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Originally Posted by JonClarke
2) The crew spends much longer times on on the martian surface. Combined with (1) this makes overal mission times very long.
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Only if the missions are always return-to-Earth missions. For missions where the passengers (colonists) stay on Mars, that is not an issue.
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Originally Posted by JonClarke
3) The cycler orbit is not a perfect match for Earth and Mars, up to five cyclers are therefore required to allow a transfer each launch window. Since each cycler is a substantial spacecraft this requires substantial investment in transit infrastructure rather than on the Mars surface, infrastrucure that furthermore is only used 2/5ths of the time. This renders the claims for less mass false.
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Another good point. Perhaps having larger but fewer missions would be the solution, that is, sending 40-50 people instead of 7-8.
Quote:
Originally Posted by JonClarke
4) Launching to the cycler means a deep space rendezvous with very narrow launch windows and little margins. If a launch is delayed even minimally then I suspect that the window is missed.
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Since the launch to the cycler would be made from orbit, I think that rendezvous would not be a big problem.
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Originally Posted by JonClarke
5) The deep space rendezvous is very much a dock or die affair, if planet to cycler ferrys are minimalist affairs. To ensure the crew survives in the eent of a failed docking they have to be large enough to make the mission without the cycler, which makes the cycler redundant.
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That is correct. But given enough maneuvering fuel, that should not be a critical problem.
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Originally Posted by JonClarke
6) Tranfering to the cycler orbit always requires more propellant than doing directly to Mars or Earth, sometimes much more.
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AFAIK, it would require almost exactly the same amount of fuel. That is because the shuttle would be accelerating to the exact same velocity as it would if it were going solo.
Quote:
Originally Posted by JonClarke
7) entry velocities at Earth and Mars are always higher than non cycler orbits.
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I dont understand why that would be the case. If the transit velocity is the same, and the orbital path is the same, the entry/reentry velocities should be the same.
Quote:
Originally Posted by JonClarke
So in the end using a cycler means much larger spacecraft, more propellant and greater risk to carry out essentially the same mission that a non-cycler would use.
I am sure cycler orbits are good for something, just not for travelling to and from Mars.
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Initially, it would be difficult if not impossible to justify cyclers. However, eventually, using large cyclers, possibly asteroids, the advantage would be in providing luxury accommodations for passengers on the long voyages between planets. Although the initial energy requirements to get the cycler into the proper orbit would be very large, the payoff would be in being able to provide perhaps 10-20 times the amount of living space for passengers as well as freshly grown food, fancy entertainment, and larger passenger loads. It would be something like the difference between a 30 foot yacht and a 600 foot cruise ship.