NGGM ASSESSMENT STUDY Progress Meeting 1 TASI Torino

NGGM ASSESSMENT STUDY Progress Meeting 1 TAS-I, Torino, 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

Agenda – Day 1 Page 2 Day 1 - 27 -Jan-2010 14. 00 Introduction, agenda 14. 15 Task 5: Mission Architectures and Task 2: Observing techniques WP 2420 Mission Architectures DEOS [GIS] WP 2110 Observing Techniques DEOS [IAPG] WP 2120 Instrument Concepts TAS-I WP 2121 Measurement Technologies ONERA 17. 00 Discussion 17. 30 End NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

Agenda – Day 2 Page 3 Day 2 - 28 -Jan-2010 9. 00 Task 3: Mission analysis and attitude and orbit control concepts WP 2210 Mission Analysis DEIMOS WP 2220 Attitude and Orbit Control Concepts TAS-I 10. 30 Task 4: Simulation Tool WP 2310 End-to-END Simulator Design and Implementation TAS-I WP 2320 Variable Gravity Model DEOS [IAPG] WP 2330 Backward Module DEOS 12. 00 Task 5: Mission Architecture Outlines / Discussion and Conclusions WP 2410 Architecture Definition and Trade-Off TAS-I Discussion and Conclusions 13: 00 End NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

Page 4 WP 2120 Instrument Concepts (TAS-I) NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

Distance metrology for increased satellite separation Page 5 Top-level requirement for satellite-to-satellite distance d = 100 km (preferred distance resulting from the parametric analyses with the quick-look tool). The distance measurement relative error is maintained as for the 10 -km case: d/d = 5 10 -13 1/ Hz. The limit is set by the achievable laser frequency stability. NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

Distance metrology for increased satellite separation Page 6 Top-level requirement breakdown for satellite-to-satellite distance d = 100 km. Same relative weight of the various error terms maintained as for the 10 -km case. All requirements are relaxed by a factor 10, but less optical power is received by the sensors degraded distance, angle measurement performance. NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

Distance metrology for increased satellite separation Page 7 Optical power on the metrology sensors (computed with a laser source output = 0. 75 W) vs requirements. S 1 S 2 The original design of the laser interferometer and of the angle/lateral metrology on S 2 is still applicable to d = 100 km. For the S 1 orientation measurement relative to laser beam, a different concept has to be devised. NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

Distance metrology for increased satellite separation Page 8 Possible concepts for measuring the S 1 orientation relative to laser beam (S 1 -S 2 line), to be assessed. Concept 1: The position of S 2 is measured in the S 1 LORF by the GPS ( ’ 1). The orientation of S 1 is measured in the S 1 LORF by the STR ( ” 1) 1 = ’ 1 + ” 1. Concept 2: Utilization of a highresolution camera pointing in the direction of S 2 and equipped with CCD or APS detector (less optical power required, but higher sensitivity to straylight and background). Concept 3: Utilization of a quadrant photodiode (qpd) in the laser interferometer. Applicable only in case the BSM is removed (not impossible with 10 x NGGM relaxed requirements). Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

Acceleration measurement with increased sat separation Page 9 Top-level requirement for non-gravitational acceleration measurement kept unchanged at any satellite-to-satellite distance in the parametric analyses with the quick-look tool (noise floor = 10 -11 m/s 2/ Hz). A slight relaxation (1. 1 10 -11 m/s 2/ Hz) is however necessary for d = 100 km in order to relax the requirements on the S/C orientation knowledge relative to the S 1 -S 2 line to the same level of those derived for the distance measurement (1. 5 10 -6 rad/ Hz). Original top-level requirement NGGM Assessment Study 27 -28 January 2010 Relaxed top-level requirement INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

Acceleration measurement with increased sat separation Page 10 Top-level requirement breakdown for satellite-to-satellite distance d = 100 km. Alternatively, the top-level requirement can remain unchanged by slightly tightening the drag-free requirements. NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

Acceleration measurement with increased sat separation Page 11 Modifications of the current accelerometer layout will be implemented if: a) The analyses/simulations will proof the benefit of adding to the satellite-to-satellite tracking the measurement of one or more gravity gradient components. b) It is beneficial for the measurement of the linear and angular accelerations. NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

