Bernd Biering

TCS Design of the Microsatellite BIRD for Infrared Earth Observation

The DLR (German Aerospace Center) plans to launch the microsatellite BIRD (Bi spectral Infrared Detection) in 1999 as part of an Earth remote sensing mission with hot spot detection as matter of priority. This project represents the begin of a line of small satellite missions with ambitious scientific and technological objectives by application of new technology and respecting the limitations of microsatellites. The spacecraft bus design is based on the proposed orbit and the payload requirements. The scientific payload is a novel multi-spectral sensor system, consisting of two cooled infrared sensor arrays and the Wide Angle Optoelectronic Stereo Scanner (WAOSS). A serious constraint of the satellite design is the required compatibility to a piggyback launch. The concept of the satellite bus fits to the requirements with the satellite dimensions of about 550x610x620 mm³ and a total mass of approx. 85 kg. The presentation describes the approach for the thermal design of the satellite bus with focus on the mission profile and the requirements of the payload.

BIRD Microsatellite Thermal Control System – 5 Years of Operation in Space

Microsatellite BIRD (Bispectral InfraRed Detection) with mass 92 kg and overall sizes 0.55 x 0.61 x 0.62 m operates in a sun-synchronous orbit morethan 5 years. The temperature range –10 +30°C forpayload with average power about 35 W and peak power of 200 W inobservation mode, continuing 10–20 min, is provided by passivethermal control system (TCS). Operation of TCS foresees a thermalstability of payload structure by use of heat transfer elements~–conductors and grooved heat pipes, thermally jointing the satellitessegments. Two radiators, multilayer insulation (MLI) andlow-conductive stand-offs provide the required temperature level.Review of TCS performance is based on an analysis of dailytelemetric data, collected by 33 temperature sensors and powerconsumption. The analysis includes the definition of minimal,maximal and averaged temperatures of satellite main units andcomparison with designed parameters. TCS successfully supports therequired temperature level of satellite components during the wholeperiod of exploitation.

Light Pressure Measurement at DLR Bremen

The solar light pressure exerted on a thin foil is the quantity that determines crucially the performance of a solar sail propulsion technology. Besides the distance from the sun and the relative position of the sail to the sun, the light pressure depends on the quality of the sail surface. The surface quality, especially the reflectivity, degrades by exposing the sail to particle and electromagnetic irradiation under space conditions. This process will be simulated by a test facility at DLR Bremen. By directly measuring the light pressure after exposing the foils to a certain dose yields a kind of integral quantity of the degradation effects. To this end a light pressure measurement facility based on a high precision balance has been developed, completed and tested at DLR Bremen.

Thermal Performance of BIRD Microsatellite Thermal Control System - 3 Years of Operation in Space

ABSTRACT Microsatellite BIRD (Bispectral InfraRed Detection), mass 92 kg, sizes 550x610x620 mm was put on October 22, 2001 in a sun-synchronous orbit. The passive thermal control system (TCS) provided a temperature range of –10…+30 0 C for a payload. It is assembled from precision optical instruments and housekeeping equipment with average power about 35 W. In the observation mode a power consumption peak of 200 W is occurred during 10-20 min. The TCS ensured a thermal stable design of the payload structure and is realised by heat transfer elements (conductors and grooved heat pipes), which thermally connected the satellite segments, two radiators, multilayer insulation and low-conductive stand-offs. Three years in space have brought an enormous volume of telemetric data about thermal performance of the TCS, based on information from temperature sensors, power consumption, attitude relative to Sun and Earth. The TCS successfully supported the required temperature level of satellite components during the whole period of exploitation. Nevertheless, the authors aimed at analysing the temperature history during these years for the main units of housekeeping equipment such as radiator, payload platform, power supply subsystem, board computer, power supply system, communication and draw conclusions on possible changes in performance. A survey is conducted for the following time scales: payload operation time (10-30 min), one orbit (96 min), shortly after launch and current time.

A Thermal Method for the Determination of Solar Absorptance and Thermal Emittance of Spacecraft Coatings.

For the determination of the solar absorptance s and the thermal emittance preferably optical methods are utilized. To these methods belong spectral reflectance αs and e measurements and / or emission measurements (only e), whereby for αs must be measured in the common range 0,3 μm to 2,5 μm and in the range 5 μm to 35 μm with an essentially better resolution than 10 nm . Besides so-called integrated reflectance measurements are known, for which special detectors are used, in the above indicated spectral ranges. These optical measuring procedures are relatively exact. They deliver also information about a perhaps spectral selective behaviour of surfaces, however, special measuring equipment is required.

Thermal Design and Pre Flight Thermal Test Program of Micro Satellite BIRD

Micro Satellites are one of promising instruments for near earth space research programs. The strong restrictions to mass and power budget of satellite subsystems and payload lead to choice of mainly passive Thermal Control Systems (TCS), often with heat pipe (HP) integration. New tendencies in micro satellite thermal requirements as multi temperature level payload instruments, thermal stability of mounting structures for precision optical devices cause the corresponding adequate modifications in thermal concept and in hardware realisation. Intended aim of this paper is to present the experience collected by authors during thermal design and preflight thermal tests of Micro Satellite BIRD, developed under the German small satellite program.

Effective Emissivity Determination of Multilayer Insulation for Practical Spacecraft Application

Multilayer Insulation (MLI) is used for thermal control of spacecraft (S/C). Built-in discontinuities degrade the performance of MLI blankets. In this paper the blanket properties are considered by defining an effective emissivity for the MLI covered S/C suface. The influence of covered area and the influence of number of layers on the effective emissivity is determined by experiments with simple MLI covered test bodies in a space simulation chamber. An equation for the calculation of the effective emissivity of Soviet EVTI-type MLI is presented. The tests are combined with investigations of thermal similarity.