448 high and are therefore only reserved for considerati on when larger budgets are available. Traditionally  space systems have been designed using a limited number of electronic components, whose limited  variety can be attributed to availability of their r adiation hardened versions. Ho wever, a migration from  traditional rad hard components is currently underway, t hanks to the commercializat ion of space. Space is  no longer the sole domain of the world’s largest governments, where programs are funded by enormous and eternal budgets aimed at fighting the cold war. Consequently, space manufacturers around the world are faced with a requirement to build satellites that are faster, better and cheaper than those made in the past. iv   Another way of dealing with the unwanted effects of radiation and thereby still achieving “rad hard,” is  through clever hardware & software designs. Comm on techniques include cold-redundancy (only one  processor powered at a time thereby minimizing ri sk of a SEE). Other techni ques such as hot-redundancy  are also employed in the case of memory access . Hot-redundancy utilizes voting schemes where the  contents of triplet and physically separate memory stores are compared and voted upon using a “majority-wins” rule to confidently obtain a valid resu lt. Similar techniques can be implemented in software  for an added level of radiation hardness. The princi ple of triplet techniques can be used with data  variables.   Over the years since this migration has taken place, select groups of readily available electronic components have made their way onto satellites and into space. The Texas Instruments MSP430 family of microcontrollers is one example of typically sought after processors that have been used over and over on CubeSat missions. Another example is the Atme l ATmega64 microcontrollers. As CubeSats are  becoming more attractive to organizations and inst itutions, more and more commercial-off-the-shelf  (COTS) type electronics are emerging as viable small satellite system components. Companies like  Pumpkin Inc v are now introducing products that are bas ed on the widely available and commonly known  8051-, Microchip PIC24/dsPIC33 as possib le design options for CubeSat engineers. 

SADA Electrical System 

The SADA's embedded control unit (ECU) was designed around a low-cost Texas Instruments MSP430F2013. The microcontroller (MCU) used was very simple but effective; having just enough memory to demonstrate the SADA’s capabilities. Wh ile motor commutation was accomplished by the  algorithm run on the MCU, the step sequences were trans lated to a motor driver IC. The motor driver IC  was used to energize the coils of our bipolar stepper  motor. The motor driver chosen was the Allegro  MicroSystems A3906 low-voltage motor driver chip. Each  output channel of this device is rated at 1A and  the device itself can operate on voltages as lo w as 2.5VDC. The A3906 was chosen for its cost,  availability and functionality and very small package (QFN-20, 4x4x1.5 mm). Other features of the device  include internal thermal shutdown and under voltage lo ck-out. For power, a low-noise, low-drop-out (LDO)  voltage regulator was chosen. The Linear Technologie s LT1763 is capable of supplying 500 mA of output  current with a LDO voltage of <300 mV. This LDO regula tor is specifically designed for low power, battery  applications.  The performance of the above mentioned electronic components are used to realize the core functions of the SADA’s prototype ECU. The pr ototype ECU is comprised of t he following major sub-systems: a  spacecraft bus power translator module (LT1763), processor unit (MSP430) and the stepper motor translator (A3906). Refer to Figure 4 for the system  block diagram. It should be noted that external  memory stores as well as the spacecraft communica tion module were not implemented in the prototype  ECU.   NASA/CP-2010-216272