STR noise from GOCE in-flight results Page 12 Star-tracker noise from GOCE in-flight results. q In the frame of the study, a preliminary processing of GOCE star-tracker measurements has been performed to assess the actual noise spectral density. q As it will be seen, the low-frequency noise spectral density is higher than the high-frequency one. q The spectral densities have been estimated considering: q uncorrelated the error on each axis; q equal the power spectral density on X and Y axes (Z axis is the boresight). NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

STR noise from GOCE in-flight results Page 13 q The attitude error power spectral densities SXY and SZ have been estimated considering two sets of data: q STR 1 and STR 2 (172799 samples at 2 Hz); q STR 1 and STR 3 (79199 samples at 2 Hz). q SXY and SZ densities have been determined comparing the inertial attitude measured by each star-tracker, after removing the mean values of the relative attitude: i, j index of the star-tracker NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

STR noise from GOCE in-flight results Page 14 One-sided spectral density from star-tracker comparison STR 1 -STR 2 (Nov 3 rd, 2009) NGGM Assessment Study 27 -28 January 2010 STR 1 -STR 3 (Nov 10 th, 2009) INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

STR noise from GOCE in-flight results Page 15 q The results obtained considering the two sets of data are consistent. q The low-frequency noise spectral density is about 10 times greater than the high -frequency one. It is due to FOV errors like: q q q residual from focal plane calibration; uncertainty on star colour; residual from differential aberration compensation; S-shape; star-tracker thermo-elastic deformation. q Above errors become random bias for inertial pointing. If during the in-orbit movement the star-tracker images the same sky regions, they become harmonic errors. q For orbit plane GOCE like (about 16 orbit/day and 1 deg/day precession), the above errors may be considered as harmonic on time span of several orbit periods. q The correct noise shape shall be considered for attitude control design, postfacto attitude and angular rate reconstitution. NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

Page 16 WP 2210 Mission Analysis (DEIMOS) NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

Mission Analysis Page 17 Presentation Contents General Considerations about Repeating Orbits Repeat Cycle Temporal/Spatial Sampling Analysis tools: coverage matrix, gap evolution graph Low resonances avoidance NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

Mission Analysis Page 18 Repeating Orbits “M orbits in D days” The satellite flies M orbits Earth makes D revolutions w. r. t. the orbital plane But the line of nodes drifts: • Polar : no drift • Sun Synchronous • Other inclinations D revolutions = D sidereal days D revolutions = D days no precise correspondence I+N/D formulation M = I*D+N: number of orbits in 1 RC D: repeat cycle duration (in “days”) I+N/D: number of orbits per “day” N/D: useful for quick identification of sub-cycles NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

Mission Analysis Page 19 Repeating Orbits [250 km – 400 km] altitude range RC < 30 days Sun Synchronous NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

Mission Analysis Page 20 Repeating Orbits [250 km – 400 km] altitude range RC < 30 days Polar NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

Mission Analysis Page 21 Repeating Orbits [250 km – 400 km] altitude range RC < 30 days i = 62. 7° NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

Mission Analysis Page 22 Repeating Orbits Spatial Sampling After 1 day: I+N/D orbits Fundamental interval: S = 360°/(I+N/D) The lower the orbit, the thinner S Typical value at the Equator for alt = 300 km, S ≈ 2500 km After 1 repeat cycle: M = I*D+N orbits Sampling interval: Si = 360°/M = S/D The longer the RC, the thinner Si Typical value at the Equator for alt = 300 km, 30 -d RC, Si ≈ 80 km NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

Mission Analysis Page 23 Repeating Orbits Spatial/Temporal Sampling The coverage pattern depends on N/D ratio 2 representations: Coverage matrix • Day-by-day filling pattern of the fundamental interval • E. g. 15+16/17 Fundamental Interval NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

Mission Analysis Page 24 Repeating Orbits Spatial/Temporal Sampling The coverage pattern depends on N/D ratio 2 representations: Coverage matrix Gap evolution graph • Max/min gap at Equator after n days • E. g. 15+16/17 NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

Mission Analysis Page 25 Repeating Orbits Spatial/Temporal Sampling The coverage pattern depends on N/D ratio 2 representations: Coverage matrix Gap evolution graph When N = 1 or N = D-1 Drifting orbit Progressive filling Slow max. gap evolution E. g. 15+16/17 NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

