# RMCSat: An F10.7 Solar Flux Index CubeSat Mission
## 4 Satellite Architecture and Subsystems  
RMCSat is a 3U CubeSat (three stacked 10 \(\times\) 10 \(\times\) 10 cm cubes) with deployable solar panels and antennas as modeled in Figure 9. The architecture is constructed around the zenith and nadir payload antennas and the need to maximize solar exposure in a noon-midnight orbit.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Operation Mode** & **Condition** & **Time (min)** &
\begin{tabular}{c} **Cumulative** \\ **Time (min)** \\ \end{tabular} \\ \hline Eclipse Cruise & Eclipse & 17.8 & 17.8 \\ Solar Cruise & Daylight & 14.1 & 31.9 \\ Communication (2 orbits per day) & Daylight & 7.2 & 39.1 \\ Solar Observations (min. 12.5 min) & Daylight & 17.5 & 56.6 \\ Solar Cruise & Daylight & 21.3 & 77.8 \\ Eclipse Cruise & Eclipse & 17.8 & 95.6 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Proposed payload operations cycle for an average noon/midnight SSO, commencing at the equator in eclipse.  
Figure 8: Concept diagram of RMCSat mission.  
The payload consists of two antennas and an S-band receiver with software-defined radio (SDR) architecture. A deployable helical antenna acts as the primary antenna recording the microwave activity of the Sun on the desired frequencies while the secondary wideband patch antenna is used to detect background radio noise from RFI and thermal Earth emissions on the same frequencies.  
The ADCS, which stabilizes the spacecraft against external perturbations, consists of three reaction wheels, a 3-axis magnetometer, two IR Earth Horizon Sensors, three electromagnetics, and an astronomy data and computing services computer. It maintains the nadir orientation of the secondary antenna throughout the orbit and points the helical antenna at the Sun with required pointing accuracy during solar observations. A global navigation satellite system (GNSS) antenna and receiver offers <10 m positioning accuracy by receiving GPS L1 and GALILEO E1 signals. GPS will be sampled once per second and used for post-processing of F10.7 data and generation of a global microwave emissions model.  
Payload and telemetry, tracking and command (TT&C) data are downlinked using a nadir S-band patch antenna identical to the payload secondary patch antenna. The bandwidth of the payload antenna cannot be extended to reach the 2250 MHz frequency of the ground station unless customized at a notable expense. A dual UHF/VHF dipole antenna with a complimentary UHF/VHF transceiver is used for TT&C uplink via the VHF frequencies. UHF frequencies could be used to downlink part of the solar observation data in the event of failures within the S-band system.  
The satellite subsystems are supported by an onboard computer and electrical power system (EPS). Power is generated by gallium arsenide (GaA) triple-junction solar cells laid out on three 1U body-mounted solar panels and four double-sided 3U deployable solar panels. A 22.4 W-h Li-Ion battery pack provides power during an eclipse. The battery pack and a heater are integrated into the EPS. Satellite thermal control is achieved passively with aluminized kapton surface coatings.  
RMCSat does not require a propulsion system as the satellite does not need to maintain its original orbit nor carry out orbital maneuvers during the mission. External perturbations experienced by RMCSat over the course of its mission are not anticipated to be large enough to disrupt the orbit to the point where the mission is impacted.  
The estimated mass budget for the Cubesat is given in Table 5. Margins are assigned to components depending on their flight heritage (5%) and technological readiness (10%),  
Figure 9: RMCSat architecture diagram. The satellite is a 3U CubeSat (10 \(\times\) 10 \(\times\) 30 cm) with deployable solar panels and payload antennas.  
customization (20%), and in-house manufacturing (25%). The total estimated mass with margins sits comfortably within the 4 kg limit for a 3U Cubesat.