GAIARVS External Interfaces Review

1
GAIA-RVS External Interfaces Review

• RVS Consortium

2
Agenda

• 1) Introduction MSC
• 2) External interfaces definition overview MSC
• 3) Optical DK/FC
• 4) Mechanical BW
• 5) Thermal BW
• 6) Electrical BKH
• 7) Data structures MSC
• 8) Summary MSC
• 9) Opportunity for presentations by SLTADS
  representatives and PDHE contract representative
• 10) Discussion on open/non-conformance issues
  ALL

3
Attendees

• MSSL/UCL
• Mark Cropper
• Berend Winter
• Barry Hancock
• John Coker
• Tony Dibbens
• GEPI/ObsPM
• David Katz
• Fanny Chemla
• Pascal Vola
• Philippe Laporte
• SRC/Leicester
• Tony Abbey

ESA ESTEC Torgeir Paulsen Astrium
Toulouse Frédéric Safa Francois
Chassat Alcatel Bruno Napierala Claude
Israbian Astrium GmbH Christoph Schaefer
4
Review Aims

• The aims of the review are
• 1) To identify the external interfaces for RVS
• 2) To provide a specification of these interfaces
  wherever this is possible
• 3) To identify problematic interfaces and a route
  for resolving them
• 4) To agree a coherent set of interfaces with
  both SLTADS teams.

5
Interfaces Overview

• Mark Cropper

6
Spectro Hierarchical Diagram
Telescope
RVS
PDHU(VPUsandPDHE)
MBPand MBP Starmapper
Spectro
7
RVS Hierarchical Diagram with principal interfaces
8
Payload and Service Module thermal
ColdWarmerWarm
2
RVS starmapperproximity electronics
Service Module290K
RVS Starmapper
External harness?
structure
camera
RVS proximity electronics
spectrograph optics

• RVS Focal Plane

RVS Pre-ProcessingUnit (RPPU)
Mechanism?
structure
structure
Payload Module 160K
radiator
radiator
9
Payload and Service Module thermal alternative
RVS starmapperproximity electronics
ColdWarmerWarm
RVS Starmapper
structure
camera
RVS proximity electronics
spectrograph optics

• RVS Focal Plane

RVS Pre-ProcessingUnit (RPPU)
Mechanism?
structure
Payload Module 160K
radiator
radiator
10
MBP and RVS Starmapper Issues

• MBP may have a mechanical and thermal interface
  to RVS
• RVS Starmapper may have a mechanical and
  electronic interface to MBP
• RVS Starmapper functionality similar to MBP
  functionality
• 3 main options

baseline
11
Primary Scientific Requirements

• Primary scientific requirement is to obtain
  radial velocities for stars in the Galaxy to a
  limiting magnitude
• Astrophysical information will be obtained for
  brighter stars
• Wavelength range and resolving power specified
• Spatial resolution requirement is to address
  crowding

12
RVS Baseline

• We work from Astrium design in System Level
  Reassessment Study (July 2002) as in SoW this is
  the current baseline
• We understand recommendations made by GAIA
  Science Team regarding scientific performance at
  the faint limits ? we permit the consideration
  of a mechanism to correct for the scan law
  (mostly internal interface)
• We understand that SLTADS teams will have made
  substantial progress since December 2002 and some
  concepts have changed which will require some
  reassessment of external interfaces and
  harmonisation between Astrium and Alenia concepts

13
Interface review Scanning Law Optics

• F. Chemla and D. Katz (GEPI)

14
Scanning law

• Spin motion (6 h)
• Precession motion (70 days)
• Revolution around the sun (1 year)
• Model L. Lindegren (SAG-LL-30)
• Earth orbit eccentricity yes
• motion around L2 no

15
Motion in the RVS FoV

• Along scan 60 arcsec/s
• Across scan periodic motion (locally sine P
  6h)
• average half amplitude 0.168 arcsec/s

velocity drift
16
Transverse motion half amplitude

• Maximum half amplitude 0.174 arcsec/s (T0)
• Minimum half amplitude 0.163 arcsec/s (T0 6
  months)
• Absolute rate error along scan (TBD) First
  derivative (TBD)
• Absolute rate error across scan (TBD) First
  derivative (TBD)

Maximum velocity drift
17
Optical Interface telescope focal plane

• Astrium Alenia/Alcatel
• entrance pupil 0.50.5 m2 0.50.5 m2
• exit pupil quasi infin. quasi infin.
• focal length 2.1 m 2.1 m
• FP along scan 74 mm 74 mm
• RVSM along scan 35 mm (TBC) 20 mm
• FP across scan 177 mm (TBC) 180 mm
• (RVS MBP)
• Full 3D allocated volume ? Telescope design ?

