Balloon Construction

 

Capsule

The capsule of Bertha 2 is a Styrfoam cooler from PenguinPak (Omaha, NE).  It has 1.5 inch thick walls to protect the electronics from the -60 F cold air at 100,000 feet.  The capsule contains 2 cameras, one pointing down towards the earth and one pointing horizontally to catch the horizon.  The cameras are powered by external batteries to give them longer life.  The batteries and cameras are held in place with Velcro straps strung through the Syrofoam walls.  The cameras are framed with a pine frame epoxied to the capsule to position them exactly through the holes in the wall of the capsule.

 

The capsule is suspended from the balloon with 4 strings.  Each string runs through the top of the capsule then through a plastic tube epoxied in the corner of the capsule, then through the bottom.  A nylon washer is attached to the bottom of the capsule to disperse the strain.  Finally, the plastic tubes in the corner are insulated with a jacket of Styrofoam to ensure the cold is kept out.

 

 

Framing the Horizon

The horizontal camera is positioned 10 degrees down so that the horizon is positioned 1/3 from the top of the frame.  The capsule is adjusted to hang level by adjusting the length of the 4 corner strings then epoxying lightweight string around them where they come together.

 

To test the positioning of the horizon, the capsule is suspended in a room.  Blue painter's tape, representing the horizon, is strung at the same height as the lens.  Photographs are taken with the camera mounted in the box.  As you can see, the view from the camera's perspective shows the horizon at 1/3 the top of the frame.

 

Camera and Battery

The cameras I used are two Canon PhowerShot Elph 300 HS.  They can take video and stills and can be programmed (see chdk.wikia.com/wiki/Downloads).  To power each camera externally, I purchased the AC Adapter Kit ACK-DC60 which allows you to plug in an external power source.  Since the voltage specification going into the DC60 adapter is close to USB voltage specs, I soldered the adapter cord  to a USB cord and purchased a New Trent iFuel IMP500 5000mAh External Battery Pack with USB output.  The battery is fully capable of powering the camera for over 12 hours (a bit over engineered).

 

GPS

 

I used two GPS tracking devices. The first is a SPOT Satellite GPS Messenger (www.findmespot.com/en/). The second is a Garmin GTU 10. The Garmin relies on being able to triangulate its position using cell phone towers, so the capsule will need to land in an area with cell phone coverage. Since it is questionable whether or not the battery will last up to the 6 hours needed, I used an external Energizer cell phone battery charger with two lithium batteries. The Energizer model is unique in that it will not shut off if the external "cell phone" battery is full. Other models turn off when the external battery is full and there would be no way of turning it back on when the GPS battery drains. The two lithium batteries will keep the Garmin powered on for almost 12 hours.

 

The SPOT meter uses satellites to determine its position, so there is no need to have cell phone coverage. You need to subscribe to a plan for both devices. I also subscribed to a tracking service for the SPOT meter which will send out its location every 10 minutes.

 

To hold the GPU units in the capsule, I built a Styrofoam insert with Velcro straps for the GPS units. The insert can be dropped in the capsule just before launch.

 

The Balloon

The balloon is from Kaymont Consolidated Industries (http://kaymontballoons.com/).  I chose the 1200 gram size based on the payload weight, my goal of 100,000 feet and other factors (see Balloon Design).  It is a precision weather balloon designed to burst at specific altitudes.

 


The Parachute

The parachute is from the Rocketman store (www.the-rocketman.com/recovery.html).  I chose the 4 foot size so the decent rate would be approximately 4.9 m/sec based on the payload weight.  This matches the assumed decent rate of the Laramie Wyoming model (see Balloon Design).

 

Radar Reflector

The radar reflector is home-made.  It is made from aluminum foil tape (used for duct work) and corrugated cardboard (to keep the weight low).  Several websites suggest having a radar reflector so planes can see the balloon.  I made it by first gluing together 3 intersecting circles of cardboard, then covering it with foil tape.

 

Strings Attached

30 feet of string will be used between the capsule and the parachute.  Heavier rope (Nylon Diamond Braided Rope from Home Depot) is used for this to ensure the capsule is not severed from the parachute.   A lighter (40 lbs. test) string (Nylon Diamond Braided Rope from Walmart) is used between the parachute and balloon.  We are planning to use 10 feet of string here.  The longer purple line should be long enough so that the balloon debris should not hang in front of the lens during the decent.

 

Launch Equipment

 

To fill and launch the balloon a few special pieces of equipment were made. The helium tank comes attached with a regulator and hose. The end of the hose is fitted with a standard CGA 580 adaptor. I constructed the fill nozzle with the other end of the 580 fitting along with enough adaptors to fit into a 1 inch PVS pipe. The neck of the balloon is 1 inch in diameter and fits nicely over the pipe.

 

To get the correct "neck lift", a water jug containing the same weight as the neck lift will be suspended from a hook connected to a clamp (the weight of the clamp will be added to the total ballast). The clamp temporarily closes off the neck of the balloon while it is weighed. Once the balloon is filled to neutral buoyancy with the water jug, the neck will be tied off and the parachute attached.

 

A portable kitchen scale is used to weigh all items suspended from the balloon so that the correct neck lift can be determined.