maandag 8 mei 2017

Delfi-C3 is feeling the power of Spring

All the trees have blossom, baby ducklings are rooming the ponds, and we get more Sun: we survived the winter! Spring is here to give us our much needed vitamine D. 
Spring on the campus of TU Delft
Not only on the surface of the Earth this is felt, but also in outer space. The Delfi-C3, now more than 9 years orbiting our Earth, notices that spring has arrived on the Northern Hemisphere. During winter, our ground station (DopTrack) only receives data during the morning and mid day (between 8:00 and 13:00 CET). Starting from April, we start receiving signal around 20:00 CET.
Fraction of a 24 hour day (UTC) at Time of Closest Approach (TCA) of the Delfi-C3 with DopTrack.
We saw this already last year, when in April the telemetry of Delfi-C3 started appearing in the evening. The Sun was already set on the ground, but at 560 km height light was still shinning on the solar cells of the satellite. The satellite is designed such that when sunlight hits the solar cells and enough power is received the onboard computer turns on and goes through its boot program. Equipment is turned on and the radio is transmitting telemetry back to Earth. The data is transmitted on a carrier frequency, that is recorded by the DopTrack at TCA, which we call Frequency at Closest Approach (FCA).
The complete dataset of DopTrack consisting of recordings of Delfi-C3's FCA for almost 2 years now. A clear distinction between mid-day and evening passes can be noticed.
We have recorded the radio transmissions of Delfi-C3 with our calibrated equipment, enabling us to accurately determining the received frequency. The mid-day passes seem more stable around an average 145888000 Hz, whereas the evening passes have a larger spread and higher averaged frequency. More analysis is needed, but we suspect that in the evening passes the thermal equilibrium is not yet obtained during recordings. Lets hope after this spring we can say more.