Swift MOC
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Instrument Control Unit (ICU)

UVOT Digital Electronics Module The ICU is the master computer aboard the UVOT experiment. A re-implementation of the ICU on the XMM Optical Monitor (OM) experiment, the ICU electronics and software boasts a strong flight heritage. The ICU is responsible for configuring the UVOT telescope module and for ensuring the health and safety of the UVOT experiment. The ICU is also the primary interface to the Swift spacecraft. It commands the DPU using information from the Figure of Merit processor.

To reduce costs and risk, Mullard Space Science Laboratory (MSSL) is making as few changes as possible to the OM ICU electronics and software to meet the requirements of the Swift UVOT experiment.

Electronics

The ICU computer is a 31750 chip which runs at 12MHz (The ICU aboard OM is operating at 8 MHz). There are three electrical interfaces to devices external to the ICU: a MACS bus control interface to the telescope module, a SSI communication interface to the DPU, and a 1553B bus interface to the Swift spacecraft.

The ICU controls the Telescope Module (TM) via a MACS interface. This interface is used to control the filterwheel mechanism and the "dichroic" mirror mechanism. It is also used to configure the Blue Processing Electronics, which is responsible for operating the MIC detector.

The ICU communicates with the DPU over a Serial Synchronous Interface (SSI). See document TBD for a specification of the electrical interface.

A major change to the ICU is the spacecraft communication circuitry. Communication aboard the Swift spacecraft will be done on a 1553B bus. MSSL has acquired a 1553 chip and has integrated it into the UVOT ICU design.

Software

As with the electronics, MSSL will make only necessary changes to the ICU software. The code is written in Texas Instruments Tartan ADA and Tartan Assembly and which runs under the TARTAN ADA Run Time. One change to the ICU software is that it does not accept science data from the DPU as it did on OM. The OM DPU did not have a mechanism to communicate with the XMM spacecraft, so the OM ICU accepted science data from the DPU and forwarded it to the spacecraft. The UVOT DPU will send science data directly to the Swift spacecraft.

Another change to the ICU software is deferred command stores. Swift is required to support up to 72 hours of autonomous operations, so the ICU must store up to 1000 observation scenarios: scripts used to configure the telescope module and to command the DPU.

The SSI logical interface for UVOT is documented in the Interface Control Document for the ICU to DPU/DPU to ICU PROTOCOL for the Ultra Violet Optical Telescope (SwRI Document Number 03691-DPUICD). The beginning of an exposure is accomplished by handshaking with the DPU. A MODE command is sent to the DPU. The DPU configures the Swift Communications Module hardware, initializes its data buffers and replies with a MODE READY message to the ICU. The ICU turns on data flow, and an observation begins. At the end of an exposure, the DPU sends a MODE COMPLETE message to the ICU. The ICU will also have the capability to STOP or ABORT an exposure.

Swift Mission Operations Center

The Pennsylvania State University
301 Science Park Road,
Building 2 Suite 332,
State College, PA 16801
USA
☎ +1 (814) 865-6834
📧 swiftods@swift.psu.edu

Swift MOC Team Leads

Mission Director: John Nousek
Science Operations: Jamie Kennea
Flight Operations: Mark Hilliard
UVOT: Michael Siegel
XRT: Jamie Kennea