I've talked before about how life on present day Mars could be vulnerable to Earth life. If only humans could be sterilized of other life, like a plant seed. But sadly, we can't do that, and it would kill us to try. Recent ideas, and experiments in Mars simulation chambers suggest that there may be liquid water habitats on the surface of Mars. They may be no more than droplets of water a few millimeters in diameter, but these still are, as Nilton Renno said, "Swimming pools for a microbe". And humans can't go anywhere without taking hundreds of trillions of microbe hitchhikers along with us in tens of thousands of species. So - if we can't go to the surface of Mars right away - where can we go?

Naturally attention turns to its moons, Deimos and Phobos. And they are actually, rather interesting places for a human to visit. In some ways they are more exciting than the surface, as we'll see, especially when combined with telerobotic exploration of Mars. Also, they are far easier places to land on safely and return. And there is almost no risk of introducing Earth life to Mars accidentally, so long as you get there without use of aerobraking.

 Good intro to the two moons - Harald Hoffmann,  planetary geologist at the DLR Institute of Planetary Research, on the debate on the formation and future of the Martian moons Phobos and Deimos. interview in 2013.

I think it may be some time myself before we can send humans even this far safely. There are many more challenges than there are for a lunar landing. The task of physically getting to Mars orbit is perhaps the least of many issues. But when we do get there, then these could be really exciting places to visit,

So which of the two moons should we visit? The most detailed proposal is by Lockheed Martin in their "Red Rocks project"  as part of their "Stepping Stones to Mars" program. And in their comparison study, Deimos beats Phobos on almost every score - though Phobos does have a couple of major advantages. 

ADVANTAGES OF DEIMOS

So - the advantages of Deimos first

• It has a South pole almost permanently shadowed - amongst the coldest places in the inner solar system. This also is a place where you are completely sheltered from the dangerous radiation in solar flares (which emanate from the direction of the sun). And it has natural cooling for any rocket fuel that needs to be kept at cryogenic temperatures (it is also ideal for infra red observation).
• The permanently shadowed craters are probably a good place to study (just as for the Moon's craters of eternal night), with an ice record of the early solar system and materials from early Mars. It may also be a source of ice for colonists.
• Close to these places of permanent shadow, you have a site of continuous summer sunlight to place your solar panels.
• You also have permanent line of sight communication with Earth 24/7 for nearly all the year except when Mars is behind the sun.
• Deimos is almost synchronous with the surface of Mars - and tidally locked - so you can have continuous line of sight access of Mars for telerobotic communication.
• Any site on the surface of Mars is accessible for 60 hours at a time from Deimos. By comparison, from Phobos, any site is only accessible for four hours at a time.
• A typical site on Mars is visible from Deimos for 45% of the time, and 97.5% of Mars is directly accessible via telepresence at some point or another.
• The required delta v to get there is somewhat less than for Phobos.
• Surface materials can be used for resource utilization and to cover the habitat to protect from cosmic radiation.
• It's an interesting place to study in its own right.

ADVANTAGES OF PHOBOS

There are two major advantages of Phobos,

• because it is closer to kMars, it has a two way time delay for telerobotic exploration of only 40 ms, while Deimos has a two way time delay of 134 ms.
• It has a crater, Stickney crater, on the Mars facing side. A party in Stickney crater would be protected from about 90% of cosmic and solar radiation, possibly more, at least according to this article (if they got it right). That's because it is protected by the crater walls, Phobos, and Mars itself which is overhead, and for solar storms it would be out of the direct line of the storms for most of the time. It is one of the places in the inner solar system most protected from cosmic radiation, even more so than the poles of the Moon. Only the lunar caves and Martian caves are more protected from cosmic radiation - or the high Venus cloud decks (and of course, Earth itself).

Stickney crater on Phobos. This large crater faces towards Mars. A base sited here would be protected from solar storms, and also from cosmic radiation. It's blocked by Mars overhead, Phobos below and the crater rim to all sides, and so gets only 10% of the cosmic radiation of an unprotected base. 

Phobos also probably has a high percentage of material from Mars in its regolith, and larger meteorites surely as well. So you can study the geology of Mars by looking at fragments of rocks on the surface of Phobos. Possibly the biology of Mars also.

MINING PHOBOS AND DEIMOS

Deimos is also an asset for mining - it's not known for sure yet, but is similar in composition to meteorites that can have a large ice content. So it may have large deposits of water ice. If so that's of great value for fuel - and the delta v budget is such that it's actually one of the easier places to mine ice to return to LEO. As well as use in Mars orbit.

David Kuck in 1997 suggested starting up a Deimos Water Company to supply Earth orbit with water from Deimos. The Kuck mosquitoes are small unmanned craft that drill into Deimos and extract water from below the surface, use part of it as fuel to transport the rest back to Earth.

See also Mining Phobos and Deimos

This makes it a project that could be commercially viable, unlike Mars surface, through sale of ice to LEO.

