People often ask, "How close are we to sending humans to Mars" and it's not surprising given the optimistic presentations by Elon Musk and others. However, Mars is just too far away to send humans at this stage. As the Canadian astronaut and former ISS commander Chris Hadfield has said, "I think ultimately we’ll be living on the moon for a generation before we get to Mars". What we need to know right now is, “How close are we to sending humans back to the Moon”.

It is of little importance to be able to send the mass of a spaceship with humans to Mars. And whether it is one human or 100 humans, makes little difference there, it's not the main problem we need to tackle at present, except in as far as it helps with the return to the Moon, and so, indirectly, with our first steps towards interplanetary travel. We could have sent a dead astronaut to Mars decades ago. The challenge is to send a live astronaut there. And that’s much more than sending the mass of the humans + food + life support, water etc.


Need for experience - we couldn't fly the Apollo missions today, lost the expertise to do it

What we need is experience. It’s a minimum of 500 days but most often a two year journey to get to Mars and back. So far we have sent humans around the Moon, and we have sent two astronauts at a time to the lunar surface for up to three days at a time, with 1960s-70s technology which we no longer have. We couldn’t even revive the Saturn V and Apollo Moon hardware as the skills to make those components are now gone. Crude as they were by modern standards, we couldn’t make safe working copies of them today.

To quote from Robert Frost's answer on Quora (he is a NASA instructor and flight controller)

The Saturn V rocket had over 3 million parts.  The command and service modules and lunar module were composed of millions of additional parts.  An individual person cannot contemplate the scale of detail needed to assemble and operate those vehicles.

So, when the Apollo program ended, the factories that assembled those vehicles were retasked or shut down.  The jigs were disassembled.  The molds were destroyed.  The technicians, engineers, scientists, and flight controllers moved onto other jobs.  Over time, some of the materials used became obsolete.

If we, today, said - "Let us build another Saturn V rocket and Apollo CSM/LEM and go to the moon!"  it would not be a simple task of pulling out the blueprints and bending and cutting metal.

We don't have the factories or tools.  We don't have the materials.  We don't have the expertise to understand how the real vehicle differed from the drawings.  We don't have the expertise to operate the vehicle.

We would have to substitute modern materials.  That changes the vehicle.  It changes the mass, it changes the stresses and strains, it changes the interactions.  It changes the possible malfunctions.  It changes the capabilities of the vehicle.

See the rest of his answer on Quora for more details

Right now we do not have a safe way to send a human to the Moon. And Apollo built up to a lunar mission step by step. We can skip the early Gemini bits, we are well experienced in shuttling back and forth to LEO. Except - only in the Soyuz TMA. That itself is hard enough. SpaceX and Boeing are still not yet ready to send their first test flights with humans into space. Nor are Virgin Galactica or Blue Origin who plan to do sub-orbital hops first.

The problem is indeed partly safety. It’s not so much that we are no longer able to take such risks. It is more that the Soyuz TMA is such a reliable spacecraft, that it doesn’t make a lot of sense to fly humans into space on anything else until it is at least as safe as the Soyuz TMA. Because for humans, unlike unmanned cargo, safety is foremost in their minds. Even astronauts and test pilots, though they are prepared to take risks, they take managed risks. They are not reckless. Indeed they pay more attention to managing the risks and keeping them as low as possible precisely because of their profession as test pilots. Even today, many NASA astronauts started off as test pilots.

If an astronaut dies in a Boeing, or SpaceX mission who would have survived in a Soyuz TMA - how would we be after that? That would be a major blow. Especially if the inevitable investigation found that the accident was preventable.

So, we need to return to orbit first, the equivalent of the Gemini missions, but much safer because we have come to expect journeys to LEO to be reasonably safe. Then we have to send humans around the Moon like Apollo 8. We have to test any hardware probably in LEO. We have to test a lunar lander. Once we have all that together we can return to the Moon. This is not a trivial thing to achieve even today. Nobody currently can do it.

