# RMCSat: An F10.7 Solar Flux Index CubeSat Mission
## 3 RMCSat Mission
### Performance Requirements and Constraints
#### 3.1.4 Orbit Parameters and Requirements  
The type of LEO orbit required for the mission is heavily influenced by the required line of sight to the Sun, access to solar energy, and the expected radio interference from Earth. The chosen design orbit has implications for sub-systems, primarily the power system. Maximum solar access is obtained by the sun-synchronous orbit (SSO), a precise inclination for a specific altitude that results in the satellite maintaining a fixed orbital plane orientation with respect to the Sun. Each SSO causes a satellite to cross the equator at the same local mean solar time. A dawn-dusk SSO offers near-continuous access to the Sun for solar observation and power generation throughout most of the year. In contrast, a noon-midnight SSO provides the least solar exposure. A diagram of the two orbits is shown in Figure 4.  
The implication of these two orbits on payload operations makes the choice of orbit more complex. In a dawn-dusk SSO, the primary payload antenna is at a near-constant 90\({}^{\circ}\) angle to nadir (side-laying). A side-laying geometry increases the risk of strong interference from the large Earth solid angle affecting the main higher gain lobe regions. It also reduces the ability to use passive physical shielding techniques. Another concern is the increase in atmospheric signal attenuation resulting from the greater atmospheric transmission distance, at a near-maximum when 90\({}^{\circ}\) angle to nadir. Although attenuation is generally low, it may be difficult to quantify as the solar signal passes through multiple atmospheric layers of varying temperatures. Figure 4: Sun Synchronous Orbit Comparison. (**a**) In a dawn/dusk orientation, the satellite maintains near-constant access to the Sun. Note that the tilt of the satellite at the extreme north and south points on the orbit in this diagram is greatly exaggerated. (**b**) In a noon/midnight orbit the satellite spends minimal time in Sun, with almost half of the orbit in eclipse. The arrows indicate antenna boresight. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Altitude** & \(c_{D}\) **= 2.2** & \(c_{D}\) **= 2.5** & \(c_{D}\) **= 3** \\  & **Lifetime (Years)** & **Lifetime (Years)** & **Lifetime (Years)** \\ \hline
500 km & 10.2 & 7.5 & 4.8 \\
550 km & 23.4 & 18.5 & 14.6 \\
600 km & 51.1 & 47.2 & 37.7 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: CubeSat lifetimes, in years, modeled for different altitudes and drag coefficients (\(c_{D}\)) using the Systems Tool Kit Satellite Lifetime tool. Two options exist for antenna pointing in a noon-midnight SSO: a fixed zenith pointing antenna and a sun-tracking antenna. Figure 5a illustrates that maximum solar observation time is achievable using a sun-tracking antenna, however, the atmospheric attenuation issues and lack of fixed pointing angle with respect to Earth-based noise sources makes this a non-viable option. The zenith-pointing antenna option shown in Figure 5b results in greatly reduced observation times. However, it has the advantage of replicating the highly effective DRAO calibration observation pattern of taking cold sky views before and after solar flux measurements [1]. In the case of RMCSat, these cold sky views are achieved as the Sun passes through the known first nulls of the antenna pattern, with the peak solar flux measurements generated as the Sun passes through the antenna boresight. Figure 6 illustrates an operation cycle for solar observations from this configuration. An orbital period of 95.6 min allows for approximately 15 solar observation windows per day, achieving the first mission objective of the increased temporal and spatial coverage of F10.7 data. Figure 5: Pointing regime examples, depicting **(a)** sun-tracking and **(b)** zenith pointing options. **(a)** The satellite orients the antenna towards the Sun as soon as a line of sight is possible, and maintains tracking for the duration of the dayside orbit sector. **(b)** The antenna maintains a fixed zenith angle with respect to the Earth.