Report on the BepiColombo Critical Equipment Review II

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.

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List of critical items reviewedSolar Arrays

Solar CellsSolar Array SubstrateShunt- and Blocking DiodesSlip Rings for Solar Array Drive Mechanism

High Temperature CablesAntennas

Thermal and RF CoatingsAntenna Reflector Assembly

Sunshield (MOSIF) Thermal Coating High Temperature MLISolar Electric Propulsion Grid Lifetime

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Design driving critical Elements

1_ MTM Solar Array

2_ MPO Solar Array

3_ Electrical Propulsion

4_ HGA (ARA coating, Feed, Waveguide)

MPO Orbit

MTA = 114° MTA = 90°

MTA = 38°

MTA

SUNMTA = 0°0.31 AU

Perihelion

MTA = 180°0.47 AUAphelion

MTA = Mercury True Anomaly

MTA = 270°

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

Baseline 4 p 34.8 m² 222.9 kg nom.

Growth Potential 5 p 40.8 m² 262.9 kg nom.

Baseline 5 p 40.8 m² 288.4 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

CER I Baseline 15 string/p 6.8 m² 46.6 kg

Growth Potential 20 string/p 8.22 m² 56.25 kg

PDR Baseline 19 string/p 8.22 m² 56.25 kg

Update of SA sizing parameters

.

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

P/L S/C

230°C compliant nominal

ca.6000 esh 1590 Watt (180 W)

205°C compliant nominal nominal

1055 Watt (100 W) (Ka-Band off)

230°C

3000 esh230°C

3000 esh

230°C nominal120 esh 840 W off (Ka-Band off)

Operations

nominal

Mercury True Anomaly(MTA)

SA PowerMaximum

Temperature

(Ka-Band off)

(Ka-Band off)

Aphelium

Perihelium

1100 W nominal

Survival Mode

840 W offMTA 20-50°

Baseline(5 days)

MTA 20-50° Longer Yoke

•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 200-230 °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 + 28.5 kg - 1.2 % 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 + 0.5 % system margin

HGA baseline and back-ups for PDR

HGA Reflector: Thermal coated Ti TBC by HT RF reflectivity test Back-up: Bare Ti TBC by HT RF reflectivity test

Antenna Feed: Ag plated Ti Process verification by 4/2009Back-up: Cu sandblasted mass impact on feed and HGA (2/09)

Waveguides: Low CTE (CSiC) TDA completion 6/2009Back-up: Ag plated Ti Process verification by 4/2009

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.

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Trend Charts of dry mass

Trend of MTM Mass from TT1 to CER2

0

50

100

150

200

250

300

350

400

Mai 08 Jun 08 Jul 08 Aug 08 Sep 08 Okt 08 Nov 08 Dez 08

PowerMEPSStructureThermalCPSHarnessMechanismsDMSAOCSTT&C

Definition of solar array loss factors

TT1

PM11

PM12

PM13PM14

Re-Definition of solar array loss factors + SAA characterisation up to 82deg + Smaller Battery

TPA mass saving (harness + pos. Sensor)

CLA feed-back (stiffening)

TT1 improvements

Higher PCDU loss factors + Ti layers in HT MLI Increased PPU dissipation more HPs

Higher PCDU dissipation

CER2Solar Array

update

m [kg]


Trend of MPO Mass from TT1 to CER2

0

50

100

150

200

250


Structure

Thermal

Coms

Power

CPS

Harness

AOCS

DMS

Mechanism

Mag Boom

CLA feed-back (stiffening)

PM12 PM13PM14

PM11

TT1

Height increase + radiator size increase

Radiator growth MLI area increase

Ti layers in Blankets

Definition of solar array loss factors

Re-Definition of solar array loss factors

Additional Failure Correction

CER

Assessment from subco for latest launch mass

Brackets

m [kg]


Trend of MOSIF Mass from TT1 to CER2

0

20

40

60

80

100

120


MOSIF total

Sunshield thermal

Structure

Mechanism

Harness

MLI

AOCS

TT1PM11

PM12

PM13 PM14

Sun sensor bktstiffening deleted

MOSIF cold plate + radiator

thicker coating (50 micron layer)

MMO protection & Stack Analysis feedback

Aluminium to Titanium

CER2

m [kg]

Mass Risks and Opportunities

Risks:HGA Feed failing Ag coating technologyLonger MPO yoke 1.2 % lower system marginSeparation Mechanism early development status

Opportunities:Solar Arrays: 4 panel MTM solar array +1.4 %

Deletion of hot spot loss factorReduction 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

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

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

Baseline Back-up

MTM SA 40.8 m² Trajectory change

MPO SA 8.2 m² Dual Junction Cell

SEPS Low 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

PDR schedule

Planning of System PDR dates (TBC CER-board):

– PDR DP inputs of core team to ASD 13 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

Report on the BepiColombo Critical Equipment Review II

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