Today’s episode, the Spaceship Propulsion
Compendium, is going to be a long one, since I am going to try to touch at least briefly
on every system including some of the more unlikely ones. I will leave out any that are just not grounded
in science at all, though if I skip one do not assume that means I am including it in
that category. Also some we have covered in more detail in
other episodes so for those I will keep it brief and mostly just refer you to those episodes. For those of you new to the channel, if my
speech impediment is giving you problems I encourage you to turn on the closed captions,
it takes most folks a little bit of time to adjust to it, though by the end of this video
you probably will be as again this will be a long one. With that in mind you also might want to grab
a snack and a drink. I also want to add that this topic was selected
from those submitted by the channels patrons over at Patreon and is the first of at least
three we will do this way. I only committed to doing three this way but
it was a lot of fun working with the first winner, Drew McTygue, who selected the topic
for this episode, so I am considering making this a regular thing. The goal today is not to discuss basic rocket
science or review the history of spacecraft, and our interest in existing propulsion methods
already in regular use is minimal, but rockets made spaceships possible for one key reason
that separates them from two other methods, they provide fast thrust to the ship, but
at the cost of devoting virtually all the ship’s takeoff mass to fuel. This is because rockets do not have a very
high specific impulse. Specific Impulse, often called effective exhaust
velocity, is the total change to momentum, or speed, delivered to a ship per unit of
propellant mass used. A rocket can deliver virtually all of that
in mere seconds or minutes, making it great for clawing your way up through an atmosphere
and gravity well. Unfortunately it means that around 90% of
a ship’s take off mass is rocket fuel, just to get it a couple hundred miles up into space. Alternatively your car can take you a couple
hundred miles off just part of a tank of gas, and a one ton vehicle usually only has 10-20
gallons of gas, or about 60 to 120 pounds or 30 to 60 kilograms more or less. Cars take you hundreds of miles while using
less than 10% of their mass for fuel, rockets often do not get to use even 10% of their
mass for payload. If they had a higher specific impulse, or
power to mass ratio, we could carry up way more. Double your effective exhaust velocity and
a rocket that originally weighed, say 1000 tons, 90% fuel and 10% for the rest, suddenly
becomes one that is only 70% fuel and 30% for the rest. If you quadrupled that exhaust velocity your
ship that weighed a thousand tons at launch would now not be 90% fuel but less than half
fuel and more than half for the ship and its cargo. That is important for spaceships because you
always want your highest specific impulse, or effective exhaust velocity, but most alternatives
we have now that can go higher have to provide it at so slow a pace your ship could never
take off, which does not mean you could not use it once you got up into space to go further. But our ideal space ship drive would have
a very high exhaust velocity and also be able to deliver all that thrust quite quickly. We tend to use rocket science as synonymous
with very hard things, like brain surgery, “This isn’t rocket science or brain surgery”
or as one of my sergeants used to say “This isn’t rocket surgery” but of course today
we are doing rocket science, and I want to emphasize it isn’t as bad as all that. The basic equation is simple and the really
hard part is calculating all the transfer orbits and performance changes of specific
fuel and rockets, we will not be looking at those today and indeed there are lots of nice
online calculators you can use to do the grunt work for you. So that was about the only math I plan to
bring up and you do not need to have followed it to follow the basic principle. Some of the systems we will be looking at
today provide way higher exhaust velocities but take longer to do it, others provide higher
velocities and just as fast as a chemical rocket. Now I have been asked a lot to cover the EM
drive or EmDrive many time recently so I will get to that at the end so I can give it a
little more time but I want warn people in advance that I am not going to be pronouncing
it a working or non-working system, I am just going to be filling in some explanation of
the terms and concepts involved so folks know what all this Q-cavity this and reactionless
drive that stuff is talking about. This is a broad survey of mechanisms for space
propulsion, some of which we have already covered in more detail in other episodes,
not a focused in look at all of them let alone a declaration of which is best or impossible. It is also worth mentioning that a spaceship
