Open main menu
Home
Random
Recent changes
Special pages
Community portal
Preferences
About Wikipedia
Disclaimers
Incubator escapee wiki
Search
User menu
Talk
Dark mode
Contributions
Create account
Log in
Editing
Hybrid-propellant rocket
(section)
Warning:
You are not logged in. Your IP address will be publicly visible if you make any edits. If you
log in
or
create an account
, your edits will be attributed to your username, along with other benefits.
Anti-spam check. Do
not
fill this in!
==Properties== Hybrid rocket motors exhibit some obvious as well as some subtle advantages over [[liquid-fuel rocket]]s and [[solid-fuel rocket]]s. A brief summary of some of these is given below: ===Advantages compared with liquid rockets=== * Mechanically simpler β requires only a single liquid propellant resulting in less plumbing, fewer valves, and simpler operations. * Denser fuel β fuels in the solid [[phase (matter)|phase]] generally have higher density than those in the liquid phase, reducing overall system volume. * Metal additives β reactive metals such as aluminium, [[magnesium]], [[lithium]] or [[beryllium]] can be easily included in the fuel grain increasing [[specific impulse]] (<math>I_{sp}</math>), density, or both. * Combustion instabilities β Hybrid rockets do not typically exhibit high frequency combustion instabilities that plague liquid rockets due to the solid fuel grain breaking up acoustic waves that would otherwise reflect in an open liquid engine combustion chamber. * Propellant pressurization β One of the most difficult to design portions of a liquid rocket system are the [[turbopumps]]. Turbopump design is complex as it has to precisely and efficiently pump and keep separated two fluids of different properties in precise ratios at very high volumetric flow rates, often cryogenic temperatures, and highly volatile chemicals while combusting those same fluids in order to power itself. Hybrids have far less fluid to move and can often be pressurized by a blow-down system (which would be prohibitively heavy in a liquid rocket) or self-pressurized oxidizers (such as [[nitrous oxide|N<sub>2</sub>O]]). * Cooling β Liquid rockets often depend on one of the propellants, typically the fuel, to cool the combustion chamber and [[nozzle]] due to the very high heat fluxes and vulnerability of the metal walls to oxidation and stress cracking. Hybrid rockets have combustion chambers that are lined with the solid propellant which shields it from the product gases. Their nozzles are often graphite or coated in ablative materials similarly to solid rocket motors. The design, construction, and testing of liquid cooling flows is complex, making the system more prone to failure. ===Advantages compared with solid rockets=== * Higher theoretical <math>I_{sp}</math> β Possible due to limits of known solid oxidizers compared to often used liquid oxidizers. * Less explosion hazard β Propellant grain is more tolerant of processing errors such as cracks since the burn rate is dependent on oxidizer mass flux rate. Propellant grain cannot be ignited by stray electrical charge and is very insensitive to auto-igniting due to heat. Hybrid rocket motors can be transported to the launch site with the oxidizer and fuel stored separately, improving safety. * Fewer handling and storage issues β Ingredients in solid rockets are often incompatible chemically and thermally. Repeated changes in temperature can cause distortion of the grain. Antioxidants and coatings are used to keep the grain from breaking down or decomposing. * More controllable β Stop/restart and [[Rocket engine#Throttling|throttling]] are all easily incorporated into most designs. Solid rockets rarely can be shut down easily and almost never have throttling or restart capabilities. ===Disadvantages of hybrid rockets=== Hybrid rockets also exhibit some disadvantages when compared with liquid and solid rockets. These include: * Oxidizer-to-fuel ratio shift ("O/F shift") β with a constant oxidizer flow-rate, the ratio of fuel production rate to oxidizer flow rate will change as a grain regresses. This leads to off-peak operation from a chemical performance point of view. However, for a well-designed hybrid, O/F shift has a very small impact on performance because <math>I_{sp}</math> is insensitive to O/F shift near the peak. * Poor [[Hybrid Rocket Fuel Regression|regression]] characteristics often drive multi-port fuel grains. Multi-port fuel grains have poor volumetric efficiency and, often, structural deficiencies. High regression rate liquefying fuels developed in the late 1990s offer a potential solution to this problem.<ref>{{cite web |title=Wax Hybrids |department=Science@NASA |publisher=National Aeronautics and Space Administration (NASA) |url=https://science.nasa.gov/headlines/y2003/28jan_envirorocket.htm |url-status=dead |access-date=June 1, 2009 |archive-url=https://web.archive.org/web/20090523003320/http://science.nasa.gov/headlines/y2003/28jan_envirorocket.htm |archive-date=May 23, 2009}}</ref> * Compared with liquid-based propulsion, re-fueling a partially or totally depleted hybrid rocket would present significant challenges, as the solid propellant cannot simply be pumped into a fuel tank. This may or may not be an issue, depending upon how the rocket is planned to be used. In general, much less development work has been completed with hybrids than liquids or solids and it is likely that some of these disadvantages could be rectified through further investment in [[research and development]]. One problem in designing large hybrid orbital rockets is that [[turbopump]]s become necessary to achieve high flow rates and pressurization of the oxidizer. This turbopump must be powered by something. In a traditional liquid-propellant rocket, the turbopump uses the same fuel and oxidizer as the rocket, since they are both liquid and can be fed to the pre-burner. But in a hybrid, the fuel is solid and cannot be fed to a turbopump's engine. Some hybrids use an oxidizer that can also be used as a [[monopropellant]], such as [[hydrogen peroxide]], and so a turbopump can run on it alone. However, [[hydrogen peroxide]] is significantly less efficient than [[liquid oxygen]], which cannot be used alone to run a [[turbopump]]. Another fuel would be needed, requiring its own tank and decreasing rocket performance.
Edit summary
(Briefly describe your changes)
By publishing changes, you agree to the
Terms of Use
, and you irrevocably agree to release your contribution under the
CC BY-SA 4.0 License
and the
GFDL
. You agree that a hyperlink or URL is sufficient attribution under the Creative Commons license.
Cancel
Editing help
(opens in new window)