A Landsat image of Santa Barbara, California, from space. The image was taken by Landsat 7's Enhanced Thematic Mapper Plus instrument. It is a false-color composite made from bands 2, 3, and 4, covering the green, red, and infrared portions of the electro-magnetic spectrum.

Maintaining the Legacy of Landsat

Steven J. Covington and Thomas R. Hill

Landsat space satellites have been gathering and relaying land imagery since 1972, offering insight into Earth's ever-changing characteristics. Aerospace has been involved in program development, launches, and anomaly resolution for Landsat missions.

The Landsat program is a series of satellite missions that collect information about Earth from space. The U.S. Geological Survey (USGS), part of the Department of Interior, has been involved with the program since its beginning, primarily as the national archive for the data. The imagery from Landsat is used by a variety of organizations for land-use monitoring and planning, agriculture, disaster response and recovery, coastal zone management, and the analysis of the impact of human development.

Aerospace first supported the USGS with the Landsat 7 development project and monitoring of flight operations for the Landsat 5 mission. Today, the USGS relies on Aerospace for daily operation of these two successful missions, and for the resolution of anomalies that threaten to end them. The agency has requested that Aerospace provide major technical advice for the successor to Landsat 5 and 7, the Landsat Data Continuity Mission (Landsat 8). Aerospace is also providing assistance with the development of a newly proposed federal initiative, the National Land Imaging Program.

Background

The Interior Department made a big splash in its initial foray into space endeavors. In 1966, Interior Secretary Stewart Udall announced plans to build and launch the nation's first civil land remote sensing satellite system to record and monitor the surface of Earth. This announcement led to the NASA-initiated development and launch of the Earth Resource Technology Satellite in 1972, later renamed Landsat 1. Since then, the United States has launched six follow-on missions (one via a commercial venture) and is currently building Landsat 8.

The Landsat class of satellites provides from 15 to 30 meter ground resolution in the visible, shortwave- and midwave-infrared portions of the electromagnetic spectrum. It also has a 60-120 meter ground resolution in the thermal infrared region. The image resolution and the eight spectral bands collected in these regions are designed to provide sufficient information to discern basic land cover, land use, and vegetation coverage. This data is collected on a global, synoptic basis with highly calibrated sensors, offering an accurate assessment of land use change, and creating a valuable archive of observations from space dating back to 1972.

Landsat is regarded by some as America's most successful uncrewed satellite.

Landsat 4 and 5, launched under National Oceanic and Atmospheric Administration (NOAA) leadership, were transferred to the EOSAT Corporation, with a mission to fly them while commercializing the land remote sensing market and building their successor, Landsat 6. Problems and concerns with this approach surfaced, however, and Congress took action to reverse commercialization in 1992. Meanwhile, Landsat 6 failed to achieve orbit in October 1993.

In 1992 Congress passed the Land Remote Sensing Act (P.L. 102-555), stating that the Landsat program had established the United States as the world leader in land remote sensing technology. The importance of collecting and using land remote sensing data from space was cited as "a major benefit in studying and understanding human impacts on the global environment, in managing the Earth's natural resources, in carrying out national security functions, and in planning and conducting many other activities of scientific, economic, and social importance."

The Land Remote Sensing Act directed the federal government to begin the Landsat 7 project as a multiagency endeavor involving the Air Force, NASA, NOAA, and the USGS. Along with the Air Force came a small contingent of Aerospace support. By 1994, changes in programmatic focus led to a new approach that no longer included the Air Force–or Aerospace. Aerospace would not be sidelined for long, however, as the work provided to the Air Force had made an impression on the then "junior partner" USGS.

The initial project plan called for NASA to manage acquisition of the Landsat 7 mission and NOAA to operate it out of a mission operations center at NASA Goddard Space Flight Center in Greenbelt, Maryland. The USGS would host the primary ground station for telemetry, tracking, command and control, and payload telemetry reception; assessment, archiving, and distribution of data would be managed at its Earth Resources Observation Systems (EROS) data center in South Dakota. NASA would design the ground station and data-processing architecture, build the ground station infrastructure, develop the ground processing systems, and deliver and install them at EROS. USGS was depending on NASA to deliver a system that would meet the operational objectives of the mission.

