Home >> February 2011 Edition >> EO-1: Ten Years Of Innovation
EO-1: Ten Years Of Innovation
author: Holli Riebeek, Sigma Space Corporation at NASA Goddard Space Flight Center


Riebeekfig1.jpg Steep cliffs surround the hot, brown valley that holds Khirbat en-Nahas, one of the largest copper mining and smelting sites of the ancient world.

The desolate valley in Jordan is not the cradle you would expect to nurture a civilization, but archeologists Stephen Savage and Tom Levy think it may be the site of an early organized state.


“Copper mining and smelting is a hallmark of early state-level society in the eastern Mediterranean,” says Stephen Savage, a researcher from Arizona State University. His team is uncovering evidence for sophisticated economic and political activity in the valley about 3,000 years ago.

Savage has never been to Khirbat en-Nahas, but he is revealing things about the site no archeologist has been able to see before. Instead of spending sweltering days in the desert, Savage logs in to a website, clicks on a map to select a location, and clicks “submit”. With that, he has requested that NASA’s Earth Observing-1 (EO-1) satellite point its instruments at his site the next time it flies over.



Dark gray piles of slag define ancient copper mining and smelting sites at Khirbat en-Nahas, in the desert between the Dead Sea and the Gulf of Aqaba. The square feature on the north side of the site is an Iron Age fortress. (See the lower image on the graphic above, which offers a NASA image by Robert Simmon of the site, using Advanced Land Imager data.)

Newteq_ad_SM0211.jpg
This type of user-driven experience was not part of the initial plans for EO-1, but it is an example of the spirit of exploration and experimentation that has characterized the mission.

Scheduled to fly for a year, designed to last a year and a half, EO-1 celebrated its tenth anniversary on November 21, 2010. During its decade in space, the satellite has accomplished far more than anyone dreamed possible.

“Earth-Observing-1 has had three missions,” says mission manager Dan Mandl of NASA’s Goddard Space Flight Center (GSFC). Its original mission was to test new technologies, a mission completed in the first year. Its second mission was to provide images and data. Its third mission was to test new cost-saving software that operates the satellite semi-autonomously and allows users to target the sensors.

Riebeekfig2.jpg All of the missions come down to one thing: “We’re the satellite people can try things on.” Mandl called EO-1 NASA’s on-orbit test bed, and the name certainly rings true.

EO-1 was commissioned as part of NASA’s New Millennium Program, set up to develop and fly technology that would reduce the risk and cost of future science missions. In short, NASA told its engineers: Find a way to fly faster, better, and less expensively.

“EO-1’s primary purpose was to demonstrate that the Advanced Land Imager (ALI — see the sidebar for additional information) was a suitable follow-on instrument for Landsat,” says Bryant Cramer, the program manager at GSFC during EO-1’s development and launch.

Like Landsat-7, ALI records seven wavelengths of light reflected from Earth’s surface. ALI also records an additional two wavelengths to improve measurements of forests and crops, coastal waters, and aerosols. Later, an innovative new instrument, the Hyperion imaging spectrometer, was added to the mission. Hyperion records more than 200 adjacent wavelengths of light to even better understand the makeup of Earth’s surface.

“EO-1 succeeded beyond anyone’s expectations,” says former project scientist Steve Ungar (GSFC). He credits the mission’s success to EO-1’s “crackerjack team” of engineers and scientists, who were drawn to the mission because they recognized that they could have a stake in the future of satellite technology.

Satellite2011.jpg In addition to the two primary sensors, the team proposed 32 new technologies for EO-1, including:


An improved antenna design that enhances the signal to the ground (a phased array antenna)


A fast data recorder and processor connected by fiber optic cables to improve the speed and capability of onboard computing systems


“Formation flying” software to keep the satellite exactly one minute behind the Landsat satellite


A pulsed plasma thruster with a Teflon fuel rod; the team wanted to know if Teflon fuel would maintain the satellite’s position without contaminating the science data


A lightweight, flexible solar panel


Carbon-coated plates (radiators) to cool the instruments


The Linear Etalon Imaging Spectrometer Array (LEISA) Atmospheric Corrector (LAC), a hyperspectral instrument designed to improve the way the atmosphere is filtered out of images taken by sensors like Landsat.


Advantech_ad_SM0211.jpg


Though each new technology had the potential to advance spacecraft design, they also posed risks. The carbon-carbon radiators used for passive cooling, for example, were much lighter and simpler than traditional cryocoolers. “But when you touched the first carbon plates, your hand would come away black,” recalls Ungar.” Since this posed a risk to the imagers, the engineers had to come up with a coating to prevent contamination.

