3.1 Balloon Tethering
Air balloon’s gaining altitude is the result of lift force’s being bigger than the force of gravity on it. Namely, if the lift force of gas inside the balloon is bigger than the weight balloon ascends. In the other hand if it is less than the weight balloon descend. Whether the lift force is bigger or less than the weight, balloon alter its altitude but if the force on it equals to zero on vertical direction balloon will keep its altitude. In other words the altitude will be stabilized.
Altitude stabilization is not enough individually to stay on the same location due to external factors such as wind. Firstly ascending, secondly dispersion must be disposed to stabilize location. Airships use their own thrust power to stabilize location (location keeping) but air balloons don’t have this ability because of low payload limit. Mounting the thrust engine to one air balloons is not logical if it’s compared with the power gain and payload loss.…show more content… In Europe and America, some companies are using tethered or controllable balloons to advertise their brands or goods.  In a similar way more complex and bigger air balloon which is produced by Raytheon Company is used by United States Army and JLENS called project is a tethered balloon. It flies at 10000 feet and has ability to warn aircraft and missile from 240 mile away. 
The projects that tethered airships are used are high-cost projects but the tethered balloons which used for advertisement are very low-cost. It is evaluated as the altitude that balloon will be hanging at can be 500-1000 meter when the wind limits and the weight caused by tethering are considered. The wind force that balloon will be exposed at 500-1000 meter and the tensile force of the tethering cable change so the distance can be changed while usage.
3.2 Carrying Observation (Optic)