The research team, led by Huixin Wang and Hui Ren of Nanjing University of Science and Technology, tackled a long-standing dilemma in the field of controllable solid propellants, or CSPs. These materials are designed for non-self-sustaining combustion: they burn only while external energy is applied, and they extinguish the moment that energy is withdrawn. The catch is that external energy input steals from a satellite’s limited power budget. The ideal propellant would release plenty of chemical heat of its own while still refusing to burn uncontrollably, a balance that has proven difficult to strike. Formulations that store too much chemical energy tend to slip into self-sustaining combustion, defeating the purpose of control.

The team’s formulation centers on lithium perchlorate trihydrate as the oxidizer, polyvinyl alcohol as the binder, and boron in place of the aluminum powder traditionally used as a high-calorific-value fuel. Each choice solves a specific problem. Lithium perchlorate is less toxic and more thermally stable than hydroxylamine nitrate, a common alternative oxidizer, and its crystalline water stores much of the liquid water that CSPs need as a conductive medium, locking it safely inside crystals rather than leaving it free to freeze or evaporate in vacuum. Its decomposition is endothermic, absorbing 158.275 kilojoules per mole, which helps keep the combustion non-self-sustaining.

Boron brings two decisive advantages over aluminum. First, it packs a higher calorific value and, crucially, does not react with water, eliminating the compatibility problems that plague aluminum in the wet, ionic-salt environment of electrically controlled propellants. Second, the boron oxide layer on each particle dissolves in water to form boric acid, which cross-links the polyvinyl alcohol into a stronger three-dimensional network. That structural reinforcement proved vital in cold conditions: at minus 40 degrees Celsius, the boron-containing propellant showed a 10.7 percent higher compressive strength and a 48.5 percent higher elastic modulus than the boron-free control. The dark, rough boron powder also slashed the material’s reflectance to an 808-nanometer laser from 69.5 percent down to just 17.8 percent, meaning the propellant absorbs laser energy efficiently without any added carbon black.

Pure boron burns incompletely, leaving residues that can clog electrodes and block laser beams, so the researchers blended it with molybdenum powder in a 9-to-1 mass ratio, drawing on their earlier work showing that molybdenum promotes boron combustion by generating oxygen vacancies. Thermal analysis confirmed the benefit: under argon, the boron-containing formulation released 24 percent more heat, at 2555.4 joules per gram versus 2060.9, and its decomposition activation energy dropped by roughly 56 kilojoules per mole. Time-resolved flame spectra showed lithium emission lines appearing first, confirming that oxidizer decomposition initiates ignition, followed by the characteristic BO2 signature of burning boron and the green flame that gives boron propellants their visual trademark.

Manufacturing was its own challenge. Conventional CSP production requires pouring a dilute aqueous solution into a mold and waiting five to seven days for water to evaporate and cross-linking to complete, during which dense additives like metal powders settle under gravity and bubbles and shrinkage mar the final bulk. The team’s rapid process instead mixes solids with minimal water, heats the sealed mixture at 70 degrees Celsius for one hour to form a pliable gel, extrudes it, dries it exposed for 24 hours, then softens and re-extrudes it into a regular cylinder. Total curing time: one day. X-ray tomography showed dense, defect-free bulks with no gravity-driven density gradients, and the process can produce columns with a length-to-diameter ratio of 4 to 1, something the old pouring method could not manage.

Electrically controlled testing revealed the propellant’s throttle behavior in detail. As applied voltage rose from 100 to 200 volts, ignition delay shortened, burning rate climbed, and ignition energy consumption fell, because stronger current heats the bulk faster and accelerates oxidizer decomposition. The boron-containing propellant burned 31 percent faster than the boron-free version at 100 volts and 11 percent faster at 200 volts. The researchers also untangled a puzzling current surge seen during ignition: by substituting inert lithium chloride for the oxidizer and observing the same surge, they showed it stems purely from water detaching from the polymer grid and dissolving ionic salts to form a conductive path, not from any chemical decomposition.

Environmental testing is where the new formulation truly separates itself. Across temperatures from minus 30 to plus 55 degrees Celsius and pressures from 3 kilopascals to 0.85 megapascals, the boron-containing propellant ignited reliably and extinguished on command without structural damage. The boron-free control, by contrast, cracked apart at minus 30 degrees as freezing water expanded inside it, and at 55 degrees it softened so badly that it deformed into the electrode holes and self-extinguished. At 0.85 megapascals the control even slipped into uncontrolled self-sustaining combustion. In low-pressure tests at 200 volts, the boron propellant burned 43.3 percent faster than the control, retaining its energy advantage where satellites actually operate.

Repeated start-stop cycles worked smoothly in both control modes. Under 200-volt electrical stimulation, four ignition-extinguishment cycles drove ignition delay down from 1.80 to 0.52 seconds and ignition energy from 1214 to 314 joules as residual heat and established ion pathways sped each restart. The team also demonstrated an energy-saving operating mode of high-voltage ignition followed by low-voltage maintenance, finding the minimum maintenance power for the boron propellant was 117 watts, 30.3 percent lower than the control’s 168 watts, thanks to its greater self-generated heat. Under a 25-watt 808-nanometer laser, ignition delays reached millisecond scale, and five rapid laser cycles cut ignition delay from 130 to 48.75 milliseconds. Laser mode offers faster response but lower energy output, since only the irradiated end heats up, while electrical mode heats the whole bulk and delivers higher burning rates.

The authors acknowledge that response times remain longer than ideal and that smoke interferes with laser ignition at high pressure, but they see clear paths forward: optimizing grain geometry to cut resistance and reformulating to reduce condensed products. For the rapidly growing constellation of small satellites needing simple, restartable, throttleable propulsion, a solid propellant that answers to both a wire and a beam of light, survives deep cold and near-vacuum, and cures in a single day could mark a genuine shift in how spacecraft maneuver.

Subject of Research: Boron-containing combustion-controllable solid propellants with dual electric and laser response for satellite propulsion

Article Title: Boron containing combustion controllable solid propellant with multi-modal response to voltage & laser

Article References: Wang, H., Ren, H., Xu, J., Xiao, G., & Yu, L. (2026). Boron containing combustion controllable solid propellant with multi-modal response to voltage & laser. Results in Engineering, 32, Article 113322. https://doi.org/10.1016/j.rineng.2026.113322

Image Credits: AI Generated

DOI: 10.1016/j.rineng.2026.113322

Keywords: controllable solid propellant, boron fuel, lithium perchlorate, electrically controlled propellant, laser ignition, space propulsion, low Earth orbit satellites, polyvinyl alcohol binder, non-self-sustaining combustion, burning rate control, thermal decomposition, multiple start-stop