It is often stated that we are living in the Information Age and that Data Makes the World Go Around. With the explosion of the internet over the past couple of decades and the role it plays in our everyday lives today, there is indeed some evidence to support the veracity of these assertions. Equally valid perspectives are that Power Makes the World Go Around and that we are living in the New Space Age. Although a lively debate could be had over these two competing viewpoints, it is indisputable that sufficient power is critical for keeping spacecraft; such as the International Space Station, operating.
Solar panels powering the International Space Station
An adequate supply of power is not a complete solution for the challenge of supplying the necessary power to operate spacecraft; including rockets and satellites. On the contrary, space vehicles are comprised of sophisticated power distribution systems (PDSs) that ensure missions are carried out effectively. And the PDS relies upon power electronics to perform the many monitoring and control functions required to drive its subsystems. The exploration of these space power systems will provide the necessary insight for us to put forth a set of aerospace power electronics guidelines to aid in designing boards for space platforms.
Space Power System Electronics
Spacecraft electrical power system block diagram 
Aboard space vehicles, the importance of sufficient power necessitates that the choice of which energy source(s) to use is based on technical requirements and specifications. And it is not uncommon to find a space platform utilizing photovoltaic (solar cells), thermochemical (fuel cells), nuclear and/or Li-Ion (battery packs) technologies together to make sure the demand is met and ample energy storage is available. Irrespective of the source for electrical power, space vehicles depend upon a distribution system to supply the power for electronic PCBs to operate and receive, process and transmit the sensor data, regulation and control signals that enable the platform to perform its mission, safely. An example of this power distribution is shown below.
Spacecraft electrical power system block diagram 
As shown in the figure above, there are a number of aerospace power electronics elements that are included in the spacecraft PDS. These critical functions include current sensors, boost and buck converters, voltage sensors for batteries and voltage regulators for load supply control. Now, that we know what aerospace power electronics functionality and devices are required, let’s see how to design for their effective utilization.
Effective Aerospace Power Electronics Design
Designing aerospace power electronics is actually designing circuit boards comprised of power electronics components that meet the requirements of applicable regulations and standards, achieve the performance objectives, can be manufactured at a high yield rate and will operate reliably over the projected lifetime. If this sounds familiar that is because these are the yardsticks that define a good PCBA development process for any application. However, successfully realization of these hallmarks is significantly more challenging for critical applications and that includes aerospace systems.
In fact, the bars that have to be transcended for aerospace board design, manufacturing and testing are probably the highest that exist for PCBA development. This certainly applies to designing aerospace power electronics boards due to their importance in enabling and sustaining spacecraft operations. Therefore, aerospace power electronics design should be governed by well-defined directives as listed below.
Guidelines for Designing Aerospace Power Electronics
- Create or utilize an accurate power equipment list (PEL)
The PEL is the listing of power requirements for all equipment.
- Create or utilize an accurate power profile
The power profile is essential for designing the spacecraft PDS. It specifies how much power is needed and when it is needed.
- Determine the power margin
The power margin is the difference between the power available and the power required.
- Design for efficiency or utilize SMPS instead of linear regulators, wherever possible and if noise sensitivity tolerance will not be violated.
- Determine bus voltage levels
These are the input and output voltages required for the power electronics (and other) devices.
- Select components
- COTS, EEE certified and/or Class-S components
- Determine if radiation hardening is necessary
- Apply derating rules and guidelines
For example, EEE-INST-002 Instructions for EEE Parts Selection, Screening, Qualification, and Derating
- Include manufacturing directives in PCB file(s)
- Specify radiation hardening technique(s) to be implemented
- Specify that CM uses at least 3% leaded solder for assembly and rework to avoid tin whiskers.
- Specify testing regimens to be performed
In addition to the guidelines above, your design process should also follow good DFM for aerospace technology PCBs methods to optimize the building of your boards to meet the quality control standard, as stipulated by AS9100D, that aerospace PCBAs must achieve.
Designing power electronics for space platforms begins with understanding the importance of a well-defined and laid out PDS, which is unlike other power distribution by the fact that the system is isolated and must meet very high quality and reliability thresholds. Failure is not an option. Success in achieving these objectives depends to a great degree on your choice of contract manufacturer (CM).
|Tempo's Custom Avionics for PCB Manufacturing Service
At Tempo Automation, the industry leader in fast, high-quality PCBA manufacturing for low volume applications; such as is typical for aerospace boards, we employ an advanced software-driven quality control process to monitor and manage each stage of the board built. Coupled with our automated inspection techniques, we ensure that your boards incorporate your design objectives and are well within the capabilities of our equipment. The result is high-quality, reliable PCBAs.
And to help you get started on the best path, we furnish information for your DFM checks and enable you to easily view and download DRC files. If you’re an Altium Designer or Cadence Allegro user, you can simply add these files to your PCB design software. For Mentor Pads or other design packages, we furnish DRC information in other CAD formats and Excel.