Interstellar travel is definitely something any deep space exploration fan has thought of, and to be fair, the idea of exploring another part of our universe can excite anyone! Today I'm going to talk about what exactly this is, and how we would achieve it. (1/20) #scicomm 
Before you read, definitely check out my blog post where I go into more detail and talk about some additional concepts: joalda.space/post/interstel… (2/20)
Interstellar travel is a way of exploring our universe to learn more about it. It requires spacecraft to travel near the speed of light, 300 million kilometers, in order to reduce travel time. We need a lot of energy in order for us to try to reach these high velocities. (3/20)
This energy needs to come from either stored fuel or materials actually within outer space itself. There are many hypothetical propulsion systems that could get us to the speeds and places we need. Before I get into them, let's first talk about space units. (4/20)
First, the astronomical unit (AU). 1 AU is equal to the average distance between Earth and Sun, 150 million kilometers. For reference, Mars is about 0.52 AU from Earth. Next is light-time. A light-year is the distance light has traveled in a year, and it is equal to... (5/20)
...9.5 trillion kilometers. For scale, Mars is around 12 light-minutes from Earth. These two, along with parsecs, is usually how distances in space are measured. Now let's talk about what our target is, aka where in interstellar space are we'd most likely be traveling to. (6/20)
The best candidate is the Alpha Centauri planetary system. It is the closest to our own solar system, being around 4.3 light-years away. It is a three-star system, and it was recently discovered that one of its stars, Proxima Centauri, has an Earth-like exoplanet in... (7/20)
...its habitable zone, named Proxima b. We would want to go explore this planet and see if it harbors any life, and possibly also have it be a new home for humanity itself.
We have our destination, let's now discuss the different propulsion systems that will get us there. (8/20)
We have our destination, let's now discuss the different propulsion systems that will get us there. (8/20)
First traditional propulsion, aka the stuff we use in present-day aeronautics. The only confirmed spacecraft that have reached interstellar space are the Voyager probes. Currently, they are both over 100 AU from Earth but don't forget that these both launched over... (9/20)
...40 years ago, and that Proxima Centauri is 260,000 AU away. So yeah, this will not cut it. But, using current technology helps us think of an interesting thought experiment that leads to the creation of what scientists have called the wait calculation. Let's discuss! (10/20)
Say you send out something called a Generation Ship out to Proxima b using current technology with around 100 people. These people would continue to repopulate until they reach the planet, probably around 20,000 years later. The issue is that around 1,000 years in... (11/20)
...humanity will have most likely found a propulsion system that goes much faster. They then will reach Proxima b like 15,000 years in advance and will have developed and populated the planet, meaning the Generation Ship's journey was a waste of time. This leads to the... (12/20)
...question of when is the right time to send an interstellar mission, and how can we make sure humanity won't find a faster method? This has led researchers to believe that we need a propulsion system that travels near the speed of light to prevent this from happening. (13/20)
Let's talk about a couple of these propulsion systems (all of them will be mentioned in my blog if you're interested). First up, electric propulsion. An ion engine, a specific version of electric propulsion, charges particles, typically Xenon, and expels them out the... (14/20)
...back of the spacecraft. It is extremely efficient but it is limited by the amount of electric energy it can supply, and also by its low thrust. If you want to learn more about this type of propulsion though, check out @astronaia's thread! (15/20)
Next, we have a method that doesn't require bringing fuel with you in the first place, a light sail. A regular light sail uses sunlight on its mirrors in order to exert pressure and basically accelerate the spacecraft. But since sunlight will not always be available,... (16/20)
...using lasers instead have been proposed, and can actually power the light sail even better, leading it to be faster. The main issue with this is that we need a way to slow down the sail once we get to Proxima b and we could possibly use a second sail to do this. (17/20)
So how close are we to seeing crewed interstellar travel in our lifetime? Not close at all, but we may see more uncrewed interstellar travel in our lifetime. There is a company called Breakthrough Initiatives that focuses on the miniaturization of different technology. (18/20)
A $10 billion mission they're developing called Breakthrough Starshot plans to use a miniature version of the light sail laser technology and send it to Proxima b at 20% light speed, ultimately taking pics to send back to Earth. So, people today are working on this tech. (19/20)
Well, that is my thread on interstellar travel, I hope you enjoyed it! It is awesome to know that this tech is being worked on today despite the fact that we won't see crewed interstellar travel in our lifetime. Look out for the asteroid/planet mining thread next week! (20/20)
