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Traditionally the launched satellites were Large ( Mass >1000 Kgs) and Medium satellites (500 to 1000 Kgs) which were high-performance, multifunctional with long lives which required larger rockets with greater thrust and expensive to launch, and took long development times. Only large commercial players and government organizations could afford to commit >$100M USD to develop, manufacture, insure, deploy, and operate these spacecraft.
As components and sensing technology has gotten smaller, and with the diversity of computing and sensing components available off the shelf, there has been a large growth of new breed of small, miniaturized satellites, or smallsat with low mass and size, usually under 500 kg (1,100 lb).
While all such satellites can be referred to as “small”, different classifications are used to categorize them based on mass. Mini satellite 100 to 500 Kgs; Micro satellite 10 to 100 Kgs; Nanosatellite refer to miniaturized satellites in terms of size and weight, in the range of 1-10 Kg ;Pico satellite 0.1 to 1 and Femto satellite <0.1 kgs.’CubeSat’ is one of the most popular types of miniaturized satellites.
Enabled by advancements in miniaturized space robotics and microelectronics systems, space technologies that are lighter, smaller, and cheaper, yet equally or more functional in terms of the tasks they can perform have been developed.
These satellites are cheap to build and lightweight, further reducing payload costs. In comparison, the total outlay for functional nano- and microsatellites and space assets start at $1M USD, with the starting cost of building a functional communications satellite estimated to be as low as $25 000 USD.
These smaller and lighter satellites require smaller and cheaper launch vehicles and can sometimes be launched in multiples. They can also be launched ‘piggyback’, using excess capacity on larger launch vehicles. To put this in perspective, a single launch of Falcon 9 rocket can accommodate the delivery of a hundred of 50 kg microsatellites onto orbit, at an approximate cost of $0.6 × 106 or less per Cubesat delivered onto orbit.
Micro- and nanosatellites have emerged as a highly versatile and economical resource for the satellite community, becoming one of the major areas of development and growth. They find application in scientific research, communication, navigation and mapping, power, reconnaissance, and others including Earth observation, biological experiments, and remote sensing. There is also growing utilization of miniaturized satellites for military and defense applications.
About 60 percent of all satellites are in low Earth orbit. This is a bit of a problem because, though on a human scale it’s a vacuum, there’s actually a thin trace of atmosphere present – enough to generate drag, which causes the satellite’s orbit to decay until it burns up on reentry. The usual way to overcome this is to use thrusters to boost the satellite into a higher orbit, but for smaller spacecraft, and especially CubeSats, this isn’t currently an option. The result is that many perfectly good pieces of hardware are destroyed prematurely, deorbiting in a matter of months or even days.
In Space propulsion
A propulsion system is the primary mobility system of a spacecraft and helps with various maneuvering operations like orbit changing and station keeping. Having a propulsion system can change your acceptable altitudes; it can let you avoid debris; it can elongate your lifetime. So that further adds into the capabilities of these new tiny satellites. However, due to their stringent mass, volume and power limitations, their mission range is limited by availability of propulsion systems.
Therefore there is growing demand for in-space propulsion systems that enable small satellites to achieve attitude and orbit control, orbital transfers, and end-of-life deorbiting. The constellation control will be an important factor in the success of these LEO and MEO constellations currently being developed.– although efforts like the ThermaSat design are looking to bring lightweight propulsion systems to CubeSats.
In-space propulsion systems are the backbone of space exploration, and they’re becoming even more important as companies and government agencies deploy ever-more low-earth orbit (LEO) satellite constellations. SpaceX alone hopes to deploy 42,000 Starlink satellites over the next several decades.
MicroPropulsion System requirements
There is currently a wide range of technologies for propulsion systems, however the miniaturization of these systems for small spacecraft has been particularly challenging. To achieve their full potential, however, CubeSats will require micropropulsion devices to deliver precise low-thrust “impulse bits” for scientific, commercial, and military space applications. The current and future nanosatellite constellation missions are also placing greater demand on the propulsion subsystem to provide complex maneuvers required to maintain an autonomous, intelligent constellation.
As the burgeoning demand for small satellite constellations increases on a commercial scale, propulsion technology that is performant, readily manufactured at scale and affordable is required. Demand for such high performing affordable propulsion solutions will only continue to increase,” said Beau Jarvis, Phase Four CEO.
The demand on propulsion systems presents new challenges, particularly with respect to accurate management of satellite position on the desired orbit, autonomous operation, and the eventual decommissioning upon completion of its mission. Furthermore, these assets need to be able to perform in the hostile environment rich in extreme temperature variations, trapped and transient radiation, and bombardment by high-velocity dust particles and space debris.
