Earth Escape Research Articles

Earth Escape by Ideal Sail and Solar-Photon Thrustor Spacecraft

Introduction S OLAR sails use the solar radiation pressure on a large reflecting surface to obtain low-thrust propulsion. This technology has been identified as enabling many recent space mission concepts. An interesting application involves the study of escape trajectories from the Earth. Early contributions to this subject date back to Sands1 and Fimple,2 who considered initial circular orbits and used other simplifying assumptions, and to Sackett and Edelbaum.3 Locally optimal steering laws for a flat sail have been considered in various forms by different authors.4−6 In a recent paper Coverstone and Prussing7 investigated the problem of Earth escape from a geosynchronous transfer orbit with an ideal flat sail through a sail-force control algorithm that maximizes the instantaneous rate of increase of the total orbital energy. In their analysis a spherical gravity model for the Earth is assumed, and only the solar gravitational perturbation is included.

Delivering fast and capable missions to the outer solar system

Concepts for science missions to the outer solar system and beyond traditionally suffer from the multiple burdens of long trips times, power starved payloads and a severe communications bottleneck for data returns. This paper will consider the use of solar sail propulsion to address some, or even all of these issues in the mid to far-term. By using a short inner-loop about the Sun, solar sails can quickly accelerate payloads to cruise speeds of greater than 10 AU per year from Earth escape, with a sail payload mass fraction of order 50% or more. The technology required for such solar sails is currently under development and there is a clear pathway from current plans for near-term technology demonstration missions to these fast trips to the outer solar system. Looking further ahead, technologies can be envisaged where the solar sail is used as a multi-functional system to provide propulsion, power collection and telecommunications. With sustained development, current ideas for embedding smart actuators and sensors in the sail structure may enable solar sails with variable morphology which can be configured as a solar concentrator for power generation and a large antenna for high-bandwidth data returns. These visionary concepts will be explored and a roadmap drawn up which will deliver fast and capable missions to the outer solar system and beyond.

Inverse Solar Sail Trajectory Problem

SOLAR sailing has long been considered for a diverse range of future mission applications. Although low-performance solar sails can be utilized for interplanetary transfer using heliocentric spiral trajectories, high-performance solar sails can enable exotic applications using non-Keplerian orbits. A simple example of such an exotic applicationis levitation,with the solar radiationpressure accelerationexperiencedby the sail exactly balancing solar gravity. Such a static equilibrium allows the solar sail to remain stationary with respect to the sun, or indeed if the sail is turned edgewise to the sun it will fall sunwards on a rectilinear trajectory. Although this static equilibrium is simple to identify, the question of transfer to it from an Earth escape trajectory remains open. This Note will derive an analytic sail steering law that allows the solar sail is be maneuvered from a circular heliocentric orbit, to a static equilibrium location at the same heliocentric distance. The required trajectory will be deŽ ned a priori with the resulting sail steering law derived from the equations of motion. An inverse trajectory problem is, therefore, being solved.

LISA — a study of the ESA cornerstone mission for observing gravitational waves

The primary objective of the Laser Interferometer Space Antenna (LISA) mission is to detect and observe gravitational waves from massive black holes and galactic binaries in the frequency range 10 −4 to 10 −1 Hz. This low-frequency range is inaccessible to ground-based interferometers because of the unshieldable background of local gravitational noise and because ground-based interferometers are limited in length to a few km. LISA is an ESA cornerstone mission and recently had a system study (Ref. 1) carried out by a consortium led by Astrium, which confirmed the basic configuration for the payload with only minor changes, and provided detailed concepts for the spacecraft and mission design. The study confirmed the need for a drag-free technology demonstration mission to develop the inertial sensors for LISA, before embarking on the build of the flight sensors. With a technology demonstration flight in 2005, it would be possible to carry out LISA as a joint ESA-NASA mission with a launch by 2010 subject to the funding programmatics. The baseline for LISA is three disc-like spacecraft each of which consist of a science module which carries the laser interferometer payload (two in each science module) and a propulsion module containing an ion drive and the hydrazine thrusters of the AOCS. The propulsion module is used for the transfer from earth escape trajectory provided by the Delta II launch to the operational orbit. Once there the propulsion module is jettisoned to reduce disturbances on the payload. Detailed analysis of thermal and gravitational disturbances, a model of the drag-free control and of the interferometer operation confirm that the strain sensitivity of the interferometer will be achieved.

Doppler Studies of Near-Antapex UHF Radar Micrometeors

A “radar micrometeor” is the radar-scattering signature from the free electrons in the plasma generated by entry of a dust-sized meteoroid into the atmosphere. We report the first direct Doppler measurements, made using the Arecibo Observatory 430-MHz radar, of the so-called meteor head echo. Our observations demonstrate that this region is moving with the speed of the meteoroid as determined from the meteor head-echo altitude–time trajectory and that this radar return is distinct spatially and in velocity from the much more commonly observed trail echo. We also report the first observations of near-antapex micrometeors which are characterized by the very slow atmospheric speeds expected from low-ecliptic-inclination objects entering the atmosphere from behind Earth's orbital path. Of the 32 meteors observed during four early evening hours of observations on 10 January 1997, velocities were determined for 18 of the meteors of which 7 were at or just below Earth escape velocity (11.2 km/s). We give heliocentric orbits for the 11 meteor events with speeds greater than the escape velocity and present a detailed analysis of these orbital parameters and their possible origins. One particle was determined to be interstellar: a preliminary analysis indicates that the ecliptic coordinates of the radiant relative to the local standard of rest (LSR) (with the solar motion relative to the nearby stars removed) are λ=43.02°, β=−43.28°, V=−25.11 km/s or, in system II galactic coordinates l II=219.8°, b II=−52.4°, V=−25.1 km/s.

