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


Earth Observing-1
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

Print this entire article