From Development Through Re-Entry: CTIM Operational Lessons Learned and Successes

The University of Colorado’s Laboratory for Atmospheric and Space Physics’ (CU-LASP) Compact Total Irradiance Monitor (CTIM) SmallSat mission was a 6U CubeSat designed full-cycle and in-house between 2018-2022 and flew for 1.5 years after launch until re-entry, overshooting the 1-year mission lifetime goal. CTIM's primary mission was to measure the total irradiance of the Sun, with ancillary measurements of the night-side Earth IR radiance, while demonstrating new technological capabilities of silicon-substrate room temperature vertically aligned carbon nanotube (VACNT) bolometers. The instrument was based on the Total Irradiance Monitor design that flew on SORCE (2003), TCTE (2013), and TSIS (2017). CTIM successfully continued the 40-year, uninterrupted measurements of total solar irradiance (TSI) with 0.017% measurement uncertainty. CTIM also hosted the first LASP-built spacecraft bus using the LASP Common Code flight software suite. Upon launch, commissioning was fast and efficient despite not having a GPS unit onboard to assist with spacecraft identification and ground station pass planning. All subsystems performed nominally throughout the mission with a few small hiccups requiring operational workarounds. Thanks to the establishment of automated ground station interfacing, command-and-control, and data processing and ingest, CTIM was able to perform at near-maximum efficiency using reduced staffing during the two months prior to re-entry. Future LASP SmallSat missions utilizing the CTIM bus and FSW designs will benefit from the CTIM "lessons learned" assessment. The most impactful lesson learned came from a series of undervoltage events seen early in flight due to a lack of power analysis and planning tool bugs. The half-duplexity of the UHF antenna, flash corruptions, and interface lockups created operational challenges as well. LASP demonstrated a highly successful in-house bus while CTIM successfully continued the TSI Climate Data Record. The lessons learned will pave the way for more low-cost missions to continue these important measurements into the future.