New results from in situ measurements of Cosmic Dust — Data from the GORID experiment

The impact detector GORID, on the Russian Express II satellite has now collected data on Cosmic Dust and Space Debris for more than one year from its geostationary location at 80° East. During this time a large number of events have been registered and these are now being analysed and categorised. Dust and Debris particles are in the first approximation separated by evaluating the velocity, assuming that particles in Earth orbit are related to Space Debris and that particles with velocities above the Earth escape velocity are Cosmic Dust particles. Now that a full year of data collected with constant instrument settings is available proper analysis is possible where the random process of the impacts best can be described by statistical methods on the whole set of data. Data sets from one or several full years are required to suppress the possible biases that can result from spatial, temporal and directional variations in the flux and to reduce the statistical errors. Interesting observations include clusters of particles and indications of highly charged particles.

Optimal Low-Thrust Interception of Earth-Crossing Asteroids

The spectacular collision of the Shoemaker–Levy 9 asteroid with Jupiter in July 1994 was a dramatic reminder of the inevitability of such catastrophes in the Earth’s future unless steps are taken to develop methods for Earthapproaching object detection and possible interdiction. In this work, optimal (minimum-time) trajectories are determined for the interception of asteroids that pose a threat of collision with the Earth. An impulsive-thrust escape from the Earth is used initially to reduce  ight time but is followed with continuous low-thrust propulsion using values of thrust and speciŽ c impulse representative of electric motors. The continuous optimization problem is formulatedas a nonlinearprogrammingproblemusing the collocationmethod inwhich thedifferential equations of motion are included as nonlinear constraint equations. The use of low-thrust propulsion after Earth escape is shown to dramatically decrease the mass of the interceptor vehicle at launch.

Mercury sun-synchronous polar orbiter with a solar sail

An innovative mission MESSAGE (MErcury Solar Sailing Advanced Geoscience Exploration) is proposed where a solar sail spacecraft of about 240kg total mass delivers a limited but highly valuable science payload to a sun-synchronous Mercury orbit in 312 years. Corresponding operation near the terminator offers favorable thermal and remote sensing conditions for the considered instruments. Since Mercury is still the poorest explored and least known planet of the inner solar system, there is a high level of scientific interest for further exploration. Science objectives and a potential payload package of about 20 kg for the proposed solar sail mission considering the special orientation and geometry of a sun-synchronous orbit about Mercury will be discussed. Determination of the elemental composition of the Hermian surface with respect to major rock forming elements and volatiles could be carried out by a gamma-ray spectrometer. In the current mission architecture the spacecraft will be launched into an Earth escape trajectory with a relatively low-cost launch option such as TAURUS or ROCKOT with upper stages. The sail is used as a transportation means for the interplanetary transfer, for orbit capture upon Mercury arrival, and subsequent adjustment of a sun-synchronous orbit about the planet near the terminator. Due to Mercury's 3:2 spin-orbit coupling the eccentric polar orbit of 200 km × 6350 km altitude with periapsis above the north pole will allow complete coverage of the planet's surface within two Mercury years. Optimized interplanetary trajectories as well as simulations of the orbit about Mercury will be shown. A conceptual design of the spacecraft including the deployment concept of the square sail of an estimated size of about 86m × 86m and its support structure will be presented. The lightweight booms are proposed to be manufactured of carbon fibre reinforced plastic profiles that can be stored on a central hub prior to deployment. Possible sail film materials, coatings and folding concepts will be discussed. In a more advanced scenario two identical solar sails could be launched in a stacked configuration by a Med-Lite to realize a dual sun-synchronous Mercury orbiter mission.

Mercury orbiter with a solar sail spacecraft

A mission to Mercury is discussed, where a solar sail spacecraft with a total mass of about 500 kg delivers a scientific payload of approximately 50 kg to an orbit about Mercury. As knowledge of this planet is very limited, a Mercury orbiter mission is proposed by scientists since many years. The solar sail, a deployable light-weight structure, is used for spiraling to Earth escape, for interplanetary transfer, and orbit capture upon Mercury arrival, while flight times of moderate length are still possible. This strategy allows very low Earth departure and Mercury arrival energies, and can significantly reduce the total mass to be delivered by the Earth-based launch system in comparison to conventional missions using chemical propulsion. Therefore, a low-cost launch option may be considered. Moreover, a sun-synchronous orbit about Mercury can be accomplished with the sail, bearing considerable advantages for the spacecraft's thermal environment and suitable conditions for remote sensing. Solar sails are promising future low-cost transportation systems and may also be used across a wide range of other planetary missions.

Axial compression corner flow with shock impingement

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The electrothermal ramjet

An electrothermal ramjet configuration is examined as a possible alternative to rail guns and mass drivers for high acceleration launch missions. For a specific mission (Earth escape), the idealized performance of electrothermal ramjet, electrothermal rocket and electromagnetic acceleration systems are compared. This comparison indicates that the gross performance of the ramjet compares favorably with that of the ideal electromagnetic acceleration system. A specific configuration for the ramjet is chosen, and models for the dynamics, thermodynamics, and fluid mechanics are presented. Results of calculations for a typical supersonic launch cycle suggest that pressure, temperature, and power demand profiles associated with ramjet operation should be reasonable. A light gas gun is proposed to accelerate the vehicle to the critical velocity where efficient ramjet operation can begin. At high velocities the theoretical performance of the ramjet is also shown to be substantially better than that of the light gas gun.

Earth escape regions near the moon

Earth escape regions near the moon