01 · Propulsion

Moving a satellite the size of a loaf of bread.

For a decade most CubeSats had no propulsion at all — they were placed in orbit and drifted until atmospheric drag pulled them down. That has changed. Electric thrusters now fit inside a single CubeSat unit, giving operators the ability to raise orbits, dodge debris, hold formation and, increasingly, leave Earth orbit entirely.

First principles

Why electric, and why it suits small spacecraft

A thruster's efficiency is measured by specific impulse (Isp) — effectively how many seconds of thrust you get per unit of propellant weight. Chemical thrusters are powerful but thirsty, with Isp in the low hundreds of seconds. Electric thrusters accelerate propellant with electric fields instead of combustion, reaching Isp of 1,000–6,000 s. They produce tiny thrust — fractions of a millinewton — but sip propellant, which is exactly the trade a mass- and volume-constrained CubeSat wants to make. The penalty is time: maneuvers play out over days or weeks rather than minutes.

The CubeSat propulsion rule of thumb: if your mission needs a lot of total velocity change (delta-V) and can afford to be patient, electric wins on propellant mass. If you need an instant, high-thrust burn, you still reach for chemical — which is why 2026's dual-mode work (below) is significant.

The families

Three ways to make electric thrust at this scale

Gridded ion (RF)

Busek BIT family

Radio-frequency gridded ion thrusters ionize propellant and accelerate it through charged grids. Busek's BIT-3 was the first iodine-fueled gridded ion thruster — iodine stores as a dense solid, eliminating high-pressure tanks. It flew on NASA's Lunar IceCube-class missions.

FEEP

Enpulsion IFM

Field-emission electric propulsion pulls ions directly off a liquid-metal (indium) surface under a strong electric field. Enpulsion's IFM Nano fits a full propulsion system in a 1U envelope and has flown on dozens of commercial satellites.

Electrospray

Emerging arrays

Electrospray thrusters are dime-sized emitters that electrically charge a liquid propellant and spray it as thrust. High Isp, sub-10 W power, and now being 3D-printed as scalable emitter arrays. The leading candidate for the smallest spacecraft.

The numbers

Flight-class CubeSat thruster specifications

Representative figures for systems sized to CubeSat power and volume budgets. Thrust and Isp vary with operating point; ranges reflect the published envelope.

System	Type	Thrust	Specific impulse	Power	Propellant
Enpulsion IFM Nano	FEEP	0.01–0.35 mN	2,000–6,000 s	8–40 W	Indium
Enpulsion IFM Micro	FEEP	0.2–1.35 mN	1,500–6,000 s	30–120 W	Indium
Busek BIT-1	RF gridded ion	0.1–0.18 mN	2,150–3,200 s	10–55 W	Iodine
Busek BIT-3	RF gridded ion	<1.25 mN	<2,300 s	56–80 W	Iodine
Electrospray arrays	Electrospray	µN–sub-mN	>1,000 s	<10 W	Ionic liquid / green

Specifications compiled from manufacturer data and the NASA State of the Art of Small Spacecraft Technology review.

2026 · State of the art

The dual-mode breakthrough

In June 2026, MIT engineers reported a propulsion concept that runs both a chemical thruster and an electrospray thruster from a single propellant. Historically the two have needed separate, bulky fuel sources — so combining them inside a CubeSat was impractical. The team showed that a green "monopropellant" originally developed by the U.S. Air Force for chemical propulsion can also power tiny electrospray thrusters.

The payoff is flexibility from one tank: a satellite can fire the chemical mode for a fast, powerful maneuver, then switch to the ultra-efficient electrospray mode for slow, precise, fuel-sipping adjustments — even, in principle, a long interplanetary cruise. Four flight units were delivered to NASA for the Green Propulsion Dual-Mode (GPDM) mission.

Why it matters for CubeSats: dual-mode collapses two propulsion systems into one mass and volume budget. That directly improves payload efficiency — the subject of section 03 — and it is the design philosophy behind the OrbitRelay project's propulsion bus.

Where it's going

Beyond Earth orbit

Efficient electric propulsion is what makes CubeSat interplanetary missions credible. In 2025, researchers described CubeSat propulsion systems capable of visiting near-Earth objects, and green dual-mode hardware is explicitly aimed at sending small satellites toward Mars. As thrust-to-power ratios improve and propellants get safer to handle, the practical reach of a 6U or 12U spacecraft keeps expanding — turning what was a classroom platform into a genuine deep-space tool.

Continue

Next: Launches → See the project's propulsion design

Sources: NASA State of the Art — Propulsion · Busek RF Ion Thrusters · SpaceNews — electric thruster startups · MIT News — dual-mode propulsion (2026) · Phys.org — CubeSat to near-Earth objects