HIFI should be back in business soon! The international team that tackles the problems with the Dutch-led international space instrument is in full swing, adapting the operational procedures and internal software on the ground. These adaptations are made in order to prevent a recurrence of the unwanted voltage peak in the electronic system of HIFI, which in August led to a faulty diode in a DC/DC convertor. Most likely the back-up system will be switched on in January and soon after HIFI will begin with the long awaited scientific observations.
“The changes in the HIFI software are threefold really,” project manager Peter Roelfsema says. “The first task is no longer using the standby switch that normally protects the Local Oscillator Control Unit (LCU) against sudden power drops. Normally it protects the precious Local Oscillator chains but now it got activated at the wrong moment. It is also necessary to subdue or eliminate as many voltage peaks in the system as possible. The team will achieve this by cutting back in all relay switching activities. Finally a software change will have to ensure that communications with the LCU – a control unit for the high frequency signal that is generated in HIFI – are not disturbed again." An in-depth investigation of the consequences of these changes in software and operations is necessary. This process is time-consuming and together with the schedule constraints from the satellite side, the window of opportunity is becoming too tight to be comfortably completed before Christmas. The main consideration still is that the any risk involved in the switch-on of the back up system should be minimized.
The coming weeks teams of SRON and ESA will upload the new software in a step-wise fashion. The current plan is to switch on HIFI in January, which will take a few days, after which the instrument will be thoroughly tested. Then the researchers will carry on with the Performance Verification (PV) phase activities which suddenly stopped on August 2nd. Finally HIFI can resume the scientific observations everybody is waiting for. Scientific leader Frank Helmich: "We all feel that it is a real pity that we can’t switch on HIFI any sooner, because we know astronomers from all over the world are waiting on our observations. But eliminating all possible risks has to be our priority right now. We need to take this extra month for testing and validating the smallest details in the software changes, making sure HIFI will be able to carry out the full scientific observation programme."
A consistent scenario
After weeks of intensive investigations only one consistent scenario for the HIFI anomaly remained. As a result of a currently unknown event – possibly a cosmic ray hit in the computer memory – on 2 August the processor of the Local Oscillator Control Unit (LCU) detects an error, reboots and loses communication with the instrument’s main computer. After somewhat more than a second inadvertently the standby switch is activated. This standby switch has been designed to protect the LCU against power drops on the main power line from the satellite, but now fully powered sends a voltage peak through the system. This peak was fatal for one of the diodes in one of the LCU DC/DC convertors.
For the next three years HIFI – on board of the ESA Herschel Space Observatory and built by a SRON-led international consortium – will study the physical and chemical conditions in gas clouds in the Milky Way and other galaxies. The instrument will measure carbon and water in these clouds and relate this to the birth and early evolution of stars and planets. HIFI will also look at planets and comets in our own Solar System.