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Leaving aside the matter of how well would humans fare on the surface of Mercury (we only have to factor in the weight of their life support: air, water, food and spacesuits), and assuming materials and methods available today, would it be possible to come back from Mercury once you landed? You'd have to either carry the fuel to thrust away from Mercury and the Sun or to produce it locally (if it's possible to produce the fuel locally, we can assume any number of previous one-way missions taking the necessary machinery to Mercury, and the crew of the return mission would only have to assemble and operate such machinery).

The B-side of the question: how much would it all cost, very roughly speaking?

Finally, if there's no way of making it, is there any current research being conducted on something that would hint at promising the possibility of such a trip? What research would that be?

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Assuming an Apollo-style mission (two-stage lander, with return vessel holding in orbit for return), this mission would just about be possible, physically, with today's rockets.

Humanly, it's not possible at all. Mercury is the hardest place in the Solar System to reach, saving only the Sun itself, in terms of the universal currency of space travel, Delta-V. You have to nearly kill Earth's orbital velocity to fall down that close to the sun, then you have to almost match velocity with Mercury to make orbit there (and without any ability to aerobrake as is often done with Mars). Your lander will be heavier, as it takes much more rocket power to reach orbit from Mercury than from our Moon -- and the descent stage has to carry that larger ascent vehicle to a safe landing on rockets only. You might wind up with a lander resembling the SpaceX Starship and Starbooster just for your lander.

And at the end, you need to have enough propellants still in the transfer vehicle to return to at least an aerobrake at Earth. The mission will take a minimum of several months, and the launch mass would be equivalent to at least four or five Saturn V launches.

Alternatively, to get a mission you could launch on a Delta IV Heavy or Falcon Heavy, the return vehicle would be too small to carry even a single human, and even then you'd have to use multiple gravity assists from Earth and Venus (and probably at least one from Mercury) to substitute for lack of fuel -- and the mission would consume years each way, instead of months. The major objection to sending humans to Mars is trip time -- with a multiple gravity assist trip to Mercury, the trip time would be several times longer.

Bottom line, nuclear propulsion (either a nuclear-thermal rocket of some kind or an Orion style pulse drive) would be the only way to send the necessary lander there and bring the crew back in a reasonable time frame.

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  • $\begingroup$ Thanks. Tough answer, because it ruins my plans, but a few rocks in the way are to be expected. I will have to ask a new question now with whole new tags regarding how would Project Orion be allowed without any change to History or the present state of things (no approaching alien fleet to "unite us against a common enemy" lol). It is hard for me to even formulate such a question... I have almost zero knowledge of the "behind the scenes" of current super-complex global politics, with so many players involved. $\endgroup$ – Davi Feb 19 at 19:23
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    $\begingroup$ It would almost certainly be politically easier to use a nuclear thermal rocket -- a descendant of NERVA. The nuclear material need not be bomb grade, never mind hundreds of actual bombs, and if you design to use water or ammonia reaction mass, you can avoid hydrogen boil off over the months-long mission. NERVA type nukes have low acceleration, but are tested technology (tested in Idaho and Siberia), can run for days at a time, and have FAR higher economy than anything chemical. These are what you need to push a Starship stack to Mercury and back. $\endgroup$ – Zeiss Ikon Feb 19 at 19:27
  • $\begingroup$ How come no space agency, private or state-owned in the world is using that stuff? It must be very hard to do that legally within the confines of international space treaties. There are more than a hundred signatory states for those treaties, and they all would have to come into an agreement to change the international law. That must be harder to achieve than the building of the craft itself, I imagine. $\endgroup$ – Davi Feb 19 at 19:42
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    $\begingroup$ Protesters. Remember the protests when they launched a plutonium RTG on board Cassini (oh, you're probably too young to remember that)? There was all that talk about how a miscalculation could send the whole spacecraft crashing into Earth on its gravity assist pass and scatter the plutonium across the Earth. Still, NERVA would be easier than Orion. Orion would cause hundred of cases of flash blindness on Earth, just because you can't ever get everyone to not watch... $\endgroup$ – Zeiss Ikon Feb 19 at 20:14
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    $\begingroup$ @Gustavo: If travel time is not an issue, solar sails both ways would be the way to go. They work just as well for deceleration as for acceleration. However, note that solar sails are only marginally "current technology" — while a few testbed and/or demonstration missions have been flown, there's still a lot of engineering and testing to be done to really make them into a reliable and practical interplanetary propulsion method. $\endgroup$ – Ilmari Karonen Feb 20 at 2:53
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If Project Orion type nuclear pulse engines count as "current rocketry", then if the political will to use them is present, a few years of research and development should suffice to build spacecraft more than adequate for a manned mission to Mercury and back to Earth.