Mission Analysis Page 26 Repeating Orbits Spatial/Temporal Sampling The coverage pattern depends on N/D ratio 2 representations: Coverage matrix Gap evolution graph Other cases Skipping orbit Possible sub-cycles E. g. 15+14/17 NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

Mission Analysis Page 27 Repeating Orbits Spatial/Temporal Sampling The coverage pattern depends on N/D ratio Sub-cycles N/D ≈ N’/D’ where D’<D E. g. 15+20/29 • 20/29 ≈ 9/13 ≈ 2/3 • 13 -day and 3 -day sub-cycles Sub-cycles allow combining Large RCs: fine sampling Homogeneous coverage after few days like with low RCs NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE Sub-cycles All rights reserved, 2010, Thales Alenia Space

Mission Analysis Page 28 Low RC Resonances Avoidance GRACE lesson learnt: M > 2 L where L is the maximum degree of L x L solution For L = 120, D must be greater than 15 Distance between ≤ 15 -day repeating orbits Drives the altitude control margin NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

Mission Analysis Page 29 Low RC Resonances Avoidance GRACE lesson learnt: M > 2 L where L is the maximum degree of L x L solution For L = 120, D must be greater than 15 Distance between ≤ 15 -day repeating orbits Drives the altitude control margin Example with all 29 -day repeating SSOs NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

Mission Analysis Page 30 Low RC Resonances Avoidance GRACE lesson learnt: M > 2 L where L is the maximum degree of L x L solution For L = 120, D must be greater than 15 Distance between ≤ 15 -day repeating orbits Drives the altitude control margin Example of preliminary candidate 15+4/5, polar • 11 -d orbit at -5 km • 14 -d orbit at +4 km • 29 -d orbit at +2 km • 26 -d orbit at -2 km NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

Page 31 WP 2220 Attitude and Orbit Control Concepts (TAS-I) NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

Activities since RRM Page 32 Performed and on-going activities since Requirements Review Meeting q Re-tuning of the drag-free control algorithms to take into account the antialiasing filter on accelerometer’s outputs. q Check on the possibility to extend the current control design for in-line formation (named also GRACE, trailing) with longer baseline. q Check on the feasibility to perform the laser beam pointing by satellite, instead of using the beam steering mechanism. q Update of the requirements for the accelerometer measurement noise profile. q Requirement specification for stochastic noise/error and harmonic noise/error. NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

Drag-free tuning update Page 33 Re-tuning of the drag-free control algorithms to take into account the antialiasing filter on accelerometer’s outputs. q This activities has been necessary since the previous drag-free control tuning has not taken into account of the anti-aliasing filter present on the DFAC channel of each accelerometer. q The anti-aliasing filter is the same considered for the DFAC channel present on the GOCE electrostatic gradiometer, i. e. 3 rd order Butterworth low-pass digital filter, 3. 5 Hz cutoff frequency. q The re-tuning has been done taking into account all the requirements, providing enough robustness toward plant uncertainty, and still improvement capabilities. q For now, the activity is considered closed. NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

Drag-free tuning update Page 34 Spectral density of the linear X-axis acceleration before tuning Damping too low! NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

Drag-free tuning update Page 35 Linear X-axis acceleration after tuning (drag-free, no FF) Good damping! NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

Extension to longer baseline Page 36 Check on the possibility to extend the current control design for in-line formation (named also GRACE, trailing) with longer baseline. q It has been verified that the actual formation flying control algorithms are able to manage in-line formation with longer baseline, by simple set-point update and re -tuning. q 100 km baseline has been checked. Results show the necessity to re-tune the control parameter to cope with the higher perturbation (gravity gradient acceleration). q The requirement R on the relative position shall be updated according to the baseline B since they come from the laser beam, i. e. R(B)=R(10 km)*B/10, B in km q The activity for the formation control re-tuning is in progress (for 100 km baseline). NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

Extension to longer baseline Page 37 Results from 100 km baseline without any re-tuning. To be reduced Earth gravity field has been limited to order 20 to speed up the simulation. NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

Laser beam pointing by satellite AOCS Page 38 Check on the feasibility to perform the laser beam pointing by satellite, instead of using the beam steering mechanism. q A laser beam pointing controller has been designed during previous study phases. It has been inserted mainly to overcome the reaction-wheel mechanical noise effects on laser beam pointing stability. q The attitude control shall constrain the angular accelerations and the angular rates to be very stable (< 10 -8 rad/s²/ Hz and < 10 -6 rad/s/ Hz respectively in [0. 001, 0. 01]Hz band). The coupling of angular acceleration and the angular rate with the accelerometer displacement from the satellite COM, produces a linear acceleration which contributes to the measurement error of the nongravitational accelerations of the satellite COM. q Above requirements impact on the attitude control closed loop and on the reference attitude trajectory to be tracked. NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

