Mars cycler
Cyclers are potentially useful for transporting people or materials between those bodies using minimal propellant (relying on gravity-assist flybys for most trajectory changes) and can carry heavy radiation shielding to protect people in transit from cosmic rays and solar storms.
A cycler is a trajectory that encounters two or more bodies regularly.
[2] A Martian year is 1.8808 Earth years, so Mars makes eight orbits of the Sun in about the same time as Earth makes 15.
Cycler trajectories between Earth and Mars occur in whole-number multiples of the synodic period between the two planets, which is about 2.135 Earth years.
[3] In 1985, Buzz Aldrin presented an extension of his earlier Lunar cycler work which identified a Mars cycler corresponding to a single synodic period.
[4] The Aldrin cycler (as it is now known) makes a single eccentric loop around the Sun.
It travels from Earth to Mars in 146 days (4.8 months), spends the next 16 months beyond the orbit of Mars, and takes another 146 days going from the orbit of Mars back to the first crossing of Earth's orbit.
[5] The existence of the now-eponymous Aldrin cycler was calculated and confirmed by scientists at Jet Propulsion Laboratory later that year, along with the VISIT-1 and VISIT-2 cyclers proposed by John Niehoff in 1985.
The only difference in these trajectories is the date in the synodic period in which the vehicle is launched from Earth.
Earth–Mars cyclers with a multiple of seven synodic periods return to Earth at nearly the same point in its orbit and may encounter Earth and/or Mars multiple times during each cycle.
[5] Some possible Earth–Mars cyclers include the following:[5] A detailed survey of Earth–Mars cycler trajectories was conducted by Ryan Russell and Cesar Ocampo from the University of Texas at Austin, Texas.
They also found hundreds of non-ballistic cyclers, ones which would require some powered maneuvers.
The effect of the gravity of Mars on the cycler orbits is almost negligible, but that of the far more massive Earth needs to be considered.
In the diagram above, a spacecraft in an Aldrin cycler orbit that starts from Earth at point E1 will encounter Mars at M1.
[9] The shape of the cycler orbit can be obtained from the conic equation:
[9] The angle at which the spacecraft flies past Earth,
A correction would therefore be required to comfortably avoid the planet.
[4] While astronauts can tolerate traveling to the Moon in relatively cramped spacecraft for a few days, a mission to Mars, lasting several months, would require much more habitable accommodations for the much longer journey: astronauts would need a facility with ample living space, life support, and heavy radiation shielding.
[11] Aldrin proposed that the costs of Mars missions could be greatly reduced by use of large space stations in cyclic orbits called castles.
Once established in their orbits, they would make regular trips between Earth and Mars without requiring any propellant.
[6][10] Two castles would be used, an outbound one on an Aldrin cycler with a fast transfer to Mars and long trip back, and an inbound one with fast trip to Earth and long return to Mars,[3] which Aldrin called up and down escalators.
[6] The astronauts would meet up with the cycler in Earth orbit and later Mars orbit in specialised craft called taxis.
One cycler would travel an outbound route from Earth to Mars in about five months.
Taxi and cargo vehicles[a] would attach to the cycler at one planet and detach upon reaching the other.
[11] The cycler concept would therefore provide for routine, safe, and economical transport between Earth and Mars.
This would require fuel to execute the braking and re-cycling maneuvers.
[10][11] The castles could be inserted into cycler orbits with considerable savings in fuel by performing a series of low thrust maneuvers:[12] The castle would be placed into an interim orbit upon launch, and then use an Earth-swing-by maneuver to boost it into the final cycler orbit.
[14] In the case of the Aldrin cycler, use of a gravity assist reduces the fuel requirement by about 24.3 metric tons (26.8 short tons), or 15 percent.
Other cyclers showed less impressive improvement, due to the shape of their orbits, and when they encounter the Earth.
In the case of the VISIT-1 cycler, the benefit would be around 0.2 metric tons (0.22 short tons), less than one percent, which would hardly justify the additional three years required to establish the orbit.
