Engineering topics

Mitchell, J. D.

Publications and source records attributed to Mitchell, J. D..

At least 19 records

NASA NTRS2003

The Altus Cumulus Electrification Study (ACES): A UAV-Based Science Demonstration

The Altus Cumulus Electrification Study (ACES) is an unmanned aerial vehicle (UAV)- based project that investigated thunderstorms in the vicinity of the Florida Everglades in August 2002. ACES was conducted to investigate storm electrical activity and its relationship to storm morphology, and to validate satellite-based lightning measurements. In addition, as part of the NASA sponsored UAV-based science demonstration program, this project provided a scientifically useful demonstration of the utility and promise of UAV platforms for Earth science and applications observations. ACES employed the Altus II aircraft, built by General Atomics - Aeronautical Systems, Inc. Key science objectives simultaneously addressed by ACES are to: (1) investigate lightning-storm relationships, (2) study storm electrical budgets, and provide Lightning Imaging Sensor validation. The ACES payload included electrical, magnetic, and optical sensors to remotely characterize the lightning activity and the electrical environment within and around thunderstorms. ACES contributed important electrical and optical measurements not available from other sources. Also, the high altitude vantage point of the UAV observing platform (up to 55,000 feet) provided cloud-top perspective. By taking advantage of its slow flight speed (70 to 100 knots), long endurance, and high altitude flight, the Altus was flown near, and when possible, over (but never into) thunderstorms for long periods of time that allowed investigations to be conducted over entire storm life cycles. An innovative real time weather system was used to identify and vector the aircraft to selected thunderstorms and safely fly around these storms, while, at the same time monitor the weather near our base of operations. In addition, concurrent ground-based observations that included radar (Miami and Key West WSRBD, NASA NPOL), satellite imagery, and lightning (NALDN and Los Alamos EDOT) enable the UAV measurements to be more completely interpreted and evaluated in the context of the thunderstorm structure, evolution, and environment.

Blakeslee, R. J.↗

NASA NTRS1999

The DROPPS Program: A Rocket/Lidar/Radar Study of the Polar Summer Mesosphere

During July of 1999, two sequences of rockets were launched from the Norwegian rocket range in Andoya, Norway. The purpose of these studies was to investigate the properties of the polar summer mesosphere, particularly relating to polar mesospheric summer echoes (PMSE) and their possible relationship to noctilucent clouds (NLC). Each of two sequences was anchored with a DROPPS Black Brant payload, consisting of 20 instruments to measure the electrodynamic and optical structure of the mesosphere and lower thermosphere. These were provided by participants from five American and two European scientific laboratories. The DROPPS (Distribution and Role of Particles in the Polar Summer) payloads were each accompanied by a sequence of meteorological rockets, and by several European payloads designed to study electrodynamics structure of the same region. ALOMAR (Arctic Lidar Observatory for Middle Atmosphere Research) Lidars, and MF (Medium Frequency) and MST (Mesosphere, Stratosphere, and Troposphere) Radars were used to continuously monitor the mesosphere for NLCs and PMSEs respectively. EISCAT VHF (European Incoherent Scatter Radar Very High Frequency) radar provided similar information about PMSEs downstream from the launch site. Sequence 1 was launched on the night of 5-6 July into a strong PMSE display coupled with a weak NLC at the low end of the PMSE. Sequence 2 was launched on the early morning of 14 July into a strong NLC with no PMSE evident. Here we describe the details of the program along with preliminary results.

Goldberg, Richard A.↗

NASA NTRS1997

Development of a new-generation active falling sphere

A new generation falling sphere, designed to measure winds and temperatures, is described. This sphere combines nanotechnology accelerometers and GaAs radiofrequency transmitters in a 100 g to 150 g package. This new instrumentation can be added to the standard inflatable sphere launched by a rocket or separately deployed from a larger rocket in which it is carried as part of a much larger scientific instrument package.

Croskey, C. L.↗

NASA NTRS1997

Comparison of plasma probes in the lower ionosphere

The instrumentation and the observations performed by four identically instrumented sounding rockets, designed to investigate the mesosphere and lower thermosphere, are reported. The four sounding rockets were launched from the Brazilian equatorial range Alcantara in August 1994. The instruments were capable of determining ion and electron densities. The results of data processing showed discrepancies hitherto unnoticed by other experiments.

