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Robotics is now well developed. Many programming languages allow you to work in real-time. Also, a new era of space missions and research is in full swing.

So here's the question: Why is the physical presence of people in spacecraft still necessary?

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    $\begingroup$ medical experiments, laboratory experiments in zero gravity conditions. $\endgroup$ – A. Rumlin Dec 30 '20 at 15:57
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    $\begingroup$ Robots aren't as good at attracting funding. $\endgroup$ – BlokeDownThePub Dec 30 '20 at 21:54
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    $\begingroup$ Which space missions are you thinking of? $\endgroup$ – user253751 Dec 30 '20 at 22:25
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    $\begingroup$ Also because some of the goals of space exploration is to “backup the hard drive” for the eventual airy of an extinction level event, self inflicted or not. You can’t have humans living on another planet without figuring out how to get humans to survive the journey and the new planet (most likely Mars). $\endgroup$ – oeste Dec 31 '20 at 6:26
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    $\begingroup$ There was no manned mission at all in this century that left a low Earth orbit. Nothing above 1000 km distance to the surface of Earth. The only manned mission above 1000 km is more than 40 years ago. $\endgroup$ – Uwe Dec 31 '20 at 23:23

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Between them, Spirit and Opportunity spent the equivalent of 22 years performing geology fieldwork on Mars. In that time, they managed a scientific output comparable to what a single geology grad student could do in two weeks.

Between them, Luna 16, Luna 20, Luna 24, and Chang'e 5 returned about 2.3 kg of material from four sampling sites. Neil Armstrong, in 20 minutes of work, collected over 20 kg of samples from a variety of sites.

Having a human on site greatly speeds the decision-making process and permits far more work to be done.

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    $\begingroup$ Trick question: which mission will be fastest returning samples from the Moon in the 21st century; Artemis or Chang'e 5? Which will cost more per kilogram? I have to agree that Robots aren't as good at attracting funding has to be included in any comprehensive view of the situation. "We choose to send robots to the Moon..." just doesn't have the same ring to it. $\endgroup$ – uhoh Dec 30 '20 at 23:05
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    $\begingroup$ Not because they're hard but because they're easy. $\endgroup$ – Mazura Dec 30 '20 at 23:12
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    $\begingroup$ "what a single geology grad student could do in two weeks" Not a fair comparison. The effort (and budget) for keeping that student alive would be huge. With robots you prefer to move slow, safe and cheap, because time does not matter for them that much. $\endgroup$ – Suma Dec 31 '20 at 6:54
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    $\begingroup$ "a single geology grad student could do in in two weeks" on Earth. Not on Mars, where you have to count all the years of time spent in preparation by that student and her entire support team. The effort required to support that student for those two weeks is orders of magnitude larger than the sum of the efforts behind those robotic missions. Except for studies of human biology, there is no activity in space where human presence is more productive than a comparable robotic effort. And, as someone who does this stuff for a living, after a mission failure I prefer hugs to a funeral. $\endgroup$ – John Doty Jan 1 at 14:04
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    $\begingroup$ On the weight of returning material, it might not be that humans are good at moving around and digging up, but the designed payload for the return trip. When payload include couple of humans, 20kg may not be much. $\endgroup$ – Aelian Jan 2 at 8:53
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One of the most important reasons is that robots don't make great interview partners.

A significant part of space missions is outreach and inspiring people. Another important part is giving people a different view of our planet. Astronauts over and over again describe the awesome feeling of being able to see how small and fragile our planet is, and the feeling of seeing borders and differences disappear. You can only get first-hand accounts like this from humans, not from robots.

Another important part is: because we can. Humans are naturally curious, naturally adventurous, and natural born explorers.

There is also the political component, to prove that we can and "they" can't. (Insert various values for "we" and "they" to your liking.)

Especially for missions further out, where latency starts to become a problem, another important trait is that humans can improvise, be creative, make judgement calls, and make spontaneous decisions in unforeseen circumstances.

Lastly, the human body is an insanely engineered all-round machine. There are lots of robots that can do one specialized thing or a small number of very narrow specialized things better than a human. But there is no robot which can do everything a human can do even remotely as good.

