Long Duration Balloon Project Known Constraints
These are major factors which must be considered when designing/selecting the mission hardware/software or making logistical choices.
This is the ultimate constraint. Weight must be considered in every decision when designing/constructing a payload and balloon. Everything on the balloon and payload should weigh as little a possible, with the exception of ballast. Weight must be removed from the payload as lift force decreases, to maintain altitude. When lift = weight the balloon will float without climbing or descending. As lift decreases through the mission, the balloon will remain in the air only as long as it can shed weight to maintain the lift = weight ratio equilibrium. Once lift is less than weight, the balloon sinks, until reaching a new equilibrium in lower, denser air, or impacts the ground.
There are 12lbs available for payload (see law section), which must be split into two separate containers. The goal is to have as much of the total weight be removable, to be dropped as ballast when lift is lost. This can include designated ballast material, as well as unneeded equipment, insulation, batteries, and structure if possible.
- lift gas will permeate through plastic/latex membranes over 72 hours enough to lose significant lift
- Permeation rate is not currently known
- ZP balloons have to have a vent at the bottom to prevent overpressurization. This can also cause slow mixing of outside air with the helium if traditional floppy hose designs are used.
- lift gas in a balloon does not separate from air like oil and water, it will become a relatively homogenous mixture in balloons this size due to turbulence.
- ZP Balloons must be designed custom to the float altitude, lift gas volume, and weight desired.
- Balloon design knowledge is very hard to come by, almost entirely protected by private companies.
- balloon and lift gas form a greenhouse in the sunlight, increasing the gas temperature by as much as 200F above ambient air, depending on balloon color
- it is very hard to measure how much helium that gets put into a balloon by other than net lift force produced.
- in anything other than complete calm wind will severely degrade the accuracy of vertical lift force measurement
GPS model selected (not the actual unit) must be previously flight proven - some GPS models stop functioning at high altitudes to prevent use as missile guidance.
- Night time ambient air temperatures will usually be around -50C
- Good lightweight insulation is required for the batteries to maintain voltage output
- All electronics should be tested to -60C to avoid having to insulate them (that's more weight)
- May want to create crystal ovens for oscillators
- Wire heaters (a few high watt resistors) into battery packs, determine temperature threshold by cryotesting batteries
- Temperature sensors are recommended for outside air, electronics, and battery pack.
- Flightpath will likely end more than 4000 miles from launch site
- Flightpath will get up to 1500 miles out to sea from major landmasses
- UHF/VHF line-of-sight radio horizon at 35,000ft is 265 miles.
- Satellite coverage of GlobalStar SPOT tracker is not worldwide, but DOES cover the northern Atlantic Ocean, from about the equator up to Iceland.
- HF telemetry is long range (worldwide from balloon), but unpredictable in distance and direction.
- HF telemetry is low bandwidth, low data rates (45 baud to 1200 baud), and longer transmit times than VHF/UHF or Satellite.
- HF transmitters are extremely cheap <$25
- HF digital telemetry may not be able to be used over the USA by law, necessitating an alternate transmitter.
- Telemetry content transmitted is usually: Latitude, Longitude, Altitude, GPS signal quality, multiple temperature values, climb rates, ballast information, and other debugging or health information.
- HF Telemetry reception requires a widely distributed array of listeners to get sufficient data back from the flight. SNOX used 250 listeners all through the continents bordering the Atlantic Ocean, and still had multi-hour signal loss periods.
- UKHAS distributed telemetry network protocol is extensible, and has an open source client dl-fldigi that will auto-decode it using any platform computer sound input.
Available power is constrained by weight. The power should be budgeted, and frequently negotiated as electronic components are reviewed. Power system other than optimal batteries must outperform the equivalent weight of optimal batteries over 72 hours of predicted actual flight conditions.
- Battery choice should be made based on three factors, high capacity, low weight, and low temperature operation. This pretty much leaves Energizer e2 lithium batteries.
|size||weight in gram||capacity mAh||mAh per gram||volt||max current||temp range||price each USD||name|
|AA||14.5||3000||206.8965517||1.5||2A||"-40C/+60C"||1.5||Energizer Ultimate L91BP-4|
- Likely about 2-3lbs of the electronics box will be available for battery weight. Minimizing the weight of the insulated payload container will increase this.
- Some battery power MUST be reserved for emergency heating of the battery stack.
Northern hemisphere winter will be the flight conditions
- low sun angle in winter
- flight to high latitudes up to 60 degrees is possible
- good for longer flights
- Jet stream must be targeted, float between roughly 30,000 ft and 40,000 ft
- Ballast should be dropped to maintain altitude within the jet stream
- Plan consumables for for 72 hour flight
- File NOTAMs 24 hours in advance with 1-800-WXBRIEF
- Notify local ATC (SDF and Indianapolis Center) 1 week in advance, several hours in advance, and at moment of launch
- Do not transport helium tanks in passenger vehicle compartments. If it must occur, open all windows.
- Ensure all flights have high descent drag to slow impact speed (parachute or large plastic balloon envelope)
Detailed rules explained at Edge of Space Society Important constraints:
- 12lbs total maximum weight
- No individual payload container may weigh more than 6lbs
- No Ham shortwave HF telemetry over USA (FCC regulation, not FAA)
- Optimal launch time: Just after sunset. This optimizes for maximum flight time. The idea is to launch as far before sunrise as possible. Reaching float altitude in the dark allows the helium to be densest when it overflows out the vent. Then at dawn, the sun heats the helium and it expands, with some flowing out of the vent, maintaining altitude.
- Try to select a launch time that that does not let the flight path cross major metropolitan cities, such as Washington, D.C. or New York City.
- Clear of obstructions taller than 50 feet and powerlines for at least 100 yards downwind
- Clear of obstructions taller than 10 feet at least 50 yards downwind
- Some paved surface is recommended for ease of setting out tarps and tools and rolling heavy tanks around.
- absolutely no sharp objects or corners in/on the ground for 100 feet from anywhere the balloon will be while laying on the ground, or while tethered to a ground handler.
- Site should be available for 3 hours before and 3 hours after planned launch time. (most launches do not happen on time, and involve a bit of DIY fixing that delays things)
- Accessible closely by pickup truck - helium T cylinders are over 100lbs
- Recommend that site should not be within controlled airspace classes B, C or D.
- Recommend that site should not allow common flight paths to pass into controlled airspace classes B, C or D. These airspaces extend up to 10,000ft MSL.
- Recommend to inquire with local ATC for where approach/departure paths for high traffic runways are, and avoid flight through these corridors as well.
- Low wind required at time of launch - safe maximum 5MPH, technical maximum 10MPH. Higher than this are likely to damage balloon or injure people holding balloon.
- Clear sky - for airplane safety, balloon should not enter clouds
- Temperature - Any is acceptable, however ensure that the balloon envelope is inflated and remains at outside air temperature if any lift force measurement is to be performed. (do not inflate in a heated hangar, and check lift force in there) When the Jet Stream is ready for balloon insertion, it will be one of the coldest nights of the year.
- Barometric pressure - Any.