Hydrazine has dominated the space industry as the choice of propellant for over six decades, due to its high-performance characteristics, despite its environment and health hazards and the challenges faced in its manufacturing, storage, ground handling and transportation. Hydrazine based propulsion systems are state-of-the-art for various applications ranging from launchers to large and small satellites. They have a long and successful heritage and a great variety of space qualified, off-the-shelf components.
However being a toxic compound of nitrogen and hydrogen that is on the EU’s list of substances of high concern. It is also the suspected cause of abnormally high rates of hormonal and blood disorders around the Baikonur rocket launch site in Kazakhstan. Hydrazine was identified as a substance of high concern by the REACh regulation in 2011 there is a threat that these systems might be forbidden in the future.
One aspect of clean space is to use more green / eco-friendly or non-toxic propellants to replace classical toxic hydrazine based systems. The need for nontoxic propellants is increasing not only since classical, hydrazine based propulsion systems are facing legislative regulations but also because non-toxic alternatives can offer significant technical and economical assets. Space agencies are trying to replace the conventional hydrazine rocket fuel, a highly toxic and carcinogenic chemical, with a greener propellant for future missions. These technologies present performance benefits such as reduced launch mass, increased scientific payload mass, and/or extending on-orbit lifetimes. The advantages are further reinforced due to the significant reduction in health risks encountered during launch site and ground handling operations.
NASA and Ball Aerospace & Technologies Corp. of Boulder, Colorado, are collaborating on the Green Propellant Infusion Mission, which seeks to improve overall propellant efficiency while reducing the handling concerns associated with the highly toxic fuel, hydrazine.
Through the Green Propellant Infusion Mission, or GPIM, NASA is developing a “green” alternative to conventional chemical propulsion systems for next-generation launch vehicles and spacecraft. The GPIM payload will fly to space aboard a Ball compact small satellite or “smallsat.” The Green Propellant Infusion Mission is scheduled to launch in 2018. The GPIM project will demonstrate the practical capabilities of a Hydroxyl Ammonium Nitrate fuel/oxidizer blend, known as AF-M315E or HAN. This innovative, low-toxicity propellant, developed by the U.S. Air Force Research Laboratory at Edwards Air Force Base, California, is a high-performance, green alternative to hydrazine.
AF-M315E also is expected to improve overall vehicle performance. It boasts a higher density than hydrazine, meaning more of it can be stored in containers of the same volume. In addition, it delivers a higher specific impulse, or thrust delivered per given quantity of fuel, and has a lower freezing point, requiring less spacecraft power to maintain its temperature. It also requires fewer handling restrictions and potentially shorter launch processing times, resulting in lowered costs.
Scientists at the Indian Space Research Organisation (ISRO) have reported progress in the development of an environment-friendly propellant to power satellites and spacecraft. Initial tests by a research team at the Liquid Propulsion Systems Centre (LPSC) here have shown promising results in the formulation and associated tests of a propellant blend based on hydroxylammonium nitrate (HAN).
The LPSC team comprising Arpita Dash, B. Radhika and R. Narayan formulated the HAN-based monopropellant and carried out a variety of tests to investigate its characteristics, like thermal and catalytic decomposition and compatibility with different materials. A monopropellant is a chemical propulsion fuel which does not require a separate oxidizer. It is used extensively in satellite thrusters for orbital correction and orientation control. The in-house formulation consists of HAN, ammonium nitrate, methanol and water. While methanol was added to reduce combustion instability, the choice of AN was dictated by its capacity to control the burn rate and lower the freezing point of the propellant.
Scientists at the German Aerospace Centre (DLR) in Lampoldshausen are working on new, greener fuels that can future-proof space exploration methods and make them environmentally friendly. The efforts are centred around a compound known as ammonium dinitramide (ADN), which when heated decomposes into only nitrogen, oxygen, and water. ‘ADN was an oxidiser salt first found in the Soviet Union, but was rediscovered in Sweden in the 1990s where they had the idea to develop it into a liquid propellant,’ said Dr Michele Negri, leader of a space propulsion project called RHEFORM.
