Kevlar Tether for Phobos

In 2020, a member of the NewMars forum with the ID of “Void” initiated a discussion that has been continuing and evolving ever since. The post that started the sequence contained a simple speculation that it might be possible to deliver gas to the surface of Mars in a “bubble”.

The question led to a mathematical analysis by a member with a PhD in Aerospace Engineering, and the clear answer appears to be a definite NO, if the “bubble” is dropped from the altitude of Phobos with zero horizontal velocity with respect to the the surface of Mars.

The pull of Mars’ gravity, though less than that of Earth (38%) will ** still ** accelerate the bubble (ie, balloon) to a velocity significant enough to insure the object impacts on the surface, instead of floating as might have naively been imagined if the contents is Hydrogen.

However, taking the judgement of the PhD (GW Johnson) in stride, other members began considering the possibility of releasing the bubble at an altitude closer to the surface. That led to renewed discussion of tethers. It turns out that tethers have received some serious attention during the 20 years the NewMars forum has been available as a public service of the Mars Society. In particular, quotations from a web site/ blog by “Hop” show illustrations of various tethers that might be constructed, including one for Phobos.

The inspiration of the vision published by Hop led to work on a concept that might be implemented with Phobos as the anchor. The distance from Phobos to just above the surface of Mars is (about) 3700 miles (5955 km).

Since the Hop blog post suggests Kevlar as a material that might be strong enough for this application, a design is in development to make links of a chain of Kevlar thread. Kevlar thread is offered commercially on Earth in various grades and lengths. A #92 thread is 290 micrometers in diameter, and it can hold 25 pounds or just over 13 kilograms. This information can be (and is being) extended to the design of a chain of Kevlar thread links that would extend 3700 miles toward the surface of Mars.

It appears that a bubble/balloon released from the lowest rung of a Kevlar chain from Phobos would have a modest horizontal velocity with respect to the surface of Mars, and since vertical velocity would be zero at the time of release, a package would have a reasonable chance of survival. In particular, the possibility that a package could be buoyant (ie, filled with Hydrogen) is greater than zero. Testing at Mars, or calculations using CFD (Computation Fluid Dynamics) software may show one way or the other.

In any case, to see images of the CushionGuide intended to bear the compression load between links of the Phobos Tether, readers are welcome to visit the NewMars forum at:


Author: Tom Hanson

I was privileged to be able to participate in the 2011 reboot of Lufteam in Yahoo Groups. I am delighted to see this latest undertaking on behalf of the LUF idea, and will attempt to help as much as possible. In case anyone is interested, I posted for a couple of years at, and I am currently participating in posting at (th)

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