Busek Company Selected for NASA Funding to Develop Spacecraft Advanced Propulsion

Busek Company will develop advanced CubeSat propulsion and Hall Effect thrusters (HETs) with the help of NASA funding.

The space agency has selected the Massachusetts-based company for five Small Business Innovation Research (SBIR) Phase 1 awards. The contracts are worth up to $125,000 apiece over 13 months.

The three proposals focused on CubeSats and small satellites include:

  • a low impulse bit electrospray thruster control system;
  • a compact high performance plasma propulsion system (CHPPPS); and,
  • an iodine-compatible photocathode for RF ion thrusters.

The passive electrospray thruster control “will enable extremely fast thruster operations and thereby unprecedented minimum impulse bits. Busek’s BET-300-P thruster is under active development as a precision reaction control system (RCS) which will provide orders of magnitude improvements over state-of-the-art alternative attitude control systems (ACS) for CubeSats and small spacecraft,” the proposal summary stated.

CHPPS is an electric propulsion system designed for 12U to 27U CubeSats. The system includes a low power HET, a hollow cathode for neutralizing the ion beam, a propellant management system, and a power processing unit (PPU).

” CHPPS is designed for high-value science missions which require high specific impulse, high reliability, and radiation tolerance….The proposed system would propel a small earth orbiting or interplanetary spacecraft, targeting 12U and 27U CubeSats and small satellites,” the summary said.

CubeSats deployed from the International Space Station. (Credit: NASA)

The third small-satellite proposal involves the use of iodine as an alternative to xenon in electric propulsion systems.

“It is easily stored in a compact volume on a spacecraft as a solid (greater than twice the storage density than pressurized xenon), which negates the need for a large pressurized tank.  This, combined with its low cost and lower ionization energy, make iodine an ideal propellant for a smallsat electric thruster system,” the summary stated.

“Busek currently is developing a line of gridded Radio-Frequency (RF) ion thrusters that utilize iodine as a propellant. In addition to their small size, the thrusters are low power and are compatible with solid-storable propellant iodine.  This makes the BIT thruster line a mission-enabling technology for situations where volume and mass are highly constrained,” the company said.

The two Hall Effect thruster projects selected for SBIR awards include:

  • a low-cost, lightweight power processing unit; and,
  • 3D printed advanced magnetic alloy (AMA) circuit components.

“Busek proposes to develop a low-cost, lightweight Hall Effect Thruster (HET) Power Processing Unit (PPU) at targeted 1kW/kg power density with more than 97% efficiency….This innovation will further miniaturize HET PPUs from today’s state-of-art by an anticipated 30% in volume and mass, with cost reductions exceeding 50% versus SOA solutions,” the summary stated.

In the second proposal, Busek will work on using 3D printing to improve HETs.

“In Phase I, Busek and Oak Ridge National Laboratory (ORNL) propose to study the feasibility of 3D printing AMA magnetic circuit components,” according to the proposal. “Our team will consider suitable additive manufacturing (AM) processes, including ebeam/laser AM processes, and a binderjet process with suitable binders. We will evaluate test coupons printed by ORNL by measuring their relevant magnetic properties and comparing them to those made using traditional machining methods.”

Summaries of the five selected proposals follow.


Proposal Title:
Low Impulse Bit Electrospray Thruster Control

Subtopic Title:
Cubesat Propulsion Systems

Small Business Concern
Busek Company, Inc.
Natick , MA

Principal Investigator
Daniel Courtney

Estimated Technology Readiness Level (TRL) :
Begin: 3
End: 4

Technical Abstract

Busek proposes to develop a new form of passive electrospray thruster control which will enable extremely fast thruster operations and thereby unprecedented minimum impulse bits. Busek’s BET-300-P thruster is under active development as a precision reaction control system (RCS) which will provide orders of magnitude improvements over state-of-the-art alternative attitude control systems (ACS) for CubeSats and small spacecraft.

The low inertia of CubeSats combined with vibrational disturbances and resolution limitations of state-of-the-art ACS presently limit precision body-pointing and position control. Busek’s electrospray thrusters aboard the ESA LISA Pathfinder (NASA ST-7) spacecraft, recently demonstrated control of a proof mass location to within ~2nm per root Hz over a wide band. The BET-300-P, enhanced by exploitation of its high-speed dynamic response in this program, seeks to extend that success to small spacecraft platforms.

