STP-H5-Limb-Imaging Ionospheric and Thermospheric Extreme-Ultraviolet Spectrographs (STP-H5 LITES) - 06.20.18

Overview | Description | Applications | Operations | Results | Publications | Imagery

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Science Objectives for Everyone
The International Space Station and other spacecraft orbit Earth in the ionosphere, a complex and dynamic region of the upper atmosphere. Energy and charged particles from the sun form plasmas and ultraviolet airglow, contributing to space weather, which can affect satellite and radio communications. The Space Test Program-H5 Limb-Imaging Ionospheric and Thermospheric Extreme-Ultraviolet Spectrograph (STP-H5 LITES) investigation studies the intensity of ionosphere airglow, which helps scientists understand the ionosphere’s density and better understand and forecast space weather.
Science Results for Everyone
Information Pending

The following content was provided by Andrew Stephan, Ph.D., and is maintained in a database by the ISS Program Science Office.
Experiment Details


Principal Investigator(s)
Andrew Stephan, Ph.D., Naval Research Laboratory, Washington, DC, United States

Supriya Chakrabarti, University of Massachusetts Lowell, Center for Space Science and Technology, Lowell, MA, United States

Naval Research Laboratory, Washington, DC, United States
University of Massachusetts Lowell, Lowell, MA, United States

Sponsoring Space Agency
National Aeronautics and Space Administration (NASA)

Sponsoring Organization
Technology Demonstration Office (TDO)

Research Benefits
Earth Benefits, Scientific Discovery

ISS Expedition Duration
September 2016 - August 2018; -

Expeditions Assigned

Previous Missions
Information Pending

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Experiment Description

Research Overview

  • While space scientists have learned much about the climatology of Earth's space environment, only sparse data exist from which to understand the details of what drives specific space weather events and their potential impact. In order to fully understand the many different phenomena that occur, researchers need new measurements from new instruments to better discern the roles that the Sun, disturbances in the lower atmosphere, electric and magnetic fields, and the interaction of ionized and neutral particles all play in determining how Earth's upper atmosphere responds.
  • Scientists use the data from Space Test Program-H5 Limb-Imaging Ionospheric and Thermospheric Extreme-Ultraviolet Spectrograph (STP-H5 LITES) to develop and test better ways to see changes in the thermosphere and ionosphere using the different ultraviolet airglow signatures that are produced in the sunlit versus the shadowed parts of the atmosphere. The STP-H5 LITES experiment is also serving as a proof-of-concept for a smaller, simpler, yet more sensitive instrument that could be easily duplicated to serve as a networked observatory on a fleet of tiny CubeSat-styled satellites or as payloads attached to larger satellites to observe space weather over the entire globe.
  • The STP-H5 LITES science team is using the measurements taken by LITES to identify the initial development of plasma structures at lower altitudes and the conditions that determine whether they evolve into larger structures seen more readily at higher altitudes. The team also develops new data analysis methods, and test existing models and methods for accuracy over different conditions with the goal of improving the approach taken for the next generation of space weather research.