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    $\begingroup$ I would argue in the reverse order of your answer, but maybe I'm just a naive engineer... $\endgroup$ – Ludo Dec 30 '20 at 21:12
  • $\begingroup$ I would argue that seeing the Earth from 300km is probably not very different than seeing it from 10km from a passanger plane. The youtube videos are similar, except that the spherical form of the planet is visible. We all still remember, how wonderful was the world as we could only buy a cheap ticket and then fly, and view the Earth from the high. I nearly always paid some $ for a window place on this reason. $\endgroup$ – peterh Dec 31 '20 at 0:03
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    $\begingroup$ @peterh-ReinstateMonica but you can't prove that Earth is flat with pictures from airplane, you need to go higher! $\endgroup$ – Matija Nalis Dec 31 '20 at 20:06
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    $\begingroup$ @peterh-ReinstateMonica, try searching for images at 10km and 300km, or even the IIS at 200km. There's a significant difference between the 2, and it's not just the curvature of the earth. The scale of details is completely different. I looked at pics and video, and I saw massive differences. In one video of 10km, it was nothing but clouds. And a pic of 200km was a continent. You don't often get continents covered by a single cloud. $\endgroup$ – computercarguy Dec 31 '20 at 21:29
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    $\begingroup$ @Ludo: That is exactly why I chose this order! $\endgroup$ – Jörg W Mittag Jan 2 at 8:54
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Why is the physical presence of people in spacecraft still necessary?

Because robotics and AI aren't so developed as to totally replace humans (who are very versatile).

Having said that, there are lots of robotic space probes and landers, but not too many people in space.

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Necessity

Why is anything "necessary"? Who gets to define that? The biological imperative, if you will, is to survive, reproduce, and exploit every niche. Look all over the planet, and you will see that living systems have done exactly that, to a degree well beyond human engineering. If space is a new niche for humans, especially other planets, then why shouldn't humans populate and exploit that environment? From this view, you could say it is as necessary as extremophiles living on undersea thermal vents or inside rocks hundreds of meters below the surface, at a metabolic rate so low it may take thousands of years for them to reproduce just a few times. Nobody has written up a TODO list that demands life fill these niches, and yet, here we are...

Redundancy

We take it for granted that planet Earth will be available as our home for as long as we care to think about the prospect. However, the way we are living right now makes it clear that this is an unreasonably optimistic presumption. Making space habitable seems like a pretty smart way to hedge any bets about our future as a species.

Also, if it turns out that we are not alone in the galaxy, and a hostile alien race visits our planet, the odds are that we will not be able to defend ourselves. At that point, our only hope will be that enough of us escape to the stars to rebuild elsewhere, or seek help.

AI

Suppose we develop a super-intelligent AI which decides for itself to expand beyond Earth and into the stars. Surely such a being will build robots and do things the smart way, right? Perhaps. But why doesn't such a being exist already, when we have petaflops of computing power available to us? One reason is that while our robotic (and computing) technology is incredibly advanced, our biological technology is even more advanced. Those petascale machines operate with electrical budgets measured in megawatts. And they offer roughly the same scale of raw computing power as your little 3 pound brain, which sips a mere 20 W of energy. The next time someone calls you a "dim bulb", you should say: "I sure am! But look at all this dim bulb can do!"

When Curiosity or Spirit or Opportunity suffer a malfunction or failure, scientists just try to make do with whatever systems are left working. The name of the game is as much redundancy as we can afford, and limited expectations for usable service life. The official mission duration for Curiosity was 2 earth years. If humans could only offer 2 years of useful working life, we would consider that an utter failure.

If a super-intelligent AI wants to travel the stars, why would it not use the best technology available? That technology is not offered by Boston Dynamics, as impressive as their offerings have become. The only truly adaptable, self-healing, energy-efficient, high strength-to-weight ratio nanotechnology exploration machines we have available today are humans. That super-AI will immediately recognize that DNA-based life is the pinnacle of nanotechnology and energy efficiency, and will build its endeavours around that technology. Humans may only be the starting point for what such an AI would send out into the stars, but I find it to be an infinitely more likely starting point than mere robots.

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    $\begingroup$ extremophiles living on undersea [...] Nobody has written up a TODO list that demands life fill these niches, and yet, here we are... -- I, for one, bow down to our undersea extremophile overlords! $\endgroup$ – Matija Nalis Dec 31 '20 at 20:10
  • $\begingroup$ Just a reminder that the question is about robotics, not AI. There have been plenty of robotic missions in space (see my comments under the question) but they are all primarily under ground control except for some very basic functionality. Sometimes they are complex sequences that have to be executed automatically because of long light-time delays (e.g. seven minutes of terror, or anything that New Horizons did at Pluto and beyond) and those would contain some decision trees, especially terrain recognition for Mars landings, but mostly these are human controlled robotic missions when possible. $\endgroup$ – uhoh Jan 1 at 2:58
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Why is the physical presence of people in spacecraft still necessary?

