Ground Sphere CubeSat Ground Station

This update is based on a couple of emails from Tim at Southern Stars. The short version of the update is that we have limited access for conducting from orbit testing, so Tim and Scott jumped at a chance this past week to run a from orbit test. Unfortunately, the results are inconclusive at best, and disappointing at worst. They were unable to receive signal from the CubeSat in question. Read on for full details.

The test in question involves attempting to receive signals from AeroCube 4C. This CubeSat only broadcasts on 915 MHz when it is over its mission control center, so we have to make special arrangements to conduct the from orbit tests. Specifically, we need to coordinate with its operators and Southern Stars team members must drive with the Ground Sphere to the LA area in order to be under its footprint.

This past Thursday (Jan 2), a test opportunity was arranged. The operators believe they picked up the CubeSat's signal (they saw what appeared to be the signal on a spectrum analyzer) but were not able to establish a radio lock. The following from Tim details our even less successful results.

We were less successful. We saw a number of "blips" right around the expected 914.7 MHz, but they were all very short. We saw nothing like a continuous signal that dopper-shifted as the satellite approached and receded. I suspect the blips were all local. We recorded about 10 GB worth of raw RF samples from the SDR, and we'll go over these in more detail tomorrow.

I should note: we used Scott's SDR, rather than the SDR that was sent to us. I didn't realize this until after the pass began. Scott's SDR does not have the same built-in preamp and has a smaller gain (a few dB difference? Scott can you put a number on it?) This was a mistake on our part.

We also noticed that the GS antenna did not seem to produce noticeably any different signal levels when the power supply to the preamp was plugged in, vs. when it was not plugged in. I don't know what that means. Something may or may not be broken. Or we're just not interpreting the SDR output correctly (?)

Discussions between Aaron and Scott over email confirm there was a hardware issue with Prototype 1. The preamp's power connection came loose during transport so it was not in use during the test.

It should also be noted that this attempt at a from orbit test, due to the challenges with securing test opportunities, came well out of the established testing order (see Testing wiki page for more details). Neither the lab tests nor the field tests have been run, and both need to be run to verify and validate the prototype. In all likelihood, even the lab tests would have turned up the problem with the pre-amp.

We will be circling the wagons here shortly to continue the testing. More news as it is available.