NPOESS Satellites Support Demanding Operational Requirements

Northrop Grumman Aerospace Systems (NGAS), based in Southern California is the system prime contractor for the National Polar-orbiting Operational Environmental Satellite System (NPOESS). To accomplish this next generation low earth orbiting environmental mission Northrop Grumman is utilizing a multi-mission bus that satisfies both the afternoon 1330 as well as the late afternoon 1730 low earth polar orbits with a single spacecraft design. This spacecraft leverages products and capabilities from the EOS Aqua and Aura spacecraft while integrating newer generation capabilities such as FireWire for accommodating advanced sensor payloads and much higher data rates than current weather systems.

The first NPOESS satellite will be launched in 2014 for a constellation that will operate well into the following decade. This paper will provide an overview of the driving NPOESS Satellite and Sensor capabilities.

NPOESS satellites must accommodate at least 10 sensor suites per satellite that observe from the ultra-violet to microwave regimes. The sensors include VIIRS, CrIS, MIS, ATMS, OMPS, CERES, TSIS, SEM-N, SARSAT, and A-DCS.

These sensors plus the flexibility to accommodate future climate sensors drove the design of a flexible data handling architecture that provides the following:

• The ability to pass all sensor and spacecraft data, which is greater then (>20 Mbps), to the NPOESS SafetyNetTM communication architecture enabling low latency (most EDRs are produced in 15 minutes) and high (99.99%) availability

• A large solid state recorder providing double downlink capability supporting the high data availability

• On-board lossless and lossy compression of VIIRS data and selected CrIS data to field users with high or low rate data abilities.

• A space qualified 1394 Firewire data bus to the VIIRS, CrIS, MIS sensors along with the ability to easily add future sensors in a plug-and-play approach

• A 1553 data bus to lower data rates sensors to include ATMS, OMPS, CERES, TSIS, SEM-N, SARSAT, A-DCS and future sensors.

The need for low data latency and connectivity to the field users drove the satellite communication architecture which includes the following:

• Ka band SafetyNet transmitter with the ability to autonomously track the world wide SafetyNet receivers

• X-band High Rate Data to field users

• L-band Low Rate Data (LRD) to field users

• S-band command receipt and telemetry downlink to the Svalbard terminal

In order to ensure co-alignment of the entire sensor manifest, the NPOESS satellite requires a composite bus. This is an upsized version of the EOS 3 meter class bus used for a Delta II class of launch vehicle. The larger variant NPOESS bus maximizes the available envelope afforded by the more capable 4 meter EELV launch vehicles to host existing manifested payloads while affording extra “deck space” future sensors.

The satellite and most sensors have high reliability designs using class A parts meeting a seven year design life to reduce overall life cycle costs.

The NPOESS satellite which has completed CDR will provide the next generation platform for low earth orbit weather and climate monitoring.