Innovation News Network takes a closer look at the pros and cons of chemical and electric propulsion, and why slow and steady wins the race.
When you think of a rocket, you probably imagine a bright flame, a thunderous roar, and a vehicle taking to the sky. It’s the most dramatic chemical propulsion and exactly what we want for launch.
But once you successfully escape Earth’s gravity and drift into the quiet of space, an entirely different kind of engine begins to make sense.
In the field of deep space exploration, new generations of spacecraft rely on sustained, efficient thrust rather than raw power. Electric propulsion, especially ion and Hall effect thrusters, can provide gentle propulsion for thousands of hours. It’s certainly slower, but over longer distances it achieves far more delta-v (the change in velocity required to reach its destination) than previous chemical rockets.
Find out why, the technology differences, and why a tiny engine with a strange name is quietly redefining the way we explore our solar system.
How a chemical rocket works
The concept of a chemical rocket is simple. The fuel and oxidizer are mixed and combusted, and the expanding gas is used to push the nozzle. Energy is obtained directly from the breaking of chemical bonds, and the release of energy is so intense that in a short period of time a huge propulsion force – several kilograms of force – is obtained. That’s exactly what is needed to leave Earth, penetrate the atmosphere, and put a payload on course for orbit or beyond.
The downside is that chemical rockets are less efficient and require more propellant. The key metric here is the specific impulse (Isp), which measures the thrust per unit of propellant. The Isp of a chemical engine is typically around 300-450 seconds. Good for short, powerful bursts, but expensive if large changes in speed are required.
Beyond a certain point, loading chemical fuels becomes impractical. Carrying 10 times more propellant would require 10 times more rockets to lift it. That quickly becomes a losing game.
Introduction of electric propulsion
Electric propulsion breaks old strategies. Instead of burning propellant, it uses electrical power (from solar panels or sometimes a nuclear reactor) to accelerate atoms (usually xenon) to very high speeds. The important thing here is the pumping speed. The faster the mass can be ejected backwards, the higher the Isp. Electrical systems can also achieve Isp values an order of magnitude higher than chemical rockets.
The two most common types are:
Ion thrusters: These use electric fields to accelerate charged atoms (ions) from the engine. ISPs of thousands of seconds can be achieved. Hall Effect Thruster: Contains electrons within a magnetic field and is used to ionize and accelerate propellant. They typically have slightly lower Isp than pure ion engines, but can provide higher thrust densities in some configurations.
Regardless of the specific technology, the theme is the same. It is high exhaust speed, low thrust.
Thrust and efficiency: fundamental trade-offs
One of the most confusing things about electric propulsion is that, despite its high efficiency, it produces very little thrust. For example, the ion engines of NASA’s Dawn mission produced a force of only about 90 millinewtons. This is approximately the same force as holding a piece of paper in your hand. Even a rocket’s main chemical engine produces millions of newtons in short bursts.
It’s not an engineering flaw, it’s in the physics and design priorities. Electric thrusters typically have limited power output. The amount of power a spacecraft can generate and feed into its engines limits the amount and speed of propellant it can accelerate. In space, slow and steady wins the race, as there is no need to fight fast explosions or atmospheric resistance.
In contrast, chemical propulsion has thrust limited by the energy density of the chemical reaction. You can get a lot of thrust in a short period of time, but the reactants run out quickly.
Why is movement slow in the vacuum of space?
In deep space, there is no air resistance or gravity. This means that even small forces can be important if they act over long periods of time. If you can keep pushing in the same direction for years, those small accelerations will add up to a very large change in speed.
This was exactly the case with the Dawn spacecraft. After launching with a conventional chemical booster, Dawn’s ion engines operated nearly continuously for thousands of days, eventually achieving a total delta-v comparable to the first launch vehicle, but using far less propellant.
Electric propulsion also comes into play when mission designers want to make significant trajectory adjustments or visit multiple targets. Dawn didn’t just fly to one asteroid, it entered orbit around two separate objects in the main asteroid belt. This kind of flexibility would have been nearly impossible in chemical systems without prohibitive fuel mass.
Chemical rockets still have their place
Electric propulsion is not a replacement for chemical rockets, at least not yet. The high thrust provided by chemical engines in short periods of time remains essential for the following applications:
Launch from the Earth’s surface Rapid orbit entry Rapid maneuvering in Earth orbit
Nothing in today’s electrical systems can match this kind of performance, as electrical systems cannot generate enough instantaneous force. Even if you run it at full power for days, you won’t be able to accelerate the spacecraft enough to function as a launch vehicle.
As a result, most spacecraft still use chemical propulsion during the early stages of a mission, switching to electrical systems for long-term course changes.
real example
Talking about principles is another thing. It’s another thing to see them in action.
Dawn used a gridded electrostatic ion engine to travel to the asteroid belt and visited both Vesta and Ceres. Although these engines were less powerful, they were incredibly efficient, allowing for cumulative delta-v comparable to the contribution of a launch vehicle.
ESA’s SMART-1 mission used Hall effect thrusters powered by solar arrays to reach the moon. Its thrust was very small, a fraction of a newton, but after several months of operation it reached an orbit around the closest thing to Earth.
Recent missions like NASA’s Psyche spacecraft also rely on electric propulsion, using Hall thrusters to propel it toward asteroids thought to be rich in metals. This reflects how electrical systems have matured to the point where they have become the primary propulsion force on major interplanetary missions.
Limitations and challenges
Electric propulsion looks great on paper, but it’s not a silver bullet. Practical challenges include:
Power source: Requires reliable power, usually from a large solar array or sometimes a nuclear power source. As you move further away from the sun, solar power decreases with distance, limiting performance. Propellant Selection: Xenon is popular because it is easy to ionize and store, but it is heavy and expensive. Researchers are exploring alternatives such as krypton and water vapor for small satellite thrusters. Thrust limitations: Because thrust is so low, electric propulsion cannot support time-critical maneuvers. Not suitable for rapid burns or atmospheric flight, best suited for gradual orbit changes.
The future: hybrids and beyond
Engineers are not satisfied with choosing one side or the other forever. Hybrid systems that allow spacecraft to switch between chemical and electrical modes depending on the mission phase are an area of active research and early development. These can combine the best of both worlds. Get a hard kick when you need it, and a long, efficient ride when you don’t.
Looking further ahead, new concepts such as high-power plasma engines and nuclear propulsion may further blur the lines and enable higher thrust without sacrificing efficiency. However, these technologies are still in their infancy or research stage.
What matters is how long you can continue.
At first glance, it seems counterintuitive that a small-thrust propulsion system could outperform a rocket engine.
However, in the vacuum of space, efficiency can outweigh explosive power over time. Electric propulsion delivers that efficiency, enabling missions that would otherwise require unsustainable amounts of fuel.
Chemical rockets continue to be useful when large-scale and rapid propulsion is required. But for missions that require long-distance journeys and lengthy adjustments, the gentle whisper of electric engines is becoming a dominant theme. What matters is not how fast you can go per second, but how far you can keep going.
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