Velocity Vector Of Spacecraft Research Articles

Highly Effective Kinetic Impact Design for Asteroid Deflection Missions Exploiting Impact-Geometry Maps

The kinetic impactor, which is a spacecraft that impacts against an Earth-threatening asteroid, is one of the potential methods for deflecting an asteroid from the Earth collision route. To improve the effectiveness of the impact, an impact-geometry map is used that visualizes the kinetic impact effectiveness as a form of impact geometry, which is the inner product of the asteroid velocity vector and the spacecraft velocity vector relative to the asteroid velocity. A locally optimal thrust control law is proposed that maximizes the change rate of the impact geometry, and it achieves a monotonic increment in it. The law is combined with a global optimization method, and a trajectory design system is developed for kinetic impactor missions. Trajectory optimizations are numerically demonstrated for fictional asteroid deflection scenarios. The results show that the proposed system achieves a larger deflection distance despite the reduction in the projectile’s impact velocity relative to the asteroid as compared to a previous method. Besides, as the proposed method focuses not on the spacecraft impact velocity but on the impact geometry, the merit to improve the mobility capability on the impact-geometry map by increasing the available thrust at the expense of increasing the fuel consumption is also indicated.

Dependence of String Electron Current on Array Plasma Aspect Angle and Temperature

In most cases, the incident aspect angle of a photovoltaic array to the local plasma continuously changes for a spacecraft in low Earth orbit. It is possible to simulate the combined effects of changing array ram aspect angle with respect to the plasma flow inside a vacuum chamber. On-orbit solar array collected current will significantly vary as a function of the angle between the spacecraft velocity vector and the solar array front surface normal vector. The purpose of this paper is to extract this angular dependence of electron current collection of UltraFlex solar array coupons, as well as to measure the dependence of string electron collection current on array temperature. It is found that collected current can be approximated by a cosine function with a 70% drop when the array coupon front surface normal vector is rotated to an angle from 15° to 90°. It was also determined in subsequent tests with two electron number densities of Ne = 0.5 · 106 cm-3 and 1.0 · 106 cm-3 that electron current collection does not depend on the sample temperature.

Energetic ion observations of the Earth’s magnetic cusps during an extended geomagnetically quiescent period in April 2001 using detectors on S/C ISTP/Polar

We present a method of polar cusp identification using high charge state heavy ions. There is reason to think that these ions would constitute shocked solar wind ions such as doubly charged helium ions, He 2+, and multiply charged oxygen ions, O (3−8)+, that appear to have relatively easy access to one or both of the polar cusps essentially at all times. The observations made with the ISTP/POLAR spacecraft were mostly obtained during geomagnetically non-storm times in April 2001 when the spacecraft orbit allowed northern cusp encounters with low trajectory angle between the spacecraft velocity vector and the overall cusp magnetic field orientation. We also show one extended cusp crossing during the modest magnetic storm of April 22, 2001 (with D st ∼−103 nT). It is found that during the study period, 1–10 keV high charge state ions are present in the cusp region at virtually all times, during storm or quiet. We also found that what appears to be the interior of the northern polar magnetic cusp region can be rather turbulent both in the local magnetic field direction and in the energetic charged particle kinetic flow characteristics. There is some evidence for temporally varying turbulent acceleration processes, either within the cusp domain itself or in the surrounding magnetosphere. In terms of the present ion observations, there is little to distinguish the dayside low latitude boundary layer (LB) ion signatures from those of the interior of the polar cusp region (high charge state ions, abundant 1–10 keV ion fluxes).

Imaging of artificial aurora in the upper atmosphere

We use continuum (white light) and filtered (427.8 nm) images from the Atmospheric Emissions Photometric Imaging (AEPI) experiment on the Atmospheric Laboratory for Applications and Science (ATLAS) 1 shuttle mission to investigate the shape and evolution of artificial auroral patches generated by the Space Experiments with Particle Accelerators (SEPAC) electron beam experiment. Auroral patches generated by this beam experiment are complex and differ in the white light and filtered images. In the white light images, the auroral patch consists of a relatively large, diffuse, and somewhat symmetric head and a tail that is directed approximately opposite the spacecraft velocity vector. From the growth of the tail during a beam pulse, the distance from the imager to the emissions is estimated to be about 200 km, consistent with expectations from a simple model of auroral emissions in the atmosphere. In addition to the auroral patch, an intense, diffuse, and variable background glow filling essentially the entire field of view of the white light imager is seen during the beam pulses. This background glow may be caused by low‐energy electrons very near the shuttle. This glow is absent in the filtered images, in which the shape of the auroral patch differed, consisting of a relatively large, diffuse, but more asymmetric head, a tail, and a smaller and less intense spot below the head. Curvature of the magnetic field and spacecraft motion during the 1‐s filtered images allows an estimate of the relative distance from the shuttle to the head, tail, and small spot. This shape is consistent with head emissions generated relatively near the spacecraft (nearest few kilometers), tail emissions somewhat farther away, and finally the small spot emissions generated the farthest away in the lower atmosphere where the natural auroras would be created. In addition, the shape of these patches in the filtered images suggests that the risetime for the head and tail emissions in the filtered images appears to be longer than that for the small spot emission. The differences between the white light images and the filtered images are consistent with the difference between the emission parent state lifetimes and the energy requirement for the emission production. The white light images contain emissions with long lifetimes, and these emissions which are produced near the observer are swept out of the field of view because they are left behind by the shuttle. This gives a bias toward emissions generated farther from the orbiter. The filtered images contain only the very fast produced N2+ emission with a substantial component generated near the orbiter and with an inverse square law attenuated auroral spot in the lower atmosphere. The presence of the tail and the apparent risetime in the near‐field emission suggest that there is a buildup and decay time associated with the hot plasma created by the electron beam.

