Roll Out Solar Array (ROSA) is a lightweight, flexible power source to be deployed and used in space. It was designed and developed by Redwire Corporation, a U.S. aerospace manufacturer and space infrastructure technology company.

A larger version, called the ISS Roll Out Solar Array (iROSA), has been developed specifically to supplement the existing ISS arrays.

Traditional solar panels used to power satellites and stations are bulky, with heavy panels folded together using mechanical hinges. ROSA is twenty percent lighter, 325 kg, and one-fourth the volume of rigid panel arrays with the same performance.

ROSA is a flexible solar array that rolls out like a measuring tape unwinds on its spool. The new design rolls up to form a compact cylinder for launch with significantly less mass and volume. This offers substantial cost savings and allows an increase in power for satellites.

ROSA has a center wing made of a flexible material which support the strings of photovoltaic cells that produce electricity. Both the sides of the wing have a narrow arm that extends through the length of the wing to provide support to the array. These arms, called a high strain composite booms, look like split tubes flattened and rolled up lengthwise.

Deployment of the wings uses mechanical energy rather than motorized power. As each boom transitions from a coil shape to a straight support arm it uses the stored potential energy to push out the end of the wing.

References: Wikipedia - Roll Out Solar Array

The photovoltaic cells on the existing Solar Array Wings of the ISS were designed for a 15-year service life. This has been exceeded by a number of arrays resulting in noticeable degradation and loss of efficiency.

To augment the older arrays, three pairs of scaled-up versions of ROSA, known as iROSA, are planned by NASA to launch from June 2021 to late 2022. The SpaceX Dragon 2 cargo spacecraft is used to carry iROSA to the ISS.

The iROSA arrays are attached to the mast cans of the existing array wings and deployed along their central part.

NASA first tested the ROSA technology in vacuum chambers on Earth. In June, 2017 a ROSA test mission was launched to the ISS aboard SpaceX CRS-11. Engineers on the ground remotely operated the ISS Canadarm2 to extract the ROSA test array from the SpaceX Dragon craft.

ROSA was unfurled and extended by tensioning booms on both sides of the 1.6-meter-wide wing. NASA conducted continuous tests for a week and observed the behavior of the solar array as it was exposed to extreme temperature swings through the ISS's orbit. Vibrations were mechanically introduced to assess the array's response to structural loads.

Subsequent to the experiments, ground controllers were unable to lock the solar panel in its stowed configuration. The solar array was therefore jettisoned from the ISS and destroyed.