SOFIA has just passed a major milestone, with the installation of the 10 ton telescope bearing and drive into the modified B747SP aircraft.

figure1: Two cranes are necessary to carefully place the 10 ton SOFIA Telescope Suspension Assembly, which contains the bearing, into the bulkhead of the modified aircraft.

figure2: The Suspension Assembly, protected in a reflective cover, is bolted to the the bulkhead of the SOFIA B747SP aircraft.   Click on image for close-up view

In this newsletter, we present the information on the important Mission Controls and Communications System for the SOFIA observatory that is being put together by the USRA and L3 Communications development team.

The SOFIA Mission Controls and Communications System (MCCS) is the assembly of dedicated hardware and software subsystems through which the on-board crew and scientists control the observatory. These subsystems will be operated from computer consoles located in the Mission area of the aircraft main deck. The flexible MCCS architecture will permit continuous improvement throughout SOFIA's planned 20-year lifetime, with the possibility of remote observing from the ground in the future.

The Mission Control Subsystem (MCS) provides the most significant portion of the MCCS operation including the majority of operator supervisory control and monitoring of observatory subsystems, particularly the Telescope Assembly (TA), but also of the Cavity Door (CDS) and Cavity Environmental Control Subsystems (CECS), which protect and condition the telescope in the extreme environments to which it is exposed. The MCS assures that the telescope and the cavity door are positioned correctly. The MCS provides the intersystem communications, control, and monitoring, as well as other ancillary functions such as storage and retrieval of a wide variety of subsystem housekeeping data; printing and plotting functions; and computations used during observations. Other major subsystems within the MCCS include the Mission Audio Distribution (MADS) and Video Distribution Subsystems (VDS), which operate within their own fiberoptic and wire networks. The MADS system is used by the mission crew and scientists to communicate with one another in flight.

The MCS includes a suite of high performance Commercial-Off-The-Shelf (COTS) UNIX computer workstations at several operator consoles and servers connected by the LAN. This allows the MCS peripherals (disk and tape drives, printers, and modems) to be accessible from any Observatory workstation. The servers and workstations execute software applications and provide access to high-capacity disk and tape storage drives. The MCS architecture allows for reconfigurable workstations and provides reliability through redundancy.

Software applications for the MCS are being developed jointly by teams staffed from USRA, L-3 Communications, NASA, and science and university researchers, along with a collaboration of the telescope contractor team members in Germany and Switzerland. The major elements of the MCCS-hosted applications are the MCS core (or infrastructure), Flight Manager, and portions of the Data Cycle System (DCS). (DCS is discussed in the newsletter of April 2002 Vol. 4).

Progressive derivation of MCS software requirements and features began with an assessment of Minimum Core Capabilities (AMCC) by science users and instrument developers to identify those features necessary for the observatory to perform efficient science with its known instrument complement at Observatory readiness and initial deployment. Detailed observing scenarios were derived and developed by a collaborative team of science users and contractors specialists. These Observing Scenarios detail step-by-step interactions among the Science Instrument, MCCS, Cavity Door and Telescope. The functions required to satisfy those scenarios "bound" the functionality required of the MCS software for computations and integrated telescope control.

MCS calculates coordinate transformations required to establish the relationship between the celestial reference frame and the telescope inertial reference frame. This enables "blind pointing" of the telescope while cavity door is closed or before tracking is established with the imagers. Use of guide stars and the star field to refine the transformation assures pointing with desired accuracies. The stability of the pointing is handled through the internal pointing control system of the telescope (see previous newsletter dated June 2002, vol.5).

In addition to controlling the telescope and the other mission systems, the MCS software collects numerous housekeeping data parameters from the telescope, the on-board water vapor monitor, and various aircraft systems. MCS software also controls the video distribution system, in which all frames from the telescope imagers are captured. If desired, overlays are generated and are displayed with the images and stored for archival purposes.

MCS software development is phased to provide the necessary operational capabilities in support of the integration and testing phases through final performance flight tests. Initial tests are planned to begin in late 2003 using HIPO as the first Science Instrument to be integrated with MCS and the telescope. Within this test series the first star observations will be made from the ground with the "core" MCS software applications providing telescope pointing and control. Actual "characterization" of the observatory will take place during flight testing in 2004 along with functional verification flight tests based at the L-3 facilities in Waco, TX. The observatory will then transfer to the NASA Ames Research Center, California for final performance flight tests. Transition to operations is scheduled for late 2004.

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