does not have to have a single drive, it might employ multiple types, in particular it might
use different methods to take off or land. We have discussed launch assist options like
Space Elevators, Orbital Rings, Sky Hooks, Mass Driver, Launch Loops, and Space Fountains
way back at the beginning of the megastructures series. We have not discussed landing and braking
mechanisms much so I will give a quick overview of those in a minute. If you want to know more about those launch
assist mechanisms you can go back and check out those episodes but in summary form, rockets
use a lot of fuel, and they use almost all of it getting out of our atmosphere. Getting a team of astronauts to Mars and back
home to us uses a lot of fuel and most of that gets used up in the first few minutes
getting all that into orbit. Fuel is also expensive, so anything that lets
us get things into orbit with less fuel and energy, or let’s use do the same for ships
leaving anywhere, is obviously quite handy. Of course once you get to your destination
you have to slow down too. A problem not helped by both how fast you
are going while making the journey and that as you approach the target, if it is massive,
you will start picking up speed from its gravity. Good timing can arrange to help reduce your
relative speed but you will always arrive with an awful lot of it. For Earth that is not too big a deal. Earth has a lot of gravity but it also has
a lot of atmosphere, so we can brake our speed off the air, unsurprisingly called aerobraking. What is a big problem for leaving Earth, getting
through all that air, is quite handy for getting back down to Earth. If you have a lot of speed, or the place has
a thin atmosphere, you can make multiple wide elliptical orbits, passing through the upper
atmosphere repeatedly, until you slow enough. Even on places without much air this sort
of trick can work, as can more conventional concept like parachutes or hybrids of them
like Ballute, a mix of a balloon and parachute. Of course you can also use balloons like airbags,
as we did when Pathfinder landed on Mars. Trying to slow down after interstellar voyages
at relativistic speeds can also be done using equivalents of aerobraking, in theory you
can loop around a solar system using the dust in space and solar wind to slow down. Space is not a vacuum, even in the intergalactic
void, but solar systems are much less a vacuum the interstellar space which is in turn less
than intergalactic space. It’s not much but it would help you slow
down somewhat without using as much fuel. And of course you need to slow down before
reaching your destination or you will smash into it. Though lithobraking, ramming into something
at high speed to stop, is also a method of landing if your ship is sturdy enough. Generally to save fuel and mass you can always
hit with some speed and anything that saves fuel and mass is worth doing, assuming you
do not overdo it and turn yourself into a pancake. Saving on board fuel takes us onto our next
subject which is reactionless and quasi-reactionless drive. Now you will often hear folks say a reactionless
drive is impossible but this is an oversimplification and an incorrect one unless you are careful
with your definition. As mentioned, rockets work by spitting matter
out in one direction and shoving the ship in the other, conserving momentum in the process. Many of the other systems we will look at
work the same way, and many others are doing it by hiding the matter that is going in the
opposite direction. For instance when I brake using the air during
re-entry, momentum is all being conserved but we do not notice it since all that air
goes flying away and eventually settles in as heat, with the entire planet being shoved
just a little bit. If you jump up in the air the planet actually
does go the other direction, it is just that the planet out masses you by around a 100
billion trillion, so even though you added just as much momentum to it when you jumped
up as it did to you, you move up a couple feet and it in turn moves distances that would
make an atom look large. You also do not have to lose your reaction
mass in all cases, same as you don’t when jumping in the air. If I am standing on ice and bounce a basketball
off a wall and catch it, I will be shoved the other way by tossing it then shoved again
when it bounces back and I catch it. You can use tricks like this as a launch assist
mechanism when you are near something to push things off of, and that would include laser
beams. Light has momentum and kinetic energy, indeed
that is essentially all it has. So bouncing stuff back and forth, be it basketballs
or photons, is an example of a system essentially without propellants, or at least a propellant
you can reuse, but you can only get so many bounces before it is not practical anymore
and it still costs energy. But we also have the notion of propellants
that just are not internal. I mentioned earlier that one of the problems
