TSIS-2 Observatory Instruments Accommodation Requirements Document (IARD), Rev - A.pdf

Effective Date: 10/24/2019

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National Aeronautics and Space Administration

Goddard Space Flight Center Greenbelt, Maryland

TSIS2-SC-TN-0003, Revision A

Total and Spectral solar Irradiance Sensor (TSIS)-2 Project, Code 424

Observatory Instruments Accommodation Requirements Document

GSFC TSIS-2 CMO

10/24/2019 Released

TSIS-2 Observatory IARD TSIS2-SC-TN-0003 Revision A ii Check the TSIS-2 TDMS Server at https://ipdtdms.gsfc.nasa.gov to verify that this is the correct version prior to use.

TSIS-2 Observatory Instruments Accommodation Requirements Document (IARD) Review/Signature/Approval Page

Prepared by:

Electronic signature on TDMS

10/11/2019

Sergey Krimchansky Date Deputy Project Manager, TSIS-2 NASA Goddard Space Flight Center

Reviewed by:

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10/19/2019

Susan Breon Date Project Manager, TSIS-2 NASA Goddard Space Flight Center

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Preface

This document is under the TSIS-2 project configuration control. Once this document is approved, TSIS-2 approved changes are handled in accordance with Class I and Class II change control requirements as described in the TSIS-2 Configuration Management Procedures, and changes to this document shall be made by complete revision.

Any questions should be addressed to:

TSIS-2 Configuration Management Office

NASA GSFC

Code 424 Greenbelt, MD 20771 iv Check the TSIS-2 TDMS Server at https://ipdtdms.gsfc.nasa.gov to verify that this is the correct version prior to use.

Change History Log

Revision Effective Date Description of Changes

- 08/06/2019 Baseline A 10/24/2019 TSIS2-CCR-0024 – Added TIM and SIM In-rush current figures

Table of TBDs/TBRs/TBSs

Item No. Location Summary TBD 2.0 Reference Documents TBR 5.7 magnetic flux density TBD 6.4 Thermal Sensors location TBD 6.5.1 Radiative Surfaces of integrated TIM assembly TBR 7.5.4 The spacecraft shall transmit commands to the instruments from the stored command buffer at the time indicated +/- 1 second v Check the TSIS-2 TDMS Server at https://ipdtdms.gsfc.nasa.gov to verify that this is the correct version prior to use.

Table of Contents

1 INTRODUCTION

1.1 Purpose

1.2 Scope

2 REFERENCE DOCUMENTS

3 TSIS-2 INSTRUMENTS SUITE OVERVIEW

3.1 Block Diagram

3.2 Total Irradiance Monitor

3.3 Spectral Irradiance Monitor

3.5 SIM Generic Channel Interface

3.6 Fine Sun Sensor

4 MECHANICAL INTERFACES

4.1 Mass

4.2 Volumetric Envelope

4.3 Footprint/Mounting Interface

4.4 Fields of View

4.5 Accessibility

4.6 Launch Environment

5 ELECTRICAL INTERFACES

5.1 Operational Orbital Average and Peak Power

5.2 Inrush Current

5.3 Survival Heater Power

5.4 Power Characteristics

5.5 Grounding

5.6 Communication

5.7 Magnetics

6 THERMAL INTERFACES

6.1 Interface Thermal Control

6.2 Thermal Conductivity

6.3 Blanketing

6.4 Thermal Sensors

6.5 Radiative Surfaces

7 DATA INTERFACES

7.1 Communication Protocols

7.2 Real Time Telemetry Output

7.3 Telemetry Storage

7.4 Telemetry Monitoring

7.5 Command Storage

7.6 Safing Commands

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8 OPERATIONAL CONSIDERATIONS

8.1 Solar Pointing

8.2 Dark Pointing

9 OBSERVATORY INTEGRATION AND TEST CONSIDERATIONS

9.1 Operation

9.2 TIM Backfill/Vacuum

9.3 SIM Backfill

9.4 Vent Valve Operation

9.5 Vacuum Door Operation

9.6 TIM Standard Watt Testing

9.7 SIM/FSS Stimulus

List of Figures

Figure 1. TSIS-2 Block Diagram Figure 2. TIM GCI Envelope Figure 3. TIM Envelope Figure 4. TIM Mounting Locations Figure 5. SIM GCI Envelope Figure 6. SIM Envelope Figure 7. SIM Mounting Locations Figure 8. TIM In-rush Current Figure 9. SIM In-rush Current Figure 10. SIM Radiative Surfaces

