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One of the criticisms I've read of Mars Direct is that it would make it too easy to do it as a one-off. My question is, would it be feasible to use a cycler for the first mission? If we have the architecture for continuous back and forth travel in place from the beginning, "It's there, we already paid for it, so we might as well use it" would be a powerful argument for more exploration and settlement.
Here's my sketch of how the mission would go. I'm not an engineer, so I welcome comments from anyone who is. The return module is sent first, as in Mars Direct, and manufactures the fuel it needs (but it won't need as much as in Mars Direct). At the next window, the cycler is sent, with the crew and a lander. They take the lander to the return module, which will be their hab on Mars. The mission's main focus is to find a suitable site for a permanent base. When they leave, the hab joins the cycler permanently; they're taken home by another vessel that docks with the cycler when it approaches Earth.
Human: the other red meat.
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Or if you want to cut out the need for a separate mission to take them from the cycler to Earth, the lander could be equiped with tracks, like a tank, and the crew could drive it to where the hab is (this would cut the need for a buggy at this point, but they'd need one anyway). They mate it with the hab, and take it back with them when the hab joins the cycler. Then they use the same lander to land on Earth, and then it's added to the Smithsonian collection.
Human: the other red meat.
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If we want to escape a repeat of the lunar missions, I think your idea has a lot of merit. Politics would almost demand that a cycler be used and I can't see it being anymore expensive to maintain than the practically worthless ISS. A Mars cycler would be a good project for the int'l community to engage in after the ISS burns up in the atmosphere.
My people don't call themselves Sioux or Dakota. We call ourselves Ikce Wicasa, the natural humans, the free, wild, common people. I am pleased to call myself that. -Lame Deer
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How about this.
A MAV (mars ascent vehicle) and a hab are sent to mars. The ascent vehicle produces propellant and the hab builds up fuel for the rover (for example) and checks everything is working. Then at the next window the cycler is launched, with crew. When they arrive they depart from the cycler in a lander(which is just another mars ascent vehicle) which produces propelant whilst they conduct their mission. Then when the cycler next comes round they hop on board using one of their MAVs and of they are home. Coincidentally the cycler has brough the next crew with it (with or without their own hab travelling in tandem) who land in their MAV (clearing a docking space for the ascending crew) who then conduct their mission and return on its next pass etc etc.
It would essentially seperate crew from cargo, alot like the way the OSP is designed to improve effiiency by catering for crew transport needs only.
Pros
Reduced costs - Whilst the cycler would cost more in the beginning (it would be larger and designed to last longer), each consecutive mission would save on launch costs and interplanetary propellant costs and thus overall mission costs and as such would save money in the long run.
Programme continuation - The constant (and effectively free) ability to send people to mars would almost gaurantee a maintained sequnce of missions and eventually presence on mars.
Cons
No abort - the inability to return to earth in an emergency should the crew need to would be problemtic (but only for the first missions - as increased infrastructure leads to increased capability and thus safety)
Long return trip - As i understand it the return leg of the journey is considerably longer than the outbound journey thus exposing astronauts to excessive radiation and long term zero-g(using two cyclers, one for each leg, would alleviate this)
Transfer time - since the cycler is not designed to slow down on approach to mars, it wouldpass by at high speed and the transfer window would be both short and dangerous - this is my opinion, i do not have the facts or stats.
Any other additions?
nick
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I'm a thinking an earth-return vehicle could be landed on Mars but that it would only be used in the case of an emergency like missing the window for catching the cycler. This way there would be no need to build an escape vehicle for each mission provided most of the crews on Mars were successful in docking with the cycler. It might also be possible to attach cargo to the cycler that would dispatch itself to Mars so that if a crew did miss the cycler they could have enough supplies until the next time it returned. If the crew is successful getting to the cycler the supplies would just be used for the next crew to land on Mars.
My people don't call themselves Sioux or Dakota. We call ourselves Ikce Wicasa, the natural humans, the free, wild, common people. I am pleased to call myself that. -Lame Deer
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I see several problems with cyclers, though they are reasonably short term and will be less serious as technology matures.
The first question to resolve is what sort of cycler orbit you want to use. One scenario is to launch a cycler from Earth into a two-year orbit around the sun so that it returns to Earth 24 months after it left. It will then pass Mars 6 months after it left Earth. You can see these details in the Mars Direct plan, which calls for the Mars Direct craft to be launched into a 2-year free-return trajectory back to the Earth that passes Mars after six months. When the vehicle passes Mars, that planet's gravitational field can be used to bend the cycler's orbit slightly so it reencounters Earth after 26 months instead of 24. Twenty-six months is the period between oppositions. Mars's gravity apparently cannot do this all the time because the planet is small. But an ion engine on board the cycler powered by solar panels could do the rest for a relatively small cost. You would need a second cycler to pass Mars heading toward Earth 6 months later, then Earth's gravity could bend the cycler into a path that would reencounter Mars in 20 months.
If you go to the "Romance to Reality" website you will see descriptions of several other cycler orbits. For example, you can set up a spacecraft to encounter Mars once every three Mars years and encounter Earth once every five Earth years. So there are other possibilities.