Laser beam pointing by satellite AOCS Page 39 q Is the tracking of S 2 by S 1 compatible with the angular accelerations/angular rate/attitude requirements? q The answer has been provided according to the following steps: q derivation of the real driver requirement starting from the provided angular requirements. This is necessary because the angular requirements have been derived without taking into account the kinematics constraint. q comparison of driver requirement with what it is induced by relative satellite movement (across-track and radial). q The tracking of S 2 induces on S 1 an angular jitter reduced by a factor equal to the baseline. S 2 attitude jitter does not have any impact. S 1 disturbing torque (environment, thrusters, etc. ) shall be reduced to the level of laser pointing stability requirement. NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

Laser beam pointing by satellite AOCS Page 40 Driver requirement for attitude control on YZ axes (requirement for S 2) q For frequency higher than 5 m. Hz, the driver requirement is the angular acceleration. For frequency below 5 m. Hz, the driver requirement is the attitude requirement. NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

Laser beam pointing by satellite AOCS Page 41 Requirement for attitude control on YZ axes (requirement for S 1) NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

Laser beam pointing by satellite AOCS Page 42 q From above analysis it is possible to observe: q the effect of satellite relative movement (S 2 -S 1) is negligible with respect to the attitude jitter naturally induced by environment; q the requirement on S 1 attitude error due to the laser pointing stability is more stringent (black bold line) than the requirement on attitude error due to LORF tracking (black line). q At the end, it is possible to conclude that the tracking of S 2 by S 1 is compatible with the angular accelerations/angular rate/attitude requirements of LORF tracking. q Impacts on thruster’s maximum force and force slew-rate is expected due to higher control bandwidth and lower noise level. The work is in progress. NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

Accelerometer noise requirement Page 43 Preliminary definition of the accelerometer noise profile requirement for DFAC channel. q The preliminary acceleration configuration is q In principle, two output channels may be considered for each accelerometer (as for GOCE): a) science channel and b) DFAC channel (considered below). q Linear accelerations are directly measured by accelerometers. q X and Z axes angular accelerations are measured as differences of linear accelerations (Z and X respectively) and scaled by accelerometers distance (L=0. 1835 m). q Y axis angular acceleration is provided directly by two accelerometers. NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

Accelerometer noise requirement Page 44 q Requirement on linear axes is < 10 -8 m/s^2/ Hz. Considering preliminarily the control engineer rule of thumb, the measurement noise spectral density shall be < 10 -9 m/s^2/ Hz. q From the following figures, the angular acceleration noise shall be <10 -10 rad/s^2/ Hz on Y and Z axes, and 10 -9 rad/s^2/ Hz on X axis. NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

Accelerometer noise requirement Page 45 Taking into account the following composition rules: the following constraints result (angular acceleration requirements drive the results): The same consideration for accelerometers on S 2 (indices 3 and 4). NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

Accelerometer noise requirement Page 46 DFAC channel – Requirement on the accelerometer noise. q The noise spectral density for frequency lower than 1 m. Hz is very important for accelerometer/star-tracker data fusion (real-time and post-facto). NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

Requirements on harmonics errors Page 47 Definition of requirements for harmonic errors q As addressed in previous slides, there are errors that may not be considered as the results of a stochastic random process. Those errors are better described as harmonic components. q It seems that requirements shall be provided for two classes of errors. q What do the scientists think about such topic? NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

Reply to ESA comments on TN 2 Page 48 Reply to ESA comments on TAS-I TN 2 “SYSTEM DRIVERS” , concerning FF and AOCS. q ESA Q 2) Pag. 25 – Section 3. 3. 7. 3 “If the beam pointing device is removed…” & Pag. 42 ESA comment/question: Let’s not forget that we have introduced and tested the Beam Steering Mechanism in order to eventually compensate the HF noise of the RWs. This brings an additional argument in removing it now, but of course not in the relaxations of the requirements (to be verified along the NGGM study). q TAS-I reply: at the distance of 10 km, the requirement remains the same. NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