They are also being designed for near- and deep-space microsatellite-enabled exploration missions which relies firmly on the development of next-generation propulsion systems, the design of which should be well-matched to the specific requirements of nano- and microsatellite technologies and provide effective and dependable means for controlling their motion in space. For Solar System and deep space exploration, e.g., of the Moon and Mars by robotic orbiters and landers, and of Saturn, comets, asteroids, and deep space by long-life probes, the development of sophisticated, multi-functional, and robust assets with the capacity to navigate towards outer space targets is necessary.
Atmospheric drag for propulsion
Many low-Earth-orbit constellations consist of multiple small satellites that are launched together in batches, and which make use of differential atmospheric drag for subsequent deployment and phasing. Depending on the initial altitude, this process can potentially take many months, or even years, to complete, and satellite altitudes can only ever be decreased, potentially affecting mission lifetimes. Miniaturized low-thrust propulsion systems are one option to achieve faster phasing and can additionally increase the constellation lifetime through drag compensation.
Solar Sails
A solar sail is a form of propellant-less spacecraft propulsion system that generates thrust by means of momentum exchange with the incoming solar radiation. Solar sails have a flat surface and are usually made of thin reflective material supported by a lightweight deployable structure. As they do not use a propellant, solar sails by definition, possess infinite specific impulse. However, the main drawback of a solar sail is very low thrust levels resulting in a long time to gain appreciable momentum change.
Gama launches its Gama Alpha solar sail mission
Gama, a French aerospace company, announces the launch of its first solar sail to space, with the support of the CNES and private companies including CMA CGM, a global player in sea, land, air, and logistics solutions. the satellite containing the solar sail was successfully placed in orbit by a SpaceX Falcon 9, on the 3rd of January 2023. The Gama Alpha mission aims to test the deployment and control of the sail, a decisive step for the democratization of this new means of space propulsion.
The first phase will be commissioning the satellite, establishing communications and checking all the vital signs are good. The second phase will be the sail deployment. The satellite will be put in slow rotation, initiating the release of four tungsten masses at the tip of each sail petal. The centrifugal force generated by the rotation is enough to ensure the deployment and the structural shape of the sail. Comments Jordan Culeux, Gama Lead System Engineer.
The primary objective of Gama Alpha is to deploy and control the sail, demonstrating that a very large sail can be controlled from a cubesat and receiving flight data to improve simulations and control algorithms. Demonstrating sustained navigation will be the objective of Gama’s second mission, Gama Beta.
The final phase for Alpha will be deorbiting the satellite, benefiting from the Earth’s remnant atmosphere at mission altitude. The large surface area and small mass will cause the satellite to rapidly deorbit, minimising the risk of debris and also demonstrating a sail can be used to deorbit satellites at end of life.
A constellation of small satellites recently demonstrated the ability to move around space without the benefit of a propulsion system, reported in July 2022
A constellation of small satellites from Millennium Space Systems, a subsidiary of Boeing recently demonstrated the ability to move around space without the benefit of a propulsion system. Because the satellites were launched off the international space station, they were not given propulsion systems due to safety concerns, Hulse said. However, the company discovered that the spacecraft could be controlled using aerodynamic drag by adjusting the satellite’s solar arrays to move it through the small amount of atmosphere in low-Earth orbit, he told reporters July 20 during a media roundtable.
Aerodynamic drag is the force an object faces when moving through the atmosphere and normally causes satellites to deorbit slowly over time. Even with the low air density of low-Earth orbit, the air resistance from the atmosphere is strong enough to manipulate a small satellite’s position, Hulse said.
“With no propulsion at all and just by modulating our drag profile … they were able to drive them apart, pull them closer together, and really just control that spacing,” Doug Hulse, the company’s Red-Eye program manager. said. For example, if two Red-Eye satellites needed to move closer together to perform a crosslink data transfer, an operator from the ground could reposition the satellites’ solar arrays in a way so the aerodynamic drag closes the distance between them. Millennium also created a ground-based automation system that allows the constellation to self-control its orbital spacing, Hulse said.
Key specifications and performance criteria of Propulsion system technologies
Propulsion systems can be classified based on their dependence on the onboard power: electric and non-electric systems. Electric propulsion systems are mainly classified into resistojet, electrospray, ion, Hall and pulsed plasma systems, and they actively require on-board power for their operation, while the non-electric propulsion systems can be classified into cold gas, liquid and solid rocket systems, and they require on-board power only to regulate (initiate and terminate) the propulsion process.
Knowing exactly what functions your thruster will need to perform, and on what schedule and duration, will make selecting a model easier. Also consider the launch stresses, testing processes and regulatory compliance that the CubeSat will need to go through, in order to make it into orbit, as well as any obsolescence procedures once the mission is complete.
One of the important performance factors for any propulsion system is specific impulse is the impulse (integral of thrust over time) generated per unit weight (at sea level) of propellant and is dependent on the thrust generated and mass flow rate of the propellant (m˙ ). This depends on mission and intended applications.
