Elon Musk, and NASA both have in mind the idea of doing interplanetary voyages straight away, aiming for Mars, with Obama going so far as to say about the Moon: “But I just have to say pretty bluntly here: We’ve been there before.”. If you hold that view, you are undoubtedly in distinguished company.

Now - there are two things here - yes we've been to the Moon before - but is that the end of all interest in it? But first - how ready are we for interplanetary voyages? 

We last visited the Moon, nearly four hundred thousand kilometers away, in the 1970s. Since then we have been shuttling back and forth to the ISS flying a few hundred kilometers overhead for decades. We have never sent humans as far as geostationary orbit since the 1970s. We have never gone beyond the safety of the Earth's magnetic field protection from solar storms since then either.

With this background, can it indeed be true that we are ready to send humans to embark on this hundreds of millions of kilometers multi-year journeys to other planets? Well actually NASA also think that we need precursor missions, the Asteroid capture mission will be a preliminary experience to start on developiong some of the technologies needed, with astronauts spending 24-25 days in lunar orbit.

Even that is quite a major step forward from the ISS. Astronauts are required to keep "lifeboat spacecraft" attached to the ISS at all times so that they can get back to Earth with a few hours notice in an emergency.

Soyuz spacecraft attached to the ISS. The crew are required to keep spacecraft attached to the ISS at all times, with enough seats to return everyone back to Earth. In January this year the crew had to evacuate the US part of the ISS after a toxic leak alarm - they took shelter in the Russian segment. In an emergency they could evacuate the ISS to the Soyuz and if necessary return to Earth.

When we feel we need these lifeboats to be safe on the ISS, so close to Earth - it seems just a little ambitious to embark on an interplanetary mission right away. From this, to then set out in a spaceship for years on end, no lifeboat, no resupply from Earth?

What happens if your astronauts have an "apollo 13 moment" half way to Mars or Venus or wherever they are going? What if they get a toxic leak alarm, or their oxygen generators stop working, or some vital bit of equipment fails...

MOON - "BEEN THERE BEFORE" - HOW MUCH DO WE REALLY KNOW ABOUT IT?

As for the idea that "we've been there before" for the Moon - it's becoming more and more clear that the Moon is a place just on our doorstep that we know very little about. In some ways we hardly know more than we did in the 1970s.

For instance, it was suggested recently that the Moon may have lava tube caves ten kilometers in diameter, large enough to house entire cities. We can see the winding 10 km width rilles from above but have no way to know if they are hollow, We see holes in the lunar surface but don't know where they lead. Nobody has ever looked, and no machine has ever looked. 

 Inside of one of these proposed lunar lave tube caves, with the city of Philadelphia shown for scale. Credit: Purdue University/David Blair See There Could Be Lava Tubes on the Moon, Large Enough for Whole Cities

When we don't yet know if the Moon has caves large enough to house cities, how much do we really know about the Moon?

There are many other things we don't know, e.g. we now know (or are pretty sure) that it has ice mixed in to the surface in polar regions, but how much, how deep, does it extend beyond the polar regions? Is there ice in lunar caves?

And what is in that ice? It's likely to have a record of the history of the early solar system. The ice at the poles of the Moon could be the "Record keepers of the early solar system" as Greg Delory put it .

We can also search for meteorites from Earth on the Moon to help fill in the gap in history of evolution on Earth. Experiments with fossil diatoms mixed into a simulated meteorite fired at speed to simulate impact on the Moon suggest that fragments of fossils could survive the impact - and that would be over the entire history of the Earth. Ancient Earth fossils could be found on the moon. There could be ancient organics from the early solar system in the lunar polar ice.

Another thing we can do on the Moon is to find out how much organic contamination accompanies human explorations. E.g. before we send humans to Phobos or Deimos or wherever they go next, we'd better know what humans will do to a celestial body when they set up a settlement there. Especially if the aim is to study ice deposits in craters and such like. Organic Measurements on the Lunar Surface: Planned and Unplanned Experiments

We don't yet know the age of the largest crater on the Moon, the Aitken crater. Just a few samples of rocks returned from this crater would establish this.

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.

Our radio telescopes on the Earth simply can't look at the sky at all on many wavelengths. All the frequencies used for terrestrial transmissions are blocked off to them. And even then they get interference from microwaves and such like that leak into regions of the spectrum intended to be kept quiet for radio observations. Radio telescopes on the far side of the Moon could search for radio emission from our galaxy and the universe in those blocked off hidden regions of the radio spectrum. And they can be quite simple to construct, especially long wave telescopes, just wires trailed across the surface of the Moon.

