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In the near future, say about 50 years, the most powerful governments are starting to compete for control of interstellar resources. The first step is to send a probe or probes to a neighbouring star system to do reconnaissance on the exoplanets there, to see what potentially exploitable resources are there and if the exoplanet can sustain human life.

I only want to use technology that could feasibly exist in the near future, based on our current understanding of science. No FTL. These governments are working to long term plans and understand that each probe will take many years to arrive, if at all.

I imagine that sending many smaller probes will have a higher success rate than fewer but larger probes. These probes can be launched en masse with a few sent together to the same star system for redundancy, since some will be lost or become non-functioning before they arrive. I'm not sure about the fuel requirements for the delta-v to achieve orbit.

What's the cheapest/most efficient way of getting the highest number of functioning probes into eventual orbit around as many different, potentially life-supporting exoplanets as possible, as quickly as possible?

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    $\begingroup$ See Breakthrough Starshot $\endgroup$
    – user71659
    May 2, 2018 at 2:04
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    $\begingroup$ @user71659 : the problem is that this project is useless if you want to put probes into orbit of the exoplanets. $\endgroup$
    – Tryss
    May 2, 2018 at 3:08
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    $\begingroup$ You need to flesh out political and economic angle more. Why there are sending anything out? Without FTL and with reasonable near future tech there's no way to bring any resources back from outside of solar system. There is no "space colonialism", to put it simply. Without FTL, reactionless engines or at the very least engines with ludicrous specific impulse, the only reasons to send anything out is science, but that tends to be international at those scales. $\endgroup$
    – M i ech
    May 2, 2018 at 11:28
  • $\begingroup$ This question is much too broad. As @Miech said: you need to set up a framework. $\endgroup$
    – MichaelK
    May 2, 2018 at 12:51
  • $\begingroup$ Worth pointing out most interesting planets are 10's of light years out with flight time of the probe and then the transmissions back this will be a 20-hundreds of year long race. $\endgroup$ May 3, 2018 at 17:32

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50 years?

We'll be launching probes to stars much sooner than that. 20 years is the estimate.

The general idea is to use lasers to push tiny probes up to relatively high speeds and radio back what they find.

See the BreakThrough Starshot initiative.

The probes are tiny (matchbox sized) and cheap. They have no propulsion and are pushed instead by a giant space laser (queue Dr Evil laugh)

They'll transmit enough information about the star system to give humans an idea what stars to head to first.

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  • $\begingroup$ As Tryss commented under the question, this will not put the craft into orbit. But the OP can of course adapt the idea. $\endgroup$
    – user3106
    May 2, 2018 at 9:07
  • $\begingroup$ Orbit is a bit of a stretch. You really don't know which planet you'll orbit or why until the probe gets there. It would take years for the results to get back to Earth and years more before and instructions could be sent back to the probe. Maybe a second larger, more expensive probe could be sent if the first probe looks promising and it would have propulsion and better sensors to orbit the planet $\endgroup$
    – Thorne
    May 2, 2018 at 12:13
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In any real race to the stars, persistence is the main ingredient for victory.

The first great question which will be faced by the rivals is whether to invest everything in existing technology in the hopes of getting into space first, or waiting for tomorrows technology with faith that its' faster propulsion will be able to make up for the later start.

The answer is to invest everything in both. Bankrupt your nation today to get your first wave launched, then recover and do it again, every time a technological breakthrough is found. As leaders of a star-faring nation, you and your people need to be persistent in your commitment to win the race. That means not only starving for a little while to get things started, but sentencing your children and their children to famines in the future, as they keep up the good fight.

The next question is whether to launch from the inner planets or out in the belts. Again the answer is both. Get a few ships racing outbound but drop off some crew and supplies as you pass asteriods which might host future probe factories. From these ever further outbound factories, launch subsequent fleets by dropping them back sunward to slingshot outbound at a greatly enhanced speed.

You will need to be persistent not only in your efforts but also in your patience, as ship after ship ventures off into the darkness with no hope of reaching its destination in your lifetime. Not only your leaders, but maybe even your nation might not live long enough to receive an answer. Even if somehow your nation does survive in name, it will be a very different country than the one which launched the first probes. Compare 18th Century U.S.A. to it's current day namesake for a glimpse of how vast that difference might be.

Reaching the stars is really a venture for our entire race. It cannot be won be any single nation, because no nation, even a long lived one, will survive long enough to reap the rewards of our diaspora. Only together as a single united species can we spread out beyond our home star.

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The Problem of Deceleration

As many here have noted, small matchbox-sized craft with laser propulsion from Earth is the easiest way to accelerate towards a nearby target star. This will give you fast fly-by's to gather some information. However, the problem is now deceleration for more in-depth analysis of what you find. You need to slow down enough when the probe nears the star system to then enable adjustments in trajectory and speed to then study the system thoroughly.

Perhaps the answer may lie in nuclear propulsion - that is something similar to say the Medusa Project, meaning a larger heavier craft with onboard nuclear devices.