List of Tables

Table 1. TIM Component Mass Allocation Table 2. SIM Component Mass Allocations Table 3. Quasi-Static Design Limit Load Factors (All Axes) Table 4. Interface Random Vibration Levels Table 5. Interface Sine Sweep Vibration Levels (All Axes) Table 6. Shock Environment at the TIM and SIM Table 7. Shock Environment at the TIM and SIM Table 8. TIM Orbit Average and Peak Operational Power Table 9. SIM Orbit Average and Peak Operational Power Table 10. GCI Telemetry 'Word' Format Table 11. GCI Command 'Word' Format Table 12. Nominal Orbit Average TSIS-2 Instrument Telemetry Rates Table 13. TSIS-2 Instrument Telemetry Allocations Table 14. TSIS-2 Instrument Uplink Allocations

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1 INTRODUCTION

The TSIS-2 instrument suite consists of two instruments, the Total Irradiance Monitor (TIM) and the Spectral Irradiance Monitor (SIM), each with its associated electronics boxes, called Generic Channel Interfaces (GCI), and one Fine Sun Sensor (FSS). TSIS-2 is an almost identical copy of the TSIS-1 instruments that is successfully flying on the International Space Station.

1.1 Purpose

This document is intended to serve as the reference for spacecraft and instruments for key instruments-to-spacecraft mechanical, electrical, thermal, optical, data and operational interfaces.

1.2 Scope

This document covers only the interfaces between the TSIS-2 instruments, GCIs, the FSS, and the spacecraft.

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2 REFERENCE DOCUMENTS

To be Determined (TBD)

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3 TSIS-2 INSTRUMENTS SUITE OVERVIEW

3.1 Block Diagram

The TSIS-2 instrument suite-to-host spacecraft block diagram is shown in Figure 1. Details on each of the interfaces between TSIS-2 instruments and the host spacecraft are discussed later in this document (Sections 5-6). Interfaces between elements of the TSIS-2 instrument suite are only discussed to the extent that they impact the instrument accommodation.

Figure 1. TSIS-2 Block Diagram

Note: All harnesses between the TSIS-2 spacecraft and the instrument components shall be provided by the spacecraft vendor (all intra-instrument harnesses are provided by the instrument vendor).

TIM

TGCI

(TIM Generic

Channel Interface)

Power

Survival Power

Analog Telemetry

C &DH (422)

Power

Survival Power

Analog Telemetry

SIM

SGCI

(SIM Generic

Channel Interface)

FSS

Cmd/Tlm

Power

Survival Power

Analog Telemetry

C &DH (422)

Power

Survival Power

Analog Telemetry

SC interface

FSS Power

FSS Tlm

Cmd/Tlm

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The TIM and SIM each have its own GCI that contains the logic and electronics needed to operate the mechanisms and collect science and housekeeping data from the instrument. Each instrument will incorporate a thermostatically-controlled survival heater that will be powered by the spacecraft bus. The SIM also mechanically incorporates an FSS that is precisely aligned with the instrument apertures. The SIM GCI provides the power and data interfaces to the FSS that is mounted on the SIM instrument.

3.2 Total Irradiance Monitor

The TIM instrument is a quad-channel electrical substitution radiometer (ESR) records the total (integrated) solar irradiance. The detectors are embedded deep within the instrument behind several layers of light baffles and a set of shutter mechanisms (one shutter per “cone” detector).

Precision apertures are incorporated to ensure that the instrument will meet its high accuracy science requirement. Four cavities are used with varying rates on orbit to provide long-term degradation corrections for the instrument. The cavity shutters not only prevent exposure of the cavities, but also modulate the solar input during science observations by cycling (typically, on a 100 second period). During orbit eclipse periods, the TIM continues to take dark data for calibration purposes.

3.3 Spectral Irradiance Monitor

The SIM instrument is a three-channel prism spectrometer that records the solar irradiance as a function of wavelength. Each channel consists of an entrance slit, shutter, prism, precision exit slit, and focal plane detectors in the form of three photodiodes and a single bolometer. The prisms for all three channels sit in a single caddy and are rotated by a single motor. A fourth optical path and mirror attached to the prism caddy couple with a charge coupled device (CCD) on the focal plane to provide position encoding for the prism drive and thus, feedback for the wavelengths incident on the science detectors. The shutters in the optical paths not only serve to prevent exposure of the prisms and detectors, but also modulate the solar input during science observations by cycling (typically with a 40 to 200 second period). SIM data is continuously produced, even while not performing a scan with the prism. Dark data are collected during some orbit day periods simply by scanning the prism while holding the shutters closed.

