General architecture of ECLAIRs µsatellite

Transcription

1 General architecture of ECLAIRs µsatellite V. CIPOLLA, M. BERGER, P. LIER, M. BACH Centre National d Etudes Spatiales 18 av. Edouard Belin Toulouse France

2 Scientific objectives Mission overview Payload description Satellite description Satellite performances Conclusion Planning of presentation XX th Annual AIAA/USU Conference on Small Satellite, Logan, 15th August

3 Scientific objective ECLAIRs is a space mission in universe science. Development in A phase (Feasabilty study) launch The aim of the mission is to detect, to localise, to alert in real time and to observe Gamma Ray Burst (GRB). Gamma ray burst are very heterogeneous phenomena : Duration : from few thousandths to several hundreds of seconds Time history : there are no typical profile Energy band : from visible to hard γ-ray Space distribution : randomly in space Two main families : Short GRB : High energy, short duration Long GRB : Low energy, long duration Number of GRB Duration (s) XX th Annual AIAA/USU Conference on Small Satellite, Logan, 15th August

4 Gamma Ray Burst origin «Fireball» model is most probable Prompt emission Due to internal shock Mainly in γ, X and visible bands High energy physic To understand the origin of GRB Afterglow emission Prompt emission Afterglow emission Due to external shock Mainly in X, visible, and IR bands Cosmolgy Measurement of Redshift, birth of stars XXth Annual AIAA/USU Conference on Small Satellite, Logan, 15th August

5 ECLAIRs mission main scientific requirement To detect more than 200 GRB of any type (i.e. either short and long) To observe these GRB before during and after the detection in the band (1-300 kev) For 100 % of detections to localise the GRB with a precision better of 2.9 mrad in less than 10 s. For 50 % of detections to localise the GRB with a precision better of 290 µrad in less than 10 s. For 100% od detections to transmit to the ground the coordinate of GRB in less then 60 s. For 20% of detections to localise the GRB with a precision better then 5 µrad and to estimate the redshift in less than 300 s. For 75 % of cases to allows to 8m class ground telescopes the observation of the afterglow emission. XX th Annual AIAA/USU Conference on Small Satellite, Logan, 15th August

6 ECLAIRs system overview Space segment 1 Microsatellite of Myrade family To detect, localize and alert in real time the occurrency of GRM Soil segment A dedicated robotic telescopes network (to be developed for the mission) Use of Very Large Telescope (like Canary island, Hawaii, Chili) To observe afterglow emission in visible and IR Ground Segment Real time alert network base on VHF network of HETE2 mission X-Band station for scientific TM S-Band station for housekeeping XX th Annual AIAA/USU Conference on Small Satellite, Logan, 15th August

7 ECLAIRs orbit and attitude Orbital Strategy To keep the satellite inside Earth magnetic field protection belt (h<1000 km) To minimize South Atlantic Anomaly influence (i <20 ) To find a opportunity of launch on piggy back Nominal Orbit h=870 Km & i=20 (use of propulsion to lower the altitude) Attitude Strategy Inertial point to avoid trail of images Antisolar pointing + Availability of Earth Telescope + Favourable thermal environment - Earth occultation (33% of time) SUN Earth Large Telescope XX th Annual AIAA/USU Conference on Small Satellite, Logan, 15th August

8 ECLAIRs main constraints for satellite architecture Mission constraint Low altitude and inclination orbit Few launches avaibles Megha-Tropiques launch by PSLV is the only identified opportunity Inertial and antisolar pointing ±Z walls favourable for thermal control of PL 2 SST to avoid no-blinding operation at each change of season Payload constraint Heavy and big instrument standard payload specification are overeach Many antennas to accomodate impact on accomodation under fairing Plateform constraint To use the same functional chain (equipment, sub-system architecture) Standard Myriade AOCS is not optimize for low inclination orbit To limit the modification of the structure to the minimum Satellite mass up to 150 kg to increase the strength of the structure XX th Annual AIAA/USU Conference on Small Satellite, Logan, 15th August

9 ECLAIRs payload overview CXG (developped by CEA) 6400 CdTe hybrid detector Energy band [4-300] kev m 48 Kg / 51.3 W SXC (developped by MIT - HETE) 4 1k 1k pixel Si CCID detectors Energy band [1-15] kev 4.5 Kg / 4.5 W Mask and Shilding SXC Complementary payload CXG Detection plane with electronics and thermal X-Band High rate TM VHF allert subsystem PL data handling unit and scientific treatment unit XXth Annual AIAA/USU Conference on Small Satellite, Logan, 15th August

10 Payload accomodation CXG radiator oriented toward ±Z to reduce thermal gradient on detection plane CXG electronic radiator toward +Y (separated Thermal control) SXC accommodated on CXG To guarantee the same FoV To reduce Thermoelastic bias respect CXG SST on payload deck To simplify the thermal control To reduce the bias respect SXC Payload electronic equipment outside the PF To make indipendent PF AIT from PL AIT X Z Y XX th Annual AIAA/USU Conference on Small Satellite, Logan, 15th August

