Published on January 22, 2008
MORE Requirements seen from ESA: MORE Requirements seen from ESA Pedro Pablos 1st MORE Team Meeting 27 Febrero 2007 Objectives of the RSE Requirements: Objectives of the RSE Requirements The RSE requirements are meant not only to define the experiment, but specially to define without ambiguity the responsibility of each party (instruments, spacecraft, ground segment) to allow for parallel work of each party to define performance in the less ambiguous way possible , such that it is possible to verify it by test, analysis or design before the launch of the satellite. Requirements for the instrument (MORE, ISA) are contained in the EIDB, requirements for the spacecraft (excluding the instrument) in the SRD. Requirements for the Ground Segment are included in the MIRD RSE Option: the RSE Ground Sement is not baselined in the ESA BC Ground Segment. All the previous RSE requirements are contained in the RSE Requirements Document in order to keep the big picture of RSE. Range and Range Rate Requirements: Range and Range Rate Requirements These requirements are defined independently for the three links, X/X, X/Ka and Ka/Ka. Each link is split in a contribution of the of the Ground Segment and the Space Segment to both range and range rate performance. The Space Segments contribution to the Ka/Ka link is further split between the instrument requirement (MORE) and the spacecraft requirement. The physical interface of MORE with the TT&C is still baselined to be a common Ka band HPA for MORE and the X/X/Ka DST of the spacecraft TT&C. A separated HPA integrated with MORE is an interesting alternative which would better decouple MORE and the TT&C subsystem. A major difficulty at this moment to split the requirements between the parties and allow for parallel work is the lack of definition of the RSE signal, in particular the ranging tones. It is expected to have a first input from MORE team on this item by June 2007. Range Requirements: Range Requirements Range requirements, specially in the Ka/Ka link, represent a breakthrough in performance, never achieved before by previous missions. The split of requirements in this situation is not without risk. Early practical demonstration of the feasibility of these requirements is a must. Range noise error requirements. The noise depends on the overall link budget. In this sense, preliminary link budget calculations have been performed by Astrium, but still the right signal and instrument bandwidths need to be provided by the MORE team. Range calibration errors (medium term). The calibration of the overall Ka/Ka link, beyond the MORE instrument itself, is still an open issue for the spacecraft: How are multiple reflections going to be taken into account? How is the influence of T variations going to be taken into account beyond the instrument? The previous problem becomes even more acute for the Ground Station, where the geometries (and probably the temperature variations) are much larger Ranging aging errors (long term). The trade-off between instrument ranging and onboard calibration (integrated in MORE) is planned to be completed before the end of 2007. ISA Acceleration Requirements (1): ISA Acceleration Requirements (1) Microvibrations out of the measurements band: the problem for the satellite is quite decouple from the ISA design. The approach should be to measure the disturbance of the moving elements and to calculate the transfer function to the ISA sensor heads. It still open how the transfer function of the satellite will be validated. Accelerations disturbance in the measurement band. In principle the requirement decouples quite well the ISA design and the MPO generated power spectral acceleration disturbance, however the requirement looks quite critical, specially at accelerations close to 0.1 Hz. A review might be necessary before PDR, when both the satellite and ISA designs are better known. It has been suggested by Astrium that it might be convenient to formulate the contribution of the accelerations disturbance due to the MPO COM uncertainty as an acceleration, instead of an acceleration power spectral density. ISA Acceleration Requirements (2): ISA Acceleration Requirements (2) The verification of the in band acceleration disturbance requires an algorithm/procedure to reduce the raw data of ISA by taking into account all the relevant spacecraft information (mainly AOCS, fuel and mechanisms HK and calibration manoeuvres information). The definition of this algorithm will require a close cooperation between Astrium and the ISA PI. The in orbit calibration manoeuvres play a crucial role in the final ISA performance. Their definition and feasibility demonstration on ground is essential for the verification of the ISA requirements. The ISA calibration manoeuvre in cruise and Mercury orbit phases need to be defined Astrium has suggested to use the electric propulsion during cruise, together with ranging (2 cm accuracy required!) for the ISA calibration. Feedback from PI is necessary. The ISA calibration during Mercury phase would need, according to Astrium, careful filtering/averaging of the electrical actuator and/or the ISA raw readings in order to determine the transducer factors removing any undesired effect. This process should be optimised together with the fuel estimation procedure. At least daily frequency is assumed. ISA Acceleration Requirements (3): ISA Acceleration Requirements (3) An MPO COM calibration manoeuvre has been outlined by Astrium following the recommendations in the ISA EIDB, which is compatible with the MPO constraints. Astrium proposes is a specific calibration manoeuvre every 44 days for the estimation of the fuel COM position by means of proprietary software Flow3D. Thermal requirements do seem to be fulfilled with ample margin according to latest simulations. Alignment requirements do not seem critical either.