Yup, it’s scary. “A moderate-sized nuclear device was estimated, at the time, to produce about 5 or 10 billion horsepower.” https://en.m.wikipedia.org/wiki/Project_Orion_(nuclear_propu...
George Dyson (Freeman's brother) wrote a book on it that is fantastic reading.
The Project Orion design (shoot hundreds of fission bombs out the back and ride the shock wave on a reaction plate) is surprisingly practical, and probably our only way to get humans past Mars. It's just kind of terrifying.
The energy required to accelerate a useful amount of mass to a high enough velocity to travel interplanetary (or interstellar) distances in a timely manner is always going to be terrifying. Even if it runs on rainbows and hugs the kinetic energy imparted to the payload would turn it into a planet killer if you ever rammed it into one. Managing that risk so you get the payoff without any accidents along the way is the…
Not building the ship of thousands of little nukelets IS managing risk.
That's not quite what I'm picturing (and let's be honest, the idea is silly). That page describes capturing the heat of a nuclear reactor, converting it to electricity, and then using that electricity to force ions out of a thruster. I'm saying, the radiation itself has momentum; don't bother with the contraption.
AFAIK, the only nuclear rocket that makes sense is landing a reactor on an icy comet and using it to shoot super heated steam wherever you want thrust. #seveneves
The Project Orion design (shoot hundreds of fission bombs out the back and ride the shock wave on a reaction plate) is surprisingly practical, and probably our only way to get humans past Mars. It's just kind of terrifying.
Should also note that the Orion design most people are familiar with is from the 60s, when the latest in engineering used vacuum tubes. Modern innovations in material science, computer assisted design, and just technology that just simply didn't exist yet such as laser ignition would permit ditching the ridiculous pogo stick pusher plate arrangement with something that's more efficient, runs smoother, and looks a lot more traditional too. I wouldn't be surprised if a modern variant looks like that one Sea Dragon concept with beefier nozzle suspension
First, you have a way to store an absurd quantity of positrons. For a sense of scale, without shielding the electric fields, 1 picogram of positrons (or electrons) confined within a 10 cm radius is going to trigger positron-electron pairs formation, thanks to free electrons in the area responding to the surface potential. Second, AFAICT if you can do that then you're either going to want to use them as an energy sour…
I proposed nickel-63 for my electron source. Let's say, aluminum-26?
And, yes. The idea is patently absurd. But I'm waiting on a ridiculously long compile.
Shooting just electrons out the back of your ship is fine for the brief period before your ship gains a positive electric potential comparable to the net potential those electrons experience due to the inside of the particle accelerator you were using, after which your ship's own field is a major source of drag. If your ship has a positive electric potential of over 1.044 MeV[0], you also start getting positron-elect…
Don't ionic thrusters typically solve this problem by also emitting oppositely charged particles from a thin rod behind the motor? Maybe that still causes drag, but overall the main problem is that while the ISP is high, the thrust is almost non-existent.
They do indeed; the oppositely charged particles being electrons. But there's no charged particles lighter than an electron, and the only one with the same mass is the positron. If you try to balance it with protons, then what you've really got is a slightly over-complicated hydrogen-based ion drive.
First, you have a way to store an absurd quantity of positrons. For a sense of scale, without shielding the electric fields, 1 picogram of positrons (or electrons) confined within a 10 cm radius is going to trigger positron-electron pairs formation, thanks to free electrons in the area responding to the surface potential. Second, AFAICT if you can do that then you're either going to want to use them as an energy sour…
I proposed nickel-63 for my electron source. Let's say, aluminum-26? And, yes. The idea is patently absurd. But I'm waiting on a ridiculously long compile.
If you're getting them from radioactive decay, it works, but those examples are 63 and 26 times heavier than just using hydrogen as your reaction mass in the first place :)
The sun is a giant fusion reactor known to cause cancer on a good day, and emit radiation bursts that can damage or disrupt power grids often enough that people can reasonably expect to read reports of them more than once in their lifetimes.
That's a useful analysis. Nuclear power gives you more energy, but you're still limited by how much reaction mass you can carry. The plans that work look like early 1960s NASA plans - build infrastructure in orbit, assemble nuclear power interplanetary craft in orbit, nuclear power is from planetary orbit to planetary orbit only. That was Wernher von Braun's "Man Will Conquer Space Soon" plan.[1] The Apollo program,…
It makes you wonder though, should you set up such space based infrastructure, is it even worth publicizing lest you trigger an arms race?
You couldnt do it without publicizing. Space stuff is big and loud. Space itself is transparent. Doing big secret stuff in space is extrodinarily difficult.