**4. Analysis**

#### **4.1 Power generation and storage**

**Tables 1** and **2** show that the Korean satellites have employed deployable solar panel (which is also shown in **Figure 1**), since the mission required high power and used direct energy transfer (DET) mode. Such approach is very much different than those used by KITSAT-1 and KITSAT-2, which have body-mounted solar panels. On the other hand, Turkish satellites use body-mounted solar panels and therefore do not have the requirement of one side of the satellite always facing the sun for battery charging.

**Tables 3** and **4** show that all TU Berlin heritage use body-mounted solar panels. It uses Si panels for its first three satellites, then opted to higher capacity GaAs panels in LAPAN-ORARI and LAPAN-IPB. Generally, the power budget for the University of Surrey heritage satellites is higher than the TU Berlin heritage, even in the ones with body-mounted solar panels. As shown in **Figure 5**, in LAPAN-IPB, one of the sides has two 46 × 26 cm solar panels. The side is projected to be Sun pointing most of the time.

Battery chosen to be used in the early University of Surrey heritage satellite design is NiCd, while in TU Berlin's satellite design is NiH2. NiCd batteries require


#### **Table 4.**

*Sample for the Technical University of Berlin microsatellite heritage system design.*

charging controller mechanism ensuring that the battery is completely drained before being charged. This is because partial charging can induce memory effect, which can decrease the battery capacity to its last partial charge state. For NiH2 batteries, they tend to have large packaging due to its cylindrical shape, as shown in DLR-TUBSAT and LAPAN-TUBSAT drawing (**Figures 4** and **5**), but its charging mechanism is very simple (can do trickle charging). As soon as Li-ion battery technology available, both designs opted out Li-ion battery for its easy handling (no memory effect) and higher power-to-mass ratio.

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

#### **Figure 4.**

*Mechanical design of DLR-TUBSAT and MAROC-TUBSAT.*

**Figure 5.** *Mechanical design of LAPAN-TUBSAT and LAPAN-IPB.*

#### **4.2 Main computer**

On the choice of main computer, the University of Surrey heritage uses microprocessor, such as 32-bit PowerPC 603, while the TU Berlin heritage uses microprocessor, such as 32-bit SH series. Advantage of using microcontroller is having shorter booting time, so that it can recover quickly in the event of latch-up and needs to be restarted. The advantage of microprocessor is its ability to handle more complex and parallel jobs. To anticipate any anomaly in the operation, the use of microprocessor is usually done by using redundancy (i.e., a second processor will take over the operation in the event of anomaly). In the University of Surrey satellite design heritage, the electronic components are connected to main computer with dual line of controller area network (CAN). Meanwhile, the TU Berlin satellite design heritage uses star configuration with dedicated line to each component from the main computer, using RS232 or 422.

## **4.3 Attitude control subsystem**

**Tables 1** and **2** show that the University of Surrey satellite design heritage uses separate attitude control computer that integrates attitude sensors, including sun and star sensors with all reaction wheels and gyros. This is done so that the attitude control system can work in closed loop all the time. Such approach is necessary for the microsatellite design with deployable solar panels, such as KITSAT-3, STSAT-1, and STSAT-3 since failure of sun pointing could be disastrous for the satellite. As shown in **Tables 3** and **4**, in the TU Berlin satellite design heritage, none of the satellites have separate attitude control computer. In the design, each reaction wheelgyro pair directly connected to the main computer, and therefore, closed loop with star and sun sensors can only be done using the main computer resources.

Differences are also found in the attitude control sensor between the University of Surrey design heritage. The Korean microsatellites use fiber-optic gyro, while the Turkish microsatellites use MEMS gyro. Meanwhile, in all TU Berlin microsatellites, fiber-optic gyros are used.

For attitude control actuators, all the selected satellites use reaction wheels and air coils for angular momentum dumping/generation. Figures and data showed that TU Berlin heritage satellites use reaction wheels in 3-axis configuration. For LAPAN-ORARI and LAPAN-IPB satellites, they used redundant wheel at satellite major inertia axis that noted as 3 + 1 as shown in **Table 4**. For the University of Surrey heritage satellites, only KITSAT-3 uses reaction wheels in 3-axis configuration. The rest of the satellites uses tetrahedral configuration (noted as 4 as shown in **Table 1**).

The TU Berlin's attitude control design was chosen to reduce computational burden for filtering out reading noise/jitter in the attitude control sensors. The TU Berlin heritage satellites offer two options for attitude control mode, in addition to regular closed loop, including (1) interactive mode for the satellite with video camera payload, such as DLR-TUBSAT and LAPAN-TUBSAT, and (2) angular momentum management mode for the satellite with line imagers, such as Maroc-TUBSAT and LAPAN-A3. The angular momentum management mode is supported by their structure design, that is, solid aluminum box, which created maximum inertia properties at 1 axis and very little cross-product inertias [30, 31]. Such design has been successfully performed highly stable open-loop angular momentum management operation as published by Utama [31] and Mukhayadi [32].

#### **4.4 Propulsion subsystem**

From a selected set of satellite designs shown in **Tables 1**–**4**, only BILSAT-1 and STSAT-3 have thrusters. The objective for BILSAT-1 thruster is to maintain the satellite orbit separation in the constellation, so that the image coverage could be optimized. In STSAT-3, the plasma thruster is part of in-orbit qualification process for the low power plasma thruster technology developed by KAIST.

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