Once we have humans back on the Moon - medevac is two days to get back - but for a Mars mission it's two years

Once we have humans on the Moon - they then can get back to Earth in 2 days. When they are in LEO they can get back in a few hours. This is a significant difference. Someone in critical condition after an accident - then the difference between a few hours and two days can easily be life or death for a medevac. And space missions are dangerous and we may well have accidents on the Moon leading to astronauts having to be medevaced back to Earth.

It’s not just that. It’s also the life support. Components of the life support on the ISS have failed many times but it’s just a minor glitch because of multiple redundancy and resupply from Earth. Spacesuits also fail and need to be repaired and eventually replaced. And they send many tons of material to the ISS every few months. That will not work as a model for interplanetary flight. Indeed, it will also be much less practical on the Moon.

For interplanetary flight to be practical - well - we can use the ISS type system up to around two years taking lots of supplies. But it has to be very very reliable. If we have failure of the life support, multiple failures, on the journey out from Earth towards Mars - instead of getting back in a few days, as for Apollo 13, the equivalent Apollo 13 moment, perhaps a fire, explosion, or chemical release (very dangerous in the enclosed space of a spacecraft where you can't just open windows to ventilate it) means they have to be able to hold out for two years before they get back.

Then, a two year mission is pushing the limits of what we can do with the ISS type life support system. Preferably we need some margin. For longer periods we need better recycling than the ISS to keep the weight of the life support within practical limits. The BIOS-3 system based on aquaponics, aeroponics, and burning the plant residues, should allow very long missions, even decades or more, with no resupply, but is not yet tested in space. The MELLiSA system, based on composting residues, would also out perform the ISS on long duration spaceflights. But, excellent though they are both on paper and in tests in simulations on the ground, how can we rely on these systems for interplanetary voyages until they have been tested in multi-year missions in space? Systems often behave differently in space conditions, especially in zero g.

Any system that produces all the food the astronauts need by growing it, automatically keeps them supplied with oxygen too, with the plants as they grow taking up the CO2 that the astronauts exhaled while eating the previous generation of crops, and producing oxygen in its place, through the magic of photosynthesis. Algae can also provide oxygen, much more efficiently with a small volume of algae and light tubes so that light reaches deep within the solution - but sadly do not provide carbohydrates and don't produce the full range of amino acids humans need in their food. But are very robust with not much to go wrong. So long as there are a few algae cells left, sterilize the system, reintroduce the algae and it is soon back and running again (try doing that when a mechanical system fails!).

Or maybe we use artificial gravity, spinning for AG. There is evidence that human spin tolerance is far greater in space than on the Earth because there is no nausea inducing extra acceleration due to gravity along the spin axis (nausea may be due to the conflict of the spin induced gravity which triggers the vestibular system, which we use for orientation, and the linear acceleration due to gravity along the axis which triggers our otoliths, a different system for sensing linear acceleration).

Studies from Skylab suggest that though the vestibular system which sense orientation is very active in space, the otoliths which sense linear acceleration de-activate because there is no gravity for them to sense. The sensation of nausea may be due to a conflict between those two systems. This shows Tim Peake spinning at 60 rpm in the ISS head over heals with no nausea or unease at all. He says he couldn't tolerate this before or after. He talks about his vestibular system being de-activated - but actually according to the Skylab researchers it is the otoliths that de-activate.

More about this here: Astronauts don't get nauseous when spun rapidly in zero g - so could a device as simple as a spinning hammock be all that is needed to keep us healthy in space? (from my Touch Mars? book).

But if so, this needs to be tested too, before we can rely on it for interplanetary journeys. Indeed the final design may be very dependent on what spin rate humans can tolerate in zero g. A high spin rate and you can have small spinning centrifuges inside a large habitat. A very low spin rate and you may need two habitats tethered together bolas style with a long cable or an air-beam access tube.

If we are going to use AG, the life support needs to be tested in the AG conditions as well as transitions to / from zero g.

Natural place to explore next - the Moon - many surprises already and expect many more

The natural place to test this is on the Moon, or near the Moon (in orbit around it or in the Earth-Moon L1 or L2 positions). We could gain the experience needed for multi-year interplanetary flights anywhere, including in LEO, but the Moon makes a lot more sense because there is a reason for the astronauts to be there. It’s largely unexplored. It’s larger in surface area than Africa. It’s like an unexplored unfamiliar new continent. In the low gravity it may have caves that are kilometers in diameter, empty lava tubes - and there is evidence that there are caves that stretch for over 100 km. Certainly a fair number of holes into caves, the lunar “skylights”.

