Upward Bound: Getting Into Space

Transcript
Space is so big it makes Earth look like a tiny pale blue dot, but the hardest part of exploring space is simply getting above the thin layer of air around that dot.

What we’re going to be doing in the future episodes of this series is taking a more in-depth look at a lot of the launch assist systems that hold promise for making space travel cheaper and easier in the future. Way back when the channel was in its infancy I did some quick episodes covering many of these but not with the sort of depth I tend to favor these days. The time seemed right to revisit these topics in proper detail, with each of those concepts getting their own episode, but I thought we’d begin with discussing some of the basics and giving each a quick overview. So that’s what we’re going to do today. Each subsequent episode will be designed to be a standalone one, able to be watched without having seen any of the others first, or even without this episode.

But today’s episode, besides giving an overview of those, is essentially about clearing up a lot of the misconceptions about getting off the planet. Something I avoided even in the Spaceship Propulsion Compendium, where I mostly focused on more high tech options to modern propulsion, particularly things like the Ion Drive which is only useful once you are already up in space. The hard part is getting up into space in the first place, something we’ve already succeeded at. Now many would wonder why if that’s the hard part we seem to have stalled out in space exploration. The simple answer is two-fold. First, we haven’t stalled out, we’ve made tons of progress in the half century since the Space Race, but it does seem a lot slower. Second, and it’s the reason for that slow down, is that we have pretty close to maximized what we can do with rockets, and those require huge amounts of resources to deliver just a small package to orbit.

Ultimately you are constrained by the rocket fuel, you typically need 20 times as much fuel to get into orbit as the mass of the ship and cargo being put in orbit. That’s all chemistry and we’ve basically maxed out what that allows. The amusing thing about it is that if we could teleport a fully fueled rocket from the launch pad into orbit, that rocket would contain nearly enough fuel to get pretty much anywhere in the solar system. Currently to get such a rocket into space would require dozens of trips into orbit first. Even then such a ship would still be quite slow. But up in space, with ships designed solely for space, we can use alternatives like Ion Drives, which are far more efficient in space but useless for getting into space. Now the important thing to understand is that when we say orbit, we don’t mean just height. Height is the easy part. First you claw your way up through the atmosphere then with the air out of the way you start picking up the lateral speed needed to get into orbit. Otherwise you’d just fall back down again. Ignoring air resistance for the moment, to get up into the Low Earth Orbit zone, defined as beginning at 100 miles or 160 kilometers up, simply requires an upward speed of about 1800 meters per second, or Mach 5. Fast but not nearly fast enough for orbit, it is only about a fifth of the speed necessary and only a tiny fraction of the energy and fuel necessary. Without that speed to get into orbit itself, you’d get up there and just fall right back down again. This is where all the technical terms start getting in the way.

A rocket consists of fuel and the tank that fuel is in, and those are pretty heavy too, so we tend to build multiple tanks and discard the empty ones. For that matter certain fuels and rocket designs are better for that initial ascent than for in space so the rockets tend to have multiple stages. Typically 2 or 3. If you had a magic rocket casing that weighs virtually nothing you’d probably just use one. Instead we drop that first stage tank, the booster rocket, right into the ocean.

This is why launch sites are typically by the ocean, and the reason why they tend to be on the east coast is because the Earth spins that direction. You can launch the opposite direction too, what is called a retrograde orbit, but this uses more fuel because instead of using the Earth’s spin to give you a nice boost up to orbital speeds, you’ve got to fight that spin first instead. You could also launch from the North Pole for instance and gain neither advantage or disadvantage. Many folks wonder why we don’t launch from on top of mountains, and indeed those would offer some benefit, but it’s fairly minimal and it’s quite a hassle to base from up there. The Russian Cosmodrome is an example of spaceport that’s pretty far from population and industry, it has to be since they need a sparsely populated area for their boosters to come falling down. You pick your location based on all the available factors and being near the equator, or on the west coast of an ocean, or up high are all advantageous but not necessary. Trying to build on top of a Mountain just isn’t deemed worth the effort, though Mount Chimborazo in Ecuador is right on the Equator and while only the 18th tallest mountain, in terms of sea level, its peak is the furthest point from the center of the Earth. The Equator bulges out a bit compared to the poles because of the same spin that would assist us in launching rockets. So it’s a better launch site than even Mount Everest if transportation were not an issue and you didn’t need to worry about boosters crashing down on people.

