Balloon, Mark 5 - "Operation Lil' Bub"

This balloon will use our new and improved “Peach1” tracker board and a small USB Key Fob camera.

• August 2, 2014. 10:30am EST: - Launch

Success!

The balloon was launched on schedule with the tracker and camera operating. Though the tracker experienced a few reboots during flight, we were able to track the payload to the landing spot and retrieve it.

1. Use our new Peach1 tracker board.
2. Move the USB Key fob camera inside the pay load container to avoid thermal concerns.

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. 12” hexagonal parachute. Note, the calculator estimated just under 6 m/s. However, experience shows that the balloon remnants often come down with the payload, speeding the descent. Rounded up to 8 m/s based on previous launch experience.

*Note: The balloon manufacturer claims 15,000m burst altitude. We are filling this balloon a LOT.

1. Launch: Hojo/KD2EAT and Dave/KD2GBX
2. Chase1: Kevin/WB2EMS
3. Chase2: Jon/KC2WAC

Using volume of a sphere for 60.2 cu ft

• Volume of a sphere
  • v = 60.2 (per predictor)
  • v = 4/3 pi r**3
• Solving for r, the radius:
  • r = cube root(3v /4pi)
  • r = 2.43 feet
• The circumference of the sphere is pi*d
  • c = pi * 2 * r
  • c = 15.27

We called it 15' 3“ circumference.

Expected pounds of gas to use:

PSI = volume / .0265 PSI = 60.2 / .0265 PSI = 2272 PSI drop in tank.

At the time of the fill, we put in more gas. The tanks were nearly empty, and we wanted a short flight, so we put in a fair bit more gas. The balloon diameter should have been about 4'8”. I'm 5'11“ and the balloon looked about as tall as me in this shot. Assuming a 6' diameter, we filled the balloon with about 113 cu ft of helium. It didn't seem to make the flight shorter, however. The balloon burst much higher than predicted.

Watch it here:

Note, given that the balloon was overfilled at launch to nearly 6' in diameter (113 cu ft), the predictor indicates that the ascent rate should have been about 8.66m/s. This very closely matches our observed ascent rate of 8.57m/s. Let's hear it for science!

The payload temperature dropped to about -4c during the peak of the flight. This did not interfere with the tracker, though the battery voltage did drop considerably due to the temperature (from 1.64v to 1.38v). It rebounded as the temps came back up.

The 808 camera performed very well. Prior to flight, it was measured at using about 110ma while recording. We used a 300mah LiPo battery for the flight, and we had over 2 hours of video on the camera when retrieved. Each 10 minute block of video used approximately a gigabyte of space. The 16G SD card had just over 12G of footage on it.

The balloon landed on the roof of a duplex. We fished it off with a few antenna whips duct taped onto an extensible pole saw.

1. The tracker had some issues with reboots. They need to be resolved prior to the next flight.
2. The 150g balloons apparently have quite a bit of variability in burst altitude! That was a surprise.
3. Although the parachute predictor estimated a descent rate of about 6 m/s, we rounded up to 8 based on previous experience with the balloon remains interfering with the parachute function. The observed descent rate was 8.9 m/s. We could have rounded even higher.
   1. In future, we might want to use a larger chute than recommended to temper the descent rate, or find a means to jettison the balloon remains after burst.