There may be deposits of platinum ore to find around the Aitken basin, splashed out from the core of an ancient impactor. There are cold spots as cold as liquid nitrogen at the poles and there is now known to be ice there, in crystal form (not just water bound up in rock).The more optimistic estimates are of millions of tons of it, but we can't see it visually in the total darkness of the craters at the poles that haven't seen sunlight for billions of years. Near to them are the "PEL"'s or "Peaks of Eternal Light" - I think best called "PEALS", or Peaks of Eternal (Almost) Light as they have "winters" with occasional dark periods of up to a few days, but for most of the year are in constant sunlight, and also have almost constant temperatures year round, both of which make design of a lunar base much simpler. And heat rejection is easy too since any horizontal heat rejection panels never see sunlight (often one of the big challenges is to keep a base cool and the ISS has huge heat rejection panels).

There will also be meteorites preserved in the ice or regolith in those craters, from Earth, Mars, Ceres maybe Venus, and at those cryogenic temperatures they should have organics preserved for billions of years. Including the organics of early life from Earth at least. There may be small shells and minute chunks of ammonites there from the Chicxulub impact into a shallow tropical ocean 66 million years ago. And Earth life from many other previous impacts over the past billions of years. If there was or is life on Mars, it may be there too. It might even be that the easiest place to study past life from Mars in exquisite detail is on the Moon! Because Mars doesn't have any spots that are quite that cold on its surface, or at depth either. Some meteorites could have got from Mars to the Moon in less than a century, and any organics preserved cryogenically ever since they got there. It may have life from Venus too if it was more habitable early on, as some think is possible. There are several papers exploring this idea of searching for traces of ancient life at the poles.

These ancient organics would be best preserved if the impact buried the meteorite deep into the regolith, or later ejecta covered it deep enough to be protected from cosmic radiation. We might find them through drilling or while extracting the ice for use by humans.

And above all to expect surprises - a place never explored before. And perhaps we need a way to make the Moon cool again? This has been promoted as a "zero gravity space race" but it can't really be, because Usain Bolt would not be able to run in zero g, just push off and glide, rather boring. He floats back to the ground at the end of each stride. How about a lunar gravity Usain Bolt sprint? With a lunar backdrop? And - on the Moon he would be so light, he could run on water! New lunar gravity sports.

Usain Bolt floats to victory in zero-gravity race (click to watch on YouTube)

So - I think we will only send humans to Mars, at least, if we are sensible, after first returning to the Moon - and not only that, after expeditions to the Moon of similar length. Before our first 2–3 year journey to Mars and back, I think we need to have at least similar length - but for a safety margin, somewhat longer missions to the Moon - where people head off with supplies for 3-4 years and are never resupplied from Earth during their mission there. That would simulate a Mars mission. And would be a huge challenge. There may well be occasions during that 3-4 years when something fails unexpectedly and they can’t fix it and have to abort back to Earth or ask for emergency supplies from Earth. That then would mean they have to do more tests until they are sure they have eliminated such issues.

I think it is only after we have had at least one and possibly 2–3 such missions (could be overlapping) before we feel we know enough to confidently send humans to Mars orbit.

2016 HO3 as an 'Ultima Thule' of the Earth Moon system, 100 lunar distances away

There are some other targets though, close to Earth, that are further away than the Moon but not nearly as far as Mars. An example would be 2016 HO3, a quasi-satellite of the Moon, about 41 meters in diameter which varies between 38 and 100 times the distance to the Moon. If you want to go to a place with a longer medevac back to Earth but not nearly as bad as Mars, then it would be a natural next most adventurous place to go. There are many asteroids that pass much closer to Earth - but if you were to rendezvous with them, you would soon be carried far away as they continue on their orbit.