While some booster rockets have parachutes built into them so they don’t actually smash into the ground at terminal velocity, in general only the ones landing in the ocean are recoverable for reuse. Even then the necessary retrieval and repair costs are significant, which is part of the reason there is interest in reusable rockets.

Now those boosters falling, on parachutes or not, is an issue. When we talk about serious exploration and exploitation of space we are not talking about doing one launch per week, or even a couple a day. Real space development needs to be involving moving thousands of people back and forth from space every single day and preferably from places near major cities. Ideally we want to be able to have a spaceport at just about every major metropolis, like we do airports. Having boosters land all over the place and near inhabited areas isn’t viable. Even if there wasn’t a risk from boosters falling down, because they were one stage rockets, the sheer noise of any sort of rocket launch is so loud that it makes an airport or train station sound quiet, and folks aren't too happy about having those near their homes either.

While having launch sites far from inhabited areas is not prohibitive to space travel, we will be looking at some options for getting into space that do not require large and loud rockets, some of which would allow direct access to space directly from cities without being a hazard or nuisance. But let me emphasize this point. This series is not about getting a few more space launches or getting them a bit cheaper or safer. We are interested in ways that let us start getting people and material into space at frequencies and costs not much higher than flying to another continent. That is our goal, because that is what allows us to build actual spaceships, ones that spend all their time in space, and aren’t confined by the design limitations of having to claw their way up through an atmosphere or survive a fall into one. That’s why we won’t be focusing too much on stuff like reusable rockets and modern initiatives like Space-X, though we will also look at the rocket issue and the huge advantages of reusable rockets, both in terms of their advantages in the here and now and in terms of their uses in spaceflight where sometimes a rocket is going to be helpful.

The stuff we will be looking at is also expensive, and I mean compared to rockets, which aren’t exactly cheap. A common question I got when I did the original short videos on some of these items was if we had the technology, why we were not using it? And the answer is that for many of them we do have the technology but even ignoring all the prototyping and developing, such things are only worth it if you are doing hundreds of launches a day. They are ‘all in’ strategies’, where you might spend a hundred billion dollars just to build the launch site, and you might spend quite a bit more in prototyping. So even though they make individual launches a lot cheaper, they only actually make it cheaper if you are launching so often that all the R&D and construction is less than the amount you’d otherwise spend shooting stuff into space. In the upcoming videos we will always take some time to discuss how close we are to the necessary technology, how much it might cost to build, in loose terms, the cost per launch, and the safety issues.

So to get into space you have to get above the atmosphere where the drag would not slow things down and make them fall down, and you need to get up to a phenomenal speed that makes the fastest aircraft look like snail. That’s the trick and we have a lot of approaches. We will survey those now. The first and most obvious is to build a giant tower into space, like the Tower of Babel. The problem here is, besides the construction issues, that you will be turning around the planet once every twenty four hours. If we built a tower 100 miles or 160 kilometers tall, stretching up to the bottom of the Low Earth Orbit Zone, things will be very different from what most people expect.

First, you wouldn’t float around. Things like the space station don’t lack gravity because they are far from Earth, the gravity they experience is only a few percent lower there. They are just in a state of freefall where their centrifugal force cancels out the gravitational pull they feel. On the equator, even on a tower a hundred miles tall, our centrifugal inertial force outward away from Earth is pretty miniscule, not even enough to decrease our weight by one percent, let alone cancel it out completely. In a natural orbit the two exactly cancel out, so to speak. So if you stepped off the side of this tower, up in Low Earth Orbit, you’d fall down, unlike stepping out an airlock on the space station where you’d remain in orbit because you still have that speed, and you’d still feel weightless even though Earth is yanking on you nearly as hard as it is right this second here on the ground.

