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Launch Planning

Page history last edited by PBworks 17 years, 1 month ago

Launch Planning



Lift Planning


The weight budget is here.  Current estimate:  6.4 lbm (2.9 kg)


    Some useful data:


Helium buoyancy as a function of altitude
Altitude (m) Altitude (ft) Buoyancy (kg/m^3)
0 0 ~1
10,000 32,000 0.356055
20,000 66,000 0.076556
30,000 98,000 0.015852
35,000 115,000 0.00728742


    Our balloon, optimally filled, will hold 2.99 m^3 at sea level, and so it will be neutrally buoyant with about 6.4 lbm load.  In order to have adequate lift, we should target a system mass, including balloon, of 5 lbm.  This calculation agrees with the manufacturers specification.


At what altitude will the balloon burst?

The balloon will burst at

 Formula, where

   a is the altidude in meters,

  M_v is the vehicle mass in kilograms

  M_f is the free lift in kilograms

  b is the buoyancy of helium in kg/m^3 as a function of altitude derived from the above chart


This happens because the maximum "neutral buoyancy" volume of the balloon is 107 cubic meters and that volume will be reached when the buoyancy function times 107 is equal to the sum of the payload mass plus its free lift.


For example, if the vehicle mass is 4 kg, and the balloon was filled until it neutrally lifted a 4.5 kg bucket, then you calculate the free lift like this:


The helium is lifting the balloon, plus the 4.5 kg bucket, and when its flying, it will lift the vehicle.


Total Lift =4.5 kg + M_balloon = 5.2 kg

Free lift   = 5.2 kg - M_vehicle  = 5.2 - 4.0 = 1.2 Kg


5.2 / 107 = 0.0486


So the balloon will burst when the buoyancy function reaches 0.0486, and a rough interpolation on the chart above shows that this happens at about 26,000 m



How much helium will we fill?

Roughly speaking 1 cubic meter of helium at sea level has a lift of about 1 kg, and 1 cubic meter of helium is equivalent to 35.3 cubic feet.

Helium is delivered in tanks that specify their equivalent cubic feet of helium (but inside the tank its compressed into a lot less space).  The tank that 3ric got has 290 ft^3 of sea-level helium in it at 2400 psi.


You can back out the fill volume by knowing how much lift you put into the balloon. If you pumped 5.2 kg of lift into the balloon, it will have about 5.2 m^3 of gas in it, which is 184 cubic feet - that's a lot of overfill for a balloon nominally targeted at 2.99 m^3.


Flight Planning



       Our flight is governed by FAR Part 101 - Moored Ballloons, Kites, Unmanned Rockets and Unmanned Free Balloons

       It's important (and easy!) to work with the FAA on high altitude balloon flights.  Imagine for a minute being a passenger in a jet plane travelling at 300 mph at 30,000 feet when the pilot suddenly spots a giant white object headed for the cockpit.  Yikes!


        The rules are pretty simple. 

        1) You can't operate in a restricted area (for us, this means over Hanford Nuclear Reservation)

        2) At least 24 hours before the balloon flight you need to call an FAA flight service station and tell them that you are going to do a balloon lfight.  This gives them time to file a NOTAM (Notice to Airmen) to warn pilots

        3) You can't fly in the dark (unless you add a lot of lighting - see regs.)

        4) You need a radar reflector

        5) Every two hours during your flight you need to call the FAA and provide a position report, and you need to tell them when you're done.


Track Planning





3/3/07:  Current weather overcast, 10% chance of precipitation, 41F.

              Overcast to Broken to Scattered cirrus in layers from 20,000 on up


NWRN...BKN020-030 LYRD FL200. VIS 3-5SM BR. 17Z BKN020-030. 21Z
SWRN...OVC020 TOP 020. VIS 3-5SM BR. 18Z SCT040 BKN150 TOP FL200.
ERN...OVC030 LYRD FL200. VIS 3SM BR. 19Z BKN080. OTLK...VFR.


The NOAA Aviation Weather Forecast and Winds are found here.


Atmospheric Environment

Density and buoyancy calculations are based on a model for the Standard Atmosphere.  On any given day, the atmosphere is unlikely to match precisely the model atmosphere.  A useful calculator for including temperature and pressure offsets to the standard atmosphere can be found here.





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