| < The costs of propulsion > |
| In the near future, the International Space Station ISS will be equipped with a newly developed electro-magnetic thruster based on ionized argon heated to about one million degrees (at this range of temperatures it makes no difference if °K or °C). The charged particles will leave the nozzle at velocities of up to 50 km/s. This Variable Specific Impulse Magnetoplasma Rocket VASIMR would reach (with some patience) higher velocities than conventional drives. More importantly, it is hoped to cut down fuel costs by a factor 10-20. |
| While argon is one of the cheapest fuels in space (both Earthen and Martian atmospheres contain about 1%), the system has its drawbacks. (1) It operates only in vacuo; (2) a whole lotta heat has to be dissipated; and (3) it needs superconducting electromagnets and (4) more electric power than the humble 200 kW the ISS can presently offer. The last problem will be solved with batteries allowing an operation duration of 15 min, sufficient for occasional thrusts to maintain the station's altitude. |
| Also my plant-populated space traveller will need some kind of propulsion for occasional orbit corrections or meteor avoidance manœuvres. Given the drawbacks listed above, I wonder if VASIMR would be appropriate for this purpose. Since for most of its time the station would be out of reach from Earth, it would be unwise to depend on liquid nitrogen to cool superconducting magnets. Also the supply with energy will be lower for most of the time, because of the greater distance from the sun on its orbit between Earth and Mars. |
| For the sake of simplicity, propulsion could rely on conventional miniature jet engines as offered for model aircrafts or race cars. If the output of energy and heat is moderate enough, such a small jet engine could be placed at the interface between a 3-m-sphere and a connected 8-m-balloon, allowing to direct the flame into the interior of the (empty) balloon. If the engine was powered by a mixture of hydrogen and oxygen, the resulting water would condense inside the balloon and thus would not be lost to space. |
| If the total volume of the station was large enough, temperature might be held down during the short periods of firing by directed convection. It remains to be seen, however, whether such a closed ensemble would move at all, for physical reasons: the burning reaction gases will exert force in the desired direction, but you may object that this is only the case, because they can leave the chamber at the other (open) side. But if they get trapped in the balloon, they probably would exert the same force at the balloon's facing wall, and the resulting total would only blow up the whole system, without any net translocation. |
| I, however, would argue that the balloon's facing wall is too far away. The exhaust jet would finally end up in some turbulence (and heat) in the middle of the balloon, and its constituent particles will, then, have forgotten about any preferred direction (so to say: Boltzmann overrules Newton). Of course, it would be wise to test such a propulsion first on Earth before realizing in space that something went wrong. The big advantage of this principle would be the closed system: All you need is water and some means to dissociate it into hydrogen and oxygen. |
| This dissociation could be done electrolytically (as is done actually on the ISS), but we could also - again - use organisms. There are skilful microorganisms knowing how to split water with the use of sunlight, releasing gaseous hydrogen and oxygen. All you have to do is to collect this valuable gases (at the ISS, hydrogen is vented into space - what a pity...) and to feed your mini jet engines with it. If this works, our station would be autarc also in terms of (moderate) propulsion. |
| The
mini jet engines could be installed in the most inner balloons, where
photosynthesis does not make sense anymore due to darkness. This would
provide some valuable purpose also to these more shady districts. Other
uses for these darker balloons might be: a swimming pool; a biological
toilet; a human running wheel; and what ever we might think of. All we still are waiting for is an efficient absorbant for storage and transport of hydrogen gas. |
| MB 8/13 |
| Pokrant S (2020) An almost perfectly efficient light-activated catalyst for producing hydrogen from water. Nature 581: 386-88 |
| next: Shielding back to: A 4-years shift on Hohmann's overview |