- Thruster delta-V capability – What changes in velocity does the thruster need to produce in order to carry out the maneuvers required in the mission?
- The Size, weight and volume are constrained by the physical volume (usually expressed in CubeSat units / U) and on-Earth weight determine what other components can be used in the unit and impact transport and launch costs.
- The Operating power or required power supply to operate the thruster is constrained by available power.
- The Integration requirements weather plug-and-play system or a more customizable solution is desired.
- Finally Flight heritage or thruster has bee fully tested in space. You need to know that the system will survive the launch and operate as expected in microgravity, so it is important to look at the product’s history.
Among a multitude of currently pursued propulsion technologies, electric propulsion systems emerged as one of the most promising technologies, with Hall-type and gridded ion thrusters being the most well-known of these systems.
The chemical propulsion systems, which include solid and liquid propellant rocket engines, feature very high thrust-to-weight ratio reaching 200, with the highest exhaust velocity of about 5000 m × s−1 for the best available chemical fuels (e.g., liquid hydrogen and liquid oxygen). Electric propulsion systems demonstrate much higher exhaust velocities reaching 104 m × s−1 , but at significantly lower thrust levels and thrust-to-weight ratios not exceeding 0.01; hence, these systems are not capable of launching the vehicle from the Earth’s surface.
By using electrical energy to increase the velocity of the ionized propellant, electric propulsion systems combine high specific impulse and excellent efficiency at low thrust, which is essential for long-term control over relative position and orientation of orbiting nano- and microsatellites. From this perspective, they compare favorably to solid and liquid propellant rockets and small chemical rockets, which both deliver a low specific impulse. Importantly, since the acceleration of the propellant relies on the action of electromagnetic or electrostatic forces, the performance of electric propulsion systems, namely, their exhaust velocity, is not physically limited below the speed of light, and thrust can be achieved at a low mass flow rate of the propellant. This means that for the same quantity of the propellant, electric propulsion can support longer missions
Plasmadynamic thrusters, pulsed plasma dynamic thrusters, gridded ion, and Hall thrusters form the primary set of electric propulsion platforms capable of powering small satellites. While the gridded ion and Hall thrusters feature the highest energy efficiency numbers reaching 75% (with a promise of even higher levels) at very high exhaust velocities, the continuously operated plasmadynamic systems are capable of producing much higher thrust-to-weight numbers; on the other hand, pulsed thrusters are the primary candidates for ultra-miniaturized systems, which could produce extremely low thrust pulses for precise maneuvering and positioning of small satellites.
Other systems currently being developed include pulsed plasma thrusters, magnetoplasma-dynamic thrusters, and numerous others. One of the critical challenges of electric propulsion systems lies in its dependence on the electric energy to increase the velocity of the ionized propellant, making the life-time and efficiency of the device power limited.
Cold Gas Propulsion (CGP) Systems
A Cold Gas Propulsion System relies on the process of controlled ejection of compressed liquid or gaseous propellants to generate thrust. The simpler design of a CGP system leads to a smaller system mass and lower power requirements for regulation purposes. However, these advantages come at the cost of a monotonically decreasing thrust profile over a period of time. The thrust produced is directly proportional to the pressure of the propellant inside the tank (propellant storage) and over the course of the mission, tank pressure decreases (due to propellant usage) resulting in a decrease of the maximum thrust that is generated by the system.
A cold gas propulsion system can use either liquid or gaseous propellants. Liquid propellants provide the advantage of reduction in storage volume; however they can result in a de-stabilizing effect due to sloshing of propellant inside the tank.
Liquid Propulsion (LP) Systems
In a Liquid Propulsion System, thrust is generated by means of ejecting the gases formed during the process of combustion of liquid propellant(s). Depending on the mission requirements, a spacecraft can have LP systems with one (mono) or two (bi) propellants.
Mono-propellant LP systems make use of a catalyst to decompose (ignite) the propellant and generate thrust. Examples of mono-propellants are hydrazine and nitrous oxide and examples of a catalyst are liquid permanganates, solid manganese dioxide, platinum, and iron oxide. A bi-propellant LP system, on the other hand, comprises of both oxidizer and fuel. Combination of liquid oxygen and kerosene, or of liquid oxygen and RP1 are examples of bi-propellants that are widely used.
Many of the emergent green propellants (Sulfur Hexaflouride (SF6), AF-M315E, Ammonium Dinitramide (ADN)) provide significant additional advantages like better physical characteristics (higher density), better performance for the propulsion system (higher thrust and specific impulse), and reduced thermal conditioning requirements for storage compared to hydrazine. However, they do pose a disadvantage with requiring higher preheat temperatures, higher than the typical 120–150 C of hydrazine thrusters.