Hyperion
Riebeekfig3.jpg “Hyperion is probably the future of remote sensing,” says Cramer. Mandl added, “Hyperion is a hyperspectral instrument, a change in technology that is like going from black-and-white to color television.”

Other remote sensing instruments — multispectrometers — measure discreet wavelengths of light. It is as if your eyes could only see red and blue light; you could tell much about the world based on how much red and how much blue you saw, but your vision would have gaps in the green tones. A hyperspectral instrument corrects this color blindness by measuring many more wavelengths of light.

ManSat_ad_SM0211.jpg


The science behind the hyperspectral instrument is spectroscopy, says current EO-1 project scientist, Elizabeth Middleton (GSFC). “Spectroscopy is the study of constituents of materials using specific wavelengths,” she notes. “Hyperion measures the chemical constituents of Earth’s surface.”

Riebeekfig4.jpg Chemists have long used spectroscopy to identify substances because everything reflects electromagnetic energy (including light) at specific wavelengths and in ways that are as unique as a fingerprint. By measuring the energy that comes from a material, scientists can figure out what the material is. Hyperion measures reflected light like many other satellite imagers, but since it is recording more than 200 wavelengths, it can detect the fingerprints of the materials on Earth’s surface.

Space-based imaging spectroscopy enables a wide range of science, including the search for those ancient copper mines and smelting sites in Jordan.

“I’m looking for the spectrographic signature of copper-bearing minerals,” says Savage. He intended to use copper’s unique light signature to find more smelting sites near Khirbat en-Nahas, but as he started to work with Hyperion data, he realized that it could do much more.

Comtech_ad_SM0211.jpg “Hyperion has really opened up a whole new avenue of analysis that we hadn’t even explored before,” says Savage. “I can tell you where in the area the ore is coming from; which parts of the site were used for smelting and which were not; and that different parts of the site were drawing ore from different regions.” Such information would be prohibitively expensive to gather in field research, but Hyperion provides Levy (from the University of California-San Diego) with an affordable map that he can use to better target excavation at likely smelting sites and mines.

Hyperion data have found a wide range of other uses, including tracking the amount of carbon plants take out of the atmosphere everywhere from the Amazon rainforest to the Alaskan tundra. It also has been used to find evidence of microbial life in the Arctic and to monitor volcanic activity.

Perhaps the most important thing Hyperion has done, says Middleton, is teach the community how to work with complex hyperspectral data. Germany will soon launch the next hyperspectral instrument, EnMap, followed by NASA’s HyspIRI satellite, which is still in the planning stage. Both missions build on lessons learned from Hyperion.

Riebeekfig4a.jpg Riebeekfig5.jpg Advanced Land Imager
The Advanced Land Imager (ALI) was built, says Cramer, to test new technology and to provide a safe technology shift for future Landsat missions. The Landsat series of satellites has provided a continuous record of changes in Earth’s landscape from 1972 to the present. ALI images the Earth at the same level of detail (30 meters per pixel), and it has a more detailed set of sensors that enable crisp, photo-like images.

ALI differs from previous Landsat sensors because of how it takes images. Previous Landsat instruments scanned from side to side, like a whiskbroom. The image is built from horizontal strips of information. ALI, on the other hand, is more like a push broom. It has detectors arranged parallel to one another and facing forward, and they collect information in vertical strips. This arrangement eliminates the need for the sensor optics to move from side to side, and fewer moving parts means less chance of failure, says EO-1 engineer Stuart Frye (GSFC).

Riebeekfig6.jpg A whiskbroom sensor, left, takes images by sweeping horizontally across the landscape as the satellite moves forward. A pushbroom sensor collects data in vertical strips as it moves forward.

After 10 years of operation, ALI has proven that the push-broom technology is stable and reliable enough that the next Landsat satellite, the Landsat Data Continuity Mission, uses the same design.

“The Landsat community is treating push-broom sensors like we’ve been building them for years,” says Cramer. “That’s a tribute to EO-1.”

The accumulation of small tweaks has had a large benefit for studying certain types of earthly events. “ALI is very useful in identifying smaller features such as floods and landslides on a local scale,” says Eric Anderson, a researcher at Cathalac, an organization that helps map disasters.

As ALI and Hyperion can be pointed at a particular location on the ground, scientists and disaster relief managers can gather images every two to five days; Landsat is usually limited to once in 16 days because it looks straight down.