You would not, incidentally, burn up on reentry by stepping off the tower. Reentry is rough because of the speed you are moving at, and since slowing down would cost a huge amount of fuel, we prefer to let the atmosphere break our speed instead. If you fell off the tower you would get quite fast during the fall, hitting hypersonic speeds, but as the atmosphere got thicker you’d begin slowing and eventually hit normal terminal velocity for the thicker atmosphere below and you could pull a parachute and land on the ground.

Of course you’d need a pressure suit. It would take you a few minutes to fall into the areas that the atmosphere was thick enough to cause real drag and not be causing you to suffer vacuum exposure. That’s an important point though because some of the structures we will discuss, like the Orbital Ring or Lofstrom Loop just hover in the sky high above where the air causes much drag, and folks wonder about it tumbling out of the sky and smashing things when it hits. In practice such things would not cause much damage even if they landed unaided, but you’d put parachutes on them and separation charges to break the things into smaller pieces. You wouldn’t want to be under one when it landed, but it's like a bridge falling down, only it is unlikely to land in traffic and has a long descent time, nobody should be under it when it lands, you can even put those charges on it to push it so that it doesn’t land on a city even if it is right over one, and even the folks on it would have a good chance to survive by just grabbing a parachute and leaping out an airlock during that last minute of descent. They might even survive the actual crash if they were inside it.

This is one of my irritations with space elevators in fiction. I’ve seen a lot of authors, even some with strong science backgrounds who should know better, refer to a snapped space elevator coming down like it was mini-apocalypse. I’ll explain in detail why it is no such thing in the episode on space elevators, but the reasoning for that, and for any of these other constructs we will discuss, is the same. They are not crashing in at re-entry speed. Some of them probably wouldn’t even kill you if they landed on your house. But the issue, besides construction, with this sort of tower is that if you do step off the side you are not in orbit, you fall down.

Now the upside is that on top of one you do have a little bit less gravity to fight and you also have no air to fight, and that is still a pretty big deal. You could launch a rocket a bit cheaper from one of those. But more importantly you could build two or more towers and have a runway, where something accelerated you up to orbital speed, like a magnetic rail line. And that option definitely has some fuel advantages, as you could be gaining speed not from on board fuel but electric cables connected to a stationary reactor powering the track. This is why levitation methods don’t tend to interest us too much for ships though. Floating up on a balloon or some magnetic levitation platform just gets you high up where the air is thinner, it doesn’t help that much. Nonetheless it does help enough that we will see variations on it in future episodes.

The other thing is the tower’s top is moving faster than the equator is, and the Earth’s spin does help a lot with getting into space, the higher up you are, the faster you are spinning even though you are staying in the same spot relative to the ground, so the bigger the boost, also the higher you are, the slower your orbital speed. Unfortunately the Earth’s is 4000 miles or 6400 kilometers in radius so being up a couple hundred more doesn’t help much. It does help though, just a little bit.

The Classic Space Elevator circumvents this. It takes you high up in space all the way to geostationary orbit where the orbital speeds are a lot less, only about 3 kilometers a second, not the 7.8 of Low Earth Orbit, and we call it geostationary because that’s the orbit where you hover over the same spot on the ground. Which means a building built that tall would have the top moving at orbital speed. And if you stepped off here, you would not fall down. You would also be weightless, because while the Earth’s gravity is still decently strong, just a couple percent of what it is at the surface, the spin of the tower is now creating a centrifugal force that cancels that out. So a tower built all the way up into geostationary orbit would be one where you could step off and float there. If you built it a bit higher and stepped off you’d start floating away rather than dropping, incidentally.

Needless to say a tower 36,000 kilometers high is not something we can easily build, but such a device is called a space elevator and was designed back in 1895 by Konstantin Tsiolkovsky, who is essentially the grandfather of spaceflight, and on top of giving us the rocket equation he came up with a ton of different approaches to get into space, including the elevator, which at the time was designed as just a very tall building. You can’t build something that tall with normal materials but we actually have several different approaches to making something that big. The more modern notion of an elevator, a long tether hanging down from orbit and relying on tensile strength, has come to be viewed exclusively as a space elevator, whereas ones that only partially hang down, either from geostationary or lower, have come to be known as skyhooks. Actual buildings that tall tend to be called Space Towers or Space Fountains, the latter because they use streams of particles to hold themselves aloft.