with rockets is that you need more and more fuel to get to higher speeds because you have
to accelerate not just the ship but the fuel you will be using to accelerate more with
later and the fuel you will use to slow down. That is core problem of any system with an
internal propellant. If you are pushing something with a laser
generated elsewhere for instance, you do not have to pay all that extra energy to push
on board fuel up to speed too. I will discuss this a bit more when we get
to photons rockets. Hybrids of this, where you are carrying a
propellant but the energy is coming from outside, like a ship that has solar panels it uses
to heat up propellant to plasma temperatures, lets you get a lot more thrust from the same
mass. This is the basic concept to a lot of the
new propulsion concepts we will look at and the big problem is that external sources like
this tend to mean you can get to a higher speed, which is great, but that it takes a
long time, which means it is no good for takeoff or landing. Ion drives, electrodynamic tethers, or electric
propulsion just does not give you the thrust you need to climb out of a steep gravity well
like a planet particularly when you need to claw your way through several kilometers of
air. This is the exact opposite of various nuclear
powered drives which can often give you all the thrust you need you just do not want to
use them in your own atmosphere. We spent a lot of time in the Interstellar
Colonization video talking about Project Orion and Daedelus, which basically operate by propelling
a ship by blowing up nukes behind it. That’s great in deep space but not for taking
off from Earth. That is not the only nuclear option though. First you can just use it to power the electrical
propulsion drives we will get to momentarily, but you can also use what is called a Nuclear
Thermal Rocket, backwards of a Thermonuclear Bomb. These come in a lot of variations and are
devices we have actually built and tested, and essentially you have a fission reactor
that you are cooling with some substance, usually liquid hydrogen, then venting the
hot hydrogen out the back. Thermal Rockets are themselves, nuclear or
not, are a fairly classic type of propulsion. You externally heat some gas rather than combusting
it, or in the case of a cold gas thruster are just letting something warm up and shift
from being a solid or liquid into a gas, no different from putting dry ice in a bottle. In a nuclear thermal rocket you are just letting
fission do the heating. They are decently more efficient than chemical
rockets but usually seen as not enough to justify the additional hazards and risks. That is debatable but Nuclear has bad Public
Relations issues and a Nuclear thermal rockets are not the safest device in the world. Same issue for Nuclear Electric propulsion,
and that is just where nuclear is the power source. Electric propulsion is neither new as a concept
or a technology. The option was kicked around by Robert Goddard
over a century ago. They tend to offer a nice slow thrust that
is good for stationkeeping and a lot of Russian satellites use this, and it is the basis for
concepts like the ion drive. One alternative before we get to ion drives
though is electrodynamic tethering. Way back in the Skyhooks episode I mentioned
this in comments, annotations, and FAQ as a way to re-generate momentum and altitude
on skyhooks but I skipped including it in the episode because I was trying for shorter
episodes then and it still holds the record for shortest video on the channel. It is pretty novel concept though. Objects with powerful magnetic fields, like
our planet, can be pushed off of, and while this is not a good approach for take off vehicles
it works just fine for things in orbit where they just need a little thrust here and there
for station keeping. Lots of thrust is good but often we just want
small amounts that use little or no propellant. Which brings us to ion thrusters. These actually come in a lot of types but
the two most well-known are HET, the Hall Effect Thruster, and VASIMR, the Variable
Specific Impulse Magnetoplasma Rocket, and we will focus on those two. But in a nutshell you are taking power, whether
it is obtained from solar or nuclear power sources, and using that to speed up ions and
shoot them out as your propellant. These are almost always very slow systems
in terms of their acceleration so you would use them on things already in orbit, not to
get up in orbit. They get up to a higher speed than a chemical
rocket but take way longer to do it. Let us start with the Hall Effect Thruster. The Hall Effect was discovered by Edwin Hall
of John Hopkins University way back in 1879 before we even knew what an electron was,
so it is old tech and designs for using it for spacecraft propulsion go back to the early
days of the Space race, but the designs were so inefficient it mostly got shelved. Now in a nutshell a Hall Effect Thruster uses
