High Volume SpaceX Starship flights Can use Space Tether to Save Fuel

by

There is a re-examination of space tethers and skyhooks to find near terms use cases. Harsimony at Greaterwrong.com provides the analysis of value for tethers when we have a lot of space launches and space activity.

A tether that spins at 1.74 km/s is ideal for some boosting to the moon. The fuel cost per launch is 293 tonnes, less than half the 713 tonnes we needed originally. The required size of a tether spinning at this speed is 1310 tonnes, which should take roughly 10 launches to build.

Boosting all the way to Mars for a dV of 9.31 km/s. In this case the ideal tether spins at 2.19 km/s and has a mass of 2560 tonnes. Now, the trip requires 813 tonnes of fuel versus 2230 tonnes without a tether.

You need to get more uses out of the tether and counter weight system to get more fuel saving value.

Tethers help you skip a level by bouncing you out of the orbit they’re in. They specialize in a particular transfer you want to make. That’s not always desirable. For instance, there’s not really a way to use tethers to get you from Earth to LEO, since the tether has to be in LEO already. The tether could do a “half-lift” to get you to LEO, but that doesn’t utilize their strengths very well.

Tethers generally want to operate close to their characteristic velocity. Slower and you’re wasting their potential, higher and your tether needs to be huge in order to handle the payload.

Tether repair is a big deal. The longer a material can last, the more it justifies building bigger and faster tethers, which leads to big fuel savings.

Tethers are surprisingly complex for a piece of string. Matching up rocket and tether velocities sometimes requires the tether to be in a weird orbit, and tethers orbit differently than a condensed object would. On top of that, you need to damp vibrations, keep the tether material cool and repair defects in order to get high performance. And they need a regular supply of falling mass to counter the momentum lost from boosting rockets. These considerations mean that tethers have to constantly adapt to their conditions, frequently repositioning and doing maintenance.

Small tethers make building large tethers cheaper by lowering the cost to reach higher orbits. So we can bootstrap to larger sizes.

5 thoughts on “High Volume SpaceX Starship flights Can use Space Tether to Save Fuel”

  1. A big issue is, by the time we’ve advanced materials to build tethers and or space elevators, we’d of advanced rockets an equal number of decades.

  2. A few years ago i was investigating space/skyhooks concept. The biggest questions was how to recover/maintain the momentum lost. One that is already in orbit are all defunct satellites. Decelerating those into our atmosphere would give some boost/deltav. But this is a limited and quite inconvenient resource.

    We will need to go a few steps further and use a system of solar sales, magnetic boosters (the same tether can be uses to bounce of the earth’s magnetic field) or even a sort of tidal-force accelerators. This system would allow reactionless (low reaction mass) boost.

    • As long as there is traffic in both directions, the tethers can just reuse momentum and save fuel both for acceleration and deceleration. A moon colony will have to make frequent return trips and hopefully also export water and fuel to LEO so there will be plenty of mass going in both directions.
      For Mars, probably just returning passenger ships.

  3. To” peter john: I agree. Like so many technologies, they are facilitated by economic factors. When the volume of space traffic reaches a “psychological tipping point”, when enough people with money and power realize they can make more by “doing space”, that’s when the nature of our reality will change. Hang on tight kids, it may not always be fun, but I doubt it will be boring.

Comments are closed.