With 2016 HO3, you can stay there for years and still remain within 100 lunar distances all the time. It's a bit like the old nineteenth century light house keepers living in a lighthouse on a distant rock in the ocean. And at 41 meters in diameter - that's large enough to have resources worth mining, and perhaps returning to the Earth Moon system or using in situ. At, say, 2 tons per cubic meter that would be over 72,000 tons of material.

It is surprising how much living space you can construct out of a small asteroid. For instance, if it was made into cosmic radiation shielding, assuming that same density, it's enough material to shield a miniature Stanford Torus type habitat with an outer radius of about 50 meters and the tube diameter about 20 meters, spinning at about 4 rpm for full g.

That gives you an internal living area over 5,000 square meters (depends how you measure it, that's the area you get if you build a circular strip inside the torus at its maximum diameter cross section) with head room for buildings of up to 6 stories inside. It would comfortably house 125 people and with multiple layers, as for the Kalpana one design of torus habitat, many more.

Techy details indented.

Techy details. If we assume 2 tons per cubic meter density, the mass is enough to provide (4/3)*π*(41/2)3/4.5 = 16,000 square meters of radiation shielding at 4.5 tons per square meter. (16,038 more exactly)

A torus 50 meters outer radius and 30 meters outer radius has a surface area of π2 * (R2 - r2) = π2 * (502 - 302) = 16,000 (15,791) square meters leaving around (16,038-15,791)*4.5= 1,100 tons spare to use for other things.

I used Spin Calc for the rpm figure. You can use this online torus volume and surface area calculator for the radiation shielding area calculations.

To approximate the living area - a cross section of the tube half way up has a living area of 2*π*40*20 or about 5,000 square meters (5026)

With the BIOS-3 system then you can grow enough food for one person from 30 square meters, and add 10 square meters for personal living space, quite generous for a space habitat, and you have enough space there for 125 people. But that's with an internal space 20 meters high in the middle of the torus, or about six stories, so you can clearly have more than that, up to several hundred people, if you have different levels inside as for the Kalpana One design.

But a more efficient way to shield the colony is to use a spherical (like Bernal sphere) or a cylinder design (like O'Neil habitats). With a radius of 40 meters and length of say, 12 meters, and 12 layers, with 3.33 meters spacing between the layers, I make it that at 10 square meters per person you could house 578 people in the outer two layers, and the remaining 10 layers would have more than enough space to grow crops to feed them all. It might be possible to go up to 1000 people with more efficient use of the agricultural areas with multiple layers and spacing dynamically changing as the plants mature from seedlings (almost zero spacing between layers) to full height, 0.6 meters for dwarf wheat. There I'm assuming that many crops will grow well with lower gravity levels than full g, after all some are fine even in zero g. That includes a total of 74 tons of atmosphere, about 128 kg per person, which would need to be imported. See my reply to Jocelyn Boily for the detailed calculation. . You could also use cylinder with partially rounded or half spherical end caps, which helps with the engineering and also increases the volume needed for low gravity agriculture with little increase in the shielding mass.

All this is assuming shielding of 4.5 tons per square meter which comes from the original Stanford Torus design, assuming lunar regolith. The amount of shielding depends on the materials, so, what the asteroid is made of, and what you decide is an acceptable life dose, if people are living there for long periods of time. It also depends on the design, for instance, a layer of water on the interior can help absorb secondary radiation produced when cosmic radiation hits other atoms as it slows down. The calculations of radiation dose are also very complex, and they incorporate details of the habitat design and the shielding layers

Also, as a way to reduce the shielding requirements, It might be better to have the outer level of the habitat reserved mainly for storage / fuel / plumbing / water tanks / sewage treatment / life support and as much as possible of the rest of the complex infrastructure needed to sustain the colony - and any remaining space there used for agriculture to act as additional shielding. Then the outer shielding mass could be reduced and people live one floor up from the outermost level.

However, this is enough to show that we could have a settlement of several hundred people using the materials of this small asteroid for radiation shielding. It's a sort of "ultima Thule" of our Earth Moon system (Ancient Greek and Roman name for a place in the distant far North beyond the known world).

