Interstellar Travel: The Wait Calculation and the Incentive Trap of Progress

TL;DR — A JBIS paper modelling when an interstellar voyage should leave, given that later ships will be faster, and finding a departure date that beats waiting.

A paper by Andrew Kennedy (The Chronolith Project, Seville) in the Journal of the British Interplanetary Society, vol. 59 (2006). It addresses an “incentive trap”: if travel technology keeps improving, a ship that leaves today may be overtaken by a faster one launched later, so travellers have a reason to keep waiting.

Using simple exponential-growth equations for travel speed and the example of a trip to Barnard’s Star, Kennedy shows there is a minimum total time to destination: before a certain point it pays to wait, after it a departure beats any later departure. He argues that waiting indefinitely is irrational, that changes in growth rates can make earlier departure the better choice, and that a sudden leap in propulsion that would justify waiting is unlikely. The result is often cited as “the wait calculation.”

This copy is the author’s upload to ResearchGate, with its cover page.

What it is: A peer-reviewed paper in a specialist astronautics journal; a simple quantitative model rather than an engineering study.

Where this came from

• A copy saved in October 2026.

9 pages. A PDF copy is held in Kyle’s private archive; it is not linked or shared here.