Dawn Aerospace is commercializing thrusters that use nitrous oxide and propene instead of hydrazine. Its 5-pound-force thruster is produced without components restricted by U.S. International Traffic in Arms Regulations, according to the company. Dawn Aerospace, based in New Zealand and the Netherlands, has its first propulsion system launching in March on a D-Orbit cubesat aboard a Vega rocket.
CUA’s newest in-Space propulsion technology being developed is a high thrust option using an ethanol and hydrogen peroxide monopropellant mixture. This monopropellant, designated CMP-X is a non-detonable yet energetic COTS formulation that possesses many system-level advantages over legacy monopropellants (such as hydrazine) including lower cost, lower thermal load (approximately 950°C flame temperature), water-like viscosity, and common materials compatibility. CMP-X is designed as a monopropellant option for customers who can accept a modest performance trade-off for the advantages of lower cost, easy transportability, considerably fewer range safety concerns, longer continuous thrust burns, and lower flame temperature, resulting in considerably less thermal soakback into the spacecraft. CMP-X retains the ability to scale in thrust magnitude and requires minimal catalyst bed warmup time.
Thrust stand tests achieved thrust levels >0.5N and specific impulse >180s with an average input power of approximately three Watts, for hot fire burns typically spanning >10 minutes.
The PM200 and The PM400 by Hyperion Technologies
The PM200 and PM400 bring high thrust propulsion capability to 3-12U and 6-12U CubeSats respectively. Low system complexity and zero propellant toxicity allow for simple and robust operations, both on the ground and when in orbit. The medium tank pressure and high storage density of liquid propellants enable high safety factor tanks to be used with little mass penalty. The standard 1U configuration of the PM200 propulsion module can deliver in excess of 230 m/s of velocity increment to a 3U CubeSat of 4 kg at a nominal thrust level of 0.5 N and the standard 2U configuration of the PM400 propulsion module can deliver in excess of 230 m/s of velocity increment to a 6U CubeSat of 8 kg at a nominal thrust level of 1 N. Both systems can be seamlessly integrated with the iADCS400 to provide a fully integrated GNC and ADCS solution. In addition, the PM200 offers active thrust vector control to minimize disturbance torque on the satellite platform.
Solid Rocket Propulsion (SRP) Systems
A Solid Rocket Propulsion System works on the principle of burning solid propellants and generating thrust by ejecting the gases formed during combustion. Similar to a LP bi-propellant system, an oxidizer is used in the SRP system. Although SRP systems do not experience sloshing, the lack of control over propellant burn rate creates difficulty for thrust regulation.
To mitigate this disadvantage, a system of hundreds of Solid Propellant Micro-thrusters (SPMs) has been proposed. In SPMs, solid energetic propellant is burnt (during combustion process) and the resultant gases are accelerated through micro-nozzles. The size of the thruster can be modified to suit the thrust requirements and programmable thrust delivery can be achieved via simultaneous or sequential firing of multiple thrusters. A typical SRP micro-thruster makes use of MEMS technology and comprises of several laminated layers containing a combustion chamber, an igniter, a nozzle, and a seal.
Resistojets
In a resistojet, the propellant is passed through a heat exchanger (or heating element) where it is super-heated and ejected through an expansion nozzle. For instance, laboratory experiments have shown exit temperatures of 600–1050 C for methanol and 300–1175 C for ammonia propellants.
The heating process reduces the gas (propellant) flow rate from a given upstream pressure through a given nozzle area, thus leading to the increase in specific impulse that is proportional to the square root of temperature. Resistojets are known to provide lower thrust and are mainly employed for attitude control on larger satellites.
Radio-Frequency Ion Thruster (RIT)
Radio frequency thrusters are electric propulsion systems that use radio frequency electromagnetic signals to accelerate a plasma propellant, generating thrust. Using RF systems for electric propulsion presents several advantages. First, a considerable knowledge base of RF plasma generation and heating has already been established through on-going efforts in the plasma processing and plasma fusion communities. Second, RF plasma systems can efficiently generate very highly ionized plasmas with relatively moderate to low input RF power, ultimately increasing an RF thruster’s efficiency. Third, RF electronic active components have been miniaturized largely through the progress made by the cellular and wireless power industries, increasing their suitability for low mass budget spacecraft applications.
Radio frequency ion thrusters belong to a subset of gridded ion thrusters that generate thrust by accelerating the ionized propellant (plasma) through an electrostatic grid. Electron bombardment and microwave thrusters are some of the other gridded ion thrusters. In RITs, the stored propellant is let into the discharge chamber where it is ionized (and becomes plasma) by means of Radio Frequency (RF) power (from RF coils). The ionized propellant is then extracted (from the discharge chamber) and accelerated by a series of grids (ion optics) called screen and accelerator grids.
