Editorial Team - SATNow
The Earth Observing-1 (EO-1) satellite was a NASA mission created to test innovative technologies and strategies for enhancing Earth observation. Launched in November 2000, it was managed by NASA’s Goddard Space Flight Center (GSFC) as part of the New Millennium Program. The goal was to lower costs and boost the efficiency of future space missions by experimenting with new technologies in space before wider use.
EO-1 carried three observation instruments along with various advanced space technologies. Although originally planned for just 1.5 years of service, its contributions were so valuable that NASA extended its mission until its final decommissioning in March 2017.
Atmosphere, Ocean, Land, Snow & Ice
Aerosol optical depth (column/profile), Land surface imagery, Vegetation type, Fire fractional cover, Earth surface albedo, Short-wave Earth surface bi-directional reflectance, Leaf Area Index (LAI), Vegetation Cover, Land cover, Land surface temperature, Sea surface temperature, Sea-ice cover, Snow cover, Normalized Differential Vegetation Index (NDVI), Sea-ice thickness, Fraction of Absorbed PAR (FAPAR), Glacier cover, Oil spill cover, Soil type
Objectives of EO-1
Spacecraft
The EO-1 spacecraft, managed by NASA’s Goddard Space Flight Center (GSFC), was developed and built by ATK Spacecraft Systems and Services (formerly Swales Aerospace, acquired by ATK in 2007). The spacecraft features a hexagonal aluminum structure, with a diameter of 1.25 meters and a height of 0.73 meters. It weighs 370 kg, with a payload capacity of up to 110 kg. The satellite is stabilized on three axes for both inertial and nadir pointing, utilizing an Autonomous Star Tracker (AST) for precise attitude control.
Equipped with a hydrazine propulsion system, EO-1's four 1N thrusters deliver a pointing accuracy of 0.03º, while jitter is kept below 5 arcseconds. It also features a new Propulsion System (PPT) that could potentially replace traditional reaction wheels in the future.
The spacecraft’s orbit and attitude are adjusted using GPS receivers and Attitude Control System (ACS) sensors, demonstrating autonomous maneuver capabilities via GPS. The ACS includes components like reaction wheels, magnetic torque bars, a three-axis magnetometer, an Inertial Reference Unit (IRU), a GPS receiver (with four antennas), and sun sensors. The advanced ACS software allows the spacecraft to track celestial bodies, perform instrument calibrations, and achieve cross-track pointing for adjacent observations. It also manages functions like attitude determination, closed-loop control, stabilization, thruster maneuvers for delta-V, and solar/lunar calibration scans following its launch.
The solar array on the EO-1 spacecraft consists of a single wing made up of three panels, each measuring 1.26 m by 1.43 m. The array is tilted at a 30º angle and uses a single-axis drive to rotate at the same rate as the satellite's orbit, keeping it aligned with the sun to reduce energy loss. During eclipse periods, the array "rewinds" itself to be ready for the next sunlit phase, allowing it to continue tracking the sun as the satellite orbits. The solar array is equipped with two types of solar cells: silicon cells with 15% efficiency and gallium arsenide (GaAs) cascade cells with 22% efficiency, the latter added to support the Hyperion instrument.
The spacecraft uses a hydrazine propulsion system with 22.3 kg of fuel for maintaining its orbit and coordinating formation flying. It also includes an onboard solid-state recorder with a capacity of up to 40 Gbit for storing scientific data. The spacecraft has a total mass of 572 kg (370 kg dry mass, 90 kg payload mass) and generates 600 watts of power at the end of its life, with a 50 Ah super NiCd battery providing 28±7 V DC power.
The onboard computer uses a Mongoose V (M5) processor operating at 12 MHz with 1.8 Gbit of telemetry, tracking, and command (TT&C) data storage. A lightweight fiber optic data bus with an Asynchronous Transfer Mode (ATM) protocol is used for transferring onboard data.
