Launch Velocity Research Articles

A gas-insulated railgun

A railgun concept is discussed in which a high-pressure prefill of hydrogen serves as the close-in insulator between the rails. The gas-insulated railgun (GIRG) approach can reduce or eliminate the velocity-limiting problem of growth and separation of the current-carrying armature region behind the projectile, and thus allow higher launch velocities, to be achieved. A hybrid armature appears appropriate for this launcher.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Implosion-driven hypervelocity accelerator

A hypervelocity accelerator has been developed utilizing the extreme condition produced by the collapse of the cylindrical imploding shock wave. The cylindrical shell of the explosive is detonated by the explosion of rows of copper wires bound around it. The wire explosion is caused by the application of an impulsive electric current. The energy concentrated at the implosion center is imparted to the projectile accelerating it. The launch velocity of 1.2 km/s has been attained for a 2 g launched weight with a 60 g explosive (PETN: pentaerythritoltetranitrate). A further increase of the launch velocity is expected by increasing either the explosive thickness or the height of the cylindrical shell within practical limit.

The atomic sodium exosphere/coma of the Moon

A Monte Carlo model is used to study the random walk process of sodium atoms created by meteoroid impacts on the lunar surface. The collisional surface interaction is parameterized by a thermal accomodation coefficient of 0.5. Sodium atoms launched with initial velocities well below the surface escape velocity of 2.38 km s−1 will be recycled and contribute to the formation of an exosphere with a temperature of about 500 K on the sunlit side. For large launch velocities (&gt;2 km s−1) there will be systematic transport of the escaping sodium atoms to the antisolar direction as a result of the acceleration effect of the solar radiation pressure. An extended coma with a significant elongation in the antisolar direction can form this way. Recent spectroscopic and imaging observations are consistent with this picture. The present model calculations suggest that meteoroid impact effect (and solar wind sputtering) should be the major supplier of the lunar sodium exosphere; the possible existence of an efficient loss mechanism of the sodium atoms during surface interaction is also indicated.

A statistical study of impact ejecta distribution around Phobos and Deimos

Impact-ejecta dynamics around Phobos and Deimos are considered for dust particles of the order of 1 mm and greater. Only the gravitational forces of the planet and the satellite as well as the centrifugal and Coriolis forces are taken into account. In the case of Phobos the ejecta generally either reimpact the surface in tens of minutes after their launch or escape rapidly away from the gravitational attraction of the satellite. Deimos, being subjected to a relatively smaller perturbation force from Mars, can keep its ejecta on reimpacting and temporary satellite orbits for hours. Phobos shows large variability in its escape velocity as a function the launch point and the direction of launch. The statistical properties of large numbers of particles moving around the satellites are determined in a series of Monte Carlo simulations. Two factors, important for the regolith-formation process, are investigated: the escape probability from a given site on the surface and the reimpact probability. Both of these functions vary appreciably over the surfaces of Phobos and Deimos. The differences of the escape probabilities between adjoining regions are greater for Phobos than for Deimos, while the reimpact probability variations are substantial for both satellites. The density patterns for Phobos exhibit an interesting dependence on the particles' launch velocities. For small velocities (4–5 m sec −1) we observe two curved tubes of enhanced density that start from the sub-Mars and anti-Mars points on the surface. The density tends to become isotropic for greater launch velocities. Deimos shows a rather regular, ellipsoidal dust halo. The overall density of dust particles—with the meteoroid flux intensity, cratering laws, and velocity distribution of ejecta taken into account—is estimated to be of about a few hundred particles per kilometer cubed close to the surface of Phobos and drops down to about tens of particles per kilometer cubed at a distance of 40 km from the satellite's center. The density of dust around Deimos is two to three times larger.