3.4 TIM Generic Channel Interface

The Instrument Provider uses a single design for the power, digital logic, and science data interface for both the SIM and TIM instruments. This GCI design also provides circuitry for the control of the shutters, vacuum doors, and vent valve mechanisms on the instruments. It incorporates a LEON3 microprocessor for low-level instrument control and command and data handling (C&DH). Software is stored in Electrically Erasable Programmable Read-Only Memory (EEPROM) that can be modified on-orbit. The GCI has interfaces to the instrument as well as to the spacecraft and incorporates EMI and soft-start filters in the power circuitry.

3.5 SIM Generic Channel Interface

The SIM GCI is nearly identical to the TIM GCI, but also incorporates an additional electronics board that provides circuitry and logic to control the prism drive actuator. Like the TIM, the SIM GCI hosts software that provides low-level instrument control and C&DH. This software is stored in EEPROM that can be modified on-orbit. In addition to interfaces to the SIM instrument and to the spacecraft, the GCI provides power and receives telemetry from the FSS that is mounted on the SIM instrument.

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3.6 Fine Sun Sensor

The FSS uses a quad diode and special filters to provide high-resolution feedback on the position of the sun. The FSS produces raw quad diode values at 10 Hertz (Hz). Incorporated into this data are a handful of basic housekeeping values, such as temperature, that can be used to produce calibrated solar offset angles in two dimensions.

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4 MECHANICAL INTERFACES

The TSIS-2 spacecraft shall provide mounting for four instrument components: (1) the TIM instrument, (2) the TIM GCI, (3) the SIM instrument and its associated FSS, and (4) the SIM GCI, as well as support for the interconnecting harnesses.

The TSIS-2 instrument-to-spacecraft mechanical interfaces will be described in more detail in Section 4.2.

4.1 Mass

The mass of the TSIS-2 TIM and SIM instrument components will not exceed the values shown in Tables 1 and 2 below.

Table 1. TIM Component Mass Allocation

Mass kg

Sensor 10.74

Sensor 6.79

Interface Plate 2.64

Arc Flexure 0.5

NASA Margin 0.6

Misc Fasteners 0.18

Survival Heaters 0.01

Thermostats 0.01

GCI 4.04

Harnesses 0.6 Total 15.38

Table 2. SIM Component Mass Allocations

Mass kg

Sensor 15.75

Sensor 15.49

FSS 0.24

Survival Heaters 0.01

Thermostats 0.01

GCI 4.63

Harnesses 0.6

Total 20.99

4.2 Volumetric Envelope

The TSIS-2 instrument suite volumetric envelope is static. The TIM and SIM instruments have vacuum doors that are designed to open and close during ground testing and open once on orbit, but these swept volumes do not extend outside the volume of the instrument cases.

See Figures 2 through 7 for the TIM GCI envelope, TIM envelope, TIM mounting locations, SIM GCI envelope, SIM envelope, and SIM mounting locations (all dimensions are in inches).

The front (apertures) of both the TIM and SIM need to be sun-pointing during non-eclipse, as indicated in the TIM and SIM envelope figures below.

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Figure 2. TIM GCI Envelope

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Figure 3. TIM Envelope

Sun

Sun ⊗

Sun ⊙

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Figure 4. TIM Mounting Locations

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Figure 5. SIM GCI Envelope

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Figure 6. SIM Envelope

Sun

Su

Sun ⊗

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Figure 7. SIM Mounting Locations

4.3 Footprint/Mounting Interface

The mounting interfaces for all TSIS-2 instrument components are shown in Section 4.2.

4.4 Fields of View

The fields of view (FOV) for the TIM, SIM and FSS are as defined below. The face of the instrument that is sun-pointing in non-eclipse (and points to cold space in eclipse as described in Section 8.2) is shown in Figures 3 and 6 for TIM and SIM respectively.

4.4.1 The TSIS-2 spacecraft shall provide the SIM instrument apertures with a full cone angle glint-free field of view of at least 2.25 degrees by 2.5 degrees.

4.4.2 The TSIS-2 spacecraft shall provide the TIM instrument apertures with a half cone angle glint-free field of view of at least 21 degrees.

4.4.3 The TSIS-2 spacecraft shall provide the FSS aperture with a full cone angle glint-free field of view of at least 18.34 degrees.

4.5 Accessibility

During Observatory integration and testing (I&T), technicians will require access to the following elements on the TSIS-2 instruments. Details on required clearance shall be documented in the Mechanical Interface Control Document (MICD).

