Categories of unmanned free balloons 

Spanish Legislation 

To know the category of our balloon, we must take into account the following terms.

 - The Combined Mass
 - The mass of the "bulk" 
 - The density of the "bulk"
 - The resistance of the rope

 The Combined Mass: that is, the total sum of what we are going to raise: the balloon, ropes, nacelle, etc. 

 The mass of the "bulk": that is, the weight of the nacelle or nacelles. 

The density of the "bulk": To understand the density of the nacelle we will give an example.  
Suppose that our nacelle is a rectangular box of porexpan. We introduce all the measurement sensors, recording cameras, batteries etc and give us 1 kg on the weighing machine, that means 1000 g. 
Suppose also that the measures of the box are: 8 cm X 10 cm X 20 cm. We have to select the smallest face, that is 8 x 10 cm. This is 80 cm2. 
Our "bulk" therefore has a density of 1000g / 80 cm2 = 12.5 g / cm2 

The resistance of the rope: the "quality" of the cable that connects the balloon with the nacelle. 
Generally the rope manufacturer indicates the maximum Kg that can hold it, then multiply this value by the Gravity to know the Newtons of force necessary to break it.

Defined the previous terms let's see how unmanned free balloons are classified: 

In Spain there are three categories:
 - Light 
 - Medium 
 - Heavy 

It is considered HEAVY with just one of the following points: 
 - It exceeds 6 kilograms of combined mass. 
 - It exceeds 3 Kilograms of mass of the "bulk" 
 - It exceeds 2 Kilograms of mass of the "package" if its density is greater than 13 g / cm2 
 - The resistance of the rope exceeds 230 N (23,47 Kg) 

If it does not meet any previous point it is considered MEDIUM if it weighs equal or more than 4 kg but less than 6 kg of combined mass.

If it does not meet any previous point and weighs less than 4kg it is considered LIGHT. 

Below is the table that has traditionally been used to identify balloons.

Once you have done the calculations you must to fill the next form and send at least 20 days before the launch to:

Dirección de Operaciones / GCAT
Dpto. Coordinación Operativa del Espacio Aéreo (COP)
Avda. de Aragón 402
Edificio Lamela, 4ª Planta
28022 Madrid
Teléfono: 913 213 378
Correo Electrónico:

And wait the resolution.

If all is ok, around a week before the launch date you receive the notification with some instructions and the NOTAM to be published.

NOTAM means "Notice to Airmen" and is used primarily to inform pilots of changes to airports, airways, and local procedures that affect safety, and in our case to inform about free balloons. Pilots check NOTAMs as a part of their daily briefing before a flight and ATC remember them the presence of a balloon when they are flying in the afected zone. Thats why enclosed the notification you receive instructions of how to proceed to inform to ATC before and after the launch.

Here is an example of NOTAM:

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