a magnetic field to accelerate plasma up to much higher exhaust velocities than chemical
rockets produces. It just does this as a thin trickle for days
or months instead of seconds or minutes like a rocket thruster. No good for launch but great for interplanetary
work. The preferred fuel is xenon, which is fairly
abundant on Mars, and which we usually get on Earth, or Mars, by distilling it out of
the atmosphere. Xenon is a good fuel because it has a high
atomic weight, about 130 times hydrogen’s, and a low ionizing potential, meaning it is
easy to strip an electron off so it will have a charge and respond to the electric field. There’s other things you can use but Xenon
has numerous advantages. The ionization is achieved by slamming electrons
off the Xenon so it knocks free an electron. VASIMR, the Variable Specific Impulse Magnetoplasma
Rocket, uses radio waves to ionize its propellant and to heat it too. Proposed by Franklin Chang Díaz is 1977,
this system does not use an anode which is good because anodes tend to corrode quickly
during use, a problem with many similar types of ion thrusters. It heats the propellant by radio waves, usually
Xenon again though most testing is done with Argon because it is cheaper. In a nutshell VASIMR works off concepts developed
for nuclear fusion and it heats its plasma to around a million kelvin, and it can launch
those particles at speeds of up to 50 km/s, faster than other ion thrust systems. Unfortunately it also builds up a lot of heat. You can also vary the specific impulse it
gives off which is handy. VASIMR is a very attractive system but is
not without its problems, and Robert Zubrin of the Mars Society has been strongly critical
of the system on several points, and one is power consumption. With both systems, or any of the other variants
essentially running on electricity, the question is always where you get your power supply. Which mostly comes down to how do you squeeze
the most energy out of the least mass. This usually excludes chemical fuels because
we could just set them on fire like a classic rocket, and also batteries since we have yet
to develop one that can push out as much energy per unit mass as chemical fuels. This leaves us solar power or nuclear power. Ideally a nice compact fusion reactor would
be great, and we have talked about fusion a lot in previous episodes, but we do not
have that yet. So the question is, what is better, solar
or nuclear? The answer to this is not as obvious as it
might sound like. In space the sun is always shining, there
is no night or clouds. Nuclear reactors produce huge amounts of power
from tiny amounts of fuel, around a million times what chemical fuels release, but they
tend to be massive when you include all the equipment and shielding. For a ground based reactor we do not care
about mass, so they are quite massive, but you could possibly get reactors potentially
generating around a kilowatt per kilogram of reactor, maybe more. In practice, as Zubrin pointed out, the largest
reactor ever put in space only produced about 10 watts per kilogram. Solar power on the other hand, in our general
region of the sun, can do a few hundred watts per kilogram with the newest systems. Of course they are also more exposed to damage
in space from micro-meteors since they are rather large and fragile, while a fission
reactor is mostly shielding already. Both of these technologies have tons of rooms
for improvement and it will be interesting to see who wins the race on power to mass
ratio. If and when fusion gets made practical it
would probably replace both, but we could easily see both win, after all solar gets
rather ineffective the deeper you go out in space away from the sun, so you might see
fission powered ion drives out there and solar nearer in. Ion Drives are very promising technology though
especially as we improve our power to mass ratio of both solar and nuclear systems. Now before we get to the EM Drive, I wanted
to cover some other hypothetical high-tech drive systems. Quite a few of these we have talked about
before in greater depth, for instance we did a whole video on the Alcubierre Warp Drive
in the FTL, Faster Than Light, series. Similarly we did a video on using artificial
black holes to power starships. So I will just refer you to those if you are
interested. In the episode on black hole powered starships
I mentioned that they give similar performance to antimatter but are less prone to explode. Antimatter is often regarded as the ultimate
rocket fuel, though of course it is actually a bipropellant fuel, matter and antimatter. Antimatter, when combined with normal matter,
turns both of them into raw energy, and you could source your normal matter from the containment
system for the antimatter or by sucking in random space gas. As fuels go, when you have to carry your fuel
with you, nothing beats antimatter. The issues with antimatter are two-fold, production