Friedrich, M.↗

NASA NTRS1997

Equatorial Dynamics Observed by Rocket, Radar, and Satellite During the CADRE/MALTED Campaign: Programmatics and small-scale fluctuations - 1

In August 1994, the Mesospheric and Lower Thermospheric Equatorial Dynamics (MALTED) Program was conducted from the Alcantara rocket site in northeastern Brazil as part of the International Guard Rocket Campaign to study equatorial dynamics, irregularities, and instabilities in the ionosphere. This site was selected because of its proximity to the geographic (2.3 deg S) and magnetic (approx. 0.5 deg S) equators. MALTED was concerned with planetary wave modulation of the diurnal tidal amplitude, which exhibits considerable amplitude variability at equatorial and subtropical latitudes. Our goals were to study this global modulation of the tidal motions where tidal influences on the thermal structure are maximum, to study the interaction of these tidal structures with gravity waves and turbulence at mesopause altitudes, and to gain a better understanding of dynamic influences and variability on the equatorial middle atmosphere. Four (two daytime and two nighttime) identical Nike-Orion payloads designed to investigate small-scale turbulence and irregularities were coordinated with 20 meteorological falling-sphere rockets designed to measure temperature and wind fields during a 10-day period. These in situ measurements were coordinated with observations of global-scale mesospheric motions that were provided by various ground based radars and the Upper Atmosphere Research Satellite (UARS) through the Coupling and Dynamics of Regions Equatorial (CADRE) campaign. The ground-based observatories included the Jicamarca radar observatory near Lima, Peru, and medium frequency (MF) radars in Hawaii, Christmas Island, and Adelaide. Since all four Nike-Orion flights penetrated and overflew the electrojet with apogees near 125 km, these flights provided additional information about the electrodynamics and irregularities in the equatorial ionospheric E region and may provide information on wave coupling between the mesosphere and the electrojet. Simultaneous with these flights, the CUPRI 50-MHz radar (Cornell University) provided local sounding of the electrojet region. A description of the campaign logistics and the measurements performed with the Nike-Orion instrumentation and their implications for turbulence due to gravity waves and tidal instability in the mesosphere and lower thermosphere (MLT) are presented here. From a study of electron density fluctuations measured by rocket probes, we have found evidence for equatorial mesospheric neutral-atmospheric turbulence between 85 and 90 km. Furthermore, falling-sphere data imply that gravity wave breaking was a source for this turbulence. Mean motions and the various planetary, tidal, and gravity wave structures and their coherence and variability are the subjects of a companion paper.

Goldberg, Richard A.↗

NASA NTRS1994

Ion properties of the high-latitude middle-atmosphere

Investigations of high-latitude, middle-atmosphere ion properties have been conducted using rocket probe techniques. Electrodynamics studies have addressed: mesospheric dynamics and small-scale structure (the MAC/EPSILON Campaign during October-November 1977); ionization effects associated with highly energetic greater than or equal to 1 MeV) precipitating electrons (the MAC/REP Program during May 1990); and the characteristics of noctilucent cloud (NLC) and polar mesosphere summer echo (PMSE) regions (the NLC-91 Campaign during July-August 1991). Recent developments in Gerdien condenser probe theory, using computational fluid dynamics to model ion collection, have resulted in more accurate evaluation of the ion mobilities and number densities. Measurements of very small ion mobilities are thought to indicate an aerosol ion presence in the upper mesosphere.

Li, C.↗

NASA NTRS1994

ROCKETMAS: A sounding-rocket-based remote sensing measurement of mesospheric water vapor and ozone

The ROCKETMAS rocketborne technique, based on the shuttle-borne millimeter wave atmospheric sounder (MAS), to obtain water vapor and ozone measurements with vertical resolution, is described. The concentrations of mesospheric water vapor and ozone are not well known, yet both contribute significantly to the chemical and radiative structure of that region. In situ measurements of water vapor are difficult to make because water that was absorbed on the instrument surfaces outgasses in space and contaminates the local environment of the payload. However, a remote sensing technique that uses a long pathlength through the atmosphere greatly reduces the effect of such local contamination. The 183.3 GHz line of water vapor and 184.4 GHz line of ozone are good choices for spaceborne radiometer measurements because one front-end mixer assembly can be used to simultaneously observe both gases. The design of a sounding rocket based millimeter wave radiometer for measuring water vapor and ozone with a height resolution not possible by either ground based or limb sounding techniques is described.

