Space Test Program-H5-GPS Radio Occultation and Ultraviolet Photometry Co-located (STP-H5 GROUP-C) - 06.20.18

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

ISS Science for Everyone

Science Objectives for Everyone
Charged particles and ultraviolet light from the Sun constantly bombard the upper layers of Earth’s atmosphere, and these interactions cause space weather, which can affect communications and power on Earth and in space. The Space Test Progam-H5 GPS Radio Occultation and Ultraviolet Photometry Co-located (STP-H5 GROUP-C) investigation uses two sensors to measure Earth’s ionosphere, the uppermost region of the atmosphere. The sensors measure horizontal and vertical ion and electron density in the ionosphere, studying the ionosphere’s structure and variability.
Science Results for Everyone
Information Pending

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


Principal Investigator(s)
Scott Alan Budzien, Ph.D., Naval Research Laboratory, Washington, DC, United States

Mark Psiaki, Ph.D., Cornell University, NY, United States
David Hysell, Ph.D., Cornell University, Ithaca, NY, United States
Steven Powell, Cornell University, NY, United States
Rebecca Bishop, Ph.D., The Aerospace Corporation, El Segundo, CA, United States
Brady O'Hanlon, Ph.D., The MITRE Corporation, Bedford, MA, United States

Naval Research Laboratory, Washington, DC, United States

Sponsoring Space Agency
National Aeronautics and Space Administration (NASA)

Sponsoring Organization
Technology Demonstration Office (TDO)

Research Benefits
Earth Benefits, Space Exploration

ISS Expedition Duration
September 2016 - August 2018; -

Expeditions Assigned

Previous Missions
Information Pending

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Experiment Description

Research Overview

  • Space weather events and ionospheric phenomena can degrade or disrupt communications and navigation signals. The Space Test Program-H5 GPS Radio Occultation and Ultraviolet Photometry Co-located (STP-H5 GROUP-C) experiment employs advanced space sensors to study the upper atmosphere's response to space weather and dynamical processes relevant to radio propagation.
  • STP-H5 GROUP-C demonstrates low-cost, high performance, compact ionosphere sensors suitable for space weather and space environment sensing on a variety of spacecraft. The high-sensitivity 135.6 nm ultraviolet photometer measures horizontal variations of nighttime ionosphere, and the GPS occultation receiver measures vertical variations in the electron density.
  • The ionospheric measurements provide insights into the origin, structure, and evolution of ionospheric plasma structures, which can affect or disrupt radio signals. This information contributes to the development of improved ionospheric models and improved forecasting of communication disruptions.


Space Test Program-H5 GPS Radio Occultation and Ultraviolet Photometry Co-located (STP-H5 GROUP-C) is an ionospheric remote sensing experiment manifested to fly on the International Space Station (ISS). STP-H5 GROUP-C operates aboard the Space Test Program Houston 5 (STP-H5) experiment pallet and provide ionospheric measurements in real‐time. STP-H5 GROUP-C includes two sensors:  the Fast Orbital TEC, Observables, and Navigation (FOTON) L1/L2 GPS receiver, which provides vertical electron density profiles and scintillation; and the Tiny Ionospheric Photometer (TIP), a far-ultraviolet photometer for measuring horizontal ionosphere gradients. The FOTON receiver includes a capability for multipath mitigation using a multi-antenna array. The TIP photometer is similar to the photometers aboard the COSMIC satellites with minor improvements in optical performance.
Ionospheric irregularities, also known as ionospheric bubbles, are transient features of the low and middle latitude ionosphere with important implications for operational systems. Understanding irregularity formation, development, and evolution is vital for efforts within NASA and Department of Defense to forecast scintillation. Irregularity structures have been studied primarily using ground-based systems, though some spaced-based remote and in-situ sensing has been performed. In combination with GROUP-C, the Limb-imaging Ionospheric and Thermospheric Extreme-ultraviolet Spectrograph (LITES) experiment on STP-H5 serves as an interactive ionospheric observatory on the ISS.
These experiments provide new capability to study low- and mid-latitude ionospheric structures on a global scale. By combining for the first time high-sensitivity in-track photometry with vertical ionospheric airglow spectrographic imagery, and simultaneous GPS TEC and scintillation measurements, high-fidelity optical tomographic reconstruction of bubbles can be performed from the ISS. Ground-based imagery can supplement the tomography by providing all-sky images of ionospheric structures (e.g. bubbles and TIDs) and of signatures of lower atmospheric dynamics, such as gravity waves, that may play a role in irregularity formation.

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Space Applications
Satellites, the International Space Station, cargo craft, and humans operate in the ionosphere, at the very edge of Earth’s atmosphere. STP-H5 GROUP-C improves understanding of particle interactions in the ionosphere and how they might disrupt communications between spacecraft and the ground. The investigation demonstrates new low-cost, high-performance ionosphere sensors that could be used on a variety of spacecraft to better understand their environment.

Earth Applications
Results from STP-H5 GROUP-C provide insight into space weather, including how plasma structures form in the ionosphere and disrupt radio signals. This data improves computer models used to study the ionosphere, as well as space weather forecasts.

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Operational Requirements and Protocols

TIP nighttime data are collected in the 19:00-21:00 local time simultaneously with GPS occultations near the ISS orbital plane on multiple orbits. Longer-term goals include UV observations the ionospheric equatorial ionosphere and GPS occultations collected over the course of 30 days. Ideally, two or more years of routine data collection will help characterize long‐term variability of the ionosphere.
The TIP UV instrument is extremely sensitive, and must be turned off during the bright daytime portion of the orbit. TIP collects data during each nighttime pass. The GPS sensor operates automatically, continuously collecting occultation data as the GPS satellites appear to set behind the ISS.

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Decadal Survey Recommendations

Information Pending

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Results/More Information

Information Pending

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Related Websites

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Image courtesy of the Naval Research Laboratory.

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

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