Large and small caliber railgun solid armatures: experimental results

Solid/transitioning armature performance results of two railgun programs is reported. Solid armature experiments continue for 15 and 90 mm bore guns. These armatures have been accelerated to over 2300 m/s. For the armatures tested, typical muzzle voltage measurements show the armature drop remains less than 50 V for velocities under 1000 to 1200 m/s; at velocities above 1000 m/s to 1200 m/s, the contact forms a hybrid armature. Armature performance data presented include muzzle voltage, gun current, armature resistance, total energy deposited in the armature, launch velocity, launch package muzzle kinetic energy, peak armature action, armature contact wear, and physical examination of recovered armatures. These data are separately summarized for each gun type and demonstrate armature survival at high current densities, bore pressures, and specific action. >

The effects of coefficient of restitution variations on long fly balls

The coefficient of restitution of major league baseballs is required to be 0.546±0.032. These allowed variations affect the launch velocity and ultimately the range of fly balls. The variations in the range for well-hit balls are calculated here to be on the order of 15 ft. These calculations provide an interesting collection of mechanics problems that might be of interest for undergraduate students.

Summary of EM launcher experiments performed at LLNL

Performance results for three railguns are summarized. The system used a helium gas-driven injector and railgun launcher to accelerate 1- and 4-g polycarbonate projectiles intact up to 6.6 and 3.0 km/s, respectively. A 625 kJ capacitor bank powered the railgun, and an adjustable inductor provided pulse shaping and peak current control. Operation in hard and soft vacuum was reliably achieved. Projectiles were accelerated without blowby of injector gas or plasma. The diagnostic system measured the projectile position and launch velocity, verified that the projectile was launched intact in the desired direction, and identified system components where improvements could enhance performance. Flash x-ray radiography measured velocity and verified that projectiles were intact. Post-launch projectile travel along the axis of the launcher without tilt was recorded with flash radiographs and impact impressions or holes in witness plates. The system performed as expected up to 4-5 km/s but below expectations at higher velocities. Our diagnostics suggest that the decreased performance was probably caused by the restriking of a second arc in the breech of the railgun, which shunted the current from the propulsive arc. Estimates of ablated launcher mass, drag forces, methods of eliminating restrike, and suggestions for improving the performance of railguns are discussed.

Estimation of some aeolian saltation transport parameters: a re‐analysis of Williams' data

ABSTRACTA new method for analysing observed aeolian sand transport rate profiles of the kind obtained by Williams is presented. The method involves a mathematical model of aeolian saltation. Detailed information about the saltation process can be calculated from the transport rate profile by means of this model. The method is used to perform a re‐analysis of Williams' trap data. Among the main findings of this analysis is that the grain borne shear stress appears to be a smaller fraction of the total shear stress than assumed by Bagnold &amp; Owen in their theories of aeolian saltation. Other findings are that the probability distribution of the jump height of the grains does not depend much on the wind speed once the saltation is established, and that the vertical component of the mean launch velocity decreases with the grain size. It is approximately inversely proportional to the grain diameter. Our estimates of the landing angles indicate that estimates of the impact angles obtained from photographically recorded trajectories are too small due to biased sampling. The influence of grain shape on the transport characteristics is mainly due to changes in the grains' ability to jump when hitting the bed. It is found that angular grains have a lower mean jump height than spherical grains.

Fusion fuel pellet injection with a railgun

Railguns have been nominated as fusion fuel pellet injectors. It appears that a railgun could launch dielectric hydrogen isotope pellets at velocities up to 10 km/s or more at high repetition rates. A railgun consists of two parallel conductors (rails) that carry current to and from an interconnecting link (plasma arc armature). The magnetic field generated by the rail currents accelerates the armature and pellet. In addition to high launch velocity, a railgun offers several potential advantages for pellet injection: (1) pellets can be dielectric, (2) pellets can be fed into the open breech as rapidly as they are launched, (3) current can be controlled to ensure isentropic acceleration, (4) the mass of the propulsive arc is less than the pellet mass, (5) cryogenic and vacuum operation is possible, and (6) the pellet is provided lateral support permitting acceleration stresses in excess of its tensile strength, which results in shorter injectors, acceleration times, and higher repetition rates. The most restrictive limitation on railgun injector operation results from the low strength of the solid hydrogen pellets. An acceleration stress limited to 30 bars would require a launcher length of 3400 times the DT projectile length to achieve 10 km/s; i.e., a 5-mm-long projectile would require a 17-m launcher. A critical area needing investigation is the potentially adverse effect of the high temperature armature on the pellet.

