Another exciting-for-the-wrong-reasons flight.........
Saturday the 26th dawned clear and calm. Most of us got to the launch site about 7am and we started right in with unloading the equipment and filling the balloon. There was for all practical purposes zero wind, a tremendous improvement from last time.
With a 11 to 12-lb payload, it normally takes a full T-tank of helium (290 cu ft) to get about 1000 ft/min, almost regardless of balloon size (a smaller balloon like a 350g or 600g goes about 1100-1200 ft/min, a larger one like a 1200g maybe about 900). Because our track was towards Creston IA, I wanted to avoid the larger lakes just north of there. Setting a ascent rate goal of 800 ft/min for our Kaymont 600g balloon seemed the best way to get away from them, by going a little longer. By my calculations, we would need 80% of a T-tank, or about 2000 psi (a full tank is about 2600, ours had 2500).
We fill the balloon, draining the tank from 2500 psi to 500 psi and hopefully yielding the # of cubic feet required to get our 800 ft/min. Everything is hooked up to the load line and all the payloads were switched on and transmitting, so we winch the balloon out to take up the payload weight. We notice there is very little free lift with the payloads suspended, so I decide to a weight and lift check prior to release.
The free lift is about 12lb 9oz - the scale is bouncing by +/- 2oz of that figure. I hang the payloads by the spreader ring - 11 lb 10 oz. OK, about a pound of free lift. I realize later I had not fully accounted for the weight of the parachute, but figured it was at least partially offset by the weight of the lanyard strings hanging from the balloon when the free lift was measured (the lanyards are pulled free and do not fly). Anyway, I figure I'm just under a pound of free lift.
If I had much of a choice, I'd have put more helium in the balloon. But, that's difficult or impossible once everything is tied and taped. I figure we have enough, let's go with it.
We winch the balloon out again. The last item before release is to switch on the camcorder, maximizing tape and battery life. I call the countdown and Mike lets the lanyards go.
The balloon rises at a "gentle" ascent rate. It seems slow, especially compared to our usual rocket-like launches. The sun glints off the still camera's face and I curse, realizing I failed to turn it on.
After a minute, the balloon looks like it's nearly stationary, both in the horizontal and in the vertical. Oh, ****. I go over to the car and look at the data. 120 ft/min. ****. 70 ft/min. Double ****. My mind starts racing - at 100 ft/min and 70,000 ft to burst, that's what, 700 minutes isn't it. 700 minutes is, holy crap, nearly 12 hours. My primary beacon is only good for about 8. The backup is normally good for about 16, but we haven't had a good flight from that in a while. The SSTV is maybe good for 5 hours of DFing. My heart sinks. We've never flown a cutdown - haven't seen the need until now. Boy, there's just not much to be done at this point. Kind of like stepping out of an airplane and realizing you don't have your parachute on. I really start kicking myself mentally as I remember we were sub-1lb on free lift. That was stupid, letting a balloon go with so little lift.
The best thing now is to see if we can possibly get people downrange to listen. The max winds aloft were 50 knots so we should be able to stay with it for the most part, but it would be better to have more ears. We get hooked up to the internet and I send an e-mail to the KNSP and APRSSIG lists hoping to get some assistance.
Just after I get the e-mail sent, things begin to brighten a little. The ascent rate is now about 200 ft/min and seems to be increasing. Now we're to about 350 minutes mission duration, or not quite 6 hours. That's within the primary beacon's battery life, but that life is at room temperature. The payload will be spending a lot more time in -50C or colder conditions. While I was sending an e-mail, I downloaded the latest wind forecasts and start running predictions. At 200 ft/min, the predicted landing shows something 30-40 miles east of I-35 and not far south of the Missouri border. Ok, this might be a recoverable error after all.
We start the chase south and east. No more reports from the backup beacon - must be the antenna after all as everything else has been changed. Primary and SSTV are going with no problem. The internal temperatures are steady or slightly rising - the sun on them must be offsetting the cold air. Even our ascent rate is slowly increasing. We're now going from "slow-motion" disaster to a long but reasonable flight.
After two hours, I expected the tape to run out in the camcorder and power down, leaving the SSTV with no video source. Another pleasant surprise - when the tape runs out in this model, it apparenlty doesn't turn off as I'm still getting pictures.
Burst happens at 70,075 ft. At least we didn't go neutrally buoyant, too. We look to be just a little too far away to get in position to see it come down - had we left the launch site even 10 minutes sooner, we might have. Oh, well, I just want the thing back even if I have to cut a tree to get it. We're about six miles away when the payload lands.
Compared to the launch, the landing was perfect. Once again, in an open field and not too far from the road, about a mile and a half from the town of Grand River, IA. There aren't any houses in sight for over a mile, so we figure we're OK to get in, recover, and leave. The payloads are intact, and we load up for the long trip home.
Some lessons relearned:
- Checklists are good. I need to write one. I'll have someone else read off the before-departure checklist to make sure I actually follow it.
- The helium left in the tank on the ground is as useless as the runway behind a departing aircraft. Using less than normal amounts of helium is fraught with uncertainty of the mission-loss kind.