Croskey, C. L.↗

NASA NTRS1992

Electrodynamics payloads for small rockets

Totally integrated design facilitates electrical cleanliness and light weight, which are necessary in subsonic parachute-borne payloads for electrodynamics investigations. 'Blunt' probes measure ion conductivity, as do Gerdien condensers. Recent finite-element computer analyses combining flow and electrodynamics have resolved problems in determining ion densities and mobilities from Gerdien data. Three-axis electric fields are measured with deployable boom-mounted electrodes from dc through VLF. Splitting the cylindrical payload with an insulator and measuring the current between halves has provided a vertical Maxwell current detector mechanically rigid enough to measure, at ELF, energy related to coupling. A nose tip 'Smith' probe turbulence measurement is usually performed on ascent. Other instrumentation, such as photo-ionization sources and X-ray detectors, can also be included. These electrodynamic measurement payloads are about one meter in length and have a mass of about 9 kg. They can be launched with an Orion-class or smaller vehicle.

Croskey, C. L.↗

NASA NTRS1990

Electric field measurements during the MAC/EPSILON campaign

The MAC/EPSILON observational campaign in northern Norway involved the taking of three-axis electric field measurements of the middle atmosphere by means of five rocketborne payloads during October and November, 1987. Simultaneous horizontal electric field measurements made by two of the rocket flights were in general agreement in their limited overlap region. The more extensive horizontal E-field measurements exhibited a decreasing mapping function with decreasing altitude, thereby indicating the presence of fields from a local auroral patch. Small-scale variations in the horizontal fields of the lights were similar to observed wavelike variations in the neutral wind field.

Croskey, C. L.↗

NASA NTRS1990

Electrodynamic response of the middle atmosphere to auroral pulsations

The MAC/EPSILON observational campaign encompassed the use of two Nike Orion rocket payloads which studied the effects of auroral energetics on the middle atmosphere. While one payload was launched during the recovery phase of a moderate magnetic substorm, during fairly stable auroral conditions, the other was launched during highly active postbreakup conditions during which Pc5 pulsations were in progress. The energetic radiation of the first event was composed almost entirely of relativistic electrons below 200 keV, while that of the second was dominated by much softer electrons whose high X-ray fluxes exceeded the cosmic ray background as an ionizing source down to below 30 km.

Goldberg, R. A.↗

NASA NTRS1990

Middle atmosphere electrical structure during MAC/EPSILON

Extensive use of rocket-launched probes during the the MAC/EPSILON campaign at the Andoya Rocket Range, Norway, has enabled the characterization of the region's electrical environment for all four flight series. The first rocket salvo was conducted during daylight (October 15, 1987) and the subsequent three occurred at night (October 21 and 28 and November 12, 1987), all of them during geomagnetically disturbed conditions. Measurements of polar electrical conductivity, ion mobility, and number density are presented, and their associated structure is investigated for local auroral ionization effects. This is believed to be the first time that Gerdien condenser mobility measurements have indicated a heavy-ion presence (positively charged aerosols) in the auroral mesopause region.

Mitchell, J. D.↗

NASA NTRS1990

Electrical stratification in the middle atmosphere

Stratification of the electrical structure of the middle atmosphere (MA) has been observed under a wide range of conditions. 'Ledges' in charged particle density at the bottom of Chapman-like layers are accentuated in conductivity profiles due to the atmospheric density gradient's effect on mobility, but the steepest gradients yet observed occurred in conjunction with the horizontal magnetic field at the equator. High-latitude conductivity ledges are produced by steeply declining energy distributions. Measurements in a noctilucent cloud showed that the free electrons essentially vanished (presumably due to attachment to cloud particles) but the positive ion conductivity remained virtually unchanged.

Croskey, C. L.↗

NASA NTRS1989

Middle atmosphere measurements of small-scale electron density irregularities and ion properties during the MAC/Epsilon campaign

Rocket payloads designed to measure small scale electron density irregularities and ion properties in the middle atmosphere were flown with each of the three main salvos of the MAC/Epsilon campaign conducted at the Andoya Rocket Range, Norway, during October to November 1987. Fixed bias, hemispheric nose tip probes measured small scale electron density irregularities, indicative of neutral air turbulence, during the rocket's ascent; and subsequently, parachute-borne Gerdien condensers measured the region's polar electrical conductivity, ion mobility and density. One rocket was launched during daylight (October 15, 1052:20 UT), and the other two launches occurred at night (October 21, 2134 UT: November 12, 0021:40 UT) under moderately disturbed conditions which enhanced the detection and measurement of turbulence structures. A preliminary analysis of the real time data displays indicates the presence of small scale electron density irregularities in the altitude range of 60 to 90 km. Ongoing data reduction will determine turbulence parameters and also the region's electrical properties below 90 km.