The Earth Resources Technology Satellite-1 (Landsat 1) in 1972.

However, EROS was located 1500 miles from the project office, and to operate effectively during most development activities, it needed "boots on the ground" at Goddard. USGS was new to flight project development and space operations in general, so it was important to have representatives at Goddard who understood the ground systems being developed and their relationship to the space segment. USGS approached Aerospace to provide technical support at Goddard based on its observation of Aerospace's contributions to the Air Force.

The USGS needed the engineering and technical skills unique to space systems acquisition for Landsat 7. The project had numerous contractors and SETAs performing various roles, and the USGS wanted insight into what they were doing. Aerospace's role as a federally funded research and development center fit the bill. At the same time, Aerospace wanted to extend the corporation's support to other federal agencies to ensure Aerospace was engaged in meaningful civil space programs. This made the USGS request for Aerospace support a natural match that would meet national as well as corporate goals.

In the early years of support to USGS, one Aerospace representative was stationed at Goddard. The primary goal was to stay abreast of development efforts on the East Coast and preparations in South Dakota, ensuring USGS was cognizant of changes and well represented in technical meetings. Then, just prior to launch, a change in civil agency roles put the USGS in charge of mission operations, with NASA as a partnering agency.

Operations

When a Delta II booster with Landsat 7 on top roared to life at Vandenberg Air Force Base on April 15, 1999, it signaled a new era in land remote sensing and Aerospace's support of the Landsat program. After on-orbit checkout, NASA managed flight operations until the USGS formally assumed responsibility for the satellite and hired its own flight systems manager. There was one problem, however: because spaceflight operations were new to the USGS, the organization had no viable candidates to technically support its manager. Aerospace, having aided in the development of Landsat 7, was well positioned to serve as a technical advisor to this flight systems manager. This arrangement gave USGS access to Aerospace's experience base, as well as ongoing support as needed.

Soon after assuming responsibility for Landsat 7 operations, the USGS found itself to be a "multi-mission" agency when EOSAT abruptly relinquished responsibility for the Landsat 4 and Landsat 5 missions. As Landsat 4 had ceased to provide useful science data, it was immediately decommissioned. However, the 19-year-old Landsat 5 was still producing high-quality imagery from its thematic mapper imager, and the decision was made to continue operations.

Since then, both the Landsat 5 and Landsat 7 missions have provided their share of excitement in day-to-day operations. Landsat 5, launched in 1984, is now one of the oldest functioning multimission modular satellite bus-based spacecraft still flying. It passed its 130,000th orbit in September 2008. Landsat 7 has surpassed its original five-year mission—it has now been functioning for more than nine years and recently passed its 50,000 orbit mark. Although they continue to deliver science-quality image data from around the globe, both missions are showing their age through ongoing operational challenges. Recent Landsat 5 anomalies investigated by Aerospace include:

A balky X-band traveling wave tube amplifier that has defied all understanding about why it continues to function, yet still does. In 2006, when the transmitter failed to power up successfully, the flight operations team and Aerospace personnel devised a new turn-on routine that has so far granted the spacecraft two extra years of life.
A battery cell failure that suspended imaging for several months while an Aerospace battery expert and the flight operations team developed and then refined a new charging scheme. This allowed the spacecraft to resume imaging operations.
An attitude control system working outside of its design parameters because of failed primary and redundant solar array drives. The spacecraft pitches multiple times each orbit to illuminate the array sooner and longer, but these maneuvers force the onboard software and hardware to work differently than planned. Aerospace is using its experience with similar spacecraft to assist in troubleshooting and long-term problem solving.

