The most expensive thing about space travel is that most the equipment only gets used once for a few minutes It's sort of like buying an expensive new car whenever the old one runs out of gas. So today's topic is reusable rockets, an emerging technology that is cutting launch costs down significantly We will also be talking about some of the fuels we use, including metallic hydrogen a possible new fuel that offers vastly better Performance. Metallic Hydrogen has been getting a lot of attention recently and an awful lot of hype as is often the case But it also has a lot of genuine potential as a game changer for rockets and space flight So I decided we should include it for today's discussion Your typical rocket launch costs hundreds of millions of dollars. Indeed we estimate that the shuttle program, when you include all lifetime costs and divide by the total number of launches, averaged about 1.5 billion dollars a launch The shuttle carried a payload of cargo and people of typically less than thirty thousand kilograms But if we use that value to divide 1.5 billion, we would get a launch costs of around fifty thousand dollars a kilogram We often say that the main cost of launches into space is fuel But that's not exactly correct. The raw fuel costs while large, typically are less than 1% of launch costs, and it is the rockets themselves that are expensive We might burn through a hundred thousand gallons of liquid hydrogen to launch a rocket But that just costs us hundreds of thousands of dollars not hundreds of millions. If you assumed, say, three million dollars of fuel for a launch, that cost would only be about one hundred dollars per kilogram. Similar to some of the better systems we have looked at in this series. The issue with rockets is indeed the fuel but it’s not its raw cost but rather all the costs associated to carrying it up to burn it to go faster. A typical rocket booster can cost you, say, a hundred million bucks, and maybe a million dollars of that would be the actual fuel, so needless to say if we could reuse that rocket, fill it up with new fuel, costs would drop immensely. Such a simple and obvious idea for saving money would one would think be a no-brainer we implemented almost immediately. That was the idea behind the space shuttle program Most of whose components were reusable, so we will use that in a moment as our example. First though, I want to emphasize how insane the forces and pressures working on Rockets can be and contrast that to an automobile Let’s say gasoline will average $2.50 a gallon over the course of your vehicle’s life, and you bought that car for 25,000 dollars and it gets 30 miles a gallon or 50 kilometers. We will also say that you pushed that call out to 300,000 miles or five hundred thousand kilometers before it finally dies and dump another and dump another 25,000 dollars in maintenance on it, and also that between insurance and interest on the principle of the loan you borrowed for it you will spend another 25,000 dollars. Most folks tend to assume the main cost of a vehicle is the fuel to operate it, but at that mileage and fuel cost, you will end up using 10,000 gallons of fuel before it dies and spend 25,000 dollars buying that. Incidentally the mass of that fuel would be 28,000 kilograms, probably about 20 times what the car weighs, which is a fairly similar ratio to what most rockets have in fuel, compared to whatever they are launching Anyway, based on those numbers you spent a total $100,000 to drive that car 300,000 miles or five hundred thousand kilometers Averaging 33 cents a mile or twenty cents a kilometer, and only a quarter of that was fuel Cars tend to be one of the most reusable types of machines we have and even then is only achieving a quarter of its cost in fuel. A rocket is also a device that burns through thousands of gallons of fuel but it does in just a few minutes and needs to be ultra light to reduce that fuel and designed to handle the stresses of burning all that fuel that fast while also traveling at mind-boggling speeds So let's look at the external fuel tank on that shuttle, the only part of which was not reusable It's a very recognizable item with that rusty orange color of its foam insulation We used to paint it white to help reflect away light, but it was quickly decided we didn't need that and getting rid of that saved a lot of weight That paint weighed almost 300 kilograms, and no it wasn't especially heavy or thick paint, that tank is simply enormous. Left over on its side in a football field it would take up about half of it keep in mind that tank weighed about 100 times that empty and about 2,000 times that when full so it gives you an idea just how precious every little bit of weight is on those rockets if we worried about 300 kilograms. As we discuss making them reusable the obvious idea is to include sturdier structure to the rocket, But this sets off of a vicious fuel to mass ratio cycle that will discuss in a bit. So that tank contained a mixture of liquid hydrogen and oxygen which need to be kept at temperatures that would make a polar bear shiver, and which we will set on fire, amusingly producing water vapor, and also smash through the atmosphere at speeds that make jets look like turtles. Imagine for the moment going out and popping your hood, draining the radiator fluid and oil, then flooring your engine in neutral, till you ran out of gas. Imagine the stress that would put on your engine, and please do imagine that. Don't actually do it since at the very least you will trash your engine in a few minutes. These are the kinds of stresses being put on the components of the rockets we use and while