Much appreciated, and a good report, Jared! Glad I'm not totally off-the-wall. -- Joe From: Jared Smith <jared@smithplanet.com> To: Utah Astronomy <utah-astronomy@mailman.xmission.com> Sent: Thursday, February 26, 2015 10:40 PM Subject: Re: [Utah-astronomy] Last night's lecture There are a primarily two viable types of orbits that would support this. The first are called cycler or VISIT (Versatile International Station for Interplanetary Transport) orbits. With a heliocentric orbital period of 1.25 years and a semi-major axis of 1.16 AU you could have "close" (see below) encounters with Earth once every five years and with Mars once every 3.75 years. Alternatively, an orbit of 1.5 years and a semi-major axis of 1.31 AU can result in Earth encounters once every three years and Mars encounters once every 7.5 years. Neither alone works particularly well for manned missions. With one vehicle in each orbit type (one to take you there and another to bring you home), you'd still be looking at no less than 5 year round trip missions. Once the vehicles are launched to orbit, they would require almost no fuel to maintain the orbits. The primary difficulty with a heliocentric orbit that is resonant or cyclical (i.e., on a regular cycle) is that you can't get too close to either planet or the gravity-assist throws everything out of whack. This requires some significant ΔV near each planet to either get from the station to the planet or from the planet to the station. Most Earth approaches would be well outside the moon's orbit with approach speeds around 4 km/s. The second and more generally accepted type of orbit utilizes planetary gravity assists and are usually called UP/DOWN Escalator Orbits. In the case of Mars, it's called the "Aldrin Cycler" after Buzz who proposed the idea. This type gets a vehicle to Mars in ~6 months, spends 16 months beyond Mars orbit, then re-encounters Mars for a ~6 month transfer back to Earth. With two vehicles, you could do repeated ~2 year missions - 6 months there, one year on Mars, and 6 months back. This second type gets you very close to the planet, but these orbits require more fuel to get started and notable (though not impossible with current technologies) trajectory adjustments every few orbits. Because the planet approaches are very close, they have very high approach speeds, especially at Mars (often over 11km/s - see Brent's wonderful post to get an idea of how many Saturn V's it would take to stop there). In short, there are orbits that do what Joe suggested, but both require fuel requirements well beyond our current capabilities if you want to stop anywhere along the way. There are many variations on these two orbit types that could make them more feasible for a manned Mars mission, but most require several vehicles to get the mission duration below a couple years. Additional reading: - http://courses.ae.utexas.edu/ase333t/past_projects/04spring/Cycler%20Website... - https://engineering.purdue.edu/people/james.m.longuski.1/ConferencePapersPre... - https://en.wikipedia.org/wiki/Mars_cycler - http://buzzaldrin.com/files/pdf/2002.AIAA_PAPER.Analysis_of_a_Broad_Class_of... - https://engineering.purdue.edu/people/james.m.longuski.1/ConferencePapersPre... Jared _______________________________________________ Utah-Astronomy mailing list http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy Send messages to the list to Utah-Astronomy@mailman.xmission.com The Utah-Astronomy mailing list is not affiliated with any astronomy club. To unsubscribe go to: http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy Then enter your email address in the space provided and click on "Unsubscribe or edit options".