ARISSat-1: Why is it cool and why do we care?

ARISSat-1 photo 2It looks like AMSAT is going to launch a new satellite! ARISSat-1 – the successor of SuitSat-1 – is ready to be launched on Progress-41P heading to the International Space Station on Friday, January 28, 2011. It will be deployed into its own orbit during EVA 27 currently scheduled for February 16. Once in orbit, it will slowly decay and eventually burn up in the Earth’ atmosphere. SuitSat-1 decayed after 7 months in orbit and that’s also a likely life time for ARISSat-1.

So, why is ARISSat-1 cool and why should we care?

ARISSat-1 primary mission is education (STEM) and it carries various experiments. I don’t have much details about the experiments but I think one of them will measure vacuum. In addition to the experiments, ARISSat-1 also carries amateur radio payload, which has shared use between hamradio traffic and telemetry downlink from the onboard experiments.

ARISSat-1 Overview ARISSat-1 IHU overview

The communication payload contains:

  • 16kHz wide linear U/V transponder (inverting)
  • FM downlink with voice messages in 15 languages and SSTV image downlink from the cameras
  • 1 kbps BPSK telemetry and experiment data downlink
  • CW beacon transmitting the callsign of the satellite RSØ1S, a subset of the telemetry and the callsign of the people actively involved in ARISSat-1

ARISSat-1 Frequency Chart

The BPSK telemetry downlink will use the BPSK-1000 protocol designed by Phil Karn, KA9Q. It fits within an SSB channel so decoding will be as simple as tuning the receiver into USB mode and feeding the audio to the demodulator and decoder software that will soon be made available by AMSAT. There is also a reference demodulator software made available under GPL by Phil.

The BPSK telemetry beacon has the possibility to fall back to the old BPSK-400 protocol used by Phase III satellites such as AO-40. Which of the two BPSK formats is in use can be determined by looking at which CW beacon is active, c.f. the band plan shown above, but let’s hope it will not come to that so that we can experiment with the BPSK-1000 downlink.

The communications module is built up around the new SDX software defined radio, see CDR presentation here (PDF).

You may have noticed that I have posted this article under GNU Radio. That’s not accidental in that I intend to build a receiver that can receive all downlink channels simultaneously. I’m thinking about a 1920×1080 screen showing the downlink spectrum, received telemetry and SSTV images, etc. Would be a nice geek-gadget on the wall. Before this can happen I need to:

  • Write an SSTV decoder (Robot 36)
  • Integrate Phil’s BPSK-1000 demodulator
  • Make a nice GUI that is worth looking at

More on these topics later. For now you can enjoy this awesome photo gallery of ARISSat-1 Flight Hardware by robot_mastor and this video by Drew KO4MA:

Author: Alexandru Csete

Embedded software engineer in the satcom industry during the day. Radio amateur and SDR hacker during the night.