November flight failure
Sometimes once you get a big ship moving it’s hard to turn it around. Thus was the lesson of our November 9th launch attempt. We had a total of 33 attendees lined up for the flight including students from University of Chicago’s Collegiate Scholars Program (CSP), members of Northwestern’s NUSTAR group, visitors from the Lake County Astronomical Society (LCAS) in addition to volunteers and staff. Conditions were not looking ideal. The temperatures were yet to dip to bone-chilling levels for the season but the winds were way in excess of our usual confident launch range. At the time of launch, we were experiencing sustained gusts of about 30mph. Not to be deterred we attempted to get the payloads off the ground.
We implemented as many preventative procedures as possible to get a successful launch. We prepositioned the payload chain so they would clear any hazards at launch. We did this by calculating the angle of ascent. Assuming an ascent velocity near 1200 feet per minute (or ~13.5mph) and 30mph winds we could use a little trig to determine the ascent angle would only be about 25 degrees. Needing the last payload element to clear the highest hazard (in this case a tree about 40 foot high), we laid the payload chain in a line upwind so the last element was approximately 90 feet from the tree.
Laying the payload chain with the top element (the parachute) upwind and the rest of the payload pointing downwind would allow the lifting balloon to “peel” the payload chain off the ground as opposed to dragging them. In theory.
We also used a 50ft tether between the parachute and the balloon. This allowed us to leave the payloads out in the field and clear the launch zone of people. Also it theoretically meant we did not have to walk the balloon out as far from the windbreak of the hanger before attaching it to the tether and releasing the balloon. The tether also allows a certain level of strain relief as the jerk from the ascent hits each payload element.
Needless to say, the launch did not work. And here’s what we learned:
- The force of the wind became too strong for me to keep my footing. By the time I released the balloon it was parallel to the payload chain instead of upwind from it. This dragged the payloads to some degree – increasing the pull on the connection points.
- The thin tether became a hazard – being in the way of my feet. It would have been advisable to have a method of keeping it away from the person handling the balloon.
- Our total mass was right at the regulated 12lb limit. Lifting this much mass while the balloon was accelerating at about 30mph tested the strength of the connections beyond their breaking point.
- Finally, the tether we used for this flight was a nylon kite string. It ended up fraying and breaking at the knot point above the parachute. In the future, we advise using Dacron string. We’ve used 100lb test Dacron on previous launches with success.
December flight success
On the brighter side, our December 11th flight went off virtually hitch-less! Though the conditions were quite cold, the threats of snow storms subsided by morning and skies and winds were clear for launch. The long awaited test of the wireless cutdown system developed by our IMSA interns Brendan and Milan lifted off just after noon local time. Like most winter flights, we do not get the benefit of reversed winds in the jet stream and stratosphere. This means we planned for separate launch and retrieval two crews. Mark, Lou, Brendan and Milan were joined by Darryl Hedges of the LCAS down in Kankakee for the launch. Cynthia and I headed out to Bryan, Ohio to await the landing.
According to the launch crew, everything went pretty smoothly except the trackers. We’ve been having a persistent problem with our Big Red Bee GPS transmitters for about a year and a half now. For some reason we’ll have no problem on the ground receiving signals from one transmitter but when the second tracker is on we’ll lose one of them. This has been a frustrating problem for some time. With the help of our HS Summer Interns, Quinn and Jocelyn, we ran all the trackers through a battery of test this summer but were unable to reproduce the problem. There’s nothing more frustrating than having a problem you can’t reproduce. It makes it very hard to diagnose. If anyone has experience with GPS, transmitters, etc or any ideas, please send them along. We are ordering and will be trying another brand of transmitter soon.
It was good we were already near Ohio when the team launched. For portions of the flight our payload was logging velocities in excess of 150mph. Here’s a screenshot Jeff pulled as he was following the flight on aprs.fi.
After a little improvisational scrambling on Buckeye backroads, we ended up being within 1km of the payload by the time it hit terra firma. That’s not bad over a 250km flight. This is now our longest flight in Far Horizons history. Interestingly, this flight beat out our previous longest flyer by only a few kilometers landing only a few kilometers east of that flight.
The good news is that the cutdown system worked according to plan. For this run, it was being triggered by a simple countdown timer. There were some anxious moments. With the winds that high if the cutdown failed to work as planned we may have been heading closer to Toledo for the retrieval. Next up for the system will be to integrate some intelligent controls such as a pressure sensing trigger for altitude-based flight termination or other sensors used to trigger the cut down.