Orbit
Spacecraft bus dry mass
Spacecraft structure
Hexagonal; aluminum honeycomb
- 350 W (average), nominal voltage = 28 V,
- Batteries: super NiCd with 50 Ah capacity
- Array: 3 panel/Si with GaAs/articulating/5.25 m
- Actuators: reaction wheel assembly, magnetic torque bars,
- Sensors: three-axis magnetometer, IRU, autonomous star tracker, coarse sun sensors
- GPS receiver (attitude measurements)
- Roll/pitch/yaw axis pointing accuracy < 0.02º, 3σ
- Pointing stability (jitter): 0.3 arcsec/s
- Slew rate: 15º / minute
- Mongoose V processor, Rad Hard at 12 MHz, RISC architecture
- MIL-STD-1773 fiber optic data bus for serial command/telemetry communications at 1 Mbit/s
- 1 tank, 4 thrusters
- propellant capacity: 23 kg
- Maximum ΔV = 85 m/s
- Science data storage capability = 48 Gbit within WARP
- Science data downlink capacity = 105 Mbit/s
- Downlink formats/network: CCSDS / STDN, DSN, TDRS
- Downlink band: S-band (variable to 2 Mbit/s), X-band (105 Mbit/s)
- Uplink band: S-band (2 kbit/s)
The EO-1 spacecraft operates in a sun-synchronous, circular polar orbit at an altitude of 705 km, with an inclination of 98.7º and an orbital period of 99 minutes. It crosses the descending node at 10:15 AM local time and follows a 16-day repeat cycle. The satellite is positioned in a closely coordinated orbit with Landsat-7, trailing by less than a minute to enable data calibration and maximize the combined use of both datasets.
Launch
EO-1 was launched from Vandenberg Air Force Base (VAFB) on November 21, 2000, aboard a Delta 7320-10 launch vehicle. It shared the ride with two secondary payloads: SAC-C, a satellite from Argentina's CONAE, and Munin, a Swedish satellite.
RF communications
The EO-1 data system uses a MIL-STD-1773 fiber optic bus for serial command and telemetry at 1 Mbit/s. It has two S-band omni antennas for transmit/receive functions and an X-band Phased Array Antenna (XPAA) for transmission only. The 64-element nadir-pointing XPAA is LHCP polarized with a beam width of 18º-30º, depending on the scan angle, and scans a full 360º azimuth. Each element has its own power amplifier.
Science data is downlinked via X-band at 8225 MHz, with a data rate of 105 Mbit/s using QPSK modulation. Telemetry and command links are in S-band, with downlink rates ranging from 2 kbit/s to 2 Mbit/s and an uplink rate of 2 kbit/s, using direct or TDRSS transmission.
The ground network includes stations at Svalbard, Fairbanks, Wallops Island, and McMurdo, with Svalbard serving as the primary station. NASA's Goddard Space Flight Center manages mission operations.
Key Components Of EO-1
The main components of EO-1 included the Advanced Land Imager (ALI), Hyperion imaging spectrometer, and the LEISA Atmospheric Corrector (LAC).
Advanced Land Imager (ALI)
The Advanced Land Imager (ALI), designed and built by MIT Lincoln Laboratory under NASA's New Millennium Program, serves as a technology demonstration tool for Earth surface reflectance measurements. Its primary goal is to provide continuity with earlier Landsat missions while reducing sensor and operational costs. The ALI system features a Wide Field of View (WFOV) telescope and a multispectral and panchromatic instrument, using a unique four-mirror design to cover a 185 km swath.
The focal plane of ALI consists of 10 spectral bands in the visible, near-infrared (VNIR), and short-wave infrared (SWIR) ranges. It operates in a pushbroom mode, unlike the whiskbroom scanners of Landsat TM and ETM+, capturing both panchromatic and multispectral imagery. The detector array includes 320 multispectral cells per sensor chip assembly (SCA) and a panchromatic row of 960 elements, providing a ground sample distance (GSD) of 30 m for multispectral bands and 10 m for panchromatic.
ALI’s design is compact, lightweight, and energy-efficient, requiring just one-fifth the power of the Landsat ETM+ instrument. With innovative materials like silicon carbide mirrors and a highly integrated focal plane, ALI can achieve high-quality imagery at a fraction of the cost, size, and power consumption of its predecessor.