https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsion)1

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  • $\begingroup$ So, currently the answer is no? $\endgroup$ – Davi Feb 19 at 18:44
  • $\begingroup$ Also, if I'd use that alternative, I'd also have to find some way to circumvent the political problems, yes. There is more to the issue than meets the eye! My knowledge of how globalized world politics works is very limited, and I am afraid I would create something unbelievable if I tried Project Orion as a route. $\endgroup$ – Davi Feb 19 at 18:52
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    $\begingroup$ If we're talking alternatives to chemical rockets that would require only a few years to get ready, how about a VASIMR rocket with on on-board nuclear reactor to power it? Ion propulsion has a much better payload mass/fuel mass ratio then chemical rocketry, and the article here suggests such a system could take astronauts from Earth to Mars in 39 days. It probably would require less research time to perfect than nuclear pulse rocketry, and without the same political problems. $\endgroup$ – Hypnosifl Feb 19 at 22:22
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    $\begingroup$ @Davi - I agree you'd need a chemical rocket for the lander, but Mercury is in free-fall around the Sun, you don't have to worry much about the Sun's gravity when figuring out the change in velocity needed to achieve orbital velocity from the surface. For example, you could analyze the problem from the perspective of a rotating frame of reference where Mercury's center is at rest, in that frame the Sun's gravity and the centrifugal force would exactly cancel each other at Mercury's center, and the difference in the Sun's gravitational pull between the center and the surface is small. $\endgroup$ – Hypnosifl Feb 21 at 19:16
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    $\begingroup$ Though on problems with VASIMR as a near-term solution, I see from this article that the estimate of being able to get to Mars in 39 days has been criticized by aerospace expert Robert Zubrin, who says it would require a nuclear reactor with a far better power-to-mass ratio (and greater power overall) than any reactor that has been built to date, and the engineer who made the estimate acknowledged he was assuming significant improvements in nuclear technology. $\endgroup$ – Hypnosifl Feb 21 at 19:52
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Physically, we have almost all the technology needed to do it right now. We don't need hypothetical engines or gigantic new launch vehicles. We can build the main vehicle in orbit, much like how we have built the International Space Station. We would have multiple launches using heavy lift launch vehicles, like the Falcon Heavy for example, which would deliver modules to low earth orbit. These would be sent up empty, assembled together, and stocked and fueled just before the journey.

There's no physical limit as to how big the whole craft can be, the only limits are financial.

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  • $\begingroup$ If nobody objects, than this is good news for my fictional project. Financial limits are not usually questioned in sci-fi. Nobody argues about how expensive the Death Star or the Enterprise would be, only about all the rest. Edit: save for recent Disney Star Wars films, which reach the "oh common!" critical point. $\endgroup$ – Davi Feb 19 at 19:47
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It would be very hard to send humans to Mercury and bring them back to Earth using today's technology, but it could be done. If near term technology is included such as the Starship / Superheavy rocket being developed by SpaceX, it should be a bit easier. When they become operational it should be possible to ship many thousands of tons of propellant and rocket technology into low Earth orbit and build and or re-tank the ship there.

One thing that would be essential is propellant production on Mercury itself. There is water ice and cryogenic temperatures in some of the deeper craters near Mercury's poles and ample sunlight and heat not far away so that should be relatively easy to arrange.

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    $\begingroup$ the hardest thing is keeping the humans alive through the trip everything else is just cost. $\endgroup$ – John Feb 20 at 0:19
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    $\begingroup$ Keeping humans alive is also just cost - as in you need food, shielding etc etc its all mass related $\endgroup$ – Slarty Feb 20 at 8:07

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