18
Baseline RVS optical design (SLTRS)
19
Quick optimisation

• A quick optimisation has been done
• Distortion slightly better (-20)
• Image quality equivalent
• Dispersion variability is higher
• It appears that an increase of the overall volume
  leads to significantly better results in terms
  of
• Distortion
• Image quality
• Optimisation flexibility

Distortion along scan has not yet been checked
20
Mechanism interfaces

• A mechanism might be implemented in order to
  cancel the apparent sky motion on the detector
  plane due to the GAIA scanning law
• Three main options are available for this
  mechanism
• Rotation mechanism on the CCD
• Rotation mechanism on the grism
• Rotation mechanism on the two reflecting mirrors
  of the RVS

21
Mechanism possible positions
22
Volume issue

• It is very important to know the allocated volume
  for the RVS or better, the proximity environment
  in order to
• Know whether some distances can be increased to
  gain optimisation flexibility
• Know what folding arrangements are required

23
Optics low T qualification

• Development plan
• Identify sensible elements (coatings? Grating?)
• Make a Zemax simulation in order to check
  whether
• The change in the refracting index is
  tolerable
• The expansion coefficients is compatible with
  the mechanics ones

• Interfaces
• Cooling velocity TBA
• Refocalisation envisaged TBC

24
Optics radiation tolerance (later phases)

• Development plan
• Bibliographic study to gather information on
  glasses behaviour under radiation
  (manufacturers data, books)
• Transmission modification under radiation
• optical index modification under radiation
• Dispersion variation under radiation
• If the two precedent points do not provide
  sufficient information ? Tests

• Interfaces
• Radiation intensity 12krad (TBC)
• Radiation type solar protons
• Tolerable darkening, fluorescence and
  scintillation TBA

25
Mechanical - Thermal - Interface

• John Coker
• Berend Winter
• Mullard Space Science Laboratory

26
Contents

• Description of RVS
• Mass
• Stiffness
• Interface
• Mechanism
• Mechanical environment
• Thermal interface
• How to move forward from here?

27
Description

• RVS (Radial Velocity Spectrometer)
• A Spectro-telescope is to be fitted below the
  main optical bench (torus). The focal plane of
  the optical chain M1-M2-M3 is in front of the
  entrance aperture of RVS. The optical chain
  inside RVS will map the focal plane on one inside
  the RVS instrument via a grism. The grism breaks
  the beam into a spectrum on the RVS focal plain.
• MBP (Medium Band Photometer)
• The location of the MBP (medium band photometer)
  is at the aperture of RVS
• Starmapper
• The star mapper is also located at the entrance
  aperture of the RVS instrument.

28
Description - block diagram
Telescope
RVS
PDHU(VPUsandPDHE)
MBPand MBP Starmapper
Spectro
29
Description - configurations Astrium envelope
30
Description - configurations Alenia/Alcatel
envelope
31
Description - configurations
32
Description - Lens Mount
33
Interface

• We dont have a specified interface yet
• We assume a volume available of about 1.3 x 0.3 x
  0.3 m3 (Astrium) and 1.3 x 1.0 x 0.3 m3
  (Alenia/Astrium) around the torus
• Need to identify mounting fixation points
• Type of fasteners
• Thermal interface definition
• Interface with radiator
• Interface with payload module
• Need a common definition
• We have some hardcopies with overall dimensions
  of different configuration for you

34
Mass - roadmap

• Design maturity will be reflected in the mass
  estimates
• Conceptual design 20 uncertainty
• More detailed design for use in trade-offs 10
  uncertainty.
• Detailed design 5 uncertainty.
• Final detailed design 2 uncertainty or less
• Measured weights less than 1 uncertainty for
  units with a mass exceeding 100 gr. Otherwise
  accuracy within 1 gram.
• On delivery the measured mass will be reported
  within measurement accuracy but at least within
  1 accurate. During the life of the project the
  mass budget will be reported taking into account
  the design maturity of the individual components
  that make up the overall mass.
• During the life of the project the mass budget
  will be reported taking into account the design
  maturity of the individual components that make
  up the overall mass.

35
Mass - RVS breakdown
Current allocation including MBP is 42 kg
36
RVS - Stiffness

• Baseline is to stay away from main spacecraft
  modes
• Assumed for the time being is the following
• Main structure modes 120 Hz (goal)
• Main sub structure modes 400 Hz (goal)
• This approach will allow us to use the design
  loads as a quasi-static design criterion and will
  allow straight forward notching on interface
  loads

37
Mechanism - Allowable Disturbances

• Rotating Components
• Maximum disturbance torque less than 1 micro-Nm
• We assume this requirement to be valid for all
  timescales

38
Mechanical Environment

• No mechanical environment specified - we assume
  for now
• Longitudinal 20 g
• Transverse 10 g
• Sine stepped down after 50 Hz (static input) to
  10 g above 70 Hz up to 100 Hz
• Allowed to notch on interface forces (not to
  exceed design loads)
• Random 0.05 g2/Hz between 100 and 300 Hz with 3
  dB/Oct ramp up between 20 and 100 Hz. And a -12
  dB ramp down to 2000 Hz