Hyperion Imaging Spectrometer
The Hyperion instrument, built by Northrop Grumman (formerly TRW), is a hyperspectral imager (HSI) derived from the technology used on the ill-fated Lewis satellite, which was lost shortly after its launch in 1997. Hyperion uses a pushbroom design with a grating imaging spectrometer, incorporating a telescope, two spectrometers, focal plane electronics, and a cooling system. The telescope has a 12 cm aperture and captures a 7.5 km swath of Earth. The light is split by a dichroic filter, sending visible and near-infrared (VNIR) light (400-1,000 nm) to one spectrometer and shortwave infrared (SWIR) light (900-2,500 nm) to the other, improving signal-to-noise ratio.
The instrument has separate VNIR and SWIR detectors, with the SWIR detectors cooled by a cryocooler. Both spectrometers use a convex grating design in a 3-reflector-offner configuration. The VNIR spectrometer has a 60 x 250-pixel detector array with a 10 nm spectral bandwidth, while the SWIR spectrometer uses a 160 x 250-pixel array with the same spectral resolution, cooled to 120 K.
Hyperion can capture 220 spectral bands from 0.4 to 2.5 µm with a spatial resolution of 30 meters. The mirrors and structure, made of aluminum, ensure that the optical components expand and contract uniformly, maintaining high-resolution imaging across the entire spectral range.
LEISA Atmospheric Corrector (LAC)
The main goal of the Linear Array Camera (LAC) is to provide atmospheric correction data, particularly for water vapor, for the ALI and Landsat-7's ETM+ instruments. This hyperspectral imager, using wedge filter technology, evolved from earlier systems like WIS and LEISA, which were originally developed for the ill-fated Lewis satellite mission. LAC has spectral coverage between 0.89 and 1.6 µm, with an additional channel at 1.380 µm to detect cirrus clouds. It is aligned with ALI to cover a 185 km swath at a spatial resolution of 250 meters.
The LAC consists of two main modules: the optics module, which includes lenses, focal planes, and electronics, and the electronics module, which handles power, cooling, and data interface with the spacecraft. Together, they weigh about 10.5 kg and consume around 35 W of power. LAC operates at a nominal frame rate of 28 Hz, generating a data rate of 95 Mbit/s, with the ability to double the frame rate for improved along-track sampling.
LAC uses three 256 x 256 pixel InGaAs infrared detector arrays placed behind lenses, providing a wide field of view (5º) to achieve the full 185 km swath. The system uses a wedged dielectric film etalon filter, which produces a 2D spatial image with varying wavelengths along one dimension, creating a detailed 3D spectral map as the spacecraft moves in orbit. Each pixel has a spatial resolution of about 250 x 250 meters at nadir.
New Technologies Introduced
XPAA (X-band Phased Array Antenna)
The XPAA (X-band Phased Array Antenna), developed by Boeing, is a communication experiment aimed at demonstrating efficient link-pointing capabilities using a body-fixed, low-cost, low-mass phased array antenna. Mounted on the Earth-facing side of the EO-1 satellite, XPAA enables high-rate data transmission to ground stations from the satellite’s solid-state recorder. It uses a flat grid of 64 radiating elements, with computer-controlled phase adjustments for beam direction, and provides an Effective Isotropic Radiated Power (EIRP) of around 160 W, transmitting data at 105 Mbit/s.
The XPAA's design includes an 8x8 array of modules, each containing circular waveguides, antenna feeds, phase shifters, and dual power amplifiers. These components are mounted on a printed wiring board that distributes power and control signals to each module. The entire system, including the array and remote service node, is housed in a compact enclosure weighing 5.5 kg. XPAA’s body-fixed design allows for simultaneous data capture and transmission, preventing disruptions to the instrument’s measurements.
The validation plan for XPAA focused on verifying communication link error performance, antenna scan pattern, and the reliability of its electronics in space. After a year in orbit, XPAA successfully exceeded operational requirements, showing consistent performance and reliability throughout its life cycle.
