In Chapter 1, I discussed the two “cases” or architectures for your picosatellite: the CubeSat or the TubeSat. You will populate these with the guts of your mission. A typical loadout will include the antenna, the radio transmitter board, the solar cells, a battery, a power bus, a processor, and the sensors.
Solar cells will have to be soldered onto Printed Circuit Board (PCB) slats. These will be wired, along with the battery, onto some sort of power bus—another PCB. The on-board processor is likely to be an Arduino or BasicX-24 PCB board. The radio transmitter will be off-the-shelf components wired onto a PCB. Finally, your sensors may or may not have their own PCBs.
That’s a lot of boards. Fortunately, fabrication and construction is very easily outsourced these days. You start with a fundamental choice: whether to do through-hole soldering (where you stick the wires for each component through the board, and then solder them with a soldering gun) or to use the lighter Surface Mount Technology (SMT) components.
Most of the MAKE, Arduino, and RadioShack kits out there still use through-hole soldering. It is, in my opinion, an easier task to accomplish. For through-hole, you heat up an iron, place the component, and solder it.
However, the industry is shifting towards SMT parts. They are smaller and cheaper. Soldering SMT requires tweezers, a magnifying glass, and (ideally) the use of a hot plate and heat gun rather than an iron. It requires more dexterity and precision.
The suggested default TubeSat configuration includes the CAD files necessary to print the Power, Antenna, Microprocessor, and Transmitter PCBs as well as the solar cells. All you have to do is fabricate the boards. There’s a standard spec—called Gerber files—all fabricators accept.
PCB board designs are typically provided as Gerber files (editable in freeware like KiCAD). These include details for each layer of the board, including
I will emphasize—you can get pre-existing Gerber files for a typical picosatellite project. This frees you from the need to do any electronics design yourself for any parts other than the actual sensors or engineering test design. Put another way, your satellite bus, into which you plug your experiment, already exists. This will make starting your picosatellite build very straightforward. There are copious links to CubeSat-ready boards at http://www.cubesatkit.com/content/links.html. Remember that CubeSat is a specification, while TubeSat is a specification and a kit; therefore, a CubeSat requires a little more integration effort on your part when designing and building your picosatellite.
There are eight standard files that cover the copper, solder mask, and legend layers plus an overall outline and where you want holes drilled. Make sure you have your PCB Gerber files (aka Gerber RS-274X files), created from a CAD program such as KiCAD. These will include, for a two-layer board, up to eight files as listed below. For a two-layer board, you could squeak by with just three files—you can skip the silkscreen layers if you don’t need labels, and you can get by with just one solder mask if it’s a one-sided board (no solder traces on the bottom). But all the TubeSat boards are fully defined two-layer boards, so let’s move on.
A generic set of Gerber files to order PCB boards includes the following:
A default single TubeSat requires four different octagonal boards, each about 3.5 inches × 3.5 inches in size, two-layer. It also requires eight 5 × 1 solar panel boards.