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In this issue:
Environmental testing of Dawn spacecraft begins
Dawn Instrument Integration Completed
Ceres a 'Dwarf Planet'
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Dawn Instrument Integration Completed
Betina Pavri
Dawn Payload Engineer, JPL
Ed Miller
Dawn Payload Manager, JPL
The Dawn payload integration to the spacecraft was completed during September, and all of the science instruments have now been tested for functionality on both primary and redundant interfaces. Integration went smoothly and all instruments checked out perfectly. As part of the comprehensive performance testing of the instrument systems, science data were transmitted from the spacecraft through the Dawn Science Center at UCLA to the instrument teams’ home institutions.
The spacecraft is fully assembled except for the two outboard thrusters of the ion propulsion system (IPS), to be installed after dynamics testing and before thermo-vac (TVAC), to avoid damage to these critical appendages. The center thruster has been installed in the spacecraft core, as well as the large high-gain antenna. The solar panels are currently being installed.
The Power Processing Units (PPUs) of the IPS system, that had been an item of concern a year ago, each underwent 500 hours of run-in testing before delivery to the spacecraft to certify their robustness against workmanship defects and early parts failures. After integration, the PPUs were exercised during IPS comprehensive performance testing and have operated trouble-free. There are no outstanding issues with the flight hardware, and the flight software needed for environmental testing has been delivered.
In the months leading up to the final integration, the Framing Cameras had been returned to MPS in Germany for investigation and rework of an anomaly in their cover operations. The MPS team worked diligently to isolate the issues and rework the system. The covers now operate flawlessly and the cameras were integrated on schedule.
The Visible InfraRed Mapping Spectrometer (VIR) instrument consists of two parts: the Optics Module (OM) and the Main Electronics (ME). The VIR ME was delivered and integrated last summer, since it is located inside the spacecraft. Before the OM integration to the spacecraft, the OM mounting panel was redesigned by engineers at Orbital Sciences, the spacecraft contractor, to resolve a thermal expansion mismatch issue. The OM was then integrated to the newly redesigned panel. This delicate integration, including the electronics, cryocooler, the OM itself, and all blanketing and cabling to the VIR panel took 6 days to complete! The panel is now attached to the spacecraft and the OM is connected to the Main Electronics.
The Gamma Ray and Neutron Detector (GRaND) instrument was integrated in August to a special radiator that will keep the instrument cool in the vacuum of space. For ground testing, a special cooler has been temporarily installed to keep the instrument in its operational temperature range. All of the Dawn science instruments will now participate in a series of increasingly realistic tests to ensure that both they and the mission operations team are flight-ready.
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Figure 1.
Top view of the spacecraft (+Z deck), showing instruments, coarse sun sensors (CSS), star tracker (ST) and reaction wheel assemblys (RWA).
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Figure 2.
View of +X panel showing 1-meter high-gain antenna (top) and thruster gimbal assembly (bottom).
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