There is one main reason why it’s much cheaper to move cargo with a jet engine than with a rocket engine. It’s because a jet engine is able to gather mass from the air for its mass-reaction that moves the aircraft forward. The fuel drives the process, but it’s all that air screaming through the jet engine that forms the fundamental reaction pair with the aircraft. In other words, do you remember from sixth-grade science class that every action has an equal and opposite reaction? For a jet plane, that means that the mass of the aircraft is essentially pushed forward by pushing a mass of air in the opposite direction. That pushing is done by the jet engine, which works through the energy stored in the jet fuel.
On the other hand, a rocket can’t gather air for the mass-reaction, because it’s in space, so it uses the mass in the rocket fuel to push in the opposite direction as the rocket’s flight. That works fine of course, since there is no air in space to gather and push out for the mass reaction. But it’s a very expensive (and thus slow) way to move the rocket, because that valuable rocket fuel is reacted and fired out the back. I liken it to pushing oneself across a frozen pond by hurling gold bars through the ice. Yeah, it will get you across the ice if there is no other way, but a less expensive way would be to gather blocks of ice, or water, or snow and throw those to get the mass reaction pair.
So, how do we find mass in space the way we find air in the atmosphere? It turns out there is a little bit of mass, within the confines in the solar system, about one molecule per cubic centimeter. This is an average, composed of things like dust, tiny bits of ice, or molecules made of things like hydrogen or helium. Stick a sufficiently large funnel on the front of a boat, and you’ll be able to gather tiny bits of mass, but would it be enough? Lessee … say the funnel can gather 1,000 cubic meters of space per second. (That seems a reasonable thing to build, and it gets easier as the funnel — and the boat to which it is attached — moves faster, but consider the 1,000 cubic meters per second as an average. So that’s 1×10^9 cubic centimeters, and thus 1×10^9 molecules, say each one has an average mass of about 3×10^-18 kg. That’s not too much. How much?
First, let’s get a handle on the speed of those hydrogen molecules if we use our fuel to heat up the molecules to say 4,000 Kelvin, and then use the root mean square velocity of those hydrogen molecules (with mass about 2 amu each), we’re looking at about 4,000 meters per second, very much non-relativistic. Just using a straight momentum conservation, with say a boat of 10,000 kilograms that would impart a maximum velocity of about 1×10^-18 m/s. That’s considerably slower than the rate of erosion of bedrock. Sure, we could gather a lot more molecules, just circling the solar system somewhere between two planet’s orbits, building speed. (And of course we would need some really good Gaussian shielding to protect the boat as it reaches higher speeds and becomes endangered from things too big for us to handle at speed, like a grain of sand, or a chunk of ice.) But it seems like a dogshit way to get anywhere. No wonder the boring Space Force uses rockets. They suck, but they’re the only game in town.
And then that’s when things start getting dicey. Because this is when the weird science comes out, and people start echoing the nuances of science fiction television shows like Star Wars with Captain Kirk and that giant gorilla guy, Chewbacca, hanging out in spaceships that go fast. Real life isn’t like that … we have established means of production. There are things that we can and cannot make with the means of production and characterization that are actually available to us.
Fundamentally, if we want Space Force 7 tourist boats to “zip across the galaxy” like Robbie Ronzoni puts, then we need a better method of locomotion. We don’t have the deep pockets at Space Force 7 to use rockets or even ion generators. We need to gather our mass for our reaction pair in space, because we can’t afford to bring it from home. So where do we get mass?
We might be able to get it from the sea of low-temperature Bosons in space itself, that exist with an energy somewhere around 3 Kelvin. We can use our fuel to raise the temperature of these bosons, but they are integral spin particles, with an even number of quarks, and thus they can’t be used for mass-reactions without taking on an additional quark. So, can we find materials and methods to interact weakly with energy and convert integral-spin particles into half-spin particles? If we could do that at will, just guide a shit-ton of bosons through our weakly-interacting device, and convert some of that energy back to mass, and do so economically, then we can potentially gather our mass for the reaction-pair in space itself. But in doing that, we’re definitely decreasing the entropy of the boson-fermion system, since we’re essentially asking the universe to allow us to convert three quark Bosons of say (UD + UD + UD) into a Fermion of say a neutron-proton pair of (DDU + UUD). We can do that, but the entropy has been reduced from (UD + UD + UD) to (DDU + UUD), because the disorder of the quark system has been reduced. We can potentially provide the work to reduce that entropy from the energy in our fuel, and then use a bit more energy to heat up these particles for the mass-reaction pair. But unlike gathering stray hydrogen molecules, we can gather most any Boson that is above the ground state energy, and there should be a lot of those, a helluva lot more than just a few per cubic centimeter. True, we have to do work to lower the entropy of the quark system, which we don’t have to do when we gather molecules, but at least the Boson flux is apparently sufficient for us to get our tourist boats to some lovely locations and back in an afternoon. The whole idea of sending people into space for the rest of their lives is a money loser. Nobody is going to want to buy a ticket on a tourist boat like that, and we don’t want to make boats that don’t return in a lifetime.
If we can find a way to interact weakly, and control that, we have a shot at making efficient engines for our line of family-fun and family-friendly tourist boats. (As mentioned before, we’ll also need to get the Gaussian shielding to work reliably, we can’t have any more of our boats getting blown to smithereens just because they impacted with a grain of ice the size of a pinhead.)
Okay, weakly interacting. There was some traction perhaps about fifteen years ago with some “blue sky research” at Pirelli in Milan, where Luca Gamberale and Flavio Fontana supposedly found a possible way to use sapphire crystals under a modulated and highly unstable pressure gradient to show significantly increased interaction potential with neutrinos. They were using it for communication and they had apparently been working on it since at least the mid 1990s, where I first ran across this type of weak interaction while in the New South Wales State Library in Sydney.
Regardless Pirelli, this does seem a tractable problem, at least not much in physics screams out that it’s impossible to perform this kind of “subatomic chemistry” in some way. We’ll need a kind of “temporary explosion” to add sufficient work to counter the entropy gradient from Bosons to Fermions, and then add some energy to the resultants so that they are warm enough to use.
I like the idea of Pirelli leading our way to affordable and fun tourist space boats. That’s a stylish company, Pirelli. Calendar girls? Wrestling in body lotion? Lloyd Cole? Good market synergy.