Reply to ESA comments on TN 2 Page 49 q ESA Q 3) Table 3. 3. 4 “Telemetry generation rate” – “ 3 linear + 3 angular accelerations per accelerometer” ESA comment/question: From each accelerometer is intended to have 6 measurements? q TAS-I reply: It should be better to provide different requirement for accelerometers’ scientific channel, DFAC channel and housekeeping. q Scientific channel: 8 electrodes voltages + validity data @1 Hz q DFAC channel: 3 linear + 1 angular accelerations + validity data @10 Hz. q Housekeeping: TBD. The estimate will be updated taking into account the GOCE EGG data. NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

Reply to ESA comments on TN 2 Page 50 q ESA Q 5) Pag 43 “. . the formation control must operate below the science BW of 1 m. Hz” ESA comment/question: This is very interesting, as proposed at the beginning of the last TAS study. In principle It can lead to a better performance and convergence of the formation controller w. r. t. the steps chosen in the last versions (from every 0. 1 s to 40 s roughly) q TAS-I reply: the above sentence shall be considered as for the control bandwidth, not for the sampling frequency. It is necessary to take into account that the lines due to sampling frequency are present at frequency 2 fs, 3 fs, 4 fs, etc. NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

Page 51 WP 2310 End-to-END Simulator Design and Implementation (TAS-I) NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

E 2 E Forward Simulator Ready Work in progress To be developed/performed Page 52 Forward Simulator Implementation Current Status Review of the Simulator architecture Adaptation of the Forward Simulator frame for the inclusion of the time variable Earth gravity field coefficients Adaptation of the Forward Simulator frame for the generation of the data files input to the Backward Simulator Interface towards the Backward Simulator Exchanged data identification and required time resolution Data anti aliasing filtering and generation of the output files as input to the Backward Simulator Tests on the generated data quality and investigation on the computational numerical error Time variable gravity field Inclusion of the time variable coefficients to be added to the EGM 96 static field Testing of the time variable gravity field behaviour Drag free, Attitude&Formation Control Optimization of the control algorithms for the satellite in-line configuration (10 km) NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

E 2 E Forward Simulator Page 53 Forward Simulator Next Steps Assessment, from the first test runs, of the simulation time needed for generating the output files to the Backward Simulator for the required mission time span. Evaluation if the run needs to be split into two or more CPUs Inclusion of the gravity gradient effects on the accelerometers test masses. Preparation of the environments for running the stated four classes of mission (satellite configuration, orbit, control etc. ). NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

Page 54 WP 2410 Architecture Definition and Trade -Off (TAS-I) NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

Analysis plan Page 55 Proposed approach: staggered sequence of Parametric studies by quick-look tool (5 wks) Selection of reference case to be subjected to numerical analysis (1 wk) Numerical studies by E 2 E simulators (5 wks) 4 study cases 1. 2. 3. 4. Grace-like in-line formation Dual Grace-like Pendulum Lisa, cartwheel 1. Non in-line formations will be addressed by E 2 E from May on Some time needed to adapt software NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

Analysis plan Page 56 NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

From PM 1 to PM 2 Page 57 1. Define parameters of reference Grace-like case Orbit: currently 79/5 polar repeat, 312 km altitude Inclination? Higher altitude? Longer cycle? (pseudo)subcycles? Intersat distance: 100 km (upper limit) Simulation duration: 1 month TBC SST measurement relative accuracy: as defined Non-grav acceleration measurement accuracy: “pessimistic” case 2. Perform numerical analysis 3. Define for sensitivity analysis range of variation of parameters of dual-Grace case 4. Begin study of pendulum formations NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space

Dual Grace-like orbit options Page 58 Bender Pair 1: 79/5, 312 km, polar Pair 2: 360/22. 7, 312 km, 62. 7 Wiese and Nerem, AGU-09 15 -day repeat considered as the most promising NGGM requirements Establish coverage requirements (simply periodic, periodic with subcycles, periodic with pseudo-subcycles. . . ) Establish optimal repeat period of (near)polar orbit Establish altitude limits for 5(10)yr orbit maintenance Effect of different altitudes during mission on science performance? . . . NGGM Assessment Study 27 -28 January 2010 INTERNAL THALES ALENIA SPACE COMMERCIAL IN CONFIDENCE All rights reserved, 2010, Thales Alenia Space