Passively fed electrospray thrusters are highly compact, including fully integrated propellant supplies, and are capable of ~100nN thrust precision with 10’s of nN noise. Thrust can be accurately throttled over >30x, up to a scalable maximum of 10’s to 100’s of uN.  While typically operated in largely continuous states they are unique in that emission can be electrically stopped/started at ms time scales. Thus, extremely low impulse bits may be achieved over very short durations, permitting throttling from <0.1uNs up to 100’s of uNs. Realization of this fundamental capability of the technology is presently limited by control circuitry. The proposed work seeks to study and overcome these limitations with a new control methodology.

These traits, combined with >800s specific impulse, and thereby low propellant mass could enable these systems to replace traditional reaction wheel ACS and high-propellant mass cold gas systems; enabling milliarcsec control authority for CubeSats versus the present arcsec level SOA.

Potential NASA Applications

Ongoing NASA mission studies include the BET-300-P for attitude control, formation flight and positioning of small spacecraft. Specific benefiting applications include deep-space missions, astronomy, solar-system observations, laser communications and space situational awareness. Mission durations are extended by increased wheel desaturation capacity. Improved body pointing would augment stability; permitting lower cost/complexity realization of existing needs and enabling new objectives.

Potential Non-NASA Applications

Compact propulsion systems that are scalable in thrust and ΔV are an enabling technology for CubeSats and therefore have numerous commercial applications. The virtual elimination of vibrations while superseding reaction wheel precision is a clear competitive advantage. The precision pointing/positioning capabilities of the BET-300-P system are otherwise unavailable. Potential non-NASA customers include, international partners (such as ESA), the DoD and commercial EO missions.


Proposal Title:
Compact High Performance Plasma Propulsion System

Subtopic Title:
Cubesat Propulsion Systems

Small Business Concern
Busek Company, Inc.
Natick , MA

Principal Investigator
James Szabo

Estimated Technology Readiness Level (TRL) :
Begin: 2
End: 3

Technical Abstract

The Compact High Performance Plasma Propulsion System (CHPPPS) is an electric propulsion system for 12U – 27U CubeSats. CHPPS is designed for high-value science missions which require high specific impulse, high reliability, and radiation tolerance. CHPPPS includes a low power Hall Effect Thruster (HET), a hollow cathode for neutralizing the ion beam, a propellant management system, and a power processing unit (PPU).

The system is highly modular and appropriate for 12U – 27 U CubeSats in terms of size, mass, and power. CHPPPS may be as small as 4U, depending upon the fuel load and specific component selection. Thrust will be 3-8 mN, depending on the power supplied (60 – 135 W) and peak specific impulse will be >1100 s. The thruster will be fueled with xenon or with game-changing iodine, which stores as a solid at very low pressure and much higher density than xenon.

The use of iodine significantly decreases spacecraft dry mass, and dramatically decreases propellant volume. The impact of switching from xenon to iodine is most significant for volume limited spacecraft like CubeSats. Whether the thruster is fueled by xenon or by iodine, the ion beam will be neutralized by a hollow cathode flowing noble gas.

The thruster will be powered by a compact, radiation tolerant power processing unit (PPU) previously developed for NASA and Air Force applications. ACS may be provided by cold gas thrusters fed from the noble gas storage system. In Phase I, the system design will be detailed and studied.  Work will include a proof of concept hardware demonstration at relevant power levels.

Potential NASA Applications

The proposed system would propel a small earth orbiting or interplanetary spacecraft, targeting 12U and 27U CubeSats and small satellites.  Applications include orbit raising and lowering, compensating for drag at low altitude, de-orbiting a spacecraft at EOL, changing orbit inclination and phase, NS and EW station-keeping in GEO, and constellation deployment and maintenance.  The system also enables a low cost demonstration of HET magnetic shielding with iodine propellant.

