Launch Vehicles and Orbits
How Rockets Work
• Newton's Laws of Motion are:
–An object at rest tends to remain
at rest
–An object in motion tends to
remain in motion
–For every action there is an equal
and opposite reaction
Conservation of Momentum
• Newton's Laws are all contained in a more
general principle called conservation of
momentum.
• Momentum is mass times velocity
• In a system that is not disturbed from
outside, the total momentum stays
constant.
Conservation of Momentum
Means:
• If velocity is zero, momentum is zero
(Newton's First Law)
• If velocity is not zero, and mass doesn't
change, then velocity doesn't change
(Newton's Second Law)
Conservation of Momentum
and Newton’s Third Law
• If mass changes somehow, then so does
velocity.
• If an object is stationary, and flings off
mass, the rest of the mass moves in the
opposite direction.
• The flung off mass has positive
momentum, the rest has negative
momentum, and the total momentum
remains zero (Newton's Third Law).
Conservation of Momentum
Rockets and Jets
• Rockets and jets work according to
Newton's Third Law.
• They fire mass out at high speed and
acquire velocity in the opposite direction.
• They do not need something to push
against. They move because they are
expelling exhaust gases at high speeds.
• Tthe rocket or jet is pushing mass away,
and the mass is pushing back (equal and
opposite reaction.)
How Rockets and Jets Differ
• Rockets and jets expel mass by burning
fuel.
• A jet gets the oxygen for combustion
from the atmosphere
• A rocket carries oxygen in some form
with it.
• Thus rockets can function outside the
Earth's atmosphere; jets can't.
Rockets are Mostly Fuel (and
Oxygen)
• A rocket or jet has to carry all its remaining
fuel with it. (And oxygen, if it’s a rocket).
• Most of the mass of the Space Shuttle is
fuel, and most of that is used to get the
remaining fuel off the ground.
• The miles-per-gallon fuel economy of the
Space Shuttle in its first foot off the ground
is pretty terrible!
About Orbits and Satellites
• Satellites travel elliptical paths with the
center of the Earth at one focus (Kepler's
First Law)
• Inertia causes object to continue moving in
a straight line
• Gravity pulls object to Earth
• Balance between the two = orbit
Newton’s
Mountain
Important Orbits
•
•
•
•
Low vs. High Inclination
Almost all are Prograde
Polar Orbits for global coverage
Circular Orbits strongly preferred
– Constant altitude
– Constant speed
• Sun-Synchronous
• Geosynchronous
• 12-Hour (GPS)
About Orbits
• You do not need to expend fuel to stay in
orbit
• Satellites need attitude control fuel to
correct for atmospheric drag, lunar and
solar gravity, etc.
• May want thrusters to help maintain orbits
• Spin stabilization helps
• Once below 200 km, atmospheric braking
leads to re-entry
About Orbits
• The focus of a satellite orbit is the center
of the earth
• The plane of a satellite orbit always
passes through the center of the earth
• There is no such thing as an orbit over the
poles, over a small region, etc.
• It is possible to have an orbit over the
equator
Precession
• Put sideways force on anything moving in
a circle, it will precess
• Precession affects planetary rotation
• Precession also affects orbits
• We can control precession of satellites by
selecting orbital inclination
• Fixed with respect to stars
• Fixed with respect to sun
Precession
Precession
Precession
Three Pioneers of Rocketry
• Konstantin Tsiolkovsky (1857-1935)
– Worked out theoretical problems of
spaceflight
• Robert Goddard (1882-1945)
– First Liquid Fuel Rocket
• Hermann Oberth (1894-1989)
– Helped create operational rockets
Robert
Goddard First
LiquidFuel
Rocket,
1926
The V-1
The V-2
From
Sapwood to
Sputnik
• An existing rocket, the
SS-6, was used.
• The warhead section
was removed
• A cluster of four more
SS-6 engines was
bolted around a central
engine
• Very Dependable
Sputnik I
• October 4, 1957
• S- (with) +
put’ (path) +
-nik (one who) =
Sputnik
• Literally, one who
follows the same
path
Early Rockets, Kennedy Space
Center
Early Rockets, Huntsville AL
V-2 Huntsville AL
V-2 shrapnel
V-2 Components
Gemini,
1965
Sensor Technology
• Passive (senses only ambient signals)
• Active (emits signals)
• Imaging
• Non-Imaging
• Scanning (mechanical or electronic)
• Non-scanning
The Single
Most
Valuable
Product of
the Space
Program
Crescent Earth
Himalayas from Space Shuttle
Volcano, Alaska
Fringing
Reefs
Icebergs,
Antarctica
A Noble Myth
“In my life, I've seen the images from space of a
blue-white-green world — there are no political
lines drawn on this planet.
• Luis J. Rodriguez
“The border between the United States and
Mexico is an imaginary line. It cannot be seen
from space”
• The Border Zone: A History of Trade between
the United States and Mexico, Julia Albright;
Age of Irony, Winter 2004
“You Can’t See Borders From Space”
Mexican
Border
Mexican
Border
Menominee County, WI
U.S.-Canadian Border
Landsat
View of
Green Bay
Landsat View of Green Bay
Landsat
view of
Washington
D.C.
Radar
Image of
New York
City
Spy Satellite
Views of Soviet
Aircraft Carrier
Spy Satellite
View of
Soviet
Airfield
World Trade Center, September 11, 2001
Pope John Paul II Funeral
Pope John Paul II Funeral
Barack Obama’s Inauguration
Barack
Obama’s
Inauguration
And Now For
Something
Completely
Different….
Gulf
Stream in
Infrared
Ultraviolet View of Earth
The Ocean Floor From Space
Earth and Moon Together
Really Remote Sensing
An Eclipse of the Sun – By Earth