Ion thrusters are characterized by high thruster efficiency (60% to >80%) resulting in high specific impulse (from 2000 s to over 10,000 s); however, they have been plagued with issues that are caused by cathode wear and contamination over prolonged usage
Phase Four Introduces Maxwell Smallsat Propulsion Solution
Phase Four introduced Maxwell, the first turn key plasma propulsion solution for small satellites. According to the release, Maxwell combines a complete propellant management system and Phase Four’s proprietary Radio Frequency (RF) plasma thruster into a compact form factor.
Designed with ease of integration and operation for scale manufacturing. Maxwell brings new small satellite constellations the performance and efficiency of legacy electric propulsion systems, while obviating the need for expensive components that have hampered high performance propulsion solutions for small satellites. In an industry first, Maxwell eliminates bulky high voltage components and electrodes, simultaneously reducing cost and removing supply chain barriers that have long plagued traditional satellite engines.
“We believe that customers shouldn’t have to choose between thrust and efficiency when it comes to propulsion. Maxwell provides the best of both worlds, delivering simple plug and play delta-V,” said Beau Jarvis, Phase Four CEO. “Maxwell will enable rapid ROI for low Earth orbit small sat constellations looking for 4-6 year operational lifetimes.”
Maxwell’s technology does not require high voltage components and electrodes — primary aspects of traditional satellite engines that are barriers to high volume manufacturing. The product architecture behind Maxwell was created to cater to the specific needs of smallsats in a range of sizes and power classes. Maxwell’s design also allows for future spacecraft to use newer, less expensive propellants that may be sourced in space, further contributing to the sustainable in-space industry. Maxwell is anticipated to be delivered to initial customers beginning in Q3 2019.
Capella Space, an aerospace and information services company providing Earth observation data on demand, has purchased six Maxwell engines for initial phase of constellation deployment. Capella Space is well-respected for its Synthetic Aperture Radar (SAR) technology designed to detect sub-meter changes on the Earth’s surface. The leader in radar imaging, tapped Maxwell as its preferred propulsion solution for Capella’s phased deployment of a constellation of 36 micro-satellites.
The REGULUS by T4i srl
Based on helicon technology, the REGULUS system is a magnetically-enhanced RF plasma thruster designed for small platforms; characterized by low power and budget constraints. Due to its simplified architecture the thruster allows for cost reduction, making it a valuable solution for small platforms down to multi U. The system is throttleable and is easily scalable to match with the customer needs, while being composed only of a discharge chamber, an antenna and a magnetic field generator. It does not use electrodes, does not require neutralizers and grids, thus allowing cost reductions and long lifetimes. A proprietary (patented) helicon technology has been developed specifically for micro and nano-satellites.
Hall Effect Propulsion/Hall Thrusters
Hall Thrusters are electrostatic devices that generate thrust by first ionizing and then accelerating the propellant in mutually perpendicular electric and magnetic fields. These thrusters work on the principle of the well known Hall Effect that states the following: when electric current is applied to a conductive material (propellant) placed in mutually perpendicular electric and magnetic fields, a potential difference is developed that is perpendicular to the applied electric and magnetic fields.
Hall thrusters have many advantageous features like high specific impulse (higher than most systems except ion engines), higher thrust density and simplicity in design (when compared to gridded ion engines due to lack of accelerator grids). However, they also face some challenges with erosion of magnetic circuitry due to discharge plasma and lower efficiency (6–30% at 0.1–0.2 kW and 50% at 1 kW)
China makes major breakthrough in Hall-effect thruster (HET) space propulsion technology
Researchers from the China Aerospace Science and Technology Corporation (CASC) have developed the country’s first HET with an input power of 20 kilowatts that can produce a thrust of one newton, marking a leap for China’s HETs from millinewton level to newton level. The applications of HETs include control of the orientation and position of orbiting satellites and use as a main propulsion engine for medium-size robotic space vehicles. During a test, the thruster showed stable operation, with a specific impulse of 3068 seconds and working efficiency above 70 percent, reaching international advanced level. Such a high-power HET with features of strong thrust, long working life and high reliability will be able to provide highly efficient impetus for the positioning, orbital maneuvering and motion control of large GEO (geostational orbit) satellites, deep space probes and space shuttle vehicles.
Plasma thrusters for small satellite systems
Orbion Space Technology, a company that makes propulsion systems for small satellites, has developed the first-ever Hall-effect plasma thrusters for small satellites, dubbed the Aurora system. Orbion has announced $9.2M in Series A funding, planning to use the capital from this round to support mass production of its thrusters.
Hall-effect plasma thrusters are a type of ion drive in which a propellant is accelerated by an electric field. The technology has been around since the 1960s, and Hall-effect thrusters were in use on Soviet satellites between 1972 and 1990. What’s new is the size of the thrusters, as well as the size of the satellites they power, which are variously dubbed smallsats, microsatellites, or nanosatellites.