LACK OF GRAVITY ON THE MARTIAN MOONS

There is one major issue of course - the gravity, almost none. Can humans stay healthy with such low levels of gravity? Or - can we create artificial gravity on the surface (spinning habs)?

But perhaps this can be done with either a carousel type approach or with centrifugal sleeping quarters for the crew. I think this all depends on what turns out to be the requirement for artificial gravity to keep a human body healthy, and on what our tolerances are for spinning motions in AG environments - which we don't know anything about as yet.

FREE FLYING HABITATS

Artificial gravity is probably an easy matter to arrange in a free flying settlement in orbit. You can use a tether system to generate gravity for the earlier settlements.

You can use materials from the Martian moons for shielding.

Long term, you could use materials from the Martian moons eventually to build Stanford Torus type settlements in Mars orbit. Deimos has a mass of 1.48 * 10^12 metric tons, which at 15 metric tons per square meter is enough to make Stanford Tori with about 100,000 square kilometers of living area.

So, if you were to mine the whole of Deimos - not suggesting we do - but if we do - that's cosmic radiation shielding for roughly the size of Iceland, larger than Scotland, or Norway, more than twice the size of Switzerland, which could be useful for Mars orbital colonies.

In terms of US states, that's about the size of Oregon or Colorado

That's just the outermost hull which you can build on top of - and larger habitats might well have multiple "shells" within it - so that's a lower bound on the total land are you could create from Deimos using it for cosmic radiation shielding.

Anyway that's obviously for some way down the road, if we ever do that.

PLANETARY PROTECTION ISSUES FOR DEIMOS AND PHOBOS

When Russia proposed a sample return from Phobos, then it was classified as an"unrestricted category V" mission, meaning that no special precautions are needed. Despite that, Russia did plan to take some precautions on return of the sample, though not required for planetary protection according to the classification their mission received.

The Russian Fobos-Grunt spacecraft, which was designed to return a sample from Phobos to Earth. The spacecraft never got there, it failed to separate and fell back to Earth and was burnt up. This sample return mission got an "unrestricted category V" classification for planetary protection on the basis that Phobos couldn't be habitable for Earth life - but the Russians did plan to take some precautions even so.

There is no chance of present day life surviving on Phobos or Deimos to the best of our knowledge, no chance of habitability on the surface or below the surface. These moons are just too small to have any chance of liquid water even below the surface, so it's thought.

But - there could be a very minute chance of dormant life, because Phobos receives material sent into orbit from Mars after meteorite impacts. Any life at least on the surface of Phobos would be sterilized over long time periods such as millions of years. But the most radioresistant life on Earth can resist the equivalent of four hundred thousand years of Mars surface cosmic radiation, although not evolved in the presence of ionizing radiation (as a byproduct of heat and desiccation resistance probably). For more on this: UV&Cosmic Radiation On Mars - Why They Aren't Lethal For The "Swimming Pools For Bacteria"

Life on Mars, evolved in presence of cosmic radiation could conceivably resist that much and possibly more. And Stickney crater gets just a tenth of those levels of radiation, so dormant spores there there could survive ten times longer, and more so if somewhat buried.

So given that material is sent into orbit from Mars every one or two million years, with the last known impact large enough to send material as far as Earth a little over 700,000 years ago, there would seem to be a small chance of dormant life on Phobos - that is if life from Mars can be transferred on meteorites at all, which we don't know yet. But theoretically it would be possible.

I think myself that this suggests it would be worth while doing robotic in situ exploration of Phobos and Deimos first before we send humans there. And if signs of life are found there, dormant life, to re-evaluate the situation and take appropriate precautions depending on what is found.

In the forward direction also - then though to best of our knowledge, there is no chance of life from Earth surviving on Phobos or Deimos, there could be regions there of especial interest for the study of organics in the early solar system and dormant life. For instance what if there are ice deposits at the South pole of Deimos - including samples of organics from early Mars itself? Then we would need to keep humans well away from these until we have a chance to study them in situ and work out what effect a human base would have on them.

Could a human occupied base there be kept so clean that there is minimal impact on the study of ancient organics in the ice surrounding the base? If not, what can we do? By then we probably have experience already of bases on the Moon so may be able to use that to assess what impact a human base has on the area immediately surrounding it.

STEPPING STONES TO MARS (ORBIT) - FIRST THE MOON

This is the title of the Lockheed Martin studies, "Stepping Stones to Mars". They assume an eventual Mars surface landing. But we can use the same approach as far as Mars orbit as stepping stones to a Mars orbital mission, as a mission of great value in its own right. So that's why I've added (ORBIT) in brackets.

They recommended a step by step approach. First, to send telerobotic expeditions to the far side of the Moon, operating rovers on the surface from a base station at the L2 position behind the Moon. This would have unique challenges and would also be of great scientific interest, as no rover or human surface mission has yet been sent to the far side of the Moon.

