| - The red vines represent one way free delta vee rides via aerobraking. Delta vee distances are in kilometers/second. I've recently (April 28, 2013) drawn a 2nd cartoon delta V map, this one with an emphasis on EML1 and EML2. - On the right is 5261 Eureka, a Martian Trojan. This asteroid lies in Mars' orbit trailing Mars by 60 degrees. Although it's the same distance as Mars and the Martian moons Phobos and Deimos, note the martian moons are closer in terms of delta vee. This is because of the Oberth effect. Small bodies are more easily reachable in terms of delta vee because of their shallow gravity wells. And, oddly enough, small bodies orbiting a steep gravity well are even more accessible. In addition to the Oberth effect, planets can shed delta vee via aerobraking. - In terms of delta vee, the Martian moons Phobos and Deimos are closer than the Moon, Mars and most Near Earth Asteroids. Their low density suggest they may be volatile rich. If so, their volatiles could be exported to the Earth Moon L1 point and other locations in near Earth space. - What I call Low Mars orbit is a circular equatorial orbit 300 kilometers above the Martian surface. - Mars Capture Orbit has a 300 kilometer altitude periapsis (the orbit's closest point to Mars) and a 570,000 kilometer altitude apoapsis (the orbit's farthest point from Mars). When an object in this orbit reaches periapsis, it is going very nearly the surface escape velocity of Mars. This maximizes the advantage of the Oberth effect. Mars capture orbits can be easily reached from the Earth-Mars Hohmann transfer orbit. The Hohmann is rarely accessible to a specific Mars capture orbit, though (The orbit periapsis would have to be in the right position at the right time). - Earth Capture Orbit has a 300 kilometer altitude periapsis and a 900,000 kilometer altitude apoapsis. Like the Mars Capture Orbit, this orbit maximizes the Oberth effect. Earth capture orbits are very easily reachable from both the Mars and Venus Hohmann orbits. But also like the Mars Capture Orbit, the Hohmann orbits are not easily reachable from a specific capture orbit unless its periapsis is at the right time and place. - The Earth-Mars Hohmann orbit is a minimum energy path from the Earth to Mars. Launch windows for these orbits occur about every 2 1/8 years. The trip takes about 7 months. - The Earth-Moon L4 and L5 points are stable Lagrange points on the Moons orbit, leading and trailing the moon by 60 degrees. The Earth-Moon Lagrange points are locations where the Moon's gravity, the Earth's gravity and centrifugal force all balance. - The Earth-Moon L1 point is a Lagrange point between the Earth and the Moon. It hovers above a fixed point on the Moon's surface. A lunar mass driver aimed at the L1 will remain aimed at that point 365 days a year, 24 hours a day. Lunar oxygen, silicon and other materials could be exported to that point. L1 moves slower than a natural orbit at that altitude (.86 vs 1.1 km/sec), so it's easier to export cargo from the L1 to lower earth orbits. In terms of delta vee, the Lagrange points are close to each other as well as close to the Mars and Venus Hohmann transfer orbits. Much of my interest in the L1 is due to an essay Rand Simberg wrote. - The Earth-Venus Hohmann is the minimum energy path from Earth to Venus. It requires a little less delta vee than the Mars Hohmann. The trip takes about 5 months. The period of this orbit is very close to .8 years. The Earth-Venus synodic period is very close to 1.6 years, almost exactly twice the period of the Hohmann orbit. This makes a system of five Earth-to-Venus cyclers possible. The Earth encounter points are at the tips of a beautiful, slowly rotating, five pointed star. See The Case For Venus for more details. - The Venus Capture Orbits have a 300 kilometer periapsis and a 600,000 kilometer apoapsis. Like the Earth and Mars capture orbits, this orbit maximizes the Oberth delta vee savings. Via aerobraking, these orbits can be made into what I call Highly Eccentric Elliptical Venus Orbits. - The Highly Eccentric Elliptical Venus Orbits have a 300 kilometer periapsis and a 68,000 kilometer apoapsis. I believe five of these orbits could be arranged to receive cargo and passengers from Earth to Venus cyclers. Five more could be arranged for Venus to Earth cyclers. These orbital period of a HEEVO is 2/5 the period of a High Venus Orbit. In terms of delta vee, objects on HEEVOs could be some of the most accessible in the solar system. - High Venus Orbit is a circular orbit at 68,000 kilometer altitude. This orbit is resonant with the HEEVO orbits and could pass by each HEEVO at apoapsis. This orbit could be used to transfer passengers from one HEEVO to another. - Venus hasn't even been on my radar screen for years due to it's hostile surface. Because of aerobraking and the Oberth effect, near Venus asteroids can be captured to Venus' orbit with relatively little delta vee. Once captured they're more accessible from Earth than most NEOs. Please see The Case For Venus. Geoffrey Landis has also pointed out Venus has a hospitable temperature and pressure 50 kilometers above it's surface (although the sulfuric acid clouds are a problem) and suggested floating cities at that altitude. My delta vee map above adds a 2 kilometer/second atmospheric drag/gravity penalty for ascending through Venus' atmosphere. This is based on ascension from a floating Landis city. Ascending from Venus' actual surface would incur a higher penalty. - 2003 SM84 is a near Earth Asteroid with a low inclination, eccentricity, and a semi major axis close to 1 A.U. In other words it has an Earth-like orbit. Such asteroids can be very close in terms of delta vee. Unfortunately, low energy launch opportunities are rare if the asteroid doesn't have an earth resonant period. For example an asteroid with a 3/2 year period can pass near the Earth every three years, or an asteroid with an 5/4 year period can fly by the earth every 5 years. SM84's period isn't a simple fraction of earth's period. It will have a good launch window in 2052. Please see my page The Case For Asteroids. - What I call Low Earth Orbit is an equatorial circular orbit 300 kilometers above the earth's surface. - |