The physical presence of people on most spacecraft is not necessary, not even those rated to carry passengers. Having humans doing the exploring in person is mostly aspirational rather than actual; most space exploration has been done remotely, using probes of varying complexity and autonomy. Most objectives would not have been possible to reach successfully had astronauts been included.

It was never really a matter of choice; there is enormous enthusiasm and commitment to using astronauts within space agencies as well the wider community. More than that, it can be an explicit Agency/Company objective. However, leaving out the astronauts greatly simplifies any mission and increases the available payload dedicated to instruments - and also allows probes to be used to destruction; return capability remains optional. Doing it without people having to come along extends the reach of our space exploration.

Probes and robots will remain the mainstay of space exploration - Landers, with and without sample return capability for Moon, Mars and (sort of landers) for asteroids, orbital mappers, flyby's. Missions that do include the physical presence of people will be missions that mandate that presence.

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Even if robots were still used for most of the fieldwork (which I think is likely even with a human presence because spacesuits, and the humans inside them, are fragile and expensive), having a human in a habitat nearby would be a great advantage for scientific research. Due to communication delays and often the lack of a stable radio connection, near real-time teleoperation is difficult on the Moon, and impossible on Mars. Controllers usually have to send commands out and wait for a response, sometimes for a long time, and that limits the productivity of the rovers, and the ability to quickly just go back a bit and inspect that interesting rock they just passed. Materials can also be shipped back to the habitat for further analysis, meaning rovers can be cheaper and lighter by removing a lot of the onboard laboratory instruments. A damaged rover could also limp back to base for repairs, further extending their productive life and reducing the need for expensive overengineering and redundancy.

The future is not going to be humans doing all the fieldwork currently being done by robots, but a human presence allowing the robots to be a lot more productive, reliable and flexible.

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  • $\begingroup$ +1 round trip light time to the Moon is less than 2.7 seconds and three 3-meter dish antennas are all that's necessary to maintain a continuous and stable radio link between Earth and Moon that would likely be accessed via internet, so while it does make certain fine and complex actions that can't be anticipated in advance difficult (like picking up a screw that falls behind a desk and then rolls under a piece of equipment) I think that complex tasks can usually be automated locally (move sample from box to microscope). $\endgroup$ – uhoh Jan 1 at 10:29
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    $\begingroup$ @uhoh It's only continuous and stable if there's an unbroken line of sight chain between rover, Earth and any relay sattlites. That limits where the rover can go and when tasks can be performed, even somewhere like the Moon. Increasing the reliability of this connection means more relays and more expense. And it's absolutely true that complex automated tasks can be performed by modern robots, but they need to be carefully planned often years in advance. There's little room for impulsive decisions based on new discoveries, at least without further weeks of planning. $\endgroup$ – Crazymoomin Jan 1 at 12:23
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    $\begingroup$ Good point! I'd forgotten about polar crater exploration, ya that's a challenge. I guess in order to have unbroken radio contact the rover will have to drop one or two little "WiFi repeaters" near the top of the crater and the antenna (or laser) link to Earth would have to be left up there. As for there being "little room for impulsive decisions based on new discoveries" that reminds me of this! $\endgroup$ – uhoh Jan 1 at 12:57
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    $\begingroup$ @uhoh I think the best way to put it would be to say that impulsive decisions have a significantly greater cost in time and effort when the humans in the loop are hundreds of thousands (or hundreds of millions) of km away. $\endgroup$ – Crazymoomin Jan 1 at 14:54
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    $\begingroup$ @Crazymoomin we weren't going to land people on the lunar farside without good communication satellite support there, either. And that's even though we had a temporary satellite in orbit to provide their ride home - sure, the CM could be a backup relay when overhead, but a manned mission wouldn't happen with a constellation or positioning providing constant coverage. $\endgroup$ – Chris Stratton Jan 2 at 21:01
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Speed of light

For Mars, at its closest point it takes 3m 22s to get a signal one way. We would need another 3m 22s to see what's happened. At its furthest we're looking at 24m each way. So good remote control is basically impossible.

We don't have good AI yet, so we only have three options for craft we send out into space. They can be pretty dumb and just send back data (e.g. Voyager); or they can carry out a single high-risk well-planned operation (e.g. Hayabusa); or they can be sent a series of very small operations, waiting for the round trip of getting the command there and seeing the results before moving to the next operation (Mars rovers). In the latter case they may only spend a few minutes a day actually doing anything, and the rest of the time is spent waiting for radio signals to go backwards and forwards.