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4.5.1 TIM Backfill/Vacuum Port

The TIM backfill/vacuum port located on the TIM sensor will be used for vacuum pumpdown during Comprehensive Performance Tests (CPT) as well as for backfill operations following CPTs, Thermal Vacuum (TVAC), and for periodic top-off due to slow leaks.

4.5.1.1 The TIM instrument will maintain slightly positive pressure without backfill for at least 90 days.

4.5.1.2 The TSIS-2 spacecraft shall provide physical access to the TIM backfill/vacuum port for backfill/vacuum operations throughout ground testing.

The location of the TIM backfill/vacuum port as well as the dimensions of the backfill/vacuum GSE connector will be detailed in the TSIS-2 instrument MICD.

4.5.2 TIM Standard Watt Diagnostic Connector

The TIM standard watt diagnostic connector located on the TIM sensor will be used for periodic science characterization throughout ground testing. The connector will be closed out with a green tag cover prior to launch.

4.5.2.1 The TSIS-2 spacecraft shall provide physical access to the TIM Standard Watt Diagnostic Connector throughout ground testing.

4.5.3 TIM GSE Stimulus

A GSE stimulus lamp assembly that provides individually controlled lights to illuminate the TIM aperture will be provided by The Laboratory for Atmospheric and Space Physics (LASP) with the flight instrument, along with GSE that controls the lamps. The assembly and associated harnesses will be vacuum compatible, as they will be needed during Observatory Thermal/Vacuum testing. The stimulus will also be used for CPTs and for Limit Performance Tests (LPT) if possible. The stimulus will be installed and removed as needed by LASP personnel.

4.5.3.1 The TSIS-2 spacecraft shall provide physical access to the TIM aperture for stimulus lamp installation and removal throughout ground testing.

4.5.3.2 The TIM stimulus assembly will incorporate captured fasteners for integration to the instrument.

The TIM stimulus assembly envelope will be included in the Computer Aided Design (CAD) model provided to the spacecraft vendor. The envelope will also be described in the TSIS-2 instrument MICD.

4.5.4 TIM Optical Alignment Cube

An optical alignment cube is integrated onto the TIM interface plate for use in pre- and post-environmental alignment verification. A green tag cover may be installed over the cube prior to launch.

4.5.4.1 The TSIS-2 spacecraft shall provide optical access to the TIM alignment cube as needed throughout ground testing for alignment verification.

The TIM optical alignment cube will be included in the CAD model provided to the spacecraft vendor. The location of the cube will also be described in the TSIS-2 instrument MICD.

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4.5.5 SIM Backfill Port

The SIM backfill/vacuum port shall be accessible during backfill operations following TVAC and for periodic top-off due to slow leaks.

4.5.5.1 The SIM instrument usually maintains positive pressure without backfill for at least 90 days.

The location of the SIM backfill port will be detailed in the TSIS-2 instrument MICD.

4.5.6 SIM/FSS GSE Stimulus

A GSE stimulus lamp assembly that provides individually controlled lights to illuminate each of the SIM and FSS apertures will be provided by LASP with the flight instrument, along with GSE that controls the lamps. The assembly and associated harnesses will be vacuum compatible, as they will be needed during Observatory Thermal/Vacuum testing. The stimulus will also be used for CPTs and for LPTs if possible. The stimulus will be installed and removed as needed by LASP personnel.

4.5.6.1 The TSIS-2 spacecraft shall provide physical access to the SIM and FSS aperture for stimulus lamp installation and removal throughout ground testing.

4.5.7 SIM/FSS Optical Alignment Cube

An optical alignment cube is integrated onto the SIM sensor for use in pre- and post-environmental alignment verification. A green tag cover may be installed over the cube prior to launch.

4.5.7.1 The TSIS-2 spacecraft shall provide optical access to the SIM/FSS alignment cube as needed throughout ground testing for alignment verification.

The SIM/FSS optical alignment cube will be included in the CAD model provided to the spacecraft vendor. The location of the cube will also be described in the TSIS-2 instrument

MICD.

4.6 Launch Environment

4.6.1 The spacecraft interface plate shall be as stiff as reasonably possible, to prevent reduction of the instrument natural frequencies (for information, SIM’s measured first mode is 80 Hz and TIM’s is 179 Hz).