It's also a great place to work on telerobotics. The far side of the Moon is the most radio quiet place near to Earth because it is shielded from all radio transmissions from Earth by the thickness of the Moon itself. So one thing you could do there is to build radio telescopes. This is something that would be easy to do from L2, controlling telerobotic rovers on the surface that unroll cables over the surface to build the telescopes. Long wavelength radio telescopes are particularly easy to build in this way.

This is an artist's impression of a telerobotic rover unrolling one leg of a radio antenna on the surface of Mars. (Joseph Lazio/JPL/Caltech)

This shows how astronauts would control rovers on the surface of the Moon by telerobotics

NASA Eyes Plan for Deep-Space Outpost Near the Moon

Another useful stepping stone would be to explore the ice deposits in the craters of eternal night at the poles of the Moon by telepresence.

We could also explore the lunar caves, which may be far larger than Earth lava tubes. One recent study suggested that the Moon, with its low gravity, could have lunar lava tubes that are kilometers in diameter, and would still be stable in the gravity there. You could build cities inside such caves, if they exist. See There Could Be Lava Tubes on the Moon, Large Enough for Whole Cities

Hadley Rille, at the foot of the Apennine Mountains encircling the Mare Imbrium where Apollo 15 landed. Credit: NASA/JAXA

These sinuous rills on the Moon are up to 10 kms in width. A recent study suggests that there could be lava tube caves beneath the surface here of similar width. They would not be stable on the Earth. But in the lunar gravity they would be stable and would be large enough to house an entire city built inside the tube.

 Inside of one of these proposed lunar lave tube caves, with the city of Philadelphia shown for scale. Credit: Purdue University/David Blair

The Moon is of great interest, far more so than we realized in the Apollo era. It's even of interest for the search for life potentially.

METEORITES FROM EARTH ON THE MOON

Impacts on Earth would of course send meteorites to the Moon. And if we find meteorites from early Earth on the Moon - those could be of great interest for filling out the huge gap in our timeline between formation of the Moon and the earliest evidence we have of life on the planet.

The reason for that gap is that more or less permanent present day continents didn't form right away on early Earth. To start with the crust was probably much more fluid than it is now continually destroyed and recreated. Eventually cratons formed, with deep roots in the Earth's crust. But these only date back to the early Archaean period.

As a result, there's nothing left at all from the very early Earth, from the Hadean period, except a few zircons (like diamonds) trapped in later rocks. These trap the early Earth atmosphere but tell us little else about what was happening then. But there must be meteorites on the Moon that got there after impacts into the early Earth. This material from early Earth would be of huge interest to geologists and biologists. And if it had organics in it, or even preserved early life, of enormous interest. We might find these organics for instance preserved in the ice at the poles of the Moon, it's been suggested. We could even find, potentially, preserved fragments of larger creatures (e.g. bits of ammonites) on the Moon.

ABILITY TO DO LONG TERM MISSIONS DISTANT FROM EARTH

As well as developing telepresence experience while exploring the Moon in this way - and new science in its own right - we'd also develop the ability to mount long term missions distant from the Earth.

The Moon isn't that far away, of course compared to Mars. But the far side of the Moon is isolated from Earth.

We could use it in this way deliberately. Send a spacecraft to the L2, so Earth is permanently blocked from view by the Moon. Anyone living there for say a couple of years on end would feel as isolated as they would be on Mars pretty much.

Yet - they can get back to Earth within a couple of days if necessary.

There are people who can handle this, such as those who spend long periods of time in submarines, or round the world yacht trips. Still, it would be good if our Mars astronauts are people who have shown they can handle long duration space flights closer to Earth first.

That's only part of what we would test though. The main thing is that we'd test the ability to do long duration spaceflights without continual resupply from Earth. And to keep humans physically healthy over those time periods. In the case of the ISS they rely on resupply every few months - and so far nobody has spent as much as two years in space.

This could also be a very inexpensive mission as far as human spaceflight missions go - far less expensive than the ISS potentially.

That's because they will have to take all their supplies with them (or it's not a fair test of an interplanetary mission). We need just one set of launches to L2, of the crew + their supplies for, say, two years. Then they are on their own for the next two years studying the Moon from the L2 position via telepresence. The only support they have from Earth during that time period is through radio communication, with nothing material sent either to them or returned from them to Earth.

If this works out, and no problems arise during the mission, then we have a very low cost way of exploring the Moon and we may possibly be ready to go to Mars. If any issues arise and they have to return to Earth or need emergency shipments from Earth to keep going, then no way are we ready yet to go to Mars.

Note, we could also explore the Moon telerobotically from the lunar surface.

This time, you build a habitat on the far side of the Moon, or perhaps inside a lunar cave on the far side. Then just as before, they operate the lunar rovers telerobotically, partly by line of sight transmission for nearby rovers, or relayed through lunar communications satellites when exploring distant parts of the Moon (you need these satellites anyway to communicate by radio from far side of the Moon to Earth).

