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The Forefront of Space Science

Thermal Control System of BepiColombo MMO
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Verification of MMO's thermal design

In order to develop, test, and verify the observation instruments, bus instruments and thermal control materials that are exposed to outer space, we built an "inner planet thermal vacuum environmental simulator" (Fig. 3) during the early stage of MMO development. The simulator is a vacuum chamber having a liquid-nitrogen cooling shroud of 1m inner diameter and 1m depth that allows simulated sunlight of 250mm diameter to enter the shroud. It can simulate the intensity level of sunlight in the range of the earth environment to the Mercury environment. We have used the simulator to test and verify at both material to component levels.

Figure 3
Figure 3. Inner planet thermal vacuum environmental simulator

Thermal design verification at the system level has been made by using (1) 13m? space chamber at Tsukuba (November 2009), (2) 4m? space chamber at Sagamihara (February 2010), and (3) Large Space Simulator (LSS) at European Space Research and Technology Centre (ESTEC) of ESA (October 2010). As we needed to accurately identify the impact of incident solar light and heat in the Mercurial environment, we used in the test a thermal model that was thermally equivalent (especially in shape) to the flight model. In test (1), we evaluated the impact of sunlight because the chamber allowed us to simulate well-aligned parallel sunlight even though its intensity is that of near-earth space. In test (2), we obtained data to verify a thermal mathematical model, which will be used to forecast temperature. This test became possible because we could simulate temperature levels while giving well-arranged boundary conditions. In test (3), we evaluated the high-temperature tolerability of MMO since we could simulate the intensity of sunlight on Mercury though it was converging rays.

By combining the material/component level tests and the system level tests (1), (2) and (3), we verified the thermal design and thermal mathematical model. In November 2010, we conducted the thermal test in combination of MOSIF and MMO jointly with ESA using LSS at RESTEC to verify the thermal design and thermal mathematical model in the configuration of its arrival at Mercury.

In conclusion

Flight predictions derived from the thermal design and thermal mathematical model, and verified by the tests, showed that the flight would be possible (i.e., operation of the satellite would be possible) although some operational limitations within the allowable range are unavoidable during the period near the Sun in the Mercury orbit.

After the overall integration test of the flight model, the MMO will be launched in 2014. In 2020, when the MMO is to be released on Mercury, we will be able to check the appropriateness of our thermal design.

Hiroyuki Ogawa


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