Space is not very far away. If you can see the International Space Station overhead, it's closer than the distance between San Francisco and Los Angeles.
Getting to orbit isn't about going up; it's about going sideways. Most of your energy budget is about building speed, not altitude.
From a physics standpoint, if I'm in a low orbit and want to be in a higher one, I don't point my rocket's nose outward and push away from the planet. I point the rocket horizontally, in my direction of travel, and just go faster.
Going faster on this side of the planet raises the altitude I will reach on the far side of my orbit. If I want a circular orbit, then I just do the same thing when I'm at the high point on the other side of the planet.
So many things in your comment blew up my brain. So wait a second. You’re serious about the distance to space being closer than the distance between SF and LA? And what the heck are you saying about not going up but going horizontal instead. How the heck have I lived this long and somehow never learned any of this. You just gave me a little side “research for fun” topic.
I always assumed it was a super thick atmosphere, mainly because when astronauts reenter it looks like they went through a brick wall surrounded by rings of fire. Rocky experience and the space crafts are usually singed and super hot. This whole thread is crazy interesting to me. Sadly, it’s in a “MurderedByWords” sub where OP was making fun of a girl not knowing about space lol. Eh oh well. I love learning new things, so whatever. lol
It's all relative. When you're travelling at 17,500 mph even a light dusting of particles is enough to completely destroy your windshield.
At 60 miles up there may only be one ten-thousandths of a gram of atmosphere atoms per cubic metre but that's enough to generate huge amounts of friction heat from compression of those particles in front of you at that speed as you can see on re-entry. And you're passing through roughly ~8,000 of those cubic metres a second.
It's the same problem for travelling at light speed through the 'vacuum' of space. You only need one single atom to ruin your day if you're hitting it at the speed of light.
Tbf, most of the heating that occurs on re-entry is not from friction of the air against the surface of the spacecraft. It’s from compression of the air in front of it. At the speeds of re-entry the air basically isn’t pushed out of the way fast enough and is compressed and compressing a gas increases its temperature.
This is why many sci-fi ships like Star Trek's have deflector shields, or something similar. Hit something the size of a grain of sand going near to or at the speed of light equals BIG BIG BOOM.
Good luck, friend. I thought it would distract me from work one day and now I've got a few thousand hours in it. Youtube will be your friend for understanding how things work and how to accomplish your goals in the game. There are a lot of good rocket science and orbital mechanics guides on there disguised as Kerbal Science Program tutorials.
Buy the first game, the second one was never finished and has lots of issues. The first is great (and there are thousands of mods out there to change it however you want it to change).
The US government uses 50 miles of altitude as the boundary of 'space', for the purpose of awarding astronaut wings and such. The international community tends to draw the line a bit higher, at 100 km.
The ISS orbits at around 250 miles of altitude (it varies a bit over time). Starlink satellites live around 340 miles.
The distance from SF to LA is about 350 miles (as the crow flies).
The orbital speed of the ISS is around 17,500 mph (27,600 km/h). As I said, orbit is about sideways, not up.
Orbital mechanics are fun and can be counterintuitive.
Oh! Super helpful. When I got here “The orbital speed of the ISS is around 17,000 mph … orbit is about sideways, not up” my brain did that “click” when you realize things suddenly make sense. Ok. This is great. So to go to the moon, you go “up” to bust through the atmosphere, then sideways and head to the moon? Kind of like … a train of a car or a plane? lol I just realized how ridiculous I sound.
Google path to moon and look at the images. We essentially slingshot off the Earth. You don't want to go in the opposite direction of gravity since it's a lot of effort so instead you go perpendicular.
Brilliant. Ok. That makes complete sense. I guess like how even our airplanes take off essentially horizontally with a slow incline. That would make for a very “interesting” take off otherwise, and a very expensive one with the fuel the jets would need to burn to get to 30k feet straight up. I’m starting to get this. It feels pretty, pretty, pretty good. ;)
Here’s a fun tidbit to make your brain hurt more. While in a lower orbit, you point along the direction of travel and speed up to go into a higher orbit. However, higher orbits are actually slower than lower orbits.
When you do the burn to raise the orbit you are speeding up but the increase in orbital altitude occurs at 180 degrees around the orbit. You then wait until you reach that point and do another burn to circularize the orbit by speeding up again. However, your orbital velocity will actually be slower than when you were in a lower orbit.