This could be somewhat analogous to exploring Mars from the Martian moons. And as before it would be a low cost mission, if a mission to Mars is possible at all. Just a single launch (or multiple launch) to send your astronauts and all their supplies to the far side of the Moon. And then no more launches, just radio communication, for the entire two or three year period of the mission. If that is possible, then ultra low cost exploration of the Moon is also possible. If that can't be done, there is no way we can send humans to explore Mars quite yet.

But before going to Phobos or Deimos, there are a couple of easier missions we can do first.

ROBERT ZUBRIN'S DOUBLE ATHENA - AN ULTRA SLOW WEEKS LONG FLYBY OF MARS

Robert Zubrin suggested a double flyby mission called Athena. It's a free return trajectory like Inspiration Mars, but works by first diverting into a sun centred orbit similar to Mars, "shadowing" Mars, then the second fly by of Mars an Earth year (half a Mars year) later diverts it back to the Earth, 700 days after the launch. Advantages of this are

• Least delta v of all the proposals, so also the cheapest
• Astronauts are close enough to Mars for direct telepresence control for several hours for each fly by, still remain close for days after the first flyby and before the second fly by, and close enough to be a major asset over Earth based control for the entire year.
• It's a "free return" mission - you don't need to do any extra delta v to get back to Earth. The second flyby, an Earth year later, takes you back to Earth even if you don't do anything.

Robert Zubrin's plan has several advantages over Denis Tito's Inspiration Mars, which is the other free return mission proposal.

• You can do it more often, roughly every two years,
• It doesn't have the high speed return of Inspiration Mars so less issues with aerobraking into the Earth atmosphere on return
• You have far more time for near to Mars telerobotics - with Denis Tito's mission you just have the one, very fast flyby of Mars and then it is over.
• But is a longer mission by 200 days.

I'm not sure that the Inspiration Mars 500 days is such an advantage over 700 days. I think if we can manage 500 days safely (surely not for a while yet) - then we can probably do 700 days also. (it is an extremely poor safety margin for Inspiration Mars if most astronauts are close to death at the end of 500 days).

Also the double Athena can be done every two years, doesn't need any special alignment with Venus, and it has a much slower return trajectory relative to Earth - can just do normal aerobraking much like the return from the Moon, which Inspiration Mars can't do because it has a far faster return velocity delta v relative to Earth.

Anyway its great advantage is that you are close enough to Mars for hours during each fly by - and in between you spend days really close, close enough to do things like drive rovers in real time and supervise experiments.

All of these missions have the disadvantage that you have to take all your shielding for the entire mission with you. You'd need "storm shelters" for solar storms also. This would be worked out with the lunar precursor missions to L2 etc - I don't think we should do a mission like this without experience of similar missions close to Earth. And any Mars mission needs to spend around a year combined (there and back) fully exposed to solar storms and the cosmic radiation anyway.

HERRO MISSION - NEAR SUN SYNCHRONOUS MARS CAPTURE ORBIT

The HERRO mission suggested a near sun synchronous Molniya orbit, which is elongated, similar to a Mars capture orbit. This is the easiest orbit to get to in terms of delta v, needing a similar amount of rocket fuel to a mission to the Moon for the same payload. This has the advantages that

• Less fuel to get there
• Approaches the sunny side of Mars twice a day, each time visiting the opposite hemisphere,
  
  So the entire surface of Mars is available for close up direct telepresence control of the landers, in full sunlight, every single day, by just the one crew.
  See:  HERRO mission to mars using telerobotic surface exploration from orbit

Turns out, if you choose just the right orbit, it's ideal for studying Mars by telepresence. You use a slowly precessing sun synchronous Molniya type half sol orbit. This is a precessing orbit that automatically keeps your spacecraft approaching Mars on the sunny side twice a day, all through the Martian year.

This shows how you get into this orbit - just directly from the Earth-Mars transfer orbit.

With this orbit, you have several hours of close up telepresence every 12 hours over opposite sides of Mars each time, also always on the sunny side of Mars. The delta v is the same, to all intents and purposes as a Mars surface using aerobraking. But without the dangerous descent to Mars and without the expense of developing human rated landing equipment -I think pretty clear it would cost less than a surface mission.

This is a video I did which simulates the orbit they would use - in orbiter. I use a futuristic spacecraft as that was the easiest way to do it. Apart from that, it is the same as the orbit suggested for HERRO.

It would be a spectacular orbit and a tremendously humanly interesting and exciting mission to explore Mars this way.

I think myself also, it might help with "homesickness" as it were.

From above, with its icecaps etc, Mars looks quite a bit like an Earth like planet. We know it isn't really, is freezing cold, vacuum, dark skies etc. But from above it looks quite Earth like.