CCR (Carbon Carbon Radiator)
The Carbon-Carbon Radiator (CCR) experiment aims to showcase the versatility of carbon-carbon composite materials. In the EO-1 spacecraft, this material serves dual functions: it acts as an advanced thermal radiator and a load-bearing structure. Key benefits of carbon-carbon include its excellent thermal conductivity and favorable strength-to-weight ratio. Implementing CCR technology can streamline the design of thermal radiators, potentially eliminating the need for actively cooled systems and allowing for higher payload capacities in future missions.
The CCR consists of a sandwich composite panel featuring facesheets made of carbon fibers embedded in a carbon matrix. To enhance the EO-1 flight panel's durability and prevent contamination of sensitive instruments, it is coated with an epoxy encapsulant. Additionally, the exterior surface is treated with silver Teflon, as specified by the spacecraft's thermal design requirements.
This 73 cm x 73 cm panel features two 0.56 mm thick carbon-carbon facesheets bonded to a lightweight aluminum honeycomb core. It effectively dissipates the 27.8 W from the EO-1 Power Supply Electronics and the 16.3 W peak from the LAC electronics while also supporting their combined weight of 28 kg along with dynamic loads during launch and orbit. The CCR panel has successfully met mission requirements, demonstrating flawless performance in orbit, with thermal conductivity measurements aligning closely with expected values of 230 W/m K.
LFSA (Lightweight Flexible Solar Array)
Photovoltaic (PV) solar arrays are essential for powering Earth-orbiting satellites, and the lightweight flexible solar array (LFSA) technology has the potential to offer higher power-to-mass ratios than traditional solar arrays. This advancement can increase the science payload fraction for certain missions. The LFSA system utilizes copper indium selenide (CuInSe2) solar cells, also known as CIS technology, which are vapor-deposited on flexible substrates, making them lighter than those attached to rigid panels. The design includes shape memory alloys (SMA) for its hinges and deployment systems, enabling a shockless deployment technique that enhances spacecraft dynamics and safety compared to conventional pyrotechnic methods.
The LFSA aims for power efficiency ratios exceeding 100 W/kg, significantly higher than the under 40 W/kg provided by solar arrays from the late 1990s. Each LFSA module measures 10 cm x 10 cm and comprises 15 monolithically interconnected CIS cells in series, achieving around 2% efficiency in AM0 conditions. The SMA hinges not only save weight but also provide a more reliable and cost-effective solution for deployment. The dual flexure concept allows for manual stowing of the hinges, which are then deployed by applying heat. The LFSA was successfully deployed shortly after launch, with indicator switches confirming nominal deployment and normal temperature profiles.
WARP (Wideband Advanced Recorder Processor)
WARP is a cutting-edge solid-state recorder aboard the EO-1 spacecraft, designed to showcase advanced electronic packaging techniques for high-density memory storage. It features innovative integrated circuit packaging, including 3-D stacked memory devices and "chip on board" bonding methods, achieving an impressive storage capacity of 24 Gbit per memory card. Additionally, WARP is equipped with a Mongoose V processor that enables on-orbit data collection, compression, and processing of land image scenes.
This solid-state recorder boasts a remarkable data transfer rate of up to 840 Mbit/s and offers a total storage capacity of 48 Gbit, all while maintaining a lightweight design of less than 20 kg. WARP stands out as the highest-rate solid-state recorder that NASA has ever deployed in space.
PPT (Pulsed Plasma Thruster)
The PPT, or Plasma Rocket System-101, was developed by General Dynamics (formerly Primex Aerospace) for NASA's Glenn Research Center. Its primary purpose is to demonstrate on-orbit electromagnetic propulsion technology while providing precision-pointing capability for spacecraft (S/C). The EO-1 spacecraft primarily relies on a hydrazine propulsion system for orbit maintenance and formation flying, but the PPT is used intermittently during the mission to act as a momentum wheel, specifically taking over the pitch axis control when in operation.
