Premature re-entry of the FACSAT-2 nanosatellite: orbital decay and attribution to the maximum of solar cycle 25

Abstract

FACSAT-2 Chiribiquete, the second satellite of the Colombian Aerospace Force and the first South American nanosatellite mission dedicated to greenhouse gases, re-entered on 27 October 2025, 926 days after its deployment into a Sun-synchronous orbit, against a declared service life of at least five years and an estimated orbital lifetime of fifteen. The orbital evolution was built from the epochs of the TLEs (two-line elements) of NORAD ID 56205. We reconstruct its decay using its 3696 orbital elements, the solar and geomagnetic indices from the OMNI2 database, and NRLMSISE-00 densities sampled along the orbit. Inverting the drag yields a ballistic coefficient of 72.3 kg/m2 (6% statistical, 20% systematic), equivalent to an effective area of 0.047 m2, consistent with the declared geometry. With it, the model reproduces the trajectory with a root-mean-square error of 7.4 km and, calibrated on 2023-2024 alone, the re-entry with a 28-day out-of-sample error. F10.7 averaged 170.8 sfu over the mission, against the 139 sfu of the environmental scenario derived from the official 2019 forecast, which lengthens the orbital lifetime by x1.52; two co-launched CubeSats give x1.50 and x1.57, a consistency check across objects rather than independent evidence. Imposing quiet geomagnetic conditions returns 102 days, 22% of the shortening, with strong sensitivity to the adopted threshold; a superposed-epoch analysis over 149 storms gives a median drag enhancement of x1.92 for the intense events. We discuss the consequences for the design of FACSAT-3 and for the public communication of a mission's expected lifetime.