ATV-4 basking in sunlight approaching ISS. Credits: ESA/NASA

ATV-4 basking in sunlight approaching ISS. Credits: ESA/NASA

Matt Quail asked us a question via Twitter to @esaoperations based on last week’s ATV fuel consumption article:

Once again, ESA’s Laurent Arzel took a short time off calculating flight dynamics for ATV to offer some illumination on the matter:

ATV’s solar panels are not fixed but can only rotate around their longitudinal axis. See the time-lapse video below for an example of how ATV-5’s solar panels rotate while attached to the International Space Station.

Roll-pitch-yaw on an ATV. Credits: ESA-I. Baroncini

Roll-pitch-yaw on an ATV. Credits: ESA-I. Baroncini

However, rotating on one axis alone is not sufficient to keep the solar panels perpendicular to the Sun. To make sure they gather as much energy as possible from our star, they would need to rotate left-right as well, also called ‘yaw steering’.

Combining the solar panel rotation (or roll) with yaw steering allows the ATV operations team to keep the solar panels absorbing as much energy as possible.

 

ATV-4 undocks from Station. Credits: ESA/NASA

ATV-4 undocks from Station. Credits: ESA/NASA

Two sides to the story

Lastly, it is not ATV’s nose that must be kept pointing to the Sun, but rather the opposite: its backside. In fact most images we see of ATV in space show its front (as it approaches the International Space Station) which then shows a view looking at the back (non-light-sensitive sides) of the solar panels.

This is one of the few images we found of an ATV in flight with its solar panels showing their solar-sensitive sides:

 

ATV-3 approaches Station. Credits: ESA/NASA

ATV-3 approaches Station. Credits: ESA/NASA

This whole issue was dealt with in more detail in an earlier ESA Technology Image of the Week; click on the image to read more:

The back of ATV solar panels on Earth. Credits: Dutch Space

The back of ATV solar panels on Earth. Credits: Dutch Space