11 Laucher compatibility Main constraint of mechanical and thermal architecture PSLV requirement for auxiliary payload Volume < mm Mass < 120 Kg (150 Kg could be acceptable) Centering : X CoG < 450 mm & Y CoG, Z CoG < ± 5 mm ECLAIRs dimensions overpass the allocated volume Along X : mm (600 mm due to CXG) Along Y : mm (117.4 mm due to SA) Along Z : mm ( mm without VHF antennas) Several configurations have been studied internally at CNES in order to submit the best one to laucher analysis and reduce the number of iteraction with ISRO XX th Annual AIAA/USU Conference on Small Satellite, Logan, 15th August

12 Laucher compatibility Modification of CXG mask geometry to reduce the encrouchement with the fairing Introduction of a Misalignment, Loss of 1 of FoV acceptable for CEA Minimum Margins SA Pyro - Tank PS4 : VHF Antenna fairing : 3.4 mm 6.25 mm Maximum encroachment of 20 mm : acceptable for ISRO XXth Annual AIAA/USU Conference on Small Satellite, Logan, 15th August

13 Antenna accomodation VHF 2 linear antennas at 180 FoV : 2π steradiants On ±Z walls no realease mechanism is needed S-Band 2 helicoidally antennas at 180 (µriade product line) FoV : 2π steradiants On ±Z supports no interefence with SST X-Band 1 antenne patch (µriade product line) FoV : cone of 140 On +Y wall no interefence with PL X Z Y S-Band VHF X-Band XX th Annual AIAA/USU Conference on Small Satellite, Logan, 15th August

14 Plateform accomodation principle Structure 5 Al sandwiches (1 for payload) equipment support 1 Al machined pannel launcher I/F et propulsion Equipment Accomodation has been optimized Same equipment of µriade No SADM is needed due to antisolar attitude Use of Pyrosoft pyronuts no bolt catcher Use of bigger wheels (1 Nms) AOCS requirement Use of higher torque MBT AOCS requirement Modification on propulsion subsystem accommodation of higher volume vessel allows to orbit down to 650 km. Changing on piping end location XX th Annual AIAA/USU Conference on Small Satellite, Logan, 15th August

15 Plateform internal accomodation +Y wall -Y wall MTB Pyro TMHD OBC Battery Wheel 1 Nms waveguide +Z wall Gyro -Z wall e SST PCDU e VHF MTB XXth Annual AIAA/USU Conference on Small Satellite, Logan, 15th August 2006 Wheel 1 Nms Wheel 0.12 Nms Tx/Rx 15

16 MCI budget Mechanical performances Satellite mass : Kg 150 kg ISRO commitment PF Kg based on µriade existing equipment PL Kg CXG mass of 48 Kg (to survey), increase due to a bigger PL panel Centering X COG = mm PSLV specification for auxiliary PL <450 mm Y COG = mm PSLV specification for auxiliary PL <5 mm Z COG = mm PSLV specification for auxiliary PL <5 mm Inertia Stiffness High value in deployed configuration (I ZZ CoG = Kg m²) Frequncies estimation based on previous µriade satellite results Lateral ƒ > 35 Hz PSLV specification for auxiliary PL >45 Hz very hard to fullfill Logitudinal ƒ > Hz XX th Annual AIAA/USU Conference on Small Satellite, Logan, 15th August

17 Thermal performances Orbit hypothesis for the study worst case scenario Altitude of 680 km Inclination 20 -X pointed toward sun Long term stability Very good due to antisolar pointing 4 faces (+X, +Y, ±Z) are very stable and cold; for exemple for ±Z : Heat flux : 71/47 W/m² T sink : 72 /-92 C Short term stability Very high variability of Earth thermal flux; for ±Z : 10/170 W/m² Difficult to guarantee to the PL a better stability than the natural one XX th Annual AIAA/USU Conference on Small Satellite, Logan, 15th August

18 Real time allert performance Telemetry balance efficiency analysis has been performed usign a satellite computed radiation diagram Need to extend the original HETE VHF network from 16 to 30 stations to cover 20 inclination orbit The probability of transmit the alert in less than 60 seconds is % Alternative solutions to VHF have been evaluated (Inmarsat, Orbcom, TDRSS) but present higher cost or worst performances 6,00 4,00 2,00 0,00-180,00-90,00 0,00 90,00 180,00-2,00-4,00-6,00-8,00-10,00-12,00 Theta [º] Phi [º]: 0,00 30,00 60,00 90,00 120,00 150,00 Théorie XX th Annual AIAA/USU Conference on Small Satellite, Logan, 15th August

19 AOCS performances Orbit hypothesis for the study worst case scenario Altitude of 680 km Inclination 20 observabilty and comandability are difficult due to direction of magnetic field Pointing requirement -X face pointed toward sun Precision : 1 (3σ) Stability : 0.1 /s Conclusion Need to increase the actuators forces (Wheels of 1 Nms, MBT of 20 Am²) No changing in existing main modes of AOCS Suppression of one existing mode XX th Annual AIAA/USU Conference on Small Satellite, Logan, 15th August

20 CONCLUSION Phase A reviews held in beginning of 2006 (Un)feasabilty of the mission on µriade has (not) been demonstraded Laucher discussion drive to positive conclusion need to be continued AOCS feasability has been demonstraded Some hard points have been detected Risk of increasing of CXG mass Risk of collision during satellite/launcher release Frequencies of lateral mode of satellite are too low Instrument thigh short term thermal stability could not be reached Mission has been judged very interesting Will to extend the mission (additional instrument) New A phase under study on a bigger plateform is running XX th Annual AIAA/USU Conference on Small Satellite, Logan, 15th August