and containment. It currently takes huge amounts of energy
to produce antimatter, orders of magnitude more than it releases, and storing it is a
tricky proposition usually assumed to involve keeping it in a magnetic bottle. Obviously you cannot keep it in a normal bottle
or it would explode when it touched the matter in the bottle. If you had a way to produce antimatter for
similar amounts of energy to what it released, and if you could safely store it, then this
is the ultimate rocket fuel and allows speeds genuinely close to the speed of light. Other than production and containment it is
the same as any other rocket fuel too, though it is arguably a photon rocket since it is
releasing its energy as photons. A photon rocket, sometimes jokingly called a flashlight drive, is where you are just
emitting photons to push you away. If you drifted away from your spaceship you
could use your flashlight to push you back toward it, same as you could vent some air
from your tanks to push you back too. The problem is it take a lot of energy to
do this and a battery does not have much. Batteries do not store as many joules of energy
in them as an equal weight of gasoline for instance or other rocket fuels. The other problem is the produce virtually
no thrust at all. A flashlight, say a 30 watt flashlight, and
one that also radiates all that light in the same direction, produces a thrust of its power
divided by the speed of light. Conveniently that would be 30 Watts divided
by 300 Million meters per second, or one ten ten millionth of newton. 10^-7 newtons or 100 nano newtons or .1 micronewtons. Now if you and your spacesuit have a combined
mass of 100 kilograms, f = ma, force = mass times acceleration, or acceleration equals
force divided by mass. 10^-7 divided by 100
equals 10^-9 m/s² or a nano-meter per second second. Not very fast. If I had been drifting
away at a meter per second it would take me a billion seconds, or a few decades to bring
myself to a relative stop, all the while I’ve been drifting further away. Obviously my battery
and oxygen ran out way before that. But there are two tricks of note for this.
First, I don’t need any fuel on board, I can just have solar panels drinking in sunlight.
Let say I had nice thin efficient solar panel of a couple square meters giving me 3000 watts
of power out of my bigger flashlight, and the whole thing only weighed a kilogram. One
hundred times the power as our last example pushing one hundredth of the mass, that gives
me 10,000 times the acceleration. Now that is not as bad. After a few decades you are
not going one meter per second but 10 kilometers per second.
Some of you might be saying now, “Hey, why even bother with solar panels and a flashlight,
why not just use a mirror? You could make that even thinner and not even need the flashlight?”
and that is true, except it’s even better since when light hits and reflects off something
you get double the effect. So a very thin mirror being hit by sunlight has a much higher
acceleration than the flashlight since you can use all that mass as just simple thin
mirrors, getting more light, and getting double the push from it. You can also bounce that
light at an angle to produce thrust in different directions.
But that’s not the end of it, because we could bounce more than once. Sort of like
our earlier example where we bounced a basketball off the wall then caught it and threw it again,
just with light instead. If I have a nice reflective surface, and a laser with a reflective
surface around it to, I can shine that laser on the first mirror which bounces it back
to the mirror around the laser which bounces it back to the first mirror and so on.
A spaceship and some space station bouncing a laser back and forth between them could
get that ship up to a pretty good speed if you can keep that beam contained, which of
course gets harder and harder the more times it bounces and the further apart they get
from scattering and diffusion, plus each bounce takes longer.
But such a thing as a launch assist system has some possibilities, and we explored laser
and light propulsion in the Interstellar Colonization and Nicoll-Dyson Beam episodes in more detail.
I discussed there the notion of a laser highway between solar systems where you have many
stations along the way using fusion to power themselves and bouncing laser off ships as
they passed by, possibly back and forth a few times if you can aim and focus the reflected
laser well enough. Now if we have the ability to alter either
what the physical constants are, like gravity, or make them not work symmetrically, say gravity
that emitted like a cone not a sphere, other options become available. Imagine for the
moment that a large and massive object did not emit gravity in all direction but just
in one direction. Something like a gravity flashlight or laser. We have no idea how to
do such things yet and maybe never will, but it may be possible in the future.
