A glimpse of the ACS 3 Solar Sail bus

Artist impression of ACS3 once the sail is deployed (image: NASA)On 23 March 2024, Rocket Lab launched the Advanced Composite Solar Sail System (ACS3), a NASA solar sail experiment. The main goal of the mission is to test the deployment of a 80 m2 (9 x 9 meter) solar sail from a 12U cubesat bus. The sail will be deployed late May or early June 2024, i.e. some 2 months after the launch. ACS3 (2024-077B) is in a 97.4 deg inclined, 993 x 1023 km sun-synchronous orbit. The 9 x 9 meter ACS3 sail (image: NASA)ACS3 orbitOn 3 May 2024, I managed to image the 12U ACS3 bus, using a WATEC 902H2 Supreme camera and Samyang 1.2/85 mm lens. Below is a frame stack of 102 video frames. The faint streak at lower right is the 12U ACS3 bus, which was at a range of 1118 km at the time. It reached magnitude +9.3, but I think I captured it during a glint, as it was visible for a few seconds only.As the solar sail has not yet been deployed, this detection is the 12U bus (i.e. a bus of 30 x 20 x 20 cm) only, seen here during assembly: the 12U bus (image: AST & Defense)It will be interesting to see what brightness the object will reach once the big solar sail has been deployed. It could potentially get quite bright. I have good memories of a similar mission (but at lower altitude, and with a smaller sail surface), Nanosail-D2, from 2011 (see for example this 2011 blogpost).The mission is sending telemetry at 401.5 MHz. Here is a radio detection from my station at Leiden from 6 May 2024:click image to enlargeA more elaborate overview of the ACS3 mission and goals can be read here.