“Many of the components on new small satellites, such as solar cells, batteries, and computers, can be leveraged from large established terrestrial markets and can easily satisfy the projected growth,” according to a spokesperson. “Propulsion, however, is a “space-only” technology that has no terrestrial counterpart and, until Orbion, there was no supplier capable of delivering hundreds or thousands of thrusters for satellites.”
The company has set up an end-to-end manufacturing pipeline that includes robotic assembly-line integration and acceptance testing perfected in high-volume production environments.
Electrospray Propulsion System/Electrospray Thrusters
Electrospray thruster is a plasma-free electric propulsion system that works on the principle of electrostatic extraction and acceleration of charged particles (ions) from a liquid (propellant) surface to produce thrust.
Electrospray thrusters accelerate positive or negative ions, respectively generating either a positive or negative ion beams thereby eliminating the need for an external cathode to neutralize the ejected ions unlike in plasma propulsion devices (ion and Hall thrusters) where an external cathode is essential. The propellants used for electrospray thrusters are usually ionic liquids, and their negligible vapor pressure serves as an advantage by resolving the need for propellant pressurization and helps with system miniaturization.
Field-emission Electric Propulsion.
Field-emission Electric Propulsion technology is an advanced electrostatic satellite propulsion concept of an ion engine that uses liquid metal as the propellant.
Pulse Plasma Thruster (PPT)
Pulsed Plasma Thrusters (PPTs) operate by creating a pulsed, high-current discharge across the exposed surface of a solid insulator (for instance, Teflon) that serves as a propellant. The arc discharge ablates (sublimates/vaporizes) the propellant material from its surface, thereby ionizing and accelerating the propellant to high speeds. A current pulse lasting few micro-seconds is generally driven by a capacitor that is charged and discharged approximately once every second.
The advantages of a PPT are its ability to provide small impulse bits for precision maneuvering, robustness by programming impulse bits to cater to mission needs, design simplicity owing to the ability of using wide variety of propellants (solid/liquid), and its ability to maintain constant specific impulse and efficiency over a wide range of input power levels. However, these advantages come at the cost of issues that result due to electrode erosion, presence of macro-particles in the plume due to non-uniform ablation and very low thruster efficiency.
Company Eyes “Steampunk” Propulsion for CubeSats
One disadvantage of the platforms, however, is that most CubeSats are essentially passive, as it’s been tough to find a way to cobble onto them a propulsion system that’s sufficiently small and powerful, yet safe enough not to endanger other payloads riding up to orbit on the same launches.
Howe Industries, a firm based in Scottsdale, AZ, USA, has looked back a few centuries to a potential alternative mode of propulsion for CubeSats: steam power. Under a US$225,000 Small Business Innovation Research (SBIR) grant from the U.S. National Science Foundation, the company has just presented the design for a system that would combine sophisticated optical filtering, photonic crystals, phase-change materials and water to create compact, light and safe propulsion for CubeSats and other nanosatellites. As the company eyes the next phase of the project, OPN caught up with is founder and CEO, Troy Howe, to learn about the project, the market and the next steps.
There are basically two key elements that are really important to making the ThermaSat work, the optical system and the thermal capacitor system, explained founder and CEO, Troy Howe. The optical system works in a way similar to the greenhouse effect on Earth. When the sun illuminates the Earth with all these different wavelengths of light, the Earth heats up and tries to radiate that energy out in the infrared spectrum. But greenhouse gases in the atmosphere reflect that infrared energy back in. The result is that the incoming sunlight gets reduced by a small percent, but the infrared emission back into space gets reduced by a large percent, so it heats the temperature of the planet.
With ThermaSat, we kind of take that to an extreme and do it on purpose. The system has multiple layers of selectively transmissive filters that really block and reflect infrared light. So when the sunlight comes in, all the infrared gets reflected away. The visible and UV energy comes in, and heats the thermal capacitor. And as that capacitor tries to radiate that heat away—because there’s no other way for it to reject heat—the heat sees that reflective IR barrier, and it comes back in. And that gets our operating temperature very high—above 1000 or 1100 K. That’s a lot hotter than you need to boil water, for sure; with rocketry, though, where you’re expanding gases, the hotter you get, the better your performance. And so that’s really what we wanted with the optics—to let us hit that high temperature level.
Basically, there are two parts to the optical system. One is a gold-coated glass, on the outside of the thermal capacitor, which itself blocks a lot of the infrared. And then, the thermal capacitor itself is basically a tantalum can, containing the phase-change material. On the outside, on that tantalum surface, is the photonic-crystal structure. Those are some very impressive surface features originally developed at MIT, and then spun off to a company called Mesodyne that we’ve been working with. And they can create tiny, tiny holes in a tantalum surface—a repeating pattern of micron-scale holes. And the long infrared wavelengths just can’t exist in those holes—they can’t be produced or emitted there, and if they try to come in, they bounce off. It makes the tantalum surface a selective emitter and a selective absorber. And that helps us absorb the short wavelengths, to heat up the thermal capacitor, and reflect the long wavelengths.
