Manned or unmanned travel between stars. It is made problematic at present
by the immense distances involved (see interstellar
distances), which are orders of magnitude greater than those of interplanetary
travel, and by the limited propulsion technologies that are available.
Although it is increasingly hard to imagine a future in which human beings
do not eventually journey to the stars, unless our species destroys itself
first, it is also difficult to see how such a mission could be undertaken
within the next century or so. Manned exploration, for the foreseeable future,
will be concentrated on the Moon, Mars, and,
beyond that, possibly the large moons of the outer planets. Robotic interstellar
missions, on the other hand, may well become practicable over the next few
Already several spacecraft from Earth are heading, slowly, toward the stars
(see interstellar probes), although they will
be defunct long before they arrive anywhere near the vicinity of any extrasolar
planetary systems. These early pioneers will rapidly be overtaken by a new
generation of star probes based on advanced technology, including artificial
intelligence and high-speed propulsion systems. One of the most detailed
designs for a purpose-built interstellar spacecraft is Project
- Crawford, I. A. "Interstellar Travel: A Review for Astronomers," Quarterly
Journal of the Royal Astronomical Society, 31, 377 (1990).
- Forward, Robert, L., "Feasibility of Interstellar Travel: A Review,"
Journal of the British Interplanetary Society, 39, 379-384,
Abstract: Interstellar travel is difficult, but not impossible.
This review paper discusses the relative feasibility of a number of
different technologies that will allow travel to the stars. It gives
examples of one-way and rendezvous unmanned interstellar probe vehicles
that can return data on the number and nature of the planets around
the target system within less than 50 years after launch. These initial
exploration probe missions will be followed by manned or robotic exploration
and colonisation missions. These can range from relatively feasible
long slow missions using "world ships" propelled by existing nuclear
pulse or nuclear electric technologies and carrying self-producing
human crews, to high risk, high speed missions using beamed power,
antimatter, or interstellar ramjet technology. For the nearer stellar
system, speeds of 0.1 to 0.3 the speed of light will suffice to explore
the 17 nearest stellar systems with 25 visible stars and hundreds
of planets in trip times comparable to a human lifetime. Some emergent
high energy density technologies that are under development for other
purposes, such as laser and electron beam imploded fusion and solar
powered lasers and masers, show promise of providing us with propulsion
technologies that will make rapid interstellar travel feasible within
the foreseeable future.
- Strong, James G. Flight to the Stars: An Inquiry into the Feasibility
of Interstellar Flight. N.Y.: Hart Publ. Co (1965).