Potential Non-NASA Applications

The integrated system will be actively marketed spacecraft platform providers, targeting CubeSats and small commercial buses.  Commercial and DoD applications include orbit raising and lowering, compensating for drag at low altitude, de-orbiting a spacecraft at EOL, changing orbit inclination and phase, NS and EW station-keeping in GEO, and constellation deployment and maintenance.


Proposal Title:
Iodine-Compatible Photocathode for RF Ion Thrusters

Subtopic Title:
Propulsion Systems for Robotic Science Missions

Small Business Concern
Busek Company, Inc.
Natick , MA

Principal Investigator
Lauren Rand

Estimated Technology Readiness Level (TRL) :
Begin: 1
End: 3

Technical Abstract

Iodine is highly attractive as an alternate electric propulsion propellant to xenon.  It is easily stored in a compact volume on a spacecraft as a solid (greater than twice the storage density than pressurized xenon), which negates the need for a large pressurized tank.  This, combined with its low cost and lower ionization energy, make iodine an ideal propellant for a smallsat electric thruster system.

Busek currently is developing a line of gridded Radio-Frequency (RF) ion thrusters that utilize iodine as a propellant.  In addition to their small size, the thrusters are low power and are compatible with solid-storable propellant iodine.  This makes the BIT thruster line a mission-enabling technology for situations where volume and mass are highly constrained.

The current generation of BIT thrusters use the BRFC-1, an RF-ion cathode to provide the neutralization current. The BRFC-1 consists of a miniaturized BIT-1 thruster, modified to extract electrons instead of ions.  This cathode realization has three main limitations: Power processing complexity, feed system complexity, and reduced system Isp (due to the need to flow propellant to the cathode that does not generate thrust).

We propose to develop a photocathode that will produce a current to both ignite and neutralize the Busek line of RF ion thrusters that is highly efficient and iodine compatible.  A photocathode emits electrons when struck by an incident light beam.  This cathode, when combined with an efficient UV light source, is predicted to significantly decrease the power requirements of the BIT thruster line while drastically improving Isp due to its propellantless operation.  The proposed work will measure the quantum efficiency of specially-fabricated photocathodes before and after iodine exposure to evaluate their potential as an RF thruster neutralizer technology.

Potential NASA Applications

A void exists for miniature thruster systems capable of delivering km/s delta-V for MicroSats. Many novel and new missions are achievable with high delta-V, low thrust propulsion systems. Example NASA missions include highly non-Keplerian orbits for communications, observation, and planetary transfers, such as lunar and deep space missions utilizing weak stability boundary transfers, Saturn Ring observer missions, and missions requiring spacecraft to ‘hover’ next to near-earth objects.

Potential Non-NASA Applications

Civil and DoD applications of highly non-Keplerian orbits enabled by electric propulsion include ‘polesitter’ type orbits for observation/communication with the Earth’s polar regions.  The Busek iodine RF ion engine system enables small, relatively low cost LEO, MEO, and GEO constellations and the technology provides a low risk method of demonstrating many novel orbital maneuvers.


Proposal Title:
Compact High Efficiency GaN-based PPU

Subtopic Title:
Power Electronics and Management, and Energy Storage

Small Business Concern
Busek Company, Inc.
Natick , MA

Principal Investigator
Xiaohu Liu

Estimated Technology Readiness Level (TRL) :
Begin: 2
End: 4

Technical Abstract

Busek proposes to develop a low-cost, lightweight Hall Effect Thruster (HET) Power Processing Unit (PPU) at targeted 1kW/kg power density with more than 97% efficiency. The proposed PPU solution adopts advanced GaN power MOSFETs and PCB based planar magnetics technology to enable high switching frequency operation. Reduced headcount of magnetics, semiconductors and associated driver integrated circuits will allow for significant size reduction of all passive components to support ultra-high power density designs. This innovation will further miniaturize HET PPUs from today’s state-of-art by an anticipated 30% in volume and mass, with cost reductions exceeding 50% versus SOA solutions.

The unique advantages of the proposed system can be summarized in three parts. First, the system utilizes a novel single-core multi-port circuit topology which integrates all the PPU subsystems through a single stage power conversion using a single multi-winding transformer. This significantly reduces system volume, weight, and cost.

