The Tyranny of the Rocket Equation (2012)
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Re: The Tyranny of the Rocket Equation (2012)
#2>Currently, all our human rated rocket engines use chemical reactions (combustion of a fuel and oxidizer) to produce the energy.
Yes, however, for completeness: an explanation of why we must limit designs to chemical rockets ought to include an explanation of why the dozen or so fusion projects underway around the world will all fail, i.e. let's inject some rational optimism. Note that the Apollo programme began before its tech was ready.
Re: The Tyranny of the Rocket Equation (2012)
#3> In the 1970’s, an experimental nuclear thermal rocket engine gave an energy equivalent of 8.3 km/s. This engine used a nuclear reactor as the source of energy and hydrogen as the propellant.
That was intriguing, but didn't go into detail on why a nuclear thermal rocket hasn't been tried since. The obvious explanation is that there could be serious consequences if such a rocket exploded, spreading radioactive material, etc. And rockets tend to explode sometimes. However, it sounds like while that is certainly a concern, it is not as great of one as it might seem:
http://en.wikipedia.org/wiki/Nuclear_thermal_rocket#Risks
And indeed there is still work ongoing on such designs.
Re: The Tyranny of the Rocket Equation (2012)
#4The soda can analogy is horrifyingly informative. I wonder what kind of efficiencies could be obtained with semi-science-fiction fuels like the Orion nuclear-explosion propulsion system (which is different from a nuclear rocket) or even straight-up antimatter.
en.wikipedia.org/wiki/Project_Orion_a(nuclear_propulsion)
Re: The Tyranny of the Rocket Equation (2012)
#5Fascinating read. Are there more blog-type posts like this from NASA? I'd be interested in reading more but I can't seem to find them from the main page and can't find links to these posts...
Re: The Tyranny of the Rocket Equation (2012)
#6Lest you despair of ever making space flight routine, a rocket is not the only way to get into orbit.
Virtually all of the needed velocity is tangent to the surface, not away from it. So you can accelerate the vehicle along the ground at least part of the way, and only then turn heavenward and burn fuel to get into orbit. With this boost you significantly reduce the amount of fuel needed.
There are many way of doing this. You can have magnetic propulsion (very futuristic and powerful), you can have a simple motor on the vehicle, powered by contact with rails on the ground (but motors have a limit of how fast they can work). You could have fuel "guns" fired into the back of the vehicle as it passes them, which would then capture the container and burn them as a normal rocket would. This has the benefit of not requiring a large rail, just fuel stations that the rocket would pass over.
These are just some basic ideas, there are many more.
Re: The Tyranny of the Rocket Equation (2012)
#7"If our planet was 50% larger in diameter, we would not be able to venture into space, at least using rockets for transport."
Don't tell hollywood.
Re: The Tyranny of the Rocket Equation (2012)
#8the rocket equation with fusion engine expelling alpha-particles at 0.05c doesn't look that bad, and at least it is good enough for Solar system colonization and for sending a probe to the closest star.
Re: The Tyranny of the Rocket Equation (2012)
#9[deleted]
Re: The Tyranny of the Rocket Equation (2012)
#10> In the 1970’s, an experimental nuclear thermal rocket engine gave an energy equivalent of 8.3 km/s. This engine used a nuclear reactor as the source of energy and hydrogen as the propellant. That was intriguing, but didn't go into detail on why a nuclear thermal rocket hasn't been tried since. The obvious explanation is that there could be serious consequences if such a rocket exploded, spreading radioactive materi…
> And rockets tend to explode sometimes.
Chemical rockets -- the only ones we've ever actually used -- explode because that's what they're intended to do. The only difference between a successful rocket firing and a catastrophic rocket failure is the speed at which the explosion happens. A nuclear rocket engine has basically no risk of explosion; tearing itself apart at speed maybe, if the aerodynamics aren't done properly or there's a structural weakness. But that's about it.