Ref.:HASI-RP-UPD-106 Issue 1 Rev.1 Date: 21 April 2006 HASI ACC Data Processing and Calibration Report Institute NAME SIGNATURE DATE Prepared by UPD/CISAS P. Lion, F. Ferri 31/01/2005 Revised by UPD/CISAS F. Ferri, G. Colombatti 21/04/2006 Approved by OU-PSSRI Table of Contents 1. Acronyms 3 2. Scope of the document 3 3. Applicable and Reference Documents 3 4. ACC description 4 4.1. ACC location and accommodation 5 4.2. Measurement principle and data sampling 7 4.3. Operational modes 7 4.4. Telemetry output 8 5. Pre-flight calibration 9 5.1. Static calibration 9 5.2. Dynamic calibration 9 6. In-flight Calibration 9 7. Post Flight calibration 11 8. ACC total error budget 11 9. ACC data processing: Engineering value reconstruction 11 9.1. Raw values extraction 13 9.1.1. XServo acceleration raw data extraction 13 9.1.2. Piezo accelerometers raw data extraction 13 9.1.3. XServo and Piezo temperature raw data extraction 13 9.1.4. XServo and Piezo statistical raw data extraction 13 9.1.5. Piezo impact trace acceleration raw data extraction 14 9.2. Raw values normalisation 14 9.2.1. XServo acceleration normalisation 14 9.2.2. Piezo acceleration normalisation 14 9.2.3. Xservo and Piezo temperature normalisation 14 9.2.4. XServo and Piezo statistical data normalisation 14 9.2.5. Piezo impact trace acceleration normalisation 14 9.3. Engineering conversion 14 10. Scientific conversion of engineering values 14 10.1. Xservo acceleration conversion 15 10.2. Piezo acceleration conversions 15 10.3. Xservo and Piezo Temperature conversions 15 10.4. Xservo and Piezo statistical data conversions 15 11. Higher level products derivation 15 12. Appendixes 16 12.1. Appendix A: ACC XServo Calibration Data 16 12.2. Appendix B: ACC Piezo Calibration Data 16 12.3. Appendix C: Huygens Probe auxiliary data 18 1. Acronyms ACC Accelerometer Subsystem COG Center of Gravity DDB Data Distribution Broadcast Piezo, PZR ACC piezoresistive accelerometer S/W Software Temp1 temperature sensor of XServo Temp2 temperature sensor of Piezos XServo ACC Servo accelerometer 2. Scope of the document Scope of the document is to report on the procedure and results of the calibration of the HASI ACC Sensors and to present guidelines for the data process and the reconstruction of the acceleration measurement. 3. Applicable and Reference documents [AD1] Cassini Mission Huygens Probe Huygens Atmospheric Structure Instrument - HASI Accelerometer subsystem Flight Model Acceptance Data Package (ACC FM ADP) PY- HASI-UKC-AD-003 (II/209.B.6) [AD2] HASI Experiment Flight User Manual Document HASI-MA-OG-002 Issue 3, 1 December 1998 (II/196.B.6) [AD3] HASI DPU Software User Requirements Document HASI-SP-OG-004, Issue 7, 7 Sep 1995 (II/179.B.1) [AD4] HASI Accelerometer Subsystem Conversion Relations - Flight Model (ACC-3), HASI- ACC-FM-EQ-1.0 (II/239.B.6) [AD5] HASI DPU subsystem Proto- Flight Model Summary Report HASI-RP-OG-047 Issue 1 04/06/96 (II/188.C.4) [RD1] Zarnecki, J.C., F. Ferri, B. Hathi, M.R. Leese, A.J. Ball, G. Colombatti, M. Fulchignoni,. In-Flight Performance of the HASI Accelerometer and Implications For Results at Titan, Proceedings of International Workshop 'Planetary Probe Atmospheric Entry and Descent Trajectory Analysis and Science', October 6 - 9, 2003 Lisbon, Portugal, ESA-SP-544, February 2004. [AD6] Huygens Probe Data for post flight analysis HUY-ASP-MIS-TN-0006 Issue 1, 3 June 2005 4. ACC description The Accelerometer subsystem (ACC) is placed at the centre of mass of the descent module of the Probe. It consists of one highly sensitive single axis accelerometer (Xservo)) and three piezoresistive accelometer (X, Y, Z piezo), their conditioning electronics and two temperature sensors (Temp1 and Temp2) used for thermal compensation. The Xservo