Balloon, Mark 3. "APRS Only Beacon"

Overview

After the failures of balloons 1 and 2, this launch was intended to be much simpler. We chose to launch a latex balloon so that we could depend on burst for cutdown, and use a light payload - just an APRS beacon, to minimize complications with the payload. We used streamers for the descent since the payload was so small.

Timeline

  • 05/04/14 - Launch

Executive Summary

Success!!!

Mission Objectives

  1. Lower cost payload, involving less risk.
  2. Gain experience with prediction software and confirm its accuracy.
  3. Learn to use hydrogen as a lifting gas for cost savings and eco-friendliness.
  4. Learn the range of the APRS tracker.
  5. Enhance the ham club's experience and preparedness for APRS tracking.
  6. Attempt NVIS communications over 40m HF during launch.
  7. Attempt mobile cross-band repeater operations during launch.

Mission Parameters

Balloon Latex 150g
Lifting Gas Helium
Payload Tracker Only
Payload container Styrofoam
Max Payoad Weight 100g
Flight Time 45-90 min
Cutdown Balloon Burst
Recovery Streamer
Tracking 300mw APRS tracker loaned to us by Alan Adamson (W7QO)
Telemetry GPS data only

* Note: Hydrogen was planned, but we discovered at the last minute that we needed a regulator that would not be available in time. We fell back to helium.

Balloon and payload Weight Budget

Item Weight (grams)
Batteries - (2) 600ma LiPo 32
Payload container 20
Tracker + Counterpoise 23
Rubber Duck Antenna 25
Streamers 13
Balloon 150
Balloon attachment (string, tape) 18
Total (goal: 250) 281

Final Package

Budget

Item Estimated Cost
Latex Weather Balloon (150g) $25
Helium (80 cu ft cylinder) $66
APRS Tracker Donated
Packaging, Streamers Donated
Total $91

Balloon Prediction Input

Predictor http://predict.habhub.org/
Payload Mass 50g
Balloon Mass 200g Kaymont
Total Mass 250g (underestimated for prediction - actual was 281)
Target Ascent Rate 5.75 m/s
Descent Rate 8 m/s
Gas Helium
Burst Diameter 2.4m
Start Location Trial and error, aiming for southeast of Ithaca

*Note: 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.

Balloon Prediction Output

Burst Altitude 13,220 m
Ascent Rate 6.78 m/s
Neck Lift 996g
Launch Volume 41.1 cu ft
Flight Range 105 km
Flight Time 0:52

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

Chase Teams:

We deployed chase teams under the projected path of the balloon for two reasons. First, we wanted to make sure we were getting telemetry, in case the transmitter was weak. We don't yet have a lot of experience with the transmitter at altitude. Second, on the chance that something unexpected happened after launch. we wanted to be able to react at any point beneath the expected flight path.

  • Launch: Hojo/KD2EAT, Dave/KD2GBX
  • Chase1: Adam/KC2ANT, Char/KC2ULK
  • Chase2: Jon/KC2WAC, Jules/KD2FOU
  • Chase3: Kevin/WB2EMS
  • Chase4: Todd/AB2MS

Launch and Recovery

Dave preparing to release the balloon

Balloon immediately after release

Actual track vs the projected track and recovery

We launched approximately 2.65 miles Northeast of the originally planned location. It turns out that Springwater, NY is in a valley. We were concerned about clearing the ridgeline to the east. and also just finding an open space to work in without disruption from the local townsfolk. We eventually found a field on a remote ridge line that served us well.

We launched at approximately 11:02am. As the balloon progressed eastward, we noticed that it was climbing slower than the forecast. We apparently had not inflated the balloon enough. It was forecast to burst over Watkins Glen. As it approached, we realized it would burst later, probably over the Ithaca area. We let the chase teams know that they should start heading east of the originally projected landing spot.

Between Watkins Glen and Ithaca, at 33 minutes after launch, the tracker stopped sending telemetry. The last report was at 37,829 feet. We suspect (in retrospect) that the tracker got cold enough that it drifted off frequency and wasn't being picked up by any of our radios. We received no telemetry for 23 minutes as it traveled eastward.

