Selenian Boondocks

Continuing with our story from last time…
The next day, your boss pokes his head in your office and asks:
“How’s those forty trans-Mars injection stages going?”
He notices that you’re checking out scuba-dive sites in the Caribbean for your upcoming vacation with your feet up on the desk, and comes into the room with the blood rising [...]

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Now that I’ve gotten the math and derivations out of the way, let’s us the payload fraction expressions in a real-world example.

Let’s say you work for the chief technologist of NASA, and he’s thinking about sending humans to Mars. He’s considering whether or not to invest in a seemingly-promising new technology: nuclear thermal propulsion. [...]

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In the last post, I attempted to calculate a basic expression for the propellant-mass-sensitive term (lambda) and in this one I will attempt to do the same thing for the gross-mass-sensitive term (phi). In so doing, I will hopefully be able to show how a number of key factors in the rocket design affect [...]

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In my last two posts I’ve been talking about calculating payload fraction of a rocket using the mass ratio from the rocket equation and some vehicle parameters that have been sensitive to propellant mass and gross mass. To use these parameters successfully, it would be helpful to have some idea what they should be [...]

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As I prepared for this post tonight, I realized that I wasn’t really modifying the rocket equation at all–I have been using the rocket equation and a summation of mass terms to find the payload fraction, which I consider an especially useful value to know.
Furthermore, if you read my previous post, you probably figured out [...]

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When I was an undergrad, I spent two summers interning on the X-33 program at the Lockheed Martin Skunk Works in Palmdale, California. It was a fantastic experience and I got to meet with and work with some wonderful people on a very exciting program. Plus I got to live in the Mojave [...]

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While using electromagnetic effects for atmospheric reentry and thermal protection is interesting, it’s only one of several promising options that have been proposed over the years.  There is another application though, where exploiting magnet-hydrodynamic effects could be a much bigger “game changer” — aerobraking and aerocapture for reusable in-space vehicles.
Traditional Aerobraking and Aerocapture
One of the [...]

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Computing the mass ratio for a tapered tether (tether mass/tip mass) was first done (to the best of my knowledge) by Hans Moravec in an appendix to his unpublished 1978 paper, “Non-Synchronous Orbital Skyhooks for the Moon and Mars with Conventional Materials.”
The expression uses the Gaussian error function, erf(x), which is not typically available in [...]

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The history of momentum-exchange tethers goes back many, many years but is bound by a common thread that, until recently, limited the realization of this technology. That common thread is the need for high specific tensile strength.
The first idea of concept of a tether dates back to the imagination of Konstantin Tsiolkovsky, the Russian [...]

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Rotating momentum-exchange tethers are a very exciting technology, but one of my first thoughts after being exposed to the technology was the tricky rendezvous. The space industry has spent all kinds of money and time on satellite rendezvous, and these are typically slow, long, drawn-out affairs with two satellites in almost precisely identical orbits, [...]

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