accelerometer output is amplified providing two channels (HIGH and LOW Gain). Each channel has a switchable range (HIGH and LOW Resolution) prior saturation or anyhow after Tdata (T0+10s)). Xservo channel selection is performed autonomously by checking the measured value against a settable threshold. Table 1. ACC Characteristics and Performance. ---------------------------------------------------------------------------- X-axis servo accelerometer (along Probe path) High resolution setting Range: 2-20 mg Resolution: 1-10 _g Low resolution setting Range: 1.85-18.5 g Resolution: 0.9-9 mg Relative accuracy: 1 % of full scale X/Y/Z-axis piezoresistive accelerometers Range: +- 20 g Resolution: +- 15 mg ---------------------------------------------------------------------------- Fig 1 Fig. 1 ACC subsystem as accommodate on the Huygens experiment platform 4.1. ACC location and accommodation ACC is placed as close as possible to the center of gravity (CoG) of the Huygens entry module (seismic mass of the XServo should be within a sphere of 3 mm-radius [AD2]). The ACC box is attached to Huygens' experiment platform with four cap head bolts. Its footprint, for mounting purposes, is a 60x80 mm rectangle centred on, and orthogonal, to Huygens' X-axis.The XServo accelerometer is aligned with the Probe X axis. The three piezoresistive accelerometers are sensitive to the acceleration in one of the X/Y/Z-Probe's axes. ZPiezo accelerometer axis is antiparallel to the Huygens Z axis. Location of ACC sensors wrt Huygens entry Probe CoG: ACC box CoG wrt ACC reference hole [AD1] and as reported in HASI IDS for ACC XACC=32 +/- 1 mm YACC=27 +/- 1 mm ZACC=-33.5 +/- 1 mm Position of sensor wrt ACC reference hole [AD1] X' Y' Z' [mm] XServo seismic mass centroid 15.64 23.5 -33.5 XPZR seismic mass centroid 15.5 36.54 -46.54 YPZR seismic mass centroid 15.7 9.19 -47.81 ZPZR seismic mass centroid 15.7 9.19 -19.19 as reported in the ACC Interface Data Sheet (drawing PY-HASI-UKC-D/AS0039) Note: ACC as close as possible to Probe CoG in entry phase configuration. XServo seismic mass should be within a 3 mm sphere radius [AD2]. Offsets/displacements between ACC XServo seismic mass and Probe CoG (in entry configuration) should be known with an accuracy better than 10% (e.g. 0.3 mm on a 3 mm offset) also in Y and Z axes to better characterize the Probe oscillations [AD2]. Probe Mass and CoG evolution [RD2] Event Mass (kg) Mass without MLI(kg) CoG position (mm) X Y Z begin Entry 318,62 318,62 75,44 1,75 5,38 end Entry 309,72 305,522 82,54 2,48 5,13 Main+Front shield 287,6 285,66 65,19 2,64 5,46 Main-Front shield 206,91 206,91 81,33 3,67 1,17 Stabiliser parachute 201,51 71,83 -0,52 3,68 without Stabiliser parachute 200,48 69,22 -1,46 5,46 Position of ACC reference hole wrt Probe axes (Probe absolute reference) X=53,8 mm Y=-7,1 mm Z=40,3 mm [as from table in Aerospatiale drawing "Experiment platform layout" 6/01/94] ACC sensors Offset/displacement from Probe CoG (in [mm]) XServo X Y Z mission time begin Entry -6 14,65 1,42 preT0 end entry -13,1 13,92 1,67 T0 Main+Front shield 4,25 13,76 1,34 T0+2.5s Main-Front shield -11,89 12,73 5,63 T0+32.5s Drogue+Drogue -2,39 16,92 3,12 T0+900s descent module 0,22 17,86 1,34 N/A XPiezo X Y Z mission time begin Entry -6,14 27,69 -11,62 preT0 end entry -13,24 26,96 -11,37 T0 Main+Front shield 4,11 26,8 -11,7 T0+2.5s Main-Front shield -12,03 25,77 -7,41 T0+32.5s Drogue+Drogue -2,53 29,96 -9,92 T0+900s descent module 0,08 30,9 -11,7 N/A YPiezo X Y Z mission time begin Entry -5,94 0,34 -12,89 preT0 end entry -13,04 -0,39 -12,64 T0 Main+Front shield 4,31 -0,55 -12,97 T0+2.5s Main-Front shield -11,83 -1,58 -8,68 T0+32.5s Drogue+Drogue -2,33 2,61 -11,19 T0+900s descent module 0,28 3,55 -12,97 N/A ZPiezo X Y Z mission time begin Entry -5,94 0,34 15,73 preT0 end entry -13,04 -0,39 15,98 T0 Main+Front shield 4,31 -0,55 15,65 T0+2.5s Main-Front shield -11,83 -1,58 19,94 T0+32.5s Drogue+Drogue -2,33 2,61 17,43 T0+900s descent module 0,28 3,55 15,65 N/A P.S. Requirement to have ACC XServo seismic mass within a 3 mm sphere centred in Probe CoG seems to not be respected. The two ACC temperature sensors are fixed one inside the servo accelerometer case (Temp 1) and one attached to the aluminium alloy accelerometer mounting block (Temp 2). 