The PPT functions by utilizing a coiled spring to feed Teflon propellant, an igniter plug for trigger discharge, and an energy storage capacitor with electrodes. Plasma is generated by ablating the Teflon propellant through the capacitor discharge, which is then accelerated by the Lorentz force within an induced magnetic field to create thrust. It can achieve impulse levels between 10 and 1000 µNs, with a specific impulse of 880 to 1170 m/s and average power consumption ranging from 1 to 100 W. Following the primary imaging mission, flight operations for the EO-1 PPT commenced on January 4, 2002, logging 26.9 hours of operation and nearly 97,000 pulses by June 15, 2002. The PPT maintained spacecraft pitch attitude within a stringent 30 arcsec requirement during imaging, often achieving even finer control, and no electromagnetic interference or light pollution was detected during sensitive tests, even with the ALI instrument's sensitive electronics.
FODB (Fiber Optic Data Bus)
The primary goal of the EO-1 mission is to showcase high-bandwidth data transfer capabilities while maintaining low mass and power requirements. The Fiber Optic Data Bus (FODB) was developed as a standard high-speed data interface, adhering to the IEEE P1393 SFODB standard, and features a ring topology that allows for 2 to 128 nodes, providing flexibility for various payload needs. The system includes a Controller Fiber Bus Interface Unit (CFBIU) as the master node and up to 127 slave nodes using Fiber Bus Interface Units (FBIUs). With fiber optic connections, the design minimizes weight and avoids electromagnetic interference (EMI) issues. The FODB supports transfer rates between 200 Mbit/s and 1 Gbit/s and employs a software-configurable Asynchronous Transfer Mode (ATM) protocol for enhanced flexibility in data handling architecture. In the EO-1 configuration, the FODB consists of four nodes, with WARP serving as the master controller and an external terminal box housing two additional slave nodes and necessary interfaces.
AutoCon (Autonomous Control for enhanced formation flying)
NASA's Goddard Space Flight Center collaborated with a.i.-solutions, Inc. to integrate the AutoCon™ software on the EO-1 spacecraft. The main goal is to demonstrate an autonomous onboard system capable of planning, executing, and calibrating routine maneuvers to keep satellites aligned in their formations. This "virtual satellite" concept allows multiple small, low-cost spacecraft to work together, enhancing science data collection while minimizing mission risks and increasing flexibility for future Earth and space science missions.
AutoCon™ automates EO-1’s maneuver planning and formation control across various orbits, including low Earth orbit (LEO) and non-Keplerian trajectories. One of EO-1's key mission objectives is to perform paired scene observations with Landsat-7 to validate its advanced imaging technology. This requires EO-1 to maintain a specific groundtrack within ±3 km of Landsat-7, with a nominal along-track separation of one minute (approximately 450 km). The precise management of this 3-D separation is essential for successful formation flying.
The AutoCon™ system incorporates fuzzy logic decision-making and natural language capabilities to address multiple conflicting constraints. It features a modular design that allows updates to algorithms without changing the software and includes a flight interface that connects to the Command and Data Handling (C&DH) system for navigation and command generation. The system was successfully activated on May 17, 2002, demonstrating autonomous formation flying for the first time. EO-1 maintained its position within one second of the target, enabling it to gather data concurrently with Landsat-7 while minimizing atmospheric distortion. Although initially intended as a technology experiment, AutoCon-F has proven reliable and now serves as the operational software for formation control maneuvers.
Extended Mission Phases of EO-1
After successfully completing its initial technology validation goals in the first year, the EO-1 mission transitioned into an extended mission phase, operating as an on-orbit testbed to validate new capabilities focused on enabling Sensor Webs. The Sensor Web Enablement (SWE) experiment is based on Open Geospatial Consortium (OGC) architecture standards and consists of several components, each incorporating models, services, or XML encodings related to the Sensor Web. For instance, SensorML (Sensor Model Language) provides models and encodings for various sensors, while the Observations and Measurements component details sensor observations and measurements.
ASE (Autonomous Sciencecraft Experiment)
In the fall of 2003, the Autonomous Science Experiment (ASE) software package from JPL and GSFC was installed on the EO-1 spacecraft as a testbed. Originally intended for NASA's ST-6 mission, the ASE was repurposed for EO-1 due to a flight opportunity. The ASE architecture consists of three main components: CASPER (Continuous Activity Scheduling Planning Execution and Replanning) for replanning activities based on prior science observations; the Spacecraft Command Language (SCL) for event-driven processing; and onboard science algorithms that analyze image data to identify significant features and events.
