What do we really know about space? The universe is an infinite expanse of scientific wonder and mystery, but it’s crazy how many people know nothing beyond the basic naming of our solar system.
Can we really blame them though? Even the best scientists know essentially next to nothing about outer space. Here’s a link to know more about what we don’t know:
As a kid, who hasn’t dreamt of blasting off in a space ship one day? The thought of seeing the Earth and the rest of space from such a different perspective is thrilling! But have you ever really thought about how we actually approach our method of transportation to space?
Today, we’re exploring ROCKETS!
Current Space Travel
Conventional rocket engines are super bulky in terms of machinery. In order to propel themselves, the engines require a lot of hardware to control the combustion reaction. Combustion can occur in either supersonic or subsonic velocities. Supersonic means that the “vehicle” is travelling faster that the speed of sound, hence the name (super = beyond, sonic = sound). Consequently, subsonic means that the vehicle is travelling lower than the speed of sound (sub = under).
Currently, a traditional rocket engine functions by burning propellant and then pushing it out to create thrust, a subsonic method called deflagration.
There are four basic types of rockets, classified by their fuel:
- Chemical — a huge chemical reaction creates energy while shooting out propellant from the back of the rocket
- Ion Engine — the rocket uses a bunch of accelerating charged particles from an electric field
- Water — similar to chemical, but using a chemical reaction involving high pressure gas with water as the propellant
- Nuclear — using the force of a smaller type of nuclear bomb to propel you away into space!
Basically, you just need to find some sort of fuel to launch out the back of your spacecraft and use its opposite force to thrust you into space!
But what exactly is thrust?
- Thrust is the force that moves aircrafts, well, through the air
- It is developed in multiple ways, usually through “propulsion systems”, but always uses the application of Newton’s third Law of Motion (For every action, there is an equal and opposite reaction.)
Pictured below is the equation for general thrust:
Within the Earth’s atmosphere, we can think of thrust as being calculated like this:
Momentum of rocket going forward = Momentum of propellant coming out the back — resistance
However, once the rocket exits earth’s atmosphere and enters space, resistance becomes less important. So, we can simplify the “equation” to look like this:
Mass x speed of rocket of propellant coming out of the back = mass x speed of rocket moving in the opposite
Why should we change current space travel methods?
Although space travel is super educational and honestly, an amazing investment, it’s really expensive. The cost of getting “stuff” into space is based on its weight and unfortunately, fuel is extremely heavy and makes up the majority of the rocket’s total mass. We tend to stick to liquid chemical fuel which, in addition to its massive weight, is quite inefficient when it comes to accelerating the rocket.
An example of this is the Saturn V, the rocket that launched Neil Armstrong and Buzz Aldrin into space, on the mission which resulted in the first human footsteps on the moon. The Saturn V weighed 6.2 MILLION pounds (crazy, right?). But what’s even crazier is the fact that 4.6 million of those pounds belonged only to fuel. That’s 75% of the rocket!
To put things into a little more perspective, here’s a picture from sciencealert.com:
In order to even blast off and get into space, we need an insane amount of fuel. We also need a lot of fuel to carry the actual required cargo (people, fireworks, equipment for the mission) beyond Earth’s atmosphere.
How can we improve space travel?
Simply put, current rocket engines aren’t fuel-efficient.
The lightest rocket in the world, Japan’s SS-520–5, weighed 2.6 metric tons. Out of that, nearly 2.0 metric tons were solely propellants.
In past years, these engines were our only options, but scientists are currently working on a new engine called Rotating Detonation Engines — and they might be the future of space travel itself!
But that’s a pretty big “might”.
According to a study conducted by the University of Washington earlier this year, the Rotating Detonation Engine (or RDE) guarantees to be more fuel-efficient, light-weight and easier to construct. Its structure consists of concentric cylinders, where propellant would flow through the gaps. Once ignited, the rapid release of heat would form a shock wave; a pulse of gas travelling faster than the speed of sound.
“This combustion process is literally a detonation — an explosion — but behind this initial start-up phase, we see a number of stable combustion pulses form that continue to consume available propellant. This produces high pressure and temperature that drives exhaust out the back of the engine at high speeds, which can generate thrust.”
James Koch, Lead Author, UW
Think of it like if a bomb had a heartbeat. Propellant would continually fly out of the gaps in the engine at supersonic speeds, thrusting the rocket forward. In a rotating detonation engine, the shock wave would naturally do everything without needing any help from engine parts.
