Logistics of manned Europa exploration?

Question

It is 2057 and a manned mission to Europa has been comissioned in the prospect of further exploring the ecosystem and energy signatures of Europa. Unlike the implied unnmanned probe, this mission logistically has to be able to do the following:

1. Be able to enter and return from the subglacial abyssal ocean in Europa.
2. Have a crew of 16 people. (12 people for the surface and 4 people for the submarine)
3. Be able to have both a surface encampment and a sub-surface exploration mission.
4. Be able to retrieve samples back to Earth.
5. Cost less than 250 billion dollars (if unattainable give me your own estimate)
6. Have a travel time of around a year to Europa (those poor bones...)

My current model of how to achieve this is as follows:

1- A interplanetary vessel is built in Earth orbit using reusable rockets descended from the likes of Falcon 9.

2- This interplanetary vessel has living space, propulsion and a solar sail (since that's totally all you need for a mission as complex as a manned interplanetary venture, right?).

3- Attached to the interplanetary vessel is a shuttlecraft designed for flying in low gravity, atmosphere lacking environments since planes wouldn't work on Europa. On Titan, it'd make sense but Europa isn't a jovian moon known for its thick atmosphere.

4- This shuttlecraft is manned and deploys both the encampment (using modular bubblehabs that can be dug into the ice for radiation protection- this is Jupiter so radiation is an inevitable issue) and the submarine that needs to be able to descend all the way to the bottom of Europa's ocean... And back.

5- Said submarine is able to gain energy from the hydrothermal vents if needed (and maybe even ride the convection current back up) and can supply the crew in said sub for about a Month with food. Oxygen in the sub can be derieved from the sorrounding water. The submarine is modelled partially on a bathoscaythe, however it is very simple in shape (very capsule-like, but with a heat drill on the front that likely can double as a defensive weapon encase a sea monster tries to eat it). There are also communication systems and some deployable aquatic probes for sample collection instead of arms like current bathoscathes use. Deploying a human in pressure suit gear might also be possible if the story demands it. However, I have a feeling that a pressure suit for Europa would be somewhat expensive (I state as I detail out a high-tech submarine and a manned space mission more ambitious than anything in human history up to this point).

The problem I have is i'm not sure how expensive or massive all this stuff would be. My intuition is that being a manned mission carrying a ship that can deploy both a encampment and a submarine which 4 people can reasonably man is that it'll be a big ship, but i'm not sure how big. The Delta-V of going to Europa, orbitting and going back with a manned vessel also will be pretty intense.

The speed of the ship on average would be 5x faster than the Juno Probe as well, putting it at a drifting speed of around 370 km/s. That is about a thousand times slower than the speed of light but still really damn fast. However, assuming no fusion energy how would getting to this speed on the scale of say, weeks be feasible? Gravity slingshot around the Earth?

I come here since I don't know anything about the logistics of space travel and want to see how many holes can be picked in it and what I should use to fill those holes in. And also because this is likely going to be insanely difficult to pull off and the more information I have on what would be needed the better, especially in regards to the mass of the three crafts, what prolusion systems to use and how to better structure the time frame of said mission. Also tell me if 16 people is too much or not enough. I just picked the number out of superstition more than anything else.

Since it's in 2057 the tech doesn't nessecarily have to be current day, but i'd prefer the tech still be based on or descended from technology in research or on the drawing board today more or less. Fusion energy is off the table, for instance.

(As for the life itself, that's all spoilers.

It's not Europa native but evolved in Europa-like conditions with the magnetic field of the nearby gas giant, acidic seas and the 'right' balance of tidal stress. The inhabitants didn't become space faring independantly, they gained space age technology from a much more distant entity and technologically degenerated in the thousand years they lived on Europa. They surveyed Earth early on but their ability to speak a human language is likely non-existent beyond a few words. Not to mention they speak more like whales or dolphins than humans. I mention this to anyone who objects to advanced life on Europa here, even if this is not the focus of the question.).

Answer 1

This answer is going to involve a lot of hand waves and assumptions, many of which might not fit your background. A pricetag of $10 billion could only occur if the dollar was revalued to something like its 1900 AD value, and to get that sort of deflation would require President Donald J Trump to repudiate all of the debt acquired since 2008. The resulting fireworks would make a manned mission to anywhere quite unlikely.

OTOH, using lightsails gives us all kinds of possibilities. Very thin lightsails can actually have impressive velocities. K Eric Drexler investigated super thin lightsails as far back as 1979 (his masters thesis was about depositing a molecule thick layer of aluminum on a "wax" substrate which would evaporate away in UV light,so this can be done. A sail with an acceleration of "only" 1mm/sec^2 can reach Jupiter in just over 2 years, for example, and very advanced sails could possibly reach accelerations in the double digits. The problem with these sorts of sails is the velocity at Jupiter will actually be too high, and the ship will need to do something like a dangerous aerobrake in Jupiter's atmosphere to shed the excess velocity.

Modifying this idea somewhat, we create a fleet of solar sails with high acceleration. We size the sail for some sort of standard sized pod (much like we use ISO containers for freight) and then start sending a train to Jupiter. We adjust the trajectory so that it takes a reasonable time to get to Jupiter (say 3 years) and the sail releases the pod to aerobrake or maybe deploy a magnetic sail. The solar sail makes a long looping trajectory past Jupiter and eventually reaches Earth, maybe 5 or 6 years later. By having enough of these sails, you can create a pipeline effect and have pods with cargo, supplies and fresh crew delivered on a regular basis. The other advantage of this scheme is each individual solar sail does not have to be very large (in relative terms). A single sail towing the entire ship, cargo and landing apparatus would be absurdly large and difficult to build or control. Much better to split the cost and risk across multiple sails instead,

Back on Earth, new pods are built and filled on an assembly line basis (reducing costs and ensuring better quality as crews learn the job and institute best practices). Manned pods start with orbiters, so the crew can do a reconnaissance of Europa for landing sites. A lander is delivered next, along with base infrastructure so they can set up shop for a multi year stay. Finally, once they are satisfied with their living arrangements and havre done the preliminary surface survey work, they can send for the submarine.

During this time, they will also be getting bits and pieces of the return ship, in the form of pods with engine modules, fuel tanks, life support and so on, which can be assembled in orbit by the crew or by robots, depending on your preference. This is needed since accelerating to match the incoming solar sails might need an absurd amount of energy, while sunlight around Jupiter is so feeble that getting a solar sail going from a standing start will take an incredible amount of time.

Modularizing the mission and sending only parts as yo need them just the cost considerably (if the orbital probe concludes there is no safe place to land, then the expensive lander and submarine are never built or sent, for example), and spreads the costs and risks over a long period of time. As well, you can essentially bootstrap the colonization of Europa and the Jovian system by reusing the lightsails to constantly send a stream of people and equipment to the Jupiter system.