Second, the power flow control for each subsystem is fully independent regardless of power stage sharing. Each subsystem has its own phase shift control to regulate the desired output voltage and current. Third, the proposed PPU circuit topology is essentially a soft-switching DC-DC converter which can ensure zero-voltage-switching operation for all the switching devices.

The proposal adopts the advanced GaN power MOSFETs and PCB based planar magnetics technology to enable high switching frequency operation, which supports a 30% size reduction of magnetics and other passive components in the high-efficiency and high-power density design.

In Phase II Busek will characterize the breadboard PPU with sub-kilowatt Hall thrusters and develop a proto-flight brass-board level unit using GaN devices. At the conclusion of Phase II, Busek will deliver a PPU to NASA for additional characterization testing.

Potential NASA Applications

HET systems are well suited for interplanetary transfers, supporting exploration and science missions. The Outer Planet Assessment Group identified high power density/high efficiency power electronics for its Titan/Enceladus Flagship and planetary exploration missions. These types of missions, including Mars Sample Return using Hall thrusters and PPUs, require advancements in power electronics. The proposed system meets requirements and is easily scalable, providing greater mission flexibility.

Potential Non-NASA Applications

EP systems have been identified as a key technology for transportation of DoD space assets for both orbit transfer and station keeping.  The AFRL IHPRPT Program continues to invest in the development of HET systems.

A high power density PPU could also find applications on an all-electric upper stage derived from Busek/ULA orbit maneuvering system, a free flying S/C based on the ESPA ring.


Proposal Title:
3D Printing Magnetic Circuit Components for Hall Effect Thrusters

Subtopic Title:
Propulsion Systems for Robotic Science Missions

Small Business Concern
Busek Company, Inc.
Natick , MA

Principal Investigator
Yu-Hui Chiu

Estimated Technology Readiness Level (TRL) :
Begin: 1
End: 3

Technical Abstract

The magnetic topography in Hall effect thrusters (HETs) plays an important role in focusing the electrons and controlling the plasma discharge which in turns governs the thruster performance. The magnetic circuit components constitute more than half of the thruster mass.

To produce low-mass thrusters, the design of the magnetic circuit needs to be optimized. The advanced magnetic alloy (AMA) is the material of choice for the ferromagnetic parts of an HET’s magnetic circuit. In addition to its superior magnetic properties, the AMA is also thought to be compatible with reactive propellants such as iodine.

Currently, traditional machining is employed to fabricate these ferromagnetic parts.  This results in removal of nearly 80% of the expensive bulk material which then goes unused.  Additionally, traditional machining can cause unwanted deformation on thin parts, reducing the production yield.

In Phase I, Busek and Oak Ridge National Laboratory (ORNL) propose to study the feasibility of 3D printing AMA magnetic circuit components.  Our team will consider suitable additive manufacturing (AM) processes, including ebeam/laser AM processes, and a binderjet process with suitable binders. We will evaluate test coupons printed by ORNL by measuring their relevant magnetic properties and comparing them to those made using traditional machining methods.

Additionally, we will apply relevant heat treatments to 3D printed test coupons and then re-measure their magnetic properties. The results will be compared to those made using traditional machining methods that were subjected to identical heat treatments. Based on the Phase I results, the best AM process will be down-selected to print a magnetic circuit component for the Busek 200W HET, with the goal of integrating it into the thruster in a potential Phase II program.

Potential NASA Applications

HETs enhance in-space maneuverability and payload capacity and are enabling for many NASA missions.  The ability to quickly manufacture complex geometries will allow for more flexibility in the design of the HET magnets.  AM will allow for more complex parts to be created and further optimization of the magnetic field which in turn will improve thruster performance.

Potential Non-NASA Applications

Improving the technique in fabricating HET magnetic circuit components will make Busek’s HET product more desirable to potential industry partners for flight missions.  Busek’s HETs span power levels from 100 W to 8 kW.  The low power Busek Hall thrusters are attractive propulsion options for highly capable small satellites.  Applications for high power Hall thrusters include orbit-raising and launch vehicle upper stages.

  • gunsandrockets

    Solid Iodine propellant? Cool!