we can't just pick them up and refuel them Which is a pity because the external tank on the shuttle in modern money costs about 100 million dollars, and not even a million of that was to fill it up. Now that external tank wasn't reusable for a different reason. We pop it off when it's empty, which is when you're already in space and moving very fast. So it falls back down and breaks into pieces under re-entry, typically crash teams of the Indian ocean. Those two other rockets on the shuttle the solid Rocket boosters or SRB's, typically got discarded about two minutes into flight about 45 kilometers up and land in the Atlantic Ocean. Where we will recover them, repair and refurbish them, and reuse them. Which sounds great, but after all the costs of building them with recovery in mind, of recovering them, and of repairing them, while no one can really give an exact figure The consensus tends to be that it cost nearly as much to do it as it would have to buy new ones. And I've seen a lot of folks argue that it not only didn't save much money, but actually cost a lot more. It's hard to say for sure since government accounting, while always very accurate and detailed, tends to be more convoluted than the actual rocket science. I sometimes suspect the accounting department at NASA has more people and computers in it then Mission Control has Now I happen to think that recovering those was the right move, even if savings were kind of ethereal and minimal at best, since it gave us a chance to study them mostly intact and see the kinds of stresses and failures occurring during launch. And a lot of improvements did come from that, but the ideal scenario would be a rocket that was easily recovered and could be almost instantly refueled after some quick inspections, and maybe a few parts replaced, like we do with airplanes. So the repairs and refurbishing were not costing as much as the fuel. This was definitely not the case the shuttles solid Rocket boosters It's also not the case for the reusable rockets we see nowadays, for all that we can watch them land back on their launch pads. Most of these designs are still multistage rockets where only the first booster stage rocket is recovered. Doing even that is very difficult, and that first stage, like the shuttle's SRBs is typically separated at altitudes and speeds where the thing is not undergoing full re-entry stresses. So let's get some specifics and look at the Falcon 9 which gets a lot of well-deserved attention, specifically the Falcon 9 Full Thrust variation. As you doubtless know this is produced by SpaceX, which was founded by Elon Musk, a guy who almost certainly needs no introduction to anyone watching this channel, so let's focus on the rocket instead. We will do so by first noting that this is a two-stage rocket and only stage one is recovered. So it is not totally reusable. We will also note that at a price tag of 60 million dollars per launch, almost none of that cost is fuel. and that it gets a kilogram of payload to low orbit at just over 11,000 dollars a kilogram. Which is way better than the shuttles estimated 50,000 a kilogram, almost five times cheaper. But is nothing like the savings we'd expect from a genuinely reusable system, where fuel was the majority of the cost, or at least a big portion of it. Indeed most of those costs save compared to the shuttle can be laid at the feet of other improvements besides reusability. Like building it cheaper and better in the first place. Don’t take that the wrong way, I love Space-X and the Falcon-9, as third Generation geek who grew up playing with Rockets, At least until I accidentally set one off in a dining room, and my mother banned that hobby, I've been one of those folks griping for years about how we needed more private space companies out there innovating. They and a lot of other groups, like my friends over at Ripple Aerospace, who are designing rockets for oceanic launch, have done an amazing job making that happen and paving the way for further improvements So what makes a rocket cheaper? What makes a rocket expensive in the first place is indeed the fuel, because it is expensive in terms of weight. You have to carry all your fuel, and the oxidizer to burn it, with you, and the thing it is inside needs to be pretty tough, which usually means heavy. One of the reasons we do multistage rockets is so that we can jettison empty tanks and not have to burn even more fuel to carry them along. Folks wonder why we don't just do tons of tanks, using one up and going to the next? But that has two costs associated to it, money costs and mass costs. Both of which run headlong into the square Cube law. Geometry tells us that if I make something twice as wide I will generally increase its surface area by a factor of 2 squared or four, while I increase its volume by 2 cubed or eight If my tank needs to be a centimeter thick to handle the stresses I'm putting on it, then if I double its size it can have eight times the fuel in it for only four times more weight for the tank itself. So if I could use one big tank that empty weighs forty thousand kilograms and holds 80,000 gallons of fuel I could miniaturize that to something that only weighed ten thousand kilograms and held 10,000 gallons of fuel. Square Cube Law. But to get 80,000 gallons of fuel for my rocket, I now need eight of those with a tank weight of eighty thousand kilograms, when the big one held the same but only weighed forty thousand kilograms You still seeing some fuel savings with the last couple tanks, with the others empty and jettisoned, But you lose a lot more in the first half from carrying that extra tank weight. Now you