Steady progress towards launch - all Herschel instruments are 'good to go'
12 March 2009 11:38
The three scientific instruments on the Herschel payload have passed their functional tests and have been declared 'good to go'. This marks another milestone in the steady progress being made in preparing the spacecraft for launch.
In the course of the past two weeks all three of Herschel's instruments, SPIRE, PACS and HIFI, have undergone short functional tests. Each instrument team carried out a number of pre-defined tests in normal (as opposed to superfluid) helium conditions in order to verify the health of the instruments after transport to Kourou. All instruments performed flawlessly and passed their pre-launch reviews. The next time that they will be heard from will be a few days after launch when they will be switched on one-by-one as part of the payload check-out process.
The instrument checks followed the completion of a number of mechanical checks on the spacecraft.
Everything in its place – alignment activities successfully completed
Checks on the mechanical stability of the spacecraft have been completed. These are performed by measuring the relative and absolute positions of a number of spacecraft elements with reference to master reference cubes on the spacecraft. These elements are primarily those which protrude from the body of the spacecraft for example, the cryostat nozzles, thrusters, sun acquisition sensor, attitude anomaly detector and the telescope mounting structure. The stability of all of these elements was comprehensibly verified during the tests.
Spacecraft 'fit check' with the Ariane 5 launch adapter
The alignment activities were followed by the 'fit check' of the Ariane 5 launch adapter. The standard adapter, or ACU, is a lightweight metal cylinder, 32 cm high and 2.624 m in diameter, which is used to secure the spacecraft to the launch vehicle, in the case of Herschel to the top of the SYLDA under which the Planck spacecraft will be installed. A clamp-band surrounding the top of the cylinder seals the interface between Herschel and the ACU. After launch, this clamp-band is loosened using a pyrotechnic device. A number of 'spring pusher' devices are then activated to push the satellite away from the launcher.
Top image: The Herschel spacecraft is readied to be manoeuvred onto the launch adapter. Bottom image: Close-up view of the Ariane 5 ECA launch adapter for Herschel. Credit: ESA
In addition to checking that the adapter will fit seamlessly to the spacecraft the electrical connections were also verified. When the adapter is attached to the spacecraft two sets of umbilical pull-away connectors carry electrical signals from the spacecraft through the adapter to the launcher. This allows the spacecraft to be monitored and commanded from the time of integration onto the launcher until lift-off, and also facilitates the monitoring of the cryogenic status of the spacecraft.
The spacecraft will be installed onto the launcher adapter once all of the pre-launch checks have been completed in the S1B clean room, and prior to moving the spacecraft to the S5 building for hydrazine fuelling.
Preparations for helium filling
In parallel with the alignment checks and the launch adapter fit check, the support infrastructure for helium filling was installed. Filling platforms and a number of Helium dewars were put in place for a first Helium I filling operation in S1B after the transport of the spacecraft from Europe.
Thermal protective covering is now in place
The completion of the mechanical checks has cleared the way for most of the final layers of multi-layer insulation (MLI) material to be placed on the spacecraft and payload.
In the course of the next week the Herschel spacecraft will be moved to the S5 building where hydrazine fuelling operations take place.
Last Update: 13 March 2009