
If you don't find the term you're looking for here, look in the GLOSSARY.
In the Basics of Space Flight, most abbreviations for units of measure are not spelled out the first time they are used, unlike the way other abbreviations are. They are all listed on this page instead.
The first list contains abbreviations you'll find most frequently in the Basics of Space Flight. Below it you'll find some of the International System of Units, SI, and a link to the The National Institute of Standards for complete details. Next is a selection of formulas for converting SI to English measures, a link to a conversions engine, and a link to a comprehensive set of conversion tables.
1. Unit Abbreviations Frequently Found in the Text
AU  Astronomical Unit, a measure of distance, based on the mean sunEarth distance. The International Astronomical Union defines the AU as the distance from the Sun at which a particle of negligible mass, in an unperturbed orbit, would have an orbital period of 365.2568983 days (a Gaussian year). The AU is thus defined as 1.4959787066E+11m (149,597,870.66 km). [More] 
bps  Bits per second, a measure of data rate 
c  Speed of light in a vacuum, 299,792,458 m/sec 
G  Giga, a multiplier,* x10^{9} from the Latin "gigas" (giant). In the U.S., 10^{9} is a billion, while in other countries using SI, 10^{12} is a billion. Giga means 10^{9} everywhere. 
g  Gram, a unit of mass (see SI units below) 
Hz  Hertz, the number of cycles per second 
k  Kilo, a multiplier,* x10^{3} from the Greek "khilioi" (thousand) 
LY  Light Year, a measure of distance, the distance light travels in one year; about 63,240 AU 
M  Mega, a multiplier,* x10^{6} from the Greek "megas" (great) 
m  Meter, a unit of length (USA spelling; elsewhere, metre) (see SI units below) 
N  Newton, a unit of force (see SI units with special names, below) 
s  Second, the SI unit of time (see this extensive definition) 
W  Watt, a unit of power (see SI units with special names, below) 
*The remaining multipliers are listed in the GLOSSARY.
2. International System of Units, SI
SI has long been the notation universally used in science and technology. It has also become the dominant language of international commerce and trade, except in the U.S.

SI base unit

Base quantity 
Name 
Symbol 
length 
meter 
m 
mass 
kilogram 
kg 
time 
second 
s 
electric current 
ampere 
A 
thermodynamic temperature 
kelvin 
K 
amount of substance 
mole 
mol 
luminous intensity 
candela 
cd 
For a comprehensive and definitive reference on all aspects of SI, as well as many other quantities and standards, please visit the National Institute of Standards (NIST) website. Some of the information on this page has been obtained from there.
See also the Solar System Temperature Reference for examples and temperature comparisons of objects and conditions in space, from absolute zero through planet temperatures, to those of stars.
Some Derived SI Quantities
Selected from NIST website

SI derived unit

Derived quantity 
Name 
Symbol 
area 
square meter 
m^{2} 
volume 
cubic meter 
m^{3} 
speed, velocity 
meter per second 
m/s 
acceleration 
meter per second squared
(meter per second per second) 
m/s^{2} 
wave number 
reciprocal meter 
m^{1} 
mass density 
kilogram per cubic meter 
kg/m^{3} 
specific volume 
cubic meter per kilogram 
m^{3}/kg 
current density 
ampere per square meter 
A/m^{2} 
magnetic field strength 
ampere per meter 
A/m 
SI Units with Special Names
Selected from NIST website

SI derived unit

Derived quantity 
Name 
Symbol 
Expression in terms of other SI units 
Expression in terms of SI base units 
plane angle 
radian 
rad 
 
m·m^{1 }= 1 
solid angle 
steradian 
sr 
 
m^{2}·m^{2 }= 1 
frequency 
hertz 
Hz 
 
s^{1} 
force 
newton 
N 
 
m·kg·s^{2} 
pressure, stress 
pascal 
Pa 
N/m^{2} 
m^{1}·kg·s^{2} 
energy, work, quantity of heat 
joule 
J 
N·m 
m^{2}·kg·s^{2} 
power, radiant flux 
watt 
W 
J/s 
m^{2}·kg·s^{3} 
electric charge, quantity of electricity 
coulomb 
C 
 
s·A 
electric potential difference,
electromotive force 
volt 
V 
W/A 
m^{2}·kg·s^{3}·A^{1} 
capacitance 
farad 
F 
C/V 
m^{2}·kg^{1}·s^{4}·A^{2} 
electric resistance 
ohm 

V/A 
m^{2}·kg·s^{3}·A^{2} 
electric conductance 
siemens 
S 
A/V 
m^{2}·kg^{1}·s^{3}·A^{2} 
magnetic flux 
weber 
Wb 
V·s 
m^{2}·kg·s^{2}·A^{1} 
magnetic flux density 
tesla 
T 
Wb/m^{2} 
kg·s^{2}·A^{1} 
inductance 
henry 
H 
Wb/A 
m^{2}·kg·s^{2}·A^{2} 
Celsius temperature 
degree Celsius 
°C 
 
K 
luminous flux 
lumen 
lm 
cd·sr 
m^{2}·m^{2}·cd = cd 
illuminance 
lux 
lx 
lm/m^{2} 
m^{2}·m^{4}·cd = m^{2}·cd 
3. A Few Handy SItoEnglish Conversions
Take the number of SI units and apply the conversion to get the number of English units. For example, 2 meters equals about 6.56 feet.
Millimeters to inches:  mm  x  0.0393700787401575  =  in 
Centimeters to inches:  cm  x  0.393700787401575  =  in 
Meters to feet:  m  x  3.28083989501312  =  ft 
Meters to yards:  m  x  1.09361329833771  =  yds 
Kilometers to miles:  km  x  0.621371192237334  =  mi 
Grams to ounces:  g  x  0.0352739907229404  =  oz 
Kilograms to pounds:  kg  x  2.20462262184878  =  lbs 
Celsius to Fahrenheit: 
(°C  x  9/5) + 32  =  °F 
Newtons to Pounds Force:  N  x  0.224809024733489  =  lbf 
4. More Conversions
Follow this link to perform conversions in real time.
Here is a comprehensive set of conversion tables.
 