There are two primary green propulsion candidate technologies, AF-M315E and LMP-103S, that align with the needs of historical Goddard Space Flight Center (GFSC) missions. Each candidate propulsion technology offers increased performance over hydrazine monopropellant propulsion, reduces personnel and environmental hazards, and simplifies transport and handling for ground operations. Other technologies such as Nitrous Oxide Fuel Blend (NOFBX) or hydrogen peroxide either do not improve performance, or do not reduce safety concerns.
The term “ADN Technology” is used for a liquid monopropellant where solid oxidizer (ADN – Ammonium dinitramide salt) is solved in water and then fuel and stabilizer are added. In the combustion chamber the oxidizer and fuel are burned with subsequent high combustion temperatures. ECAPS LMP-103S Technology: LMP-103S is a liquid propellant where the solid oxidizer (ADN) is solved in water and Ethanol is used as fuel. The ADN technology is closely linked to the Swedish company ECAPS that developed the propellant LMP-10S and subsequent thrusters which are for the first time used on a commercial mission.
The problem is that ADN is a salt, so it is solid. While it can be dissolved into other fuels like methanol or ammonia, it takes a high temperature – more than 1500ºC – to ignite it. Hydrazine thrusters do not require pre-heating, if you just open the valves then they start firing. On the other hand, with an ADN thruster if you just open the valve the blend would come out in liquid form. It would not react,’ Dr Negri said. The RHEFORM project looked at the ADN-based propellant LMP-103S used by a Swedish space company called ECAPS, which was a project partner and has already launched 13 propulsion systems based on the compound.
Hydroxyl Ammonium Nitrate fuel/oxidizer blend, known as “AF-M315E.”
Hydroxyl Ammonium Nitrate fuel/oxidizer blend, known as “AF-M315E.” This innovative, low-toxicity propellant, developed by the U.S. AFRL (Air Force Research Laboratory) at Edwards Air Force Base, CA, is a high-performance, green alternative to hydrazine. AF-M315E has significantly reduced toxicity levels compared to hydrazine, making it easier and safer to store and handle. It also requires fewer handling restrictions and potentially shorter launch processing times, resulting in lowered costs.
AF-M315E also is expected to improve overall vehicle performance. It boasts a higher density than hydrazine, meaning more of it can be stored in containers of the same volume. In addition, it delivers a higher specific impulse, or thrust delivered per given quantity of fuel, and has a lower freezing point, requiring less spacecraft power to maintain its temperature.
Hydrogen peroxide is a chemical compound with the formula (H2O2). In its pure form it is a colourless liquid, slightly more viscous than water. Hydrogen peroxide is a strong oxidizer and is used as a bleaching agent and disinfectant. Concentrated hydrogen peroxide, or ‘high-test peroxide’ (HTP) is used as a rocket propellant since 1934. Currently HTP is being used on the Sojuz Launcher for the first stage gas generator and on the Sojuz capsule for the reaction control thrusters used during re-entry. In the frame of the H2020 project HYPROGEO the manufacturing and transport of 98% was qualified and this propellant blend is now commercially available on the market.
Water propulsion is defined as propulsion that uses water as a stored propellant which is decomposed into gaseous Oxygen and Hydrogen via an electrolyser in orbit. These gases are then exothermic combusted for generation of thrust. It is a semi electric propulsion where propellant is generated over a longer time period with low power and is then exploited during short boost.
However green propellants like AF-M315E and LMP-103S have operational restrictions that do not exist for hydrazine propulsion systems. The main operational restriction for both systems, is that the thruster must be preheated. There is no cold start capability for either type of thruster. This is a significant restriction, since a common contingency requirement for hydrazine thrusters is to be able to detumble a spacecraft when it comes off the launch vehicle, and the thrusters often cannot be preheated to meet this requirement.
With the higher temperatures, materials in the thrusters are likely to be more expensive, driving the cost of the thrusters significantly higher than hydrazine thrusters. Although the hardware is likely more expensive, the savings for ground operations are significant. In addition, when environmental aspects of the complete life-cycle costs are considered, there are additional significant savings, as analysed by Eric H. Cardiff, Henry W. Mulkey, and Caitlin E. Bacha, of NASA Goddard Space Flight Center.
