**4.6 Payload**

The payload profiles for both satellite design heritages showed that the platforms are suitable for both Earth observation, science, and low data rate communication missions. All of the selected satellites, except Korean STSAT-1, are Earth observation missions, which are considered important by stakeholder of satellite developer in Korea, Turkey, and Indonesia. KITSAT-3, BILSAT-1, RASAT, and LAPAN-IPB are for land cover that can be applied for estimating crop yield. The payload data showed that combining mission is typical for microsatellite applications. The multiband infrared (MIRIS) payload in STSAT-3 is used for Earth and space observation. LAPAN-ORARI has three kinds of missions, including Earth observation, communication, and ship data collecting platform.

### **4.7 Mission data downlink**

The quantity and quality of the payload in **Tables 1–4** showed that mission data are increasing with time, which increase the required downlink data rate. For the University of Surrey heritage, the data rate started with 3 Mbps in KITSAT-3 and increased to 100 Mbps in RASAT. For the TU Berlin heritage (the digital transmission cases), the data rate started with 256 kbps in Maroc-TUBSAT and increased to 100 Mbps in LAPAN-IPB. In the early missions, the mission data downlink is transmitted in S-band, and as the data rate requirement increases, the downlink has been shifted to X-band.

### **4.8 Payload computer**

Payload computer is typically separated from satellite main computer, which mainly manage the satellite bus. As the payload data rate increased, the payload processing electronics is also evolved, from microcontroller/microprocessor to FPGA based, which is known to be able provide high computing power with less risk from space radiation as compared to high capacity microprocessor.

## **4.9 Orbit determination**

None of the microsatellite has ranging system. Therefore, in early missions, their orbit determination is mainly depending on NORAD's data. The use of GPS for Position-Navigation-and-Timing by the University of Surrey heritage satellites started with BILSAT-1, while for the TU Berlin heritage satellites, it started with LAPAN-ORARI. The accuracy of orbit determination becomes crucial in Earth observation mission, as part of the parameters used in satellite image geometric correction.

#### **Figure 6.**

*Microsatellites' weight versus launch year.*

#### **Figure 7.**

*Microsatellites' density versus launch year.*

#### **4.10 System level parameters**

**Figure 6** shows the weight of each microsatellite sample. It shows that the weight of TU Berlin heritage satellites grows in time. This is due to the increase in mission quantity and complexity, which therefore requires more components in the satellites (bigger batteries, more attitude sensors, larger lens for imager payload, etc.). For the University of Surrey satellites heritage, such pattern is not found. The density of (weight/volume) the satellites is shown in **Figure 7**, indicating that the TU Berlin heritage satellites are more compact than the University of Surrey heritage satellites. For the University of Surrey satellites heritage, the design uses maximum volumetric envelope for maximizing the solar panel area.

#### **5. Conclusions**

The chapter has discussed the differences between the University of Surrey design heritage microsatellites and the TU Berlin heritage microsatellites. Five

*System Designs of Microsatellites: A Review of Two Schools of Thoughts DOI: http://dx.doi.org/10.5772/intechopen.92659*

sample satellites from each satellite design heritage are compared, including 15 bus parameters, payload profiles, and satellite weight and volume at launch. From the comparison, it is found that major differences in the satellite bus are in the choice of main computers and their associated link configuration and in the attitude control modes that also affect the design. Another major difference is in the satellites' structure design, which resulted in much higher density in the TU Berlin heritage satellites than the University Surrey heritage satellites. In the early design, there are differences in the choice of satellite's batteries. However, as soon as Li-ion batteries became available, both design heritages used such technology. In answering the increasing needs in payload data handling, both design heritage use FPGA-based payload data handling and high downlink data rate in X-band. GPS is also the technology adopted by both design heritages for orbit determination and imager's ancillary data.

For further studies on the topic, it is suggested that comparison to be done on the power budget of the satellites and on the operation performance parameters of the satellites with similar missions.
