WPenner's Blog

Space is big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the drug store, but that's just peanuts to space. — Douglas Adams

Because space, as Douglas Adams so cleverly put it, is enormous, propulsion is crucial. To get anywhere interesting requires either a very long time or a really high speed.

Getting out of earth's gravity well and into orbit requires incredible amounts of force and currently is only workable with chemical propulsion systems. Chemical systems are the oldest and most studied, with great overviews and deep dives by people like Tim Dodd.

In Orbit! Now What?

Once in orbit and no longer fighting gravity or the friction of the atmosphere, more energy efficient propulsion systems with less thrust become usable. An ion propulsion system uses electricity to create xenon ions (positively charged), which are accelerated and emitted from the back of a spacecraft to generate forward movement. The speed the ions reach is determined by the amount of voltage applied, with measured exit speeds of 144,800 km/h.¹

Ion propulsion produces very little thrust, but can do so for a very long time, which escalates the spacecraft to high velocities. The Dawn spacecraft (2007-2018), sent to the asteroid belt, travelled 4 billion miles over 8 years using an ion propulsion system that fired for a record 5.9 years and reached 41,360 km/h.¹

In 2010, JAXA's project Ikaros (Interplanetary Kite-craft Accelerated by Radiation of the Sun) used an ion drive powered by a solar sail. While a solar sail provides little electricity, it was enough to power the craft around the solar system for 5 years.²

Ion propulsion systems are widely used on satellites today to move around in orbit. A company like SpaceX can launch a modern satellite into roughly the right place and the ion drives pushes it into the best possible position. Small ongoing corrections are possible. So is controlled decommissioning, where a satellite is deliberately pushed into the atmosphere at an angle that assures its destruction

Where do we go from here?

The new propulsion player on the block is plasma. When I was in school I learned there are three states of matter: solid, liquid and gas. Plasma is a fourth state that comprises 99% of the visible universe. It is created by super-heating matter (solid, liquid or gas) until an ionized gas — i.e. mass of ions (positive charge) and electrons (negative charge) — forms. Stars, nebulas, auroras and lightning are all forms of plasma.³

Mergers & Acquisitions

This week, propulsion got a boost into the public's awareness when Benchmark bought AASC. The US company Benchmark Space Systems, known for its chemical propulsion systems, will pair its engines with Alameda Applied Sciences Corporation (AASC) offerings to produce a hybrid propulsion system. AASC makes plasma systems from metal, which dramatically reduces the number of parts in the engines. Benchmark's chemical engines provide more thrust, which can quickly get satellites into a "revenue generating orbit" or manoeuvre to avoid collisions. AASC's engines are perfect for high-endurance operations that don't require a lot of thrust. The combination of the two systems provides Benchmark customers with the best of both worlds. Although not much is known about AASC and its offerings, it's not the only company working on plasma propulsion.

UK's Take on Plasma

Pulsar Fusion, a UK Company, is experimenting with plasma engines, achieving 161,000 km/h with a prototype in February, 2020. The difference lies in the forces employed: nuclear compared to electromagnetic. Richard Dinan, CEO, claimed that the technology will be standard "a few decades" into the future. ⁴

Looking further into the future, the company proposes using nuclear fusion to create a drive propulsion system to push spacecraft into deep space quickly and efficiently. Powerful electromagnets would shape the reaction directly into a propulsive stream. This change would effectively scale the plasma engine to speeds of 804,600 km/h. Using the drive, a 1,000 kg craft could reach Pluto in about 4 years. Since the engine produces both thrust and electrical power, once in orbit around the planet, approximately 2 MW of power would be available for use, dramatically improving the amount of power available for exploration and reporting. The dual nature of the engine makes it attractive for deep space missions.^{5 6}