Figure 10 - uploaded by Marcus G. F. Kirsch
Content may be subject to copyright.
Source publication
ESAs XMM-Newton space observatory is the flagship of European X-ray astronomy. After launch from Kourou, French Guiana on 10 December 1999, it is the most powerful X-ray telescope ever placed in orbit. The mission is solving many cosmic mysteries of the hot X-ray universe observing objects like neutron stars, black holes or active galaxies. The mis...
Context in source publication
Context 1
... Spacecraft Operations Manager at ESOC. "It's been a thrilling moment for our team. We even feared the spacecraft could be lost, but hard team work and a good star helped us turn this into a new success story for ESA." A more detailed failure investigation on what happened on-board could now be started. The design of the RF subsystem is shown in Fig. 10. Two coaxial transfer switches, which are of pulse latching type and operate in break- before-make mode, interconnect the RF harness between the transponders and the two omni-directional antennas located on opposite sides of the spacecraft. The signal attenuation observed in-orbit was consistent with the RF American Institute of ...
Citations
The AOCS of XMM-Newton was designed to use three reaction wheels (RW) with a fourth wheel in cold redundancy. The three wheels configuration has been used for more than 12 years for the momentum management, to re-orientate the S/C with slews in order to achieve the required science pointing. With 3 wheels, frequent reaction wheel unloading is used both to compensate the external torque and to re-orientate the angular momentum to allow the slew execution, which results in fuel consumption of around 6 Kg per year. A fourth wheel in control gives the advantage of a higher momentum envelope and introduces the null space in the wheels matrix, allowing a wheel speed variation without changing the total angular momentum. With four wheels the reaction wheel bias will compensate only for the accumulation of angular momentum due to the external torque, resulting in saving a significant amount of fuel and extending the mission lifetime. The use of all four RW implies the development of new attitude control algorithms and a software change on board which needs to be made in parallel to execution of the science mission. A design phase of this change has already started, and an initial test to check the functionality of the redundant wheel has already been successfully completed. A review of the safety failure detection criteria and thresholds will be needed. From operations point of view this is a major change, since the review of the nominal and contingency procedure will be needed, together with mission control system (MCS) changes. The Flight Dynamics System (FDS) as well needs to be adapted to the new four-wheel drive concept, with the new algorithm reflected in its system. At the end of the development of the algorithm and of the software patch, after the necessary changes on the MCS and on the FDS side, an end-to-end test campaign needs to be implemented. This paper describes the process and the challenge to implement and validate such a change.
