  Technologies have often been observed to improve exponentially over time. In
practice this often means identifying a constant known as the doubling time,
describing the time period over which the technology roughly doubles in some
measure of performance or of performance per dollar. Moore's law is,
classically, the empirical observation that the number of electronic components
that can be put on a chip doubles every 18 months to 2 years. Today it is
frequently stated as the number of computations available per unit of cost.
Generalized to the appropriate doubling time, it describes the rate of
advancement in many technologies. A frequently noted competitor to Moore's law
is known as Wright's law, which has aeronautical roots. Wright's law (also
called power law, experience curve and Henderson's law) relates some quality of
a manufactured unit (for Wright, airplanes) to the volume of units
manufactured. The Wright's law equation expresses the idea that performance -
price or a quality metric - improves according to a power of the number
produced, or alternatively stated, improves by a constant percentage for every
doubling of the total number produced.
  Does exploration of outer space conform to Moore's law or Wright's law-like
behavior? Our results below are broadly consistent with these laws. This is
true for many technologies. Although the two laws can make somewhat different
predictions, Sahal found that they converge to the same predictions when
manufacturing volume increases exponentially over time. When space exploration
transitions into an independent commercial sector, as many people hope and
expect, spacecraft technology will then likely enter an era of unambiguously
exponential advancement.