That could be a prototype for later habitats throughout the asteroid belt. See my Asteroid Resources Could Create Space Habs For Trillions; Land Area Of A Thousand Earths

Mars flyby and Mars orbit

There’s a really nice free-return mission to Mars by Robert Zubrin called the “double Athena” where the astronauts do one flyby of Mars, fly almost parallel with it for half a Martian year, and then do another flyby and return to Earth. It is “free-return” which means that apart from minor course corrections, when you leave Earth you are already on a trajectory that will return you to Earth two years later. This makes it a particularly safe mission. Also during the flybys and for a long time before and after, the crew are able to control rovers on the Mars surface with much less delay time than anyone on Earth. So it’s a great mission for science too.

Longer term, I think humans should study Mars from orbit, not on the surface. Because there may be biology on Mars. And if so - it could have a biochemistry different from Earth life.

Need to understand the Mars biochemistry - and it is not guaranteed to be safe for Earth life, or Earth life safe for Mars

Diseases are actually more virulent if they are not adapted to the host, which is why bird flu is so much worse than human flu. Well, we can’t have viruses from Mars. But we can have diseases like Legionnaires’ disease which is a disease of biofilms that uses the same methods to infect amoebae and also human lungs. A similar disease from Mars could easily be far more dangerous. Especially if it is based on an unfamiliar biochemistry. In the worst case, Earth life simply has never developed any defences, never having met its like in the past billions of years nothing like it - and it just grows in our lungs like a petri dish culture, with no resistance at all. The nobel prize winning astrobiologist and microbial geneticist Joshua Lederberg put it like this, when discussing a Mars sample return:

"If Martian microorganisms ever make it here, will they be totally mystified and defeated by terrestrial metabolism, perhaps even before they challenge immune defenses? Or will they have a field day in light of our own total naivete in dealing with their “aggressins”?

from: "Paradoxes of the Host-Parasite Relationship"

There are many other things could go wrong biologically. These are worst case scenarios, but we have to consider them. There is no guarantee at all that Earth life will be unaffected in the clash of two biospheres that have been separated from anything from millions of years to most likely billions of years or never had any connection biologically (it is not easy to transfer life between those two planets via meteorite and it may never have happened).

So, I think our top priority first has to be to study Mars astrobiologically and discover if it is safe to land humans there -safe for humans and Earth - and also - safe for Mars too. It would be so sad to make all Martian life extinct - and the worst case in that direction is some early lifeform that has not yet developed resistance to fight off even the most unaggressive of modern Earth life. In that direction it might be Earth life that is like the microbes growing on a petri dish of Martian life it doesn’t even notice and the Martian life doesn’t recognize it as a threat until it is gone.

We need to know such things first before we can make informed decisions.

Benefits that would flow from developing a 100% sterile rover - feasible with Venus lander technology

This, particularly, is a personal view for discussion. I think our top priority should be to develop sterile rovers for Mars. 100% sterile. It is possible using the technology explored for Venus surface landers able to withstand temperatures that would destroy all Earth amino acids. Temperatures of 300 C are enough for that and they found that there are many commercial components designed to withstand such temperatures in high temperature applications. There may be other methods too of achieving 100% sterile rovers.

Could we design astrobiological instruments that can be 100% sterile as well? And integrate them into a 100% sterile rover without compromising its sterility? If we can do that then our rovers could explore even locations with liquid water or habitable brines without any risk at all of confusing the searches with Earth based biology and we'll be able to find out what is there in the clearest most unambiguous way possible.

It seems not impossible. Brian Wilcox is working on a 100% sterile probe to descend into the Europan ocean. It would have vacuum insulation like a thermos flask, a blade that cuts ice chips that the body then melts and analysed. It would be heated to over 900 °F (500 °C) during its cruise to Europa.

With sterile landers then we can plan to send vast numbers of them to Mars - small sterilized, highly capable and then maybe we can tease out its present day astrobiology and then make properly informed decisions about whether and how to keep Mars safe for Earth life and Earth safe for Mars life. And it is not ruled out at this stage that the only way to keep both safe is to keep the two biospheres physically separated from each other. I do not think we should assume that it is going to be okay to land humans on Mars.

For more about this: Can we achieve 100% sterile electronics for an Europa, Enceladus, Ceres, or Mars lander? in my "Touch Mars?" book.

