Table of Contents

Balloon, Mark 4. "Operation Charlie Brown"

Overview

Building on the success of Launch 3, we will use the same APRS beacon and 150g balloon. We will just add a micro-camera and a little “Charlie Brown” doll to the payload, in honor Todd Brown's father Charlie, who is battling cancer.

Timeline

Mission Summary

Success!

The payload landed 3.1 miles from the forecasted location, and hung up in a tree about 80 feet above the ground. Recovery teams were able to locate it, but could not get it down immediately. Adam & Char (KC2ANT & KC2ULK) did some door-knocking in the area to get permission to go back into the woods. As it happened, they came upon Chris Preston, a local arborist. Though busy at the moment, he very generously climbed the tree the next day and retrieved our payload.

Mission Objectives

  1. Use bottle and bubble wrap technology to insulate the payload, hoping to keep the tracker working.
  2. Get pictures back from spaaa… spaaaa.. spaaaa… spaaaaace!
  3. Add a temperature sensor to the tracker (optional)
  4. Hydrogen lifting gas for part or all of balloon (we have 1/2 tank of helium)

Mission Parameters

Balloon Latex 150g
Lifting Gas Helium
Payload Tracker, Micro camera, Charlie Brown Key Fob
Payload container Plastic bottle and bubble wrap
Max Payoad Weight 200g
Flight Time 45-90 min
Cutdown Balloon Burst
Recovery 15“ parachute
Tracking 300mw APRS tracker loaned to us by Alan Adamson (W7QO)
Telemetry GPS and temperature data.

Balloon and payload Weight Budget

Item Weight (grams)
Batteries - (2) 300ma LiPo 18
Payload container 28
Tracker + Counterpoise 23
Parachute + guyline 32
Balloon 150
Balloon attachment (tape) 10
Camera 1 13
Camera 2 19
Camera tape 10
Charlie Brown Doll 23
Tie off for doll 10
Total (goal: 350) 336

Final Package

Budget

Item Estimated Cost
Latex Weather Balloon (150g) $25 - Donated by Todd Brown
Helium or Hydrogen (80 cu ft cylinder) $66 - Donated by fox hunters
Additional 80 cu ft lifting gas tank $150 - Donated by Mike Hojnowski
Mini cameras & SD cards $60 - Donated by Mike Hojnowski
APRS Tracker $100 - Donated by Alan Adamson (W7QO)
Packaging, Parachute $10 - Donated by Mike Hojnowski
Total $411

Balloon Prediction Input

Predictor http://predict.habhub.org/
Payload Mass 150g
Balloon Mass 200g Kaymont
Total Mass 350g
Target Ascent Rate 5.0 m/s
Descent Rate 6.55 m/s
Gas Helium
Burst Diameter 2.4m
Start Location Southwest of Watkins Glen

Notes:

  1. The predictor does not have 150g balloons, so we used a 200, deducted 50g from the payload weight, and specified an explicit burst diameter based on manufacturer specs.
  2. Descent rate calculated using Model Rocket Descent Rate Calculator. Total weight 200g. 15” hexagonal parachute.

Balloon Prediction Output

Burst Altitude 14630 m
Ascent Rate 5.93 m/s
Neck Lift 784 g
Launch Volume 33.9 cu ft
Flight Range 48.7 km
Flight Time 66 min

*Note: The balloon manufacturer claims 15,000m burst altitude. The GPS on this tracker is rated to 18,000m.

Chase Cars

Launch and Recovery

Balloon fill

We wanted to get the neck lift as close as possible. It's difficult to measure while filling, so we decided to base it on the size of the balloon. These smallish balloons are nearly spherical when filled. So, we elected to calculate how full the balloon should be based on the volume of a sphere. We knew the volume of gas we needed, we just needed to measure the balloon. From the spherical volume formula, and given the volume of gas we had, we could calculate the circumference we needed.

We called it 12 1/2 feet in circumference. We measured out some para-cord and made a loop of that circumference. We filled the balloon, and slipped the cord around it. We stopped filling when the balloon was just touching the cord all the way around. We slipped off the paracord and gave the balloon one more little squirt of gas.

Launch

An infrequently used ball field outside Watkins Glen was selected as the launch site. It was abandoned, and sufficiently out of view that we weren't worried about anyone bothering us. We filled the balloon without incident, attached the payload, turned on the tracker and cameras, and let 'er go.

The Flight

Only one of the two video cameras had data onboard after launch. It's entirely possible that the other camera was improperly activated. It was very difficult to see the status LED on the camera at launch time due to the bright sun.