You also have continually changing views with these regular spectacular flybys, twice a day, passing close to the polar caps.

When exploring it by telepresence, we can arrange. through white balance, to have blue skies also when you look at it on the surface via VR. That would have scientific advantages also, because then you can see the colours of the rocks more clearly and under Earth equivalent illumination, so making it easier to identify them than if they are all a dull muddy red brown (same reason that the images from our Mars rovers are are optically enhanced by white balancing).

It's also better for science, the study for HERRO found that a single mission to explore Mars by telepresence from orbit would achieve more science return than three missions by the same number of crew to the surface - which of course would cost vastly more. Here is a powerpoint presentation from the HERRO team, with details of the comparison.

Russia suggested a similar mission as an international effort, with US participation for the landers, called the Mars Piloted Orbital Station

With all of these, we have to be really really careful that the human occupied ships can't impact on Mars, or any of our debris, human wastes etc.

IMAGINING A TELEPRESENCE MISSION IN THE HERRO MOLNIYA TYPE ORBIT

Imagine yourself in orbit around Mars - in a Molniya orbit - comes round to the sunny side of Mars twice a Martian day - you go really close to the surface - and spend some time there controlling rovers on the surface - driving them around - with reality headsets like the Occulus Rift -

- the Mars astronauts in orbit could explore the surface with headsets like this - and haptic feedback gloves so you can feel what you are doing, and omni directional treadmills like the virtuix omni

and automatically enhanced vision

with everything you see on Mars streamed back to Earth so everyone back here can join in and see what you see exactly as you see it whenever you explore the surface of Mars.

Then after a few hours of that you see that Mars is now getting further away, becomes smaller, and then 12 hours later you come in again for another close approach and real time exploring - you can continue to explore all the time - but when you are really close you can control things on the surface in real time as if you were there.

SMALL PLANES AND ENTOMOPTERS ETC

You could fly planes around on Mars, small planes, or entomopters - same design as a bumble bee. Lightweight, you could carry many of these along with the humans in a human mission to Mars orbit or the Mars moons to send on to the Mars surface.

Many other ideas like that - surely much more fun, to operate those from orbit around Mars, in a shirt sleeves environment than living a troglodite existence on the surface under meters thick layers of soil, going out only rarely to keep down your lifetime radiation dosage - and knowing all the time that just by being there you have contaminated Mars and made it far harder for scientists to find out interesting things about biology and alternative forms of biology and the early history of evolution.

Also all this would be great for collaboration - probably need a big international expedition to send the humans out to orbit around Mars. But as well as that, anyone who can send a spacecraft to Mars (probably many countries by then) can send landers, for them to operate telerobotically. The more the better really. So it is something that all countries with interest in space could work on together, each contributing different things depending on their expertise.

MORE IDEAS FOR THESE EARLY ORBITAL OR FLYBY MISSIONS

With of HERRO, and indeed for the other missions also, you could send supplies to Mars in advance in separate duplicate spaceships before the human mission gets there. Most of the cost of an innovative mission is in the design, so it often adds little to the costs, percentage wise, to make several duplicates of the spaceship.

So, you have a habitat there already, in orbit around Mars,and with all the systems functioning including life support. Preferably, have two such ships filled with extra supplies, before you send the first humans there.

They would be fully fueled lifeboat ships able to get the crew back to Earth, or for them to survive in if systems in the main ship fail. You can also use them as extra living space at Mars during the mission, and as long term assets in Mars orbit.

Since these lifeboat ships don't need crew or provisions for the journey out - they could be filled with extra supplies, fuel and spare parts instead. These supplies could then be transferred to the main ship and used as extra shielding for the stay at Mars. In the worst case you can cannibalize the other ships themselves, for repairs, or if the main ship fails, transfer the mission to another ship.

And - if we were looking forwards towards such an expedition - all rovers to the surface of Mars could be fitted with binocular vision and hands with haptic feedback by default. Anyone who sent a spacecraft to Mars would be sure to set it up so that it can be controlled easily by telepresence whenever there are astronauts in close orbit around Mars.

Suppose we had a lead time, say of a decade in the run up to the first human missions to Mars orbit (during which we have human missions to L2 etc). Then by the time humans get there, we'd have a decade worth of Mars rovers and landers, all equipped to be controlled via telepresence, ready for use when the first human missions get to Mars orbit.

Later orbital missions could mine Deimos for materials, using the likes of the Kuck mosquitoes - dedicated small spacecraft to shuttle materials back and forth from the moons to the settlements. If there is ice in Deimos; you could use this as rocket fuel to export this extra shielding to the habitat,

ARTIFICIAL REAL TIME

But there is another thing we can do - and that's to do autonomous exploration from Earth, using "artificial real time" which lets you drive a rover around on Mars even with a huge time delay of minutes. At the moment the way we control our rovers on Mars is hugely time inefficient. We could as easily control rovers on Pluto, because they download the data for one day, and use that to direct the rover's operations for the next day.

