Headlines

Gabriel Spera

Powering Small Satellites

Miniature satellites are generally cheaper to build and deploy than larger units, but also provide less capacity for generating power. A recent Aerospace invention could overcome this obstacle while enhancing the thermal performance of such small spacecraft.

The invention, called the PowerSphere, is essentially a geodesic globe or "buckyball" formed from pentagonal and hexagonal solar panels. Prior to deployment, these panels remain stacked flatly at the two ends of a strut attached to the payload. During deployment, each stack of panels unfolds, creating two hemispheres that lock together like a clamshell to encase the satellite.

The resulting solar-array sphere can convert a constant amount of solar radiation into electrical power regardless of its attitude relative to the sun, explained Ed Simburger, project lead. The design also eliminates the excess mass of a standard solar array along with its requisite attitude-control system. An added advantage, he said, is that the PowerSphere provides a controlled thermal environment for the electronics and battery it encases, which are subjected to extreme temperatures in space.

Simburger's team has already been granted a patent for the deployable geodesic solar-panel array. Another patent has been filed for the deployment method.

The NASA-funded project calls for completion of an engineering development model by June 2003 and an engineering development unit by June 2004.

Milstar Block II Satellite Launched

(Lockheed Martin Space Systems. Photo by Russ Underwood)

The successful launch of the Milstar 5 communications satellite in January 2002 will significantly reduce the time it takes for U.S. armed forces around the world to exchange critical information. The Aerospace Corporation has supported the Milstar program through development, production, and operations, said Ron Thompson, principal director of the Milsatcom Systems Engineering division. "Our launch and early-orbit test team played a key role in the successful launch and deployment of Milstar 5," he said.

The huge spacecraft is the second Milstar Block II satellite to carry the medium-data-rate payload, which can reportedly process data at speeds of 1.5 megabits per second. Special antennas will provide added security for military users.

The pivotal launch completes the planned constellation of four operational satellites evenly spaced around the equator. With this configuration, the system can provide jam-proof, secure, unbroken communications around the globe, with each unit exchanging signals directly with counterparts to the east and west.

The joint-service system will link command centers with ships, submarines, aircraft, ground stations, and related military resources.

New Tools for Testing Antennas

A new testing facility will enable Aerospace to provide more accurate and secure assessment of large, complex satellite antennas.

The near-field antenna range uses a large planar scanner to characterize the radiation patterns of antennas and scale models. It's also used to investigate new measurement techniques and methodologies. Specialized data-processing routines enable the Aerospace range to capture an antenna's entire radiation pattern—an achievement that would be impossible using conventional planar near-field techniques, said facility director Paul Rousseau.

The previous facility, though much smaller, made key contributions to a National Reconnaissance Office program, determining, for example, that the far sidelobes (unwanted spikes in the radiation pattern) of an antenna system were caused by electromagnetic scattering from struts. Mock-up measurements developed at the range also helped validate a numerical analysis, saving the program an estimated $5 million, Rousseau said.

The near-field range became operational in October 2001, but additional enhancements are planned. New material for absorbing microwaves will be installed, with slightly larger dimensions to allow measurements at lower frequencies. Researchers will also install a larger 12-by-12-foot scanner that will enable them to analyze antennas up to 10 feet in diameter.

Upgrades are also planned for the facility's compact range, which uses a large parabolic reflector to simulate the long-range performance of a satellite antenna.

Experimental Satellites Achieve Orbit

When NASA's original payload for an Athena-I launch vehicle was delayed, the Department of Defense Space Test Program—with Aerospace assistance—was able to negotiate an attractive joint mission. The agency already had three small satellite payloads almost ready for launch. These spacecraft—PICOSat, PCSat, and Sapphire—joined NASA's Starshine 3 to become the Kodiak Star mission.

"To accommodate four spacecraft in place of one, a new payload upper deck had to be designed for the launch vehicle," explained Steve Weis, project leader for Aerospace. His team in Albuquerque provided critical support during the integration of this unique deck configuration.

"As for PICOSat," said Weis, "our support started long before the launch opportunity was identified." Aerospace provided technical and programmatic oversight for space vehicle acquisition, development, and testing. Because the original launch vehicle became unavailable early in the

PICOSat development and a specific launch opportunity was not identified until the spacecraft was complete, Aerospace developed a launch-vehicle interface specification to determine the suitability of the potential U.S. launchers. Aerospace also reviewed test plans, provided independent assessments, and generated a finite-element model to analyze test load cases.

Similarly, Aerospace analysis helped ensure the flight-readiness of PCSat. For example, when an actuator in the separation system failed, Aerospace determined the cause, validated the replacement, and verified that other payloads were not at risk.

In addition, Aerospace wrote procedures for replacing and retesting a defective electrical connector on PCSat's launch-vehicle interface harness at the launch site.

The Kodiak Star mission marked the first orbital flight from the launch complex in Kodiak, Alaska, and the first multiple-payload mission for an Athena-I rocket. In addition, the three Space Test Program spacecraft were deployed at one altitude and the NASA spacecraft at another. These launch challenges were successfully completed, thanks in part to the technical work of The Aerospace Corporation.

Supporting the Nation's Needs at Ground Zero

When the twin towers of New York's World Trade Center collapsed after the terrorist attacks on September 11, 2001, public officials faced the formidable task of sifting through the wreckage to find victims and collect forensic evidence. The Aerospace Corporation immediately offered its assistance and resources. As a result, a remote-sensing instrument developed by Aerospace helped generate and analyze data to support the investigation.

The left image shows a nighttime false-color infrared picture constructed from data gathered in 15 passes over lower Manhattan in a Twin Otter aircraft on October 24, 2001. In the right image, the infrared data have been processed to show the debris-fallout pattern, which appears not to cross the East River into Brooklyn.

The instrument, known as the Spectrally Enhanced Broadband Array Spectrograph System (SEBASS), is a midwave and long-wave hyperspectral imager optimized for airborne sensing. It was flown over the site in October to characterize the distribution of gas and materials.

The information was used to confirm or refute the presence of asbestos in and around the wreckage area as well as the landfill where the debris was deposited. The concentration of asbestos was not high enough for the sensor to detect, but the distribution of fiberglass (which would be expected to have a distribution pattern similar to that of asbestos) was mapped out. SEBASS also detected and mapped the spread of freon and ammonia gas.

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