Now, we have the head of the ESA proposing a "lunar village" on the Moon. This is something we can certainly do, as we've been to the Moon already, so is no doubt that we can send humans to the Moon. 

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ESA idea of a lunar village on the Moon.

So - the Moon has plenty of interest and I'm sure someone will go back there soon, if not NASA.

Humans may not be totally needed on the Moon. Perhaps we can do much of this with telerobotics and robotic missions from the Earth. Same may be true for Mars also.

But given that we are going to continue to have a human astronaut program, then the Moon seems a place where human presence may be of value.

LAUNCHING HEAVY MASSES ON AN INTERPLANETARY JOURNEY IS THE EASY PART

Technically challenging though it is - it doesn't require 2010s technology to send heavy weights to Mars. They could have sent lunar module sized vehicles to Mars with the 1970s technology - the delta v needed is the same as you need to go to the Moon. We no longer have that capability but may have it again soon.

But it is no use sending human corpses on these voyages. The complications arise when you want to send a living breathing healthy human on an interplanetary voyage. 

USING ISS TECHNOLOGY

If we did want to do this right away, in some ways maybe the best is to just use the ISS technology. 

The ISS is not at all self contained. They have to ship tons of water for the oxygen, CO2 is just discarded, solid wastes returned to Earth, burn up in the atmosphere. They can't even do their own laundry - but instead just put dirty clothes into the Soyuz to burn up in the atmosphere and get a bunch of clean laundry sent up in the next Soyuz from Earth.

But we could do that. Ship many tons of water, also used for oxygen, spare clothes for the entire journey so they don't need to do laundry, food for the entire journey, use multiple redudundant systems, with spares, and only use technology that's already been proved to work on the ISS.

With some of the approaches under development for heavy lift we may be able to launch that much mass on an interplanetary journey. That would be - if not nearly as safe as the ISS because there is no "lifeboat" - at least - they would have a decent chance because they would be using equipment that is reasonably well tested close to Earth, and we've had time to find out some of the things that can go wrong. 

But it seems an expensive and inefficient way to do it. The ISS just was never designed as a test bed for interplanetary travel. And the system was not designed as you would design it for a long distance voyage - it's all based around this idea of regular resupply every few months.

And there are still many questions to address, things that don't arise with the ISS. For instance, what do you do about the many tons of waste that have to be burnt up in the atmosphere every few months from the ISS? Take that with you and pack it around you to protect from solar storms? Could do, it's one suggestion. But if so - that's an untested system also.

What if your food all spoils when you are half way around the voyage. Or if all that waste in some way interferes with the environment control system. And how do you protect from solar storms? That's one thing never tested in the ISS.

And what do you do about the effects of zero gravity? Lots of exercise, two hours a day, and medicine to help combat effects of zero g. Or do you spin your spacecraft with tether system or centrifuge?

Perhaps all this and more can be solved, but is this the best way to go ahead, to adapt the ISS technology to interplanetary spaceflight as best we can do it?

OTHER APPROACH, DEVELOP BETTER METHODS CLOSER TO EARTH FIRST

The other approach is, that we can do research closer to Earth first, learn to develop more closed system methods, new systems not used in the ISS. 

Generate oxygen with algae (something proved to work with Russian research but never tested in space), reuse that CO2. Do experiments with artificial gravity. Learn to grow food in the habitats, and to recycle more of the wastes. Experiment with many different ways for surviving long term in space settlements. Do experiments in artificial gravity and find out for sure if it helps or not, and how much and how to generate it.

All the time we are exploring the Moon and doing good science here, discovering things we never knew before about our nearest neighbour.

If we do it this way, then we have many years, perhaps a decade or so, exploring the Moon and developing experience in using this technology to work at a distance from Earth, with ability to come back to Earth within two days, instead of the few hours of the lifeboats for the ISS.

If your overriding aim is to get humans to Mars orbit as soon as possible, and other discoveries you make along the way are of no interest to you, then this may not be the quickest way to do it. If there was some big "moon project" with the only aim to send a human on an interplanetary voyage, then maybe you wouldn't do it this way.

But it is the safest, surely, and it lets you explore the Moon as well as Mars. We don't give up on Mars, or the outer solar system or many other interesting places. But we explore them with robots, for as long as that's the best way to explore them. And leave sending humans there until we are able to do it safely and relatively easily.

COAST HUGGING

When Columbus discovered the New World by crossing the Atlantic, or indeed earlier the Vikings in their longboats when they reached Canada - they both sailed in boats that were the result of many centuries of development.

