QinetiQ Proprietary BepiColombo TDA

Transcription

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2 Bepi Colombo TDA Technology Status Review

3 Agenda 1. Objectives of TDA 2. Technology Requirements 3. Scope of TDA 4. Schedule 5. Deliverables 6. Critical Technologies not met 7. Critical technology items not covered by scope of TDA 8. Planning to Flight Model status

4 Objectives of TDA 1. Define requirement specification for the SEPS units 2. Assess the SEPS systems with respect to the Bepi Colombo mission requirements 3. Modify the SEPS systems for the specific mission requirements 4. Validate the technology through functional and characterisation test activities

5 Technology Requirements From the outset of the thruster Technology Demonstration Activity (TDA) the following critical technical issues have been identified with respect to the technology requirements Thermal environment Simultaneous operation of thrusters in close proximity Compatibility of thrusters with the launch environment Thrust range and total impulse capability

6 Technology Requirements Thermal Environment The main analysis addressing this aspect was performed relatively early in the TDA and was reported in the Technology Assessment Study (TAS) report QinetiQ/KI/Space/TA In summary analysis was performed to investigate The operating temperatures of thruster elements when operated at max. thrust (200m) in Earth (1.36kWm -2 ) and near Mercury (14.5kWm -2 ) orbits and impacts on thruster design/materials & ion optics The thermal effects of close proximity to other thrusters The effects of non-symmetrical illumination (3 illumination angles) and any thermal gradients on grid assembly and impacts on ion optics

7 Technology Requirements Thermal Environment Although the temperature increases predicted in the Mercury environment are significant they are within the thruster material and operational limits with one exception The earth screen assembly has to date been manufactured from aluminium alloy sheet Analysis of thruster operation in the near Mercury environment however indicated an earth screen temperature of up to 313 This exceeds the safe working temperature of the aluminium and therefore the earth screen on the T6 is now manufactured in titanium

8 Technology Requirements Thermal Environment 14.5 kw m -2 Maximum grid temperatures experienced with normal illumination Predicted temperatures are not a concern to thruster performance and grid spacing remains acceptable at elevated temperatures Since heating of grids is from thruster discharge and normal illumination there are no thermal gradients and hence negligible drift of thrust vector

9 Technology Requirements - Close proximity Thrusters located in close proximity to other thrusters Configuration will influence view factors between thrusters and the concern was that this could result in elevated and asymmetrical operating temperatures The effects of simultaneous operation in close proximity are negligible Q = A1F1-2 ε1σt1 Energy radiated by thruster which is intercepted by second (< 2% dissipated internal power) F 1 2 = F 2 1 = π X 1 + sin 1 X X View factor of parallel spaced cylinders of infinite length

10 Technology Requirements - Asymmetrical Illumination The principal concern with asymmetrical illumination/view factors is that thermal gradients could develop in the thruster structure producing relative radial movement of the grids and therefore a thrust vector drift To assess the magnitudes of any thermal gradients a number of configurations where modelled Only considered two thrusters because of the uncertainty in the final thruster configurations Side illumination results in the worst case thermal gradients

11 Technology Requirements - Asymmetrical Illumination Side illumination Case 1/2 45 degrees illumination Case 2/2 Downstream illumination Case 3/2 45 degrees illumination Case 4/2 Side illumination Case 5/2

12 Technology Requirements - Asymmetrical Illumination Analysis of thruster asymmetrical illumination (in conjunction with simultaneous operation in close conjunction with a 2nd thruster) suggested that very small thrust vector deviations would be expected (<0.1 ) To verify this analysis and the compatibility of the thruster with the thermal environment testing was performed with a single T6 in conjunction with a heater eater was designed to reproduce the same thermal gradient across the thruster structure and could be placed in close proximity with the thruster and withdrawn without breaking vacuum Testing performed for approximately 500 hours

13 Technology Requirements - Asymmetrical Illumination Photograph shows the primary thruster with the heater array partially withdrawn. The heater array is constructed from sheet steel, sandblasted on the concave side to increase emissivity. The plate is heated using a cartridge heater (up to 600 C). The ends of the two heaters (2 nd heater included for redundancy) can be seen protruding from the copper block attached to the external surface at the base of the array.

14 Technology Requirements - Asymmetrical Illumination Photograph from below primary thruster with heater array in close proximity Photograph from side showing thruster with heater array in close proximity

15 Technology Requirements - Asymmetrical Illumination Results of 500 hour thermal test indicated that the thruster construction and materials are fully compliant with the anticipated thermal conditions of near Mercury Measurement of the thrust vector between heater in close proximity and withdrawn indicated a slightly larger thrust vector variation than modelled and specified in Thruster sub system requirements specification (SSRS) issued at start of TDA ± 0.1 originally specified ± 0.15 originally specified

16 Technology Requirements - Asymmetrical Illumination Initial specification Side view Thruster geometric axis Parallel ion beam 22 cm diameter Beam divergence < 15 degrees half cone angle Beam divergence <15 half cone containing 95% beam current Thrust vector ± 1 Thrust geometric centerline measured from thruster mechanical axis Thruster geometric axis Thrust vector radial offset < 1.0 mm Thrust vector stability Thrust vector origin Thrust vector angular offset < 1.0 degree ± 0.1 w.r.t. nominal Downstream view Side view