might be wondering, "Why we don't just make bigger rockets if fuel is cheap, and a lot of our problems come from tank weight? Why not scale things up even more to take advantage of the Square Cube Law?" This option has been considered and one of the results was a rocket design called the Sea Dragon, a giant rocket 150 meters long and 23 wide. That's three times wider and taller than the shuttles external tank and almost 30 times heavier. It would have been able to carry over 500 tons into orbit, too. There's a lot to be said about this design, often called a Big Dumb Booster, since it does start letting you make things cheaper when it comes to the tanks. This design was intended to just use regular old steel and got closer to that hundreds of dollars per per kilogram to orbit that you can achieve when fuel is your main financial cost. The Sea Dragon was an enormous design and sadly never got built, but as the name implies, it was launched from the sea where it could be pulled vertical for launch by ballast. Oceanic launching has quite a few advantages too. One is that you can tow it down to the equator, almost all of which is ocean not land, and gain full advantage of the rotational spin of the Earth for getting into orbit. A Spiritual Successor to the Sea Dragon is the Sea Serpent design from Ripple Aerospace. The SS-1 is scaled down designed to lift a few tons of low orbit, and the SS-2 design is a heavy reusable launch vehicle, able to list about 10 times that and hopefully prove the viability of Oceanic launches to eventually resurrect the sea dragon design, though properly modernized, of course. Oceanic launches also have the nice upside that you could have as big a launch as you want. There's a tremendous amount of force involved in a launch, and a lot of vibration as a result. We often spray huge jets of water under the rocket to dampen those vibrations out, so they don't damage things. Needless to say that is not an issue with an oceanic launch and while it isn't a technical advantage you also don't need to go through truly massive and expensive amounts of paperwork and licenses to launch in International Waters. Ideally you can also take advantage of existing Shipyards to manufacture most of your stuff in. They are already very experienced at building stuff even bigger and with similar precision and quality control. Submarines and oil rigs being just as hard as rockets or floating launch pads to build. The other nice thing about the ocean besides letting you do equatorial launches, is that if you all planning on using liquid hydrogen and oxygen as your fuel you are sitting right on top of a ton of both, so you can use electrolysis to make your fuel on-site. Forgetting for the moment the practicality issues, I personally like the notion of some big floating rocket base covered in solar panels, electrolyzing all the fuel you need, and able to shift its location around to avoid the weather. Which scrubs a lot of launches and adds a lot overall launch costs doing so. Of course a lot of the advantage of the Sea Dragon, as mentioned, was that through sheer size it cut down on a lot of the cost of building a rocket, since the Square-Cube Law cuts into the effective cost of a rocket per kilogram launched. Bigger tank, same thickness walls and insulation, less tank per gallon of fuel. Bigger is better in that regard, though you start hitting your theoretical maximums with payloads of 1000 tons or so. A friend of mine in the industry said that even when they looked at using graphene, that super tough material we talk about using for space elevators or skyhooks, they can only push it up to about 2000 tons, again for the payload not the rocket. Bigger lets you spend less mass on the tank body of the rocket fuel, but there are limits. That is another way to make rockets cheaper by making those tanks cheaper This very appealing as an option as the raw material costs are quite low, though nothing to sneeze at in comparison to the raw fuel costs either. In manufacturing there are four things guaranteed to drive costs up. Very big objects, low quantity of production, high quality controls on that production, and government red tape. Rockets have all four in spades. The facility costs are also a big deal, as is the transport cost to the launch facility, the storage and fueling at that facility, and manning and maintaining the launch facility itself. Just renting a launch pad for single launch can run you around a million dollars. So if you're doing a lot more launches all those costs go down If we could mass-Produce rockets they would doubtless be much cheaper We could rely on economy of scale to help out there even if no major production breakthroughs occurred, But we'd also be able to test more of them and see where we can get away with going a bit thinner, a bit cheaper, that sort of thing. Of course ultimately your goal is not a cheap throwaway rocket you can use once or even reuse several times with a lot of repair in between But one you can use hundreds of times and needs very little repair and downtime. Something we could run a quick inspection on then re-fuel. In such a case even if your rocket costs you a billion dollars, you’d only be paying a few million per flight. Before we jump into discussing fuels and metallic hydrogen I want to take a moment to note that reusable doesn't always have to be using it for the original purpose as a rocket. As noted before on the old shuttleand on a lot of new reusable rocket designs, It was only the first stage that was reused. The second stage usually being abandoned to fall down and break up since it will need to do re-entry Those don't have to fall back