Water propulsion
Sony has adopted Pale Blue’s water thruster for its new nanosatellite program, STAR SPHERE. The water thruster will prolong the satellite’s life by 2.5 years with the ability to enter and keep the orbit at 500-600 km altitude. Furthermore, Pale Blue will conduct its first space demonstration at the end of January 2023.
SpaceX’s Falcon 9 launched the project’s nanosatellite on January 3, 2023, on the transporter-6 mission marking Pale Blue’s first on-orbit space demonstration of a water vapor propulsion system.
More companies are working to reduce environmental impact and handling costs by adopting green propellants in the space industry. Accordingly, Pale Blue tackles environmental issues and growing demand by providing safe, sustainable, and low-cost propulsion systems that use water as a propellant.
Little nozzles could propel nano satellites
Researchers have developed a new type of micropropulsion system for miniature satellites (called CubeSats) that uses tiny nozzles that release precise bursts of water vapor to maneuver the spacecraft. Water is also a very clean propellant, reducing risk of contamination of sensitive instruments by the backflow from thruster plumes.
The new system, called a Film-Evaporation MEMS Tunable Array, or FEMTA thruster, uses capillaries small enough to harness the microscopic properties of water. Because the capillaries are only about 10 micrometers in diameter, the surface tension of the fluid keeps it from flowing out, even in the vacuum of space. Activating small heaters located near the ends of the capillaries creates water vapor and provides thrust. In this way, the capillaries become valves that can be turned on and off by activating the heaters. The technology is similar to an inkjet printer, which uses heaters to push out droplets of ink.
“There have been substantial improvements made in micropropulsion technologies, but further reductions in mass, volume, and power are necessary for integration with small spacecraft,” Alexeenko says. The FEMTA technology is a micro-electromechanical system, or a MEMS, which are tiny machines that contain components measured on the scale of microns, or millionths of a meter. The thruster demonstrated a thrust-to-power ratio of 230 micronewtons per watt for impulses lasting 80 seconds.
“This is a very low power,” Alexeenko says. “We demonstrate that one 180-degree rotation can be performed in less than a minute and requires less than a quarter watt, showing that FEMTA is a viable method for attitude control of CubeSats.” The FEMTA thrusters are microscale nozzles manufactured on silicon wafers using nanofabrication techniques common in industry. The model was tested in a large vacuum chamber. Although the researchers used four thrusters, which allow the satellite to rotate on a single axis, a fully functional satellite would require 12 thrusters for 3-axis rotation.
Engineers Of Samara University Presented A electrothermal Propulsion System For Nanosatellites
The scientists of the Inter-University Department of Space Research of Samara University presented a prototype of a propulsion system for the maneuvering nanosatellite SamSat-M.
The presented propulsion system for the maneuvering nanosatellite SamSat-M (its dimensions are 10x10x30 cm) is electrothermal. The scientists proposed a mixture of distilled water and ethyl alcohol as the working body of the propulsion system. Their choice was explained by the fact that a small molecular mass of water allows obtaining high rates of steam outflow, and, accordingly, a high maneuvering speed. And the addition of alcohol (about 40% of the mixture) prevents the working body from freezing at low temperatures in near-Earth orbits. According to the developers, such mixture is safe, since it does not contain self-igniting components, it is non-toxic and does not cause environmental damage.
The use of the propulsion system greatly expands the capabilities of the nanosatellites. As part of a grouping in outer space, they can solve applied problems, which cannot be solved by a single spacecraft. Thus, a group of nanosatellites can study geophysical fields, the thermosphere and the ionosphere of the Earth to predict natural disasters, to detect an asteroid hazard, and to inspect the state of spacecraft in space.
CubeSat to test harnessing Earth’s magnetic field for propulsion
Scheduled to launch from the Mojave Air and Space Port on Virgin Orbit’s Launch Demo 2 on January 10, 2020, the Miniature Tether Electrodynamics Experiment-1 (MiTEE-1) will test the concept of using the Earth’s magnetic field to generate thrust.
The MiTEE project will test the feasibility of using electromagnetism to provide propulsion by stringing a wire tether 33 to 100 feet (10 to 30 m) long between two CubeSats. The idea is that solar panels would provide electricity, which would run through the wire. As the satellite orbits the Earth, the ionosphere completes the circuit and, because a force is exerted on a wire when it conducts a current in a magnetic field, the tether generates thrust that can be used to boost the spacecraft into a higher orbit. As the force isn’t very great, such an approach wouldn’t be feasible for larger satellites, but the hope is it will be enough to allow small satellites to compensate for the drag of the atmosphere.