39
RVS - Alignment budget

• External alignment
• Defocus 2.5 microns (TBC)
• Decentre across scan 1.5 mm (TBC)
• Decentre along scan direction 0.13 mm (TBC)
• Tilt about axis corresponding to cross-scan
  direction 0.0004 (TBC)
• Other tilt 0.0017 (TBC)
• Inside the RVS instrument optics need to be kept
  aligned as follows (TBC)
• 50 micron lens spacing
• 200 micron tube location
• 5 micron stability
• Need information of temperature influence on CTE

40
Thermal

• Maximum allowed heat flow into spacecraft 1 W
• Thermal stability of the heat flow better than
  0.1 of the flux
• Heat flow towards radiators TBD
• Radiator area TBD
• Currently about 14 W heat is generated inside the
  RVS (excluding MBP) (TBC)
• Hence the flow will likely be about 1 W into
  payload module and about 13 via the radiators
  into space.

41
How to move forward?

• Mass is the big issue for now
• We need to find areas where mass can be saved
• We need to assess basic structural properties
• Mass distribution in more detail
• Create simple FEA for main structure resonances
• Continue the thermal analysis
• The basic thermal and structural analysis should
  allow us to save mass if possible. Since it will
  minimize the interface from a structural/thermal
  point of view, stiff and strong enough to meet
  required frequency and strength but not more than
  that. Minimizes the thermal heat flow.
• This will be fed back into the design and updated
  mass breakdown.

42
How to move forward? - continued

• We need to assess the interface with the s/c in
  more detail. Need to convey meetings with
  potential s/c primes asap
• Also we need to know (soon) if we should take
  into account the mounting of the MBP. This will
  have an impact on the thermal and mechanical
  performance. Or alternatively look at the impact
  as part of design trades

43
Electrical

• Barry Hancock

44
Contents

• Overall concept
• VPU interface
• Power interface
• Power allocation
• Survival heaters/spacecraft monitoring
• EMI requirements
• Grounding
• Radiation issues
• Parts qualification issues

45
RVS Option 1 PRIME OPTION
46
RVS Option 2
47
RVS Option 3
48
RVS Option 4
49
RPPU Functions

• Data volume reduction
• Co-adding CCD frames with fractional pixel
  resolution
• Application of windows using co-ordinates from
  the star mapper
• CCD readout control
• Removal of CCD cosmetic blemishes
• Removal of cosmic ray induced data
• Diagnostic functions
• Mechanism control (with data input from the
  VPU/PDHE)
• Power conversion and control for RVS and RVSM
• Power dissipation control in RVS and RVSM focal
  planes and Proximity electronics
• HK data acquisition

50
Architecture Options Trade Off
51
RVS External Interface Summary
52
RPPU-VPU interface

• SpaceWire seems an appropriate interface standard
  for SPECTRO and GAIA.
• Fast 200Mbits/sec.
• Use of bus routers increase flexibility and fault
  tolerance.
• Conform to ECSS-E-50-12A.
• LVDS drivers and receivers have good EMI
  properties.
• Power consumption 5mW per Mbps per link
  interface (500mW max).

53
Power Dissipation Control

• To maintain power dissipation stability it will
  be necessary to implement an active management
  system. RVS constantly will consume maximum power
  consumption, taking into account transient peaks
  and end of life projections. The required
  stability of each unit is shown below.
• Focal Plane 0.01 over 6 hours TBC
• Proximity Electronics 0.01 over 6 hours TBC
• Service module TBD

54
Power distribution

• Single primary power interface
• Power conversion in RPPU and secondary power
  distributed to subsystems
• RVS Subsytems to regulate and filter power.

55
Budgets Power Astrium baseline
56
RVSRVSM Power Breakdown TBC(6CCDs with optional
Mechanism)
57
Survival Heaters

• RVS will require S/C powered survival heaters,
  these will need to be powered when RVS is off.
• Dual redundant thermostatic control to avoid
  short circuit and open circuit failures.
• RVS will require TBD S/C powered temperature
  sensors situated at strategic positions on the
  RVS. Measurement accuracy TBD.

58
Grounding EMC Requirements

• RVS will be galvanically isolated from GAIA S/C
• RVS will convert its own secondary power
• Each Spectro instrument will define its own
  secondary reference.
• All communication links will have differential
  interfaces (SpaceWire LVDS is current loop).
• All interconnecting harnesses will have an
  overall shield connected to the S/C chassis

59
Radiation Issues

• Transfer trajectory total dose very low.
• GAIA total dose for 6 year mission assuming 2mm
  Al shielding 12Krads silicon.
• Dose mainly solar protons.
• Safety factor of 2 required on total dose.
• Necessary to understand EOL conditions to assess
  peak power consumption.
• Where possible all technology should be latchup
  resistant (precautions must be taken.
• Sufficient data in the test report to assess SEU
  and SEL effects of selected technologies.
• CCD radiation study.

