Frequently Asked Questions

Frequently Asked Questions


What does GUVI stand for?

GUVI stands for Global UltraViolet Imager, which measures the composition and temperature profile of the MLTI region as well as its auroral energy inputs.

What does SSUSI stand for?

SSUSI stands for Special Sensor Ultraviolet Spectrographic Imager, which measures the composition and temperature profile of the MLTI region as well as its auroral energy inputs.

What does TIMED stand for?

TIMED stands for Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics. The TIMED mission will study a region of Earth's atmosphere between 60-180 kilometers (approximately 40-110 miles) - the Mesosphere and Lower Thermosphere/Ionosphere, sometimes referred to as the MLTI region. The TIMED mission will study how energy is transferred into and out of the MLTI region (energetics), as well as the basic structure of the atmosphere (i.e. pressure, temperature and wind) that results from the energy transfer into the region (dynamics).

What is the purpose of the TIMED mission?

The TIMED mission is to study the influences of the sun and humans on the least explored and understood region of Earth's atmosphere: the Mesosphere and Lower Thermosphere/Ionosphere (MLTI). With TIMED, we will gain a better understanding of the dynamics of this gateway region and its effects on communications, satellite tracking, spacecraft lifetimes, degradation of spacecraft materials and on spacecraft reentering Earth's atmosphere.

What will TIMED accomplish that other spacecraft have not?

TIMED will be the first mission to conduct a comprehensive global study of this region, including its basic structure and thermal balance, how the mesosphere is coupled to the thermosphere/ionosphere, how the MLTI region is coupled to space and the lower atmosphere below, and how energy is transported vertically and horizontally through this region. The TIMED mission will establish a baseline against which future studies of changes within this region can be compared and analyzed.

How does TIMED fit into NASA's overall science program?

The Sun-Earth Connection (SEC) is one of four principal science themes around which missions within NASA's Office of Space Science are organized. The Sun-Earth Connection focuses largely on explaining the physical processes that link the sun and the Earth. TIMED is the first mission within the Solar Terrestrial Probe Program, which falls under the SEC theme. It will investigate one of the Sun-Earth Connection's quests: How does the Earth's upper atmosphere respond to solar inputs? The Solar Terrestrial Probe Program offers a continuous sequence of flexible, cost-capped missions designed to systematically study the Sun-Earth system. Solar Terrestrial Probe missions will focus on studying the sun and the Earth as an integrated system using a blend of in situ and remote-sensing observations, often from multiple platforms.

Where is the MLTI atmospheric region located, and why is it important to study this region?

The MLTI (Mesosphere and Lower Thermosphere/Ionosphere) region, part of Earth's upper atmosphere, is located between 60-180 kilometers (approximately 40-110 miles) above Earth's surface. This region is where the sun's energy is first deposited into Earth's environment. The sun's energy can have profound effects on Earth's upper atmospheric regions, particularly during the peak of the sun's 11-year solar cycle when the greatest amounts of its energy are being released. TIMED is focused on understanding and characterizing exactly how the sun interacts with the Earth's environment. It will allow us to establish the first-ever baseline of the MLTI region against which future studies of changes within this region can be compared and analyzed.

Why have studies of this region been limited?

A comprehensive global study of the entire MLTI region has never before been accomplished for several reasons. Ground-based instruments can only see a small portion of the upper atmosphere located over an observation site. It's too high for balloons to reach. Sounding rockets (rockets that go up into the upper atmosphere for just a few minutes before falling back down) can only provide a brief snapshot of the MLTI region's activity near the rocket.

How will TIMED provide the first-ever global picture of the MLTI region?

The TIMED spacecraft will observe the MLTI region and its basic structure from the spacecraft's 625-kilometer (388-mile) circular orbit around the Earth. Employing advances in remote-sensing technology, the spacecraft's instrument suite will work with a worldwide network of ground-based observation sites to collect information necessary for us to test their current understanding of the processes that change the winds and composition in this part of the atmosphere, and determine how energy is absorbed, emitted and transported within the MLTI region.

How many and what types of instruments are onboard the spacecraft?

TIMED's payload consists of four instruments. The Global Ultraviolet Imager (GUVI) is a spatial scanning ultraviolet spectrograph designed to measure the composition and temperature profiles of the MLTI region, as well as its auroral energy inputs. The Solar Extreme Ultraviolet Experiment (SEEis comprised of a spectrometer and a suite of photometers designed to measure the solar soft X-ray, extreme-ultraviolet, and far-ultraviolet radiation that is deposited into the MLTI region. The TIMED Doppler Interferometer (TIDI) is designed to measure the winds and temperature profiles of the MLTI region. And a multichannel radiometer known as SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) is designed to measure the pressure, temperature, key gases in the oxygen and hydrogen families, infrared cooling, and effects of solar and chemical heating of the MLTI region.

Who will have access to GUVI data and how will it be distributed? How quickly will data be available?

Data obtained during the GUVI mission will be available to the public and accessible through GUVI's Web site, located at Within 54 hours of receiving data on the ground, we and the public will be able to look at the GUVI data.

How long will the mission last?

GUVI will collect data, while in orbit around the Earth, for two years. An additional two years of data analysis will be supported by the GUVI Data Processing Payload Operations Center and the GUVI Engineering Payload Operations Center, located at The Johns Hopkins University Applied Physics Laboratory in Laurel, MD.

Who is building GUVI?

The Johns Hopkins University Applied Physics Laboratory in Laurel, Md., and the Aerospace Corp. is responsible for the design, construction, integration, testing and operation of the spacecraft.