Certain hypothetical materials, like negative matter, a type of exotic matter we have discussed
before in the Faster Than Light Series, could let us achieve such effects or equivalent
ones. These sort of ideas are used for concepts like the Diametric Drive or Pitch or Bias
Drives. These are totally hypothetical craft relying on science we do not have yet but
I feel they deserve a mention. Lastly we have the idea of picking up fuel
in route, gathering up either space gas or dark matter to use as fuel. This is the basic
idea of the Bussard Ramjet, which we discussed in the Interstellar Colonization episode,
and for how to refuel a black hole powering a spaceship, which we discussed in Black Hole
Spaceships. Using Dark Matter as a potential fuel is something we looked at in the Dark
Matter episode and has to be classified as totally hypothetical since we still do not
know the properties of Dark Matter or any way to manipulate it, but we discussed it
more in that episode if you are curious. Okay, on to the EM Drive at last. I saved
this one till the end so we could spend a bit more time on it since it is a big news
item with an awful lot of confusing and often contradictory reporting. It hit the news again
recently when someone said that NASA would be releasing a peer-reviewed paper on it.
At the time of this episode that paper has not been confirmed to be released, let alone
released, but the assumption it was being released is what rekindled interest.
Now the EM drive, or just EmDrive, is often called a radio frequency, or RF, resonant
cavity thruster. Its sibling device, the Cannae Drive or Q-Drive works off the same concept.
This is a type of electromagnetic thruster in which electromagnetic radiation, photons,
are confined to a microwave cavity, and provides thrust to the cavity in a particular direction
as the radiation reflects within the cavity. Now what is a Microwave cavity? Well basically
a box with mirrors inside that reflect that frequency of radiation, in this case microwaves.
You probably have one in your kitchen, a microwave oven is a simple microwave cavity.
There are two special notes about this though. First, a terminology one. Whenever we discuss
cavities you will hear people refer to its Q-Factor, and irritatingly most do not bother
explaining what this mundane thing is so many folks assume it is some weird physics thingy.
A Q-Factor is just short for Quality Factor, and it basically measures how good the cavity
is at keeping the waves bouncing around inside it rather than dissipating as heat.
It isn’t quite as simple as just saying that a perfectly reflective mirror would have
infinite Q, but for basic conceptual purposes it amounts to how good a reflector the cavity
is. That’s important since as I mentioned back when we were discussing reflecting lasers
repeatedly, every time you can get it to bounce you get more thrust imparted. So higher Q
is good, it is also very hard to get from a practical standpoint when you are trying
to dump tons of power into a cavity. Something with really high Q would make an excellent
battery for instance. You could just keep dumping more and more microwaves in and lose
very little of it to heat dissipation. Now the other difference is that these kind
of cavities are usually cylinders, for the EmDrive though it is a tapered cylinder, wider
on one side than the other, and the basic notion is that the wider end will get more
force exerted on it, generating a net thrust. Now in principle this device produces thrust,
but it does not seem to have any sort of propellant, which would make it violate conservation of
momentum. Remember even our laser or solar sail drives use photons as their propellant.
The EM drive is not supposed to be emitting any, just bouncing them around inside. So
this drive got dismissed as total nonsense by most until one got built by NASA and seemed
to produce some thrust. Now it wasn’t much thrust, so little it
might even be noise, and actually less than you would get by shining a flashlight using
the same power. Indeed there is a concern that it is just asymmetrically emitting radiation,
again like a flashlight, since it is hardly a nice symmetric sphere.
At this point many would say “Okay, so even if it does produce thrust, it is less than
a flashlight or laser, so what good is it?”. Fair point, BUT, it would still be interesting
until we knew how it was producing any thrust and the notion is that this device does not
necessarily scale its thrust linear to its power. By which I mean, if we double the power
to it we would expect to get more than double the thrust.
So you would next say, “Why have we not just done that then, this experiment was only
using around a kilowatt of power, why not throw in 10 kilowatts, or a 100, and see what
happens?” The simple answer is that high Q-factor cavities
than can also handle tons of power without melting are very, very hard to make. Which
obviously also means very expensive. Now a few more notes. First, the EmDrive is
not the quite the same as the Cannae Drive, but the two get used synonymously a lot so
you should probably treat them that way when reading about either one, because folks use
them interchangeably. Second, it is in no way a warp drive. That was just bad reporting.