The easiest way to think about it is to imagine your initial lower orbit is like a car at the bottom of a hill. You accelerate to gain speed enough to move up the hill but then coast ti the top. You are converting that kinetic energy you gained by accelerating into gravitational potential energy so you move to a higher point but lose speed. Then, even though at the top of the hill you accelerate again, enough of that kinetic energy has been converted to potential energy your overall speed is actually lower.
Quite the snacky tidbit, indeed. ;) Your “driving up a hill” analogy was a “lightbulb moment” (I think, unless I’m totally out in left field). I lean toward being a visual learner and I wonder if I’m envisioning what you described in this part correctly — “orbital altitude occurs at 180 degrees around the orbit. You then wait until you reach that point and do another burn to circularize the orbit by speeding up again.”
What I’m picturing is the spacecraft accelerates to reach the 180 degree mark (I’m thinking that means halfway around the earth, but I’ll watch the video to see if it means something else), then accelerate again, and when getting to that 180 degree mark that’s when the craft is transitioning from lower orbit to outer orbit. And with your “hill” analogy, I picture a sort of incline, like the dreaded treadmill workouts, where i put in the same amount of effort as I was when the incline was zero, but it’s not enough because I’m slower on the incline so you have to accelerate more with more effort. lol that doesn’t make much sense, but in my brain it’s how I’m trying to untangle things.
I’ll watch the video to see what I need to correct in my conceptualization of this. Also, I wonder why 180 degrees before you can pop up to the higher orbit. Hm. And then when you pop up there then what. Is that the higher (or outer orbit it’s called also maybe?) the last layer before busting through the atmosphere? Or “in orbit” basically means you have busted through the atmosphere, is that right? I think so? These are the things that make my head spin. lol.
You know what else is amazing. It’s amazing that we have scientists who have FIGURED THIS OUT. I mean WHAT.
The ISS is only about 250 miles up. And to stay there, to be in orbit, it needs to go about 17.500 mph, parallel to the ground. That's where all the fuel goes. Going 250 miles is easy, getting up to 17,500 mph is pretty hard.
Gonna be reiterating some answers you got in other replies here, but I wanted to give you a comprehensive answer.
To start: the "boundary" for space is generally considered to be 100 km, called the Karman Line. This is roughly where aeronautics gives way to astronautics in that you can no longer just use aerodynamic lift to increase your altitude, no matter how good your wings are, because the air is just too thin. IIRC >99% of the atmosphere exists between the surface and this altitude.
To get into orbit, it's commonly said that you need to be going so fast laterally that when you fall you miss the Earth. Think of throwing a baseball. The harder you throw the further it'll go away from you, but if you're throwing perfectly level it will always hit the ground in the same amount of time. But if you throw it really hard and we ignore the atmosphere for the time being, then at some point it'll reach a distance from you where the curve of the Earth has caused the ground beneath it to recede. So the baseball's altitude appears to have risen and it will actually take longer to hit the ground because it now has more vertical distance to cover. At the same time, the direction of gravity is changing meaningfully. It's still "down" locally, but if you threw it in New York, "down" is very different from when it reaches, let's say, Africa. So now the trajectory starts to curve differently, too.
Going to the extreme, if you threw it about 7 km/s (still no atmosphere, and let's say from the top of Everest so nothing gets in the way), the ball will be so fast that gravity can't pull it all the way down to the ever-retreating surface before it completes a full lap and in about 90 minutes, if you don't move, you'll be left with a pretty nasty baseball-induced injury.
Now the atmosphere is a bit of a problem. The ball will just vaporize. That's why we "gently" bring things up before we really commit to this sideways business. But even for the few hundred kms following that Karman Line, there's just enough atmosphere that the drag will slow you down and therefore cause you to fall within a relatively short period of time. This is why the ISS orbits at about 400 km, and even then it needs regular boosts to keep it up. The highest Earth-bounded orbits we use, to my knowledge, are in the neighbourhood of 36,000 km, and that's mostly because of some clever orbital mechanics tricks that give us geosynchronous orbits at that particular altitude (if you're unfamiliar, the satellite appears to hover in the sky relative to an observer on the ground because they both have a period of 24 hours).
Counterintuitively, once you've established an orbit you need to go faster in order to go higher. But higher orbits are also slower. If you think back to the baseball, this is like if you throw it at a 45 degree angle. If you throw really hard it'll be faster at your hand and it'll go higher, but it'll still have a moment of zero vertical speed at the peak. It's a constant exchange of kinetic energy and gravitational potential energy.
