Earth Observing-1

At the beginning of the new millennium, NASA has an ambitious vision for its space program: to accelerate space exploration through the development of highly advanced technology. Enter NASA's New Millennium Program (NMP), an advanced-technology development program created to infuse a new generation of technologies and mission concepts into future Earth and space science missions.

the EO-1 Satellite
The Earth Observing-1 satellite. (Image courtesy Swales Aerospace Space Systems)

The program is unique in that it tests its advanced technologies in space flight. Though many space-related technologies can be tested sufficiently in laboratories on Earth, the technologies and concepts NMP selects—such as solar electric (ion) propulsion or spacecraft flying in formation—present a fairly high risk to missions that will use them for the first time. A full test in orbit is needed before these risky technologies are built in to an operational system. Flight testing in space is also important for some technologies because spacecraft may encounter environments or situations that cannot be replicated on the ground such as zero gravity, or high levels of radiation exposure or solar wind.

The value of the NMP missions is to lower the risk for future missions that use these technologies to carry out challenging scientific exploration. Every few years starting in November 2000, NMP will send a mission into deep space or into low Earth orbit to test new suites of technologies. On November 21, 2000, NASA launched the first NMP mission, Earth Observing-1 (EO-1), on a Delta 7320 rocket from Vandenberg Air Force Base, California. Flying at an altitude of 705-kilometers, EO-1 will orbit in a circle around the Earth very nearly from pole to pole and descend across the equator at about 10:02 am local time (referred to as a "sun-synchronous" orbit).

While the primary focus of the EO-1 mission is to test advanced instruments, spacecraft systems, and mission concepts in flight, EO-1 will also return scientific data as a by-product of its testing. At least once or twice a day, both Landsat 7 and EO-1 will image the same ground areas. All three of the EO-1 land-imaging instruments will view all or segments of the Landsat 7 swath and scientists will be able to compare these "paired scene" images. By comparing scenes from each of the spacecraft, scientists will be able to recommend improvements to future instruments and spacecraft and ensure the continuity of land-imaging data in the future.

next: The Earth-Sensing Legacy

 

by Steve Graham
November 15, 2000

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Earth Observing-1
Introduction
The Earth-Sensing Legacy
Advanced Technologies

Related EO-1 Links
EO-1 Home Page
EO-1 In Depth with Images & Movies
Landsat 7 Project Page

 

Earth Observing-1

   
 

The Earth-Sensing Legacy
NASA pioneered the first remote-sensing Earth satellites with the "Landsat" series. The first of these spacecraft, originally called ERTS (Earth Resources Technology Satellites), was launched on July 23, 1972. Landsat 4, a second-generation Landsat satellite, was launched on July 16, 1982, followed by Landsat 5 on March 1, 1984. Landsat 5, which is still providing data, contributed to the production of the first composite multispectral (multiple spectral bands) mosaic of the 48 contiguous United States.

Landsat 7, launched on April 1, 1999, is designed to extend and improve upon the more than 25-year record of images of Earth's continental surfaces provided by the earlier Landsat satellites. The continuation of this work is an integral component of the U.S. Global Change Research Program. Landsat 7 is providing essential land surface data to a broad, diverse community of national security, civilian, and commercial users.

Enter EO-1
Future NASA Earth-observing spacecraft will be an order of magnitude smaller and lighter than current versions, thus saving millions of dollars in launch costs alone. The EO-1 mission will provide the on-orbit demonstration of six revolutionary spacecraft technologies which if successful, will enable future Earth and space science missions to be conducted using smaller, lower weight and reduced power spacecraft buses.

EO-1 will also demonstrate three advanced land-imaging instruments, each having unique filtering methods for passing light in only specific wavelengths of radiant energy, called "spectral bands." EO-1 spectral bands will allow researchers to best look for specific surface features or land characteristics based on scientific or commercial applications. These advanced imaging instruments will lead to a new generation of lighter weight, higher performance, and lower cost Landsat-type imaging instruments for NASA's Earth Science Enterprise.

