Notes from Zubrin
ENTERING SPACE, Creating a Spacefaring Civilization by Robert Zubrin.
(Many thanks to Mr. Zubrin for a wonderful book, and many apologies for any mistrakes which might be unintentionally placed in following material which freely extracts from his text. Any such misteaks are entirely my fault and not the fault of Mr. Z or anyone else.)
Page 35. FOCUS ON: FUNDAMENTALS OF ROCKETRY AND SPACEFLIGHT.
Newton's law of reation. By expelling mass at high velocity to rear of space vehicle, an equal amount of momentum contributes to the forward direction of travel. Resultant thrust (T) is simply product of propellant mass flow times exhaust velocity.
Eq. 1: Thrust = propellant mass flow * exhaust velocity.
T = m C
I'll take the liberty of restating same concept with different terms which I've previously used.
For propellant mass flow, I'll use fuel flow per sec, ffsec.
For exhaust velocity, use vExh.
Thus, very same equation, restated as follows
T = ffsec * vExh
The higher the exhaust velocity, the greater the thrust. Thus, rocket engineers use exhaust velocity to rate rocket engines by "specific impulse" (Isp) defined as number of seconds a pound of propellant can deliver a pound of thrust.
Stated another way:
Isp is the number of seconds a quantity of propellant produces its own weight in thrust.
A common factor between thrust and weight is the force of gravity.
Force equals mass times acceleration, f = m a.
Force of gravity equals mass times acceleration due to gravity, f = m g.
Numerous observations result in the axiom that free fall due to near Earth gravity is 9.8 meters per second per second (g=9.8 m/sec2). For convenience, I'll subsequently use g=10 m/sec2.
The term, g, can be a common factor between thrust and weight, because thrust is often rated as a weight related unit such as "pounds". Term, g, can also be a common factor between specific impulse and propulsion particle velocity,
Eq. 2.
vExh = g * Isp.
Isp = vExh / g
Specific impulse - Wikipedia, the free encyclopedia Specific impulse (usually abbreviated Isp) is a way to describe the efficiency of rocket and jet engines. It represents the impulse (change in momentum) per ...en.wikipedia.org/wiki/Specific_impulse - 33k - Cached - Similar pages
Variable specific impulse magnetoplasma rocket - Wikipedia, the ... The variable specific impulse magnetoplasma rocket (VASIMR) is a hypothetical form of spacecraft propulsion that uses radio waves and magnetic fields Cached - Similar pages[ More results from en.wikipedia.org ]
Specific Impulse We can divide this equation by the weight of the propellants to define the specific impulse. The word "specific" just means "divided by weight". ...www.grc.nasa.gov/WWW/K-12/airplane/specimp.html - 13k - Cached - Similar pages
What is specific impulse? Specific impulse is the change in momentum per unit mass for rocket fuels, or rather how much more push accumulates as you use that fuel. ...www.qrg.northwestern.edu/projects/vss/docs/Propulsion/3-what-is-specific-impulse.html - 5k - Cached - Similar pages
How do you calculate specific impulse? To calculate the specific impulse, we first need to calculate the exhaust velocity. Since the real exhaust velocity is exceeding complex to calculate, ...www.qrg.northwestern.edu/projects/vss/docs/Propulsion/3-how-you-calculate-specific-impulse.html - 7k - Cached - Similar pages
Rocket Engine Specific Impulse Program Specific Impulse (Isp) is a measure of the “fuel efficiency” of a rocket. The necessary thermodynamic calculations for Isp are performed by a package of ...www.dunnspace.com/isp.htm - 183k - Cached - Similar pages
Specific Impulse Inc. Information Architecture, Web Development ... Specific Impulse: Information Architecture, Web Site Design, and Intranet and Web Site Management Solutions.www.si9.com/ - 22k - Cached - Similar pages
NASA Tech Briefs - Variable-Specific-Impulse Magnetoplasma Rocket NASA Tech Briefs, This rocket is expected to enable long-term human exploration of outer space. Johnson Space Center has been leading the development of a ...www.techbriefs.com/content/view/1768/32/ - 41k - Cached - Similar pages
PROPELLANTS Chemical propellants in common use deliver specific impulse values ranging from about 175 up to ...
Plasma Propulsion in Space: http://www.tipmagazine.com/tip/INPHFA/vol-6/iss-5/p16.pdf
Specific impulse of some typical chemical propellants 1 ...www.hq.nasa.gov/office/pao/History/conghand/propelnt.htm - 16k - Cached - Similar pages
(Many thanks to Mr. Zubrin for a wonderful book, and many apologies for any mistrakes which might be unintentionally placed in following material which freely extracts from his text. Any such misteaks are entirely my fault and not the fault of Mr. Z or anyone else.)