4.2. Measurement principle and data sampling The servo accelerometer (Sundstrand QA-2000-030) senses the displacement of a seismic mass and drives it back to a null position. The required current is a direct measurement of the acceleration. The X-axis servo accelerometer's output is conditioned and amplified by two non-inverting amplifiers, one with a gain of 1 and the other with 10. They provide the two X-axis servo channel outputs. Besides these two channels, the servo's range is switchable between high resolution and low resolution ranges, achieved by switching the output of the servo accelerometer (a current) between two load resistors by using a single analogue switch. The piezoresistive accelerometer (ENDEVCO 7264A-2000T) consists of a suspended silicon seismic mass supported by two strain-dependent resistances. The accelerometer is incorporated in a Wheatstone bridge; a small output voltage dependent on acceleration is produced when an external voltage is applied. Temperature is measured by an AD 590 sensor included in the servo package. Temperature variations are measured by an AD 590 sensors (Temp1 and Temp2), respectively monitoring XServo and Piezos temperature for compensation. ACC has in total 7 channels, each channel is sampled at 400 Hz. The data are processed with a lower rate by extracting one every 'n' samples. The ACC channels and their sampling rate: - Xservo LOW gain at 100 Hz - Xservo HIGH gain at 100 Hz - Xpiezo at 50 Hz - Ypiezo at 50 Hz - Zpiezo at 50 Hz - Temp 1 (Tservo) at 1.5625 Hz - Temp 2 (Tpiezo) at 1.5625 Hz Values are arithmetically averaged by the HASI onboard S/W to produce lower sampling rates.For acceleration there are two types of data: 'raw' and statistic data. Statistic data are obtaining by integrating over a statistic time period (0.1 Hz) taking one sample every 32 from the 400 Hz samples. 4.3. Operational modes HASI starts to sample ACC sensors during entry at TACC= -0:21:30 preT0 (DDB time,since probe ON). ACC data are stored in a telemetry queue for later transmission, till when the Probe relay link is set (TdataH=T0+0:02:30). ACC data are continuously sampled and transmitted till impact detection state. IMPACT state devoted to Probe impact detection and starts at 1 km latitude (triggered by DDB information). No ACC data transmitted until SURFACE state. During this state the 400 Hz XServo low gain values are quadratic filtered to compare to a threshold value in order to detect the impact (threshold value in HASI S/W set to 2.3 V corresponding to _3.99 g= 39 m/s2).The impact trace is constructed from the 200Hz Piezos data corresponding to a period of .5 s before impact and 5.5 s after detection. ACC channels readouts are summed in order to get the following sampling rate: ACC Xservo 3.125 Hz in ENTRY; from Tacc till T0+10 s 4.167 Hz till T0+32 min (=Tradar) DESCENT 1&2 states 1.754 Hz till last km (~132 min) Impact detection DESCENT 3& SURFACE state ACC X, Y, Z piezo 1.6129 Hz in ENTRY and last km and in Surface state Statistics 0.1 Hz always, except in impact detection ACC Servo & piezo Temperature 0.097 Hz always, except in impact detection Impact trace (0.5 s before & 5.5 s after impact) X piezo 200 Hz Y piezo 200 Hz transmitted after