Dynamics Explorer 2 (DE-2 or Explorer 63) was a NASA low-altitude mission, launched on 3 August 1981. It consisted of two satellites, DE-1 and DE-2, whose purpose was to investigate the interactions between plasmas in the magnetosphere and those in the ionosphere. The two satellites were launched together into polar coplanar orbits, which allowed them to simultaneously observe the upper and lower parts of the atmosphere.
Mission
The DE 2 spacecraft (low-altitude mission) complemented the high-altitude mission Dynamics Explorer 1 and was placed into an orbit with a perigee sufficiently low to permit measurements of neutral composition, temperature, and wind. The apogee was high enough to permit measurements above the interaction regions of suprathermal ions, and also plasma flow measurements at the feet of the magnetospheric field lines. The Dynamics Explorer mission is to investigate the strong interactive processes coupling the hot, tenuous, convecting plasmas of the magnetosphere and the cooler, denser plasmas and gases corotating in the Earth's ionosphere, upper atmosphere, and plasmasphere. Two satellites, DE-1 and DE-2, were launched together and were placed in polar coplanar orbits, permitting simultaneous measurements at high and low altitudes in the same field-line region.
Spacecraft
The general form of the spacecraft was a short polygon of in diameter and high. The triaxial antennas were tip-to-tip. One boom was provided for remote measurements. The spacecraft weight was . Power was supplied by a solar cell array, which charged two 6-ampere hour nickel-cadmium batteries. The spacecraft was three-axis stabilized with the yaw axis aligned toward the center of the Earth to within 1°. The spin axis was normal to the orbit plane within 1° with a spin rate of one revolution per orbit. A single-axis scan platform was included in order to mount the low-altitude plasma instrument (1981-070B-08). The platform rotated about the spin axis. A pulse code modulation telemetry data system was used that operated in real-time or in a tape recorder mode. Data were acquired on a science-problem-oriented basis, with closely coordinated operations of the various instruments, both satellites and supportive experiments. Measurements were temporarily stored on tape recorders before transmission at an 8:1 playback-to-record ratio. Since commands were also stored in a command memory unit, spacecraft operations were not real-time.
Experiments Atmospheric Dynamics and Energetics Investigation The purpose of this investigation was to study the dynamic responses of the thermosphere and ionosphere to energy deposition in the form of Joule heating, particle precipitation, and momentum transfer by electric field-generated drifts. The objective was to determine the relative importance of the various phenomena and the conditions under which ordering occurs. Because the relative importance of the different processes varied with geomagnetic activity, both geomagnetically quiet and disturbed conditions were examined. Using theoretical models as tools, the principal goal was to quantitatively analyze the physical processes involved in the energy coupling between the magnetosphere and the thermosphere. In addition to data obtained from various DE satellite instruments, the investigation planned to use ground-based correlative measurements.
Fabry-Pérot Interferometer (FPI) The Fabry–Pérot interferometer (FPI) was a high-resolution remote sensing instrument designed to measure the thermospheric temperature, meridional wind, and density of the following metastable atoms: atomic oxygen (singlet S and D) and the 2P state of ionic atomic oxygen. The FPI performed a wavelength analysis on the light detected from the thermospheric emission features by spatially scanning the interference fringe plane with a multichannel array detector. The wavelength analysis characterized the Doppler line profile of the emitting species. A sequential altitude scan performed by a commandable horizon scan mirror provided a cross-sectional view of the thermodynamic and dynamic state of the thermosphere below the DE-2 orbit. The information obtained from this investigation was used to study the dynamic response of the thermosphere to the energy sources caused by magnetospheric electric fields and the absorption of solar ultraviolet light in the thermosphere. The instrument was based on the visible airglow experiment (VAE) used in the Atmospheric Explorer program. The addition of a scanning mirror, the Fabry–Pérot etalon, an image plane detector, and a calibration lamp were the principal differences. Interference filters isolated lines at (in Angstroms) 5577, 6300, 7320, 5896, and 5200. The FPI had a field of view of 0.53° (half-cone angle). From 16 February 1982 to 11 September 1982 the DE-2 satellite was inverted and the FPI measured galactic emissions.
