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.
// Rappel du titre //
19/12/2006
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
// Rappel du titre //
19/12/2006
3
Design driving critical Elements
1_ MTM Solar Array
2_ MPO Solar Array
3_ Electrical Propulsion
4_ HGA (ARA coating, Feed, Waveguide)
Page 4
MTA = Mercury True Anomaly
MTA = 114°
MTA = 90°
MPO Orbit
MTA = 38°
MTA
MTA = 180°
0.47 AU
Aphelion
SUN
MTA = 0°
0.31 AU
Perihelion
One revolution of Mercury
around Sun: 88 Earth days
One Mercury day:
59 Earth days
MPO orbit
inertially fixed
MTA = 270°
Page 5
MTM Solar Array Changes since CER I
Status at CER I:
Baseline 4 p
34.8 m²
222.9 kg nom.
Growth Potential 5 p
40.8 m²
262.9 kg nom.
Compliant power output assuming 230 °C qual. Temp.
(BC-ASO-TN-69257)
PDR Baseline today:
Baseline 5 p
40.8 m²
288.4 kg nom.
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
MPO Solar Array Changes since CER I
CER I Baseline
Status6.8
at CER
15 string/p
m² I:
46.6 kg
Growth Potential
20 string/p
56.25 kg
8.22 m²
Compliant power output for baseline assuming 230 °C qual. Temp.
(BC-ASO-TN-69256)
PDR Baseline today:
PDR Baseline
19 string/p
8.22 m²
56.25 kg
1 string less due to HDR design inside panel
Power analysis targeting for minimum solar array temperature
Page 7
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 MTM
time
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)
↓
Page 8
Mercury True Anomaly
(MTA)
Aphelium
Perihelium
Maximum
MPO
PowerSAStatus
Power
Temperature
Operations
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)
840 W
off
(Ka-Band off)
1100 W
nominal
(Ka-Band off)
off
nominal
(Ka-Band off)
MTA 20-50°
Baseline
(5 days)
MTA 20-50°
Longer Yoke
3000 esh
Survival Mode
230°C
120 esh
230°C
230°C
3000 esh
840 W
nominal
•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
Page 9
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
Page 10
HGA baseline and back-ups for PDR
HGA Reflector: Thermal coated Ti
Back-up:
Bare Ti
TBC by HT RF reflectivity test
TBC by HT RF reflectivity test
Antenna Feed: Ag plated Ti
Back-up:
Cu sandblasted
(2/09)
Process verification by 4/2009
mass impact on feed and HGA
Waveguides:
Back-up:
TDA completion 6/2009
Process verification by 4/2009
Low CTE (CSiC)
Ag plated Ti
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.
// Rappel du titre //
19/12/2006
12
Trend of MTM Mass from TT1 to CER2
Trend Charts of dry mass
m [kg]
400
350
Definition of solar
array loss factors
PM12
PM11
Re-Definition of solar array loss
factors + SAA characterisation up
to 82deg + Smaller Battery
PM14
PM13
300
CER2
Solar Array
update
Power
MEPS
Structure
Thermal
CPS
Harness
Mechanisms
DMS
AOCS
TT&C
TT1
250
TPA mass saving
(harness + pos. Sensor)
200
CLA feed-back (stiffening)
150
TT1 improvements
100
50
Increased PPU dissipation more HPs
Higher PCDU dissipation
Higher PCDU loss factors
+ Ti layers in HT MLI
0
Mai 08
Jun 08
Jul 08
Aug 08
Sep 08
Okt 08
Nov 08
Dez 08
Page 13
Trend of MPO
MassCharts
from TT1 of
to CER2
Trend
dry mass
m [kg]
250
PM11
TT1
200
PM13
PM12
CLA feed-back (stiffening)
Assessment from subco
for latest launch mass
Height increase +
radiator size increase
150
Structure
Thermal
Coms
Power
CPS
Harness
AOCS
DMS
Mechanism
Mag Boom
Ti layers in Blankets
Radiator growth
MLI area increase
100
Definition of solar
array loss factors
50
CER
PM14
Re-Definition of solar
array loss factors
Brackets
Additional Failure
Correction
0
Mai 08
Jun 08
Jul 08
Aug 08
Sep 08
Okt 08
Nov 08
Dez 08
Page 14
Trend Charts of dry mass
Trend of MOSIF Mass from TT1 to CER2
m [kg]
120
PM13
PM14
CER2
PM12
100
PM11
TT1
MOSIF total
Sunshield thermal
Structure
Mechanism
Harness
MLI
AOCS
80
MMO protection &
Stack Analysis
feedback
Aluminium to Titanium
60
Sun sensor bkt
stiffening deleted
40
thicker coating (50 micron layer)
MOSIF cold plate + radiator
20
0
Mai 08
Jun 08
Jul 08
Aug 08
Sep 08
Okt 08
Nov 08
Dez 08
Page 15
Mass Risks and Opportunities
Risks:
HGA Feed
Longer MPO yoke
Separation Mechanism
Opportunities:
Solar Arrays:
75° SAA
failing Ag coating technology
1.2 % lower system margin
early development status
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
Mass impact of opportunities will be assessed for PDR
Page 16
Antenna Systems
Identified Critical Technologies
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:17
Page
MOSIF Thermal Coating
2. MOSIF sunshield design
Design at CER1:
Single screen sunshield
Sunshield: 44kg
(with reinforcements: 85kg)
New baseline:
Truss framework with HT MLI
49 kg
Page 18
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 Ti with term. coating
WG Low CTE WG
Feed Ag plated Ti
Bare Ti
AG plated Ti
Cu sandblasted
Page 19
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 ASD
Delivery of System Data Package to ESA
Kick/off Meeting / Presentation at ESA
RIDs to Industry
Answer to RIDs to ESA
Colocation Meetings
System PDR Board Meeting
13 Feb 09
6 Mar 09
10 Mar 09
22 Apr 09
30 Apr 09
4/7 May 09
29 May 09
For information, the next SPC is planned on 17/18 June 09
Page 21