Blood, S. P.↗

NASA NTRS1988

Studies of high latitude mesospheric turbulence by radar and rocket. II - Measurements of small scale turbulence

Measurements of mesospheric small scale turbulence and associated larger scale wave structures were obtained from rocket probe flights during equinox in spring 1985. The measurements were verified by data from the mesosphere-stratosphere-troposphere radar at Poker Flat, Alaska. Electron density irregularities down to an altitude of about 62 km and fluctuations in positive ion density in the altitude region from 50 to 90 km were measured. Turbulence in the inertial subrange was observed at heights where the fluctuations generally were largest. Measurement of background electron density exhibited gradients relative to the monotonically increasing density profile, suggesting the presence of large amplitude wave motions transporting the plasma by mixing. The radar detected the occurrence of 1-3 km wavelike perturbations superimposed on a 7-km wave in the wind velocity field. It is suggested that the 1-3 km waves are more important in the transport of energy and momentum and in the production of turbulence in the lower mesosphere.

Blood, S. P.↗

NASA NTRS1985

Electrical measurements in the atmosphere and the Ionosphere over an active thunderstorm. II - Direct current electric fields and conductivity

On August 9, 1981, a series of three rockets was launched over an air mass thunderstorm off the eastern seaboard of Virginia while simultaneous stratospheric and ground-based electric field measurements were made. The conductivity was substantially lower at most altitudes than the conductivity profiles used by theoretical models. Direct current electric fields over 80 mV/m were measured as far away as 96 km from the storm in the stratosphere at 23 km altitude. No dc electric fields above 75 km altitude could be identified with the thunderstorm, in agreement with theory. However, vertical current densities over 120 pA/sq m were seen well above the classical 'electrosphere' (at 50 or 60 km). Frequent dc shifts in the electric field following lightning transients were seen by both balloon and rocket payloads. These dc shifts are clearly identifiable with either cloud-to-ground (increases) or intercloud (decreases) lightning flashes.

Holzworth, R. H.↗

NASA NTRS1985

A diurnal study of the electrical structure of the equatorial middle atmosphere

Electrical parameters measured from 115 km down to below 20 km during the Project Condor campaign at the Punta Lobos Rocket Range near Lima, Peru, are presented. Ten rocket-launched payloads measured electrical conductivity. A strong diurnal influence due to solar ultraviolet radiation is shown. Nine of the payloads also measured electric fields. No large mesospheric vertical electric fields are found in the data. A calculation of the dc global conduction current density at 18 km is smaller than previously measured at low latitudes and does not show the conventional diurnal variation.

Croskey, C. L.↗

NASA NTRS1985

Response of the middle atmosphere to Sco X-1

On the night of Mar. 9, 1983 (UT) at Punta Lobos Launch Site, Peru (12.5 deg S, 76.8 deg W, magnetic dip -0.7 deg), a sequence of sounding rockets was flown to study the electrical structure of the equatorial middle atmosphere and to evaluate perturbations on this environment induced by the X-ray star Sco X-1. The rocket series was anchored by two Nike Orion payloads (31.032 and 31.033) which were launched at 0327 and 0857 UT, near Sco X-1 star-rise and after it had attained an elevation angle of 70 deg E. An enhanced flux of X-rays was observed on the second Nike Orion flight (31.033). This increase is directly attributed to Sco X-1, both from the spectral properties of the measured X-ray distribution and by spatial information acquired from a spinning X-ray detector during the upleg portion of the 31.033 flight. Simultaneously, a growth in ion conductivity and density was seen to occur in the lower mesosphere between 60 and 80 km on the second flight, specifically in the region of maximum energy deposition by the Sco X-1 X-rays. The results imply the presence of a significant number of ionized heavy constituents within the lower mesosphere, with masses possibly in the submacroscopoic range.

Goldberg, R. A.↗

NASA NTRS1985

Middle-atmosphere positive ion measurements during solar eclipses

Solar effects on middle-atmosphere electrical parameters, as demonstrated by eclipse-associated responses of conductivity, ion mobility, and charge density, are considered for the total solar eclipses at Red Lake, Ontario, Canada on February 26, 1979 and at San Marco range, Kenya, on February 16, 1980. Negative-conductivity measurements for the Canadian eclipse and probe-current measurements for the Kenyan eclipse demonstrate a rapid loss of free electrons below 80 km at totality. During the Kenyan eclipse, positive-ion responses were different for each of two distinct ion mobility groups. Between 45 and 60 km, eclipse-related positive-ion responses are associated with the low-mobility ions. It is shown that these ions are lost at totality and that an excess buildup occurs following totality. Above 70 km, positive-ion loss at totality is associated with the more mobile ions and only low-mobility positive ions are measured in this region. The buildup in total ion density following totality is thought to result from a reduction in ion loss associated with weak-electron recovery in the region.

Mitchell, J. D.↗