We will get to all of those in turn in future episodes, along with options for floating up on balloons or having runways held aloft above the main atmosphere by balloons, or towers held up by being made of balloons, or runways held aloft, like the Lofstrom Loop or the Orbital Ring, by streams of matter. We still have some entirely different approaches though. First is that instead of using rockets to get up to speed you use a long runway down here on the ground. However to do this properly you need a tunnel, preferably one evacuated of air, for the thing to race along and when it does shoot out, it still slam right into the air anyway, essentially undergoing re-entry right here on the ground. To get around that problem you often have it ascend a ramp to exit on top of a mountain where the air is thinner or even higher up. This is the idea behind concepts like Star Tram, and various other mass drivers that are essentially giant rail guns. It’s also a lot like the Hyperloop, a type of vacuum train popularized by Elon Musk. Instead of burning rocket fuel and dropping booster tanks you get up to speed using some electrically powered system, using magnetics, or up to enough speed that you can do the rest with more modest rockets.

The next option is better rockets. And we still can improve chemical rockets in many ways but what we usually mean is nuclear ones. Needless to say there are some safety issues with this but I am going to give them their own episode because they can be used decently safely in an atmosphere and in the past I’ve only ever discussed their use in space, which uses a different design.

Now lastly we have hybrids of these, which would work to the strengths of multiple systems. Sometimes hybrids aren’t advantageous because of all the extra effort and mass of multiple systems, but they’re very appealing for spacecraft where we might, for instance, have a long ramp that exited out dozens of kilometers above the ground at the top of a space tower and then used some rocket fuel to match speeds with a low hanging, rotating skyhook. That hybrid scenario by the way, is the one I would deem best for if we needed to get a lot of material into space and couldn’t expect any significant new scientific breakthroughs. Major breakthroughs might change that equation, which could include advantages from Economy of Scale. On the other hand the grand-daddy of getting material up into space cheaply is the Orbital Ring, or rather several of them built at different heights and angles, in that it rivals or surpasses the space elevator in terms of usefulness but does not require any materials that are arguably impossible to make, whereas this object is more of feat of engineering than science.

We’ll get to them all in turn, some episodes will be longer than others and we might occasionally combine two decently related topics, especially where I feel like I’d need to explain the basic science over again for both, but I want to close out by saying not what this series is about, but what it isn’t about. It’s not about fringe science concepts where ships shaped like saucers will magically rise into space on anti-gravity or magnetic thrusters, though we will use a lot of magnetic levitation where we can. I don’t do conspiracy stuff on this channel, either for or against, not my cup of tea to buy into such theories or spend my time poking fun or ranting at those who do. We stick to the realms of known science here, not because we think we know all of science but because that’s what we’ve got, and speculating about unknown theories we might one day discover has always struck me as counterproductive. Some of the things we will discuss are so immense in scale they might make the blood drain out of the face of any engineer, but they will rely only on known science and nothing else.

We will also always take as a given that we want to get into space in a big and bold way. Not everyone feels that way and we’ve discussed before some good reasons why you might not want to do this, but this series is focused on ways of getting huge amounts of people and cargo into space in a way that is a lot more affordable and safe than now. That’s our goal for this series and hopefully it will be a fun trip. Next week will continue that trip by looking at the best known option, Space Elevators, and we will hack away a lot of the misconceptions that have grown up around these in recent years. For alerts when that and other episodes come out, make sure to subscribe to the channel. In the links below in the episode description you can also find the audio-only versions of these episodes, with or without music, over at Soundcloud or visit our website or join in the discussion at the channel’s Facebook and Reddit groups, Science and Futurism with Isaac Arthur. Until next time, thanks for watching, and have a great week!