Timpact Z piezo 200 Hz p.s. NO ACC data are transmitted during impact phase 4.4. Telemetry output ACC telemetry data are organized in telemetry (TM) packets per sensor, mode and data type: Data Format Content format name #32 ACC XServo ENTRY (3.125 Hz) sum of 32 samples at 100 Hz ENTRY #33 ACC XServo DESCENT (4.167 Hz) sum of 24 samples at 100 Hz DESCENT1&2 #34 ACC XServo RADAR (1.754 Hz) sum of 57 samples at 100 Hz DESCENT3 & SURFACE #35 ACC X Piezo (1.6129 Hz) sum of 31 samples at 50 Hz only in ENTRY #36 ACC Y Piezo (1.6129 Hz) sum of 31 samples at 50 Hz only in ENTRY #37 ACC Z Piezo (1.6129 Hz) sum of 31 samples at 50 Hz only in ENTRY #38 ACC XServo T(Temp1)(0.098 Hz) sum of 16 samples;always except in IMPACT #39 ACC Piezo T (Temp2) (0.098 Hz) sum of 16 samples; always except in IMPACT #40 ACC XServo Statistics (0.1 Hz) sum of 128 samples @ 12.5 Hz, except in IMPACT #41 ACC XPiezo Statistics (0.1 Hz) sum of 128 samples @ 12.5 Hz, except in IMPACT #42 ACC YPiezo Statistics (0.1 Hz) sum of 128 samples @ 12.5 Hz, except in IMPACT #43 ACC ZPiezo Statistics (0.1 Hz) sum of 128 samples @ 12.5 Hz, except in IMPACT #48 ACC X Piezo impact trace 200 Hz impact trace data of X Piezo #49 ACC Y Piezo impact trace 200 Hz impact trace data of Y Piezo #50 ACC Z Piezo impact trace 200 Hz impact trace data of Z Piezo Each TM packet is time stamped with mission time (=DDB time) when the first data is written in Time relevant to each data value is derived from the packet time stamp and the ACC sampling rate of the relevant data format. 5. Pre-flight calibration 5.1. Static calibration For ACC sensor data sheet and calibration data refer to ANNEX 1 and ANNEX 2. At subsystem level: _ ACC calibration at +/- 1 g by rotation of 180 deg performed at UKC (ref. PY-HASI-UKC-FMQFS-036 15/05/1995 contained into HASI ACC FM APD PY-HASI-UKC-AD-003, II/209.B.6) 5.2. Dynamic calibration Tests performed at subsystem level and system level at ground (AIV-AIT): At subsystem level: _ ACC PZR calibration by pendulum motion UKC (ref to M. Patel's Master Thesis HASI_ACC_Manish_MPhysproject.pdf) _ Impact tests UKC _ ACC displacement tests at UPD At System level: _ HASI ACC FM Special Test (SET) rotating the Probe dolly - DASA 1/08/1995 (HASI-RP-OG-034 II/169.B.6) - DASA 31/10/1996 rotation around Z-axis only during DPU reintegration - DASA 3-4/03/1997 after ACC box moved closer to Probe CoG (HASI-RP-UPD-?) 6. In-flight Calibration During the cruise phase HASI experiment and the Huygens probe have been switched on regularly for performing in-flight CheckOut (CO). These COs have been performed approximately every 6 months since launch, to test the probe and its subsystems during simulated entry, descent and surface proximity phases and also to upload S/W patches. These in-flight checkouts were useful for checking the ACC performance and monitoring any drift in the accelerometer outputs due to ageing or any degradation. Specifically in-flight data have been used in order to monitor the offset at zero g of the ACC sensor and estimate the long-term stability in the zero offset [RD1]. Analysis of the In-flight CO data has demonstrated that the offset in zero g of the XServo in high-resolution range has varied within a range of 4 _g (_39 m/s2) [RD1]. The zero offset of the XServo will be estimated from the first measurements (at _ 1900 km) recorded during the mission at Titan (when the Probe will be still outside Titan's atmosphere). Comparison with similar instrumentation flown on probes and landers of other missions shows that ACC XServo is the one of the most sensitive and stable sensor launched to date. Figure 2 Fig. 2 ACC Servo output vs. temperature (in engineering units) for all the in-flight checkouts, plus second-order polynomial fits. ACC