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NPOESS Satellites Support Demanding Operation Requirements

Derrick Day,1 MaryAnn Chory2 and Jim Nelson3 Northrop Grumman Aerospace Systems, Redondo Beach, CA 90278 USA

Major Mike Perz4 and Major Jared Burdin5 U.S. Air Force NPOESS IPO, Silver Spring, MD 20910 USA

Nomenclature NPOESS = National Polar-orbiting Operational Environmental Satellite System

I. Introduction N 2002 the Integrated Program Office, responsible for the development, deployment and operation of the nation’s next generation weather and climate monitoring satellites, awarded the NPOESS system prime contract to

Northrop Grumman (then TRW). To accomplish this next generation, low earth orbiting environmental mission, Northrop Grumman is utilizing a multi-mission bus that satisfies both the afternoon 1330 Local Time of the Ascending Node (LTN) and late afternoon 1730 LTN sun synchronous orbits with a common spacecraft design. This spacecraft leverages products and capabilities from prior EOS Aqua and Aura spacecraft while integrating new capabilities such as FireWire, for accommodating advanced sensor payloads in a plug-and-play architecture, with much higher data rates than current weather systems; and Safety Net, for ensuring minimal latency in delivering science data to multiple processing centers. This bus is designed to provide the next generation of low-earth orbiting, weather satellites with a capable, expandable platform engineered to facilitate multiple missions and to enable easy incorporation of state-of-the-art weather, climate, and space environmental sensors into the NPOESS constellation. Figure 1 below summarizes the NPOESS key spacecraft features that fully support all mission requirements. The paper will focus on the new capability for operational users that the NPOESS spacecrafts will provide.

II. Plug-and-Play NPOESS was envisioned by the IPO and developed by Northrop Grumman to be an easily expandable system to

address evolving climate and weather missions over the next several decades. Figure 2 summarizes the key mission requirements that drive the design. The NPOESS spacecraft fulfills this vision, providing a precision optical bench platform that can fly in a broad range of orbits, host multiple sensors, and provide open fields of view with precisely controlled alignments and dynamics. Key to this flexibility is ensuring robust power and well characterized and controlled thermal, and EMI environments on a bus with the data handling, fault-tolerance, and reliability crucial for Operational Missions. Not only does NPOESS provide these environments, but it has been engineered to do so in such a way that adding new capabilities does not result in redesign of primary hardware. Figure 3 illustrates the key features of the spacecraft design that allows flexible and economical accommodation of sensors. The following sections describe some of these capabilities in more detail.

A. Data Handling and Processing

1 NPOESS P3I Lead, Civil Space, One Space Park/R10-2830 2 Director, NPOESS Space Segment, Civil Space, One Space Park/R10-2880 3NPOESS Deputy Space Segment Manager, Civil Space, One Space Park/R10-2880 4 NPOESS Space Segment Lead, NPOESS IPO, 8455 Colesville Road/Suite 1450 5 NPEOSS Deputy Space Segment Lead, NPOESS IPO, 8455 Colesville Road/Suite 1450

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Copyright © 2009 by Copyright © 2009 by Northrop Grumman Corporation." . Published by the American Institute of Aeronautics and Astronautics, Inc., with permission.

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While NPOESS has the resources and flexibility to accommodate custom sensor data interfaces, it was engineered from the start to provide plug-and-play resources to sensors designed to standard electrical communications interfaces. Recognizing that not all payload throughputs are the same, the NPOESS bus architecture employs an IEEE 1553 standard interface for lower data-rate users and a fault-tolerant IEEE 1394 standard interface for higher rate users. Both of these standards allow for simple extensions of the networks to accommodate new users without bus hardware “breakage.” Figure 4 below depicts the NPOESS bus data architecture.