The centerpiece of this mission is the Advanced Land Imager (ALI) instrument. This new instrument will demonstrate remote-sensing measurements of the Earth that are consistent with data collected by the Landsat series of satellites. These data are used by farmers, foresters, geologists, economists, city planners, and others for resource monitoring and assessment. ALI will lay the technological groundwork for future land-imaging instruments to be more compact and less costly. A Landsat-style instrument based on ALI would have a mass of 106 kilograms, consume only 118 watts of power while performing scans, occupy a volume of .25 cubic meters, and possess finer spectral coverage over the current Landsat 7 imager, the Enhanced Thematic Mapper Plus (ETM+). In comparison, the ETM+ has a mass of 425 kilograms, consumes 590 watts of power while performing scans, and occupies a volume of 1.7 cubic meters.
 

  pullquote

Earth Observing-1
Introduction
The Earth-Sensing Legacy
Advanced Technologies

Related EO-1 Links

EO-1 Home Page
EO-1 In Depth with Images & Movies
Landsat 7 Project Page

 

Whisk Broom

 

  Sensors aboard the Landsat satellites were built in a “whisk broom” (across track) configuration. In a whisk broom sensor, a mirror scans across the satellite’s path, reflecting light into a single detector which collects data one pixel at a time. The moving parts make this type of sensor expensive and more prone to wearing out.
 

Pushbroom

Data from the ALI might help ranchers identify the most suitable lands for livestock grazing, or help farmers improve crop yields by identifying areas that need additional fertilizer or irrigation.

EO-1 will also carry an advanced high-resolution hyperspectral (capable of resolving a large number of spectral bands per pixel) imager, called Hyperion. Hyperion will be capable of resolving 220 spectral bands at wavelengths from 0.4 to 2.5 micrometers with a 30-meter resolution (i.e., the smallest object observed will be 30m x 30m). This is a vast improvement over the current Landsat technology, which supports only eight multispectral bands at a similar resolution. Because of the large number of spectral bands on Hyperion, complex land ecosystems can be imaged and more-accurately classified.
 

  A “pushbroom” (along track) sensor like ALI consists of a line of sensors arranged perpendicular to the flight direction of the spacecraft. Different areas of the surface are imaged as the spacecraft flies forward. Pushbroom sensors are generally lighter and less expensive than their whisk broom counterparts, and can gather more light because they look at a particular area for a longer time, like a long exposure on a camera. One drawback of pushbroom sensors is the varying sensitivity of the individual detectors. (Animations by Robert Simmon)

Hyperspectral Data

For example, detailed classification of land assets will enable improved remote mineral identification and hazardous waste monitoring. Researchers estimate that there may be more than 20,000 active and abandoned mines in the western U.S. alone. It is a daunting task to use field methods alone to inventory and assess how acidic drainage from mines affects surface water quality and impacts the environment. EO-1 will help land resource managers greatly accelerate this inventory.

The third instrument on EO-1 is the Atmospheric Corrector. Earth imagery from space is often degraded by the absorption and scattering of solar radiation due to the aerosol and water vapor content of the atmosphere (analogous to looking through a dirty window). The Atmospheric Corrector is a moderate spatial resolution (250 meters) imaging spectrometer with a 185-kilometer (115 mile) swath, the same as Landsat 7's ETM+. Using the Atmospheric Corrector, instrument measurements of actual, rather than modeled, absorption values will enable more accurate measurement and classification of land resources and better models for land management in the future. Additionally NASA will provide its Atmospheric Corrector technologies to U.S. industry with the explicit purpose of expediting technology transfer to the commercial sector.
 

