Nuts and Volts - August 2015

rover robot project I built five years ago. It uses a PICAXE-

08M2 to interface a PC to its XBee radio.

Communication with the PC is through the Terminal program included in the PICAXE Program Editor. This means the ground station’s PICAXE coordinates and formats communicate between the radio and PC so that an operator can easily understand what information the Model CubeSat is telemetering.

What's Next?

The Model CubeSat is still a work in progress. In the near term, however, I want to develop the following additions.

First, the Model CubeSat needs more I/O in order to take advantage of its volume. I’ve already designed the PCB for a PICAXE-18M2 microcontroller plane; I just need to design additional PCBs before I can send it out for manufacture (I prefer to combine several different PCBs and then panelize them in order to save money).

Second, the Model CubeSat needs a communications protocol. I designed one for my moon rover and plan to use a variation of it for the Model CubeSat. That would allow the CubeSat to store and download data like real CubeSats do when they’re out of range of a ground station.

I want additional science and engineering planes. That way, the Model CubeSat can be restacked and reconfigured for new missions. The latest plane I’ve designed is a sun sensor and magnetometer plane. It detects which surface of the CubeSat faces the Sun and the orientation of Earth’s magnetic field relative to the CubeSat. This will permit the Model CubeSat to determine its attitude in space.

Another plane I’d like to create is a Geiger counter plane to allow the CubeSat to determine the amount of radiation around it.

What does a CubeSat do with attitude information? Aside from transmitting that information to the ground station, it can be used to help hold the attitude of the CubeSat with magnetorquers. That’s not really practical with this model, but I will create a plane to simulate magnetorquers.

In place of magnetorquers will be bi-colored LEDs that illuminate when the magnetorquers are energized. So, when the Model CubeSat is out of its desired orientation, the LEDs turn on indicating the magnetorquers are active. The color of the LEDs will indicate the polarity of the magnetorquers. Then, when the Model CubeSat is turned back to its desired attitude, the LEDs are turned off.

A more difficult addition, I think, is using real solar panels to recharge the CubeSat’s battery. The solar panels would measure 4” square and would need to be encapsulated for durability. The panels would mechanically attach to the Model CubeSat airframe and electrically connect to their own plane. The solar panel’s current would then feed into the Vin pin of the Model CubeSat bus. The recharging circuit would need to be an upgraded power plane.

Finally, I want to add a camera. A slow scan camera would be ideal, but even a baby monitoring camera would be fine. The Model CubeSat would activate the camera when commanded to do so by the ground station. I’m assuming I’ll use different transmitters and frequencies for the camera and XBee. Therefore, while the camera is transmitting an image, there would be no further communication over the XBee in order to simulate the CubeSat using the same radio for both functions.

When I think about it, I guess I’m only half way done with just the design of the Model CubeSat. There’s still a lot of work developing new planes, writing code, and writing directions for students. However, it’s my hope to make this kit available to schools as a complete curriculum that teaches electronics, programming, and engineering. With space as its focus, I think many students will find it a motivating project to work on.