VIIRS

MIS

CrIS

P3I

DSU

SCP

PSP

1394 Ring• SCP Manages 1394 Bus

1553 Payload Buses• PSP manages P/L 1553B busses

SuS

ATMS SARR TPS SEM

OMPS TSISALT &GPS

APS

Aurora CERES ERBS P3I

A-DCS4

ACSEPS

1553 Spacecraft Buses• SCP Manages S/C 1553B Bus

VIIRS

MIS

CrIS

P3I

DSU

SCP

PSP

1394 Ring• SCP Manages 1394 Bus

1553 Payload Buses• PSP manages P/L 1553B busses

SuS

ATMS SARR TPS SEM

OMPS TSISALT &GPS

APS

Aurora CERES ERBS P3I

A-DCS4

ACSEPS

1553 Spacecraft Buses• SCP Manages S/C 1553B Bus

In this diagram one can see the multiple 1553 busses and dual-redundant 1394 network interconnecting the

payloads with the spacecraft data processing units. This architecture allows new sensor developers to apply their resources to engineering the science end of their product and leverage off-the-shelf hardware and software for the data interfaces. This minimizes costs at the sensor suppliers and allows the spacecraft to accommodate multiple payload manifests without changing command, telemetry or data processing hardware. Not only does this plug-and-play architecture minimize development challenges and expenses, it also means that integrators, testers, and operators familiar with 1553 and 1394 functionality can apply that expertise to new payloads without having to climb the learning curve of custom electrical and protocol interfaces. Also apparent in this diagram is the PSP or Payload Support Processor. This unit employs an advanced, high performance PowerPC processor-based single board computer, providing auxiliary processing to support limited bandwidth real time Low Rate Data (LRD) downlinking of data. This capability has already been leveraged for the first NPOESS satellites to enable delivery of vital VIIRS weather information to users in the field. The Figure 5 below provides some indication of the data processing and memory resources available on this Spacecraft to support advanced missions.

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The unique capabilities provided by NPOESS’ advanced data handling architecture, processing robustness, and memory capability ensures this system meets the requirements of key operational missions today and into the future -- science and weather, military and civilian, centralized and field processing. Early risk reduction activities for the critical advanced data handling hardware have been a spacecraft focus activity. Figure 6 shows the status of all the essential hardware that has entered into subsystem validation activities this summer on the Electrical Engineering Model Test Bed (EEMTB), with a verified version of the NPOESS flight software.

B. Infrastructure and Precision While data handling and processing is essential for today’s multi-mission platform, the platform must also ensure that the infrastructure and precision are there to support both the basic needs of advanced payloads and their stringent requirements. The modularity of the spacecraft, as shown in Figure 7, is a discriminator in ensuring all the operational mission requirements are met while allowing flexibility in the integration and test buildup.

SARSAT A-DCS RX ANTENNA

PROPULSION MODULE

AFT COMPARTMENT

PANEL 9

PANEL 10

PANEL 6

SEM-DPU

TPS-ICE

SEM-MEPED

SOLAR ARRAY

PANEL 1

PANEL 2

PANEL 4

VIIRS

PANEL 7

OMPS

ALTIMETER

ATMS

CrIS

BATTERY MODULE

PANEL 8

CERES

SMD ANTENNA

SEM-TED

AURORA

SuS

PANEL 5

MIS

TSIS

TPS-ES

TPS-PS

+Y SIDE PANELTSIS TPS GCI

PANEL 3

SADA

MIS RWA

This modularity facilitates an easily re-configurable Electrical Engineering Model Test Bed (EEMTB) used for validating satellite interfaces, functionality and software, as shown in Figure 8.

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NPOESS EEMTB Facility operational for C&DH EMs

NPOESS EEMTB

Sensor EDUs

EPS & ACS EMs

C&DH EMs

To ensure basic needs are addressed, NPOESS is designed with a common electrical power subsystem; robust power generation, storage, and delivery, that allows all LTAN orbit operation with multiple sensor manifests. To ease accommodation of new sensors, power taps are brought out to bulkheads so that new sensors can easily be wired in with secondary harness installations. In addition to power, the NPOESS satellite also has core provisions to ensure the thermal environment accommodates standard electronics, thermal control systems can be added for payloads with unique requirements, the deck provides sufficient room for unobstructed fields of view, and the avionics compartments are sufficiently RF tight to provide the necessary EMI environments demanded by high frequency sensors. These core capabilities reside within a graphite composite bus structure that provides precision control of alignments and pointing. This enables not only the accommodation of precise pointing applications but also facilitates multi-sensor applications demanding strict control and knowledge of relative alignments and pointing. In order to ensure long-term co-alignment of the sensor manifest, a composite bus is mandatory. This precision has been engineered to ensure compliance over operational thermal and dynamic variations.