Just as we were about to give up hope, we got one last packet from 3,937 feet. The tracker was nearly to the ground, but had not gone as far east as anticipated. We then lost reception.

Chase teams fanned out around the expected landing zone. Approximately one hour later, at 1:10pm, a chase team picked up the signal of the tracker, and iGated the packet. The tracker was traced to a field approximately 400 meters east of the last received signal while it was in the air (much closer than we had expected). Thankfully, the field was plowed but nothing had grown in yet. As the search teams walked across the field, Kevin/WB2EMS found the payload laying on the ground.

The payload landed 9.45 miles from the originally projected location.

The payload on the ground

Note that it landed with no sign of the balloon or streamers. They tore off completely. The payload free fell.

The orange you see in this picture is duct tape. Adam/KC2ANT peeled it back to “cut the red wire” and unplug the tracker from the battery. The yellow streamers tore off at their attachment points on the payload and were nowhere to be seen. The bit sticking out from between his fingers is all that remained of the balloon.

Clues from the telemetry

Descent Velocity

The last aerial data point, and the landing zone data looked like this:

The distance between the last two points was 1,728 feet (.33 miles). The last telemetry indicated that the payload was moving at 27mph at a bearing of 107 degrees. 27mph = 39.6 feet/sec. It would take 43.6 seconds to cover 1,728 feet at that velocity. So, we can assume the package fell to the earth in that amount of time.

The last altitude in the air was 3937 feet, and the final resting elevation was 1361 feet. We fell 2576 feet in 43.6 seconds - 59 feet/sec (17.98m/sec). The “planned” descent velocity was 8m/sec. Without streamers, or the remains of the balloon, the payload fell at just over double the planned speed. Fortunately, the package survived impact and continued tracking!

Burst Location and altitude

More math required here. However, empirically, it appears that we burst very close to Ithaca. Looking at the altitude data and rate of climb in APRS, it appears that we were climbing about 1,000ft/minute (5.0m/sec). We had targeted 5.75m/sec. The last data point before we lost the tracker was at 37.829 feet. Projected burst was at 43,372 feet. It would have taken about 6 more minutes to reach burst altitude. The balloon traveled half way to Ithaca from Watkins Glen in 6 minutes. Just looking at the progression of dots, it seems the burst would have been just west of Ithaca.

We know we were falling at about double the projected descent rate. Looking at the curve, the final resting location seems very consistent with a descent from just west of Ithaca to the landing zone in about 1/2 of the projected distance.

Some more mathematical calculations on the GPS distances can help validate this, but it appears that the balloon burst at approximately the expected height.

Tracker Performance

The tracker was heard by a number of distant stations. It was picked up in Ithaca within three minutes of launch. Three stations that logged on aprs.fi were over 100 miles away.

WB2ZII-15 Yorktown Heights, NY 179 Miles
VA3BAL-4 Newmarket, Ontario, CA 135 Miles
K2JJI-10 Johnstown, NY 135 Miles

It would appear the 300mw tracker with a 20“ counterpoise on the rubber duck antenna is more than sufficient for our needs. We shouldn't need to worry about fanning out iGates below the flight path with this tracker.

Lessons Learned

  • The tracker stopped transmitting, or went off frequency at 37k feet.
    • We presume this is temperature related.
    • There is a suggestion to try packaging the tracker in a plastic bottle for greenhouse effect and insulation value.
    • Hand warmers have also been suggested, but the experienced people on the balloon e-lists discourage them.
    • An SDR might be be handy to have along to check for frequency drift if we lose a tracker in the air again.
  • Finding the tracker would have been easier with a buzzer on it.
    • Add a buzzer to the package on the next mission.
  • Hydrogen will take more planning and effort
    • We will need a special regulator we don't have, a carrier outside of the vehicle, and grounding equipment before we can safely use hydrogen as a lifting gas.
  • NVIS testing still needed.
    • We did not get a chance to test DF on this mission.
  • We under-inflated the balloon.
    • It was difficult to tell when it was full “enough”. It was too windy to measure the neck lift.
    • These balloons are small enough that we could probably consider them a sphere and measure the circumference to estimate volume of gas used. We'll try that next time.
Last modified:: 2014/05/07 14:32