There's no point in trying to speed that up though, because it is hard to get a data link from Mars to Earth. Once a day is about all we can manage easily, because our orbiters have their own work to do.

If we have a dedicated link though between Mars and Earth, satellites in orbit around Mars just to relay signals to Earth - our rovers could be hugely speeded up.

And - in a situation like that, we could also speed them up so much that using this idea of "artificial real time" from computer games, we could control them almost as easily as a rover on the Moon (say).

Standing Space found this interesting video about the idea:

BALLISTIC TRANSFER TO MARS - PLANETARY PROTECTON ADVANTAGES

With new ideas for ballistic transfer, it might be possible to send robotic missions to Mars orbit at any time, not limited to the traditional launch window every two years for Hohmann transfer, and also get supplies to Mars orbit using low thrust ion thrusters. The idea is that you send it to a sun centered orbit with aphelion just ahead of Mars in its orbit, and then Mars captures it into a very high orbit around Mars with almost no fuel - and without the need to apply thrust at just the right moment of time.

Then it can gradually go down to lower orbits. You don't need a big impulse but can do it gradually over as long as you like. It takes a few months longer than a Hohmann transfer orbit - but unlike Hohmann transfer you can also do it any time, not limited to a launch window once every two years.

And then because there is no delta v for Mars capture, then your total delta v to get down to low Mars orbits is similar to the delta v needed to get to the Mars surface with aerobraking.

The same method has already been used several times to send spacecraft from the Earth to the Moon without any need to apply any extra delta v to capture it into lunar orbit.

Technically what happens is that the v_∞ of your spacecraft relative to the Moon changes from positive to negative due to three body interactions (something that would be impossible if you study it as patched together two body interactions). This allows your spacecraft to be captured by the Moon with far less delta v than is possible for a Hohmann transfer which keeps a positive v_∞ throughout. This was used in 1991 by the Hiten spacecraft from Japan, using a ballistic transfer that takes the spacecraft beyond the Moon first, before it is captured. The same method was used by NASA's Grail mission in 2011.

Another type of ballistic transfer was used by ESA's Smart 1 mission in 2004, called an interior transfer, captured without the spacecraft ever going further than the Moon in its orbit - this uses less delta v.

The capture to this distant orbit around the Moon is temporary, but then you can use more delta v to spiral in closer to the Moon for a stable orbit around it.

It's also a bit like the way that sometimes NEAs get captured into temporary orbit around the Earth for a few months. For those also, the v_∞ of the NEA relative to Earth has to change from positive to negative, which would be impossible with patched together 2 body interactions.

The new thing is that orbits have been found that do the same thing for Earth to Mars transfer.

For details see A New Way to Reach Mars Safely, Anytime and on the Cheap (Scientific American). And Making the Trip to Mars Cheaper and Easier: The Case for Ballistic Capture (Universe Today). The technical article is Earth--Mars Transfers with Ballistic Capture

Note - that more work is needed, as they say in the Scientific American article.

"This potential breakthrough research is admittedly still in an early, theoretical phase. Ongoing work includes reworking the calculations of the physics by factoring in smaller influences on a Mars-bound spacecraft than the pull of gravity from Mars itself, such as Jupiter’s gravitational pull. NASA's Green said he envisions the agency wanting to test ballistic capture transfers at Mars in the 2020s."

This ballistic transfer method - even if it doesn't have all the fuel savings that it seems to have in the preliminary studies - it still has a major advantage for planetary protection.

The way that you send orbital missions to Mars at present involves a trajectory biased away from Mars, then a single burn to put the spacecraft into orbit around Mars. That burn could continue for too long, and then put the rocket into a collision course with the surface. That's what lead to Mars Climate Orbiter impacting Mars (due to mix up of SI and imperial units).

With a human mission on Deimos especially, you'd have many multi ton spacecraft eventually going back and forth between Mars and Earth. From time to time, with the single impulse method, there's a chance that something would go wrong, and maybe one of those spacecraft would impact Mars. After a spacecraft with astronauts, or food supplies for astronauts, crashes on Mars, that could well be the end of planetary protection of the planet. After materials spread out over the surface of Mars of a crash site like that get caught up in the Martian dust storms, how could you ever reverse what you did?

But with this ballistic capture method, there's not much chance of that happening. It's more like the methods we use for navigation between the moons of a planetary system, with lots of time to work out trajectories in advance, and gentle nudges to get there. Unlike the all or nothing single impulse transfers to planetary capture - those gentle nudge type trajectories have never gone wrong. Worst that would happen if your engine fails is that your spacecraft gets caught in a too high orbit around Mars.

COMPARED WITH MARS SURFACE MISSIONS

First of all, whatever the cost, I think that Mars surface missions couldn't pass planetary protection anyway, with present knowledge of surface conditions. All the COSPAR studies so far of planetary protection for human missions to Mars have been inconclusive, they always say in the conclusion that more research is needed.