Riebeekfig7.jpg NASA’s On-orbit Test Bed
As the EO-1 mission has aged, perhaps the most critical innovation has come from the onboard computer. “EO-1 has two separate computer processors with 256 megabytes of extra memory each,” says Mandl. That may seem paltry compared to a modern desktop computer, but it was enough to reshape a spacecraft’s mission. “It meant we had excess capacity to try new things.”

The first new software loaded onto EO-1 was the Autonomous Science Experiment, an onboard intelligent scheduling tool that allows the satellite to decide for itself which images Hyperion and ALI should take. Before the software, says Mandl, it took a flight engineer 67 steps to tell the satellite to acquire an image. “Now we send one command with a goal,” says Frye. “If the goal conflicts with another goal, the onboard scheduler decides which to image. Targeting is 100 percent automated.”

As the satellite can think for itself, the system can accept a target request as late as five hours before the satellite flies over the target compared to two to three days required for most other sensors. The on-board scheduler prioritizes requests based on what they are for (ranked by theme) and the weather. The software uses predictions of cloudiness from the National Oceanic and Atmospheric Administration, so if a site is too cloudy, the next least-cloudy target will get priority.

“It’s a customer-driven method of running a mission,” says Mandl. Anyone from an archeologist to a disaster response agency can request images. “Flying a mission with a customizable user experience is one of EO-1’s greatest achievements.”

Sometimes the “customers” targeting EO-1 are other satellites. As part of SensorWeb, EO-1 automatically acquires images that are triggered by other satellites. For example, EO-1 monitors 100 volcanoes. When the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra or Aqua satellites detects a hot spot at any of them, EO-1 automatically acquires an image on its next overpass. Hyperion can then record the temperature and position of lava flows, while ALI tracks ash plumes. If the onboard software detects a hot spot in the Hyperion measurement, the on-board systems automatically re-schedule another acquisition of that target at the next opportunity. The images are distributed to local officials. The SensorWeb system is a pathfinder to help build international satellite collaborations, particularly for disaster response.

Paradise_ad_SM0211.jpg SensorWeb and the scheduling tool have created significant cost savings. “Initially, we were spending about $7,500 per image to acquire them. Now the cost is less than $600 a scene,” says Cramer. “EO-1 is one of the cheapest of NASA’s Earth missions,” confirms Middleton. These cost savings mean that anyone can now target EO-1 and access all data free of charge, making it useful to a growing range of people.

In the end, EO-1’s value far outweighs its price tag. “EO-1 has done so many different things, NASA got three or four missions for the price of one,” says Cramer. “We achieved all of the things that we hoped for and then some.”

Editor’s Note
This article courtesy of NASA’s Earth Observatory, http://earthobservatory.nasa.gov

References
Earth Observatory. (n.d.) Earth Observing-1. NASA.Accessed November 22, 2010.
Earth Observing-1 (n.d.) Advanced Land Imager validation summary. (pdf) Accessed November 18, 2010.
Earth Observing-1 (n.d.) EO-1 extended mission. Accessed November 18, 2010.
Earth Observing-1. (n.d.) Hyperion validation summary. (pdf) Accessed November 18, 2010.
Earth Observing-1 (n.d.)Technology validation. Accessed November 18, 2010.


For more information regarding EO-1 and its extended mission, head over to
http://eo1.gsfc.nasa.gov/


Integral_ad_SM0211.jpg


EO-1’s Advanced Technologies
The future of Earth science measurements continues to require spacecraft to have ever-greater capabilities packaged in more compact and lower cost spacecraft. To that end, EO-1 tested, for the first time, six new technologies that now enable new or more cost-effective approaches to conducting science missions in the twenty first century.

Riebeekfig8.jpg Advanced Land Image
The Earth Observing-1 (EO-1) Advanced Land Imager (ALI) was the first Earth-Observing instrument to be flown under NASA’s New Millennium Program (NMP). The ALI employed novel wide-angle optics and a highly integrated multispectral and panchromatic spectrometer. MIT Lincoln Laboratory developed the ALI with NMP instrument team members: Raytheon/Santa Barbara Remote Sensing (SBRS) for the focal plane system, and Sensor Systems Group, Inc. (SSG) for the optical system.

The focal plane for this instrument is partially populated with four sensor chip assemblies (SCA) and covers 3° by 1.625°. Operating in a pushbroom fashion at an orbit of 705 km, the ALI provides Landsat type panchromatic and multispectral bands. These bands have been designed to mimic six Landsat bands with three additional bands covering 0.433-0.453, 0.845-0.890, and 1.20-1.30 µm. The ALI also contains wide-angle optics designed to provide a continuous 15° x 1.625° field of view for a fully populated focal plane with 30-meter resolution for the multispectral pixels and 10 meter resolution for the panchromatic pixels.