4.6.2 Tables 3-7 include the expected flight environment for the TSIS-2 instruments and electronics boxes.

Table 3. Quasi-Static Design Limit Load Factors (All Axes) Unit Limit Load (g)

TIM 19

SIM 18

GCI 30

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Table 4. Interface Random Vibration Levels (All Axes, GSFC-STD-7000A Table 2.4-3)

Frequency (Hz) ASD Level (g2/Hz)

20-50 50-800

800-2000

0.013 +6 dB/oct

0.08 -6 dB/oct

0.013 Overall 10.0 Grms

Table 5. Interface Sine Sweep Vibration Levels (All Axes)

Frequency (Hz) Level (g) 5 to 15.8 0.5 in (double amplitude)

15.8 to 50 6.4

Table 6. Shock Environment at the TIM and SIM

GCI Boxes Interface to the Spacecraft (Q=10) Frequency (Hz) Level (g)

100 160 630 1000

10000 1000

Table 7. Shock Environment at the TIM and SIM Instrument Interface to the Spacecraft (Q=10) Frequency (Hz) Level (g)

100 80 630 500

10000 500

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5 ELECTRICAL INTERFACES

The electrical interfaces between the TSIS-2 spacecraft and instrument suite are summarized in Figure 1 above. All harnesses between the TSIS-2 spacecraft and the instrument components shall be provided by the spacecraft vendor (all intra-instrument harnesses are provided by the instrument vendor).

5.1 Operational Orbital Average and Peak Power

The TSIS-2 spacecraft shall provide orbital average and peak power to the TSIS-2 instrument suite per Tables 8 and 9 below.

Table 8. TIM Orbit Average and Peak Operational Power

Table 9. SIM Orbit Average and Peak Operational Power

Power (W) Power (W)

Door Operation 13.65 Door Operation 13.65

GCI 13.29 GCI 13.29

Sensor 3.05 Sensor 3.47

Operational Heater FERRY PRISM DRIVE (FPD)

Operational Heater (peak) 16.8 FPD Scanning 3.99

Operational Heater (orbit avg.) 9.6 FPD Peak (31% FPD duty cycle) 6.65

Margin 2.23 FPD (orbit avg.) 1.47

Orbit Average Power 28.17 Operational Heater

Peak Power 49.02 Operational Heater (peak) 39.48

Operational Heater (orbit avg.) 13.76

FSS 1.26

Orbit Average Power 33.25

Peak Power 71.14

5.2 Inrush Current

The TIM and SIM turn-on inrush current shall not exceed 15% of the typical plots shown in Figures 8 and 9 below.

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Figure 8. TIM In-rush Current

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Figure 9. SIM In-rush Current

5.3 Survival Heater Power

During survival (non-operational mode), the spacecraft shall be capable of providing survival heater power to the TSIS-2 instrument components. The instruments’ survival heater power will be less than one half of the average orbital power. Survival heater power shall be on a separate feed.

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5.4 Power Characteristics

5.4.1 The TSIS-2 instrument components will accept any input voltage in the range from 0 to +34 V Direct Current (DC) without permanent damage or degradation.

5.4.2 The TSIS-2 instrument components and survival heaters will operate with an unregulated input steady-state voltage in the range from +22 to +34 V DC.

5.4.3 The TSIS-2 spacecraft operational power and survival heater services to the instruments shall be a steady-state voltage in the range from +22 to +34 V DC.

5.4.4 The TSIS-2 spacecraft operational power service to the instruments shall limit transients above 34V DC to not exceed 39 V DC at the instrument interfaces.

5.4.5 The TSIS-2 spacecraft operational power service to the instruments shall limit transients above 34V DC to not exceed 10 milliseconds in duration at the instrument interfaces.

5.4.6 The TSIS-2 spacecraft operational power service to the instruments shall limit transients below 22V DC to not go below -2 V DC at the instrument interfaces.

5.4.7 The TSIS-2 spacecraft operational power service to the instruments shall limit transients below 22V DC to not exceed 100 microseconds in duration at the instrument interfaces.

5.4.8 The ripple on the operational power services provided by the spacecraft shall be less than

0.5 V peak to peak as measured over the bandwidth from DC to 10MHz when the power system is delivering the maximum rated current into resistive loads.

5.5 Grounding

5.5.1 The TSIS-2 instrument components’ operational power returns will be isolated from the instrument chasses by at least 1 MOhm.

5.5.2 The impedance between the spacecraft and the TSIS-2 instrument component chassis shall be 10 mOhm or less.

If required, grounding straps will be provided as Government Furnished Equipment (GFE) and the design will be described in the instrument MICD.