If you have a human on site, all of this is avoided. Even if the human stayed in orbit, they could still accomplish orders of magnitude more work with the same rover.

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    $\begingroup$ I don't think that Mars rovers spent only "a few minutes a day actually doing anything, and the rest of the time is spent waiting for radio signals". I think that they were kept pretty busy, especially Curiosity How much can the Mars rover Curiosity do autonomously, after four years of operation? $\endgroup$ – uhoh Jan 2 at 4:19
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    $\begingroup$ @uhoh, there's still a roughly one-day decision loop for task designation. Curiosity can't just decide "this rock looks like a conglomerate; I should inspect more parts of it" the way a human can. $\endgroup$ – Mark Jan 2 at 20:27
  • $\begingroup$ @Mark indeed that's the way things are currently: Who discovered “Egg Rock”? The Curiosity rover or people? but I think that a "hey, that looks interesting" algorithm might be possible in Perseverance at some point (just a guess). $\endgroup$ – uhoh Jan 2 at 21:56
  • $\begingroup$ @Mark sure Curiosity can't make its own priorities, that would indeed require an AI that can work without training data. However, mission specialists will not see a single interesting conglomerate, they'll look at what interesting spots were found (likely a multitude of them) and plan the next day's course to revisit those spots that look "interesting enough". Sure, a human on Mars would have the ability to make a faster and more accurate decision what's interesting and what isn't. OTOH maybe not: A team of mission specialists has more thinking time than an astronaut. $\endgroup$ – toolforger Jan 3 at 11:39
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There is a serious advantage to being able to make complex decisions, perhaps even moral decisions, on board the spacecraft without any lag due to the speed of light. For the sake of argument, imagine a robotic emissary encounters life on the nearby Jovian moon Europa, which immediately offers some kind of complex moral test to determine whether they will interact with us (or our emissary) and requires an answer within minutes. We would currently only be able to handle such a situation with any hope of success by sending humans to Europa, as the round trip time for radio comms is 1.5 hrs. While I'm not saying there is complex life on Europa, there might be similarly complicated situations that arise far from home.

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  • $\begingroup$ I was just thinking about that when I mentioned deep space monitors :-) $\endgroup$ – uhoh Jan 1 at 10:20
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    $\begingroup$ I doubt that this is even on the list of consideration that go into mission planning. The probability of having a meaningful moral decisions is so absurdly low. If it's a test, any moral entity will allow for the signal transmission time (or their moral is so different from ours that any interaction will be far too difficult even for a human to handle directly - in fact that would be more risky than a mere automaton malfunctioning). $\endgroup$ – toolforger Jan 1 at 13:36
  • $\begingroup$ I can come up with difficult decisions without involving extraterrestrial life, but yea I agree for small space probes to measure weather on other planets or something this is not such a big worry. A instance where complex decision making capabilities might receive a very high weight in mission planning is if the cost of the ship is excessive (decades of work, multinational effort,... etc). $\endgroup$ – samfr Jan 3 at 2:58
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Apart from everything else that's been mentioned: many times, one of the questions that the mission is trying to answer is "how well can humans do X in space" for some value of X. It should be reasonably obvious that you need some humans in space in order to answer such questions. NASA's website currently lists some 249 such experiments (plus 40 "title not found" ones), from "BP Reg (A Simple In-flight Method to Test the Risk of Fainting on Return to Earth After Long-Duration Spaceflights)" to "Wearable Monitoring (Wearable System for Sleep Monitoring in Microgravity)". None of these experiments could be done by any means other than putting humans in space.

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  • $\begingroup$ I'm not sure but this sounds like circular reasoning. I agree that an anthropomorphic robot would not provide as discerning of a data set and evaluation of a next generation wearable system for sleep monitoring in microgravity as an actual human sleeping in space, but since robots don't sleep, robotic missions don't need systems like that in the first place! $\endgroup$ – uhoh Jan 1 at 10:47
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    $\begingroup$ @uhoh it's actually not circular - it's experiments to gather the data so we even can make a rational decision about when a human would be effective and when not. $\endgroup$ – toolforger Jan 1 at 13:38
  • $\begingroup$ I see,so to choose between a Cadillac and an Accord, we should buy and then drive both of them first? To choose between a substantially more expensive solution that puts human lives at risk and a cheaper solution that doesn't we should first do both? To me, as long as robotic solutions exist, there is no rational reason to test the alternative. $\endgroup$ – uhoh Jan 1 at 13:43
  • $\begingroup$ @uhoh But we don't want to go to space just to do a few experiments. In the long term, we want to have large numbers of humans living somewhere other than earth. Thus, we need to do these experiments at some point, and might as well do them now and have the humans do some other experiments while they're at it. $\endgroup$ – user3482749 Jan 1 at 15:19
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    $\begingroup$ What do you mean "we"? :-) $\endgroup$ – uhoh Jan 1 at 15:21
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While robotics has made huge strides, robots have not even approached surpassing many of the basic general-purpose abilities of humans equipped with suitable tools, and the potential for robots to actually do that does not belong to the field of mechatronic engineering or controls theory , but to the wild dreams and nightmares of "futurists".

