Getting to Mars with PDF Propellent

What's the ISP of PDF? Unfortunately, PDF isn't actually a propellent, it's a publication format. Too bad, because there is a lot of it floating around the web. This bizarre thought was triggered by yet another "humans to Mars" study that I hadn't seen before, this one by the European Space Agency (thanks for the link, Andy). It's quite an interesting study. Here's a link to it, and a few more you might find interesting. Of course a Google search will turn up even more, and if you want to keep your search within NASA sites, you can always add the qualifier site:nasa.gov to your Google search string. All links below are PDF files.

• HMM Study: ESA Human Mission to Mars, executive summary
• Mars Direct by Robert Zubrin et al (1991 AIAA paper, the original - more Zubrin works here)
• MarsDrive Reference Mission, "Mars for Less"
• Mars Direct Project for Orbiter (project planning document)
• Mars Surface Reference Mission (NASA 2001, 114 page PDF, quite detailed, see also this)