5.6 Communication

The TSIS-2 instruments communicate with the host spacecraft over asynchronous RS-422 connections. The TIM and SIM use heritage ‘GCI Packet’ data formats for both commanding and telemetry. No input or output discretes and no sync pulse is used on the instrument interface.

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5.6.1 The communication link between the TIM and the spacecraft shall be an asynchronous RS-422 connection operating at 460.8 kilobaud (kbaud) with 8 bits of data, 1 start bit, 1 stop bit, and no parity bit.

5.6.2 The communication link between the SIM and the spacecraft shall be an asynchronous RS-422 connection operating at 460.8 kbaud with 8 bits of data, 1 start bit, 1 stop bit, and no parity bit.

5.6.3 The communication link between the TIM and the spacecraft shall conform to the EIA- 422 standard for 3.3 V signaling with 45 Ohm source series termination.

5.6.4 The communication link between the SIM and the spacecraft shall conform to the EIA- 422 standard for 3.3 V signaling with 45 Ohm source series termination.

5.7 Magnetics

The magnetic flux density (magnetic induction) due to the TSIS-2 instrument components will be no more than 350 nT (TBR) at a distance of 1.0 meters (m) from the instrument component center of gravity.

The TSIS-2 instruments will have a residual magnetic dipole of less than 0.1 A-m2.

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6 THERMAL INTERFACES

6.1 Interface Thermal Control

6.1.1 The spacecraft shall maintain the temperature of the mounting interface of the TIM sensor within the range from -30 deg C to +45 deg C.

6.1.2 The spacecraft shall maintain the temperature of the mounting interface of the SIM/FSS sensor within the range from -30 deg C to +45 deg C.

6.1.3 The spacecraft shall maintain the temperature of the mounting interface of the TIM GCI within the range from -30 deg C to +45 deg C.

6.1.4 The spacecraft shall maintain the temperature of the mounting interface of the SIM GCI sensor within the range from -30 deg C to +45 deg C.

6.2 Thermal Conductivity

6.2.1 The conductive heat transfer across the TIM mounting interface will be less than 3 W.

6.2.2 The conductive heat transfer across the SIM/FSS mounting interface will be less than 3 W.

6.2.3 The conductive heat transfer across the TIM GCI mounting interface will be less than 3 W.

6.2.4 The conductive heat transfer across the SIM GCI mounting interface will be less than 3 W.

6.3 Blanketing

LASP will deliver one set of flight blankets for the TSIS-2 instrument components with the flight instrument.

6.4 Thermal Sensors

The spacecraft shall provide 7 thermal sensors, location TBD, for the instrument.

6.5 Radiative Surfaces

6.5.1 TIM

The radiative surfaces of the integrated TIM assembly is TBD (for information, on TSIS-1 TIM was completely blanketed).

6.5.2 TIM GCI

The radiative surface of the integrated TIM GCI is the plane opposite its mounting feet.

6.5.3 SIM

The radiative surfaces of the integrated SIM/FSS assembly are as shown highlighted in red in the Figure below.

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Figure 10. SIM Radiative Surfaces

6.5.4 SIM GCI

The radiative surface of the integrated SIM GCI is the plane opposite its mounting feet.

Radiator

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7 DATA INTERFACES

7.1 Communication Protocols

Per Figure 1 above, the TSIS-2 instruments communicate via a heritage “GCI Packet” format.

Because this format is somewhat complex and the spacecraft has no need to parse instrument commands and telemetry, the spacecraft will treat the interface to the instruments as a simple “bent-pipe” or bytestream.

The communication link between all TSIS-2 components and spacecraft shall be an asynchronous RS-422 connection operating at 460.8 kbaud with 8 bits of data, 1 start bit, 1 stop bit, and no parity bit.

7.1.1 Telemetry

Telemetry from TIM and the SIM/FSS assembly consists of 64-bit ‘words’ where one or more ‘words’ constitute a packet. The format of a GCI telemetry ‘word’ is shown in Table 10.

Table 10. GCI Telemetry 'Word' Format GCI Telemetry Header (1 byte) Data (7 bytes) Bit: 63 62:60 59 58:57 56 55:0

Parity (1 bit)

Channel

ID

(3 bits)

Immediate Pkt (1 bit)

Packet Grouping (2 bits)

Housekeeping Pkt (1 bit)

Data (7 bytes)

The SIM, TIM, and FSS each have unique Channel IDs. Since the FSS data are routed through the SIM GCI, the Channel ID can be used to separate FSS data from SIM data. The Packet Grouping bits distinguish a ‘word’ as either the first, middle, last, or single ‘word’ in a packet.

