When most people think of space, they think of astronauts, rockets, and space ships. Since the late 1950s, people have been sending people and probes into space aboard rockets to explore, allowing us to see the Earth and the Universe in ways we haven’t seen before. From space stations to space telescopes to interplanetary probes, our exploration of space has changed our understanding of ourselves, our solar system, and all of astronomy.
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You don’t ever really need to “break” the atmosphere since there’s no solid boundary where the atmosphere ends. As you go higher and higher, the air pressure/density just gets lower and lower until it’s effectively nothing. This is why people climbing up Mount Everest have to carry oxygen tanks, because otherwise the air would be too thin for them to breathe. “Space” above Earth is really just the altitude where the air is so thin that it doesn’t really matter to the spaceships and satellites that are there.
This works out to just a simple problem of proportions. The Earth is approximately 53 million times larger than a basketball, so it would have to be about 53 million times further away to appear the same size. If your arm is 1 meter long, then this corresponds to about 53,000 km or 33,000 mi, which is about 14% the distance to the Moon.
Funnily enough, even though the day was originally defined by the rotation of the Earth, it actually isn’t anymore, and we have clocks that can keep time more consistently than the rotation of the Earth now. The Earth actually changes its rotation speed by several milliseconds randomly over time, which is enough that every few years we have to adjust the clocks by one second to keep our time aligned with the Earth’s rotation, meaning that the Earth loses one second of time every few years (this is called a leap second). By contrast, our most accurate atomic clocks only lose one second ever 300 million years, so if we want to keep our time accurate then we should look to the lab, not the skies! In fact, the real problem with timekeeping in space is that Einstein’s theory of relativity tells us that time moves at different speeds on objects moving at different speeds (like satellites or other planets), so things like GPS satellites have to adjust their clocks to stay consistent with us on the surface of the Earth.
Currently, nothing is really being done with old satellites and I am not aware of any plans to use them at all, so all of my answers will be entirely hypothetical, but I’ll give my opinions based off of what I know about orbital dynamics.
Satellites are incredibly hard to get to because they are very small and are moving very fast in seemingly random directions. If you sent a spaceship of some kind up into Earth orbit to capture satellites, it would have to expend a lot of time, effort, and fuel to go rendezvous with each individual satellite it wants to capture. For instance, going from the ground to docking with the International Space Station takes days for spacecraft to do because it is very hard to create the appropriate orbit to match yourself up. And if you were to capture one satellite, you would have to expend a ton of energy to change your orbit to capture another one because they are so far apart (there are about 4000 satellites in orbit, which works out to about one every 50,000 square miles / 130,000 square kilometers, and there’s also the height dimension to worry about). You would probably end up expending more weight in fuel to get to the satellite than the amount of material you would gain from the satellite.
Beyond all of the difficulty you would face in getting to the satellite, the things you would find on a satellite would probably not be too useful. Many satellites die because their electronics short circuit because of the radiation of space, so their old broken electronics would probably not be useful for modern purposes. Their solar panels may be useful, but for old satellites, their solar panels are not going to be as energy efficient as newer ones. Raw materials like sheet metal may be the most useful components, but that hardly seems worth the journey.
The best thing to do with old satellites is just to return them to the Earth. Despite the fact that space is so large and satellites are so sparse, popular orbits are actually becoming cluttered enough that people are worried about satellites colliding (it has already happened at least once). Newer satellites have equipment for removing themselves from their orbits once they are decommissioned, but many older satellites are just sitting in space going around in circles forever. The most productive use for old satellites is to somehow destroy and remove their debris from orbit to make way for new ones, but that’s just as hard of a problem to solve.
This is a complicated question that has scientific and political answers to it but no real conclusive answer. Though no people have been to the Moon since 1972, there have been plenty of missions to the Moon before then and since then (here is a list of all of them). The main motivation for sending people to the Moon was of course the Space Race, and when the US first put people on the Moon in 1969, most of that political motivation was taken away. The lunar programs for the US and USSR were hugely expensive (the NASA budget was about 9x larger in the 60s than it is now), so once the prize was claimed, the USSR stopped pursuing Moon landings, and the US followed suit a few years afterwards. Since then, computers have become much more capable, so scientific missions to the Moon don’t require actual people to perform their experiments and they instead send robotic landers. It has been more cost effective to have a lot of cheap robotic missions than a few expensive manned missions, so that is what has happened. There is currently a push to return people to the Moon with bigger and better landers in the mid 2020s for political and economic reasons (the Trump administration wants to land by 2024 so they can have a potential political win), so we’ll see how that turns out in the next few years.
