Orbits Around Small Irregularly Shaped Bodies

Recently there has been a lot of interest in spacecraft missions that visit the smaller objects in the solar system, such as asteroids and comets. These types of objects are essentially debris scattered across interplanetary space, which are fragments left over from the processes that formed the Sun and planets. And therein lies their attraction as targets of scientific interest for spacecraft probes. Asteroids, sometimes called minor planets, are usually solid bodies which vary in size from...

Gravity Anomalies

If the Earth were perfectly spherical, and its internal density distribution had a particularly simple form, then the gravity field of Earth would be a perfect inverse square law, as described by Isaac Newton. However, Earth is not perfectly spherical, nor does it have a simple internal mass distribution. There are topographical features that spoil that perfection, such as mountains that are 8 km (5 miles) high and ocean trenches that are 11 km (7 miles) deep. In addition, Earth's shape is...

Popular Operational Orbits

Now that we have a grasp of the three principal distinguishing characteristics of orbits shape, size and orbital inclination we can begin to look at the Earth orbit types that are most commonly used by spacecraft operators. Obviously, if we allow all possible variations in these three characteristics, then there is an infinite number of resulting Earth orbits to choose from The popular orbits that we are about to introduce, therefore, are a small subset of this vast number of possibilities, and...

Trapped Particle Radiation

As we saw earlier, some of the solar wind particles emanating from the Sun, generally charged particles such as electrons, protons, and atomic nuclei stripped of their attendant electrons, penetrate the protective shield of Earth's magnetic field. Some are focused by the field into the atmosphere above the north and south polar regions, causing auroral displays. Others are trapped by the magnetic field, producing radiation belts that pose a hazard to people and spacecraft alike. These belts are...

Communications Frequencies

Information on a satellite communications link is carried by electromagnetic (EM) waves Figure 6.2 in Chapter 6 illustrated the various parts of the EM spectrum. As a consequence, the speed of communication is the speed of light, which is around 300,000 km per sec (186,000 miles per second), so that communication with spacecraft in LEO is effectively instantaneous. However, for a communication satellite in GEO, the altitude of the satellite is around 38,000 km, so that EM waves take just over a...

SwingBy Trajectories

If a spacecraft passes close by a planet, as it journeys through interplanetary space, then the path it takes is described as a swing-by trajectory. It may be worth recalling some of the background we discussed in Chapter 1 about this type of trajectory, and indeed you may wish to reread the text associated with Figures 1.9 and 1.10 to refresh your memory. The shape of the curve describing the spacecraft's path is called a hyperbola, and it is one of the four basic conic section shapes found by...

Weightlessness

Weightlessness The Weight Body

Now that we have a good feel for the nature of orbital motion essentially a spacecraft is in a state of free-fall under gravity we can also achieve a similarly good understanding of the phenomenon of weightlessness. Weightlessness is something we see routinely on news coverage of manned space missions. In this book I use the phrase manned space missions to mean flights involving people both men and women. I know that the phrase may not be quite politically correct, but I dislike the other...