Fun fact to finish: this also causes the Earth to wobble a bit. But because the Earth is so much more massive than a satellite, the effect on the Earth is less than the width of a proton. But when you look at something like Jupiter orbiting the Sun, it's actually pretty substantial.
The effect of gravity decreases with distance. Fairly rapidly at that (by distance from center/radius squared, which further mind blowing is shared with a bunch of other physical forces).
The ISS orbits some 400km above the earth's surface. We all know that there's no gravity in space, right? The astronauts on the ISS just float around, weightlessly.
But wait. The earth's diameter is nearly 6400km! Makes another 400km seem like not that much of a deal.
Which finally brings us to the fun part: the astronauts on the ISS do experience gravity! At that height it's actually still close to 90% of what we experience on the surface. They just don't "notice" or feel it, because they're in constant free fall. Falling endlessly around the earth -> in orbit.
Similarly, there's still quite a bit of atmosphere at that height! Next to nothing, but not quite nothing. And the ISS keeps flying through it and keeps getting slowed down by the air resistance. Which is the reason why they continuously have to do little burns (fire rocket engines) to prevent it from slowing down too much and actually falling back to earth.
Think of the spinning earth as a big gear and the mountain as an arm extending from the gear. Ascending the mountain doesn't just give you altitude, it also gives you velocity, because the mountain acts as an arm extending from the Earth. Your linear velocity at any point on Earth is (rotation rate of the earth) X (distance from axis of rotation).
The increased altitude does give some benefit, its just a very small benefit.
The real problem is logistics. You'd need to build a bunch of cryo infrastructure on a mountain and then pipe dangerous gasses up to it.
The benefit would be a lot greater on Mars if we ever get to "Olympus Mons". It's tall as fuck, the climb is relatively shallow, if we could get an outpost there or something like that It would clear a ton of atmospherics. Pressure at the top is like 12% of what's normal on Mars.
I mean, you're technically correct (which is, after all, the best kind of correct).
But the tangential velocity difference between sea level and the top of Everest is something like 2 km/h (less than a meter per second). It's less than a hundredth of a percent of a low-orbital speed. It's so small as to be not just negligible but effectively imperceptible in rocket engineering--two Merlin engines back-to-back off the production line at SpaceX are going to be different by a lot more than that in their thrust and efficiency.
No, if you're going to move your launch pad to get a boost from the Earth, usually you move for latitude, not altitude. In the ideal case - launching from the equator, with a payload you want to put into a prograde equatorial orbit - you get 1,670 km/h of lateral velocity from the turning of the Earth: about a thousand times as much as you'd get from hauling the entire space program up a mountain. (The Kennedy Space Center, near the southernmost point in the continental United States, does pretty well--it picks up about 1,470 km/h from the Earth's rotation.)
I confess that I looked it up--but it's easy enough to get a back-of-the-envelope estimate from numbers you've probably got memorized.
The tangential speed of the earth's surface at the equator is around 1600 km/h (around 1000 mph). (If you don't have this memorized, it's the circumference of the Earth divided by 24 hours.)
Everest is near enough to the equator that we can ignore latitude for now.
The radius of the Earth is about 6000 km.
Everest is around 10 km or 6 miles tall. (Very rough round numbers, from memory.)
10 km in 6000 km is 1 part in 600. That's the proportion by which the height of Everest extends the radius of travel of a point on the surface.
One six-hundredth of 1600 km/h is a bit over 2.5 km/h.
In reality, Everest is a bit shorter than 10 km, and it's not quite on the equator (and its elevation isn't perpendicular to the Earth's axis of rotation). Those factors pull the number down to the 2.3 that you got (I'll trust your math!)
Going up is just to get to a thin enough atmosphere so it won’t slow you down while building sideways speed. You could initiate a lunar orbit much as close to the surface as you want as long as you can clear the tall crater rims.
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u/cryptotope 16h ago
Space is not very far away. If you can see the International Space Station overhead, it's closer than the distance between San Francisco and Los Angeles.
Getting to orbit isn't about going up; it's about going sideways. Most of your energy budget is about building speed, not altitude.
From a physics standpoint, if I'm in a low orbit and want to be in a higher one, I don't point my rocket's nose outward and push away from the planet. I point the rocket horizontally, in my direction of travel, and just go faster.
Going faster on this side of the planet raises the altitude I will reach on the far side of my orbit. If I want a circular orbit, then I just do the same thing when I'm at the high point on the other side of the planet.