What do you think of this idea? Do say in the comments.

Our vast solar system to explore

There are many other places in the solar system we can send humans - including the asteroid belt with materials enough to make radiation shielding and habitats with a total surface area for living of a thousand worlds the size of Mars, or the land area of Earth.

Further afield, Titan seems to be by far the easiest place for humans to live outside of Earth because its atmosphere is so thick, indeed, somewhat higher in pressure than Earth and with reliable strong winds a few kilometers above the surface (although calm at the surface) and other energy sources such as “hydropower” from differences in levels of the ethane / methane lakes, to power a colony.

On Titan, instead of a $2 million spacesuit, you need little more than a very thick wet-suit and a closed system air breather. Although the suits are thicker, it’s about the same technology level as equipment on display in a shop for diver’s equipment. And you have natural protection from cosmic radiation from the atmosphere, - and in those cold conditions it’s so cold Earth life can’t survive and it is possible that any native titan life finds Earth habitats too warm for it too.

So anyway there are lots of possibilities here.

I do not think we should fixate on landing humans on Mars. I think our goal should he Mars orbit and the two moons of Mars and to explore it from orbit -and then after that, decide what to do as a result of whatever we discover about Mars as we explore it telerobotically.

Timescale - another generation - optimistically first humans to Mars orbit by the 2030's, land by 2040's (if safe to do)??

As for the timescale - at least 10 years but the clock doesn't start ticking until mid 2020s or later because all the available finance is tied up in the ISS. Once that reaches the end of its life - will we have the finance that’s enough to return to the Moon and do something as ambitious as three year missions to the Moon with no resupply from Earth? I don’t know. Maybe commercial space can help there.

Anyway, let's suppose optimistically that by the late 2030's we already have a decade of experience on the Moon. By then hopefully we have had several successful 3–4 year missions to L1 or L2 or similar that needed no resupply from Earth for the entire duration of the mission, and had no incidents that required medevac to Earth or resupply from Earth or the crew aborting back to Earth. Either that or we have new technology that significantly reduces the journey time to Mars, perhaps to a few weeks. This is all rather optimistic.

If we do that then in the late 2030's we may see our first manned missions to Mars orbit. Meanwhile we explore it from Earth robotically. And then telerobotically from Mars orbit. I doubt if you could get a good estimate for the timescale for a thorough astrobiological survey. It could be speeded up though by then with miniaturized rovers, if we could send them by the thousand, sterile miniaturized telerobotically controlled rovers with even more advanced instruments than we have today, who knows how fast the survey could be done. Perhaps a decade, perhaps just a few years.

We could do the survey faster if we can deploy thousands of miniature rovers and have perhaps 100 or more people tel e-robotically exploring Mars - perhaps in an instant space station in orbit around Mars consisting of a couple of BFR's tethered for AG, if Elon Musk's bold plans come to fruition.

Remember the surface is as vast as the Earth's land area, and there are now many potential habitats to explore. It could take a while. Then you have to study the life to see if it is safe once you find it.

If it is safe for humans to land there, then I’d imagine perhaps the mid 2040's but it could be 2050's before we feel we know enough about Mars especially if the survey turns up challenging questions to solve, or the Martian life is potentially hazardous and needs careful investigation. All this could easily be extended by a decade or two. If we think of a generation as 30 years, then - that's about a generation into the future from now, assuming a vigorous return to the Moon, and then several multi-year focused missions to test systems needed for multi-year interplanetary journeys.

As Chris Hadfield put it: in a New Scientist article: "We should live on the moon before a trip to Mars"

"I think ultimately we’ll be living on the moon for a generation before we get to Mars. If the world and the moon were threatened and the only way to preserve our species was to launch from Earth, we could go to Mars with yesterday’s technology, but we would probably kill just about everybody on the way."

"It’s as if you and I were in Paris, paddling around in the Seine in little canoes saying, 'We’ve got boats, we’ve got paddles, let’s go to Australia!' Australia? We can barely cross the English Channel. We’re sort of in that boat in space exploration right now. A journey to Mars is conceivable but it’s still a lot further away than most people think."

