# Monthly Archives: February 2010

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 … Continue reading

Posted in Rocket Design Theory | 62 Comments

## Using Payload Fraction Expressions in an Example

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. … Continue reading

Posted in Rocket Design Theory | 47 Comments

## Calculating Gross-Mass-Sensitive Term

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 initial-mass-sensitive term (phi). In so doing, I will hopefully be … Continue reading

Posted in Rocket Design Theory | 4 Comments

## The Meaning of “Characteristic Velocity” for Tethers

On my earlier post where I first showed the Moravec mass ratio, I introduced the concept of the “characteristic velocity” of a material, without making any attempt to explain what, if anything, this might mean. When I first read about … Continue reading

## Calculating Propellant-Mass-Sensitive Term

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 … Continue reading

Posted in Rocket Design Theory | 5 Comments

## Payload Fraction Accounting for Gross-Mass-Sensitive Term

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 … Continue reading

Posted in Rocket Design Theory | 2 Comments

## A Simple Modification of the Rocket Equation

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 … Continue reading

Posted in Rocket Design Theory | 12 Comments

## MHD Aerobraking and Thermal Protection Part III: Aerobraking and Aerocapture

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.Â  There is another application though, where exploiting magnet-hydrodynamic effects could be a much bigger … Continue reading

## Recursive Algorithm for Moravec’s Mass Ratio

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 … Continue reading

Posted in Space Tethers, Space Transportation, Technology | 9 Comments

## Momentum Exchange Tethers — Early History

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 … Continue reading

Posted in Space Tethers, Space Transportation, Technology | 5 Comments