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 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 selectssuch as solar electric (ion) propulsion or spacecraft flying in formationpresent 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.
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The Earth-Sensing Legacy
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.
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
|Sensors aboard the Landsat satellites were built in a whisk broom (across track) configuration. In a whisk broom sensor, a mirror scans across the satellites 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.|
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)|
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
|Hyperion, the hyperspectral imager on EO-1, will measure much finer spectral information than the ETM+ or ALI. In nature, spectral information is continuousthe amount of sunlight reflected off a point on the Earths surface varies smoothly with changes in wavelength. Hyperions 220 bands (green line) provide a more accurate depiction than the discrete bands of Landsat (blue dots). (Graph by Robert Simmon)|
||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.|
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.
|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)|
X-Band Phased Array Antenna
Light Weight Flexible Solar Array
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
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
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 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.
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