Railgun Accelerators for Gram-Sized Projectiles

In this paper, we describe the operation and critical parameters of railguns, we compare the potential and actual performance with other types of macroparticle accelerators, and we discuss their research and industrial applications. Railgun accelerators have the potential to accelerate massive projectiles to very high velocities in very short distances. Recent research has demonstrated the usefulness of railguns for research and industrial applications. The railgun accelerator is essentially a linear dc motor consisting of a pair of rigid parallel conductors that carry current to and from an interconnecting moveable conductor. The connecting link functions as an armature, and the parallel rails serve as a single-turn field winding. The resulting Lorentz force on the armature is proportional to the square of the current. A 1-MA current will produce about 2(105) N of thrust. A one-gram projectile will experience an acceleration of 2(108) m/s2 and in one meter achieve a velocity of 20 km/s. Conventional projectile launchers are limited to launch velocities of the order of 10 km/s. Hence railguns will enable research and applications at previously unattainable velocities. Velocities in excess of 10 km/s will lead to new research at high pressure and high-energy density. Behavior of matter in the 1-10 TPa or perhaps 100 TPa range will provide valuable insight to terrestrial and extraterrestrial phenomena. Furthermore, velocities of the order of 20 km/s will permit orbital launching from the earth's surface. These and other applications of railguns will be discussed.

Guidance and trajectory considerations in lunar mass transportation

Flight-mechanics problems associated with large-scale transport of lunar mass to a space colony or manufacturing facility are discussed. The proposed transport method involves launch of payloads from a mass-driver on the lunar surface, onto ballistic trajectories to a passive mass-catcher located near the L2 libration point, with the caught mass subsequently being transported to the colony. Arrival velocities at L2, sensitivities in arrival dispersion due to launch errors, and effects of launch site location are treated, via numerically integrated orbits in the restricted three-body problem. From any launch site it is possible to define a target point reached with zero dispersion due to errors in a selected component of launch velocity. Effects of lunar geometrical librations and of obliquity, as well as the conditions for biasing a trajectory away from L2 so as to reduce stationkeeping costs, are dealt with along with transfer orbits from L2 to the colony. The theory of capture and the theory of resonance lead to a colony orbit, with period approximately two weeks, reached from L2 with velocity increment as low as 9.02 m/sec.

Planetary exploration - Earth's new horizon /12th von Karman Lecture/

Planetary exploration is examined in terms of the interaction of technological growth with scientific progress and the intangibles associated with exploring the unknown. The field is limited to unmanned exploration of the planets and their satellites. A descriptive model of the endeavor, its activities and achievements in the past decade, a characterization of the current state of the art, and a look at some of the planetary mission opportunities for the next decade are presented. A case is made for the value to civilization of ongoing planetary exploration. The pioneering U.S. planetary explorers, Mars, Venus, and Jupiter, are discussed in the second part of the work. Launch velocity, navigation, the remote system, the earth base, and management technology are considered in the third part. Authorized near-term U.S. planetary projects and opportunities of the next decade are described in the last section.

Air launch for space shuttles

Air launch for space shuttles is investigated parametrically according to launch velocity, from zero (ground launch) to Mach 9. The results indicate that as a means of reducing space transportation costs, air launch concepts do not appear competitive with ground launched single-stage rocket shuttles. While airbreathing vehicles may offer special operational advantages as mobile platforms for launching smaller payloads to orbit, and while hypersonic airbreathers may offer special benefits for suborbital atmospheric missions; it does not appear that their development could be justified on the basis of their contributing to the economics of space transportation. For missions in which air launch platforms are required, significant reductions in gross liftoff weight and system dry weight are possible through use of mixed-mode propulsion in the orbiter stage. In hypersonic airbreathing vehicles, whether used as launch platforms for orbiters or as atmospheric cruise vehicles, mixed-mode propulsion may offer worthwhile reductions in dry weight and vehicle size, a possibility which may merit further investigation.