Page 35. FOCUS ON: FUNDAMENTALS OF ROCKETRY AND SPACEFLIGHT.
Newton's law of reation. By expelling mass at high velocity to rear of space vehicle, an equal amount of momentum contributes to the forward direction of travel. Resultant thrust (T) is simply product of propellant mass flow times exhaust velocity.
Eq. 1: Thrust = propellant mass flow * exhaust velocity.
T = m C
I'll take the liberty of restating same concept with different terms which I've previously used.
For propellant mass flow, I'll use fuel flow per sec, ffsec.
For exhaust velocity, use vExh.
Thus, very same equation, restated as follows
T = ffsec * vExh
The higher the exhaust velocity, the greater the thrust. Thus, rocket engineers use exhaust velocity to rate rocket engines by "specific impulse" (Isp) defined as number of seconds a pound of propellant can deliver a pound of thrust.
Stated another way:
Isp is the number of seconds a quantity of propellant produces its own weight in thrust.
A common factor between thrust and weight is the force of gravity.
Force equals mass times acceleration, f = m a.
Force of gravity equals mass times acceleration due to gravity, f = m g.
Numerous observations result in the axiom that free fall due to near Earth gravity is 9.8 meters per second per second (g=9.8 m/sec2). For convenience, I'll subsequently use g=10 m/sec2.
The term, g, can be a common factor between thrust and weight, because thrust is often rated as a weight related unit such as "pounds". Term, g, can also be a common factor between specific impulse and propulsion particle velocity,
Eq. 2.
vExh = g * Isp.
Isp = vExh / g
Specific impulse - Wikipedia, the free encyclopedia Specific impulse (usually abbreviated Isp) is a way to describe the efficiency of rocket and jet engines. It represents the impulse (change in momentum) per ...en.wikipedia.org/wiki/Specific_impulse - 33k - Cached - Similar pages
Variable specific impulse magnetoplasma rocket - Wikipedia, the ... The variable specific impulse magnetoplasma rocket (VASIMR) is a hypothetical form of spacecraft propulsion that uses radio waves and magnetic fields Cached - Similar pages[ More results from en.wikipedia.org ]
Specific Impulse We can divide this equation by the weight of the propellants to define the specific impulse. The word "specific" just means "divided by weight". ...www.grc.nasa.gov/WWW/K-12/airplane/specimp.html - 13k - Cached - Similar pages
What is specific impulse? Specific impulse is the change in momentum per unit mass for rocket fuels, or rather how much more push accumulates as you use that fuel. ...www.qrg.northwestern.edu/projects/vss/docs/Propulsion/3-what-is-specific-impulse.html - 5k - Cached - Similar pages
How do you calculate specific impulse? To calculate the specific impulse, we first need to calculate the exhaust velocity. Since the real exhaust velocity is exceeding complex to calculate, ...www.qrg.northwestern.edu/projects/vss/docs/Propulsion/3-how-you-calculate-specific-impulse.html - 7k - Cached - Similar pages
Rocket Engine Specific Impulse Program Specific Impulse (Isp) is a measure of the “fuel efficiency” of a rocket. The necessary thermodynamic calculations for Isp are performed by a package of ...www.dunnspace.com/isp.htm - 183k - Cached - Similar pages
Specific Impulse Inc. Information Architecture, Web Development ... Specific Impulse: Information Architecture, Web Site Design, and Intranet and Web Site Management Solutions.www.si9.com/ - 22k - Cached - Similar pages
NASA Tech Briefs - Variable-Specific-Impulse Magnetoplasma Rocket NASA Tech Briefs, This rocket is expected to enable long-term human exploration of outer space. Johnson Space Center has been leading the development of a ...www.techbriefs.com/content/view/1768/32/ - 41k - Cached - Similar pages
PROPELLANTS Chemical propellants in common use deliver specific impulse values ranging from about 175 up to ...
Plasma Propulsion in Space: http://www.tipmagazine.com/tip/INPHFA/vol-6/iss-5/p16.pdf
Specific impulse of some typical chemical propellants 1 ...www.hq.nasa.gov/office/pao/History/conghand/propelnt.htm - 16k - Cached - Similar pages
posted by JimODell at 6:02 AM
0 Comments:
Post a Comment
<< Home