NSL-52

Burlington Maker Faire, NC Science Festival (UNC), Earth Day, March for Science Day

On April 22nd, 2017, we held another public launch at the annual Burlington Maker Faire.

We operated a booth at the event to explain our hobby and also to act as Mission Control for this flight. At noon, we filled and released a balloon for the Faire visitors. At the same time, Paul T. staffed a lecture hall over at Morehead Planetarium (NC Science Festival) to view the simulcasted launch and track the payload.

Right before launch, a child attached his Cub Scout sticker to the payload

The payload for this flight was another of Paul L's "greenhouse" boxes. A cheap, clear plastic box filled with black foam to keep the payload toasty warm. As it could land in a lake, the center of gravity was kept low, and the only holes in the box were near the top. This 900g payload was under a 81cm chute and 600g balloon. The payload contained:

GCM-320+ recording Geiger counter
Mobius Mini Action Camera -- first flight
AP510 APRS tracker
TK106 GSM backup tracker -- first flight for this model
Outside Hung Compact Rain-Activated Pull-down -- first flight
Directed Arborial Recovery Node with Integrated Tether -- the remote control cut-down used in previous flights -- yellow/blue straw and spool in above photo.
Arduino Low-power LoRa Image Telemetry Experiment -- first flight

The jet stream was a bit strong that day. The projected flight path had the payload traveling northeast and landing either in Kerr Lake or far up into Virginia. We intentionally overfilled the balloon, to 2500g of neck lift, to send the payload up quickly and bring it down early. The 81cm chute would also allow for a quicker than usual descent.

Filling and launching the balloon

Images from the on-board camera

At launch, the payload shot up into the sky and quickly headed to the northeast. Chris G. loaded up his car with a pile of chase/tracking gear and headed up I-85. The visitors to Mission Control were able to watch his progress against the very fast balloon.

APRS.FI track of the flight

NC Near Space's annual roof inspection of the Holly Hill Mall!

Passing up through some upper level cirrus (later, passing back down through them, the video captured little suspended ice particles snowing upwards).

NC from 100,000 feet

Storm clouds growing during descent

Burst at 60fps captured plenty of great shots

Coming in over the Roanoke River

Bright green trees are indicative of a swamp

By overfilling the balloon, the hope was that it would fail at 27km. Instead it held out to 30.958km (101570 feet). This caused the payload to travel into southern Virginia. To add to the excitement, severe thunderstorms were starting to form in southern Virginia. The storms, and the RF-damping properties of a pine forest, wreaked havoc on GPS reception during recovery.

The blue cross-haired circle shows the recovery crew's location -- The red polygon is a tornado warning

Chris was able to dodge storms and locate the payload, safely on the ground in a young pine grove

Chris grabbed the payload and headed south out of the storm area. We then all met up to view the wonderful video (and after a long day, a well deserved pint).

Flight Visualization

There was a typical ascent and descent rate with only mild gravity waves visible. The slightly smaller chute, and mild chute tangle, brought the payload in at 7m/s.

A slightly elevated radiation flux was seen as a solar storm neared earth.

The "greenhouse" box worked very well! During the coldest part of the trip, the fast descent with in-rushing cold air, the center of the payload stayed 60C above the outside! The internals stayed above 10C the entire flight. Most of this was due to the "greenhouse" design trapping the strong sunlight. Part is due to minimizing the amount of open cavity within the payload that could take in the cold air. The heat-pipe from the camera fed to a section of the payload 15cm from the temp sensor, so it may not have registered much. Also note how slow the heat transfer takes place. It takes 6 minutes for the cold to start affecting the temperature in the core of the payload, and by then the external temperature is starting to shoot upwards again.

=== Flight notes from Paul L. ===

Arduino Low-power LoRa Image Telemetry Experiment

This was a tangle of devices based upon the Adafruit Feather Datalogger that I flew in NSL-50. The Feather is a M0 processor Arduino with built-in LiPo battery and microSD card. Then add an external temperature sensor. Add to that a Bluetooth chip for talking to the AP510 APRS tracker. Then add a TTL camera chip and finally a LoRa 900MHz transceiver chip running under 80mW. This had a directional antenna aiming down. A state machine was coded up that would poll all of the devices and perform various functions at various times, including:

DX APRS: Record overheard APRS traffic to see how far they can be heard.
Send additional APRS messages with payload status, external temp, etc.
Listen for special coded APRS messages to perform commands.
Send a basic 915MHz LoRa telemetry packet every minute.
Record a photo with the TTL camera every few minutes.
Send a LoRa SSDV copy of the recorded photo back to a ground station.
Listen for LoRa telemetry from the ground. This could be instructions to resend certain image packets or change resolutions, transmission types, etc.

