[Ground-station] Balloon Launch - experiments?

[Zach Leffke]

I like this idea......it has elements of a couple projects that I've 
worked on in the last year or so.

I just did similar math from a slightly different angle......

10 Msamp/sec complex capture (so 10 MHz of spectrum, using GNU Radio 
Complex datatype) at 64 bits per sample yields roughly 1.86 hours of 
record time on a 500 GB SSD......about perfect for this type of balloon 
flight.......go up, burst, come back down.  The recording could be 
triggered at a specific time or altitude to optimize the collect.

I'd recommend the XU4 over the RPi as it has two USB 3.0 ports, one for 
a B200 mini, and one for an external USB3.0 SSD.  also its got a beefier 
processor and more RAM, better to keep up with the write speeds.

A B200 mini is tiny and relatively cheap, though it would probably need 
a 10 MHz reference of some sort (could be a GPSDO, but would need to 
make sure the GPS works at altitude......standalone OCXO might be a 
better solution).  It also has a similar RF front end to the Astrod SDR 
(an ADXXXX whatever whatever, I can't remember off the top of my head, 
but same family at least).

For the 2017 Eclipse experiment (recording satellite downlinks, looking 
for Scintillation effects due to the eclipse) I used a very similar 
setup to this and used a simple script to control the flowgraph 
recording....one minute on, one minute off.  I ended up with hours of 1 
minute IQ recordings started at every odd minute. Something like that 
could be used here, with the possibility of tweaking parameters between 
each recording (like stepping the USRP gain in 10dB increments each 
time, or possibly changing center freq).  Log files or the filename 
itself could be used to keep track of which IQ capture had what settings.

Marc Franco has designed and I believe built some 5 GHz pre-amp 
prototypes for the uplink band...might be good to give them a test.

Ground based 'reference beacons' might be useful/fun.  Maybe sending out 
CW at known center freqs at known power levels to give a reference to 
hunt for in the collects.

Any ideas on antenna types?  patch array? horn? conical spiral? circular 
or linear (I vote circular on the balloon, pointed at Nadir)?


This sounds like a perfect summer project for some of our undergrads!

-Zach, KJ4QLP

Research Associate
Aerospace Systems Lab
Ted & Karyn Hume Center for National Security & Technology
Virginia Polytechnic Institute & State University
Work Phone: 540-231-4174
Cell Phone: 540-808-6305

On 4/22/2018 1:20 AM, Phil Karn via Ground-Station wrote:
> On 4/20/18 10:07, Douglas Quagliana via Ground-Station wrote:
>> I would like to suggest sending up a software defined radio that can
>> recording on (and around) the proposed uplink frequencies.  It should
>> sample at the highest sampling rate possible to capture the widest
>> bandwidth possible into the recording.
> Let's see... what sample rate would fill a 256GB thumb drive during a
> typical 2 hour balloon flight?
>
> 256e9 bytes / 4 bytes/sample = 64 gigasamples assuming 16 bit complex
> samples. Over 2 hours that would be a sample rate of 64e9/7200 = 8.89
> megasamples/sec. I.e., we could collect 8+ megahertz of spectrum,
> depending on the anti-alias filters. You'd have to make sure that the
> drive can write continuously at that rate. A SSD might be necessary.
>
> Plenty for the 2m/70cm satellite subbands or for the entire 2m band, but
> not the entire 70cm band. It would be fun going through these recordings
> with my 'radio' program.
>
> Most latex weather balloons maintain a remarkably constant ascent rate
> of 1,000 fpm (5 m/s) and burst at 100,000-120,000' (30.5-36.5 km). Ergo
> the ascent time would be 100-120 minutes or from 1 hr 40 minutes to 2
> hr. The ascent is somewhat turbulent until the turbopause, then things
> usually smooth out in the stratosphere. At altitude it's positively
> serene until the balloon bursts. Then all hell breaks loose.
>
> This assumes hydrogen. Pretty much everybody uses it now since helium is
> getting scarce and bloody expensive. Treat it with respect and you'll
> have no problems.
>
> The descent by parachute usually takes about 30 minutes. Descent is VERY
> quick at first because of the thinner air (1% of surface density at 32.6
> km) but then slows as it descends into exponentially denser air.
> Descents are pretty violent due to turbulence (especially if the remains
> of the balloon are still attached) so it might not be worth collecting
> data on the way down since you're seeing much the same area anyway. It's
> easy to get sick watching HDTV of a descent on a large screen...
>
> Phil
>
>
>
>
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