The day’s program called for medicine, but the ground decided to give us a rest day, and we gave ourselves a day of intense work. We decided to study the upper atmosphere autonomously, without the ground’s involvement, using only the station’s onboard control systems. We asked permission to determine the work plan ourselves, choose the orientation mode and implementation method, including the “Delta” navigation system in the control loop. We got the go-ahead.

We worked in two modes: orbital orientation with transition to stabilization using angular rate sensors — when the station’s position is fixed relative to the stars but changes relative to Earth due to orbital motion — and in the predicted orientation mode POR, when the station’s position is fixed relative to Earth, meaning one of its axes, and thus the instrument, is constantly pointed where needed, for example at the horizon or at some constant angle to it depending on the experiment’s tasks. This requires imparting rotation to the station at an angular rate equal to its orbital rate around a pre-selected axis perpendicular to the orbital plane. The calculation and correction of this rate is done by our onboard computer, since we fly on an elliptical orbit and our speed varies. The machine calculates it at each moment and maintains it with engines. This mode is very convenient when studying the atmosphere by tracking stars setting or rising beyond the horizon, or photographing the twilight horizon before sunrise and sunset, as well as the structure of nighttime emission layers at altitudes of 100 km and 300 km, or zodiacal light, and auroras. We completed several sessions. The impression from the work is excellent. Everything is very flexible. Knowing the experiment’s goal, the instrument’s characteristics, the station’s control capabilities, and the orientation requirements, we ourselves determined when to start and stop, what to shoot.

We did significantly more than before — recorded 7 stars, and also used the PSN to photograph zodiacal light.

I looked at the ocean in the sun glare. The volume of surface structures is visible: ripples, eddies, waves, contrast bands on the water reflecting the bottom relief, and their rises and falls are noticeable. This is well highlighted by light due to the different optical characteristics and angles of the structures. And now to sleep.

Today at the porthole, while looking at the ocean for a long time, I fell asleep, and the airflow carried me, sleeping, to the ventilator by the transfer compartment hatch. Good thing the ventilators have screens, or I’d have gotten a whack on the nose.