- The radiation in space doesn’t cause any specific problems to bones. Bones are mostly just made of solid material, so the small radiation particles in space are not that harmful to it (other than elevating your risk for bone cancer along with every other type of cancer since you’re receiving at least 10 times the normal amount of radiation). Astronauts have to worry about their bones a lot though because they have a tendency to deteriorate while in zero gravity. Since the bones aren’t being used to support any weight when astronauts are just floating around, they get lighter and weaker over time (like the bones of old people but 10 times as fast). This condition is called spaceflight osteopenia and is a serious risk for long term space travel.
- The main thing astronauts do to stay healthy is exercise. As I mentioned above, floating around in weightlessness puts much less stress on the body than being in gravity, so bones and muscles deteriorate quickly. On the International Space Station, there is a stationary bike and a treadmill to keep the astronauts in shape (the treadmill has tethers to keep the astronauts pulled down, otherwise they would float away while running). However, these treatments still don’t work very well, which is another serious risk for future space travel.
- Astronauts don’t get sick in space because they’re completely isolated from all of the germs on space. Nothing can get up to them while they are up there, and they are basically put into quarantine for 10 days before launch to ensure that they don’t carry any diseases up to space with them. There are big problems with motion sickness though since being in space really messes with your inner ear. Astronauts have to take anti nausea medicine while they are in space suits so they don’t throw up in zero gravity and have it float everywhere, which can be dangerous or fatal.
This is certainly a complicated topic and I don’t necessarily have expertise in the right areas to answer it fully (this is probably better posed to someone at NASA or something) but here’s my opinion:
Robots can do a lot of the things that humans can do in space like run experiments, take observations, and send back data. They can move around, travel great distances, and go for decades. But what they can’t do is solve problems. A Mars rover that costs hundreds of millions of dollars can get stuck forever because of a small rock (Spirit), and a probe’s orbit can be forced to change because its operators are too afraid to reactivate its engine because they don’t know if it is faulty (Juno). Essentially, a robot can do exactly what its job is reasonably well, but once it is faced with an unexpected challenge, it frequently can’t recover.
There have obviously been huge developments in robotics over the years that have led to very capable and and adaptable (see Boston Dynamics robots for a good example), but you will notice that these aren’t the types of robots that go into space. The technology that is included in these missions is usually older and well-tested because if you spend hundreds of millions of dollars putting something on a rocket and sending it across the solar system, you really don’t want it to fail because of a bug in new software or hardware. So it’ll probably be a while before the robots going to space are less conservative and more advanced than the ones today.
It’s worth talking about a few of the disadvantages of sending people to space though. Mostly these are health benefits that result from low gravity and radiation, as I’m sure you know from your research. There are already ideas for countering both of these, with rotating spaceships creating artificial gravity (see 2001: A Space Odyssey) and water/fuel storage tanks lining the walls to block radiation (see SpaceX). Of course, there are still risks and there is ongoing research in other effects, but science has overcome many challenges in the past so I personally think we’ll get there.
Beyond all of these immediate scientific considerations, I believe the most important function of people in space is to expand the horizons of humanity and inspire technological development. There were several computerized landers that went to the Moon before the Apollo program, but it was still a pivotal moment in human history when people first walked on the Moon. Ultimately I believe that humans can and should travel to other planets to expand its reach, and that is something that a robot could never adequately do. Sometimes these scientific pursuits are not entirely objective and there has to be some human emotion involved on occasion.
So that’s my own individual opinion.
Your question is a very interesting and difficult one that is hard to answer in a rigorous way. There are some concrete reasons why people want to go to other planets, but many of them are difficult to articulate in a logical way. Here are some ideas though:
- Science: We can learn a lot of things about how the solar system was formed by visiting other planets. Landers on the Moon, Mars, and Venus have discovered interesting things about their structure that has told us how they formed and what their conditions have been like over their lifetimes, giving us a better understanding about what makes Earth the way it is. By looking for planets around other stars, we can see other kinds of solar systems that can form, telling us even more about how we came to be.