17 Technology Requirements - Asymmetrical Illumination 0.60 Thrust vector variation between nominal and heater cycles (1) Thrust vector error is between measured and the nominal mechanical axis denotes heater present, denotes nominal operation Degrees orizontal thrust vector Vertical thrust vector /04/03 24/04/03 26/04/03 28/04/03 30/04/03 02/05/03 04/05/03 06/05/03 08/05/03 10/05/03 12/05/03 Beam Probe Measurement

18 Technology Requirements - Asymmetrical Illumination 0.25 Thrust Vector Variation between average and heater cycles (2) Thrust vector error is between measured vector and the average thrust vector denotes heater present, denotes nominal operation Degrees /- 0.1 degree vector stability defined in Thruster Specification orizontal Error Vertical Error Absolute error /04/03 24/04/03 29/04/03 04/05/03 09/05/03 14/05/03 Date

19 Simultaneous Operation in Close Proximity To investigate thruster performance during simultaneous operation and to verify that adverse interactions did not occur between thrusters a test campaign was performed using 2 T6 thruster Testing was performed with the thrusters at 3 spacings between thruster centres of (0.8m, 0.5m & 0.3m) Thrusters operated at 200m and 75m with both and single neutralisers

20 Simultaneous Operation in Close Proximity

21 Simultaneous Operation in Close Proximity A discussion of the test results is beyond the scope of this presentation In summary however the conclusion was that measurable thruster interactions do not occur It should be noted however that it is not possible to conclusively prove that small interactions are not occurring, particularly at the minimum thruster separation

22 Thrust Range and Total Impulse The original TDA SOW requirement was; Thrust range and maximum thrust - TBD Specific impulse s Lifetime > 15,000hrs Subsequent discussions with Agency concluded with 15,000 hrs at 200m; i.e. total impulse requirement of 10.8 x 10 6 s Recently the requirements have changed significantly Total impulse increased to 14x10 6 s Thrust range m

23 Thrust Range and Total Impulse QinetiQ made the assessment early in the TDA programme that common thruster technology with AlphaBus had a number of significant programmatic advantages for both programmes If T6 was successful and selected for AlphaBus then a power conditioning system, XFCU and pointing mechanism would be developed and qualified eritage and confidence could be gained for BepiColombo from AlphaBus testing and development programmes A full system life test for AlphaBus would be performed providing extensive heritage for BepiColombo and confidence in system design The main technical disadvantage was that this approach increased the W/m of the AlphaBus system considerably in excess of what would be required to meet the AlphaBus requirements (>4000s and >110m)

24 Thrust Range and Total Impulse Recognised early in TDA Phase 1 that the ion optics would need to be optimised in order to meet the total impulse requirements IOS design was initially developed during the TDA Phase1 with a further iteration following the completion of the AlphaBus 1000 cycle partial life test To verify the total impulse capability of the optimised ion optics system a 2500 hour endurance test is ongoing To date the thruster has been operated for approximately 2000 hours Grid inspections performed at 608 hours and 1717 hours (@ 175m) continuous operation

25 Thrust Range and Total Impulse Accel grid central aperture bore diameter Accel grid (circle 1=0.1mm, circle 2=0.25mm, circle 3=0.4mm, circle 4=0.55mm, circle 5=0.7mm, circle 6=0.85, circle 7=1.0) mm 0.45 Centre of web Aperture radius increase (mm) alf of accel web 0.1 mm from top surface 0.25 mm from top surface 0.4 mm from top surface 0.55mm from top surface 0.7 mm from top surface 2.45mm E E E E E E E E E+07 Total Impulse (s, accumulated continuously)

26 Compatibility of thrusters with the launch environment Frequency Qual PSD db/oct Random Environmental requirements (TBD) Applying AlphaBus requirements Frequency Acceleration Duration /- 10 mm pk to pk g 2 Oct/min Sine Frequency Acceleration Acceleration Lateral Perpendicular Shock

27 Scope of TDA Establish requirements specifications Technology Assessment Analysis and modification of existing thruster 500 hour characterisation test Analysis of possible interactions and coupling effects Correlation of experimental results with existing models to evaluate performance, lifetime, interactions Analysis and modification of thruster from 500 hour test results 2500 hour characterisation test Further 3000 hour endurance test as part of TRP activity Technology Readiness Level is TRL5/6

28 Schedule of TDA (post February 2005) Complete final 500 hours of 2500 hour characterisation test. igh temperature operation Analysis of grids Further 3000 hour endurance test as part of TRP activity

29 Deliverables Key Documentation: SEPS unit specifications Technology Assessment Studies 500 our test report 2500 our test report following conclusion of 2500 hour test T6 thruster and ion optics system, tested in 500 hour and 2500 hour test

30 Critical Technology Requirements ot Met one

31 Critical Technology Requirements ot Covered Interface to Gimbal Mechanism QinetiQ have adapted T6 to use same interface for both AlphaBus and Bepi Colombo. QinetiQ s experience is that changes here can result in significant development activities and recommend the AlphaBus interface adopted if possible

32 Planning to Flight Model Status Initially within scope of AlphaBus development activity Coupling tests between thruster and EM / EQM PPU Including EMI/EMC testing Lifetest of EP system critical activity