Earth’s ionosphere is a complex and dynamic region of the space environment consisting of a sparse plasma with a reasonably well-known climatology, interspersed with transient structures, depletions and bubbles, and irregularities. Global scale dynamical processes such as solar heating, waves, tides, electric fields, and auroral precipitation drive strong density gradients in the ionosphere. At both low and middle latitudes, plasma irregularities in the ionosphere create fluctuations in electron density and electric fields over a wide range of scale sizes. The larger bubbles and traveling ionospheric disturbances (TIDs) can span hundreds or even thousands of kilometers and can cause errors in differential navigation solutions. The nighttime low-latitude ionosphere is also characterized by smaller-scale bubbles or plumes that are particularly severe at low latitudes under geomagnetically quiet conditions. The gradients associated with these plasma depletions serve as the breeding ground for the development of smaller secondary instabilities and perturbations. It is these phenomena that create scintillations on radio waves propagating through the affected region, affecting all frequencies less than a few GHz and causing interference and outages of radio navigation and communication links. Because of this impact on operational navigation and communication systems, understanding and forecasting irregularity formation, development, and evolution is a vital and vibrant area of research for the space weather community.
Space Test Program-H5 Limb-imaging Ionospheric and Thermospheric Extreme-ultraviolet Spectrograph (STP-H5 LITES) measures the intensity of ultraviolet airglow that occurs naturally due to photochemical processes in the upper atmosphere. STP-H5 LITES is an imaging spectrograph that returns one-dimensional, vertical (altitude) profiles of 60-140 nm airglow from Earth’s limb. By measuring the intensity of these emissions versus altitude on the limb, scientists are able to model and invert the intensity of specific emission features to determine the density of the corresponding species over this altitude range. The spectrograph design uses a toroidal grating to image the airglow scene vertically while recording spectra of the entire 10 degree scene horizontally. This combination of imaging in the vertical direction and spectroscopy in the horizontal direction is a result of the highly anamorphic toroidal grating. The radius of curvature of the grating along the dispersion axis is that of a Rowland spectrometer while the curvature along the orthogonal axis is approximately a factor of two larger and creates a one dimensional image of the sky at the focal plane. The grating images the sky onto the focal plane along the vertical axis while imaging and dispersing the pupil (the slit) along the horizontal axis. The sensitivity of the instrument is also greatly enhanced by the use of a single reflecting surface, the grating, since each reflectance at these ultraviolet wavelengths typically reduces the throughput by a factor of 2.

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Space Applications
STP-H5 LITES measures the intensity of naturally occurring ultraviolet airglow in the upper atmosphere. Studying this airglow improves scientists’ understanding of the space environment near Earth, including changes in the atmosphere’s density that can cause drag and affect a satellite’s orbit. The airglow also provides information about the density of ionospheric plasma, which affects ground-to-space radio communications and can affect telecommunications and power grids on Earth.

Earth Applications
Space weather refers to electromagnetic activity in the Earth’s upper atmosphere, which can disrupt electronics and communications on the ground and interfere with global positioning system navigation. These storms can also cause surges in electrical lines that can cause major power outages and force airlines to re-route traffic from trans-polar routes. Better measurement of the ionosphere improves space weather forecasting, benefiting people on Earth.

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Operational Requirements and Protocols
STP-H5 LITES is oriented on the payload to optimize measurements between 150-350 km altitude on the limb where the data of greatest scientific value are collected. STP-H5 LITES operates nearly continuously, with the exception of when the instrument field of view is within 30 degrees of the Sun. The minimum mission is for 30 days of routine data collection, to allow for science data at a range of local times as the ISS orbit completes one full precession cycle, and one full year for comprehensive mission success to identify seasonal patterns in the data.
STP-H5 LITES on-orbit procedures are limited to updating the schedule for autonomous on/off commands, when the ISS orbit beta angle is such that the instrument field of view is within 30 degrees of the Sun. Additional real-time on/off commanding is done in situations such as ISS orbit maneuvers that could introduce risk to the instrument safety and health. Rarely (anticipated 2-4 times per year), small adjustments to the instrument high voltage levels will occur during the course of the mission to offset normal instrument wear and reduced efficiency.

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Decadal Survey Recommendations

Information Pending

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Results/More Information

Information Pending

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Results Publications

    Geddes G, Douglas ES, Finn SC, Cook T, Chakrabarti S.  Inverting OII 83.4 nm dayglow profiles using Markov chain radiative transfer. Journal of Geophysical Research: Space Physics. 2016 November; 121(11): 11249-11260. DOI: 10.1002/2016JA023168.

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Ground Based Results Publications

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ISS Patents

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Related Publications

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Related Websites

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NASA Image: ISS050E052652 - Space Test Program-H5 (STP-H5). Photo taken during Expedition 50.

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