60
Parts Qualification

• Use of FPGA technology
• SpaceWire implementation
• Top level project requirements
• COTS component usage
• Proximity electronics ADC selection

61
Data Handling

• Mark Cropper

62
Telemetry SLTRS (Astrium July 2002)
63
Data Format

• Data format will be dispersed spectra from CCD
  detectors with spatial width 2 pixels and
  spectral extension over 690 pixels, set by
  resolution requirement and bandpass (see earlier)

• Data windows around objects are typically 690x3
  pixels
• Most stars are detected at the limits of
  visibility

64
Telemetry requirement

• No of stars/sq degree (average) 2900
  ESA-SCI(2000)4
• Area of each CCD (one of six) 0.463 sq degree
• No of stars per CCD 29000.463 1340
• Area of each star window 666x3 pixels 1998
  pixels
• Total pixels with stars per CCD 2677320 pixels
• Total bits for stars per CCD 267732016
• Time taken to read 1 CCD 16.5 sec
• Total bits/sec per CCD 267732016/16.5
  2596189
• Total bits/sec for 6 CCDs 62596189
  15577134 15.6 Mbit/s (cf 0.824)
• Fraction of CCD pixels occupied by stars
  2677320/(10004000) 67

65
Telemetry Requirement (ctd)

• Telemetry data rate for satellite is 3.6 Mbit/s
  (SLTRS Table 5.4A)during one 8hr shift ? 1.2
  Mbit/s average per day
• Total raw data data rate (payload) 4.6 Mbit/s
• Assumed compression (excl. overhead) 4.6/1.2
  3.6
• Assumed allocation to RVS 0.824/3.6 Mbit/s
  0.25 Mbit/s(if the compression
  allocation is held within RVS).
• Ratio of average data rate to allocation
  15.6/0.25 65
• ? serious under-allocation of telemetry
  resources to RVS

66
Data Handling Strategies

• In order to reduce telemetry combine
  CCDs factor 6 lossless compression factor 2.
  5 select reduced window for faint stars
  around Ca lines factor 2 Total factor 3
  0 Required 65 ? shortfall is still a
  factor 2 on average (worse for peak)
• Notes that lossy compression is not a feasible
  solution
• Note also that since on average 67 of the CCD
  is covered with source spectra, it makes more
  sense for thermal reasons to read entire CCD all
  the time and window subsequently

67
Data Interface

• RVS Pre-Processing Unit will supply spectra that
  are
• Coadded
• Windowed
• Cosmetic and cosmic ray preprocessed
• Windowing will select only the regions around the
  Ca triplet lines for fainter (V15 TBC) objects

• RVS compression will take place in PDHU
  (lossless)
• RVS data structures are TBD. Will probably
  consist of nominally formatted data areas with
  unwanted areas zerod.

68
Summary

• Mark Cropper

69
Overview

• We have identified the external interfaces for
  GAIA-RVS
• We have addressed several options for mechanical
  and electronic architecture to investigate impact
  of these on the external and internal interfaces
• We have made a recommendation as to which option
  is preferred in each case

70
Overview

• Many of the interfaces are still TBD
  (particularly attachment locations and
  accommodation).
• Many of the interfaces will require revision in
  the light of developments within other GAIA
  studies
• External Interfaces Document (MSSL/GAIA-RVS/SP/001
  ) will be issued shortly with as many revisions
  as are available

71
Instrument Resource Budgets

• RVS mass, power and telemetry allocations appear
  inadequate
• Telemetry Considerable effort already expended
  in searching for feasible solutions in telemetry
  allocation shortfall subsequent options are
  available but significantly impact science and
  raise instrument coordination issues
  (chequerboard sampling of the sky)
• Power Power allocations appear also to be
  inadequate even if considering only the RVS focal
  plane and proximity electronics RPPU saves power
  consumption elsewhere and simplifies interfaces
• Mass A significant fraction of the mass
  allocation is consumed simply by the spectrograph
  optical elements (without cells or support
  structure) lower mass solutions here are being
  investigated to include
• thinner lens elements
• fewer lens elements
• alternative optical concepts

72
The mass issue example lower mass optical designs

• Off-axis Schmidt Camera in double-pass (RGB)

73
MBP Interface

• The RVSMBP interface is a complex one, including
  the respective starmappers and thermal interfaces
• No investigation yet on MBP resource allocation
  requirements (and not sure whether this is
  covered in other GAIA contracts)
• There may be some advantages in treating the
  RVSMBP as a combined Spectro instrument, but
  RVSRVSM can also be treated separately