The Moon is not only safer, it's also a natural place to begin to develop reliable technology for multi-year missions throughout the solar system. If we can achieve that then the cost of human missions to the Moon will go down dramatically to a fraction of the normal cost. Imagine what a cost saving it would be if we could send a crew to the Moon for two years with no resupply from Earth, as if it was an interplanetary mission to Mars? We need these shake out cruises close to Earth first.

Lunar L1 and L2 positions as ideal for interplanetary flight shake-out cruise

If we want to simulate a Mars mission more exactly, then we can have missions at the Earth -Moon L1 or L2 positions. These are points where the Earth and lunar gravity balance, allowing a spaceship to "hover" above a single spot on either the near or far side of the Moon. They aren't stable positions, typically the spaceship has to do occasional station keeping maneuvers, but "halo orbits" around them are nearly stable. There are also interesting similar nearly stable orbits that let a spacecraft approach close to one or the other pole of the Moon, and even more useful, a spacecraft can navigate between all of these orbits with only meters per second of delta v. So - they would not be "stuck" in the L2 position above the far side of the Moon, unless they want to stay there to test the psychological isolation of being unable to see Earth (perhaps with simulated delays in communications). If they don't need to do that, they could move their spaceship around from time to time to explore either poles close up, or the near or far side of the lunar surface and provide remote operations support for support surface missions too. They could be useful in their own right for exploring the Moon while at the same time simulating the conditions of an interplanetary cruise rather faithfully.

Once we have biological closed systems working on the Moon, then missions throughout our solar system that last for a decade or more could be as easy to support as ones that last for a couple of years or less. Once we have that capability, we can go to Venus, Mars and beyond, even to Mercury, the asteroids and Jupiter's Callisto, and then eventually out to Titan too, with no worry about narrow safety margins.

Isn't this just because of NASA being over-cautious?

We are often told by Elon Musk and others that the reason is that NASA is over cautious. But, they just do what the politicians ask them to do for human spaceflight, and have little more than an advisory role. They have a lot of autonomy for unmanned spaceflight, but by tradition it's the president and Congress who decide the goal for human spaceflight. There was no way they could have just continued through the space shuttle disasters and continued to lose astronauts. They had to solve those problems. If SpaceX has similar disasters, say one of its BFR's crashes with 100 people on board, that would lead to immediate halting of their program as they figure out what happened. They can't just go off into space killing astronauts by the hundred every 20 launches or something. Not when we know it can be done safely with the Soyuz TMA. And I am sure they won't do that. It is just spin basically, I am sure they wouldn't really be reckless, they would do managed risk just as NASA does.

Indeed, I think their early customers, commercial tourists, would actually be more sensitive to such things than NASA astronauts - the astronauts after all, many of them are still test pilots to this day, and are used to dangerous missions where they know they can die. One of the things that hit people particularly hard with the Challenger disaster was the death of Sharon Christa McAuliffe, a school teacher. How would they react to a spaceflight crash that kills Brad Pitt, Angelina Jolle, Lady Gaga, Justin Bieber, Tom Hanks, Katy Perry, Leanordo di Caprio or princess Beatrice to name a few who have signed up for the Virgin Galactica suborbital hops.

The multi-millionaires and the billionaires who fund the first commercial tourist space flights will decide with their wallet, for instance if Boeing has no crashes and SpaceX does - who would you fly with, if you can afford the price to orbit? Even if Boeing cost twice as much , I think most people would try to save up more to fly with Boeing if it meant there was a far higher chance of surviving the flight.

I don't think it is anything to do with NASA. If they had a directive from the president to send humans back to the Moon, for instance, they would rise to the challenges. Put a new administrator in place if the current one was not in support of the idea and then go ahead and do it.

As for shuttling back and forth to the ISS, that's a matter of the vision of politicians. They can only do what politicians ask them to do. They are much free-er when it comes to unmanned missions. But for manned missions, they are not the one who "pays the piper". The president does, by tradition, in the US, ever since Kennedy. NASA only advise.


What about the BFR?

