SB-1 Payload Design
After a couple of years hiatus, we have a hankerin’ to send up a balloon again, so, of course, we need a new payload. First, some things from past flights that worked well:
The now-classic AF7EZ jack antenna. This started out back on mission LE-1 as a jack with just a single 2m dipole antenna for the APRS transmitter. It changed on LE-3 to use two axes for antennas. In these designs the payload box was fastened inside the jack frame on a non-antenna axis. For mission AZHAL-1, the jack antenna evolved to use all three axes for antennas, and was suspended a few feet below the payload module. The pic shows the jack antenna bouncing up into view at about 80,000 feet during AZHAL-1 descent. We have seen the jack design being used by other HAB groups, which is a nice compliment.
Energizer Ultimate Lithium primary (non-rechargeable) batteries (the Advanced batteries are likely just as good for this application). Excellent capacity, specified for cold operation down to -40C (best to derate the capacity a bit), and pretty lightweight. We will use packs of AA and AAA driving efficient buck regulators again.
APRS transmitters from Byonics (http://byonics.com). Not only do they make great gear, but Byon, Allen and Mike have really supported our last couple of balloon launches. This new mission will be SB-1 (surlee-byonics-1). We have a new 1000 mW primary APRS transmitter, which will replace the 400 mW unit we used in the past. We will also be flying the little 15 mW transmitters again, for both APRS and RDF beacon use.
Mobius video cameras. We only had the one camera on the last launch, but we got great video. We tried to switch it on and off at different altitudes to conserve battery life and SD card space, but after balloon-burst our algorithm must have gotten confused and we got no descent video except the first couple of minutes after burst. We will add bigger lipo batteries to just let the camera run the whole flight. Also, we want to put three cameras on the payload: one facing sideways, one facing straight down, and a third one facing up at the balloon (solely to capture burst). There is no need for a still camera, as great stills can be pulled off of the 1080p video.
Transmitting APRS on both the standard 144.390 MHz channel for internet tracking, and on a quiet 2m channel so we can see data in the chase cars. This is important for three reasons: on a quiet channel we will only be decoding our packets without dozens of other station packets interspersed, there will not be packet loss due to tx collisions as on the main freq, and when we are out of cell service in the boonies, we can still listen for gps updates and find our payload.
The geiger counter was pretty cool, so we may fly that again.
There are some things we want to do differently. External temperature during ascent was higher than expected, likely due to solar heating of the black plastic sensor case. We will fashion some sort of shield that blocks direct light, yet allows free airflow.
When calculating descent velocity, we neglected to account for a portion of the burst balloon still attached — this extra weight caused the payload fall faster than planned.
The particulate and ultaviolet experiments were inconclusive. Unsure if we will re-run those. The Canon still camera is getting the boot.
(c) 2016 SurlEE