Equatorial spacecraft‐plasma interaction phenomenon observed with DE 2

Data from the retarding potential analyzer and ion drift meter on Dynamics Explorer 2 indicate that an unusual spacecraft‐plasma interaction phenomenon occurs at times when the spacecraft velocity vector becomes nearly aligned with the local geomagnetic field lines. The primary signature of the interaction is a transient increase in the ion collection currents obtained with these instruments, up to approximately 15% in magnitude and typically a few tens of seconds duration. This signature is indicative of an increase in the net ion and electron currents to the satellite and is accompanied by a small positive increase in the spacecraft potential relative to the plasma. We present here a case study covering six of the strongest such events observed with DE 2 and discuss a possible physical mechanism. We suggest in particular that what might be called a collisional electron “snowplow” effect may be occurring, and we derive a simple numerical model based on this scenario. Least squares fitting is employed to test the model and to derive new estimates of the ambient ion concentration at times when the measurements are being perturbed by the interaction.

Visible light emission excited by interaction of space shuttle exhaust with the atmosphere

Ground‐based video photography of firings of Space Shuttle Primary Reaction Control System (PRCS) engines show optical emissions extending nearly 4 km from the vehicle after steady state is reached. The total intensity and spatial distribution of these emissions depend on the angle between the spacecraft velocity vector and the engine exhaust axis. Candidate sources for this radiation are reviewed and the conclusion is reached that it is most likely due to vibrationally excited OH, formed by the reaction of fast ambient O atoms and H2O molecules in the exhaust.

Modeling of Atmosphere Explorer‐D Return Flux Experiment

Codes for the prediction of spacecraft environments are currently in widespread use; however, few if any comparisons of code results with experimental measurements have been performed. In this paper we report the results of calculations performed for the Atmosphere Explorer‐D satellite at an altitude of approximately 250 km. Measurements of the atmospheric composition at the ram surface of the spacecraft were obtained by a closed source mass spectrometer before and during the operation of a return flux experiment in which a neon plume was directed into the spacecraft velocity vector. Calculations using the Integrated Spacecraft Environment Model (ISEM) reproduced the measured fluxes of the ambient species immediately before and during the venting operation. The presence of the neon plume reduced the flux of ambient species reaching the detector. The model reproduced these trends and gave a range of calculated neon return flux with a mean approximately equal to the value derived from the measurements. The model predicted a surface density of ambient species approximately 33 times the ambient level with and without the plume and nonnegligible scattering of neon into the wake of the spacecraft during plume operation.

Venus “lightning” signals reinterpreted as in situ plasma noise

Electric field noise bursts detected from the Pioneer Venus Orbiter across the nightside of Venus have been interpreted in a number of papers as providing evidence of extensive lightning at Venus. Moreover, the asserted clustering of these 100‐Hz signals over mountainous topography has encouraged widespread speculation that present‐day volcanism is prevalent. Earlier studies have noted, however, that the 100‐Hz signals were often associated with ionospheric perturbations, prompting the suggestion that the electric field signals were being produced in situ and were thus unrelated to the lower atmosphere or surface. In this more detailed analysis we find a statistically persistent correlation between the 100‐Hz noise and ion troughs marking the solar wind interaction with the nightside ionosphere. Clusters of closely spaced 100‐Hz noise bursts attributed to lightning often “turn on” in the troughs, simultaneously with sharp density gradients in which the plasma concentration drops by an order of magnitude or more and the direction of the magnetic field changes significantly, within a few seconds. Analysis of the 100‐Hz noise also shows two other important statistical characteristics, namely (1) the noise is most frequently observed near 180 km and above but much less frequently at lower altitudes and (2) the noise is most often detected when the angle between the spacecraft velocity vector and the direction of the B field approaches 90°. We interpret the foregoing characteristics as evidence that the 100‐Hz noise is produced from solar wind/interplanetary magnetic field related plasma perturbations occurring near the spacecraft and that the noise is unrelated to the lower atmosphere and surface of Venus. Unfortunately, we do not have access to sufficient high‐resolution data to specifically identify the type of ionospheric noise involved.

Initial Observations of the Pioneer Venus Orbiter Solar Wind Plasma Experiment

Initial results of observations of the solar wind interaction with Venus indicate that Venus has a well-defined, strong, standing bow shock wave. Downstream from the shock, an ionosheath is observed in which the compressed and heated postshock plasma evidently interacts directly with the Venus ionosphere. Plasma ion velocity deflections observed within the ionosheath are consistent with flow around the blunt shape of the ionopause. The ionopause boundary is observed and defined by this experiment as the location where the ionosheath ion flow is first excluded. The positions of the bow shock and ionopause are variable and appear to respond to changes in the external solar wind pressure. Near the terminator the bow shock was observed at altitudes of approximately 4600 to approximately 12,000 kilometers. The ionopause altitutde ranged fromn as low as approximately 450 to approximately 1950 kilometers. Within the Venus ionosphere low-energy ions (energy per untit charge < 30 volts) were detected and have been tentatively idtentified as nonflowing ionospheric ions incident from a direction along the spacecraft velocity vector.