(It is worth noting that, even as fairly "general purpose" robots have been invented, I do not believe that any "general purpose" robot has ever been launched on an uncrewed space mission).

(This is also the reason why, even though modern warfare is heavily dominated by armor, artillery, aircraft, and guided missiles, infantry are still very important and no modern military has seriously proposed an exclusively robotic force.)

Humans have a great deal of sensory ability (with heavy redundancy, so as to be able to maintain significant sensory ability even when impaired) and locomotion ability (once again, with heavy redundancy, such that a human with a disabling injury can still often be pretty effective in ways that robots rarely are). While the size and weight of a habitation module capable of supporting a crew for months are formidable, the ability to repair damaged equipment, maintain things that would otherwise need to be designed for ultra-reliability at high cost, set up and operate non-automated equipment which may even be commercial-grade, etc is simply not matched by robotics -- we don't have the ability to build robots that can do that for any size, weight, or cost.

A man, an EVA suit, and 50kg worth of tools are simply not something that robotics is anywhere near rivaling. This is then massively compounded by the intelligence / teleoperation issue mentioned by other answers.

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  • $\begingroup$ "This is also the reason why... no modern military has seriously proposed a robotic force." I'm not at all confident that no modern military has seriously proposed a robotic force in classified settings, and even if nobody has, I'm not sure this would be the reason why not. $\endgroup$ – uhoh Jan 1 at 10:35
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    $\begingroup$ It's still cheaper to send 10 unmanned missions than 1 manned one, and humans are so impaired in space that their ability to repair anything is ridiculously low (hours of preparation and debriefing even for a five-minute EVA, and they're seriously exhausted). $\endgroup$ – toolforger Jan 1 at 13:37
  • $\begingroup$ @toolforger that doesn't account for how many Things can be repaired without EVA, or The amazing benefits you get from that. $\endgroup$ – ikrase Jan 1 at 20:29
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    $\begingroup$ @ikrase I see your point, it's just hard to justify a factor-10 cost increase. There may be experiments where you want to have a human around, but I find it hard to believe that ISS is worth the cost. I also suspect that it's not just a cost increase but a weight increase, which means the rocket equation will put the factor into the exponent. Even reaching Mars seems to be a technical challenge, and nobody is even thinking about Jupiter moons. $\endgroup$ – toolforger Jan 2 at 5:32
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    $\begingroup$ @toolforger can you give an example of a five-minute EVA? Especially one that left the crew "seriously exhausted"? $\endgroup$ – Organic Marble Jan 3 at 2:58
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I don't think humans are necessary. The cost of keeping a human alive in space, and getting them back again still in that condition, is so immensely high that a mission with a crew doesn't have any budget left over to do actual science, so I find the presence of living humans counterproductive. Perhaps they are necessary to maintaining funding for the actual space program that has actual accomplishments, but they are a hellishly expensive kind of advertising cost to have to suffer. Humans have always been put into space mainly just to show off that we could do it, for the sole purpose of getting to brag about it. I would much rather all the humans stayed firmly planted on the ground, and sent only robots into space.

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    $\begingroup$ "a mission with a crew doesn't have any budget left over to do actual science" factually incorrect hyperbole $\endgroup$ – Organic Marble Dec 31 '20 at 0:25
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    $\begingroup$ The point of human missions is NOT to do science, it's to have humans in space. Science is just something they can do while they're there. $\endgroup$ – jamesqf Dec 31 '20 at 3:49
  • $\begingroup$ While I mostly agree with your sentiment, I think an answer should be more than an opinion piece here. Can you back "The cost of keeping a human alive in space... is so immensely high that a mission with a crew doesn't have any budget left over to do actual science" with some references? $\endgroup$ – Suma Dec 31 '20 at 6:37

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