On Feb 19, 2017 we flew an early morning mission to answer some questions and try out some tech. Namely:
A sunrise flight has a few complications. Without solar heating, the payload must be built to handle the cold right from the start. Video/images require a steadier mount as the low-light exposure times are longer. And the biggest complication is that you must wake up early to prep and launch.
A summer sunrise launch would require the team to be up at 2am. Ummm... no. Winter has a more reasonable sunrise time, but flying in the winter requires the jet stream to be just right. The forecast for this day showed a small "hole" in the jet stream around 300mb that fit the bill.
The payload for this flight was simply an AP510 tracker and a Mobius camera. Both were mounted in a clam shell of black foam and then secured with day-glow duct tape. It took about an hour for Paul L. to put it together [and he admits it looks like it]. The Mobius would provide reasonably nice images and allows for some tweaking of its sensor/algorithm to get the most out of it. The AP510 would be the APRS tracker and also monitor the battery and internal temperature. An under-hung parachute (see NSL-33) was added.
The new tech on this flight was the addition of a bit of Poly Vinyl Alcohol water-soluble synthetic polymer. In this application, we used PVA string that looks/feels like your typical 40-weight sewing thread. It was used to secure the balloon/parachute bridle to the payload. The idea being, if the payload ended up stuck high in a tree, then a drop of dew or rain would cause the thread to dissolve. This would then release the larger bridle line and the payload would fall. The bridle line was looped in a way to keep some of the tension off of the PVA. Like previous 'descender' tests, a 20m spool of strong waxed string [cheap dental floss] was added to help the payload lower from the tree gracefully. It would also act as a backup in the event that the PVA dissolved at altitude.
All together the entire payload came to 200g. We had a 350g cell that was gifted to us from the NSL-37/38 team, so we used that with hydrogen. The expected altitude was ~26km. That would allow for quick 2.5 hour flight from Raleigh, down I-40, with plenty of room to spare before reaching the ocean.
Payload activation began at 0515EST with launch at 0545. The plan was to be have the flight film the first 20 minutes of sunrise before burst. Keeping in mind, that the sun rises earlier the higher you go.
Due to the long exposure times at dawn, it was expected that the images of Raleigh would be blurred. The winds turned out to be VERY turbulent below 9km. The small payload was tossed about a great deal, so very little of the dark video was usable. Sadly, the battery ran low, and at 15km the camera shutdown. The system had run for over four hours in a test earlier in the week, but on the flight it lasted only 1.5 hours. A third of that time was spent in launch prep. [In the future we could keep this type of payload on 'shore power' until right before launch.]
The small 350g balloon was predicted to burst before 27km, but for some strange reason it held out all the way to 34.1407km (112010 feet) !!
During ascent, the chase team would periodically stop along the roadside and watch for the balloon. It was easy to pick out with binoculars as it was fully lit by the sun long before anything else was. The chase crew had sight of it above 28km, but was driving between highway exits when it burst.
No need to try out the PVA recovery system. A 3.75 hour flight ! An amazing flight for a 350g cell.
The parachute was over-sized for the payload, so a hole was cut in it. The hole could have been even bigger as the descent rate fell to 2m/s at times.
The dramatic load on the battery needs to be researched. It doesn't fit past dry-ice cold tests. Does the Mobius use more current when it is in a dark quickly-moving environment?
We will have to try another flight to get a high altitude sunrise shot. The light level is so low right at dawn, that it is difficult to get really nice looking images with our current cameras. Low sun angle shots (hour or two after sunrise) would be cool though.
This will take some digging to figure this out. What was up with the battery? ...with the great performance of the balloon?
That was pretty cool. The balloon was much brighter than expected in binoculars. About -1 magnitude. Paul L. was able to follow it as it drifted back and forth. As he was standing, and directly under it, he got a crick in his neck pretty quickly. It would be nice to lay back and watch it burst. Could we set up a webcam on some optics and record burst from the ground?
It held up just fine. No signs of issues during the flight. Afterwards Paul L. hauled the payload into a restaurant and dribbled a little bit of water on it from his drinking straw. In less than five minutes it failed and the dental floss spool played out perfectly. This could be a very inexpensive and simple alternative to hiring a tree climber.
On some active chases we've needed two folks running the myriad of toys; to pull in telemetry, crunch numbers, send out chase car positions, and handle social media. We have noted that separating chase "Navigator" from the social media "Public Affairs Officer" can really help get updates out quicker. Another desire is to cut down on the toys, or at least the cable mess, so that possibly a single navigator can run things. One of the items tested on this flight was another attempt to create this consolidated/centralized telemetry console. It consisted of an Android tablet and a "dash gateway". The dash gateway was just a piece of foam that held a MiFi cellular hotspot and another AP510 APRS transceiver. They both need to be in a car window (or outside) to work well. The foam kept all of the parts together and prevented it from sliding around in the back window of the chase car. The Android tablet had a handful of tools available:
Paul L. was solo on this recovery (couldn't wake any kids up), so having just a single device in the car helped. Using it though required him to pull over a lot. But that also gave opportunities to spot the balloon with the binoculars. Each application worked to some degree. Although switching between the apps was cumbersome. Often the Tracker.Habhub map would reset itself back to the default screen when it was brought forward. He also found LTE/3G coverage holes in eastern NC that caused the IP based apps to hiccup. Each device had sufficient battery for the long chase. This might be a good solution to hand students that are going out on a chase. APRSdroid can be set to receive only, and that would allow the students to hunt the payload without having a licensed HAM operator.