At the time of writing, the launch of the Chandra X-ray Observatory is scheduled for no earlier than July 9 on the Space Shuttle. The Spacecraft was shipped from TRW in Redondo Beach, CA to Cape Kennedy on February 4, and is in the Vertical Processing Facility (VPF) being prepared for integration with the Inertial Upper Stage, interface checks with the Shuttle, fueling and final tests from the OCC. A live video picture from the VPF can be seen at:
In the recent months prior to shipping, the team at TRW has been working very hard to complete the remaining spacecraft testing and generate the final changes to flight software and operations database. During this time a series of test opportunities have been provided to the OCC and CXC teams to run flight procedures against the spacecraft and to check out displays and data flow end-to-end to the CXC. These included the End-to-End (ETE) tests, Thermal Vacuum testing, the Mission Sequence Tests (MST) and the Enhanced Systems Tests (EST).
Following the excitement of the first command sent to the spacecraft from the OCC on December 24, 1997 (for the record, the unassuming ``no-operation'' command) the Flight Operations Team prepared for the first of two ETE tests. These tests were run through the Deep Space Network (DSN) Compatibility Test Trailer and demonstrated end-to-end data flow via RF to the spacecraft and through the DSN network we will use on orbit. These tests demonstrated the basic commanding and telemetry functions.
The Thermal Vacuum testing allowed testing of the ACIS and HRC instruments in vacuum. These tests were run with flight-like procedures and resulted in the first full data sets for the ASC Data System team to use as test data for telemetry processing. The Science and Flight Operations Teams also worked closely together to prepare for and conduct the tests and established many of the processes to be used during flight.
The most extensive tests occurred in late August and again in December. The Mission Sequence Tests covered all the commanding planned during the Space Shuttle and Transfer Orbit phase of the mission. This includes the initial turn-on and loading of the on-board computers, communication systems activation, solar array deploy and the activation and firing of the Integral Propulsion System to take the spacecraft to its high earth orbit (10,000 km x 140,000 km).
The Enhanced System Tests were designed to exercise the spacecraft in the conduct of normal science operations for an extended period. For these tests, the CXC generated Observation Requests from the year 1 target list, generated aspect star positions (second test), the OCC data system generated the mission schedule and corresponding command loads, and uplinked them to the spacecraft via a Deep Space Network test interface during contacts just as we will on-orbit. Data were dumped from the Solid State Recorders during the next ``pass'' and transferred back to the OCC and then to the CXC for data processing. There were two EST tests of 56 hours and 24 hours respectively, and both were invaluable in shaking out end-to-end issues with the data flow. During the second EST, the ACIS thresholds were set to produce some photon events - the resulting processed images represented the first true end-to-end data flow from CXC to spacecraft and back to CXC.
In parallel with the testing, the Operations Teams have begun detailed simulations of critical operations activities including the Launch, Shuttle and transfer orbit phases, as well as nominal science operations. The simulations have recently expanded to include the Shuttle Crew led by Commander Eileen Collins, and the Inertial Upper Stage team at Onizuka Air Force Base who will provide Chandra the ride to high earth orbit.
The next few months will be both busy and exciting, and will culminate with the launch, orbital activation and checkout of the observatory and start of science observations. The GTO and GO targets for the first year promise a wealth of stunning results that are anticipated by the the entire team.
- Roger Brissenden