down. We mostly did that to keep low orbit from getting further cluttered with debris. Something that is a serious problem, and which will be looking at in an upcoming episode called Space Trash. Quite a few folks over the years have suggested possible uses for these as an alternative to littering space or oceans. with them Welding them together to form space stations for instance. NASA looked at a lot of studies for doing that but never found one they felt was quite worth the additional costs and risks. It remains an attractive option for recycling them though. Especially as we get a bigger presence in space, since just one of those old shuttle external tanks has more volume than the entire international space station does. We still have one more avenue for getting cheaper, and that's fuel. I know it gets confusing, I keep saying how fuel is cheaper than dirt compared to the other costs, and how it is also our main cost. But this always comes back to the rocket equation and having to carry your fuel with you. If I could double the exhaust velocity or specific impulse of fuel or basically get the same bang out of half the weight of fuel, things change a lot. Let's take a simple case to illustrate this. I have a rocket whose fuel mass on the pad is 110 thousand kilograms, and its dry mass, the mass when all the fuel is burnt, is 10,000 kilograms. And we'll say eight thousand of that is the tanks, or tank singular. We will assume a single stage rocket, for simplicity. Also a single stage rocket is often considered the ideal end goal for reusable Rockets anyway. So 100 thousand kilograms of fuel, 8,000 of tank and 2,000 for the capsule and its payload. We will say that rocket has an exhaust velocity of 3,300 meters per second or a specific impulse of three hundred Thirty-seven seconds. Which would just get us into orbit ignoring air and other variables. Let's say we doubled that exhaust velocity to sixty six hundred meters per second or a specific impulse of 674 seconds. Incidentally before we churn through that, a quick note on specific impulse. You can get that by dividing the exhaust velocity by Gravity or nine point eight m/s2 Which is why specific impulse always looks like the exhaust velocity divided by about ten in metric. Or dividing by 32 in American units Fortunately both systems use a second for time, which is what specific impulse is measured in. But this does give rise to some confusion since a lot of folks think that's how long a rocket will burn. Which is further complicated since it is generally in about that range. Our systems of measurement for such things is based largely on Earth and its gravity and it is that we are usually using the rocket to escape from. So it is not coincidental that it's close. It is generally best not to think of specific impulse as an actual measurement of time and just some number, usually in the hundreds, that tells you how efficient efficient a rocket is, with higher being better, and thus avoid confusion. This is also why I almost always use exhaust velocity and not specific impulse when explaining rockets, so let's get back to that explanation. 110,000 kilogram rocket with 100 in fuel, 8 in the tank and two in the actual Payload, just scrapes into orbit with an exhaust velocity of 3,300 meters per second. Now we double that to 6600. What changes? Let us assume the same amount of fuel in the same size tank. Instead of two thousand kilograms that final Payload What is it now? Is it double loop? Nope. If we pump that into the rocket equation, we’ll get a dry mass of 33,200 kilograms, and 8000 of that was our tank, so 25,200 kilograms of payload instead of 2000 kilograms. That's an increase of twelve hundred sixty percent in our Payload just from that. Doubling exhaust velocity or specific impulse for fuel we get almost 13 times more payload. If both versions of that rocket had cost us 100 million dollars, the first got us a launch cost of $50,000 per kilogram, like the space shuttle, the for scarce a large cost of 50,000 per kilogram like the space shuttle and a second about and the second about $4000 a kilogram. Now obviously we do not have such a magic fuel. Rocket Fuels generally get us in the low hundreds for specific impulse and most model rockets you can buy don't even break a hundred. There's a lot of details in trying to get rockets going that results in us sometimes getting better performance by using some rocket fuels that have lower Specific Impulse than others and it actually tends to be different at sea level than up in the vacuum. which is part of why first stage boosters often use different fuel than the second stage, but as an example, liquid hydrogen and oxygen, one of the more popular propellants, has a specific impulse of 451. Probably the most common fuel is again liquid oxygen as the oxidizer With RP1, which is either short for rocket propellant one or refined petroleum one and is basically modified Kerosene, which we also use a lot. It's specific impulse is lower than liquid hydrogen, only 353. this is what the falcon 9 uses and what most rockets use, and the reason is that it's much easier and safer to handle and store and use the Liquid hydrogen One of the earliest Rocket fuels, by the way, was ethanol, or Alcohol. With a specific impulse of 338. Just a little lower, so yes, you can run a space program on biofuels. The fuel with the highest specific impulse ever test-fired was a tri-propellant mix of lithium, fluorine, and hydrogen that Rocketdyne tried in the 1960s it came in at five hundred Forty-two seconds. But this fuel was deemed impractical. Still it holds the record for rocket fuel for the last half century. That