  Hyperion, the hyperspectral imager on EO-1, will measure much finer spectral information than the ETM+ or ALI. In nature, spectral information is continuous—the amount of sunlight reflected off a point on the Earth’s surface varies smoothly with changes in wavelength. Hyperion’s 220 bands (green line) provide a more accurate depiction than the discrete bands of Landsat (blue dots). (Graph by Robert Simmon)
 

True Color
 

  This true-color image of Houston, Texas, (acquired by the Moderate-resolution Imaging Spectroradiometer) was not corrected for the effects of the atmosphere. Note the blue tone of the image, and the overall brightness.
 

Atmospherically Corrected

For each scene, EO-1's three sensors will collect more than 20 gigabits (20 trillion bits) of data that are stored at high rates on the on-board solid state recorder. When the EO-1 spacecraft is in range of a ground station, the spacecraft will automatically transmit its recorded image to the ground station for temporary storage. The ground station will store the raw data on digital tapes which will be forwarded to NASA's Goddard Space Flight Center for processing and sent to the EO-1 science and technology teams for validation and research purposes.

next: Advanced Technologies
back: Introduction

  This image is based on the same data as the image above, but the red, green, and blue channels have been corrected for the scattering that occurs as light passes through the atmosphere. The Atmospheric Corrector aboard EO-1 will allow scientists to improve their data even further, a necessity for the precise measurements made by EOS sensors. (Images courtesy Jacques Descloitres, MODIS Land Team)

Earth Observing-1

 

Advanced Technologies
The future of Earth science measurements requires that spacecraft have ever-greater capabilities packaged in more compact and lower cost spacecraft. To this end, EO-1 tests, for the first time, six new technologies that will enable new or more cost-effective approaches to conducting science missions in the 21st century.

X-Band Phased Array Antenna
New generations of Earth science missions will generate terabytes (1,000,000 megabytes) of data on a daily basis which must be returned to Earth. EO-1 will demonstrate the X-Band Phased Array Antenna (XPAA) as a low-cost, low-mass, highly reliable means of transmitting hundreds of megabits per second to low-cost ground terminals. The XPAA offers significant benefits over current mechanically pointed parabolic (dish) antennas, including the elimination of deployable structures, moving parts, and the torque disturbances that moving antennas impart to the spacecraft.

Light Weight Flexible Solar Array
All spacecraft use the sun as a source of electrical power produced by solar arrays. EO-1 features a new lightweight photovoltaic solar array system called the Light Weight Flexible Solar Array (LFSA). While most photovoltaic cells are made from silicon, selenium, or germanium crystals, the LFSA uses solar cells made of copper indium diselinide (CIS) in a vapor form. Not only is CIS significantly lighter than solar cells designed as crystals, but it can also operate on a flexible, less rigid surface, with significantly higher returns on its electrical output.

EO-1's solar array is built with shape memory alloys instead of typical hinge and deployment systems. Shape memory alloys are novel materials that have the ability to return to a predetermined shape when heated. When the material is cold, or below its transformation temperature, it has a very low yield strength and can be deformed quite easily into any new shape, which it will retain. However, when the material is heated above its transformation temperature, it undergoes a change in crystal structure that causes it to return to its original shape. If the shape memory alloy encounters any resistance during this transformation, it can generate extremely large forces. This phenomenon provides a unique mechanism for remote actuation.

The combination of the new solar cell and alloy technologies provides significant improvement in the power-to-weight ratios. Plus, the new alloys foster a "shockless" solar array deployment, a much safer method than conventional solar array systems that use explosives for deployment. The goal of the LFSA is to achieve greater than 100 Watts/kilogram power efficiency ratios compared to today's solar arrays which provide less than 40 Watts/kilogram.

