it is a set of giant, foldable solar “wings” that pack up small for launch and then spread open once they reach orbit.

Quick facts

• Job: the sole electrical power source for the ISS.
• Two generations: eight original Solar Array Wings (SAWs), installed 2000-2009, plus newer roll-out arrays (iROSA) added starting in 2021.
• Original wing size: about 35 m (115 ft) long and 12 m (39 ft) wide, holding roughly 33,000 silicon solar cells and producing about 31 kilowatts each.
• iROSA size: about 18.2 m (60 ft) by 6 m (20 ft), each producing more than 20 kilowatts.
• Combined output: headed toward roughly 215 kilowatts at peak once the upgrade is complete, about a 30% increase over the aging original wings alone.
• Makers: Boeing (ISS prime contractor), Spectrolab (cells), and Redwire (roll-out arrays).

What they are and how they work

A deployable solar array is a large light-collecting surface that folds or rolls into a small package for launch, then expands in space. A solar cell turns sunlight directly into electricity; thousands wired together make real power. A kilowatt (kW) is a unit of power roughly equal to what a hair dryer uses, so a single wing producing 31 kW could run dozens of homes’ worth of appliances.

The original Solar Array Wings work like an accordion. Two flat “blankets” of cells fold concertina-style into a flat box. A telescoping mast (a coilable pole that extends like a fishing rod) pushes out between them, pulling each blanket taut into a flat rectangle.

The newer ISS Roll-Out Solar Arrays (iROSA) are simpler. A flexible blanket of cells is wound around a spool, flanked by composite booms — stiff split tubes flattened and rolled up lengthwise, much like a steel tape measure. The stored spring energy in those rolled-up booms makes them straighten and unroll the blanket on their own, with no motors. Fewer moving parts means less weight and fewer things that can break. Both array types feed direct-current electricity into the station and stay pointed at the Sun using motorized joints called gimbals: the Alpha gimbal swivels a whole truss segment, while the Beta gimbal angles each individual wing.

Why they matter

Because the arrays are the station’s only power supply, they run everything: air, water, experiments, communications, and the computers that keep the lab flying. After 15-20 years in the harsh environment of space, the original wings degraded as expected, slowly losing output. That threatened the power budget needed for new research, commercial activity, and technology tests tied to NASA’s Artemis Moon program. The iROSA upgrade restores and boosts capacity without removing the old wings. The roll-out design also matters far beyond the station: it is much lighter and packs into about a quarter of the volume of equivalent rigid panels, so it has become a popular choice for many spacecraft.

Notable examples

• Original Solar Array Wings: the first pair arrived on the P6 truss during space shuttle mission STS-97 in December 2000, with the full set completed between 2006 and 2009.
• iROSA upgrade: six roll-out wings launched inside SpaceX Cargo Dragon capsules on resupply missions CRS-22 (June 2021), CRS-26 (November 2022), and CRS-28 (June 2023), each installed during spacewalks. A final pair is targeted for around 2026.
• 2017 ROSA test: an early roll-out array was unfurled on the ISS to prove the deployment method worked in orbit.
• NASA’s DART mission: the asteroid-deflection spacecraft was an early operational flight of roll-out arrays.
• Ovzon-3 (2024): the first commercial geostationary satellite to use roll-out arrays, showing how far the technology has spread.

Worth knowing

Each iROSA covers only a little more than half the length of a legacy wing, so the older arrays keep generating power from their uncovered edges while the new ones add to the total. The motorless spring design removes a whole class of failure points, but deployment is essentially a one-shot, carefully controlled event. Installation is demanding work — each iROSA pair takes multiple spacewalks, and the very first deployment in 2021 hit snags before fully extending. Finally, published power figures vary because they describe different cases (one wing versus the whole station, full sunlight versus an orbit average), so numbers like “215 kilowatts combined” describe specific operating conditions rather than a single fixed value.