#02: Mercury Planetary Orbiter wraps up for hot work
5 September 2011The installation of high-temperature thermal blankets on the Structural and Thermal Model of the BepiColombo Mercury Planetary Orbiter has been completed. The spacecraft has been mounted on its Thermal Test Adapter and transferred to the Large Space Simulator in preparation for thermal-balance testing.
The high-temperature thermal blankets were installed first on the +Z (Nadir) side of the Mercury Planetary Orbiter (MPO). On 8 August, the spacecraft was removed from its ground handling trolley using an overhead crane equipped with a special lifting adapter and rotated through 180° about its Y-axis. It was then mounted on the ground handing trolley via its –Z (top, in launch configuration) face, to enable technicians to access the +Z face for thermal hardware installation.
Once the spacecraft had been rotated using the crane, the ground handling trolley rotated it so that its Z-axis was vertical, enabling the crane to lift the mounting adapter off of the +Z face once it had been unbolted.
Over the following three weeks, the remaining thermal blankets were installed. To cope with the extreme thermal conditions in Mercury orbit, the MPO is fitted with two sets of thermal insulation blankets. The inner blanket, which appears metallic in the images, is a conventional Multi-Layer Insulation (MLI) with 10 layers. The high-temperature blankets (white in the images) that have now been installed have in total more than 20 layers made of different materials. The outer blankets employ a special fastening technique to avoid holes through the blanket and the protrusion of stand-offs that might be illuminated by the Sun. To minimise conductive coupling between the two blankets, they are kept 15 mm apart and their facing surfaces are highly reflective, to minimise radiative coupling.
The outer layer of the high-temperature blankets is made from electrically non-conducting fabric; to control the build-up of electrostatic charge on the surface of the spacecraft, conducting threads have been woven through the outer layer every 10 cm. The separate parts of the outer blanket were hand-sewn together once they had been installed.
On the weekend of 27/28 August, after completion of the blanket installation, the MPO was removed from its ground handling trolley and installed on its Thermal Test Adapter (TTA). As the spacecraft heats up during thermal-balance testing, it will expand. If it were rigidly mounted to the interface in the Large Space Simulator (LSS), this expansion would give rise to large mechanical stresses. Instead, the TTA connects the MPO to the LSS interface through four bipods that are allowed to move and relieve the mechanical stresses.
On the afternoon of 31 August the MPO and TTA were moved into the LSS. Once additional preparations have been completed, thermal-balance testing is scheduled to commence towards the beginning of week 37.
BepiColombo is Europe's first mission to Mercury. It is scheduled to launch in August 2015 and arrive at Mercury in January 2022. It will endure temperatures in excess of 350 °C and gather data during a one year nominal mission, with a possible one-year extension. The mission comprises two spacecraft: the Mercury Planetary Orbiter (MPO) and the Mercury Magnetospheric Orbiter (MMO). During the journey to Mercury, the MMO will be shielded from the Sun by the Magnetospheric Orbiter Sunshield and Interface Structure (MOSIF), which also provides the interface between the MMO and the MPO. The fourth component of the composite spacecraft stack is the Mercury Transfer Module (MTM), whose primary task is to provide solar-electric propulsion for the journey to Mercury.
BepiColombo is a joint mission by ESA and the Japan Aerospace Exploration Agency (JAXA), executed under ESA leadership. The Prime Contractor for BepiColombo is Astrium GmbH.