Pulse Plasma Thruster
EO-1 will provide the first on-orbit demonstration of a low-mass, low-cost, electromagnetic Pulse Plasma Thruster propulsion unit for precision spacecraft control. The thruster uses solid Teflon propellant and is capable of delivering very small impulse bits (low thrust per pulse) which are desirable for some precision pointing missions. The thruster consists of a coiled spring to feed the Teflon propellant, an igniter plug to initiate a small trigger discharge, and an energy storage capacitor and electrodes. Plasma is created by the sudden change from a solid to a gas of the Teflon propellant caused by the discharge of the storage capacitor across the electrodes. The plasma is accelerated by an electromagnetic force in the induced magnetic field to generate thrust. By using a high velocity, low-mass propellant like Teflon, as opposed to conventional liquid fuel such as hydrazine, there is a higher net propulsion for a given energy input, thus saving substantial amounts of weight in fuel.

The Pulse Plasma Thruster will be used to precisely maneuver the spacecraft and maintain the highly accurate pointing of the instruments. A series of fine pitch maneuvers will be conducted with the thruster after the EO-1 mission has completed its primary land scene comparisons with Landsat 7 to demonstrate its feasibility.

Enhanced Formation Flying
Because NASA has plans to launch a substantial number of Earth-observing spacecraft over the next 15 years, it would be more efficient to operate these spacecraft in groups, as opposed to single entities. Enhanced formation flying technology will enable a large number of spacecraft to be managed with a minimum of ground support. The result will be a group of spacecraft with the ability to detect navigation errors and cooperatively agree on the appropriate maneuver to maintain their desired positions and orientations. Formation flying technology enables many small, inexpensive spacecraft to fly in formation and gather concurrent science data in a "virtual platform." This concept lowers total mission risk, increases science data collection, and adds considerable flexibility to future Earth and space science missions.

Formation Flying
EO-1 will fly two minutes behind Landsat-7 along the exact same ground track. (Image by Chris Meaney, GSFC Studio 13)

Carbon-Carbon Radiator
Satellites in orbit around the Earth must dissipate tremendous amounts of heat from absorbed solar radiation and internal heat sources (spacecraft electronics). The primary way to disperse thermal energy is through a series of special aluminum radiator panels attached to the outside of the spacecraft. Researchers would like to enhance the thermal management capability of these panels even further by reducing the costs and weight and possibly extending the operational life of the spacecraft. To accomplish this, EO-1 will carry an experimental radiator panel made of Carbon-Carbon (C-C), a special class composite material made of pure carbon.

C-C has a considerably lower density and higher thermal conductivity than aluminum. Since the trend for future satellites is towards smaller electronics in combination with smaller spacecraft size and weight, C-C offers improved performance for lower volume and mass and will enable more compact packaging of electronic devices because of its ability to effectively dissipate heat from high power density electronics.

Wideband Advanced Recorder Processor
The EO-1 imaging instruments present a significant challenge to the traditional development of spacecraft. Due to EO-1's high-rate imaging—almost 1 gigabit per second when all three instruments are on—a new compact data-handling system needed to be designed.

The Wideband Advanced Recorder Processor (WARP) is a solid-state recorder with the capability to record data from all three instruments simultaneously and store up to 48 gigabits (2-3 scenes) of data before they are transmitted to the ground. By using advanced integrated circuit packaging (3D stacked memory devices) and "chip on board" bonding techniques to obtain extremely high density memory storage per board (24 gigabits per memory card), WARP will be the highest rate solid state data recorder NASA has ever flown. It also includes a high-performance processor (known as Mongoose 5) that can perform on-orbit data collection, compression, and processing of land image scenes. WARP's compact design, advanced solid-state memory devices, and packaging techniques enable EO-1 to collect and downlink all recorded data.

EO-1 is a technology demonstration that has been planned as a one-year mission. By planning for only one year, NASA was able to lower the cost of the spacecraft while still meeting their technology evaluation objectives. But, many of the parts on the spacecraft were designed to operate for two years, so mission personnel expect EO-1 to perform well into 2002.

back: The Earth-Sensing Legacy

  pullquote

Earth Observing-1
Introduction
The Earth-Sensing Legacy
Advanced Technologies

Related EO-1 Links
EO-1 Home Page
EO-1 In Depth with Images & Movies
Landsat 7 Project Page