So, I don't see myself how COSPAR could possibly approve a human mission to Mars on the proposed timescale based on the level of knowledge we can hope to have of Mars surface conditions by then. Given what we know about potential habitats on the surface of Mars, and given that a crash landing on Mars would lead to materials from the spacecraft and human remains spread over the surface of Mars and the dust storms could then pick up microbes from that material and spread them throughout Mars - how could a COSPAR workshop come to the conclusion that this is a reversible contamination free way of landing humans on Mars?

And - there is no way that NASA would send a mission to Mars if it didn't pass planetary protection. This is an idea suggested in internet forums, that they would be so keen to land a human on Mars that they would withdraw from the Outer Space Treaty and with the aim to "plant a flag on Mars" just go there anyway. But nobody has ever suggested this as a NASA or US policy, and I simply can't see it happening. 

Artist's impression of a human astronaut on the Mars surface holding Oskar Pernefeldt's proposed International Flag of the Earth - the linked rings symbolize how the different parts of Earth are linked together. (This is the latest of several proposed "Flags of the Earth").

Before a mission like that could be approved, a COSPAR workshop would need to show that it is consistent with planetary protection requirements, and would not risk introducing Earth life to Mars surface habitats.

Either that or there would need to be international agreement that Mars no longer needs to be protected from Earth microbes. To my mind, seems unlikely that either could happen before the 2020s or 2030s.

Meanwhile we could use telerobots to plant flags on Mars if that is the main aim of the mission. Or if humans are considered vital to this mission, we can plant flags on Phobos or Deimos.

In more detail there - the Outer Space Treaty is the only treaty we have to prevent siting weapons of mass destruction in orbit, or nations laying military claim to the Moon, etc - it's the main reason that we are able to do peaceful co-operative exploration of space. As well as the outcry from space scientists, the international upheavals resulting from something like this would be enormous. There is no way that the US or NASA could do this.

Or indeed any US citizen either or anyone using US hardware (or indeed any other signatory of the OST which includes all nations either space faring or with space faring ambitions). They are like quarantine laws; it doesn't matter how you get into space, you are still bound by them as a citizen of your country, which in turn is a signatory of the OST.

COST SAVINGS COMPARED WITH SURFACE MISSIONS

However it's interesting to notice that these orbital missions would cost less than a surface mission. Especially HERRO and the double Athena which Robert Zubrin proposed as a lower cost precursor mission. Have already mentioned this - this is a powerpoint presentation from the HERRO team, with details of the comparison.

The reason the orbital missions can do so much more in the same time period compared with a surface mission is that

• You can control rovers anywhere on the surface of Mars, so can explore multiple sites at once.
• There is no need to suit up and travel to the area of interest, you can do it all with shirt sleeves environment within the spacecraft.
• When you take account of the reduced mobility of a human in a spacesuit, with clumsy pressurized gloves, then there's no great advantage of humans over telerobotically controlled rovers on the surface as far as mobility is concerned. Spacesuit technology of course will advance, but so also does telerobotic technology.

Then as well as that, there is no need at all to develop technology to land a human mission on the surface of Mars. That's not just a matter of delta v. You can land on Phobos or Deimos with a gentle use of delta v over a long period of time, and right up to the last minute, as for the Moon, if anything is wrong with your trajectory, you just abort and move away from the moon a bit, figure out what went wrong and try again, with hardly any waste of delta v due to the low gravity of these moons.

With a landing on Mars surface, everything has to go exactly right during the "eight minutes of terror" of the Curiosity landing. There's also almost no chance of humans intervening to save the mission if something goes wrong, as everything happens so quickly.

So - that's a whole new technology needed for a Mars surface landing that isn't needed at all for a Mars moon landing. And major human safety issues with a Mars surface landing that again are not issues at all for a Mars moon landing.

Then with the new ballistic trajectory idea, it's possible that you could get to a low Mars orbit for similar delta v to a surface mission anyway.

Even if it weren't for the planetary protection issues then telerobotic missions would seem to be the way to go for more science return and indeed a more immersive way to explore Mars than a surface mission.

