inst. overview alice preliminary design review jrs / 1 instrument overview and system engineering...

Inst. Overview Alice Preliminary Design Review JRS / 1

Instrument Overview and System Engineering

John Scherrer

[email protected]

(210) 522-3363

July 24, 2002

mailto:[email protected]


Topics

• Requirements• Instrument overview• S/C interface• Rosetta Alice vs. New Horizons Alice• Resources• System Engineering• Risk Management


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


Flowdown of Requirements


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:

• 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.


Mechanical Layout

Detector

Grating

Zero Order Trap

Solar OccultationChannel

SOC Pick-off Mirror

Baffles

Aperture Opening

OAP Mirror

Slit Assembly

Aperture Door (Shown Open)


Simplified Block Diagram


Optical Path

Detector

GratingZero Order Trap

Solar OccultationChannel (SOC)

SOCPick-off MirrorBaffles

ApertureOpening

OAP Mirror Slit Assembly

Failsafe Door(Shown Closed)

Aperture Door (Shown Open)


Rosetta Alice


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.


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).


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.


New Horizons Alice vs. Rosetta Alice(1 of 2)

• Environments:– 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.


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.


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):– 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.


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.


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.

• Risks ranked by Consequence and Likelihood.• Mitigation Plans with trigger dates included.• Team is polled weekly for their “worries”.• Risks are statused monthly.


Top 5 Current Risks


Reynolds 600 HV Connector Discussion


Backup Material

• 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

inst. overview alice preliminary design review jrs / 1 instrument overview and system engineering...

Documents

alice soc

rosetta alice slide

alice sensor

general description

exposed surfaces of

open slide

solar occultation electronics

spectral resolution