Me picking up LoRa signals from the payload after launch

The thumbnail-sized images captured by the arduino for transmission back

Paired with the system, back on the ground, was another Feather with LoRa unit. It was mounted directly on a 900MHz Yagi antenna. This was connected via USB to an old laptop running Processing (Arduino IDE-looking C/Java mashup). The ground system would gather packets and automatically request re-transmission of any missing ones. Correctly downloaded images were automatically emailed to me.

Results: Not bad. The ground system went along with Chris in the chase car, but due to the balloon's fast track out of town, we lost contact as the payload went over 6200m. The last received packet was at a distance from the ground station of 19km (12 miles!). The system continued to operate as expected and I was in contact with it via the APRS back-channel during the flight. It periodically took photos and stored them to flash. Before I lost contact, I should have instructed it to switch to a larger image resolution. Instead it recorded images in its smallest size -- more like thumbnails. Perhaps I code it to automatically switch to larger images if contact with the ground is lost for a period of time -- or maybe direct it via the APRS back-channel.

On the APRS side of things, it was able to copy a packet from as far as a car driving around Columbus Ohio!

Outside Hung Compact Rain-Activated Pull-down

This is simply a spool of ~16m of string. One end of the string is tied to the spool, the other is tied to the payload. The entire spool is suspended from the payload with several strands of PVA string (thread). A strip of cardboard loosely wraps around the spool to keep it from banging around.

Rain was in the forecast for that night. In the event that the payload became stuck high in a tree, the rain would have dissolved the PVA string allowing the spool to fall, providing a chance to pull the payload down.

Results: We didn't need to use it. I might've worked.

TK106 GSM backup tracker

Paul T. used a TK102 unit back on NSL-44 with good results. I tried its cousin, the $30USD TK106.

Results: Getting the $10 SIM-card for these things is always a challenge. But once that is done, this is a usable, lightweight, cheap backup tracker. Much lighter and cheaper than a Spot. It only works close to the ground, but text it, and it will send you a text message with a Google Map URL. What else do you need? The problem was the GSM coverage. There are a few big holes in T-mobile's coverage in the less populated parts of NC. And we flew right into the edge of one (blue star below). I was in contact with the unit in the final feet of descent, but once on the ground, it went silent. Not much RF survives a pine forest. I kept texting it with hopes that the storms in the area may change propagation enough to reach it. This just resulted in me getting spammed with a bunch of texts once Chris drove the payload back into a coverage area (pink below). It seems that the messages are queued up on the T-mobile end -- good to know.

Mobius Mini Action Camera

I wasn't sure about this little camera, but oh man! I think it was the star of this flight.

So you can pick the camera up for $69USD ($10 less than the older Mobius). Because of my recent bad luck with wide angle, I chose the narrow angle (lens A) model. Instead of wiring it up to a LiPo, I kept the internal battery and just added a small USB phone charger battery pack yielding 3.5 hours of record time. It uses the same programming interface as the 808 and Mobius but has several new features. Programming one of these could be daunting at first as there are a TON of options. I used an old class-6 32GB microSD, so I wanted a relatively low write speed/size. So I picked MP4 1280x720 at the lowest fps -- which was 60 ! I usually set the white balance to florescent, but on this flight I kept it Auto. This resulted in more vivid greens. I also discovered that there was a new exposure metering option of "lower weighted", so I went for that (earth being on the bottom half of the image). Otherwise it was a pretty default configuration.

Results: Nice! This is my new recommendation for a inexpensive, lightweight (27g) camera. Chris G. thinks the video is superior to the Mobius.

There are so many resolution and fps options that it has me thinking. 1440p? Film the balloon burst at 480p but 240fps?!

The unit runs hot, like the Mobius, so I hooked a little 1g heat-pipe up to its metal mounting tabs and directed the warmth over to the various payload batteries. I have yet to test its RFI effect upon GPS, so I added the aluminum foil RF shield that I usually do on flights.

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