A complementary ground software, ASPEN (Automated Scheduling and Planning Environment), collaborates with CASPER by processing and prioritizing triggers and imaging requests. The ASE's goal is to showcase integrated autonomy technologies that facilitate onboard science applications, particularly using Hyperion data. This instrument captures detailed spectral images of a 7.5 km by 42 km area across 220 channels, enabling automatic discrimination between clouds, ice, snow, and other reflective features. The developed sensor web and autonomy capabilities have successfully reduced operational costs by over 50%.
Additionally, the Livingstone software package version 2 (LV2) was uplinked to EO-1 in summer 2004. This AI tool detects and diagnoses simulated failures in the spacecraft's payload instruments by comparing predicted performance with actual readings. The LV2's reasoner function identifies discrepancies, helping controllers to address potential issues promptly. Overall, the ASE on EO-1 demonstrates significant advancements in autonomous missions, enhancing onboard decision-making and paving the way for future NASA missions with greater scientific returns at reduced risks and costs.
EO-1 Examples in Sensing-Based Web Applications
In 1999, NASA's Earth Science Technology Office (ESTO) launched the Advanced Information Systems Technology (AIST) program to explore and demonstrate advanced information system technologies. The Sensor Web initiative aims to enhance Earth observation by implementing innovative data acquisition methods that respond to environmental events for both scientific and practical applications. By integrating multiple sensing platforms, Sensor Webs can achieve objectives that exceed the capabilities of individual systems. They do this by reducing response times during rapid events and improving the scientific value and quality of observations through collaborative efforts among different sensors.
The EO-1 spacecraft serves as the primary platform for demonstrating various mission autonomy technologies within the Sensor Web framework. A Sensor Web is defined as a network of spaceborne and ground-based sensors and computation nodes connected through a communication system that acts as a unified, adaptive observing entity. Key features include autonomous event detection, monitoring, observation request generation, and rescheduling to enhance data collection in terms of temporal, spatial, and spectral resolution. The architecture of the sensor web is designed to support autonomous tasking of the EO-1 spacecraft in response to science events, accommodate diverse sensor sources, ensure timely observations, and minimize operational impacts on the EO-1 staff.
VSW (Volcano Sensor Web)
In 2004/2005, JPL implemented the Volcano Sensor Web (VSW) to autonomously trigger the EO-1 spacecraft using data from ground-based and space-based sensors that detect volcanic activity. Over 18 months, this fully automated system enabled high-resolution observations of active volcanoes. Data products containing key information, such as the number, location, and spectra of hot pixels, were rapidly transmitted, often within 48 hours, though theoretically possible in 2-3 hours. This marked a significant improvement over previous processes, which took weeks to gather such data, allowing scientists to quickly assess the extent and intensity of eruptions.
The Model-based Volcano Sensor Web (MSW) advanced beyond simple detection and response. While traditional sensor web operations typically generated a spacecraft observation request after detecting volcanic activity, MSW aimed to gather more detailed information on the eruption's magnitude and scope. This approach allowed for more informed decisions by determining what additional data was needed to understand the state of the eruption.
The MSW employed web services to facilitate communication between sensor web assets. These services, defined by the Open Geospatial Consortium (OGC) Sensor Web Enablement (SWE) standards, helped manage workflows, exchange metadata, assess data quality, and communicate between sensors. This system allowed for the discovery of assets and data products while streamlining observation requests and the extraction of high-level information from datasets.
As environmental challenges continue to intensify, the innovations introduced by EO-1 remain essential in our efforts to study and safeguard Earth's intricate systems. The mission highlighted the importance of ongoing technological advancements in Earth observation, setting a strong example for future technology demonstration missions. EO-1's impact endures, influencing the design of present and future Earth observation systems, which build on its achievements to deliver increasingly detailed and valuable data about our planet.
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