XServo offset at zero g CO (V) (mu g) (m/s2) F1 -2,04567 9,09 8,9146E-05 F2 -2,03229 11 0,00010788 F3 -2,03371 9,56 9,3756E-05 F4 -2,03363 10,8 0,00010592 F5 -2,03359 10,7 0,00010494 F6 -2,03351 11,4 0,0001118 F7 -2,03348 11,6 0,00011376 F8 -2,03346 10,5 0,00010297 F9 -2,03341 10,8 0,00010592 F10 -2,03337 9,32 9,1402E-05 F11 -2,0333 9,68 9,4933E-05 F12 -2,03325 9,06 8,8852E-05 F13 -2,03323 10,1 9,9052E-05 F14 -2,03317 11,7 0,00011474 F15 -2,03314 11,2 0,00010984 F16 -2,03311 11,3 0,00011082 (values reported are averages of standard data in High range, High gain). 7. Post Flight calibration The zero offset of the ACC sensors has been estimated looking at the first measurements recorded during the mission at Titan (before the atmospheric entry). The ACC Xservo zero offset has been calculated averaging the values (256) recorded during the first 81s of measurements (when the Probe was still outside the atmosphere). This value is -2.2654E-5 m s-2 (corresponding to -2.045 V) and has been subtracted to the ACC Xservo measurements. The high sensitivity of the Xservo allowed detecting pre-entry oscillations due to the coning of the Probe. The pre-entry oscillations observed in the Xservo data can be fitted by: a_XServo(t)=Acos(2_f(t-t_0)+epsilon) where A = 1.8E-5 m s-2, f = 0.085 Hz a and epsilon ~ 1 radiant. 1/f is the period of the oscillation that corresponds to 38 Xservo measurements. The zero offsets of the Xpiezo, Ypiezo, and Zpiezo sensors, based on analysis of their measurements before atmospheric entry (values derived as average on the first 60 s of sampling) are 0.1967 m s-2 (3.980 V), 0.1286 m s-2 (-1.453 V), and 1.2282 m s-2 (2.876 V), respectively. 8. ACC total error budget Absolute accuracy: Temp +/- 0.5 K XServo +/- 35 _g (in high resolution, high gain) Piezos= +/- 0.4 g Resolution Xservo 1-10 mu g depending on mode Piezo 0.1 g ACC uncertainty is 1% of full scale. ACC XServo uncertainty Ranges Acceleration limits (m/s2) Uncertainty (m/s2) High Resolution / High Gain 20 E-3 20 E-5 High Resolution / Low Gain 200 E-3 200 E-5 Low Resolution / High Gain 20 0.2 Low Resolution / Low Gain 200 2 9. ACC data processing: Engineering value reconstruction Figure 3 and Figure 4 9.1. Raw values extraction The first step is the extraction of the sub-fields from the packet for each data format. Raw values are positive or negative (16 bit integer signed). If the value is negative (first bit set to 1), it is necessary to apply two's complement arithmetic inverting every bit. 9.1.1. XServo acceleration raw data extraction The first 52 words in packets in df#32, 33, 34 are raw XServo data. XServo_RawVal bit 15-0 The following 3 words plus 4 bits (for a total of 52bit) of the last word give indication for every raw value if the gain was high (bit set to 1) or low (bit set to 0) . 9.1.2. Piezo accelerometers raw data extraction For data formats 35, 36, 37 in each packet are contained 56 words for raw PIEZO (X,Y and Z) values. XPiezo_RawVal bit 15-0 9.1.3. XServo and Piezo temperature raw data extraction For data formats 38, 39 (HKD1 and HKD2) in each packet are contained 56 words for raw Temp (1 and 2) values. Temp1_RawVal bit 15-0 9.1.4. XServo and Piezo statistical raw data extraction For data formats 40, 41, 42, 43 in each packet are contained 56 words divided in 37 statistics subfields of 24 bit each. Each datum is composed by S2a,S1a,S0a. XServo_Stat_RawVal bit 21-0 XPiezo_Stat_RawVal bit 21-0 The bit#23 is the channel selection flag, 0 = LOW and 1= HIGH. The bit#22 is a spare bit. 9.1.5. Piezo impact trace acceleration raw data extraction For data formats 48 (ID1), 49 (ID2), 50 (ID3) in each packet are contained 56 words for raw values of the Piezo impact trace. XPiezo_Impact_RawVal bit 15-0 9.2Raw values normalization Raw values for each sensor are normalised as follows. 