This article highlights the importance of green propellant and how it can increase the rideshare opportunity for spacecraft that require chemical propulsion.
It also highlights Rubicon Space Systems‘ product lines of thrusters and propulsion systems.
This piece is developed in collaboration with Rubicon Space Systems, a paying participant in the satsearch membership program.
Introduction
The space industry continues to transition from traditional heavy systems to new, smaller spacecraft systems. This has brought about several changes in the technology, including propulsion. The rising wave of rideshare missions, a cost-effective approach to space missions, involves launching multiple payloads on a single launch vehicle. With so many payloads now co-manifested on a single launch vehicle, it is necessary to manage and balance the multiple competing interests, risks, and hazards that payloads may pose to the launch vehicle and each other – not to mention, the drop-off location is up to the launch provider as opposed to where the payload customer needs to be to accomplish their mission. Let’s consider propulsion. According to National Aeronautics and Space Administration (NASA) and United States Air Force (USAF)/ United States Space Force (USSF), traditionally used chemical propellant called hydrazine poses significant risks and safety hazards to both the launch vehicle, payloads onboard and humans ground testing / integrating systems with hydrazine onboard. Green propellants have the potential to increase the rideshare opportunity for smallsats that require chemical propulsion and safety.
In this article, we will take a deeper look into this topic as well as a high-performance, low toxicity “green” monopropellant that addresses the hazards that rideshare missions must navigate called ASCENT. We will also take a look at one company, Rubicon Space Systems, who has achieved flight heritage and whose product line is a compelling consideration for your payload.
ASCENT propellant and the benefits to rideshare missions
ASCENT (Advanced Spacecraft Energetic Non-Toxic) propellant, formerly known as AF-M315E, is an advanced monopropellant formulation developed by the Air Force Research Laboratory (AFRL) Rocket Propulsion Division (RQR). ASCENT delivers a 50% increase in density-specific impulse over the present state-of-the-art hydrazine monopropellant. In addition to its performance advantages, ASCENT decreases handling hazards compared to hydrazine. ASCENT is an ionic liquid (IL) derived of hydroxylammonium nitrate (HAN), water, and other compounds to yield a low-toxicity and highly stable mixture of negligible vapor pressure.
Rideshare missions have been essential in democratizing access to space. Historically, only a few commercial companies with significant resources and government organizations controlled the majority of space missions. With launch costs below $3,000 per kilogram, a wider spectrum of individuals and interests can now afford to participate in scientific research, technological advancement, and extraterrestrial exploration. This has ultimately led to an increase in the number of rideshare missions. Smaller businesses, start-ups, and educational institutions now have the opportunity to launch their payloads into space.
Propulsion systems are considered the most hazardous single subsystem of any spacecraft. Traditional chemical propellants like hydrazine have been used for decades, but such propellants are characterized as a “Catastrophic Hazard” per AFSPCMAN 91-710. Even a minor leakage of hydrazine vapor could result in severe damage to the launch vehicle and every other mission that is part of that launch. That is why ASCENT, a low toxicity “green” and safe propellant is gaining prominence.
Some other benefits of ASCENT includes:
- Preeminent performance: ASCENT demonstrates a nearly 50% increased performance over hydrazine. Factor in its volumetric-ISP, and ASCENT monopropellants have MMH/NTO bi-prop level performance with the simplicity of a monopropellant.
- Simpler systems: A hydrazine fuel leak is considered “catastrophic,” whereas ASCENT propellant hazard severity is considered “critical” and possibly “marginal” per MIL-STD-882E (Standard Practice for System Safety). This means that an ASCENT propulsion systems requires only two seals to inhibit external leakage, meaning no additional latch valves or other isolation devices are required.
- Fueling flexibility: ASCENT spacecraft fueling operations do not require Self-Contained Atmospheric Protective Ensemble (SCAPE) suits, meaning that fueling operations can be performed with greater flexibility and lower cost. And fueling operations may generally be permitted as a parallel operation, and requires only a smaller exclusionary zone, allowing for concurrent and accelerated launch readiness operations. ASCENT can be shipped cross country with your online shopping goods. ASCENT is classified as a 1.4C explosive (minor explosion hazard; largely confined to the package). Ground operations are significantly reduced due to the decreased hazard of ASCENT. Hydrazine requires more significant crew training, size, and personal protective equipment. Also, hydrazine requires more complex transfer equipment for spacecraft loading.
- Does not Freeze: Hydrazine has a similar freezing point to water and heaters must be kept on much of the time. ASCENT has an ultra-low minimum storage temperature. There is no need for long-duration system thermal management, unlike hydrazine. Save power for other uses, and only warm it up when you need to.
ASCENT Space Missions
To date, two missions have flown the ASCENT propellant – NASA’s Green Propellant Infusion Mission (GPIM, 2019) and Lunar Flashlight (LF, 2022). Both missions were part of rideshare missions. On both missions, NASA and the US Air Force characterized the propellant as a “Non-Catastrophic” Critical Hazard”, per AFSPCMAN 91-710. As a result of that characterization, those ASCENT propulsion systems employed fewer components than would have been required for hydrazine version.