SUMMARY OF ADVANTAGES OF TELEROBOTIC EXPLORATION

• Best solution for planetary protection. It is hard to see how you could send humans to the surface of Mars without a risk of a hard landing which would contaminate a random area of Mars with all the hundreds of trillions of microbes in tens of thousands of species that accompany humans. If you introduce Earth life to Mars there is a major risk that you will detect life on Mars only to find that you brought it there yourself.
• Costs far less for more science return
• Far safer for the crew to get there. The landing on Mars is the most risky landing almost anywhere in the inner solar system, because the atmosphere is too thin for a parachute landing - and yet - there is just enough atmosphere so that once you start the landing sequence you are committed, unlike e.g. the Moon where right up to the touch down itself, the crew could blast off into space again. You can't do that on Mars because to go up into space again you need enough fuel to overcome the resistance of the atmosphere.
• Exploring is also far safer. Crew at all times remain in shirt sleeves environment in the orbiting spacecraft. All they can endanger is the "avatar" rover they control on the surface. And that, if damaged, can be repaired potentially. While if e.g. you damage your air supply to a spacesuit you die. The rover can spend days, weeks, even months just at one spot on Mars using only electricity from sunlight while a human explorer has to return to base for provisions, oxygen etc. It doesn't have to put on a spacesuit every day, which takes up an hour or two of every day.
• Crew can explore several parts of Mars simultaneously, and "teleport" instantly from one experiment to another - leave one rover doing routine analysis while they drive another, or direct sampling for another - so the crew do all the interesting stuff and the rovers do all the dull stuff by themselves.
• Mars from orbit looks quite Earth like, an interesting planet and the elongated HERRO Molniya orbit is especially stunning with close flybys of the spectacular landscape and the polar caps every twelve hours, with the landscape skimming past below your spaceship followed by a long fly out so far that Mars becomes quite small. Every day you have that experience, twice, and each time coming in over a slightly different part of Mars. On the surface you'd be stuck in a single spot from then on and probably not see that much, and in the dust storms, nothing at all.
• When you drive the rovers on the surface with telepresence and haptic feedback, and virtual reality goggles to see the Mars landscape in 3D - you'd experience the surface vividly, far more so than if you were really there. Our eyes are not adapted to the Mars light and everything would seem dim and reddish brown, with colours hard to discern and a dull butterscotch sky. Exploring via avatars we can colour adjust automatically to resemble Earth lighting conditions, indeed with a blue sky if you like.
• Whatever you see and feel is already digital streaming, so can easily be recorded and streamed back to Earth and so we can experience it here, just as you did. And examine the images to see if we spot anything you missed. And if anything goes wrong on the surface, again, you have everything recorded and streamed, so we can figure out what happened, no possibility of an unknown accident where someone falls and dies and nobody is sure why it happened.

COLLECTIVE SENSE ORGANS FOR HUMANKIND ON MARS

This idea that perhaps we shouldn't send humans to the surface of Mars because we'd contaminate it with Earth life is not much mentioned in the news. Out of dozens of news stories about ideas for human missions to Mars, perhaps only one or two will ever even mention it as an issue.

But it's frequently mentioned in the academic literature on spaceflight, with many publications debating the issue, and several planetary protection workshops on human missions to Mars. It's just that their deliberations rarely get into the news.

Here is a quote from "When Biospheres Collide":

"One of the most reliable ways to reduce the risk of forward contamination during visits to extraterrestrial bodies is to make those visits only with robotic spacecraft. Sending a person to Mars would be, for some observers, more exciting. But in the view of much of the space science community, robotic missions are the way to accomplish the maximum amount of scientific inquiry since valuable fuel and shipboard power do not have to be expended in transporting and operating the equipment to keep a human crew alive and healthy. And very important to planetary protection goals, robotic craft can be thoroughly sterilized, while humans cannot. Such a difference can be critical in protecting sensitive targets, such as the special regions of Mars, from forward contamination.

Perhaps a change in the public's perspective as to just what today's robotic missions really are would be helpful in deciding what types of missions are important to implement. In the opinion of Terence Johnson, who has played a major role in many of NASA's robotic missions, including serving as the project scientist for the Galileo mission and the planned Europa Orbiter mission, the term "robotic exploration" misses the point. NASA is actually conducting human exploration on these projects.  The mission crews that sit in the control panel at JPL, "as well as everyone else who can log on to the Internet" can observe in near real-time what is going on. The spacecraft instruments, in other words, are becoming more like collective sense organs for humankind. Thus, according to Johnson, when NASA conducts it's so-called robotic missions, people all around the world are really "all standing on the bridge of Starship Enterprise". The question must thus be asked, when, if ever, is it necessary for the good of humankind to send people rather than increasingly sophisticated robots to explore other worlds"

See When Biospheres Collide

FIND OUT MORE ABOUT SETTLEMENT OF THE MARTIAN MOONS

Slide presentation: One Possible Small Step Toward Mars Landing: A Martian Moon - and more details: Page on caltech.edu

Spaceshow talk about the idea Dr Josh Hopkins on David Livingston's Space Show

Concept map: Rationale for Human Exploration of Phobos and Deimos

The Scientific Rationale for Robotic Exploration of Phobos and Deimos : Scott L. Murchie

FIND OUT MORE ABOUT WHY WE SHOULD GO TO MARS ORBIT RATHER THAN TO THE SURFACE

For more background on why we should go to Mars orbit see Why Mars is NOT a Great Place to Live - Amazing to Explore From Orbit - with RC Rovers, and Nature Inspired Avatars