Eagleworks is NASA’s department for looking at novel and sometimes fringe propulsion systems,
headed up by Sonny White, so they are always looking at various strange systems and Sonny
White also examined the Alcubierre Warp Drive around then and lots of bad reporting jumbled
them together. If you see an article talking about EmDrive and warp drive, you can pretty
much just skip it. Either the author is using a clickbait title or they didn’t do their
research, so either way it probably is not worth your time.
I get asked for my opinion on the EmDrive a lot and personally I do not expect it to
actually work. Or if it does then the thrust will turn out to be something quirky where
it is being provided by photons leaving the drive but interfering with each other so we
have problems detecting them or bouncing off Quantum Vacuum Plasma, or a Q-Thruster, where
in this case the Q is for Quantum not Quality. Sonny White tossed that notion out there as
an option but the idea of Virtual Plasma, as a type of Virtual particles which we have
discussed before, is not too popular with theoretical physicist at the moment.
Fundamentally we are at the wait and see stage, nobody has gone and proved the EmDrive works,
that is just sensationalist journalism, but nobody has successfully killed it yet either.
I would not suggest holding your breath it will work but I would say it is still on the
table for now. That is true of a lot of the systems we have
discussed today, and hopefully at least one of those will turn out to be both possible
and practical so we can replace chemical rockets. I think we are justified in being optimistic
and putting some faith in human ingenuity, but we also always want to keep our exuberance
dampened and scientific. As I’ve said before, there is a big difference
between proper skepticism and naysaying, as well as just trusting to science as a magic
wand. It can often seem like propulsion technology is proceeding at a snail’s pace and sensationalist
journalism constantly reporting every new theory like it was proven fact can make a
person pretty jaded, but we are making good and constant progress.
For my part I am very optimistic about that progress, if properly skeptical too, and while
we could only cover the basics here you should have a good place to continue your own research
into these. I’ll be placing several links in the episode’s description to good places
like Project Rho to either follow up on these or get more specific data, but this is where
we end for today. Some quick announcements. First I wanted to
thank Drew McTygue, he was the first winner of our Patreon subject selection and chose
today’s topic. We spent a lot of time on the phone discussing what to cover and what
to bypass for time constraints and we worked on the script together which was a lot of
fun, and I’m looking forward to future collaborations with folks on such topics.
Next, we have our second winner for a topic. That topic is going to be Star Lifting, and
that winner was Bill Mains, so congratulations to Bill and that was an excellent topic pick
and one I have been considering covering for a while.
Star lifting is term given to various hypothetical processes for lifting matter of stars, as
the name implies. This has quite a few possibilities and uses, the two most obvious being that
99% of the matter in our solar system is in our star, so it is create source for matter,
and secondly, that you can use this process to extend the lifetime of a star. We will
look at that and some other awesome things you can do with star lifting when that episode
comes out on October 6th, 2016. That will be after we take a look at Dark
Energy next week, and that will be followed by a look at Cryptocurrency and BlockChain,
then get followed by a look at the Kardashev Scale on the 20th, that topic was selected
by a poll over on our new Facebook group, Science & Futurism with Isaac Arthur which
Drew is now a moderator for too. I want to thank everyone who came over and joined that
last week and everyone who volunteered to moderate and administrate it, and we will
be selecting a lot of our topics by polls conducted over there and topics selected there
from now on, as it is a better place to discuss the ideas.
This week though, while I’d encourage you to join the Facebook group, we are also launching
the identically titled Sub-Reddit Science & Futurism with Isaac Arthur so I will be
over there after this episode comes out answering questions and I hope you will join us on both.
We will have one more Patreon Topic selection in a few more weeks so it is not too late
to join and submit topic suggestions over there, and indeed I am considering doing it
more in the future. You can opt to submit anonymously if you do not want to me saying
who you were during the videos but I prefer to be able to say who’s idea it was and
to be able to sit down on the phone and discuss the idea with the person who submitted it,
that won’t affect whether or not the topic gets selected but do let me know if you do
not want your name used, or want a pen name used, or are not comfortably chatting about
the idea on the phone. That third episode will probably come out in Early November.
