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While reading through the comments on a question on the difficulty of a manned mission to Mars, people brought up the issue that sending supplies in advance would lock in the landing site. It seems to me that one solution would be to bring the supplies into orbit around Mars instead, possibly even constructing a space station in orbit as a form of base camp.

What tangible benefits can an orbiting station offer for (manned) Mars exploration? What are the possible limitations or concerns?

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Lilienthal
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  • A return vehicle by definition will be in Mars' orbit. – Deer Hunter Nov 20 '14 at 18:44
  • Well, I'm assuming that in your scenario the cargo gets launched into Mars orbit first, and then the crew is launched on the next available Mars launch window. If, when the crew gets there, the cargo vehicle fails to land (either crashes or something else happens), then the crew have to go home, having wasted a trip. But that's just one of many factors in the immense calculation that is a human Mars mission. – Nickolai Nov 20 '14 at 19:16
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    One factor is that it takes more fuel to go into orbit than to use aerobraking to land supplies on a planet with an atmosphere. Though of course, aerobraking can be used to lower the aphelion of an orbit. Personally I'd send the supplies being pushed by a far more propellant efficient means such as an Ion Engine, where that extra velocity can be bled off slowly.. – Andrew Thompson Nov 20 '14 at 21:20

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Actually, there is one very sensible place to build an orbiting station - the moon Phobos. For example in the fictional Mars series by Kim Stanley Robinson, the majority of colonists land on Mars, but a small number establish a base on Phobos.

Compared with Earth's moon, Phobos orbits much, much closer to Mars. In fact it completes an orbit in less than 8 hours, compared with 1 month for Earth's moon. This puts Phobos almost in 'Near Mars Orbit'.

A colony on Phobos would be in many ways easier than one on Mars, the delta-V requirement for reaching Phobos from Earth (and vice-verca) is very low - in fact less than for the Moon. Putting aside the long travel time, and the restrictive launch windows, it would be cheaper to put a base on Phobos than the Moon.

Phobos is very dark and likely rich in volatiles, such as water and hydrocarbons. These could be a valuable resource, including for export to Earth Orbit (i.e. to help fuel rockets from low Earth orbit to Mars). Conceivably fuel mined on Phobos could be used for both legs of the journey from Earth to Mars.

A manned colony on Phobos would have some advantages - one is teleoperating robots on the Martian surface without the time delay for communications from Earth. It could thus act as a staging ground for establishing the surface colony. Fuel could also be refined on Phobos then launched to the surface colony, a refinery on Phobos would not lose solar power during global dust storms. Compared with a space station in open space, a station on Phobos also enjoys protection from solar flares as the bulk of the moon can be used as a shield - this might be a minor matter as the journey in open space is already 7 months so the spaceship would have to be reasonably well protected, but it certainly doesn't hurt to have additional protection from radiation. Unlike a Mars colony, a colony on Phobos could easily lift off and move to another location, as the gravity is very low.

Here is a pdf on missions to the moons of Mars and their role in exploration of Mars. Also a pdf on a phobos space elevator which indicates the kind of neat things a Phobos station might lead to.

Blake Walsh
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    Wow, I had to check a delta-V map to confirm that Phobos is actually so reachable. Neat! – Russell Borogove Nov 21 '14 at 06:14
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    If Phobos and Deimos were asteroids orbiting freely at Mars distance from us, they would be prime targets for human exploration. But because they orbit Mars, they are in our minds reduced to just moons. And everyone is Mars-crazy, wanting to go to Mars, walking on Mars, living on Mars, dying on Mars, Mars Mars Mars! As obsessed by that retrograding little red dot in the sky as Johannes Kepler. As if the desert was an oasis. – LocalFluff Nov 21 '14 at 06:58
  • You mention a space elevator on Phobos. This is such a BAD IDEA! I don't understand why it is repeated since it is already obviously refuted. You could fly off Phobos using a bicycle. And from any point on it in any direction you want. No need to construct a stationary "elevator" there. Staying on Phobos is the problem, not leaving it. You could almost by accident sneeze yourselves away from Phobos. – LocalFluff Nov 21 '14 at 07:14
  • @LocalFluff I think you miss the point of the elevator on Phobos. Sure, you can bicycle off Phobos - but only at a few m/s, you can then drift in the same orbit as Phobos, um yay? But with the elevator you can simply step off the elevator and get places - Earth, Jupiter, etc. It wouldn't be quite as useful as a full Mars elevator, but would be a small fraction of the cost, and would be very useful in opening up more frequent launch windows to/from Mars by effectively giving a much higher delta-v budget. – Blake Walsh Nov 21 '14 at 08:31
  • @Bhante Nandiya If there is a point with a space elevator in microgravity, then I am indeed missing it. Completely. Isn't a bicycle cheaper and more flexible than a space elevator on Phobos? – LocalFluff Nov 21 '14 at 11:43
  • @LocalFluff: Such an elevator will work on a rapidly rotating asteroid, but since Phobos is tidally locked to Mars, it simply wouldn't get enough centrifugal force to stay upright, not to mention even if it did, the speed of its end wouldn't be significantly higher than speed of Phobos (and it can't be overly big or it will just pull Phobos off the orbit!) – SF. Nov 21 '14 at 12:25
  • @SF. you are incorrect. tidal forces would keep a Phobos elevator vertically aligned with regard to Mars. To maintain tension the tether need only extend a short distance beyond Mars-Phobos L1 and L2. And MPL1 and MPL2 hover about 3 kilometers above Phobos' surface. – HopDavid Nov 21 '14 at 14:39
  • @LocalFluff Can a Phobos bicycle provide enough velocity to reach the asteroid belt? No. Can a bicycle provide enough velocity to reach earth? No. Can a bicycle come within .6 km/s of Mars' surface? No. Once again, there are other possible uses for an elevator besides getting off a body's surface. – HopDavid Nov 21 '14 at 14:42
  • @HopDavid: Okay, on first point. Still, its end would move at the same speed as Phobos (+/- a fraction of percent). No propulsion advantage whatsoever. The whole point of elevator is $v=\omega r$ by extending $r$ you gain $v$. With pathetic $\omega$ this won't work. – SF. Nov 21 '14 at 14:49
  • @SF. A 2435 km length provides Mars escape velocity. A 6155 length provides enough delta V for Trans Earth Insertion. A 7980 km length provides enough delta V for Trans Ceres Insertion. I talk about a Phobos elevator at http://hopsblog-hop.blogspot.com/2012/09/beanstalks-elevators-clarke-towers.html about 3/5 of the way down. – HopDavid Nov 21 '14 at 15:02
  • @LocalFluff - I guess the key is to start pushing Phobos exploration as a necessary step toward manned Mars exploration. – Russell Borogove Nov 21 '14 at 17:32
  • @Russell Borogove No, I actually argue for the opposite! That a mission to Phobos should be motivated on its own merits, not as a halfway trip to Mars. Ignore Mars, see Phobos. Going to Mars and going to Phobos have many important differences, such as atmosphere, gravity, potential resources. Phobos and Deimos are overlooked, in the popular debate anyway. The Russian space agency seems to like them. They are two of the five nearest celestial objects we have. – LocalFluff Nov 21 '14 at 17:45