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The NPOESS Satellite is designed to be compatible with both the Delta IV and Atlas V launch vehicles (EELVs) and leverages their 4-meter diameter capability as depicted in Figure 9.

Delta IV

Atlas VDelta IV Atlas V1330 1730

III. Robust Data Delivery NPOESS is engineered to provide the best platform available for today and tomorrow’s weather and climate

remote sensing satellite applications. As such, it will serve numerous missions and provide crucial, operational and science data to multiple users. The NPOESS enterprise incorporates numerous features to ensure that data is available quickly and reliably directly to the users who need it.

A. Multiple Links The NPOESS satellite is designed to accommodate numerous, simultaneously operating RF links. This allows missions such as life-critical Search and Rescue to operate in conjunction with the delivery of hurricane imagery. Figure 10 below depicts the multiple links supported by the Spacecraft.

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While the Svalbard (Norway) Ground Station and TDRS provide Command and Control links, the SMD (Stored Mission Data), HRD (High-Rate Data), LRD (Low-Rate Data), ADCS (Advanced Data Collection System) and SARSAT (Search and Rescue) downlinks all provide mission data to various operational users. The NPOESS bus has been designed to ensure these transmitters and receivers can all operate in conjunction with one another without unacceptable interference or link degradation.

B. Latency The NPOESS system utilizes a network of Ka-Band, unmanned ground receptor stations, termed SafetyNet™,

which are connected to central data processing facilities via fiber optics. That ensures data collected on the spacecraft gets to the end users with minimal latency and high reliability. Most Environmental Data Records (EDRs – processed at the central facilities after delivery from SafetyNet™ will be available to users within 15 minutes of photons being collected by the satellite, and they will be available 99.99% of the time over the 7-year (design) life of each satellite. Figure 11 depicts all the numerous RF communication interfaces that satisfy the operational NPOESS mission requirements.

HRD FTS Sites

Wideband ground communications

LRD FTS Sites

C3S

Svalbard, NorwayPrimary T&C

NGNCommand & Telemetry2106.4/2287.5 MHz

TDRS

LRD DownlinkLow Data Rate1707 MHz, 7.76 Mbps

HRD DownlinkMedium Data Rate7834 MHz, 40 Mbps

SafetyNetReceptors

SARSAT Link1544.5 MHz D/L406.05 MHz U/L

A-DCS Link399.5-400.05, 401-403 MHz U/L465.9875 MHz D/L

GPS

SMD DownlinkHigh Data Rate26.7 GHz, 300 Mbps

Command & Telemetry2106.4/2287.5 MHz

L2: 1227.6 MHz L1: 1575.4 MHz

Reliable delivery of the data is enhanced with autonomous re-transmission of all stored mission data. This is

achieved using a solid-state recorder with multi-orbit capacity. Additionally, the NPOESS satellite is designed with a parts reliability program, redundancy, robust fault management architecture, production program (Mission Assurance), and test program that ensures reliable operation over its seven-year design life.

In addition to delivery of data to the central processing facilities via SafetyNet™, NPOESS also supports users in the field with delivery of key data to HRD and LRD terminals. The NPOESS satellites selectively compress data using JPEG2000 to ensure delivery of the maximum available information to those users with limited bandwidth.

IV. Conclusion N 2009 the NPOESS successfully completed numerous Critical Design Audits and its Critical Design Review (CDR). The program is currently well into the production and test of engineering models, well along the path to

launch in 2014. The satellite bus provides a precision optical platform able to meet the exacting requirements of future precision sensors and deliver their data quickly and reliably to worldwide users. The system leverages standard interfaces and pre-planned resource expansion to meet future missions and host future sensors with minimal adaptations. This performance, flexibility, and accommodation strategy, combined with reliability and fault

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management capabilities of a Class-A satellite program, makes the NPOESS satellite the premier platform for the future generations of low-earth orbiting weather and climate remote-sensing missions.