Future satellite communication systems proposed use geosynchronous (GEO) satellites, medium earth orbit (MEO), and low earth orbit (LEO) constellations with fast packet switching and quality of service (QoS) provisioning. In this paper, we present broadband GEO, MEO and LEO satellite network QoS models and simulated performance results. This paper proposes a new method of bandwidth allocation d...

We study the problem of carrying voice calls over a low-earth-orbit satellite network and present an analytical model for computing call-blocking probabilities for a single orbit of a satellite constellation. We have devised a method to solve the corresponding Markov process efficiently for orbits of up to five satellites. For orbits consisting of a larger number of satellites, we have develope...

Van Allen radiation belts consist of relativistic electrons trapped by Earth's magnetic field. Trapped electrons often drift azimuthally around Earth and display a butterfly pitch angle distribution of a minimum at 90° further out than geostationary orbit. This is usually attributed to drift shell splitting resulting from day-night asymmetry in Earth's magnetic field. However, direct observatio...

A prominent astronomical fact is that the Moon always shows the same face to the Earth. This means that the Moon rotates once about its axis each Earth month. It turns out that the “days” of Mercury and Venus are nearly equal to their respective “years,” and that the periods of axial and orbital revolution are equal for most of the moons of Jupiter, Saturn, Uranus and Neptune. In 1879, George D...

Earth-crossing asteroids and comets pose a long-term hazard to life and property on Earth. Schemes to mitigate the impact threat have been studied extensively but tend to focus on asteroid diversion while neglecting the possibility of a comet threat. Such schemes often demand physically intercepting the target by spacecraft, a task feasible only for targets identi ed decades in advance in a res...

Whether life exists beyond Earth is a fundamental question. To answer this and related questions requires access to space, making the search for life within our solar system and beyond a quest that only the National Aeronautics and Space Administration (NASA), along with its international partners, can answer. The Terrestrial Planet Finder (TPF) is one of the key missions in NASA’s Astronomical...

Transatmospheric vehicles (TAVs), with aerodynamic properties similar to conventional aircraft, have the promise of flying into space and delivering payloads into low earth orbit (LEO). A key distinguishing feature between TAVs and aircraft is propulsion. Jet engines or pure air-breathing propulsion systems cannot provide the thrust levels needed to ascend into space. Traditional rockets overco...

Analysis of Lunar Laser Ranging (LLR) data provides science results: gravitational physics and ephemeris information from the orbit, lunar science from rotation and solidbody tides, and Earth science. Science from the orbit: Sensitive tests of gravitational physics include the Equivalence Principle, limits on the time variation of the gravitational constant G, and geodetic precession. The equiv...

In this paper, optimum trajectories in Earth Transfer Orbit (ETO) for a lunar transportation system are proposed. This paper aims at improving the payload ratio of the reusable orbital transfer vehicle (OTV), which transports the payload from Low Earth Orbit (LEO) to Lunar Low Orbit (LLO) and returns to LEO. In ETO, we discuss ballistic flight using chemical propulsion, multi-impulse flight usi...

Ψ NASA GSFC has developed a GPS receiver that can acquire and track GPS signals with sensitivity significantly lower than conventional GPS receivers. This opens up the possibility of using GPS based navigation for missions in high altitude orbits, such as Geostationary Operational Environmental Satellites (GOES) in a geostationary orbit, and the Magnetospheric MultiScale (MMS) Mission, in highl...