We captured about 3 minutes of “fussing” getting the payload ready, and about 17 minutes of flight.

The balloon was launched at 11:36 (the video camera showed 11:33). The video cuts out at 11:50 on the video (11:53 actual). At that time, the balloon was at 16,555 feet.

Here are a few photos of Charlie, swinging around under the balloon:

The balloon climbed steadily until something happened at 12:17. The GPS telemetry stopped updating, though the tracker kept beaconing. The tracker was at 39,961 feet at this time. According to Winds Aloft data, the temperatures at that altitude were below -57 degrees. We believe that the GPS module (which was mounted outside of the protective plastic bottle and bubble wrap) failed. It is rated to -40.

At 12:26, some 9 minutes later, the telemetry started updating again. The balloon was now descending, and was reporting 43,995 feet.

Extrapolating ascent rates from prior to the loss of telemetry and descent rates just after, we estimate that the balloon burst at approximately 14856m, quite close to the predicted altitude.

Actual track vs projected track

Projected
Actual
Actual
Predicted Actual
Burst Altitude 14630 m 14856 m
Ascent Rate 5.93 m/s 6.33 m/s
Descent Rate 6.55 m/s 5.5 m/s
Flight Range 48.7 km 48.10 km
Flight Time 66 min 64 min

The balloon followed the track very well. A later prediction was run the morning of the flight which more closely matched the final result. Unfortunately, the web page was inadvertently closed and the prediction was lost. Still, this prediction from the night before was quite accurate. The payload landed 3.1 miles from target.

The high descent rate may be attributable to the fact that a large portion of the balloon remaining on the tether. It probably interfered with the full deployment of the chute as it flopped around, as the balloon was attached to the center of the chute.

Payload Temperature

On our third balloon mission, we lost telemetry when (we presume) the tracker got too cold. This time, we wrapped the tracker in bubble wrap, and fit it snugly inside a sealed bottle. While the tracker definitely got cold, it never stopped transmitting. We added temperature data to the telemetry, so we were able to graph it post-flight.

On this flight, we lost telemetry for 10 minutes at the peak altitude from the GPS, but the tracker continued to function. The GPS module was mounted outside of the bottle. Winds Aloft data indicates that, at that altitude, air temperatures were below -40c, the rated temp limit of the GPS module. For the next mission, we'll put the GPS module inside the bottle and bubble wrap.

Recovery

Had we consulted Google Earth before going in for the recovery, we would have guessed the outcome.

Given that the tracker was in this “block” somewhere, we attacked it from two different directions. Hojo went due north and ran afoul of the big pond pictured, and had to circle around. Adam and Char went at it from the East, after getting permission from a landowner to traverse their property. They had a much easier go at the landing site.

After about 1/2 hour of walking around, we discovered the payload high in a tree. We were unable to retrieve it. However, Adam and Char had met Chris Preston, who was visiting his Mother's house nearby. He's an arborist, and offered to climb the tree the next day and retrieve our payload.

Chris climbing the tree:

Here he is descending after knocking the branch down. Tiffany, the camera operator, pans down so you can get an idea of how high up this thing was!

Tiffany triumphantly displays the fruits of their labors. Charlie Brown is back on the ground after spending a rainy night in the tree.

Lessons Learned

  1. The string/circumference method worked VERY well for measuring the balloon volume. We should do it again.
  2. Likewise, having a third person at launch was very handy for managing the balloon and helping with photography.
  3. We need to move the GPS chip inside the bubble wrap and test, to assure it can handle the cold temperatures.
  4. I would like to display battery voltage in the packets and telemetry data next time. I will see if we can retro in a voltage sensor.
  5. Alan Adamson (W7QO) found a handy way to tell APRS to convert the temperature telemetry (sent in Kelvin) to Celsius for display
    1. 12:00:00 EDT: W2CXM-11>APRS,TCPIP*,qAS,w7qo-6::W2CXM-11 :UNIT.C
    2. 12:00:01 EDT: W2CXM-11>APRS,TCPIP*,qAS,w7qo-6::W2CXM-11 :PARM.Temp,,,,,,,,,,,,
    3. 12:08:04 EDT: W2CXM-11>APRS,TCPIP*,qAS,w7qo-6::W2CXM-11 :EQNS.0,1,-273.2
    4. As we add/modify telemetry, we can send these command into the APRS stream to make sure the graphs display properly.
  6. We should take a moment to consult Google Earth before we begin bush-whacking for payloads. A few minutes double-checking the overhead view could save some time (and wading through thigh-high muddy water).
  7. If we use these little cameras again, we should find a way to insulate them and make it easy to activate/de-activate them.