Report on the BepiColombo Critical Equipment Review II held at ESTEC, Noordwijk, 18. Dec. 2008

Critical Equipment Review Objectives The objectives of the Critical Equipment Review are: 1.Assessment of the status of readiness and the development schedule of critical equipment items, for which a Technology Readiness Level (TRL) of 5 (“Component and/or breadboard validation in relevant environment”) has not been fully reached. 2.Identification of backup solutions and their maturity at technological and/or system design level. 3.Establishment of cut-off dates by which a decision on backup solution has to be taken. 4.Initiation of any identified near-term urgent counter-measures. 5.Recommendation on PDR schedule. 19/12/2006 // Rappel du titre // 2

List of critical items reviewed Solar Arrays Solar Cells Solar Array Substrate Shunt- and Blocking Diodes Slip Rings for Solar Array Drive Mechanism High Temperature Cables Antennas Thermal and RF Coatings Antenna Reflector Assembly Sunshield (MOSIF) Thermal Coating High Temperature MLI Solar Electric Propulsion Grid Lifetime 19/12/2006 // Rappel du titre // 3

Design driving critical Elements 1_ MTM Solar Array 2_ MPO Solar Array 3_ Electrical Propulsion 4_ HGA (ARA coating, Feed, Waveguide) Page 4

MPO Orbit Page 5 One revolution of Mercury around Sun: 88 Earth days One Mercury day: 59 Earth days MPO orbit inertially fixed

MTM Solar Array Changes since CER I Status at CER I: Compliant power output assuming 230 °C qual. Temp. (BC-ASO-TN-69257) PDR Baseline today: Changed to 5p to avoid temperature > 200 °C qual. temp. (CER I recommendation). Less risk, proof by test until 5/2009. Provides surplus power before Venus for partial compensation of SEP Isp reduction Page 6 Baseline 4 p34.8 m²222.9 kg nom. Growth Potential 5 p40.8 m²262.9 kg nom. Baseline 5 p40.8 m²288.4 kg nom.

MPO Solar Array Changes since CER I Status at CER I: Compliant power output for baseline assuming 230 °C qual. Temp. (BC-ASO-TN-69256) PDR Baseline today: 1 string less due to HDR design inside panel Power analysis targeting for minimum solar array temperature Page 7 CER I Baseline15 string/p6.8 m²46.6 kg Growth Potential20 string/p8.22 m²56.25 kg PDR Baseline19 string/p8.22 m²56.25 kg

Update of SA sizing parameters. Page 8 Modified Cosine law for high temperatures↓ Miss-pointing reduced from +/-1° to +/- 0.5 deg↑ Progressive UV degradation calculated over life time MTM MPO ↑→↑→ Gridfinger degradation removed↑ 3G28 cells with Al AR coating (-5% power)MPO↓ Qual. Temperature 200°C instead 230°C↓ 20 mA reverse current Diodes (instead 2 mA)↓

MPO Power Status Page 9 Fully power compliant except for MTA 20-50° baseline (11 % of Mercury year) Compliance for MTA 20-50° achievable by longer yoke Solar Array temperature °C for about 9120 esh

Electrical Propulsion Status at CER I: – Grid erosion problem identified (Working group initiated) PDR Baseline today: Use of unmodified grid design and beam voltage (schedule) Implement Anode Voltage reduction to 31 V according to 2000 h test Isp reduced from 4640 s to 4378 s Mass Impact Xe kg  % system margin Surplus SA power until Venus allows higher thrust in early cruise 20 % higher thrust saves delta v of 146 m/s Xe saving -12 kg  % system margin Page 10

HGA baseline and back-ups for PDR HGA Reflector: Thermal coated Ti TBC by HT RF reflectivity test Back-up:Bare TiTBC by HT RF reflectivity test Antenna Feed:Ag plated TiProcess verification by 4/2009 Back-up:Cu sandblastedmass impact on feed and HGA (2/09) Waveguides:Low CTE (CSiC)TDA completion 6/2009 Back-up:Ag plated TiProcess verification by 4/2009 Page 11

Mass Budget Mass margin achieved for PDR design amounts to 14.0%. Positive result: This takes into account robust design solutions for Solar Arrays, Solar Electric Propulsion and Chemical Propulsion System. Risks: Finalisation of SCA at high temperature still not completed. The Board recommends … “that full evidence and traceability of the sources of mass estimates be provided immediately, that a mass risk assessment be consolidated and that a working level review be conducted.” This translates that also for the MMO these data shall be available on demand by the PDR Board. 19/12/2006 // Rappel du titre // 12

Trend Charts of dry mass Page 13

Trend Charts of dry mass Page 14

Trend Charts of dry mass Page 15

Mass Risks and Opportunities Risks: HGA Feedfailing Ag coating technology Longer MPO yoke1.2 % lower system margin Separation Mechanismearly development status Opportunities: Solar Arrays:4 panel MTM solar array +1.4 % Deletion of hot spot loss factor Reduction of solar array contamination (by analysis) Dual Junction Cell for MPO BR Reflective cover glass coating optimised for 75° SAA Mass impact of opportunities will be assessed for PDR Page 16

Page 17 At CER-1 the following technologies were identified as critical, and so plan/actions to manage them were presented  Thermal Coatings: potentially needed to reduce the temperature of exposed surfaces  RF Coatings: potentially needed for better RF performance of selected materials (i.e. Ti for ARA)  Antenna Reflector Assembly (ARA) Materials: to cope with the predicted temperatures  Feed and Waveguides: Material & technologies needed to cope with RF/RSE requirements  Antenna Pointing Mechanism (APM): improve system I/F to not exceed technology temp. limit Following actions were assigned by the Board in the frame of CER I: -TN on RSE performance in case of HGA in uncoated Titanium -RF Characterisation of ARA uncoated Titanium -Update MGA & HGAAPA ITT with relaxed TH requirement to get updated proposals Identified Critical Technologies Antenna Systems

2. MOSIF sunshield design Page 18 Design at CER1: Single screen sunshield Sunshield: 44kg (with reinforcements: 85kg) New baseline: Truss framework with HT MLI 49 kg MOSIF Thermal Coating

Summary of PDR Baseline Page 19 BaselineBack-up MTM SA40.8 m²Trajectory change MPO SA8.2 m²Dual Junction Cell SEPSLow Isp 4378s No modification HGA ARA WG Feed Ti with term. coating Low CTE WG Ag plated Ti Bare Ti AG plated Ti Cu sandblasted

Conclusion 1_ Design baseline and back-ups for critical technologies are defined for PDR 2_ The system mass margin is below 20 % for PDR 3_ SA temperatures require cell qualification for 230°C/4 SC for 9120 esh Page 20

PDR schedule Planning of System PDR dates (TBC CER-board): –PDR DP inputs of core team to ASD13 Feb 09 –Delivery of System Data Package to ESA 6 Mar 09 –Kick/off Meeting / Presentation at ESA 10 Mar 09 –RIDs to Industry 22 Apr 09 –Answer to RIDs to ESA 30 Apr 09 –Colocation Meetings 4/7 May 09 – System PDR Board Meeting 29 May 09 For information, the next SPC is planned on 17/18 June 09 Page 21