"EO-1's advanced technologies will set the pace for future Earth Science missions in the new millennium."

Riebeekfig9.jpg 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 demonstrated 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 offered significant benefits over then-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.
The XPAA is composed of a flat grid of 64 radiating elements whose transmitted signals are combined spatially to produce the desired antenna directivity. The phases of each of the radiating elements are varied by computer to point the beam in the desired direction. For the EO-1 mission, the radiating elements are combined with low power, high efficiency solid state amplifiers to achieve the required radio frequency power level. The antenna is mounted on the Earth-facing side of the spacecraft to allow communications with ground stations. The antenna’s mass is 5.5 kilograms. It has an Effective Isotropic Radiated Power (EIRP) of approximately 160 watts, and transmits data at 105 megabits per second. Boeing Phantom Works, located in Seattle, Washington, developed the antenna for GSFC.

Riebeekfig10.jpg Light Weight Flexible Solar Array
All spacecraft use the sun as a source of electrical power produced by solar arrays. EO-1 featured 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 was 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.

Riebeekfig11.jpg The combination of the new solar cell and alloy technologies provides significant improvement in the power-to-weight ratios. Plus, the new alloys fostered 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 provided 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 delivers 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 such as Teflon, as opposed to a conventional liquid fuel such as hydrazine, there is a higher net propulsion for a given energy input, saving substantial amounts of weight in fuel.

Riebeekfig12.jpg The Pulse Plasma Thruster is used to precisely maneuver the spacecraft and maintain the highly accurate pointing of the instruments. A series of fine pitch maneuvers were conducted with the thruster after the EO-1 mission had completed its primary land scene comparisons with Landsat 7 to demonstrate spacecraft feasibility.

Enhanced Formation Flying
As NASA had planned, and continues to schedule, launches for a substantial number of Earth Observing spacecraft, more efficiency is obtained when operating spacecraft in groups, as opposed to single entities. Enhanced formation flying technology enables a large number of spacecraft to be managed with a minimum of ground support. The result is 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 now 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.

Riebeekfig13.jpg Unique features of the EFF technology included an innovative use of fuzzy logic decision making capabilities and natural language to resolve multiple conflicting constraints; a scripting environment to enable algorithm updates without software changes; a flight wrapper that interfaced directly with the command and data handling subsystem for input and output; multiple operating modes that allowed for execution control; generic closed-loop formation flying control algorithms applicable to many missions; and a modular architecture design flexible enough to control the execution of multiple and varying algorithms from several partners (JPL, Phillips Laboratory, SPA, and Microcosm) in addition to NASA’s Goddard Space Flight Center.

Riebeekfig14.jpg 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.

Riebeekfig15.jpg C-C has a considerably lower density and higher thermal conductivity than aluminum. Since the trend for satellites is toward 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.

Carbon-Carbon uses pure carbon for the fiber and matrix. EO-1 was the first to use this material in a primary structure, where C-C is used as an advanced thermal radiator and a load bearing structure.

Wideband Advanced Recorder Processor
The EO-1 imaging instruments presented 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 had 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 transmittal 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 became the highest rate solid state data recorder NASA had flown. It also included a high-performance processor (known as Mongoose 5) that could perform on-orbit data collection, compression, and processing of land image scenes. WARP’s compact design, advanced solid-state memory devices, and packaging techniques enabled EO-1 to collect and downlink all recorded data.

Riebeekfig16.jpg


LA-II Thermal Coating
The thermal control coating was referred to as LA-II and is a low absorptance, inorganic, white paint. An absorption coefficient is a measure of the rate of decrease in the intensity of electromagnetic radiation (as light) as it passes through a given substance; the fraction of incident radiant energy absorbed per unit mass or thickness of an absorber; “absorptance equals 1 minus transmittance. Two flight calorimeters were flown on the Earth Observing-1 (EO-1) spacecraft. They were attached to the EO-1 equipment bay panel, Bay 4 (Carbon-Carbon Radiator panel), as shown in this photo. One calorimeter was coated with the LA-II Paint. The other calorimeter was coated with a known NASA/GSFC Z93P White Paint and used as a baseline for comparison. The data provided from the calorimeters was used to validate the performance of the LA-II paint.



Mitec_ad_SM0211.jpg