Is a Mercury sample return mission possible?

[Star One]

Was intrigued by this Twitter exchange and it made me wonder if such a mission is actually possible, and do you agree that it would be scientifically more significant than a Mars sample return as unlike Mars we probably have no meteorites from Mercury, as one party in this discussion is arguing?

https://mobile.twitter.com/Astro_Wright/status/893787248478519296

[Bynaus]

In terms of delta-v, its far more challenging than a Mars sample return (and we are not even there yet). Essentially, same surface gravity, but no atmosphere to help you slow down, and the planet is also deep in the gravity well of the sun. Its not a coincidence that we do have meteorites from Mars, but not from Mercury!

Scientifically, depends on what you are interested in. Indeed, seen through the eyes of someone interested in the formation of the solar system as a whole, sample return from Mercury would be more interesting than a Martian sample with a "geotag" -it would tell us, e.g., whether there was indeed an "inner solar system disk" of material from which the innermost three planets, but not Mars, formed (as some scientists suspect). Or whether we need an exotic formation history for Mercury. However, seen through the eyes of someone interested in astrobiology and the question of habitability of early Mars, sample return from Mercury is just not worth the effort.

I tend to agree with the first view.

[ncb1397]

With high power SEP, a powerful launch vehicle and using the higher intensity of the sun's rays between Mercury and Earth(solar irradiance is ~7x more intense at Mercury), it should be well within the margins of near term technology.

[Star One]

I suppose Venus return might actually be harder because of the difficulty getting to the surface, surviving on the surface long enough to get a sample and then getting away from the planet again?

[Bynaus]

I suppose Venus return might actually be harder because of the difficulty getting to the surface, surviving on the surface long enough to get a sample and then getting away from the planet again?

Yes, if you want to one-up Mercury sample return, try Venus sample return.

But Mercury is hard enough. Even a lander is quite tough - BepiColombo was originally supposed to have a lander, but the costs and the complexity led to its early cancellation.

[Star One]

I suppose Venus return might actually be harder because of the difficulty getting to the surface, surviving on the surface long enough to get a sample and then getting away from the planet again?

Yes, if you want to one-up Mercury sample return, try Venus sample return.

But Mercury is hard enough. Even a lander is quite tough - BepiColombo was originally supposed to have a lander, but the costs and the complexity led to its early cancellation.

I've seen it suggested that comparatively the easiest body to explore in the solar system might be Titan as it would be possible to both fly in its atmosphere and sail its seas. If I could have a fantasy mission there I would have one with both a boat and drone. Perhaps the drone being able to pickup and carry the boat to different locations. I know people get enthused by places like Europa but I still wonder if your intention is to find life elsewhere in the solar system that your best bet is Titan.

[Krankenhausen]

I suppose Venus return might actually be harder because of the difficulty getting to the surface, surviving on the surface long enough to get a sample and then getting away from the planet again?

I'm just engineering student with no practical experience, but I like to speculate about these sort of things. So my quick but likely flawed assessment would be (back of the envelope using this: https://imgur.com/WGOy3qT

Venus:
To get your surface sample back from Venus you'd need to land a near full scale, presumably multi stage Earth rocket that can withstand and launch at 700K and almost 100 bar. All the while somehow keeping your LOX at 90 K.. At least your terminal velocity is quite low, which helps the landing but comes back to haunt you on your ascent..

An atmospheric sample may be feasible though you'd still need significant dV, the gravity well of Venus is quite deep.

Mercury
A Mercury sample return on the other hand just requires an insane dV in the order of 20km/s (from your Earth Escape,) but at least you can get away with SEP for most of this[1]. Thermal environment is harsh though.

As a sidenote, I think picking a good landing location at Mercury could also be tricky. The Sun side is very hot, not just from the Sun but also the conducted and radiated heat from Mercury's surface. There also aren't many good places to place your radiators to get rid of this heat.
The dark side has no sunlight for months (I think it sort off funny that a dark side Mercury probe would likely need a heater) and the poles are unfavourable for your return trajectory (although if you manage to build something with a dV of 20km/s, a few km/s extra may not be that big a deal.) One could aim for the transition area between the day and night side but that would limit the duration of your surface mission (relative to the Sun Mercury rotates in about 176 days.)


For comparison, a Mars sample return would require somewhat over 5km/s from your Earth escape trajectory (how much over mostly depends on the means of landing.)

_{[1]SEP trajectories usually require more dV than traditional chemical trajectories on which most of these numbers are based.}

[Proponent]

Why would a polar landing site present trajectory difficulties?  For landing on the dark side, couldn't one just use LIDAR or an old-fashioned flood light?

[Phil Stooke]

A sampling strategy for airless bodies which has been discussed several times is an impactor to throw up a plume of debris and a flyby module with a device to capture some of the debris and bring it back.  No landing, not even braking into orbit.  Of course, it's not for the faint of heart.  But it might be possible.

[savuporo]

Some kind of crazy electric/solar sail combo cycler craft as the return vehicle ? Would Mercurian cycler even be feasible ?

[stefan r]

I'm just engineering student with no practical experience, but I like to speculate about these sort of things.

"Engineering student" might be about average education for this forum.  Not aware of any hard data.  People with careers tend to avoid speculation that could look bad when taken out of context.  If you are really writing a professional answer to a question why not publish it?

...assessment would be (back of the envelope using this: https://imgur.com/WGOy3qT

Venus:
To get your surface sample back from Venus you'd need to land a near full scale, presumably multi stage Earth rocket that can withstand and launch at 700K and almost 100 bar. All the while somehow keeping your LOX at 90 K.. At least your terminal velocity is quite low, which helps the landing but comes back to haunt you on your ascent..

An atmospheric sample may be feasible though you'd still need significant dV, the gravity well of Venus is quite deep....

I doubt you need 27 km/s for the Venus mission.  I suspect they got the number from by including atmospheric drag.  A balloon would avoid a lot of that.

Mercury
A Mercury sample return on the other hand just requires an insane dV in the order of 20km/s (from your Earth Escape,) ...


For comparison, a Mars sample return would require somewhat over 5km/s from your Earth escape trajectory (how much over mostly depends on the means of landing.)

_{[1]SEP trajectories usually require more dV than traditional chemical trajectories on which most of these numbers are based.}

Your map says 12.9 to Mercury and 6.1 to Mars.  Round trip earth-escape and return to earth escape would be 25.9 and 12.2. 

Just to throw out more amateur ideas... Could you leave earth orbit into a high elliptic orbit around the sun and then skip/aerobrake using Venus's atmosphere on the way to Mercury?  Could that work both ways?

[Patchouli]

I think it's possible but you'll probably end up needing a New Glenn to  SLS class LV to launch but the good news since it's close to the sun you can really leverage solar electric propulsion esp for the return leg.