The Immediate Pkt and Housekeeping Pkt bits help indicate the packet type; these packets are produced by the GCI Field Programmable Gate Array (FPGA). If neither bit is set, the ‘word’ was created by the instrument flight software and the packet type is embedded within the first byte of the Data field. TIM flight software produces 9 different telemetry packets and SIM flight software produces 14 different telemetry packets. The FSS and GCI Housekeeping and Immediate packets are fixed length as are most, but not all of the flight software packets.

Instrument telemetry packet generation is configurable on a per-packet basis for those packets that are not event driven.

The parity bit is the most significant bit of the most significant byte of the GCI telemetry ‘word’.

GCI telemetry ‘words’ are transmitted by byte in bit order from 64 to 0, as labeled in Table 10.

Parity of GCI telemetry words is even.

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7.1.1.1 The spacecraft shall verify parity of each TSIS-2 instrument GCI telemetry ‘word’ received.

7.1.1.2 The spacecraft shall maintain in telemetry unique counts of GCI telemetry ‘words’ received with bad parity on both of the SIM and TIM telemetry streams.

7.1.1.3 The spacecraft shall include GCI telemetry ‘words’ with bad parity in the real-time downlink stream and recorded telemetry buffer. This helps facilitate troubleshooting efforts and may allow for partial data recovery.

7.1.2 Commands

The FSS does not have command capability. Commands to the TIM and SIM consist of a single 32-bit GCI command ‘word’. There is no higher level packetization structure for instrument commands. The format of a GCI command ‘word’ is shown in Table 11.

Table 11. GCI Command 'Word' Format GCI Header (1 byte) Data (3 bytes) Bit: 31 30:28 27 26:25 24 23:0 Parity

(1 bit) Channel

ID

(3 bits)

Reserved (1 bit)

Reserved (2 bits)

Reserved (1 bit)

Data (3 bytes)

The SIM and TIM command ‘word’ Channel IDs match those used for GCI Telemetry ‘words’.

Embedded within the Data bytes is a command identifier (opcode) that is interpreted by the GCI FPGA. Commands to the embedded instrument flight software are indicated by a single GCI opcode. Due to the limited size of commands to the flight software, many instrument commands require multiple command words to be sent to achieve a single task (setting a telemetry packet production period, for example); however, there is no requirement on the time between receipt of these command ‘words’- it can be as long as necessary given round-trip uplink times, latencies, command execution verification requirements, etc.

The spacecraft shall have the capability to immediately route uplinked commands to the TSIS-2 instrument components (SIM, TIM) for real-time execution.

7.2 Real Time Telemetry Output

To conduct TSIS-2 instrument testing during Observatory I&T and during on-orbit commissioning and troubleshooting, instrument telemetry data shall be included in the real-time downlink telemetry stream from the spacecraft.

7.3 Telemetry Storage

The nominal orbit average TSIS-2 instrument telemetry rates at the instrument interface are given in Table 12. The telemetry rates may be higher during ground testing and on-orbit commissioning and troubleshooting. The values shown in the table are those that are used to size the allocation for instrument telemetry in the recorder.

Check the TSIS-2 TDMS Server at https://ipdtdms.gsfc.nasa.gov to verify that this is the correct version prior to use.

Table 12. Nominal Orbit Average TSIS-2 Instrument Telemetry Rates

Nominal Orbit Average Telemetry Rate (bits per second)

SIM/FSS 3417

TIM 1633

The nominal daily telemetry volume allocations shown in Table 13 are generated based on the values in Table 12.

Table 13. TSIS-2 Instrument Telemetry Allocations

Downlink Allocations (millions of bits per day)

SIM/FSS 360

TIM 175

7.4 Telemetry Monitoring

No instrument telemetry needs to be monitored by the spacecraft bus for fault detection or any other purpose. The complex nature of the instrument telemetry format makes any such monitoring impractical.

7.5 Command Storage

The TSIS-2 instruments require periodic commanding to perform their science observations.

The instrument uplink allocations are shown in Table 14. These allocations are at the instrument interface.

Table 14. TSIS-2 Instrument Uplink Allocations Uplink Allocations

(thousands of bits per day)

SIM 133

TIM 22

7.5.1 The TSIS-2 instruments’ command volume at the instrument interface for nominal operations will not exceed the values Table 14.

7.5.2 The spacecraft shall have the capability to store instrument commands for later execution.

7.5.3 The spacecraft shall have a time resolution of 1 second or better for instrument stored commands.

7.5.4 The spacecraft shall transmit commands to the instruments from the stored command buffer at the time indicated +/- 1 second (TBR).