Ion Drift Meter (IDM) The Ion drift meter (IDM) measured the bulk motions of the ionospheric plasma perpendicular to the satellite velocity vector. The measured parameters, horizontal and vertical ion-drift velocities, had an expected range of ± . The accuracy of the measurement was expected to be ± for the anticipated 0.5° accuracy in vehicle attitude determination. The nominal time resolution of the measurement was 1/32 seconds. This investigation yielded information on: (1) the ion convection (electric field) pattern in the auroral and polar ionosphere; (2) the flow of plasma along magnetic field lines within the plasmasphere, which determines whether this motion was simply a breathing of the protonosphere, a refilling of this region after a storm, or an interhemispheric transport of plasma; (3) the thermal ion contribution to field-aligned electric currents; (4) velocity fields associated with small-scale phenomena that are important at both low and high latitudes; and (5) the magnitude and variation of the total concentration along the flight path. The ion drift meter measured the plasma motion parallel to the sensor face by using a gridded collimator and multiple collectors to determine the direction of arrival of the plasma. The instrument geometry was very similar to that used on the Atmospheric Explorer satellites. Each sensor consisted of a square entrance aperture that served as collimator, some electrically isolating grids, and a segmented planar collector. The angle of arrival of the ions with respect to the sensor was determined by measuring the ratio of the currents to the different collector segments, and this was done by taking the difference in the Logarithms of the current. Two techniques were used to determine this ratio. In the standard drift sensor (SDS), the collector segments were connected in pairs to two logarithmic amplifiers. The second technique, called the universal drift sensor (UDS), allowed simultaneous measurement of both components. Here, each collector segment was permanently connected to a logarithmic amplifier and two difference amplifiers were used to determine the horizontal and vertical arrival angles simultaneously. The IDM consisted of two sensors, one providing the SDS output and the other providing the UDS output. During the period from 17 March 1981 to 7 May 1982, the instrument memory suffered a critical upset and ion temperatures and drifts were not available during this period.
Langmuir Probe Instrument (LANG) The Langmuir Probe Instrument (LANG) was a cylindrical electrostatic probe that obtained measurements of electron temperature, Tellurium (Te), and electron or ion concentration, Ne or Ni, respectively, and spacecraft potential. Data from this investigation were used to provide temperature and density measurements along magnetic field lines related to thermal energy and particle flows within the magnetosphere-ionosphere system, to provide thermal plasma conditions for wave-particle interactions, and to measure large-scale and fine-structure ionospheric effects of energy deposition in the ionosphere. The Langmuir probe instrument was identical to that used on the Atmospheric Explorer satellites and the Pioneer Venus Orbiter. Two independent sensors were connected to individual adaptive sweep voltage circuits which continuously tracked the changing electron temperature and spacecraft potential, while autoranging electrometers adjusted their gain in response to the changing plasma density. The control signals used to achieve this automatic tracking provided a continuous monitor of the ionospheric parameters without telemetering each volt-ampere (V-I) curve. Furthermore, internal data storage circuits permitted high resolution, high data rate sampling of selected V-I curves for transmission to ground to verify or correct the inflight processed data. Time resolution was 0.5 seconds.
Low Altitude Plasma Instrument (LAPI) The Low Altitude Plasma Instrument (LAPI) provided high-resolution velocity space measurements of positive ions and electrons from 5 eV to 32 keV, and a monitor of electrons with energies above 35 keV. Pitch angle measurements covered the full 180° range. Data from this investigation and supporting measurements were used to study: (1) the identification and intensities of Birkeland currents, (2) auroral particle source regions and acceleration mechanisms, (3) the existence and role of E parallel to B, (4) sources and effects of polar cap particle fluxes, (5) the transport of plasma within and through the magnetospheric cusp, (6) dynamic configurations of high-latitude flux tubes, (7) loss-cone effects of wave-particle interactions, (8) hot-cold plasma interactions, (9) ionospheric effects of particle precipitation, and (10) plasma convection at high altitudes. The instrument contained an array of 15 parabolic electrostatic analyzers of the ISIS 2 type, each with an electron channel and an ion channel, in order to obtain detailed pitch-angle distributions as a function of energy. Two Geiger–Müller counters were mounted on the scan platform. The basic mode of operation provided a 32-point energy spectrum in the range 5 eV to 32 keV every second. The voltages on the electrostatic analyzers were programmable to allow for greater space/time resolution over limited portions of the energy and angular distributions. The instrument was mounted on a one-axis scan platform controlled by a magnetometer, whose purpose was to maintain the detector array, which spanned 180°, at a nearly constant angle to the magnetic field. From 16 March 1982 to 4 April 1982 the instrument was turned off for corrective action.
Low Altitude Plasma Investigation High Angular Resolution This investigation used the suprathermal particle distribution functions measured by both the high-(1981-070A-05) and low-(1981-070B-08) altitude plasma instruments. The objectives were: (1) to study the properties and locations of auroral acceleration mechanisms, (2) to determine the nature and distribution of electric fields parallel to the magnetic field, (3) to identify the charge carriers of the major electric current systems coupling the magnetosphere and ionosphere, and (4) to determine relations between these quantities and the convection electric field and auroral light emission patterns.
Magnetic Field Observations (MAG-B)