The result of two and half years of work, MiTEE-1 won’t actually produce any thrust. Instead, it will consist of a satellite about the size of a loaf of breadbox and another about the size of a smartphone that deploys on a one-meter (33-in) rigid boom. This will measure how much current can be drawn from the ionosphere under various conditions. The data from the mission will be used for planning and building the next MiTEE satellite, which will demonstrate the electric propulsion system concept in operation.
Propulsion Market
The global space propulsion market size was USD 6.23 billion in 2020. The market is expected to grow from USD 7.31 billion in 2021 to USD 19.74 billion in 2028, exhibiting a CAGR of 15.24% during the forecast period. The global LEO-focused satellite propulsion technology market is expected to reach $13,212.7 million by 2031, with a CAGR of 6.98% during the forecast period 2021- 2031
The space propulsion market faced a slight decline from 2018 to 2019 due to a decrease in the number of space launches. COVID-19 has also affected the space industry’s import and export trading activities. However, the expected rise in space launches from 2021 and beyond will drive the space propulsion market.
Rise in demand for low earth orbit-based services, surge in space exploration missions, and increase in demand for satellite data have boosted the growth of the global space propulsion system market. However, issues regarding space debris and increase in emission due to number of space launches hinder the market growth.
The market is driven by factors such as an increase in the number of space exploration missions, demand for LEO-based services, and increasing demand for advanced electric propulsion systems. The increasing number of satellite constellations for applications such as communication, technology development, Earth observation, and remote sensing is expected to be the major driving factors for the market. In addition, increasing demand for building efficient propulsion systems at low cost are key drivers for the growth of the global LEO-focused satellite propulsion technology market.
Market Segmentation
The commercial end user segment is estimated to dominate the global LEO-focused satellite propulsion technology market due to the increasing development of small satellite constellations for communication, remote sensing, Earth observation, and navigation by commercial industries.
The growth of the government & defense segment can be attributed to increasing space exploration missions and rising space budgets. Defense organizations support the use of various types of satellites, such as remote sensing satellites, communication satellites, and surveillance satellites, for military operations and cyber operations.
Support operations usually involve the launch of satellites with high-value payloads in space through Expendable Launch Vehicles (ELVs). They also ensure monitoring by facilitating the friendly use of space for various operations, such as surveillance, protection, and space intelligence analysis. For instance, the US Air Force regularly launches GPS and missile-defense tracking satellites and operates two classified X-37B robotic space planes.
By platform, the satellite segment is estimated to be the largest and fastest-growing segment in the space propulsion market. The growth of this segment can be attributed to rising small satellite launches for commercial and government applications. Large satellites, medium satellites, CubeSats, and small satellites, including nanosatellites, microsatellites, and minisatellites, play an important role in Earth observation, communication, and meteorology applications. These satellites are capable of monitoring cyclones, storms, El Niño, floods, fires, volcanic activities, earthquakes, landslides, oil slicks, environmental pollution, and industrial and power plant disasters.
By system component, the thrusters segment is projected to lead the space propulsion market in 2020. The growth of this segment can be attributed to the extensive use of propulsion thrusters for the maneuvering and orbit control of satellites. Chemical propulsion thrusters are primarily used for attitude control applications, whereas electric propulsion thrusters are widely used to extend the operational life of satellites and to reduce launch and operation costs.
Electric propulsion is the most prominent propulsion system contributing to the global LEO-focused satellite propulsion technology market.It is anticipated that, by 2031, the market penetration of electric satellites will grow to more than 40% in the overall satellite launches.
However, the high cost, development complexity, and low thrust capability are restraining the growth of the electric propulsion system segment. However, technological advancements are anticipated to overcome these challenges, and electric propulsion systems are anticipated to witness huge growth.
North America is expected to account for the highest share of the global LEO-focused satellite propulsion technology market, owing to a significant number of companies based in the region, increased spending by government and commercial organizations such as the National Aeronautics and Space Administration (NASA), Aerojet Rocketdyne, Ariane Group, Exotrail, Space X, and Enpulsion for LEO-based propulsion systems.
Some of the major market players include Airbus S.A.S, Ariane Group, Aerojet Rocketdyne (Acquired by Lockheed Martin Corp.), Busek Co Inc., CU Aerospace, IHI Corporation (Japan), Lockheed Martin Corporation, L3Harris Technologies, Inc., Moog Inc., Nano Avionics, Northrop Grumman Corporation, OHB SE, Safran S.A. (France), Space Exploration Technologies Corp. (SpaceX), Thales Group
References and Resources include
https://aip.scitation.org/doi/full/10.1063/1.5007734