7.5.5 The spacecraft shall allocate sufficient command storage space to store instrument commands between scheduled uplink opportunities with allocations no smaller than those derived from Table 14 and the uplink schedule including any additional overhead incurred prior to the instrument interface.

Check the TSIS-2 TDMS Server at https://ipdtdms.gsfc.nasa.gov to verify that this is the correct version prior to use.

7.6 Safing Commands

Before safing the instrument, the Spacecraft shall allow time for the instrument to close its shutters.

Check the TSIS-2 TDMS Server at https://ipdtdms.gsfc.nasa.gov to verify that this is the correct version prior to use.

8 OPERATIONAL CONSIDERATIONS

8.1 Solar Pointing

The spacecraft shall perform solar pointing for nominal science data collection for the full sunlit period of each orbit.

8.2 Dark Pointing

8.2.1 The spacecraft shall point the instruments towards dark space (i.e., moon and earth out of the instrument FOVs) for calibration data collection during the eclipse portion of each orbit.

8.2.2 The spacecraft shall transition from normal solar pointing to dark space pointing within 200 seconds of eclipse entry.

9 OBSERVATORY INTEGRATION AND TEST CONSIDERATIONS

9.1 Operation

The TSIS-2 instrument suite will be operated by the instrument provider personnel during each phase of ground testing.

9.2 TIM Backfill/Vacuum

The TIM instrument will be maintained at positive pressure with respect to ambient during ground testing, with the exception of during high-vacuum thermal vacuum testing.

The Instrument Provider will arrange for provision of the Ultra High Purity argon gas required for the backfill at both Observatory I&T and launch site I&T.

9.3 SIM Backfill

The TIM instrument will be maintained at positive pressure with respect to ambient during ground testing, with the exception of during high-vacuum thermal vacuum testing.

9.4 Vent Valve Operation

The SIM and TIM instruments may be vented during Observatory-level Thermal Balance and TVAC testing. The volume of gas for each instrument is small relative to the TVAC chamber, but chamber operators will need to be prepared for the vent operation. The venting will be performed well in advance of vacuum door operation, if necessary.

9.5 Vacuum Door Operation

Any time the TIM and SIM vacuum doors are opened, there is a contamination risk to the instrument. The doors may be opened during Observatory-level Thermal Balance and TVAC testing. When returning to ambient pressure, the instruments will need to power on briefly so that the doors can be closed prior to chamber door opening.

9.6 TIM Standard Watt Testing

The TIM instrument requires periodic characterization of its science electronics circuitry, which is performed in a Standard Watt Test. This test requires GSE to be connected directly to the instrument sensor as described in Section 4.5.2 of this document. The TIM standard watt testing will be conducted by LASP personnel.

Check the TSIS-2 TDMS Server at https://ipdtdms.gsfc.nasa.gov to verify that this is the correct version prior to use.

9.7 SIM/FSS Stimulus

A stimulus GSE assembly will be mounted on the SIM instrument for certain tests as described in Section 4.5.6 of this document. The SIM/FSS stimulus will be operated by LASP personnel throughout I&T.

Check the TSIS-2 TDMS Server at https://ipdtdms.gsfc.nasa.gov to verify that this is the correct version prior to use.

Appendix A Abbreviations and Acronyms

C&DH Command and Data Handling CAD Computer Aided Design CCD Charge Coupled Device Cmd/Tlm Command/Telemetry CPT Comprehensive Performance Tests Db Decibel DC Direct Current Deg degree EEPROM Electrically Erasable Programmable Read-Only Memory ESR Electrical Substitution Radiometry FOV Dield of View FPD Fery Prism Drive FPGA Field Programmable Gate Array FSS Fine Sun Sensor GCI Generic Channel Interface GSE Government Furnished Equipment Hz Hertz IARD Instrument Accommodation Requirements Document I&T Integration and Testing kbaud Kilobaud LASP Laboratory for Atmospheric and Space Physics LPT Limit Performance Tests MICD Mechanical Interface Control Document MOhm Mega Ohm mOhm Milli Ohm nT NanoTesla oct Octave opcode Command Identifier ppm parts per million SC Spacecraft SIM Spectral Irradiance Monitor TBD To be Determined TBR To be Refined TGCI TIM Generic Channel Interface TIM Total Irradiance Monitor TSIS Total and Spectral solar Irradiance Sensor TVAC Thermal Vacuum V Volt W Watt