9.2.1. XServo acceleration normalisation XServo_Norm_Val= XServo_RawValue/16 9.2.2. Piezo acceleration normalisation XPiezo_Norm_Val= 2* XPiezo_RawValue/31 YPiezo_Norm_Val= 2* YPiezo_RawValue/31 ZPiezo_Norm_Val= 2* ZPiezo_RawValue/31 9.2.3. Xservo and Piezo temperature normalisation Temp1_Norm_Val= Temp1_RawValue/16 Temp2_Norm_Val= Temp2_RawValue/16 9.2.4. XServo and Piezo statistical data normalisation XServo_Stat_Norm_Val= XServo_Stat_RawValue/128 9.2.5. Piezo impact trace acceleration normalisation XPiezo_Impact_Norm_Val = XPiezo_ImpactRawVal 9.3. Engineering conversion The normalised value with sign is converted in engineering units (volts) using the same coefficients for every sensor: Eng_Val= 10* 2**-11 * SF* Norm_Val where SF is the scale factor (for the Flight Model its value is 1,02405) 10. Scientific conversion of engineering values Hereafter are reported the formulas for the scientific conversions for each sensor [AD4]. 10.1. Xservo acceleration conversion 10.2. XServo(m/s2) = (XServo_Eng_Val/(R*sf)-offset)*9.80708 Eq. 1 where R, sf and offset are calibration data reported in appendix A. 10.3. Piezo acceleration conversions XPiezo(g)= (XPIEZO_Eng_Val-m*Temp2_Eng_Val+offset)/sf/9.80655 Eq. 2 For the calculation of m (temperature gradient), offset (temperature offset) and sf (scale factor) values see Appendix B to this document. These values are recalculated for every in-flight checkout and for the mission must be used the values calculated from the data of the last in-flight checkout. 10.4. Xservo and Piezo Temperature conversions Temp1(K)= 109,23 (0,1Temp1_Eng_Val+2,5) Eq. 3 Temp2(K)= 109,71 (0,1Temp2_Eng_Val+2,5) 10.5. Xservo and Piezo statistical data conversions. For XServo, Piezo statistical and piezo impact trace the scientific conversions uses the same formulas reported in par. 6.1 and 6.2. The XServo statistic data resulting from the integration executed while a range change occurred should be discarded, since the values are meaningless. After a range change, X Servo outputs (high and low gain) need about 1 s to stabilize. 11. Higher level products derivation ACC measurements will be performed during the entry, descent and landing phases in order to characterize the atmosphere and surface of Titan. In particular, vertical profiles of atmospheric density, pressure and temperature will be derived during entry using the accelerometer data considering the drag force exerted by the atmosphere on the Probe and using the assumption of hydrostatic equilibrium and the perfect gas law (refer to ZARNECKIETAL2001 [RD1] and FULCHIGNONIETAL2002). The probe trajectory and attitude can be reconstructed by analysing vehicle acceleration. The profile of axial and normal accelerations during the Huygens entry and descent in Titan's atmosphere will be used in order to retrieve the probe entry track, velocity and altitude profiles, and attitude, during the high-speed entry phase (ref. FULCHIGNONIETAL2002).The auxiliary data necessary to for post flight analysis are reported in Appendix C as from [RD2]. 12. Appendixes 12.1. Appendix A: ACC XServo Calibration Data XServo data conversion parameters Xservo acceleration conversion XServo(m/s2) = (XServo_Eng_Val/(R*sf)-offset)*9.80708 Eq. 1 sf=1.30675E-03-1.35046E-07*(T(K))+4.02821E-10*(T(K))^2 (A.1) offset = -8.9642327E-04+3.83652E-06*(T(K))-0.00761E-06*(T(K))^2 g (A.2) obtained as polynomial fit of the value reported in table, page 5 of [AD4] where T(K)= temperature sensor is Temp1 [K]: Temp1(K)= 109,23 (0,1Temp1_Eng_Val+2,5) Eq. 3 Figure 5 g is the terrestrial acceleration of gravity: 9.80708 m/s2 (as provided by manufacturer [AD4]) 12.2. Appendix B: ACC Piezo Calibration Data Piezo parameters