The Environmental Lab, whose main objective is to characterize the radiative thermal environment would be placed out of the gondola structure through two brackets attached to the upper and lower part of it. On the called Upward Environmental Lab, a pyranometer and a pyrgeometer sensor will be placed as well as in the Downward Environmental Lab. These are commercial components commonly used for meteorological stations. They would be thermally protected from the wind to provide them with a suitable environment.

Pyrgeometers aims at measuring the infrared thermal radiation in a bandwidth from 2 to 100 μm while the pyranometer aims at measuring the Solar radiation which goes from 0.2 to 2 μm. The selected infrared radiation sensor, IR20 from Hukseflux, will provide the incoming radiation in a bandwidth from 4.5 to 40 μm where most part of the emitted radiation by the sky and the Earth is included. The selected solar radiation sensor, SR20 from Hukseflux, will provide the incoming radiation in a bandwidth from 0.285 to 3 μm where most part of the Solar radiation, accounting with the atmosphere absorption, is located. Ranges of the selected sensors are drawn in next figure together with the atmospheric infrared spectrum and perfect blackbody temperatures (black).

Pyranometer and pyrgeometer measuring wavelength (dashed lines).

As Hukseflux state in the User’s manual, the downwelling longwave radiation from the Earth surface essentially consists of several components:
• Low temperature radiation from the universe, filtered by the atmosphere,
• Temperature radiation emitted by atmospheric gasses and aerosols.
• In presence of clouds or mist, the low temperature radiation from the universe is almost completely blocked by the water droplets.

In contrast, the upwelling longwave radiation is mainly affected by the emitted radiation by the Earth surface. It would only depend on its temperature and infrared emissivity. As the experiment will be increasing its altitude during the ascent phase, the equivalent sky temperature will be decreasing up to a value of 3 K which is the equivalent blackbody temperature of the deep space.

In contrast, direct solar radiation will account for the “beam” radiation which varies with the cosine of the angle of incidence. The upwelling solar radiation together with the upwelling solar radiation reflected by the Earth would be used for obtaining the Earth albedo during the flight.

IR20 and SR20 has an onboard heater and a temperature sensor. Heating the sensor, measuring the body temperature and using the correction of the temperature response, all contribute to the dependability and accuracy of the measurement.

Both the Upward and the Downward Environmental Labs follow the same main design philosophy, but different adjustments were made for each of them due to its specific circumstances of positioning in the gondola and requirements from the experiments.

The Upward Environmental Lab is attached to the gondola roof through the clamp system describe on a previous section. The Upward Environmental Lab only carries the pyrgeometer and the pyranometer, which have a 150 mm diameter, hence the support plate was designed to be as short as possible so that they wouldn’t touch each other (250mm x 150mm). The support plate with the radiation sensors is connected to the gondola through two parallel tubes of length 735 mm and exterior diameter 18 mm (interior diameter 16mm), and four shaft supports, the same used in the clamps, one in each corner for better weight istribution. The rods are made of Woven Finish Carbon Fibre Tube.

Upward Environmental Lab configuration

The Downward Environmental Lab is directly fixated to the Main Structure with the system described in the previous section. The rods are shorter (400mm) as they don’t have a secondary support interface. The support plate length has the same dimensions as in the Upward Environmental Lab.

Downward Environmental Lab configuration