The younger sibling, Landsat 7, is quieter day-to-day, but has had its share of challenges as well. It has faced anomalies with its primary imager, the Enhanced Thematic Mapper+, where a scan-line-corrector mirror failure in 2003 degraded the imaging products. Aerospace had a leadership role in the anomaly investigation and served as test director during an effort to recover the failed component. Although unsuccessful, additional ground processing has partially mitigated impacts to the image data's utility. Aerospace also had a role in the analysis and response to the failure of one of three gyroscopes onboard the spacecraft, using experience gained from other spacecraft that use the same model gyros to establish a way forward for Landsat 7.

Landsat 4 and 5 shown in an early configuration study.

As both spacecraft age, Aerospace and the operations team face increasing questions as to how much longer the spacecraft can function. This leads to analyses relating to such topics as fuel use and orbital debris mitigation.

The Future

The director of the Office of Science and Technology Policy initiated in 2005 an interagency effort to develop a long-term plan for the nation's land remote sensing capabilities, organization, and investment.

In the office's final report, "A Plan for a U.S. National Land Imaging Program," the Future Land Imaging Interagency Working Group proposed formation of a new federal initiative under the Department of the Interior, the National Land Imaging Program. This program is designed to provide a mechanism within the Interior Department to assess the land imagery needs of federal agencies, state and local land management officials, scientists, and geographic researchers, and to translate those needs into the technical capabilities of future satellites. Aerospace supported the USGS in this working group, attending meetings, developing content, and helping organize the structure and messages within the final versions of the report.

While the Interior Department waits for congressional authorization and funding to start up the new program, Aerospace continues to support the Land Remote Sensing Program within the USGS. Aerospace activities range from ad hoc studies for development of requirement management and decision support tools, to providing subject matter experts at space systems development reviews so that USGS headquarters receives a truly independent assessment. Occasionally, when greater depth is required, the program requests specific support from Aerospace in areas such as spacecraft communications, optical systems stray-light analysis, and documentation development for procurements and future studies, such as statements of work and requests for information.

The Landsat 7 space mission has been successfully returning land images in multiple wavelength bands since 1996. Data from the mission is used by national and international partners including federal, state, and local governments as well as disaster agencies.

Aerospace will continue to provide the USGS with flight operations support, engineering support during on-orbit anomalies, and technical assistance in support of the various initiatives advanced by the projects. With both the Landsat 5 and Landsat 7 missions continuing to operate well beyond their design lives, the USGS is relying on Aerospace to technically support the contracted flight operations teams through good times and bad. When anomalies occur, Aerospace will continue to offer its expertise, leading in response and recovery and bringing in subject matter experts as necessary to ensure a successful return to service or, eventually, an orderly decommission and disposal.

Aerospace will provide onsite support to the U.S. government for the Landsat Data Continuity Mission. The work will involve offering systems engineering advice; helping to integrate best practices into the development, integration, and test procedures and processes; and preparation of the operations and maintenance teams.

Aerospace will continue supporting the USGS in the concept development, design, and implementation of the Landsat Data Continuity Mission ground system, which will be built at the EROS. Aerospace instrument experts are advising the USGS on the development of the primary flight instrument, the operational land imager. The USGS is relying on Aerospace to bring its extensive experience in both ground system development and acquisition and instrument design to help ensure a successful continuation of more than 36 years of land remote sensing data.

Conclusion

Aerospace currently supports USGS at its headquarters in Reston, Virginia, EROS in Sioux Falls, South Dakota, and two mission operations control centers in Greenbelt and Columbia, Maryland. While working a variety of sides of the same issues for different parts of the USGS, Aerospace strives to maintain an independent yet coordinated support group among the program office and the projects. This ensures continuity of objectives without compromising the positions and actions of the disparate organizations within the USGS.

The objective for civil satellite programs is the same as for other Aerospace customers: mission success. For civil customers, the goals are the same, the challenges are the same, the processes and techniques are the same–but the budgets are smaller. The good news for Aerospace researchers: they can talk about their work when they go home at night.