Novel gel propulsion to slash cost of communication satellites
Propelling the largest of those satellites requires costly and highly toxic jet fuel, while launching smaller satellites requires other liquid fuels that could benefit from improvement. Israeli startup NewRocket is developing gel propulsion – a cheaper, more environmentally friendly rocket-engine technology offering the same level of performance and control as toxic “legacy fuel” and a better solution for smaller satellites, too. Prof. Benny Natan at the Technion-Israel Institute of Technology has developed gel technology that fits between the two existing propulsion alternatives: solid fuel, which burns for a single burst to launch rocket ships, and liquid fuel such as hydrazine, typically used to position satellites.
The NewRocket gel is based on standard liquid kerosene airplane fuel. “It’s much more ‘green’ than any other material used today in space. The stable gel provides several attributes that offer very cheap, flexible and powerful propulsion. It will open the door for many applications in space,” says Privman. He estimates that compared to legacy fuel, gel fuel could lower the overall cost of the satellite system and operation by five times. The weight of the gel fuel is similar to liquid fuel but it’s safer to transport
The fast-growing international private communications satellite market is the main focus for NewRocket. “Companies like OneWeb and SpaceX are building smaller, cheaper satellites that orbit Earth 100 times closer than the big communications satellites so they can provide very fast Internet data services to every cellphone on the globe. We are enablers for this industry,” says Privman. He notes that smaller satellites need more powerful alternatives than they have now, and makers of the larger billion-dollar communications satellites also seek safer, greener solutions.
“Current liquid fuels used on satellites are made of very hazardous materials because they need to be very powerful,” Privman says. “Therefore, many precautions need to be taken when handling the fuel. For the last decade, the space industry has been searching for something less toxic.”
Astranis selects ECAPS green propulsion for geostationary communications constellation
Astranis, a startup developing geostationary satellites to offer broadband internet access, announced plans June 14 to equip its MicroGEO spacecraft with Bradford of the Netherland’s high performance green ECAPS thrusters.
“This is a huge step towards abolishing hydrazine from spacecraft worldwide,” Ian Fichtenbaum, Bradford ECAPS director, told SpaceNews by email. “We think once people realize that there is an operational hydrazine alternative (with better performance than hydrazine) currently being used almost nobody will want to go back to hydrazine.”
Under the agreement, Astranis will purchase eight ECAPS thrusters for each MicroGEO satellite. The initial order covers as many as 12 spacecraft. In addition, the agreement calls for Bradford’s Space Group to supply the Astranis constellation with electrical propulsion feed systems and a set of eight Cosine Sun Sensors for attitude control.
Astranis plans to launch dozens of 300-kilogram satellites to provide capacity of up to 10 gigabits per second to underserved communities. In March, the San Francisco-based startup announced it raised $18 million in Series A funding.
“The ECAPS technology is mature and ready to be deployed on a large scale,” John Gedmark, Astranis founder and chief executive, said in a statement. “Their team impressed us with their ability to move quickly and their ability to execute.”
The deal marks the introduction of ECAPS, which stands for Ecological Advanced Propulsion Systems, to geostationary orbit, which is dominated by large telecommunications satellites with hydrazine-fueled thrusters. ECAPS thrusters burn LMP-103S, a storable liquid monopropellant that blends ammonium dinitramide with water, ammonia and methanol.
Because ECAPS is less toxic than conventional propellants, Astranis will be able to fuel satellites in its factory rather than at the launch site, Fichtenbaum said. “Hydrazine thrusters cannot be fueled at the factory because of toxicity, handling and transportation [requirements], but the ECAPS propellant can,” he added.
The Astranis agreement is one of the largest orders to date for ECAPS. Bradford also supplies ECAPS thrusters for San Francisco-based Planet’s SkySat Earth imaging constellation, Fichtenbaum said.
A dozen satellites have used ECAPS propulsion systems in orbit and several more, including imaging satellites and U.S. government spacecraft, slated for launch later this year will employ the technology, according to the Bradford announcement.
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