RockSat-C Space Program 2017-2018

Introduction

For the past eight years or so, my school has participated in the RockSat-C Program in conjunction with NASA and the New Jersey Space Grant. I’ve been on the team for the last 3 years, and my role has been electronics hardware design and a bit of software development wherever needed. The 2017-2018 experiment built upon progress made in the 2015-2016 experiment, making vast improvements to the hardware in both electrical and mechanical robustness. We also decided to take advantage of pre-existing digital sampling hardware, which made it much easier for us to focus on the system design and make sure our system meshed properly with the other experiment on-board our canister, which was a Vibration Reduction experiment using active solenoids to cancel out the massive vibrations inherent in a rocket launch.

During this project, I learned a whole lot about Printed Circuit Board (PCB) design, using EAGLE CAD to design the signal conditioner board. In essence, our system (“the brick”) consisted of three main components: a Beaglebone Black microcomputer running Linux, a PRUDAQ digital sampling board (which fits very nicely onto the Beaglebone), and a signal conditioning board which I designed to fit nicely on top of the PRUDAQ. It made a really neat sandwich of boards that held together firmly and was very resistant to shock and vibration.

Signal Conditioner PCB

The signal conditioner board did three different functions:

  1. Provided a constant 10 mA excitation current to the pressure transducer
  2. Provided signal amplification via a network of 2 opamps, which provided “Automatic Gain Control” on the signal. Because we didn’t know how big the signal was expected to be, we didn’t want to make the gain too big or too small and risk missing the signal – so we built an AGC circuit to ramp up the gain when the signal was small, and decrease the gain when the signal was too large.
  3. Provided a Low Pass Filter with 2.3 MHz cutoff frequency
  4. Fed the signal into the PRUDAQ to be digitally sampled at 5 Megasamples/second
  5. Provided smooth, regulated power rails for the Beaglebone, PRUDAQ, and the analog circuitry

Power Requirements

There were 4 different power rails onboard: 5 volt digital, 5 volt analog, 10 volt analog, and 24 volt analog (for the sensor). The op amp circuits required +5 volts and -5 volts, as well as a 0 volt reference. So I decided to use 10 volts as the +5 volts, 0 volts as -5 volts, and +5 volts as the ground reference. Confusing, huh? Not really. I just shifted the signal so that it was centered around 5 volts, and varied from 0 to 10 volts. I then DC level shifted the signal to 0-2 volts, centered at 1 volt, for the PRUDAQ input. Lots of level shifting was used between stages and between the signal conditioner board and the PRUDAQ input.

Our section of the report can be read below. If you wish to read the full Stevens report including the Vibration Isolation experiment, you can download that here.

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