Propulsion
CubeSat33 uses ASCENT — an ionic liquid green monopropellant — to feed both a chemical thruster and electrospray thrusters. One tank, two thrust profiles, less mass wasted on dual systems.
How it works
Dual-mode means the bus can switch between high thrust and high efficiency without carrying two complete propulsion architectures.
High thrust · fast response
ASCENT is fed to a catalytic monopropellant thruster. Decomposition produces relatively high thrust for rapid orbit changes, collision avoidance, or phasing into a better ground track.
High efficiency · long dwell
The same ASCENT is fed to electrospray thrusters. High voltage extracts and accelerates charged droplets and ions, producing low thrust with very high specific impulse for station-keeping and fine control.
Chemistry
ASCENT (formerly AF-M315E) is a hydroxylammonium-nitrate-based ionic liquid monopropellant. One fluid stores chemical energy for catalytic decomposition and carries mobile ions for electrospray extraction.
An ionic liquid is a salt that stays liquid near room temperature. ASCENT is built from energetic ions rather than a classic neutral hydrazine molecule. That is why the same tank can support two very different thruster types: decompose it for chemical thrust, or extract charged species for electric thrust.
Hydroxylammonium nitrate (HAN) supplies oxygen-rich chemistry through nitrate anions paired with hydroxylammonium cations.
An energetic fuel salt and controlled water content form a stable, handleable liquid with density suited to small spacecraft tanks.
Mobile ions make the liquid electrically usable for electrospray, while low vapor pressure keeps it practical in vacuum.
Chemical path
In chemical mode, ASCENT contacts a preheated catalyst bed. The energetic mixture decomposes into hot gas products that expand through a nozzle. No separate oxidizer tank is required — the monopropellant already carries both the oxygen-rich and fuel-side chemistry in one liquid.
Electric path
In electrospray mode, a strong electric field at micro-emitters pulls charged droplets and ions from the liquid surface. Those charged particles accelerate in the electric field, producing very low thrust with high specific impulse for long station-keeping burns.
Why one chemistry enables dual-mode
Chemical thrust
Energetic nitrate-based salts that release heat and gas over a catalyst
Electric thrust
Ionic liquid conductivity and low vapor pressure for electrospray extraction
Shared tank
One storable liquid instead of hydrazine plus a separate electric propellant
CubeSat packaging
Dense liquid storage without high-pressure noble-gas tanks
Green means lower toxicity than hydrazine — not zero hazard. Feed cleanliness, materials compatibility, and thermal design still decide whether dual-mode works in flight.
Comparison
Hydrazine is the proven monopropellant baseline. ASCENT trades decades of heritage for lower toxicity, higher density, and a path to dual-mode chemical + electrospray from one tank.
| Aspect | Hydrazine | ASCENT |
|---|---|---|
| Chemistry | Neutral molecular monopropellant (N₂H₄) | HAN-based ionic liquid monopropellant |
| Toxicity & ground ops | Highly toxic; specialized ranges and heavy PPE common | Much lower acute toxicity; still hazardous, easier facilities |
| Density / packaging | ~1.0 g/cm³ class — more tank volume for the same mass | Higher density — more impulse in CubeSat volume |
| Flight heritage | Decades of thrusters, processes, and failure data | Growing green-monoprop line; dual-mode still maturing (GPDM) |
| Dual-mode (chemical + EP) | Not a practical shared electrospray propellant | Ionic conductivity enables chemical + electrospray from one tank |
| When you pick it | Maximum heritage; hydrazine range already available | Safer handling, denser packaging, dual-mode architecture |
Prefer hydrazine when
Prefer ASCENT when
Neither is free. Both need catalyst thermal control and clean feed systems. Dual-mode ASCENT adds pressure step-down and electrospray power electronics that a pure hydrazine monoprop system does not carry — complexity spent to free payload mass elsewhere and open safer ops.
Propellant in the bus
ASCENT is a lower-toxicity alternative to hydrazine for chemical thrusters — safer ground handling for smallsat teams.
Because ASCENT is an ionic liquid mixture, it is compatible with electrospray extraction, enabling the dual-mode architecture.
Sharing tankage, valves, and feed plumbing reduces mass and volume compared with separate chemical and EP systems.
Flight path
The Green Propulsion Dual Mode (GPDM) mission is the first integrated chemical + electrospray ASCENT system on a 6U CubeSat class vehicle — the practical reference for CubeSat33.
| Element | GPDM reference | CubeSat33 intent |
|---|---|---|
| Form factor | 6U demonstration | 3U–6U operational bus |
| Chemical thruster | ~100 mN class monoprop | Fast maneuvers when needed |
| Electrospray | MIT iEPS-class units | Efficient station-keeping |
| Propellant | Shared ASCENT tank | Same dual-mode architecture |
CubeSat33 is not affiliated with NASA, MIT, Rubicon, or the GPDM team. GPDM is cited as public technology context only.
Trade-offs
Pros
Cons