Thrust Tubes

The ‘thrust tube’ has been the primary form of engine used in space craft in my Jack Mack novels. I have gone into very little detail of how they work, nor is it necessary to know. A bit of information is dropped here and there, such as that their workings are related to the super-heavy element technology used in many roles, or that their fuel is ‘inert,’ and that there are gravity fields involved. I am unlikely to go into any of it much deeper, but may drop the occasional detail. That’s how we make it more real.

By making my lead character a bit of a technophobe, I have an excuse not to say too much, anyway. I did mention that ion drives were still used by freighters that did not require a more sophisticated—and costly—propulsion system.

The simplest form of thrust tube is the steady-tube, commonly referred to as an onoff. In other words, it is either on, delivering full power, or off. This certainly can work but is far from ideal for most craft. Onoffs are most typically used for large freighters, typically with an array of tubes that can be sequentially switched. They are also used for small-scale propulsion at times, hand-held devices, probes, couriers, even torpedoes.

If the steady tube is switched on and off rapidly it becomes, in essence, a pulse-tube. A truly practical pulse-tube was a goal that had only been achieved shortly before the period when the Jack Mack stories are set. More on that, but first, the variable-tube, or varitube.

The varitube was the go-to drive for most craft for some some centuries. It allowed power to be increased or decreased smoothly, by varying fuel supply (using the term ‘fuel’ very loosely here). This was not as efficient as an onoff, nor did it allow the same power to be generated. However, it was the best choice available. Varitubes continued to be used in many roles, especially civil craft, air cars, and so on. They were also favored by some for maneuvering tubes in craft with pulse-tube main drives.

Why for maneuvering tubes? Because these were often a single tube, and prone to the vibration problems that had hindered pulse-tube development. The best solution for some time was to attempt to synchronize multiple-tube engines to cancel out the vibrations. Some large ships used big arrays of small pulse-tubes that allowed random firing to even things out. These solutions worked, in their fashion, but were not suited to a typical small craft.

So along came Davi Jager, an engineer and inventor in the Corvan sphere, who developed a new pulse-tube design, capable of operating nearly as smoothly as a varitube. Its operation was more efficient; simply increasing the speed of its on-off cycle allowed it to work at its ideal fuel ratio at all times. In conjunction with the Nativ company, Jager founded Corvanaut, and his design—and those based on it—soon spread through human space. With small improvements, to be sure, but his was the big step forward.

Multi-tube engines still tended to be favored for dampening vibration, but the new pulse-tubes were quite usable in single and double tube engines. We have the Riley engines built by the McFee Concern using this technology. Indeed, pretty much every military ship mentioned in the novels has pulse-tubes. Those I might explore some other time.

None of this is the sort of thing I’m likely to explain in any detail in the books. An occasional hint is enough. But I might drop in a bit of this world building here, now and again. I might even explain why one can safely stand behind a thrust tube. 😉