Instrument Overview and System
Engineering
John Scherrer
[email protected]
(210) 522-3363
July 24, 2002
Inst. Overview
Alice Preliminary Design Review
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Topics
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Requirements
Instrument overview
S/C interface
Rosetta Alice vs. New Horizons Alice
Resources
System Engineering
Risk Management
Inst. Overview
Alice Preliminary Design Review
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Top Level Requirement
• The ALICE sensor shall obtain ultraviolet
spectral maps over a 520 Å -1870 Å
bandpass. The spectral resolution shall be
1.7 Å per spectral element. The FOV shall be
6° x 0.1º and the spatial resolution shall be 5
mrad/pixel. ALICE shall accommodate a solar
occultation channel.
* From section 3.3 of Mission Science Definition document
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Flowdown of Requirements
Inst. Overview
Alice Preliminary Design Review
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General Description
Alice is an integrated UV spectrograph composed of the
following major elements:
– A 41 x 65 mm off-axis paraboloidal primary telescope mirror.
– A 50 x 50 mm toroidal holographic diffraction grating.
– A 2-D imaging photon-counting microchannel plate (MCP)
detector assembly with vacuum cover/window assembly.
– Two entrance apertures: Airglow and Solar Occultation
– Electronics that include:
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Microcontroller and C&DH electronics
Double Delay line detector electronics
Driver circuitry for actuators / heaters / switches, etc.
Redundant high voltage power supplies
Redundant low voltage power converters
These elements are all packaged in a highly-baffled aluminum
housing.
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Alice Preliminary Design Review
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Mechanical Layout
Slit Assembly
Detector
Zero Order Trap
Grating
OAP Mirror
Baffles
SOC Pick-off Mirror
Aperture Opening
Solar Occultation
Aperture Door
Channel
(Shown Open)
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Simplified Block Diagram
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Alice Preliminary Design Review
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Optical Path
Detector
Zero Order Trap
Grating
Failsafe Door
(Shown Closed)
Aperture
Opening
OAP Mirror
Slit Assembly
Baffles
Inst. Overview
SOC
Pick-off Mirror
Solar Occultation
Channel (SOC)
Alice Preliminary Design Review
Aperture Door
(Shown Open)
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Rosetta Alice
Inst. Overview
Alice Preliminary Design Review
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Modes of Operation
• Histogram – builds up 1024 x 32
(spectral vs. spatial) array 16 bits
deep. Primarily used for Airglow
observations.
• Pixel List – Photon counting
mode where the location of each
photon event on the detector
array (i.e. spectral and spatial
location) is stored and
transmitted. Time hacks are
inserted to provide temporal
resolution. This is primary mode
of operation for Solar
Occultation.
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Alice Preliminary Design Review
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Interface Summary (1 of 2)
• Mechanical:
– Hard mounted to S/C (or S/C bracket)
– FOV is “aligned” with other optical instruments.
• Alignment:
– Alice SOC shall be aligned to HGA (REX) within 0.23º
(knowledge to 0.02º). Will use in-flight calibration to
re-verify alignment.
• Thermal:
– Desire to be at S/C temperature and coupled to S/C as
much as possible (to minimize heater requirements).
– Blankets cover most of exposed surfaces of Alice.
(FOV’s are clear).
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Alice Preliminary Design Review
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Interface Summary (2 of 2)
• Electrical:
– Alice uses standard High Speed (LVDS) and Low Speed (UART)
instrument interfaces.
– Max telemetry rate is 480 kbits/sec (includes margin) which will
occur during Solar Occultation (30 ksamples/sec).
– Alice is equipped with SA 3865 microcontroller which allows for
instrument flexibility and simplifies S/C interface.
• Microcontroller minimizes number of needed commands.
• Alice releases all doors via S/C telecommand
• Alice has internal autonomous safing functions (that can be disabled).
• Other:
– Alice (as with all UV instruments) is contamination sensitive and
will impose requirements on the spacecraft and other instruments.
– GN2 (Grade C or 99.999%) purge through launch is required.
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Alice Preliminary Design Review
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New Horizons Alice vs. Rosetta Alice
(1 of 2)
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NH is slightly wider temperature range.
NH is higher radiation environment.
Currently, NH loads are higher than as tested for on Rosetta.
Duration of the NH mission is longer though ON time is less.
• Optical:
– Identical optics and detector
– Slightly different bandpass required moving detector
• Electrical:
– NH requires ping-pong memory.
– For increased reliability, NH Alice has redundant LVPS and
HVPS.
– LVPS is custom design rather than hybrid.
– Instrument controls actuators rather than spacecraft.
– Different spacecraft interface.
Inst. Overview
Alice Preliminary Design Review
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New Horizons Alice vs. Rosetta Alice
(2 of 2)
• Mechanical:
– On NH, pyro’s are not allowed. Switched to wax pellet and shape
memory alloy actuators.
– Added Solar Occultation Channel aperture and pick off mirror.
– Pump out tube length reduced.
• Thermal:
– Very similar thermal design.
• Software:
– NH is simpler spacecraft interface.
– Simpler operations (reduced modes of operation and simpler
requirements).
• Testing:
– Very similar plan and series of tests.
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Resources
• Mass:
– Current Best Estimate = 3.86 kg
– Mature value (with uncertainty 12.6%) = 4.35 kg
– Values are known and approved by project.
• Power (data acquisition mode):
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Current Best Estimate = 4.74 watts
Mature value (with uncertainty 15%) = 5.45 kg
Assumes 65% efficiency of LVPS
Current allocation is 5.64 watts
• TM Rate
– Maximum expected rate is 480 kbps
– This rate is based on highest expected count rate during Solar
Occultation plus margin.
– S/C capability on TM interface is 16 Mbps.
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Alice Preliminary Design Review
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System Engineering
• Main responsibilities:
– Verification of technical requirements
• DOORS, Verification Plan, Test Procedures
– Management of technical resources
• Monthly reports
– Oversight and control of system interfaces
• ICD’s, specs, Div. 15 Change Control process
• John Stone is lead of System Engineering
– Dave Slater (Proj. Scientist), as well as PM and
subsystem leads support SE activities.
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Alice Preliminary Design Review
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Risk Management: Process
• We are transitioning to use of Web-based Risk
Management Tracking System from more
traditional spreadsheet system.
– Similar to NAIMS (New Horizons Action Item
Management System)
– Automatically emails responsible person for updating
of status of risk item and mitigation plans.
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Risks ranked by Consequence and Likelihood.
Mitigation Plans with trigger dates included.
Team is polled weekly for their “worries”.
Risks are statused monthly.
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Top 5 Current Risks
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Alice Preliminary Design Review
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Reynolds 600 HV Connector Discussion
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Alice Preliminary Design Review
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Backup Material
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Alice Instrument Performance Specification (Draft)
Mechanical Interface Control Drawing (Draft)
Thermal Interface Control Drawing (Draft)
Fault Tree
Project Schedule
Contamination Control Plan
Verification Test Plan
Radiometric Calibration Plan
Software Development Plan
Software Requirements Document (Draft)
Preliminary Structural Analysis
Preliminary Thermal Analysis
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