3689652395?profile=originalThe final Low Orbit Helium Assisted Navigator (LOHAN) test flight -  codenamed PRATCHETT - will take off tomorrow (Saturday) from Colorado Springs East Airport at 13:30 local time (19:30 GMT).

The mission - designed to test our Vulture 2 spaceplane's avionics rig at altitude - is being conducted by our US allies at Edge Research Laboratory. They'll send this payload up to around 30,000m under a mighty meteorological balloon:


3689653978?profile=originalThe test is a second pop at seeing how our Pixhawk autopilot, servos, batteries, etc, perform in extreme cold at altitude. This time around, however, we've got a 900MHz radio rig on board, by which Andrew Tridgell will monitor the flight live from the comfort of his sofa in Australia. There are more details on that and the payload here.

It should be entertaining, so if you fancy cracking a beer and coming along for the ride, you'll be able to follow the flight live here.

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  • Developer

    Good Job! Congratulations guys.

  • Developer

    One of the major aims of the test flight was to test the comms link, so we could be confident of being able to control the aircraft in the final Lohan mission.

    The radio setup was a RFD900 running at 27dBm on the ground station, with a 6dBi yagi. The payload in the balloon had a RFD900u running at 15dBm.

    Note that the RFD900 is capable of transmitting at 30dBm (1Watt) but we reduced it to 27dBm on the day to prevent issues with drawing too much power from the laptops USB bus. The RFD900u is capable of transmitting at 20dBm but we reduced it to 15dBm as we had an issue in preflight checks with the power supply to the Pixhawk browning out the radio when the RFD900u was set to full power. Reducing by 5dB fixed that.

    This graph shows the comms quality for the test flight

    Lohan-radio-link.pngThe olive line is the distance from the payload to the ground station (including both horizontal and vertical components). So the payload got to a maximum of 34km away from the ground station. The line stops at the right side of the graph when the payload lands and we lose link completely, about 25km from the ground station.

    The red and green lines are the signal strength and noise levels in RSSI units as seen at the ground station. A link can be maintained as long as the red line stays above the green line. It shows that a good link from the payload down to the GCS was maintained over the whole flight, with only a few very brief periods where the link dropped (you can see when the link dropped when the yellow line goes to zero).

    The blue and yellow lines are the signal strength and noise levels as seen by the payload radio and recorded by the ground station. It shows that the payload got a stronger signal than the ground station did (as the ground station had a more powerful transmitter). What is more interesting is that the noise level in the payload was very high (the yellow line). It is very clear that the limiting factor in the communications system was RF noise level in the payload.

    On the far left of the graph you can see where the noise level in the payload suddenly jumps shortly after the system is turned on. That is likely a sign that some other pieces of equipment in the payload was switched on at that point and was radiating a lot in the 900MHz band. To improve the communications link we need to identify what piece of equipment this was and reduce its level of interference.If that noise hadn't been introduced then the blue line would have been above the yellow line the whole flight and we could have had continuous two-way link. As it was, we ended up with a one-way link for large portions of the flight, as RF noise in the payload blocked incoming signals from the GCS. So we knew exactly what the vehicle was doing, but we wouldn't have been able to change the settings in the Pixhawk reliably if we needed to.

    Still, it was a good result and the RFD900 radios performed extremely well! Congratulations to Seppo from RFDesign.

    Note that RSSI units scale approximately as 2x dB. So a difference of 12 in RSSI between signal and noise represents a fade margin of 6dB, which equates to a available range of 2x the current range. It is clear that the link from the payload to the ground station had a fade margin of well over 10dB.

  • Developer

    Next up the roll and pitch, giving us some idea of how much the balloon swung, and how much it swung on the chute after the burst.

    Here is the overall roll-pitch graph against altitude (degrees of roll/pitch, altitude in meters above sea level)

    Lohan-roll-pitch1.pngHere is a zoom into part of the ascent:

    Lohan-roll-pitch2.pngyou can see a typical 20 degree swing, with occasional 50 degree swing. The frequency of the oscillation is between 1 and 2Hz.

    Here it is at burst:


    you can see the amplitude really went up when on the chute, but frequency dropped to about 0.5Hz

  • Developer

    I've started having a look at the DF log from the flight. Here is a temperature plot from all the logged temperatures. The airspeed sensor got to -48 degrees C at an altitude of around 18km. The other sensors stayed much warmer as they are warmed by the electronics.

    I'm uploading the full DF log to droneshare now. It is rather large (255MByte)


  • Moderator

    I think I would be inclined to shoe horn an NTX2B in there for some distributed tracking goodness. I can't remember is there one in the main aircraft? @Melih hyper pressurized floating balloon project Do tell more in another thread!

  • 3D Robotics

    I think that's an altitude record for Droneshare ;-)


  • Fantastic work by Edge Research Lab and Andrew Tridgell. Beers all round, and details on the mission to follow.

  • Developer

    Many thanks to the great team from Edge Research Lab for their flight today!


    Edge Research Lab - Home
  • Developer

    Droneshare link for tlog:


  • Developer

    Telemetry log is here: http://uav.tridgell.net/Lohan/EdgeFlight2/flight.tlog

    DF log will be uploaded once the payload is retrieved

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