If SpaceX succeed in building Elon Musk’s BFR, and it fulfills their expectations, it makes no difference to this. He has to show it is safe to get into space - even more so with potential of 100 people dying in one crash. He’d still have the same situation, that it will have an unproven life support system - not proven in space anyway - and he’d surely want it tested on the Moon or somewhere closer to hand first. An Apollo 13 type scenario with a BFR departing from Earth for Mars with some failure in is life support means 100 people who have to somehow last out for two years before they can return to Earth in an emergency. I don’t see it as speeding up the timescale.

Yes, it leads to more people able to travel in one go. But also more people who would die in an Apollo 13 type disaster for a mission to Mars. So it has to be tested in equivalent length shake out cruises with easy return to Earth in an emergency and a natural place to do that might be to put it in L1 or L2 and see if 100 people can last there for two years studying the Moon from orbit via telerobotics with no resupply from Earth.

So, his BFR makes little difference here in my view, except in as far as it may help humans get back to the Moon, and so perhaps help us to start building up the experience we need for our interplanetary journeys at an earlier date. If we are going to do this in a robust way with an eye to the future, this must be tested in space conditions nearer to hand, first on the Moon, or other nearby targets. Places close enough for emergency resupply from Earth and the ability to return to Earth within days if the integrity of the base or station or its life support is threatened, e.g. after a fire, chemical release or equipment failure.

However, if we do get that interplanetary travel capability, not just Mars but the entire solar system, eventually out to Saturn and beyond, will be open to us to explore with human missions, perhaps a generation from now, maybe in the 2040's or 2050's if you are optimistic. The key to that is efficient closed system recycling, robust life support, and systems tested in multi-year shake-out missions in the Earth Moon system. Luckily for us, we have a fascinating world right on our doorstep, the Moon, our nearby "eighth continent" as it is sometimes described, nearly as large as Asia, five times the size of Australia and larger than Africa, largely unexplored.

Originated on quora

This originated as my answer to

on Quora.

Open ended human exploration in space with planetary protection at its heart

I am a keen supporter of humans in space, but responsible human spaceflight. Managed risks but not reckless, it is dangerous exploring in a hard vacuum, and astronauts reduce risk as much as they possibly can. Also that respects the integrity of science, not extinguishing any native life until we know what is there and can make an informed decision, and keeping Earth protected at all times. This is just sensible in my view and many agree with this.

There is much we can do by way of exciting missions for humans consistent with this approach, starting with the Moon. Then further afield the entire solar system eventually will be open to us, but only if we develop safe ways to do our interplanetary voyages. For the details see my:

I have written three books on the topic of humans in space and ways to do both - to explore in space with humans in an exciting and ambitious way - and at the same time to do it responsibly, to protect both Earth and other planets and to leave the future open, not to do things that close down our options before we know what they are.

My Touch Mars? book also looks at the history of planetary protection and some of the many possible locations for life in our solar system, and indeed elsewhere, and how we can search for it. Further into the future it raises the broader question of whether we need "Galaxy Protection" once we develop the capability to visit other stars, and I explore the idea of Galaxy Protection as one solution to the Fermi paradox of "where is everybody?" I also cover nitty gritty questions such as trash on the Moon, how you would grow plants in space, possible science surprises from our explorations and many other topics. I look at the practicality of human settlement and look at questions that might arise as we try to send humans further and further afield into our solar system.

I hope it's a fun read. The sections are self contained as far as possible so that you can use it as a book to dip into, rather than one you read from cover to cover.

You can read my Touch Mars? book free online here:

Touch Mars? Europa? Enceladus? Or a tale of Missteps? (equivalent to 1938 printed pages in a single web page, takes a while to load).

You can also buy it on Amazon kindle.

My other books, which cover human exploration as well as planetary protection, and explore the case for going to the Moon first (for humans), are:

My books are all designed for reading on a computer with links to click to go to the sources, and I have no plans to attempt printed versions of them.

Facebook groups

Notifications of future posts

You can get notifications of new posts on my Science 2.0 blog by following the announcements on twitter. You can also 'like' my Facebook page: Science20 Blog Alerts

Thoughts or comments

Any thoughts or comments - do say below. Also if you spot any errors in this, however small, be sure to say.