- Resources: Other places in the solar system likely have different resources than the Earth does, making them useful for different purposes. Because of the Moon’s low gravity and lack of atmosphere, it has been proposed as a good place to build telescopes and rockets so they don’t have to deal with the complications of the Earth. Asteroids contain lots of valuable metals that could be used in manufacturing on Earth or in space to significantly reduce the prices of some goods.
- Safety: If something bad happens to the Earth, be it a giant meteor, climate change, or some other unforeseen threat, humanity currently has no backup plan. If we could set up a settlement on another planet or something, then we would know that at least some humans could be safe in the event of an Earth-ending disaster. If we explore other planets in our solar system and look for planets in other solar systems, we can find good places to live
- Exploration: This one is a little more abstract, but humans are naturally curious about their environment and they have always done things that may not have been the safest or the most logical in pursuit of exploration. Brazil would not be the way it is today if European explorers didn’t set off across an ocean with no idea what they would find. Nobody would know about Antarctica if some very reckless explorers hadn’t sailed south just because they wanted to. The same applies to going to other planets. Humans just want to go look at things.
There are definitely a lot of arguments for staying on Earth, like safety, cost, and resources, and I’m sure nobody is ever going to force you to go to space if you don’t want to. But sometimes people have to do things that don’t make sense in the moment because they will lead to big advances later down the line. Hopefully this answers your question.
This idea has been floating around for a while but it would be hard to actually implement. In order to build a space station that was actually capable of supporting its own weight (as a rotating space station would have to), you would have to do a lot more structural engineering, which would mean larger and heavier materials being sent up to space. The International Space Station is really not that strong since is held together by relatively small docking adapters and don’t have any large exterior structure. The solar panels and radiators don’t have anything holding them up either, so they’re pretty weak. Building a circular rotating space station would be kind of like building a bridge in space, and right now it would be too expensive to launch that many steel beams (or whatever) would be super expensive, and we barely have the money to maintain the current space station as it is.
Deep Space Exploration
There has been a fair amount of consideration given to using the gravity of planets or the Sun as the lens of a telescope and would allow unprecedented views of extrasolar planets, but there are a lot of technical factors that make it wildly impractical. General relativity allows us to use anything with mass as a lens, but the distance you have to go for the light to actually come to a focus is absolutely insane. The Sun’s focal point is at about 550 AU, which is almost 4 times further away than the Voyager spacecrafts which have been travelling outwards since the 1970s (and other planets have focal points that are even further), so it would take decades (at least) to get there, meaning whatever you send out there would likely be outdated by the time you got to use it. Even if you get there, you have to be able to block out the Sun’s light extremely well to actually see what you are looking for, which would push the limits of modern telescope design. Furthermore, if you wanted to look at more than one thing, you would have to stop the spacecraft and make it travel another huge distance to get in the right alignment to look at something else. With the amount of fuel, effort, and time that would take, it would likely be easier to just launch a different telescope for every observation, which would again be wildly expensive and impractical. Even getting the data back would be really hard, since it takes huge radio telescopes to pick up the signals from the Voyager spacecrafts, which adds more expense to deep space missions. So overall, cool idea, probably won’t happen any time soon.
Extraterrestrial Life & Astrobiology
This is obviously a very sci-fi question that is impossible to give a real answer to, but I can actually give a pretty reasonable scenario based on some recent events. In 2017, an object called ‘Oumuamua entered the inner Solar System from interplanetary space. It was a thin sliver (likely a fragmented comet or something like that) that was several hundred meters long and around 100 meters wide, and it dove closer to the Sun than Mercury before being slingshotted back out of the Solar System forever. And it did all of this before we even noticed it at all. It was only randomly discovered by a telescope survey about 40 days after its closest approach, when it was already on an escape trajectory. So while we obviously have never seen an alien spaceship coming into the Solar System, we have seen this thing, which is similar in size, shape, and trajectory to a hypothetical spaceship (so much so that it prompted some conspiracy theories). If we believe this example, then it is reasonable that we wouldn’t see a spaceship of similar scale until it had already arrived (unless they wanted to be found). New telescopes coming online in the next few years will significantly improve our ability to see dim, fast-moving objects like this though, so our space defenses should soon improve dramatically.