For many centuries, long coast hugging voyages were done in ships like this

Phoenician ship, 2nd century AD

They had the boats, and more importantly, also had experience in equally long journeys closer to shore first. Any emergency that they were likely to encounter on a long sea voyage, they had already encountered close to shore, before anyone attempted to sail right across the Atlantic.

I'd argue that we are still at the coastline hugging phase for planetary exploration. We need to do it one step at a time. Otherwise we'd be a bit like a Phonecian trader heading off on a westerly heading into the open Atlantic

KEY TO APOLLO'S SUCCESS - STEP BY STEP

This was the key for success for the Apollo missions. Before they went to the Moon they did many flights first in the Gemini series to Earth orbit. Including testing of docking maneuvers. Then in Apollo, first to Earth orbit, then flyby of the Moon, then orbiting the Moon, and in case of Apollo 10, the astronauts went nearly all the way down to the surface, and returned to orbit again without ever touching down. Which turned out to be just as well as they turned up an issue with the spacecraft that could easily have been fatal if they had gone on to land.

Then finally Apollo 11 lands on the Moon.

In the same way I think we need many precursor missions before it is safe to do our first interplanetary missions. And because the interplanetary mission is multi-year - I'd have thought those should include multi-year missions closer to home also - which increases the timescale a fair bit.

The main things we need to develop are

• Closed systems able to function on long journeys for years on end - not needing continual resupply from Earth and disposal back to Earth. This is perhaps most challenging.
• Keeping astronauts healthy - what is the "gravity prescription" for health and can it be supplied with either centrifugal sleeping compartments, or tether system - or is it better just to fly in zero g with lots of exercise and drugs? 
• Protection from cosmic radiation and solar storms.

Now - if a private individual, say Elon Musk, or Dennis Tito with his Inspiration Mars, wants to set out on an interplanetary cruise, you could say they can take the risks on themselves. So long as they keep to the requirements of planetary protection.

But then - is that really the case? It would be a major set back for human exploration of the solar system if everyone died on a mission like that. As well as a tragedy for everyone concerned.

I think we have an obligation to take a really hard headed look at these proposals and ask the proponents challenging questions - can we really do it? Should we not do the planet hugging missions to the Moon first, in the same way that early sea voyagers did continent hugging journeys long before they crossed the larger oceans?

As a discourse of course, not rhetorical questions trying to win them over. As real questions and listening to their answers.

And then, if you are confident enough that you have the technology to send humans to Mars orbit or Mars flyby - still - why not send humans back to the Moon first? 

This will give a low cost way of exploring the Moon also, because if you can send everything in one launch from Earth, or a couple of launches, as you'd do for an interplanetary mission, and send it all to the Moon and all other communication is by radio for the next two or three years - it surely will cost a whole lot less than the ISS with its many launches every year. 

And if that doesn't work out, then you can learn from that, redesign and test again until it does work.

For me, it's a "no brainer" we should go to the Moon first. So the ESA's lunar village, for me, wins hands down over ideas to try to send humans to Mars (orbit).

I keep saying Mars (orbit) in this in order to avoid getting caught up in the discussion of whether we'll be ready to go to the Mars surface. As far as Mars orbit then there's no great issue with planetary protection so long as it is done with great care so that there is no chance of impact onto the surface of Mars. 

If we are ready, then great, let's head off and explore the Mars moons of Phobos and Deimos and explore Mars by telepresence from orbit. That much we can do without any planetary protection issues if we do it carefully. See To Explore Mars With Likes Of Occulus Rift&Virtuix Omni - From Mars Capture Orbit, Phobos Or Deimos.

But the issues of safety for humans arise strongly, in my view - at least on basis of what I've found out so far. 

I'd go so far as to wonder if it is a responsible thing to send humans on interplanetary voyages, for years on end, hundreds of millions of kilometers from Earth, until we've had a fair bit more experience, say a couple of decades or so, of sending humans first a couple of days travel away and a few hundred thousand kilometers away to the Moon. 

Otherwise - and this is just an analogy, don't want to draw too close a parallel. But I think that's a bit like a phoenician trader attempting to sail across the Atlantic in a boat designed for voyages around the shores of the Mediteranean.

Yes physically we can send humans on interplanetary voyages - but - do we have the experience to do it responsibly and safely yet? Would our astronauts have any reasonable chance of surviving such a voyage without previous experience of "coastline hugging" voyages closer to home in the Earth Moon system?

What do you think?