The parachute is finished, the payload layout finalized & balanced, and I am now waiting on one thing: the jet stream. The jet stream, as most of you probably already know, is a relatively high-speed wind that can easily be over 100 miles-per-hour. While we could potentially launch into the jet stream, I want to maximize the chance that our humble near-space nanosatellite will land as close as possible to our launch site. I love a good road trip, but I'd rather not drive a hundred miles or more to pick up our payload. The balloon we're using has a normal inflation rate diameter of 10 feet, and the volume of a sphere (4/3 X pie X r^3; so, I computed 4/3 X 3.1416 X 5^3 which equals 522 cubic feet of helium at "normal" inflation). I weighed the payload at 1.8 pounds, and I read from the students at MIT that they calculated a "free-lift" ascent rate of 300 feet per minute for each 1 pound of free lift (free lift is the force of lift the balloon will have in addition to the payload; more free lift means a faster ascent rate, which is good so long as the balloon is not filled up to the point where it will burst before reaching 100K feet). If we want our balloon to reach 90-120K feet in about 30-45 minutes, it will need 10 pounds of free lift, or about 12 pounds of lift entirely. 15 cubic feet of helium lifts one pound, so we are looking at 12X15 = 180 cubic feet of helium. At 10 pounds of free lift, the balloon should rise at 3,000 feet per minute and reach 120K feet in 40 minutes. Additionally, we will be filling the balloon about 1/3 of it's "normal" inflation size, so there should be enough room for expansion.
Well, that about does it. If anyone has anything to add or something I might have missed or miscalculated, please don't hesitate to let me know. This is a first-time launch by someone without an engineering or physics background/training. I will be checking the weather reports, and plan the launch for the early hours so we can get our sunrise photo. With an estimated 30-40 minute ascent to a decent view of our planet, and the fact that at 100K feet the sun rises as if you are 6-degrees further towards the direction the sun rises (about 20 minutes earlier), I'm taking a stab at launching about an hour before sunrise. That gives us time to obtain a great photo, and I'm not having to launch too early in the morning! It is spring break, and sleeping in is almost a tradition for those of us in higher education! I'll post the evening before launch. Wish me luck, comrades!