The TIMED Mission: Exploring One of the Atmosphere's Last Frontiers

FS-2001-09-026-GSFC

The TIMED Mission: Exploring One of the Atmosphere’s Last Frontiers

NASA’s Thermosphere Ionosphere Until TIMED, the MLTI was one of the Mesosphere Energetics and Dynamics last frontiers for atmospheric exploration (TIMED) mission will study a mysterious region because this region is too high for air- in our atmosphere called the Mesosphere, planes or balloons to explore, and too low Lower Thermosphere/Ionosphere, or MLTI. for direct measurement by satellites. Al- though the air here is very thin, satellites Located about 40–110 miles (60–80 travelling at orbital speeds still encounter kilometers) above the Earth, the MLTI is at enough particles to burn up. Ground obser- the edge of space where air pressure is a vations can only study a small area located thousand to a trillion times less than at sea above the observatory, and sub-orbital level. Atoms here have their electrons ripped rockets sent to investigate this region can away by X-rays and ultraviolet (UV) light from only study a limited area before they fall to the Sun, creating an electrified gas used by Earth after a few minutes. ham radio operators as a mirror to bounce their transmissions around the world. Electric TIMED will circumvent these problems currents surge through this region, serving as by orbiting above the MLTI. The spacecraft’s home to that blue-green fire in the sky known remote sensing instruments will work to- as the aurora. gether with a network of ground-based ob- servation sites gathering an unprecedented This region also contains white veils of set of comprehensive global measurements noctilucent clouds, so thin and so high they can of the MLTI region. only be seen from the ground at twilight when the Earth’s shadow blocks sunlight from the During its two-year mission, TIMED lower atmosphere. Once considered to be calm will study the basic structure of the MLTI and unchanging, ripples in these noctilucent region, its chemistry and the flow of energy to clouds along with other measurements indicate and from this layer of the atmosphere. Scien- that this region is actually very turbulent and tists will analyze how the MLTI affects, and is highly variable. This new data has recently changed by, the lower atmosphere, how it stimulated scientific interest in the MLTI. Today, influences the space near Earth occupied by many scientists believe that such fluctuations low-Earth orbiting satellites, and how events may serve as early warning signs of global on the Sun affect the MLTI. climate change.

1 Why TIMED? where the Sun’s energy is first deposited into the Earth’s environment. TIMED will focus on The TIMED mission is vital to research- understanding the processes behind how ers for several reasons. Intense solar activity energy and energetic particles from the Sun dumps energy into the MLTI, causing it to change the chemistry, dynamics and electri- expand and reach further out into space. As a cal properties of the upper atmosphere. With result, low-Earth orbiting satellites encounter TIMED, scientists will be able to develop more MLTI particles, which increases their drag better predictive models of space weather’s and reduces their orbital velocity. Without a effects on communications, satellite tracking, reboost, this drag shortens the spacecraft’s spacecraft lifetimes, degradation of space- lifetime by causing it to decay as it re-enters the craft materials, and on spacecraft reentering Earth’s atmosphere. Geomagnetic storms and the Earth’s atmosphere. solar activity also can heat the atmosphere considerably at these altitudes, increasing drag on orbiting satellites. After a major magnetic The TIMED Spacecraft and Its storm in 1989, ground-based controllers had to Instruments relocate hundreds of satellites in space and record their new orbits. NASA’s Solar Maxi- The TIMED spacecraft weighs in at mum spacecraft was destroyed when this storm 1,294 pounds (587 kilograms). In its stowed knocked it to a lower orbit, causing it to burn up configuration for launch, TIMED measures during its reentry. 8.9 feet (2.72 meters) high by 5.29 feet (1.61 meters) wide. On orbit and after solar array The MLTI region also is a gateway deployment, the spacecraft grows to 38.5 feet between Earth’s environment and space (11.73 meters) wide.

Artist concept of the TIMED spacecraft 388 miles (625 kilometers) above the Earth collecting data about the MLTI region. (Illustration courtesy of JHU/APL)