Here are the problems:
1. You need at least two spacecraft cycling back and forth, and they will have people on board 1/4 of the time or less. That's a lot of time for complex systems to be controled remotely.
2. There won't be any "dry dock" time when the cycler can be repaired. If it has an Apollo-13 style accident two months before it passes Earth, the Mars mission that opposition would have to be canceled, or the astronauts would have to fly out to the big cycler in a small ship and hope they can repair the big ship. It might be quite a gamble; the transfer ship would not be designed to serve as a life boat for six months.
3. You can't change the flyby time of a cycler very much; maybe by a month or so a year in advance, but not by much if, three weeks before the crew is supposed to leave Mars, they have a minor problem with the Mars ascent vehicle that requires a week's delay to effect repairs. Or more seriously, if the crew gets into Mars orbit and can't return to the surface, any repair problem that could cause a departure delay of even an hour or two could be the difference between life and death.
So I don't see cyclers as a reasonable strategy for the early missions. it's too risky.
As for ISS, it takes two crew almost full time to maintain. I wouldn't want to send it out into interplanetary space and hope for the best for six months heading to Mars with a crew on board, then 18 months with no one on board. We are not close to having the technology for a cycler yet.
What makes more sense is a semicycler; a spacecraft that carries crew between planets, then aerobrakes enough to stay in a very elliptical orbit around the planet until the crew is ready to return. About nine months or so Robert Dyck raised the issue of how to developed a new, updated Mars Direct, and I think that's basically what he favored. It's what I favored in my "Mars 24" proposal that you can still read. Advantages of this system:
1. The interplanetary vehicle waits in Mars orbit for the crew and thus can depart when they need it to depart. They can effect repairs on something and delay departure if they have to.
2. The vehicle then hangs around in an orbit around the Earth for about twenty months before reuse; plenty of time to repair and upgrade it. If the orbit around the Earth were one that carried it all the way to the moon, the vehicle could be used as a cycler/rescue vehicle for transportation between the Earth and moon; in other words, a vehicle heading for the moon could time its trip to have the cycler nearby in case of emergency. The vehicle could also be parked at lagrange 1 (the gravitational balancepoint between the Earth and moon) to serve as a temporary staiton there, or augment a station already there.
3. Since the vehicle is reusable, it would promote returns to Mars. It would not have to be untended for long periods of time; if it suffered a serious breakdown while waiting, someone could go out and fix it or figure out what happened.
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What makes more sense is a semicycler; a spacecraft that carries crew between planets, then aerobrakes enough to stay in a very elliptical orbit around the planet until the crew is ready to return. About nine months or so Robert Dyck raised the issue of how to developed a new, updated Mars Direct, and I think that's basically what he favored. It's what I favored in my "Mars 24" proposal that you can still read. Advantages of this system:
This idea seems safer and easier than using a "full time" cycler. I never really thought of a ship that hangs around in orbit waiting to take crews back and forth as a cycler but it fits the bill. Ideally these ships should be as big and luxurious as we can reasonably make them since they can be reused and repaired and won't have to be lifted off the surface of a planet each time we want to use it. If we want to make colonizing Mars a reality the tuna can approach doesn't seem very appealing.
My people don't call themselves Sioux or Dakota. We call ourselves Ikce Wicasa, the natural humans, the free, wild, common people. I am pleased to call myself that. -Lame Deer
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Of course, you still have to worry about the delta-vee. A Deimos transfer orbit (elliptical orbit with the apopasis the height of Deimos and a periapsis just above the Martian atmosphere) requires 5.6 km/sec to reach from the Martian surface, but is about 0.2 km/sec short of Martian escape. You need another 0.9 km/sec to achieve a Hohmann (minimum energy) flight back to Earth (I don't know what Mars Direct's six month flight needs; maybe another 1 km/sec more). At any rate, a small craft is doing most of the work and the big mass is staying near the edge of Mars's gravity well. For the Earth, the Lagrange 1 point is about 0.7 or 0.8 km/sec short of a Hohmann transfer ellipse to Mars; add another 0.8, I think, for the six-month flight proposed by Mars Direct.
Note that Phobos and Deimos are harder to reach than this might suggest because they are in circular orbits. The data I have suggests that the velocity from the surface of Deimos to Mars escape is 0.9 km/sec and from the surface of Phobos to escape, 1.0 km/sec. But if that extra fuel penalty is not a problem--for example, if one is making fuel from the chondritic rock of the moons--then the extra penalty of delta-vee is worth it. Clearly, until we have antigravity propulsion or warp drive, Mars's moons are a refueling station of great potential value.
L1 is easier to escape from than the Martian moons because it is higher and because one get a gravity assist from the Earth's moon. L1 orbits the Earth at 800 or 900 miles per hour (0.4 km/sec). To fall to the Earth in order to fire ones engines deep in the Earth's gravitational well (which produces a great fuel savings) one would need to cancel out that forward motion. But one can fly to the moon with less energy than that and use the moon's gravity to fling the spacecraft back to the Earth, where one fires one's engines to go to Mars.
-- RobS
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