ITT Advanced Engineering & Sciences is leveraging its heritage in space communications technology to help NASA expand the range and efficiency of its space communications capabilities.

Long History of Engineering Support at NASA Goddard

The mission of the NASA Goddard Space Flight Center is to expand knowledge of the earth and its environment, the solar system, and the universe through observations from space. To accomplish this, communications to and from spacecraft orbiting the earth is tremendously important.

Key to satellite communications for NASA is the TDRSS, the Tracking and Data Relay Satellite System. The TDRSS geosynchronous orbiting satellites relay information from low orbiting manned space vehicles and experimental satellites. With the TDRSS system, low orbiting satellites can be seen from anywhere on earth and thus can communicate from any place in their orbit.

AES has a long history of providing engineering support to NASA Goddard for TDRSS. According to Lenny Schuchman, Vice President & General Manager of the Communications Systems Integration Business Unit at AES, "AES personnel have been dedicated to NASA Goddard's mission in communications for over 25 years." AES has provided significant contributions to the initial specifications of TDRSS and to the design of improved upgrades. AES also works to ensure compatibility between user spacecraft and TDRSS, to ensure that NASA's allocated bandwidth is optimally used, to plan the next-generation TDRSS, and to develop technology which provides new, lower cost services for TDRSS.

Systems Engineering

For over 25 years, AES has provided a full range of RF communications systems engineering support to NASA Goddard related to the TDRSS and other NASA Space and Ground Network assets. This support encompasses requirement assessment, architectural trade studies, communications technology studies, conceptual designs, specification development and procurement support, and communications performance analyses.

AES has played key system engineering roles in a number of major programs at NASA including the TDRSS H, I, J program. This program will procure three, new next-generation TDRSS spacecraft to meet NASA track and data relay needs to 2010 and beyond. AES reliability analyses of the existing TDRSS spacecraft constellation, in conjunction with user mission modeling were used to determine the earliest need dates, required launch dates, and number of required spacecraft to replace the aging fleet. AES performed feasibility and architecture studies, and then developed the spacecraft telecommunications requirement specification and in-house cost estimate for the NASA procurement. Since the award of the spacecraft contract by NASA, AES continued to support NASA on the TDRSS H, I, J program by providing oversight of the implementation contractor to ensure all telecommunications requirements are met.

On a similar task for NASA, AES supported the procurement and implementation of the Second TDRSS Ground Terminal (STGT) at White Sands, NM. AES initially performed studies to define the STGT system and subsystem architectures, particularly taking into account the lessons learned from the current White Sands Ground Terminal operations and current state-of-the-art technologies.

To support these and other NASA system engineering activities, AES has designed and developed a large number of software tools now serving the telecommunications and spectrum engineering communities. With over 100 analysis and simulation packages (in software form) operating in a workstation or PC environment, AES is capable of analyzing all aspects of RF communications. These tools are used to ensure user spacecraft design and performance compatibility with the Space Network and/or Ground Network, and to assess, via modeling and simulation, performance and risks associated with advanced technology applications.

Spectrum Management

AES fulfills spectrum management roles and performs communications and spectrum analyses in support of the NASA Spectrum Managers. AES plays a critical role in ensuring that quality RF spectrum is available to NASA missions.

As part of the spectrum management efforts, AES has performed analyses on a variety of space communications topics including radio frequency interference, frequency sharing, power spectral densities, geographical distribution of interference, technology risk assessment, and visibility and network coverage. Much of these analyses are performed in direct support of the NASA Spectrum Manager or in support of U.S. contributions to national and international spectral policy conferences, study groups, and task groups.

The AES team works closely with NASA project offices in frequency selection and management, spacecraft design, mission planning, networks scheduling, and post-mission error analysis in order to optimize RF performance and avoid data loss or degradation of the communications links due to interference.

The AES team uses in-house tools to analyze various types of spectral interference.

Technology Development

In the mid-1980's Dr. Aaron Weinberg, AES Vice President of Communication Systems hypothesized that by using charge coupled devices (CCD) for communication, acquisition time for the TDRSS multiple access service could be reduced from minutes to seconds. The CCD transceiver technology triggered new operational concepts and further technology development. As an example, new NASA services could be provided that allowed experimental satellites to transmit data "on demand" rather than on a scheduled basis. The CCD transceiver also had the ability to be reprogrammed.

Building on this "software receiver" technology with Field Programmable Gate Arrays (FPGA), AES is now realizing small size, low power and affordable transceivers for use in space applications. In recent years, AES has been focused on supporting NASA in developing demand access and is developing a Low Power Transceiver (LPT), which, when implemented, will demonstrate that new technology can significantly reduce the cost of communicating via the TDRSS.

Expanding Space Communications with TechSat 21

AES is currently working with the Air Force Research Laboratory for flight testing on a new program called TechSat 21 (Technology Satellite of the 21st Century). A new way to perform missions from space is the concept of microsatellite clusters that operate cooperatively to perform the function of a larger, single satellite. Each smaller satellite communicates with the others and shares processing, communications, and payload or mission functions to form a "virtual satellite".

The key to the TechSat 21 concept requires the microsatellites to perform "formation flying". AES will perform research for TechSat 21 that will require testing advanced communications between satellites to maintain the distance needed for formation flying. Schuchman notes that, "This will require using a phased array antenna, a need to do beam forming, multiple transmitters, multiple receivers, as well as GPS navigation."

In order to meet the weight and power requirements of these microsatellies, AES engineers are currently working on a miniaturized version of the LPT. Called the Miniature Terminal (MIN-T), it will measure approximately 2-inches square. Schuchman observes that, "We originally designed the LPT and the MIN-T for spacecraft that communicate with the TDRSS. Now we see that they have applications for any spacecraft program whether it connects into TDRSS or not. The goal is to set up very effective communications to allow the world of space to communicate with earth. That includes low power receivers that allow for the multiple access techniques and reconfiguration of a spacecraft's navigation and communications without having to take it down."

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