Explosive Volcanic Eruptions-II The Atmospheric Trajectories of Pyroclasts

The formulation and solution of the general equations of motion of pyroclasts in the Earth's atmosphere are described. Ranges of particles ejected from a vent, and times of fall of particles released from an eruption column or ash cloud, are computed for those values of particle radius (0·01 to 100 cm), density (0·5 to 3·5 g cm−3), launch velocity (10 to 1000 ms−1), elevation (45, 66 and 87 degrees) and release height (0 to 50 km) of practical importance. The values so obtained are presented in tabular and graphical form, and their use in determining the physical parameters of an explosive eruption is described.

Planar Shock Wave Experiments Using Very Small Bore Guns

Small caliber (7.62–13.7 mm) smoothbore powder guns have been developed to generate planar shock wave data in solid materials. Basically the experiments consist of launching flat plates of materials whose shock properties have been predetermined against targets made from materials with unknown properties mounted beyond the gun muzzle. A rotating-mirror streak camera is used to monitor the impact velocity and the recoil velocity of the target rear surface. These results, together with shock properties of the known material, are sufficient for determining a point on the shock Hugoniot of the unknown material when the assumption is made that target rear surface velocity is twice material velocity. The impact process is reversed (i.e., unknown material is launched against standard material when this assumption is not valid). To date, impact velocities have been limited to 2.5 km/sec because a powder gun was used for projectile launching but impact velocities can be extended to 7 or 8 km/sec by using a small light-gas gun.

Vacuum-Tube Launchers and Boosters

Abstract : Systems are being developed to Investigate the feasibility of using an evacuated (vacuum) tube as either a launcher or booster for small to medium size projectiles. Two eight-inch diameter tubes are being fabricated to propel a one-to three-pound meteorological probe into the lower atmosphere. A 70-foot long tube can propel this projectile to approximately 7000 feet above ground level, while a 20-foot tube will send the same projectile to an altitude of approximately 3500 feet. A vacuum tube may be used to impart initial velocities in the range of 300 to 500 ft/sec to the ARCAS. This increased launch velocity will result in a 10 to 20 percent increase in peak altitude, with a simultaneous reduction in wind effect of 30 to 60 percent.

Longitudinal impact of two mutually plastically-deformable missiles

This paper develops an improved theory of large plastic deformation of metallic cylindrical flat ended missiles striking each other with prescribed launch velocities and compares results with experimental data.The groups of comparison studies which have been used for comparison with this analysis are: 1.(a) G.I. Taylor and A.C. Whiffin2.(b) E.H. Lee, S.T. Tupper, A.C. Whiffin and H.L.D. Pugh3.(c) N. Davids, C. Graberek, D. Raftopoulos and A. RicchiazziIt has been found from the above comparisons that the results given in this paper show that the theory predicts large deformation of the aforesaid missiles satisfactorily for low and intermediate velocities.

Launch vehicles for future automated space missions.

Future launch vehicle programs for automated space missions, discussing higher launch velocities and economics

A Solution of the Boundary Value Problem for Space Trajectories

This paper discusses a solution to the boundary value problem for space trajectories which has been found to be easily mechanized. Specifically, when the initial time, initial position, terminal time, and terminal position have been prescribed for a space flight, a method for finding the initial velocity that satisfies these constraints is presented. Three examples are given. They are the boundary value problems associated with an artificial satellite, a lunar impact trajectory, and an interplanetary trajectory. For purposes of illustrating the method and to assess the quality of the results, the lunar impact trajectory investigated was a 1963 Ranger trajectory and the interplanetary orbit selected was a 1969 Mars fly-by trajectory of the Mariner type. Each of the orbits was obtained through the courtesy of the Jet Propulsion Laboratory; however, it is to be emphasized that the ground rules adopted only permitted that the launch date, launch position, arrival date, and arrival position be known. The launch velocity was determined independently.

Earth-moon rocket trajectories

This imposing three-body problem is attacked in the approximation of an adiabatic limit for which the formalism of securing orbital information is posed. An expression is developed for evaluating flight times for rectilinear orbits, but because of computational difficulty, an approximation based upon an earlier work is called upon. In this manner, lunar flight periods for different launching velocities are established.