The Starship

Perhaps the most frequently used concept in science fiction to push, pull, and spread intelligent life around the galaxy is the starship—a space vehicle that is capable of traveling the great distances between star systems within a reasonable period of time. Building such a vehicle is a considerable engineering challenge because even the closest stars in the Milky Way galaxy are generally light-years apart. In this book, the word starship is used to describe interstellar spaceships that are capable of carrying intelligent beings to other star systems, while purely robotic interstellar space vehicles are called interstellar probes.

What are the performance requirements for a starship? First, and perhaps most important, the vessel should be capable of traveling at a significant fraction of the speed of light (c). Ten percent of the speed of light (0.1c) is often considered as the lowest acceptable speed for a starship, while cruising speeds of 0.9c and beyond are considered highly desirable. This optic velocity cruising capability is necessary to keep interstellar voyages to reasonable lengths of time, both for the home civilization and for the starship crew.

Consider, for example, a trip to the nearest star system, Alpha Centauri—a triple star system about 4.23 light-years away. At a cruising speed of 0.1c, it would take about 43 years just to get there and another 43 years to return. The time dilation effects of travel at these "relatively low" relativistic speeds would not help too much either since a ship's clock would register the passage of about 42.8 years versus a terrestrial ground elapse time of 43 years. In other words, the crew would age about 43 years during the journey to Alpha Centauri. If the expedition started with 20-year-old crewmembers, who departing from the outer regions of the solar system in the year 2100 traveled at a constant cruising speed of 0.1c, the crew would be approximately 63 years old when they reached the Alpha Centauri star system—some 43 years later in 2143. The return journey would be even more dismal. Any surviving crew members would be 106 years old when the ship returned to the outer fringes of the solar system in the year 2186. Most, if not all, of the crew would probably have died of old age or of boredom.

A starship should also provide a comfortable living environment for the crew and the passengers (in the case of an interstellar ark). Living in a relatively small, isolated, and confined habitat for a few decades to per haps a few centuries can certainly overstress even the most psychologically adaptable individuals and their progeny. One common technique used in science fiction to avoid this crew stress problem is to have all or most of the human crew placed in some form of "suspended animation"—while the vehicle travels through the interstellar void, tended by a ship's company of smart robots.

Any properly designed starship must also provide an adequate amount of radiation protection for the crew, passengers, biological materials, and sensitive electronic equipment. Interstellar space is permeated with galactic cosmic rays. Nuclear radiation leakage from an advanced thermonuclear fusion engine or a matter/antimatter engine (photon rocket) must also be prevented from entering the habitation compartment. In addition, the crew will have to be protected from nuclear radiation showers that are produced when a starship's hull, traveling at near light speed, slams into interstellar molecules, dust, or gas. For example, a single proton (assumed for mathematical convenience as being "stationary" in this simple example) that encounters a starship moving at 90 percent of the speed of light (0.9c) would appear to those on board like a one gigaelectron volt (GeV) proton being accelerated at them. Imagine traveling for years at the beam output end of a very high-energy particle accelerator. Without proper deflectors or shielding, survival in the crew compartment after such an enormous dose of nuclear radiation is doubtful.

To function truly as a starship, the vessel must be able to cruise at will, light-years from its home star system. The starship must also be able to accelerate to significant fractions of the speed of light, cruise at these near optic velocities, and then decelerate to explore a new star system or to investigate a derelict alien spaceship that has been found adrift in the depths of interstellar space.

This chapter does not discuss the enormous difficulties of navigating through interstellar space at near light velocities. It will be sufficient to mention here simply that when the crew "looks" forward at near light speeds, things appear blueshifted; while when they look aft (backward), things appear redshifted. The starship and its crew must be able to find their way independently from one location in the Milky Way galaxy to another.

What appears to be the major technology needed to make the starship a credible part of humans' extraterrestrial civilization is an effective propulsion system. Interstellar class propulsion technology is the key to the galaxy for any emerging civilization that has mastered spaceflight within and to the limits of its own star system. Despite the tremendous engineering difficulties that are associated with the development of a starship propulsion system, several concepts have been proposed. These include the pulsed nuclear-fission engine (Project Orion concept), the pulsed

An artist's rendering of an interstellar ramjet. The conceptual starship is characterized by a huge (39-square-mile [100-km2]) scoop to capture interstellar hydrogen for use as fuel in sustaining the thermonuclear reactions that propel the vehicle to upward of 90 percent of light speed. (NASA/Marshall Space Flight Center)

An artist's rendering of an interstellar ramjet. The conceptual starship is characterized by a huge (39-square-mile [100-km2]) scoop to capture interstellar hydrogen for use as fuel in sustaining the thermonuclear reactions that propel the vehicle to upward of 90 percent of light speed. (NASA/Marshall Space Flight Center)

nuclear-fusion concept (Project Daedalus study), the interstellar nuclear ramjet, and the photon rocket.

Unfortunately, in terms of the way scientists and engineers currently understand of the laws of physics, all known phenomena and mechanisms that might be used to power a starship are either not energetic enough or simply are entirely beyond today's level of engineering technology. In fact, starship propulsion systems appear to require a level of space technology that is not envisioned for several decades, if not a century or more. Perhaps there will be major new insights as to how scientists perceive the physical laws of the universe, or perhaps engineers will develop better ways to manipulate energy and matter. But until such breakthroughs actually occur (if they ever do), the notion of human beings traveling in a starship to another star system must remain in the realm of future dreams and science fiction.

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