This is a summary of the various types of flights we might use to send a mission to another star (Round trip, pickup and return by follow on flight, construction of return equipment at target star, Multi-star, Multi generation, hibernation, and one way). It briefly describes each flight type and its advantages and disadvantages.
Ship and crew return to Earth at mission end.
Advantages
Simplest option, and one with little likely hood of public objection.
More likely to get more volunteers and better qualified volunteers for flight.
This option implies that the mission is fairly short. I.E. within the professional life of the crew. This would imply its short enough to return information in a useful amount of time. (I.E. it would get there and back, before a later faster flight could do it.)
It would return far more information than an interstellar communications link could manage.
It obviously avoids the grisly public relations and crew morale problems of a one way mission.
Disadvantages
Technically more challenging. Getting a ship to the target starsystem is hard enough. Getting it back would make it harder. But this must be traded off against the added complexity of a ship capable of supporting its crew for the rest of their lives.
It has to be a fast enough ship to get back in an acceptable amount of time. Too slow and theirs no practical reason to send it.
Advantages
Most of the advantages of the round trip model, and would allow the first ship to be a mobile research station or other specialized ship, with faster courier ships providing round trip flights.
Disadvantages
High risk and more complicated. Multiple ship types, and concerns that the first ship might be left stranded. The multiple ship types (the first being a big heavy slow boat, the latter faster smaller ships) is probably manageable and might even have advantages. The problem of assured crew return would have to be handled conclusively.
This option come up with light/microwave sail craft, beamed power craft, and fuel launcher craft. The crew would construct automated duplicates of the systems that launched the ship from Sol space.
Advantages
Would establish launcher facilities in both star systems. Which could allowing faster two way flights with specialized fast light ships.
The crew might get back faster with their ship using the constructed launcher systems for assistance.
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Disadvantages
If they can't build the equipment, they don't get home.
The construction phase may require so many resources that the first flight is devoted just to infrastructure construction. With little or no exploration being done in the first mission. This obviously would cool public interest and slow down the return of productive information. At the very least the crew would have to be divided into a exploration, construction, and support sub-crews.
Ship proceeds to, and explores, another starsystem after completion of first mission, in first starsystem.
Advantages
One mission explores multiple star systems.
Disadvantages
Technical feasibility is low since wear and tear on the ship would accumulate, dramatically increasing the likelihood of a catastrophic failure.
Because of the extremely long flight times with likely technology, the mission would take so long as to be undesirable. At some point the ship would be superseded by newer faster ships sent straight out from earth, decades after its launch.
Advantages
This is the one of the standard concepts suggested to get around the extremely long flight times.
Could allow extremely long flight times.
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Disadvantages
The ship would have to be huge to support the active crew, retired/incapacitated crew, children, and all the extra support facilities and personnel they would require.
The crew, ship, and equipment would need to be even larger than that to allow them to be able to completely rebuild the ship from the inside out as it, and its systems, exceeded their service lives.
Any ship that takes that long to get to where it wants to go, will probably find it gets there after newer faster ships from earth. So their is little reason to launch it.
The flight would take so long few people would be enthusiastic in launching it, even if they didn't consider the likelihood of faster follow on craft. I.E. why spend money on something you'll never see the results of, nor even ever know if they made it.
The follow on generation(s) in the ship will have no allegiance or commitment to the mission or its originators (they, never agreed to anything).
The follow on generations would have no hands-on experience with the exploration systems they would be expected to use. Or for that matter, any experience with planets and starsystems.
Its harder to get qualified people to go on such a flight. People who want to explore wouldn't want to spend the rest of their life stuck in a ship, knowing they will never contribute anything but their genes.
Advantages
This is the other one of the standard concepts suggested to get around the extremely long flight times.
The ship would not need to support the inactive crew.
The crew wouldn't need to spend years of their lives waiting around in the ship with nothing to do until they get to the star system.
The crew will still be fresh and familiar with their jobs when then are waken up in the star system.
Disadvantages
The ship systems will still exceeded their service lives, but their may not be enough people around to service them. The sleepers could wind up dying on route as the ship died around them.
The sleepers would have to be extremely well shielded from radiation, since their cell repair mechanisms would be as dead as they are.
Any ship that takes that long to get to where it wants to go, will probably find it gets there after newer faster ships from earth.
The flight would take so long few people would be enthusiastic in launching it.
Advantages
The ship need only be designed for a one time, one way flight. This limits the technical mission risk and requires less resources. (Assuming you don't want to try to upgrade the ship to be self sufficient, which would take far more resources.)
Least likelihood of back contaminating Earth.
Establishes temporary outpost in starsystem.
Allows investigation of the starsystem to continue until all exploration resources are exhausted or worn out. Presumably for a decade or so, depending on the service life of the shuttles or their support facilities, or the service life of the remotes.
Disadvantages
To put it mildly the public acceptance of sending explorers out to die the mission and die on the frontier is low. Risking dying maybe, but assigned/left to die by superiors -- no way. Every politician within ear shot will run in front of the closest camera to announce that he or she will personally lead the witch-hunt to track down everyone connected with suggesting this idea.
Mission Type | Technical Risk | Technical Feasibility | Political Risk | Political Feasibility | Desirability |
Round trip | medium | medium | low | High | high |
Pickup | Med-high | medium | medium | medium | medium |
Construction and return | high | med-high | medium | medium | medium |
Multi-star | Ex-High. | Med-low | low | Medium | medium |
Multi-gen | Ex-high | Low | high | medium | low |
Hibernation | high | Low | medium | medium | low |
One-way | med-low | Medium | Ex-high | Nil | Low |
Alternative Robot Missions
Advantages
Could use a smaller lighter ship and could tolerate longer flight times.
Disadvantages
Requires extremely good A.I. systems and reliability (which may or may not be likely by 2050), and would generate far less public interest.
Why bother? You could do nearly as well with huge telescope arrays in our star system, and do it a lot faster and cheaper.
Advantages
Could use a far smaller lighter ship and could tolerate longer flight times.
Would provide ground survey data that could be worth launching an interstellar mission. (I.E. The telescopes back home couldn't do it as well.)
Disadvantages
Again requires extremely good A.I. systems and reliability, and would generate less public interest.
Would be less capable than a manned mission.