Space Test Program-H5 Automated Plume Sentry (STP-H5 APS) - 06.20.18

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

ISS Science for Everyone

Science Objectives for Everyone
Space is a vacuum, but it is far from empty, containing countless micrometeoroids and charged particles that interact with each other, and with scientific equipment. The International Space Station is constantly bombarded by these particles, as well as gases from cargo ships ferrying equipment to and from the station. The Space Test Program-H5 Automated Plume Sentry (STP-H5 APS) investigation studies how thrusters on approaching spacecraft interact with the station, including whether they can contaminate experiments housed on the station’s exterior.
Science Results for Everyone
Information Pending

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


Principal Investigator(s)
Geoff McHarg, Ph.D., U.S. Air Force Academy, Colorado Springs, CO, United States

Rick Adams, Ph.D., Barron Associates, Inc., Charlottesville, VA, United States

Barron Associates, Charlottesville, VA, United States
Johns Hopkins Applied Physics Lab, Laurel, MD, United States
US Air Force Academy, USAF Academy, CO, United States

Sponsoring Space Agency
National Aeronautics and Space Administration (NASA)

Sponsoring Organization
Technology Demonstration Office (TDO)

Research Benefits
Space Exploration

ISS Expedition Duration
September 2016 - August 2018; -

Expeditions Assigned

Previous Missions
STP-H3 - Canary

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Experiment Description

Research Overview

  • The research is needed in order to develop models of the interaction of the approaching spacecraft with the International Space Station (ISS).
  • Measurements are taken of the electrical current resulting from charge exchange of the neutral effluents from approaching spacecraft.
  • These data are used in combination with a detailed model of the charge exchange process in order to calculate the flux of particles striking the outside of the ISS.
  • The Space Test Program-H5 Automated Plume Sentry (STP-H5 APS) investigation is used to estimate possible contamination of different places on the outside of the ISS.


Charge-exchange plasma interactions have been extensively studied. However, there are few in-flight investigations because of limited spaceflight opportunities.
The APS sensor monitors the electrical current resulting from charge exchange of the neutral effluents from approaching spacecraft. This allows characterizing of spacecraft surface charging, the interaction of spacecraft and the ambient environment, and detect and map significant natural events in the ambient environment.
The STP-H5 APS sensor provides a better understanding of the impact of low-energy charge exchange ion environment of an approaching spacecraft with the International Space Station (ISS). Charge distribution and accumulation near spacecraft is a potential contamination source for instruments and solar arrays. The development of such a technology demonstrates the availability of low-cost techniques for monitoring these conditions.

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Space Applications
A constant stream of charged particles from the sun and cosmic sources surrounds Earth and its artificial satellites, including the International Space Station. These particles are often the subject of scientific investigations, but they can also interfere with equipment. This investigation studies the interactions among charged particles in the spaceflight environment and the fuels in spacecraft thrusters. Results point the way toward protection efforts that might be necessary to shield sensitive equipment from rocket exhaust.

Earth Applications
This investigation studies how approaching spacecraft propulsion systems might interfere with experiments on the International Space Station, which include investigations of charged particles, solar phenomena and more. Understanding these interactions improves efforts to safeguard sensitive equipment, including equipment used to study solar radiation, which affects human health and the safety of communications spacecraft.

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Operational Requirements and Protocols
The STP-H5 hardware complement are installed with the SSRMS and activated via ground based commands. Instrument health, status and operational data are downlinked via standard ISS 1553 communications protocols. Using the NASA TReK interface, APS is commanded from, and data downloaded to, the US Air Force Academy in Colorado Springs, CO. Cadets and faculty operate the ground station as part of the final year cadet capstone project.

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

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