calculation Piezo acceleration conversions XPiezo(g)= ((XPIEZO_Eng_Val-m*Temp2_Eng_Val-offset)/sf)*9.80655 Eq. 2 g is the terrestrial acceleration of gravity: 9.80665 m/s2 (as provided by [AD4]) The values of m (temperature gradient) and offset (temperature offset) are calculated as the slope and the intercept of the line (passing for the points corresponding to readings at 21:39preT0, 45:51postT0, 1:56:49 postT0) in the graphic reporting the piezo reading on the X axis and the corresponding Temp2 value on the Y axis during the most recent inflight CO. ACC Piezo m (temperature gradient) offset (temperature offset) as derived during In-Flight CO (at 0 gravity) XPZR YPZR ZPZR m offset m offset m offset FCO1 -0,388 4,315 -0,279 -0,957 -0,441 3,850 FCO2 -0,389 4,406 -0,281 -0,939 -0,443 3,833 FCO3 -0,400 4,488 -0,286 -0,920 -0,433 3,806 FCO4 -0,395 4,508 -0,284 -0,920 -0,437 3,810 FCO5 -0,399 4,548 -0,286 -0,912 -0,432 3,794 FCO6 -0,398 4,562 -0,285 -0,912 -0,437 3,804 FCO7 -0,393 4,574 -0,285 -0,914 -0,439 3,809 FCO8 -0,401 4,618 -0,287 -0,906 -0,434 3,790 FCO9 -0,407 4,663 -0,289 -0,900 -0,420 3,762 FCO10 -0,406 4,681 -0,290 -0,898 -0,416 3,747 FCO11 -0,409 4,707 -0,293 -0,894 -0,413 3,735 FCO12 -0,410 4,723 -0,291 -0,897 -0,412 3,730 FCO13 -0,403 4,721 -0,289 -0,899 -0,434 3,778 FCO14 -0,403 4,740 -0,288 -0,899 -0,429 3,757 FCO15 -0,407 4,752 -0,289 -0,896 -0,419 3,721 FCO16 -0,408 4,764 -0,288 -0,892 -0,416 3,705 The value of sf (scale factor) for each sensor (X,Y,Z) is calculated as follow [AD4] from calibration data: sfx= 0,3122-0,0007(Temp2(K)-300) (B.1) sfy= 0,2395-0,0007(Temp2(K)-300) (B.2) sfz= 0,1826-0,0007(Temp2(K)-300) (B.3) where Temp2(K)= 109,71 (0,1Temp2_Eng_Val+2,5) Eq. 3 For the EGSE software for Titan encounter values for m (temperature gradient) and offset (temperature offset) have been taken from F16. Piezo calibration data as from Calibration data sheet in [AD4] Sensor Sensitivity (@100Hz, 10 g pk) Transverse sensitivity X PIEZO 0.3122 mV/g 0.7% YPIEZO 0.2395 mV/g 0.4% ZPIEZO 0.1826 mV/g 0.6% Thermal sensitivity shift -0.07% deg C typical 12.3. Appendix C: Huygens Probe auxiliary data Probe Mass, CoG & products of Inertia evolution Figure 6 Reference cross -sectional area - Characteristic lengths Values provided by Alcatel/Aerospatiale in 1997. Reference: HUY-MBA-3200-RE-00013 Issue 01 and reported confirmed in [RD2]. Item Diameter (m) Area (m2) Front Shield 2.6937 (+0.9 / -4.9 mm) ejected at T0+32.5 Descent module 1.3 not measured Pilot parachute 2.59 5.27 inflated at T0+0.25s Main parachute 8.30 54.06 inflated at T0+2.5s Stabiliser/drogue chute 3.03 7.23 inflated at T0+15 min These values correspond to the characteristic lengths of the items Parachute physical characteristics Three parachute systems are used in the descent phase (ref 4): Pilot parachute inflated at T0+0.25s Main parachute inflated at T0+2.5s Stabilizing drogue chute inflated at T0+15 min Only the latter two parachute systems are used for mission analysis. Both are Disk Gap Band (DGB) parachutes. Parachute parameters values have been derived from [R2] . Reference: Huygens DCSS descent control design report HUY-MBA-3200-RE-00001 8/06/1992 Issue 01 Fig. 7 Huygens entry and descent scenario Aerodynamical Coefficients The complete Huygens aerodynamical data base has been provided by Alcatel [RD2] and is archived within the Huygens HK data. The aerodynamical database includes: - Entry phase: 1) Free Molecular Flow (FMF) regime: Kn=1.25 gamma**0.5_Ma/Re>5 => H>780 km 2) Transitional flow regime 5>Kn>0.001 => 780 km>H>360 km 3) hypersonic and supersonic Continuum flow regime: 360 km>H>159 km =>21.8>Ma>1.5, 3.4 104>Re>1.8.105 Entry Module aerodynamic coefficients: CA and CN, Cm and Cmq values as function of AoA and Mach 0 deg