record is now being challenged though. There is a substance called metallic hydrogen which started getting looks a few years back and has recently made a lot of news. So let's discuss it for a minute. This is not a new substance, it was first predicted in the 1930s, and we figure deep below the atmospheres of places like jupiter and Saturn we might see compressive Forces strong enough to turn Hydrogen from a gas into a liquid and finally into a solid. This stuff has a lot of impressive properties, potentially including being a room-temperature superconductor and very recently researchers at Harvard thought they made it in the land The main research of this in recent years is Isaac Silvera from Harvard. And I will link a short report he wrote some years back for NASA on its possible use as a rocket fuel, and another by him shortly before that discussing the basic theory. In that we have a predicted specific impulse of not 3-500 of other rocket fuels, but 1700. Let's contemplate that for a single stage rocket, again if we had a full mass of 110 thousand kilograms again down on the pad we would end with a dry mass of sixty-eight thousand kilograms. Again assuming an 8,000 kilogram tank that would give us a payload of sixty thousand kilograms. Not the 2,000 from our original example. If that were a hundred-million-dollar rocket, that's just sixteen hundred and sixty seven dollars per kilogram to low orbit Rather than the 50,000 per kilogram of the shuttle or when we calculated this one earlier with a specific impulse of 337, basically one using alcohol for fuel. That's 30 times cheaper. But moreover, this opens us up to the idea of single stage rockets again. Ones that could take off and land and refuel. No need for any of the problems that come with multiple stages. And you can get away with a sturdier structure, making easy reusability an option. Basically space planes that can take off just from internal fuel and go into orbit, divest their passenger,and cargo, land, and do it again. Needless to say we are a long way from using metallic hydrogen as a fuel and it may turn out to be not as good as we think or less than practical to use. In the more long term, since this is a futurism channel, if we could get Industrial scale production of graphene to build the space ships out of and metallic hydrogen to fuel them, you don't need any other new technologies you don't need any other new technologies for space. Because you've got a design that can reach low orbit with just forty percent of its mass being fuel and you can really build light and durable and reusable with a material like graphene. Of course, that same material lets you pull off a long non-Rotating skyhook. Even if you can't get it reliable enough for a space elevator. And then you only need to be about twenty five percent fuel and your ship doesn't need to be nearly as tough either. So you finally have a rocket system that has more payload than fuel, rocket, and ship. And you can finally take your family on a rocket ship ride up to orbit for a vacation or off to Luna Disney. So we've looked at a lot of launch assist systems. Most of which incidentally are entirely compatible with the ideas we spoke of today. But this classic approach of rocketry still has a lot of life in it, especially if someone can find a way to mass-Produce metallic hydrogen and store it and use it safely for rocketry. If we can make building rockets cheaper or making the recovery and refurbishment cheaper, especially in tandem with some new super fuel like metallic hydrogen, then launch costs will plummet to zones pretty close to what some of those launches systems we discussed before can offer. Do reusable rockets replace them, or render them redundant? No, probably not even with metallic hydrogen. You are always confined to dynamics of the rocket equation so that these other options still achieve better results, plus many of them benefit from what benefits rockets. A rocket hull made out of diamond hard Graphene might make rockets way lighter and more reusable for instance, but it would suddenly make skyhooks or space elevators a lot more viable too. Same idea, a possible warm temperature superconductor like metallic hydrogen makes a mass driver or space gun a lot more viable also. But they show a lot of promise for making space travel a lot cheaper in the here and now, and also help to open the market up by making space travel cheaper, so that the demand for it can rise, and justify the enormous R&D and capital costs of some of these ideas we've discussed, and will discuss in future episodes. I don't think they are the true future of space travel, but they show great promising in being the gateway that finally opens the door to the technologies that might make it affordable for regular people to take a vacation up there and start making Commercial and industrial use of space a major sector of our economy. In that respect the reusable rocket is without a doubt one of the best things to happen to space exploration in a long time. Next week we will be returning to the topic of Transhumanism for a look at cyborgs, and will extend on some of what we discussed before about that topic and try to clear away a lot of the fog and misconceptions we get about the concept from science fiction The week after that we will come back to this series to look at alternatives to chemical rocket engines in the form of atomic rockets, in "The Nuclear Option". For alerts when those and other episodes come out, make sure to subscribe the channel, and if you enjoy this episode, hit the like button and share it with others. Until next time, thanks for watching, and have a great week!
