Monthly Archives: November 2019

Refueling in Lagrange – Part 3

Titan in sunlight

Refueling in Lagrange Part 1
Refueling in Lagrange Part 2

Assuming a Lunar Space Elevator, but limited Lunar supplies of methane, is there another option?

Earth is ruled out due to the gravity-well penalty of over 12 km/s. We’re trying for independence from resupply from Earth.

Near Earth Asteroids quite possibly have supplies of tarry organics known as kerogens, which on Earth form the basis of Oil Shale. Cracking methane from oil shale is well known technology and a tar-encrusted dead Comet could be an amazing supply source.

Mars – aside from being the Next Frontier – has Carbon Dioxide and Water in abundance. But it’s at the bottom of a significant Gravity Well. To get back to EML-2, the delta-vee is about ~ 5.892 km/s.

Titan – methane is abundant and can merely be piped in from the atmosphere. Delta-vee is 5.131 km/s, which is better than Mars.

OBJECTDISTANCE (AU)OUTBOUND (km/s)ARRIVAL (km/s)RETURN (km/s)Round-Trip* (km/s)
MARS1.5240.7445.5575.8926.636
CALLISTO5.2043.4365.2945.62914.358
TITAN9.5404.4144.7965.1319.545

*Round-Trip assumes aerobraking at Mars & Titan on arrival. Callisto has a very high round-trip due to the need for a full braking landing.

Given a supply of LOX from the Moon, via space elevator, delivering methane from Titan to EML-2 actually becomes a viable option. A Space Elevator at Titan would be shorter than one at the Moon, only 49,800 km to the STL-1 (Saturn-Titan-Lagrange-1) point, versus ~62,000 km for EML-2. Titan has huge potential for wind power from floating turbines, which would allow a laser bank to power a Space Elevator crawler. Plus there’s abundant hydrocarbons and nitrogen on the surface for making kevlar and similar para-aramid high strength polymers. The dunes of Titan are probably acetylene derivatives, made via cosmic-ray interaction. Additionally acetylene-ammonia co-crystals are likely to form in large quantities around the lakes.

Thus Titan has a distinct materials resource advantage over the Moon. Given the mass required, exporting from Titan could be an early goal, to build a Lunar Space Elevator able to sustain multi-thousand ton payload traffic. An ambitious early goal for a nascent Titan economy.

Methane & polymers launched from SLT-1 to EML-2 has a much lower delta-vee penalty. Thus a mature Moon-Mars-Titan economy could have a vigorous trade in Titanian hydrocarbons & polymers. Even Mars would benefit from the access to nitrogen.