3 ms·

The fact that the abstract does not mention laser driven sails, the currently most viable approach to relativistic propulsion (ie, the current breakthrough star

The fact that the abstract does not mention laser driven sails, the currently most viable approach to relativistic propulsion (ie, the current breakthrough starshot plan), does not give me much hope in this researchers credibility in the rest of the paper. Furthermore, the performance of this engine is abismal. To put it into perspective,a modest ion engine would produce about a million times more thrust per power. While the ion engine of course requires carrying fuel, and is thus governed by the tyranny of the rocket equation and not directly comparable in performance, this engine still requires a power source and thus effectively requires fuel anyway. Also worth mentioning is that the least efficient possible massless thruster, a simple blackbody radiator with reflector to aim all of the photons behind you, is only about 1000x worse than this unit in terms of propulsion force per power, and essentially infinitely better than the unit in terms of propulsion force per mass, since this structure is incredibly massive where as you can usually generate blackbody radiation directly from you power source.

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vidarh 7y ago
The author is Robert M. Zubrin. To write it off because the abstract doesn't mention a specific technique seems a bit silly, especially given that Zubrin personally knows a lot of the people involved in Breakthrough Starshot and surely is aware of it, including its massive caveats. It's worth noting that the paper specifically discusses the need for methods that are not limited in travel direction, and in that respect Breakthrough Starshot has the same caveats as a solar sail and so treating laser driven propulsion separately is pointless. Another major difference that is so obvious as to not require a mention of every specific alternative is that it is talking about a propulsion method that avoids the need for us to provide a source of thrust. Laser driven systems doesn't require the ship to carry propellant, but we're still paying the cost to provide thrust, while this design is basically 'just' relying on there being a source of protons and electrons with a speed differential relative to the current speed and direction of travel of the ship that it can 'scoop up'. That makes for fundamentally different tradeoffs relative to classical sail based propulsion.
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choeger 7y ago
> Furthermore, the performance of this engine is abismal. To put it into perspective,a modest ion engine would produce about a million times more thrust per power. Would it, though? The proposal mentions 14mN/kW. What ion engine produces 14N/W ? I think that such an engine would be a massive improvement of current designs. VASIMIR, for instance, is designed with 1N/14kW.

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vidarh 7y ago

The author is Robert M. Zubrin. To write it off because the abstract doesn't mention a specific technique seems a bit silly, especially given that Zubrin personally knows a lot of the people involved in Breakthrough Starshot and surely is aware of it, including its massive caveats. It's worth noting that the paper specifically discusses the need for methods that are not limited in travel direction, and in that respect Breakthrough Starshot has the same caveats as a solar sail and so treating laser driven propulsion separately is pointless. Another major difference that is so obvious as to not require a mention of every specific alternative is that it is talking about a propulsion method that avoids the need for us to provide a source of thrust. Laser driven systems doesn't require the ship to carry propellant, but we're still paying the cost to provide thrust, while this design is basically 'just' relying on there being a source of protons and electrons with a speed differential relative to the current speed and direction of travel of the ship that it can 'scoop up'. That makes for fundamentally different tradeoffs relative to classical sail based propulsion.

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choeger 7y ago

> Furthermore, the performance of this engine is abismal. To put it into perspective,a modest ion engine would produce about a million times more thrust per power. Would it, though? The proposal mentions 14mN/kW. What ion engine produces 14N/W ? I think that such an engine would be a massive improvement of current designs. VASIMIR, for instance, is designed with 1N/14kW.