In an earlier post we detailed the publication of a paper that discussed the design of a world ship, a large vessel with a carrying capacity of 1 million people (growing to 10 million) over a trip time of order one millennia to the nearest stars. This was based on an earlier 1984 study for a Mk2A world ship, and we renamed it Ra after the Egyptian God of the Sun.
The first paper mostly dealt with demographics issues but also some discussion on the creation of artificial gravity through spinning of the habitat. This first paper was:
K. F. Long, Population Demographics and Other Issues for the Massive Ra World Ship Model - Part 1, Journal of the British Interplanetary Society, Volume 76, November 2023.
We are pleased to report that a second paper has also now been accepted for publication and this paper deals specifically with the propulsion issues for how to propel such a massive vessel. This is using inertial confinement fusion engines, via laser drivers, as opposed to the original 1984 study which used external nuclear pulse propulsion such as in the historical Project Orion.
The new paper is:
K. F. Long, Inertial Confinement Fusion Propulsion for the Massive Ra World ship Model - Part 2, Journal of the British Interplanetary Society, Volume 77, April 2024.
After some research on the different design configurations for the engine, a layout of using 1024 engines was adopted as a compromise between minimising the number of engines (which increases the system mass) and minimising the ICF capsule mass; since too high a capsule mass then requires much higher laser drivers to implode and ignite them.
For the world ship Ra the large spacecraft would accelerate for around 35 years, coast for around 853 years and then decelerate for a further 15 years, reaching the target destination after a total trip time of 854 years. Its maximum cruise velocity would be of order 1,557 km/s or 0.52% of the speed of light. Throughout the voyage many generations of humans would be born, live out there life and die on the ship.
With its huge 10^12 tons mass the parallel thrust engines would deliver a thrust of 978 GN, using an exhaust velocity of 1,880 km/s and a mass flow rate of 5.2*10^5 kg/s. The individual ICF capsules would have a mass of 230 grams but would be augmented by 4.853 kg of expellant propellant which under thermalisation helps to boost the mass flow rate and thereby thrust. Each capsule would require 166 GJ of driver energy and correspond to an energy gain of 240. For all of the 1024 engines combined the total driver energy requirement would be around 170 TJ.
This paper, along with the earlier one, may be one of the most up to date comprehensive reviews of a world ship architecture but within the nuclear pulse propulsion paradigm. Also discussed in the most recent paper were the sourcing of the world ship regolith, atmosphere and water.
Who is to say if such vessels are to become a part of our plausible future, or will other options be adopted such as much smaller and lower mass vessels but containing Artificial Intelligence and embryo seed banks for growing at the destination. Yet it is interesting to see these architectures sketched out and to visualise what may be possible and what it would take.