What are we doing?
The goal of this project is to able to fly a weather balloon probe at a constant altitude.
Why are we doing it?
The current method for a VAST launch is to send the probe with all of its data measuring devices up into the atmosphere using a helium filled balloon. Ideally, the balloon rises through the atmosphere until the balloon, overinflated from the low pressure of the upper atmosphere and bursts. The probe then floats down on a parachute, where it is collected.
The problem with this system is that measurements cannot be taken at a certain altitude. It is difficult to distinguish changes in data measurements caused by lateral movement from changes caused by vertical movement. It is for this reason that the VAST science team has begun work on an "altitude leveling" balloon.
How are we doing it?
The method that the VAST science team has centered its design around is truly a study in buoyancy. Buoyancy is a function of density; a weather balloon floats because it is, on average, less dense than the air it displaces. Another approach to the issue of buoyancy is to say that the balloon will float if the weight of the balloon is less than the weight of the air it displaces.
The operating principle behind the design of the VAST altitude leveler is that a change in weight with no change in volume will effect the buoyancy of the balloon. While pumping a heavy ballast, such as water, would allow the weight of the balloon to be changed rapidly, it was preferred that the ballast be renewable. For that reason, air was chosen as a ballast. The balloon lever will change its buoyancy by pumping air in and out of an array of 50 2-liter pop bottles. Because the pop bottles will not expand (significantly) when air is pumped into them, the overall density of the system will change as a function of the pressure inside the bottles. Because there is no net change in volume, a change in volume will result in a change in buoyancy.
As the balloon makes its initial ascent to its desired elevation, on board digital altimeters will monitor its height. At some predetermined altitude, a microprocessor will signal a pneumatic pump to begin pumping air into the bottles. This will cause the balloon to slow its ascent and, eventually, begin to fall. When the balloon begins to fall below the specified altitude, the microprocessor will signal a pressure valve to release air from the bottles.
What We Have Done
Moored Launch
Parameterization
Drop Test
What We Plan To Do
In early March, we will coordinate with the CDH Team to outfit ARIAL with the new generation of ARM boards they have been developing. Then we plan to do a full launch in April.
Project Resources
- Dual Head Miniature Air Pump [Specifications]
- 100 ft 1/8" Pneumatic Tubing
- Electronic Pressure Release Valve - Donated by NOAA
- 50 2-Liter Bottles - Free at the Recycling Center
Air Pump Specifications
- Voltage = 12V
- Current = 0.8V
- Max Pressure = 22 psi
- Max Air Flow = 5.5 LPM
- Length = 1.18 in.
- Width = 1.20 in.
- Height = 3.00 in.
Budget
| Item | Unit Price | Quantity | Total Price |
|---|---|---|---|
| Air Pump | $139.00 | 1 | $139.00 |
| Tubing | $0.17/ft | 100 | $17.00 |
| Bottle Carriage | $50.00 | 1 | $50.00 |
| $206.00 |
Project Deliverables
A balloon and probe capable of maintaining a constant altitude.