Again, next week we will look at Dark Energy, and clear up some of the confusion about this
mysterious force that seems to be shoving the Universe apart. Until then you can try
out some of the other episodes on the channel or at the website, IsaacArthur.net, or follow
me on facebook or twitter or reddit, and if you enjoyed this episode, make sure to like
it and share it with others. Thanks for joining me today and until next
time, have a great day!
Obligatory link: the Atomic Rockets Engine List, a similarly thorough listing of all spacecraft drives that work within known physics.
Speaking of which, I'm really surprised I haven't seen either /u/IsaacArthur or /u/nyrath reference the other's work, especially since they're both working towards the same goal - summarizing lots of different scientific ideas in the context of space sci-fi.
Great episode,
Love the series so far, although a part of me kind of wants to see at some point extensions onto some of the covered topics from summary level detail to full on potential action plans / roadmaps to implement some of this. but maybe that just a bit to much to ask :)
Great video, I'm really excited watching this group evolve outside of YouTube into more social media platforms.
Assuming we will be able to use fusion as a method of propulsion in sometime in the future and also assuming we could reach speeds close to the speed of light - as Isaac mentioned in the video - I wonder how the human body will react to such velocities and accelerations.
I mean, obviously if we were to accelerate very slowly the body would probably accomodate but considering the huge distances of interstellar travel we surely want to avoid taking even longer than it will already take.
What - if anything - do you guys think will happen to the human body while accelerating and decellerating from such speeds noone has ever even dreamt of experiencing?
Lovely episode, enjoyed it thoroughly.
One nitpick, though, regarding anti-matter drives - assuming the anti-matter will be made of anti-atoms and -molecules, almost all the mass will be in baryons (anti-protons and -neutrons), which prefer to annihilate to mesons (bound pairs of a quark and an anti-quark), and not to photons.
Some charged mesons are relatively long lived and are easily manipulated using magnetic fields, and should yield decent drive efficiency. The rest of the mess will need an ablative dish to make any use of, or simply shielded against to prevent it from irradiating the ship too much and breaking the containment.
What about fission/fusion "catalyzed" by antimatter?(admittedly, i dont know much about that at all) But like many these topics, it seems impossible to catch them all. Well done, imo.
Expect the EMdrive doesn't work. When i read one of the original articles, i kindah just thought they're abusing approximations.
The Maxwell equations(+special relativity, not classical mechanics) are guaranteed to just conserve momentum. Could wonder if it is somehow such that gravity and electrodynamics are interacting. However if this thingy can do that, you'd expect experiments to already have-been done. This whole "new fundamental physics" thing is kindah ignored. Sow.. why isn't this is a physics experiment like the LHC..
I am not sure if there are experimentally-excluded graphs limiting how much EM can affect gravity before "we'd have seen it already". Those graphs are often related to alternate theories, for instance the Higgs(before we found it) had mass ranges where we'd have seen it already if it existed. Supersymmetry has(/had?) the same for multiple masses. Maybe these graphs aren't being whipped out because of lacking "counter models". (or they just like the interest in science, even if wrong)
(Note: The parameterization (x,y,z)=(r⋅(z'-z0)⋅cos(φ), r⋅(z'-z0)⋅sin(φ), z'), zero at an r, and a z on the ends, can probably do exact solutions "assuming" perfect shape&wall conductivity Possibly for an GR+EM approximation too)
Some of the concepts for powering ion drives, such as fusion, are not viable in the near term. Even a megawatt level fission reactor is not a near term solution. We have a good working knowledge of fission so it's doable but will take many years of r&d to get something dependable working for space. NASA & Russia developed some small experimental reactors for space in the good old days so it's not virgin ground.
The only near term solution to power ion drives is solar and possibly augmented with Pu238 fueled RTGs.
I know you generally look at future tech and the layman concepts behind the possibilities, but i am interested in some of the processes that go into developing and researching these propulsion methods, besides the general concept being far out to some.