This involves a large solar sail, which in acceleration could be used to catch powerful lasers emitted from Earth, and then on the deceleration flips and uses onboard nuclear devices exploded to slow down.

As it is unmanned you could save a lot on safety systems and shielding, and decelerate fast. If manned you would need it to be more gradual, and may require more nuclear devices and general upscaling of the operation.

The Problem of Information Gathering

Once nearing the system, you need a way for decisions to be made to react to new information gathered that will affect the mission. The distance away is so vast that communication with Earth is impractical. Therefore you need a way for the craft to make decisions without our help.

The answer is AI - you need a smart enough computer to be able to choose the best course of action given new data - for instance determining which moon of which planet to study first (as this information won't be revealed until you get close). The AI needs to account for remaining fuel, energy and most likely choose actions that determine success of the mission.

The Real Problem of Resource Gathering

You mentioned resource gathering - there is little value in sending resources from interstellar destinations back to Earth. It is far more easier and practical (with plentiful resources) to do that here in our solar system.

Therefore resource extraction is really not viable - except if the plan is to establish a colony and secure the system for habitation. If this is the case too, likely it is easier in our own solar system, but say there is a reason to colonise a nearby star instead, then we need onboard robots to begin the slow process of terraforming/mining/building colonies in preparation for our arrival. Self-replication is the only solution here, which means 3D-printers and resource gathering, to print more 3D printers and more robots.

The Tyranny of Time

Space is big - really really big. Even the distance to the nearest star is huge (much larger than we can comprehend). This also means everything takes a long time. Long time to go there, long time to receive data, long time to establish any meaningful endeavour. The problem you would have is the long-term vision needs to sustain itself during the mission, and follow-up missions, and so a shorter time to do the above is desirable.

Otherwise your ultimate goal might not have to last just decades, but almost a century.

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Have you taken a look at the exoplanet missions currently being done? NASA missions such as Tess cant tell you specific details (such as where exactly on a planet a methane source is) but they can tell a lot more than the first exoplanet missions. (When I was a kid, such planets were still only theory). My answer then is expand the current programs rather than probes that are riskier and more expensive. A failed probe is probably a lost investment, a failed telescope can maybe be salvaged. At very least programs like Tess will limit the number of probes needed by helping select the best targets to begin with.

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Investigating Exoplanets

To investigate the possibly habitable exoplanets, countries will want to invest in making laser-propelled lightweight spacecraft, which utilizes solar sail, to be sent to the exoplanets. This is the best kind of spacecraft for this mission because this spacecraft is going to be propelled by laser from the home planet, which means that it's not going to have to carry fuel, which makes it lightweight and can be accelerated very quickly. And as long as you have energy to power the laser, you can keep accelerating it, which can make it go really fast.

Gathering Resources

Countries can gather resources from celestial bodies such as asteroids, moons, and planets by sending out swarms von Neumann probe, which is self-replicating spacecrafts, capable of traveling between star systems and extracting resources at their destinations to build copies of themselves. The mined minerals then can be used for construction materials in space or taken back to Earth. The use of this kind of resource-gathering spacecraft enables them to not having to constantly launch them out of orbit.

Suggestion

I think we understand that the idea of countries from the same planet competing for space resources is rather improbable. So, if I may suggest, maybe at least one of the countries has the kind of government that is ideological and autocratic. Or, maybe the country is controlled by an AI that had been developed and implemented long in the past when the government had strong ideology. The AI had been told to preserve the ideology, and it has been carrying it out even until the country becomes so advanced in technology.

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Unless the initial groups doing the launching are going to be satisfied with flypasts, there is no practical way with current technology to launch exoprobes that will be capable of decelerating and going into orbit around planets anytime soon.

The conceptual breakthrough which allows us to consider probes to the stars at all is to shrink everything down to postage stamp size and send the probes on their way via external power, such as the laser sails of the Starshot initiative. This, by the way, also satisfies the "as many probes as possible" theme, since hundreds or thousands of Starshot probes can be launched at once.

You can have variations of the idea, for example using microwave beams to power the sails instead of lasers, or launch them out of improbably long mass drivers, or even a nuclear cannon, but the issue is the actual probes are so small and simple they have no on board propulsion systems to decelerate (and indeed they are moving so fast that the amount of energy to decelerate them would be ridiculously large).

Perhaps much farther into the future, the probes could be built out of exotic materials which would let you launch them into the target star and "Heliobrake" (i.e. let the drag of the solar corona slow them down sufficiently to go into long, looping orbits around the solar system). This would require them to plunge from the interstellar medium into the ferociously hot solar corona, and deal with heat, magnetic fields and a very exotic plasma environment without losing structural integrity or destroying the instrument package or internal computer and programming. You would also be decelerating at hundreds or thousands of "g" while doing so, which will give you an idea of the sort of probe you would have to build.

The other way to learn about the planet is to "lithobrake" (i.e. slam into the planet itself), but there may be a few issues with data collection and transmitting the results back to Earth using these means.

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