Carleton Hybrid Rocket Research Project
The Carleton Hybrid Rocket Research Project (CHRRP) is a student engineering group devoted to the study of hybrid rocket propulsion. Our goal is to collect data and develop innovations to aid in the design of more efficient rocket engines - for use both in engineering competitions and the burgeoning field of private spaceflight. We currently have six members and eagerly welcome more.
Hybrid rocket engines lie halfway between regular solid-fuelled and liquid-fuelled engines, burning a solid fuel (eg. synthetic rubber, paraffin wax) with a liquid oxidizer (eg. liquid oxygen, nitrous oxide). Hybrids offer numerous advantages over traditional engine designs, including simplicity, cost-effectiveness (inexpensive materials and propellants), reliability and - especially - safety. They are thus being extensively investigated by the private aerospace sector for potential use in low-cost space launch applications. Scaled Composites' SpaceShipOne - which made the first private manned spaceflight in 2004 - was hybrid powered, as is its successor,Virgin Galactic's SpaceShipTwo.
The cornerstone of CHRRP is a static test-bed hybrid rocket engine and test stand of our own design, which is currently being manufactured. Fully modular, this test equipment will allow us to study various aspects of engine design such as fuel composition, nozzle geometry and ignition/control systems. The engine and stand will be fully instrumented, allowing thrust, chamber pressure and temperature to be recorded and analyzed. Earlier this year, CHRRP was generously granted access to the R.W. Tomlinson concrete quarry in Nepean, where we can conduct test-firings in safety. In March 2011 we successfully demonstrated a simple prototype rocket engine at this test site.
CHRRP operates in cooperation with the University of Waterloo Space Society (WSS), which is currently manufacturing our test equipment. The data CHRRP collects with its test-bed engine will be used by the WSS to improve their rocket design for the Intercollegiate Rocket Engineering Competition (IREC). This competition, held every June in Green River, Utah, challenges competitors to launch a 10lb payload to an altitude of 10,000ft with the greatest possible accuracy. CHRRP will cooperate closely with the WSS in the development of next year's competition rocket and may eventually design and build a robust test-bed rocket for flight-testing rocket engine components and design innovations.
The static test equipment is estimated to be ready by September 2011. We will conduct a series of preliminary test-firings to refine the engine and calibrate the data-collection equipment before moving on to actual experiments.
Among the research topics CHRRP plans to investigate are:
Paraffin and 50P Fuels:
The traditional fuel for hybrid engines is HTPB, a synthetic rubber carried over from solid rocket motor technology. HTPB, however, is a relatively inefficient fuel and may soon be replaced by so-called liquefying fuels – such as paraffin wax – which deliver much higher performance. 50P is a 50/50 mix of Paraffin and HTPB that combines advantages of both fuels; research on this composition has thus far been limited.
Fixed-geometry rocket nozzles are optimized for only one altitude and will lose efficiency as the rocket climbs higher. One solution to this problem is the aerospike, an “inside-out” nozzle that automatically adjusts itself to atmospheric pressure and improving efficiency along a rocket's entire trajectory. Few aerospike nozzles have ever been flight-tested.
Regular hybrid engines have two main controls: a valve to control oxidizer flow into the combustion chamber and an igniter – usually a pyrotechnic charge – to start the engine burning. However, certain oxidizers commonly used in hybrids – specifically hydrogen peroxide and nitrous oxide – can decompose exothermically in the presence of a catalyst. If a catalyst bed is integrated into the oxidizer injector, the separate igniter can be dispensed with; the hot decomposed oxidizer exiting the catalyst bed will spontaneously ignite the fuel on contact. This reduces the engine controls to one, as the engine will ignite every time the oxidizer valve is opened. This technology was developed by researchers at Tsinghua University Taiwan but has not been widely investigated since.
One disadvantage of traditional hybrid engines is that the combustion chamber volume – and consequently the chamber pressure – changes as the solid fuel is consumed. Thus, thrust decreases with time during an engine burn. The boundary layer fuel-oxidizer mixing that occurs in hybrids is also inefficient compared to the diffusion mixing processes in liquid-fuelled engines. One solution to these problems is the aft-injected hybrid, in which a solid-fuel gas generator produces fuel-rich combustion products that are subsequently fed into a post-combustion chamber. Here, more oxidizer is injected to complete combustion. Mixing is thus improved and a steady chamber pressure can be maintained. Unfortunately, such designs tend to offset the simplicity and safety advantages that make hybrids attractive in the first place. CHRRP is currently working on developing simpler, safer designs for aft-injected hybrids.
Hybrids for Sounding Rockets:
Most sounding rockets (small rockets for high-altitude atmospheric research), such as the Canadian-manufactured Black Brant, utilize solid rocket motors. Though such motors are simple, reliable and can be stored for long periods, the hazardous nature of their fuel (essentially explosives) means they cannot be automatically mass-produced and are time and labour-intensive to manufacture. Hybrid engines are more complex and must be fuelled before launch, but are much safer and easier to manufacture than solid motors. CHRRP is currently investigating several hybrid engine designs with which to potentially replace solid motors in sounding rockets.
Modular Launch Systems:
In the 1970s, German engineer Lutz Kayser and his company OTRAG developed a modular launch system that promised to reduce orbital launch costs by tenfold. The system consisted of simple, self-contained rocket engine units that could be bundled together to create any size and power of launch vehicle desired. The engine units could be easily mass-produced, greatly reducing the cost of the launcher. Political pressure forced the company to disband, however, and the idea has not since been revived. Given the recent rise of the private space industry, however, the time may be ripe for the resurrection of the OTRAG concept. In the future, CHRRP hopes to build a subscale hybrid-based demonstration model of a modular launch system in order to re-evaluate this technology.
CHRRP Founder and Project Leader