PYSY-4 Launch Announcement 13.4.2013

[mclane]

Hello HAB community,

since the weather forecast starts to become a little more favorable, we plan to launch now this weekend on the 13th of April.

Launch will be from our location close to Regensburg.

Launch is planned for 9.30 CEST (7.30 UTC).

Payload will be a small tracker with the following data: RTTY 50 baud, 7N2, 434.650 MHz carrier, 450 Hz shift. Look for microPYSY in dl-fldigi.

Trackers in south of Germany and Czech Republic are highly welcome. I will post an update Friday evening to confirm the launch.

-- mclane

[mclane]

Hello HAB community,

thanks to everybody listening to our failed attempt for a high altitude launch; special thanks go to the polish hab/ham community (SP9MCY, SP9UOB, SP9 OHY) who picked up the signal during the flight.

Immediately after launch, we realized that the telemetry data did not change; so we did not receive valid data. Analysis of the dl-fldigi log file indicates that after I installed the batteries for the 808 camera, transmission was stuck. The only explanation which we have so far is that one of the two temperature sensor became loose so that the onewire readout routine went into an infinite loop - hyphesis to be confirmed after a thorogh code analysis of the Dalas TempSensor library.

Filling and launch have been quite a challenge since it was very windy. We could not precisely determine neck lift but we believe that we have filled to reach roughly 4-5 m/s lift. Launch was around 9.30 CEST and we could track the signal until 12.55 CEST using a 7 elem. yagi + habamp + Yaesu VR500. We assume a balloon burst around 12.10 since at that time, the signal became wobbly and started to drift considerably. Assuming a 160 min flight until burst and 4-5 m/s ascent we might have reached an altitude around 40 km. Signal reception was lost around 12.55. According to the prediction, the payload may have landed in the bohemian forest in the area where the borders of the Czech Republic, Austria and Germany come together. Now we hope that someone finds it and reports back...

So instead of a chase we went into the beer garden (even though it was still quite cold) and had a nice "Bretznschnitzel" and some beer to compensate for the frustration.

Next attempt beginning of May...

--mclane

[mclane]

We have flown these sensors 3 times without problems; temperatures measured have been as low as -55 °C. The lock was already before launch, so this cannot be the reason.

--mclane

Am Sonntag, 14. April 2013 11:39:10 UTC+2 schrieb MikeB:

Hello,

How low do you estimate your temperature sensors reached? Semiconductor temperature sensors may not work below -40C, and if they have 1-wire or I2C interfaces a failure could bring the whole bus down. I'm therefore planning to connect a simple thermistor to an ADC port for measuring external temperature.

MikeB 

[Mike Bessant]

Thanks for that, but  please can you let me know what type of sensor you used because I don't seem to be able to find any smart devices that are specified to work below -40C?

MikeB

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[Costyn van Dongen]

Mike,

Be aware that the DS18B20's exhibit some strange behaviour in their
accuracy when they've been down to those temperatures. The STS project
in Slovakia sent up a Vaisala radiosonde along with their own to
compare the accuracy of the DS18B20. As you can see, they match up to
about -50, but when the DS18B20 warms up again, it is no longer
accurate. Blue is vaisala, red is DS18B20:

http://stsproject.net/wp-content/uploads/2012/09/Screen-Shot-2012-09-18-at-17.12.09.png

You can see the rest of the post and a test of the BMP085 as well here :

https://groups.google.com/d/topic/ukhas/PN-jecH_zzo/discussion

Kind regards

Costyn.

p.s. and just because they are mindblowing, burst pics from their
flight as well: http://stsproject.net/?p=282


On Tue, Apr 16, 2013 at 10:04 AM, MikeB <mikebes...@gmail.com> wrote:
> Many thanks.
>
> The specified error of +/- 3C down to -55C is certainly better than anything
> I had found. The external temperature may of course drop below this and it
> would be interesting to know if the error just increases or whether the
> sensor crashes the 1-wire bus. Time to breakout the dry ice!
>
> MikeB

[Ed Moore]

This could be down to self-heating or solar absorption or both - in a vacuum a temperature sensor is only going to measure its own temperature, rather than their air around it (because there is none). Obviously high altitude are not quite a vacuum but they're on the way.

What determines the DS18's own temperature will be a mix of the power it is dissipating (it's using a few mW which is nontrivial in a small package) and energy it's absorbing from radiation, which will principally be from the sun. Being a black package, if it can see the sun it will get some solar heating. The Vaisala sonde's temperature sensors are reflective solver for this reason.

If you want serious accuracy then a PT100 (do the self-heating calcs!) and some kind of silvered heatsink might be a good way to go. I can draw you up an interfacing circuit if you want (it needs a constant current supply and an op-amp with good dc performance - but still only of the order of £10-£20 parts count in single quantities).

Ed

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[Mike Bessant]

Thanks for the useful practical feedback on the use of semiconductor temperature sensors.  

Could solar absorption errors be avoided simply by placing the sensor in the shade (under) of the payload?

Few digital sensors seem to like operating below about -40C and that's why I had planned to use a good old thermistor for external temperature measurement. Not as linear as PT100, but adding a couple of resistors (or post processing) can provide acceptable results. 

MikeB

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[Ed Moore]

On Tue, Apr 16, 2013 at 3:59 PM, Mike Bessant <mikebes...@gmail.com> wrote:

Thanks for the useful practical feedback on the use of semiconductor temperature sensors.  

Could solar absorption errors be avoided simply by placing the sensor in the shade (under) of the payload?

I think this is a good idea yep. Especially if the shade is reflective but holey (to allow ambient temp air to circulate)- the white vented shades used for weather stations are for this purpose. They're called Stevenson shields. I believe white star balloon might have 3D printed one (Dan?) for Speedball 1.

e.g:

http://www.eltekdataloggers.co.uk/graphics/stevenson.jpg

[mclane]

Hello everybody,

two weeks ago, we received an email from someone in the Czech Republic who has found our payload and recovered it. Today we went there and got back the box in exchange with some "thank you" chocolate. The box landed close to the small village "Dolni Dvoriste" (I do not have the czech accents on my keyboard ;-) on a plain field; just a few kilometers away from the border between Czech Republic and Austria. The landing spot has been some 20 km away from the predicted spot.

The box and electronics are in very good shape; we could read out the memory cards and got some very nice 5 hours video footage. A first rough analysis shows a flight time of about 150 minutes from launch to burst; so assuming an ascent rate between 4-5 m/s we may have reached between 36 and 45 km altitude. We will publish some parts of the video in some days on our homepage www.stratosphaere.net.

We are very happy that luckily we got our payload back. Now we prepare for the next launch (PYSY-5) which had to be postponed for some time. The payload is ready; now only the weather needs to improve and we need to find some spare time during one of the next few weekends.

-- mclane