This has the benefit of increasing system reliability and reducing costs. The potential hazard to the launch vehicle, personnel, and other rideshare payloads was assessed as low, even if there was a leakage of propellant. AF-M315E derives its low-toxicity-hazard characteristics and high mixture stability (even to very low temperatures) from the high solubility and negligible vapor pressure of all solution constituents, such that indefinite exposure to the open environment poses no safety issue. Lunar Flashlight’s propulsion system, whose thrusters were produced by Rubicon Space Systems, was fueled and shipped across the US to the launch site and loaded onto the launch vehicle.
Rubicon Space Systems
In 2022, the propulsion division of Plasma Processes LLC was rebranded as Rubicon Space Systems and given the mandate to commercialize its line of thrusters and develop a line of propulsion systems for the small satellite industry. Rubicon Space Systems is a developer and provider of in-space propulsion systems and thrusters that use ASCENT. With more than 30 years of combined experience in green propulsion and thousands of hours of thruster testing experience, Rubicon leads the world in the development and commercialization of ASCENT-propulsion technology.
Selecting the right product for your mission
The success in the operation of any space mission is not only assured by the quality of components and systems used in the mission. You must also select the right component as per mission requirements, and also consider cost, rideshare opportunity, hazards, and logistics. Therefore, considering factors like the desired destination, payload capacity, mission duration, maneuverability needs, etc. are crucial before selecting the right propulsion system/thrusters for the mission. The entire space industry is also moving towards a good stewardship culture; now gradually adopting sustainable technologies as well as putting more spotlight on issues like space debris, the green propellants are the way ahead for the industry. Rubicon’s product lines of thrusters and propulsion systems are designed to serve the needs of small and large satellites alike. Rubicon Space Systems is a committed champion in creating a more verdant space economy. The company has multiple products available to suit differing mission requirements. Following is a partial list of products from Rubicon Space Systems:
The Rubicon Space Systems 0.1N High Throughput (HT) Thruster is designed to use in space systems. Rubicon's four 0.1N high throughput (HT) thrusters were successfully demonstrated in space from December 2022 through May 2023, accumulating more than 90 minutes of total firing (on) time and achieving expected nominal thrust and performance. It was developed through a NASA SBIR Phase I/II/III program.
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The Rubicon Space Systems 1N High Throughput (HT) Thruster is designed for propulsion applications in space systems. Through a US Space Force SPRINT BAA, Rubicon developed an instrumented 1N HT thruster to demonstrate these design processes and relative thermal characteristics, achieving record throughput and performance, accumulating over 1.4 hours of firing time, and ~1.6kg throughput, and more than 5700 pulses.
The Rubicon Space Systems 5N High Throughput (HT) Thruster is designed for space applications. Rubicon Space Systems is now on pace to complete flight qualification of the 5N HT thruster in mid-2024 and a target throughput of >100kg. Specific Impulse (Isp) on an engineering development unit (EDU) was measured at >260s. The first 5N HT thrusters will be assembled in late 2023 with the qualification campaign expected to be in mid-2024.
The Rubicon Space Systems 5N Low Throughput (LT) Thruster is designed for small satellite applications. Its design enables cheaper and faster manufacturability whilst still maintaining high performance, only sacrificing on total throughput. This low-throughput thruster design targets small satellite mission applications where their primary function would be orbit insertions, breaking maneuvers, and de-orbiting.
The Rubicon Space Systems Sprite Propulsion System is a self-contained plug-and-play designed module for satellite applications. Sprite fits a 10cm x 10cm x 15cm envelope plus a “tuna can.” The module is outfitted with an externally accessible fuel port allowing fueling after the module is integrated into the spacecraft. It can be fueled prior to integration or afterward, depending on the customer's requirement. It uses a single 0.1N ASCENT thruster in blow-down operation.
The Rubicon Space Systems Phantom Propulsion System is a large, self-contained propulsion module designed for space applications. The module is outfitted with an externally accessible fuel port. It uses four 0.1N ASCENT thrusters in pump-fed operation. Phantom delivers approximately 9000 Ns of total impulse with a mass of less than 10kg.
Conclusion
This article does not attempt to adjudicate all pros and cons of various propulsion options available to rideshare missions. It does attempt to demonstrate that for missions requiring high thrust chemical propulsion, ASCENT propellant technology is a compelling options that addresses the hazards that rideshare missions must navigate.
Rubicon’s advancements of ASCENT-based thrusters and propulsion systems, as well as the increased encouragement from agencies like NASA and US Space Force has significantly influenced the space industry to transition towards low-toxicity, and higher performance chemical propulsion systems. As the number of businesses and interests in the space economy increases, the number of rideshare will continue to increase as well. As that relates to propulsion, there is a clear need for safer, non-toxic propellant options.
To find out more about Rubicon Space Systems and for more information on its product and services portfolio, please view the company’s supplier hub on satsearch.