2 TIMED’s science payload consists of ture of the MLTI region. It determines four instruments - wind speed and direction by examining tiny changes in the color of light emitted • The Global Ultraviolet Imager (GUVI) is from chemical constituents in the atmo- a collaborative effort between The Johns sphere. Similar to how the change in pitch Hopkins University Applied Physics Labo- from a passing ambulance’s siren helps to ratory (APL) and The Aerospace Corp. of determine its speed, particles blown by El Segundo, Calif. GUVI observes the the wind have the color of their emitted glow of the MLTI region in UV light, provid- light changed slightly, allowing scientists ing scientists with its chemical composi- to determine their speed and direction. tion and temperature range. It also measures the energy input by solar UV light The principal investigator for TIDI is Timothy and the aurora. Although invisible to the Killeen of the National Center for Atmo- human eye, UV light is detectable using spheric Research in Boulder, Colo. The POC special instruments like GUVI. The spec- is located at the University of Michigan, Ann trograph in GUVI breaks UV light into its Arbor. component “colors,” much like a prism separates white light into a rainbow. • The Sounding of the Atmosphere using When the MLTI is energized by solar UV Broadband Emission Radiometry light or the aurora atoms and molecules (SABER) is a multichannel infrared radi- that comprise the MLTI glow in specific ometer that measures a wide range of UV colors, allowing scientists to determine infrared light emitted by the atmosphere at its composition and temperature. different altitudes. SABER explores the MLTI to determine its energy balance, The principal investigator for GUVI is Andrew atmospheric structure, chemistry and Christensen of The Aerospace Corp. The dynamics between atmospheric regions. payload operations center (POC) is located at SABER is a collaborative effort between APL in Laurel, Md. Hampton University (Va.), which leads the science team; NASA Langley Research • The Solar Extreme Ultraviolet Center, which has overall project manage- Experiment (SEE), built by the University ment and mission implementation respon- of Colorado, Boulder, observes solar UV sibility; Utah State University (Logan), irradiance, the primary energy deposited which built the instrument; and GATS, Inc. into the MLTI region. SEE determines (Newport News, Va), which developed the how much this energy varies and how it software and manages the data. affects the atmosphere and changes its composition, and will establish an index of The principal investigator for SABER is solar variability so scientists can James Russell III of Hampton University. The understand the solar UV changes in the POC for SABER is located at NASA Langley MLTI even after the mission ends. Research Center.

The principal investigator for SEE is Thomas Woods of the University of Colorado, Boulder, Launch Details where the POC also is located. The TIMED spacecraft is scheduled to launch • The TIMED Doppler Interferometer aboard a Boeing Delta II rocket from the (TIDI), built by the University of Michigan, Western Test Range at Vandenberg Air Force Ann Arbor, measures winds and tempera- Base, Calif. TIMED will be inserted into a 3 388-mile (625-kilometer) circular orbit around The estimated cost for the spacecraft, the Earth, inclined at 74.1 degrees from the instrument payload, and launch vehicle is equator. $189 million. An additional $41.8 million is set aside for data analysis, ground operations TIMED is being launched along with and mission operations costs. Jason-1, an oceanography mission managed by the French Space Agency CNES (Centre National d’Etudes Spatiales) and NASA’s Jet NASA Mission Management Propulsion Laboratory in Calif. TIMED is sponsored by the Office of Space Science in Washington, DC, and Mission Operations managed by NASA’s Goddard Space Flight Center in Greenbelt, Md. An innovative operations approach is being used for the TIMED mission. The four STP Program Executive TIMED principal investigators have direct Victoria Elsbernd, NASA HQ control over their instruments and experiments TIMED Program Scientist from the individual Payload Operations Centers. Mary Mellott, NASA HQ This innovative approach was possible in part TIMED Project Manager due to the spacecraft’s autonomous design, Bruce Campbell, Goddard which helps avoid potential conflicts between TIMED Project Scientist the principal investigators’ requirements and Richard Goldberg, Goddard other on-going spacecraft operations. TIMED carries out many functions on its own, including determining its position, orientation and orbit, APL Mission Management reacting accordingly. This unique design allows the spacecraft and its instruments to be con- The Johns Hopkins University Applied trolled from separate locations during the Physics Laboratory in Laurel, Md., designed, mission. constructed, integrated, tested and will oper- ate the TIMED spacecraft for NASA.

Mission Themes and Costs TIMED Project Manager Dave Grant TIMED Project Scientist TIMED is NASA’s initial mission under Jeng-Hwa (Sam) Yee its Solar Terrestrial Probes Program, part of the Agency’s initiative to lower mission costs and provide more frequent access to space Internet Information to systematically study the Sun-Earth system. Falling under NASA’s Sun-Earth Connection For further details about the TIMED (SEC) theme, which seeks to trace the flow of spacecraft and its science mission, visit these energy and matter from the Sun and deter- web sites: mine its effects on the solar system and our planet, TIMED will provide a comprehensive http://stp.gsfc.nasa.gov/missions/timed/ study of the MLTI from which future studies of timed.htm changes within this region can be compared http://www.timed.jhuapl.edu and analyzed.