High Altitude Balloon Carrying Amateur Radio - Burst!

I'm surprised nobody mentioned the lawn chair pilot tethered to a bunch of Helium Ballons with a BB gun for altitude control!

 

Lawn chair Larry!

Lawnchair Larry flight - Wikipediahttps://en.wikipedia.org/wiki/Lawnchair_Larry_flight

 

NOTAM not a flight plan. NOTAM is an acronym for Notice To Airmen. All pilots should read these before takeoff.

 

This is one of the things I ask every new group of high school students in the ham club where I mentor. I usually have to give them several hints before they figure it out.

The temperature drops and then begins to rise again with increasing altitude because we have oxygen in our atmosphere. Oxygen is opaque to very short wavelength ultraviolet (UVC) and ozone (which is formed from oxygen by UV) is opaque in both the short and medium UV wavelengths (UVC and UVB). When it absorbs solar UV, that energy doesn't just disappear -- it warms the air. That's why we have a stratosphere in the first place, which is characterized by temperatures that rise with altitude. The tropopause is the layer closest to earth where there's a normal lapse rate (decreasing temperatures with altitude). The boundary between the two, where temperatures reach their minimum, is the tropopause.

 

The typical ascent rate for a standard weather balloon with a well-matched payload and gas fill is about 5 meters/sec or 1,000 feet per minute. It remains remarkably constant with altitude as the balloon expands and the air thins. I've tried to work out the physics on this, and it's surprisingly complex.

We no longer use helium, as it has become very expensive and scarce. Hydrogen is much cheaper, and it's perfectly safe if you treat it with the appropriate respect. I think the cost is something like $35, but the tank rental accounts for much of the cost so it depends on how often you fly.

There is a small but noticeable sudden decrease in ascent rate maybe halfway up. At first I thought this was the tropopause, but we were already above that. Turns out the balloon's coefficient of drag abruptly increases as the "Reynolds number" (a measure of viscous vs inertial forces) increases. This is what I mean about the physics being surprisingly complex.

Descent with a typical parachute takes maybe 30 minutes. The rate decreases exponentially as it falls, because the density of the air itself increases exponentially with decreasing altitude.

I don't know anyone who uses fans. We usually stuff everything inside Styrofoam and hope for the best. I think there's a lot of room for improvement here. In many ways, the thermal design of a balloon payload is actually much more complex than an orbiting spacecraft.

I see many people flying GoPro cameras without any insulation at all. I think this is OK because they're pretty power hungry and keep themselves warm, at least until the batteries run out.

 

That's certainly an interesting idea, Bonnie. Note that you can already get high altitude wind data from the many balloons the weather service launches every day (a minimum of two per day, at 0000Z and 1200Z). The raw data is available on the web.

You can also look at wind vs altitude data maps here: www.windy.com. Invaluable for balloon flight planning.

 

Embry-Riddle Aeronautical University (their local campus here in Prescott , AZ), in conjunction with AZ Near Space Research - ANSR regularly conducts HAB experiments, which includes both FAA notification AND at least 1, sometimes 2 FAA transponders, so the RAPCON (radar approach controllers and local tower) can see them and vector any aircraft around them.
de W1DGL

 

If you're light enough, you don't even need to notify the FAA. But we do, as a matter of courtesy and to give the students practice in dealing with government bureaucracies...

 

A few additional thoughts on temperature. We've been seeing temperatures in the range of -60F to -70F on the last several flights of our balloons. There really isn't any type of economical electronic components that can withstand these low temperatures for any length of time. The GoPro cameras that we use are good to about -42C or so even though we have them in airtight enclosures. The batteries do produce some heat but it is not enough to keep the cameras going.

We used a combination of 1/4" insulation and hand warmers to better insulate our cameras on our last flight and these improvements allowed us to get through the -70F zone during our flight and keep the "looking up camera" on to see our balloon burst. We lost the "looking out" camera at about 48,000 ft due to the cold temperatures so we still have some more work to do to prevent low-temperature problems.

Our solutions to these problems are consistent with our lightweight and simple philosophy that we've been successful with to date.

 

Considering this has been going on for more than 25 years without incident there will always be those who are not impressed with themselves either.

 

Yeah, I know. But you also don't want components to overheat, either. That's possible when you have some small, high power stuff embedded in styrofoam, especially if you just stuff in a bunch of uncontrolled hand warmers.

I'd like to find some simple way to actively regulate everything. Because the air gets very thin at altitude, ideally you'd not depend on convection but fasten everything to some sort of conductive "cold plate" and then regulate the temperature of that plate. On short flights you can use a thermostatically controlled electrical heater if the heat requirements aren't too great, but getting rid of too much heat can be a problem. I'd like to find some sort of "thermal switch" that would connect the cold plate to an external radiator (e.g., a thin sheet of aluminum covered with thin Kapton tape to increase the emissivity, i.e., make it look black in the far IR). Thermal switches do exist for spacecraft but they're rather new and, like everything else for space, very expensive. I wonder if there's some cheap and innovative way to accomplish the same thing.

 

We have not had any problems using hand warmers. We put them on the cameras just before launch and they take some time to build heat. By the time they are warm, the balloon is up several thousand feet and its cold. The approach works well and is very lightweight.

 

Aww

 

And I thought the earth was flat. Damn

 

You hit the dome. Nothing can go past the dome.........Yes I'm just kidding before someone tries to give me a lecture...