Hunter has pointed out that by using a Jupiter swingby to approach the Sun and then giving a velocity boost at perihelion, a solar system escape velocity... is possible with present-day chemical rockets... [M]ost other stars should have planets (or companion stars) with characteristics sufficiently close to... the Jupiter-Sun system to use this launch strategy in reverse to slow down in the other solar system.

[T]he information to manufacture a human being is contained in the genes of a single human cell. Thus if an extraterrestrial intelligent species possessed the knowledge to synthesize a living cell—and... experts assert... the human race could develop such knowledge within 30 years—they could program a von Neumann machine to synthesize a fertilized egg cell of their species. If they possessed artificial womb technology—and such... is in the beginning stages... on Earth... they could... synthesize members of their species... As suggested by Eiseley... these beings could be raised... by the robots... free to develop their own civilization...

[M]aterials [to reproduce the von Neumann machine] should be available in virtually any stellar system—including systems—in the form of meteors, asteroids, comets, and other debris from the formation of the stellar system. ...[M]aterial in asteroids are highly differentiatied; many... are largely nickel-iron, while others contain large amounts of hydrocarbons.

The payload of a probe to another stellar system would be a self-reproducing universal constructor with human level intelligence (...a von Neumann machine) together with an engine... travelling... within the stellar target system—[the engine] could be an electric propulsion system... or a ...

What one needs is a self-reproducing universal constructor... a machine capable of making any device... capable of making a copy of itself. Von Neumann has shown... that such... is theoretically possible, and... a human being is a universal constructor specialized to perform on the surface of the Earth.

I shall assume that such a species will... develop a self-replicating universal constructor with intelligence comparable to the human level—such a machine should be developed within a century, according to the experts...—and... combined with present-day rocket technology would make it possible to explore and/or colonize the Galaxy in less than 300 million years, for an initial investment less than the cost of operating a 10 MW microwave beacon for several hundred years, as proposed by SETI...

[I]t seems likely that a species engaging in interstellar communication would possess a fairly sophisticated computer technology. ...Sagan has asserted that 'Communication with extraterrestrial intelligence... will require... computer actuated machines with abilities approaching... intelligence'.

[T]hat any intelligent species which develops... interstellar communication will also have... rocketry... is... a consequence of the principle of mediocrity... (that our own evolution is typical)... [T]he human species developed rockets 600 years before... radio waves...

[A]n intelligent species with the technology for interstellar communication would necessarily develop the technology for interstellar travel, and this would automatically lead to the exploration and/or colonization of the Galaxy in less than 300 million years.

The basic idea... is straightforward and... has led other authors, such as Fermi... Dyson... Hart... Simpson... and Kuiper & Morris... to conclude that extraterrestrial beings do not exist: if they did exist and possessed the technology for interstellar communication, they would also have developed interstellar travel and thus would already be present in our solar system.