Rocket

About: Rocket is a research topic. Over the lifetime, 14018 publications have been published within this topic receiving 95852 citations. The topic is also known as: rockets.

Closed-Loop Precision Throttling of a Hybrid Rocket Motor

Abstract: A closed-loop throttle controller for a laboratory-scale N2O and hydroxyl-terminated polybutadiene hybrid rocket motor is presented. Closed-loop throttling was achieved using commercial off-the-shelf valve hardware and a commercially available motor case adapted for hybrid rocket testing. Multiple and open- and closed-loop tests were performed to demonstrate that closed-loop control can significantly reduce the run-to-run burn variability typical of hybrid rocket motors. Closed-loop proportional/integral control algorithms featuring thrust or pressure feedback were used to track prescribed step and linear ramp profiles. Because the relationship between the selected throttle control valve position and the effective valve flow area was highly nonlinear, the effect of valve position on motor thrust/chamber pressure was measured open loop and curve fit to allow direct command of either total thrust or chamber pressure. Control law gains were tuned a priori using a numerical model and then adjusted using the a...

Scaling of Erosion Rate in Subsonic Jet Experiments and Apollo Lunar Module Landings

Abstract: Small scale jet-induced erosion experiments are useful for identifying the scaling of erosion with respect to the various physical parameters (gravity, grain size, gas velocity, gas density, grain density, etc.), and because they provide a data set for benchmarking numerical flow codes. We have performed experiments varying the physical parameters listed above (e.g., gravity was varied in reduced gravity aircraft flights). In all these experiments, a subsonic jet of gas impinges vertically on a bed of sand or lunar soil simulant forming a localized scour hole beneath the jet. Videography captures the erosion and scour hole formation processes, and analysis of these videos post-test identifies the scaling of these processes. This has produced important new insights into the physics of erosion. Based on these insights, we have developed an erosion rate model that can be applied to generalized situations, such as the erosion of soil beneath a horizontal gas flow on a planetary surface. This is important to lunar exploration because the rate of erosion beneath the rocket exhaust plume of a landing spacecraft will determine the amount of sand-blasting damage that can be inflicted upon surrounding hardware. Although the rocket exhaust plume at the exit of the nozzle is supersonic, the boundary layer on the lunar surface where erosion occurs is subsonic. The model has been benchmarked through comparison with the Apollo landing videos, which show the blowing lunar soil, and computational fluid dynamics simulations of those landings.

Ion temperature determination in the ionosphere by retarding potential analyzer aboard sounding rocket

Abstract: A vertical profile of the ion temperature in the ionosphere at local afternoon in the region from 95 to 310 km has been measured directly by means of an improved retarding potential analyzer (RPA) system aboard a space sounding rocket. This rocket was launched at Kagoshima Space Center of Japan (geomagnetic latitude: 198° 4′E; longitude:20° 0′N). In this paper the method of measurement of the ion temperature by two RPA's and the experimental results are discussed. Two RPA's were flown. One of them measured the probe characteristics and the other one measured the angle of attack of the plasma. To measure the angle of attack, this RPA was tilted at 30° from the rocket spin axis. The probe curves were not distorted, as is often the case with rocket probes, since the clean surfaces of mesh grids and other electrodes were stored in a clean room and the nose cone contained dry N2 gas. The angle of attack is measured directly by the tilted ion trap. The measured angle of attack data agree with the data obtained by geomagnetic and solar aspect sensors aboard the rocket. The tilted probe was most useful in the nighttime experiment when no solar aspect data were available. The results show that the ion temperature below 150 km is the same as that of the neutral temperature at high solar activity. Above 150 km the average ion temperature gradually becomes higher. In this region the ion temperature profile contains a wavelike structure. The peak to trough amplitude of the temperature variation is about 250°K and a vertical wave length of about 25 km is determined. The relationship between this experimental vertical temperature profile and the horizontal atmospheric motions measured by simultaneous ground observations was examined. As a result it was found that these wave data do not fit on the branch of the φ-k diagram of theoretical internal atmospheric gravity wave (IGW) by Hines (1960). It may also be difficult to regard another vertical profiles showing wave lengths of several tens of kilometers measured by some other workers as simply manifestations of IGW.