Mission Update - June 2004
This month, guest writer Monte Henderson, Deep Impact project manager for Ball Aerospace gives us the update for the mission.
The stacking of Deep Impact's flyby and impactor spacecraft was the inaugural activity for a series of important tests that will be performed on the flight system prior to both spacecraft being shipped to the launch site. This test series, collectively known as the Environmental Test phase, validates the flight system's performance capabilities in the various extreme conditions the spacecraft will see during the launch, the cruise phase, and the final encounter with Tempel 1.
At Ball Aerospace, many of our spacecraft systems undergo testing on a piece of equipment called the "Wooly Wobbler." The Wooly Wobbler, named after the innovative Ball Aerospace engineer (Dick Wooly) who created it, is a turntable that oscillates (wobbles) two or three degrees in a circular direction. The Wobbler allows us to determine with high precision where a spacecraft's center of gravity lies. There are several instances during the mission for which the spacecraft must be in perfect balance and knowing and maintaining that center of gravity is critical during those times.
After completion of the Wobble testing, both spacecraft were returned to the test stand for performance testing. After all environmental tests it is important to know that all the flight subsystems still perform correctly so a full set of verification tests for all systems are run. The DI flight system completed the testing with good results in all cases.
Deep Impact also performed well on its solar array deployment test, where the mechanisms that release the solar array panels from their launch position were tested using the same commands that will be used in flight.
Once prior testing was determined to be successful, Deep Impact made one giant leap... outside the cleanroom for the first time since we began assembling it. Moving a spacecraft, either on a special wheeled cart or with a crane, is a stressful time for all of us on the program, and many extra precautions are taken to make sure these moves go smoothly. Often at Ball Aerospace, a spacecraft is moved from our large cleanroom to our testing facilities through a long series of hallways. The spacecraft must be bagged in an anti-static material and attached to a grounding line. The grounding line is attached to a grounding fixture in the cleanroom and it trails behind the spacecraft as we move it through the halls. The grounding line ensures that we minimize the risk of static discharge to the system.
Deep Impact's flight system is too large for the halls and doorways, and had to be moved through large doors and outside between buildings. The same precautions are taken when moving outside. Deep Impact was bagged and grounded to make its journey to the testing facilities.
Deep Impact spent several days in our large electro-magnetic interference chamber where it underwent radiated susceptibility testing to make sure the flight system can withstand the exposure to electro-magnetic interference it will have to endure during launch. Next, the Deep Impact spacecraft underwent a self-compatibility test to test all of Deep Impact's components independently to make sure there was no electro-magnetic interference between individual components within the flight system. The flight system completed the testing with no problems detected.
Verification tests were successfully run again, and then, the spacecraft moved down the hall to the acoustic test facility so we could see how they will be affected by the low frequency noise we will encounter during the launch. The spacecraft was bombarded with 145db (decibels) of sound. Rock concerts are typically 112 db of sound. Again, no problems were detected.
After successful completion of a series of verification tests, the spacecraft were moved on their cart to our vibration test facility and the stacked spacecraft were transported by a crane onto our vibration table. During this test, vibrations were introduced on the spacecraft both vertically and horizontally up to 2000 times per second. This massive amount of shaking simulates the vibrations the flight system will encounter during the launch phase of the mission. The flight system passed these tests with no mission significant anomalies discovered.
Through out these physical tests, we have also been exercising the flight system with Mission Scenario Tests (MSTs). The MSTs are essentially dry runs of the various phases of the Deep Impact mission, such as launch, trajectory change maneuvers, flyby encounter, and impactor encounter. The MSTs allow us to test the flight system using the exact same sequences of commands that will be used during the actual mission phase.
Deep Impact will spend much of the summer and early fall in additional environmental tests, such as thermal vacuum testing prior to our shipment date in October. Then, the flight system, and many of us, will be making a trip to Cape Canaveral, Florida to make sure Deep Impact gets off the ground successfully. Our launch period opens on December 30th, and we will be ready.
Contribution from Monte Henderson and Don Hampton of Ball Aerospace and Technologies Corp.
(Note: The Deep Impact launch period has since been changed to begin in January 2005).