Space Test Program-Houston 4- Small Wind and Temperature Spectrometer (STP-H4-SWATS) - 10.01.14
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The Space Test Program-Houston 4-Small Wind and Temperature Spectrometer (STP-H4-SWATS) investigation demonstrates a lightweight, low-power space-based weather sensor. Every second, the instrument gathers detailed data on atmospheric density, composition, temperature and winds in the ionosphere, the uppermost layer of the atmosphere that includes the orbit of the International Space Station. The data is used to improve computer models that simulate Earth’s atmosphere.
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Naval Research Laboratory, Washington, DC, United States
Goddard Space Flight Center, Greenbelt, MD, United States
Sponsoring Space Agency
National Aeronautics and Space Administration (NASA)
National Laboratory - Department of Defense (NL-DoD)
ISS Expedition Duration
March 2013 - March 2015
Previous ISS Missions
This is the first flight of the SWATS instrument, also known as WINCS. The instrument is manifested on three other flights, STP-Sat3, the USAF SENSE CubeSat developed by Boeing and the CADRE CubeSat developed by Universityof Michigan via the National Science Foundation (NSF).
The Space Test Program-Houston 4- Small Wind and Temperature Spectrometer (STP-H4-SWATS) sensor is an innovation in minimal resource Space Weather sensors.
Global pattern of low latitude ionosphere is driven by F-Region (150-800 km above sea level) neutral winds arising from atmospheric tides.
The STP-H4-SWATS sensor can be effectively used as an ionospheric bubble detector with sub-kilometer spatial resolution on temporal scales of 0.1 second.
The data can feed both assimilative ionospheric models and be used in the development of full-physics models.
The thermosphere and ionosphere are two tightly coupled, overlapping regions of the atmosphere. Below the thermosphere, the atmosphere is relatively well mixed and is dominated by neutral dynamics such as tidal structures and gravity waves. Within the thermosphere, individual species start to separate from each other, the ionosphere forms, and the dynamics become dominated by the interaction with charged particles (ions). The forces on the ionized plasma are significantly different than the neutral fluid below. For example, the magnetospheric electric fields cause the ions to move across magnetic field lines at high latitudes, while these fields do not directly influence the neutrals. The ions, which have a density roughly 1/1000th the neutral species, exert both a frictional drag and a frictional heating on the neutrals. Therefore, while the neutrals are not directly influenced by the magnetospheric electric fields, they are indirectly forced through the ion drag.
The high-latitude ion flows in the F-region ionosphere (150-800 km above sea level), which are mostly described by the magnetospheric electric field, are quite variable and are controlled by the interplanetary magnetic field (IMF) and solar wind conditions. Many forces, such as ion drag, viscosity (resistance to flow), Coriolis (deflection of the path of an object that moves within a rotating coordinate system) and gradient in pressure, on the other hand, influence the neutral winds. The balance between these forces is strongly dependent on location, the density of the ionosphere, the temperature difference between the nightside and dayside thermosphere and the strength of the ion flow. Further, because the neutrals have so much more mass than the ions, the neutral winds tend to be quite sluggish in their changes, while the ion flows tend to change quite rapidly. This can then influence the frictional heating that occurs because of the difference in flow velocities between the ions and neutrals. This heating is extremely important because it strongly controls the mass density of the thermosphere at a constant altitude, which, in turn, controls the drag on low-Earth orbiting satellites. Further, the neutral winds, at mid- and low- latitudes, can push the ionosphere up and down magnetic field lines, which strongly controls the plasma density, affecting over-the-horizon communication systems and GPS accuracy.
The Space Test Program-Houston 4- Small Wind and Temperature Spectrometer (STP-H4-SWATS) mission provides a means to measure the neutral winds and ion drifts as well as the temperature, density and composition of both the ions and neutrals. STP-H4-SWATS was developed as a small space weather sensor to enable investigations on nano- and micro- satellites in orbit between 120 and 550 km altitude. The four STP-H4-SWATS instruments are: the Wind and Temperature Spectrometer (WTS), the Ion Drift and temperature Spectrometer (IDS), the Neutral Mass Spectrometer (NMS) and the Ion Mass Spectrometer (IMS). STP-H4-SWATS has dimensions 7.6 by 7.6 by7.1 cm3, and a mass of approximately 630 g (including interface electronics) with total power consumption less than 2 W.
The mission provides a proof of concept for small space-based weather sensors, which may be attached to nanosatellite platforms or other small satellite structures. The sensor could be used in a future constellation of 30 to 50 nanosatellites studying Earth’s ionosphere and thermosphere, the uppermost layers of the atmosphere.
The STP-H4-SWATS sensor provides detailed measurements of Earth’s upper atmosphere, which could be used to improve computer models. The investigation yields a more thorough description of the upper layers of the atmosphere, which is used to improve the accuracy of global positioning systems as well as Earth-observing satellites studying agriculture, aviation, public safety, disasters and more.
The STP-H4-SWATS payload must be a RAM-facing exterior payload on the ISS. Ideally data is routinely telemetered to the ground daily and collections continue for one year. Collecting data over this time period allows for correlation of data with seasonal impacts as well as to the solar and geophysical drivers of the atmosphere across several 27-day solar rotations.
On orbit operations consist of instrument checkout, initial high voltage operation, cathode activation, followed by nominal operations. Data is routinely telemetered to the ground via TReK workstations. Flight rules have been established to safe the instrument during certain conditions (solar illumination, South Atlantic Anomaly crossings, pluming events, etc…). On-orbit performance of the instrument is monitored and commands sent to ensure the STP-H4-SWATS instrument is operating nominally. It is expected that high voltage increases will be required over the course of the mission.
Computer generated image of STP-H4.
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