Engineering topics

Siefring, C. L.

Publications and source records attributed to Siefring, C. L..

9 records

NASA NTRS2013

Ground and Space-Based Measurement of Rocket Engine Burns in the Ionosphere

On-orbit firings of both liquid and solid rocket motors provide localized disturbances to the plasma in the upper atmosphere. Large amounts of energy are deposited to ionosphere in the form of expanding exhaust vapors which change the composition and flow velocity. Charge exchange between the neutral exhaust molecules and the background ions (mainly O+) yields energetic ion beams. The rapidly moving pickup ions excite plasma instabilities and yield optical emissions after dissociative recombination with ambient electrons. Line-of-sight techniques for remote measurements rocket burn effects include direct observation of plume optical emissions with ground and satellite cameras, and plume scatter with UHF and higher frequency radars. Long range detection with HF radars is possible if the burns occur in the dense part of the ionosphere. The exhaust vapors initiate plasma turbulence in the ionosphere that can scatter HF radar waves launched from ground transmitters. Solid rocket motors provide particulates that become charged in the ionosphere and may excite dusty plasma instabilities. Hypersonic exhaust flow impacting the ionospheric plasma launches a low-frequency, electromagnetic pulse that is detectable using satellites with electric field booms. If the exhaust cloud itself passes over a satellite, in situ detectors measure increased ion-acoustic wave turbulence, enhanced neutral and plasma densities, elevated ion temperatures, and magnetic field perturbations. All of these techniques can be used for long range observations of plumes in the ionosphere. To demonstrate such long range measurements, several experiments were conducted by the Naval Research Laboratory including the Charged Aerosol Release Experiment, the Shuttle Ionospheric Modification with Pulsed Localized Exhaust experiments, and the Shuttle Exhaust Ionospheric Turbulence Experiments.

Bernhardt, P. A.↗

NASA NTRS1995

Overview of the effects of neutral gas releases on high-voltage sounding rocket platforms

Four recent sounding rocket experiments demonstrate that the release of neutral gas from both positively and negatively charged vechicles returns the vehicle potential to near the plasma potential. Early active experiment payloads, CHARGE-2 and Space Power Experiments Aboard Rockets 1 (SPEAR-1) observed enhanced currents from/to the vehicles during unplanned attitude thruster firings. The follow-on CHARGE-2B ad SPEAR-3 payloads directly measured the changes to the vehicle potential caused by both planned argon and unplanned nitrogen releases. The gas releases from positively charged CHARGE-2B consistently reduced the potential to 20-50 V, wheras the gas releases from negatively charged SPEAR-3 brought the potential to between -200 and -500 V. The difference in grounding levels for positively and negatively charged payloads suggests that the gas responsible for grounding is near the vehicle, within a small fraction of the sheath size.

Berg, G. A.↗

NASA NTRS1994

Small-scale plasma irregularities produced during electron attachment chemical releases

In situ measurements of small-scale plasma density irregularities made during sounding rocket experiments that released electron attachment materials into the ionosphere are presented. A 2D electrostatic simulation model that includes attachment chemistry is used to study the source and evolution of these irregularities. The simulation shows (1) that large electron flow velocity shears develop on the boundary of the electron depletion and (2) these shears drive a plasma instability that is the likely source of the irregularities.

Scales, W. A.↗

NASA NTRS1991

Field-aligned dynamics of chemically induced perturbations to the ionosphere

Ionospheric modification using photochemically reactive vapors is studied with a one-dimensional, multiion, fluid model of plasma flow along magnetic field lines. The magnitudes of ion and electron density changes are determined by considering both chemical processes (i.e., photoionization, ion-molecule reactions, dissociative recombination, electron attachment) and transport processes (i.e., multispecies diffusion, electric currents, ambipolar electric fields). The numerical treatment in the model is not specific to any type of release or any interaction chemistry. It has been used to simulate releases of Ba, CO2, and CF3Br in the ionosphere, but generalization to other species may be easily accomplished. The results of the calculations are found to be in good agreement with experimental observations. The feasibility of modifying the parallel current paths in the auroral F region is examined.

Bernhardt, P. A.↗

NASA NTRS1985

Electrical measurements in the atmosphere and the ionosphere over an active thunderstorm. I - Campaign overview and initial ionospheric results

The first simultaneous electric field observations performed in the ionosphere and atmosphere over an active nighttime thunderstorm are reported here. In the stratosphere, typical storm-related dc electric fields were detected from a horizontal distance of about 100 km, and transient electric fields due to lightning were measured at several different altitudes. In the ionosphere and mesosphere, lightning-induced transient electric fields in the range of tens of millivolts per meter were detected with rise times at least as fast as 0.2 ms and typical duration of 10-20 ms. The transients had significant components parallel to the magnetic field at 150 km altitude. This implies that either considerable Joule heating occurs or a collective instability is present because of the high drift velocities induced by the transient electric fields. Copious numbers of whistlers were generated by the storm and were detected above but not below the base of the ionosphere. The outline of a new model for direct whistler wave generation over an active thunderstorm is presented based on these observations. The intensity of the observed two-hop whistlers implies that they were amplified along their propagation path and suggests that particles were precipitated in both hemispheres.

Kelley, M. C.↗

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 NTRS1984

A model for equatorial explosive spread F

Explosive spread F was first described by Woodman and LaHoz (1976). In such events the 50 MHz radar signal rises at Jicamarca to 10-20 dB above the noise level within a few milliseconds but then disappears within 100 ms or less. It has been suggested that electric fields from thunderstorms might drive a plasma instability which could cause these echoes, and recent observations (Woodman and Kudeki, 1984) provide convincing evidence for this triggering. Here, the instability mechanism is discussed and it is shown that transient thunderstorm electric fields comparable to those recently observed by rockets in the midlatitude ionosphere could excite a rapidly growing two-stream plasma instability that is driven by the ExB drift of the F region electrons in the short period (less than the ion gyroperiod) before the ions reach the same velocity.

Kelley, M. C.↗

NASA NTRS1983

Large amplitude middle atmospheric electric fields - Fact or fiction?

An analysis of the measurements of large apparent dc fields in the middle atmosphere, previously gathered by two sounding rockets, shows these fields to be spurious. In the case of one of the rockets, the evidence presented suggests that the measured electric fields, aligned with the rocket's velocity vector, may be due to a negatively charged wake. A comparison of measurements made by various electric field booms also suggests that the insulating boom coatings in one experiment may have affected the results obtained. It is recommended that insulating coatings should not be used at mesospheric altitudes, because of the detrimental effects that frictional charging may have.

Kelley, M. C.↗

NASA NTRS1983

Controlled stimulation of magnetospheric electrons by radio waves Experimental model for lightning effects

Magnetospheric electrons precipitated by ground-based coded very low frequency radio transmissions have been detected by rocket measurement of bremsstrahlung X-rays, caused by impact of the electrons with the upper atmosphere. The direct correlations obtained between the very low frequency signals and the X-rays demonstrate the limits of sensitivity required and indicate that this remote sensing technique would be useful for future study of very low frequency effects induced by single lightning strokes.

Goldberg, R. A.↗