Wind (spacecraft)

The Global Geospace Science (GGS) Wind satellite is a NASA science spacecraft designed to study radio waves and plasma that occur in the solar wind and in the Earth's magnetosphere. It was launched on 1 November 1994, at 09:31:00 UTC, from launch pad LC-17B at Cape Canaveral Air Force Station (CCAFS) in Merritt Island, Florida, aboard a McDonnell Douglas Delta II 7925-10 rocket. Wind was designed and manufactured by Martin Marietta Astro Space Division in East Windsor Township, New Jersey. The satellite is a spin-stabilized cylindrical satellite with a diameter of 2.4 m (7 ft 10 in) and a height of 1.8 m (5 ft 11 in).

The spacecraft's original mission was to orbit the Sun at the L₁ Lagrangian point, but this was delayed to study the magnetosphere and near lunar environment when the Solar and Heliospheric Observatory (SOHO) and Advanced Composition Explorer (ACE) spacecraft were sent to the same location. Wind has been at L₁ continuously since May 2004, and is still operating as of 2024^[update]. As of 2024^[update], Wind currently has enough fuel to last over 50 more years at L₁, until at least 2075. Wind continues to collect data, and by the end of 2024 had contributed data to over 7,850 scientific publications.

Mission operations are conducted from the Multi-Mission Operations Center (MMOC) in Building 14 at Goddard Space Flight Center in Greenbelt, Maryland. Wind data can be accessed using the SPEDAS software. Wind is the sister ship to GGS Polar.

The aim of the International Solar-Terrestrial Physics Science Initiative is to understand the behaviour of the solar-terrestrial plasma environment, in order to predict how the Earth's atmosphere will respond to changes in solar wind conditions. Wind's objective is to measure the properties of the solar wind before it reaches the Earth.

The Wind spacecraft has an array of instruments including: KONUS, the Magnetic Field Investigation (MFI), the Solar Wind and Suprathermal Ion Composition Experiment (SMS), The Energetic Particles: Acceleration, Composition, and Transport (EPACT) investigation, the Solar Wind Experiment (SWE), a Three-Dimensional Plasma and Energetic Particle Investigation (3DP), the Transient Gamma-Ray Spectrometer (TGRS), and the Radio and Plasma Wave Investigation (WAVES). The KONUS and TGRS instruments are primarily for gamma-ray and high energy photon observations of solar flares or gamma-ray bursts and part of the Gamma-ray Coordinates Network. The SMS experiment measures the mass and mass-to-charge ratios of heavy ions. The SWE and 3DP experiments are meant to measure/analyze the lower energy (below 10 MeV) solar wind protons and electrons. The WAVES and MFI experiments were designed to measure the electric and magnetic fields observed in the solar wind. All together, the Wind spacecraft's suite of instruments allows for a complete description of plasma phenomena in the solar wind plane of the ecliptic.

The electric field detectors of the Wind WAVES instrument are composed of three orthogonal electric field dipole antennas, two in the spin plane (roughly the plane of the ecliptic) of the spacecraft and one along the spin axis. The complete WAVES suite of instruments includes five total receivers including: Low Frequency FFT receiver called FFT (0.3 Hz to 11 kHz), Thermal Noise Receiver called TNR (4–256 kHz), Radio receiver band 1 called RAD1 (20–1040 kHz), Radio receiver band 2 called RAD2 (1.075–13.825 MHz), and the Time Domain Sampler called TDS (designed and built by the University of Minnesota). The longer of the two spin plane antenna, defined as E_x, is 100 m (330 ft) tip-to-tip while the shorter, defined as E_y, is 15 m (49 ft) tip-to-tip. The spin axis dipole, defined as E_z, is roughly 12 m (39 ft) tip-to-tip. When accounting for spacecraft potential, these antenna lengths are adjusted to ~41.1 m (135 ft), ~3.79 m (12.4 ft), and ~2.17 m (7 ft 1 in) [Note: these are subject to change and only estimates and not necessarily accurate to two decimal places]. The Wind WAVES instrument also detects magnetic fields using three orthogonal search coil magnetometers (designed and built by the University of Iowa). The XY search coils are oriented to be parallel to the XY dipole antenna. The search coils allow for high-frequency magnetic field measurements (defined as B_x, B_y, and B_z). The WAVES Z-axis is anti-parallel to the Z-GSE (Geocentric Solar Ecliptic) direction. Thus, any rotations can be done about the Z-axis in the normal Eulerian sense followed by a change of sign in the Z-component of any GSE vector rotated into WAVES coordinates.

Electric (and magnetic) field waveform captures can be obtained from the Time Domain Sampler (TDS) receiver. TDS samples are a waveform capture of 2048 points (16384 points on the STEREO spacecraft) per field component. The waveforms are measures of electric field versus time. In the highest sampling rates, the Fast (TDSF) sampler runs at ~120,000 samples per second (sps) and the Slow (TDSS) sampler runs at ~7,500 sps. TDSF samples are composed of two electric field components (typically E_x and E_y) while TDSS samples are composed of four vectors, either three electric and one magnetic field or three magnetic and one electric field. The TDSF receiver has little to no gain below about ~120 Hz and the search coil magnetometers roll off around ~3.3 Hz.

The TNR measures ~4–256 kHz electric fields in up to 5 logarithmically spaced frequency bands, though typically only set at 3 bands, from 32 or 16 channels per band, with a 7 nV/(Hz)^1/2 sensitivity, 400 Hz to 6.4 kHz bandwidth, and total dynamic range in excess of 100 dB. The data are taken by two multi-channel receivers which nominally sample for 20 ms at a 1 MHz sampling rate (see Bougeret 1995 for more information). The TNR is often used to determine the local plasma density by observing the plasma line, an emission at the local upper hybrid frequency due to a thermal noise response of the wire dipole antenna. One should note that observation of the plasma line requires the dipole antenna to be longer than the local Debye length, λ_De. For typical conditions in the solar wind λ_De ~7–20 m (23–66 ft), much shorter than the wire dipole antenna on Wind. The majority of this section was taken from.