Cool, right?
Will these engines be put to use soon?
The problem is, the engine is just too unpredictable to be put to use right now and there are multiple reasons for this. As we explained before, the engine detonates and releases shock waves, which propel the rocket forward. However, once begun, the explosions are violent and erratic. Obviously, in an aircraft designed to leave the planet, unpredictability is exactly what we don’t need.
Any other ideas?
Ion thrusters and other electric propulsion techniques are becoming more popular due to their higher acceleration and fuel efficiency when compared to their chemical fuel counterparts.
They are also being used as a main propulsion source for deep-space , for attitude control (controlling the positioning of the spacecraft/satellites), and many more applications.
In the vacuum of space, the atmospheric drag force is negligible so a higher amount of thrust is not required, even when travelling at such high speeds. In fact, a lower amount of thrust or acceleration over a longer period of time can be way more beneficial to sustain longer, deep-space missions. Enter, plasma propellant systems! Plasma propulsion is composed of electrons and ions which were converted from the propellant (in this case, usually xenon!). Although, currently researchers are testing out a new propellant of krypton! This is very commonly seen in Hall effect thrusters at the moment, with a picture shown below.
How exactly does Electric Propulsion work?
Because ions are electrically charged, electric fields can be used to accelerate the particles and make them move really, really fast! They would reach speeds of about 15–30 km/s!
Most ion thruster engines use xenon as its main propellant, however a big downside is that it’s a pretty expensive endeavour! By switching to krypton, another noble gas and a significantly less expensive propellant (up to 10x less than xenon!), we can also reap the benefits of a lighter fuel source.
Additionally, krypton requires less acceleration power than xenon to reach the same velocity! Although it takes more energy to produce these ions, it can be a very useful fuel source option for future missions, such as reaching Mars!
Cool! But what else could there be?
The EmDrive engine is another new, fantastic idea to tackle and increase rocket fuel efficiency. It’s a RF (radio frequency) resonant cavity thruster (long name, I know!), originally created by Roger Shawyer. He first proposed his idea, in regards to space research back in 2001, after founding Satellite Propulsion Research (SPR) Ltd.
It’s designed as a cone-shaped metal cavity which only requires input energy to create thrust, without emitting any exhaust! The EmDrive uses really high frequency electromagnetic waves for power without the use of an external propellant.
This may seem completely strange, as that doesn’t seem to follow the laws of physics! Don’t worry, momentum is still conserved, and the open system of the EmDrive still follows Einstein’s theory of Special Relativity. Also, just because there is no propellant doesn’t mean the EmDrive is a reaction-less engine.
NASA researchers are still heavily in the testing phase for this technology and are hoping to find the answers to this controversial invention.
Key Takeaways
The rockets we use right now are super bulky and use crazy amounts of fuel
- There are 4 basic types of rockets in use currently: Chemical, Ion Engine, Water and Nuclear
2. Thrust is the force that moves rockets through the air
- It is always developed using Newton’s Third Law, “Every action has its equal and opposite reaction”
3. Fuel is insanely heavy and accounts for the majority of a rocket’s weight
- The Apollo 11 Rocket Saturn V was 6.2 million pounds, and fuel made up 75% of that weight!
4. Scientists are working on a new rocket engine called a Rotating Detonation Engine
- It promises to be more lightweight, easy to construct and most importantly, fuel-efficient
- It propels the rocket forward with continual supersonic shock waves
5. But, they’re probably not going to be put to use anytime soon
- Believe it or not, explosions faster than the speed of sound are a little hard to control
- Once started, the explosions are unpredictable and violent
6. Other rocket technologies are also being researched and developed
- Ion thrusters and EmDrive engines are being looked into as better alternatives to current rocket tech
And that’s basically it for this article, but we have barely scratched the surface of Space Tech!
If you want to learn more about Rockets and Space Tech, here are some useful resources:
https://www.sciencedaily.com/releases/2020/02/200218143706.htm
https://www.sciencedaily.com/releases/2011/10/111006084023.htm
https://www.popularmechanics.com/science/a31000649/rotating-detonation-engine/
https://www.wired.com/2015/10/whatd-make-better-rocket-nuclear-ion-engines/
Stay curious! And we’ll see you next time!
Uma Darbha & Sanjana Adiga
