Spaceflight I

Leaving Earth

How Rockets Work• Newton's Laws of Motion are:

1. An object at rest tends to remain at rest

2. An object in motion tends to remain in motion

3. 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).

Newton’s Third Law

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

Three Pioneers of Rocketry

• Konstantin Tsiolkovsky (1857-1935)• Robert Goddard (1882-1945)• Hermann Oberth

Robert Goddard

-First

Liquid-Fuel

Rocket, 1926

World War II

The V-1

V-1

Japanese Okha

The Very First Cruise Missile

The V-2

V-2

History That Might Have Been:

• If World War II had lasted a bit longer, it might have been fought with:– Nuclear Weapons– Guided Missiles– Cruise Missiles– Jet Aircraft

The Right Stuff

• Chuck Yeager - Supersonic Flight, 1948• Career fatality rate among military jet pilots

is 25%• To cope, they cultivate a superstition of

“the right stuff”• Title of Tom Wolfe book

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

Sputnik II and III

How Did Russia Beat the U.S?• German scientists were not involved• German scientists were not involved• German scientists were NOT involved!!• Germans built V-2 clones but did not work

on main program• All returned home by the early 1950’s• They were debriefed on return - this has

been known for decades

So why does the myth persist?

Because it’s what we wanted to believe

Rockets and Geopolitics

• We relied on manned bombers• We had bases close to Russia• We led in miniaturization• We decided to wait until nuclear weapons

became smaller before putting them in missiles

• Result, we had smaller rockets• And, most surprising of all---

Much of our early efforts went into cruise missiles!

How the World

Looked to Russians in the 1950’s

The Russian Decision• They had no bomber bases from which to

attack the U.S.• Missile Submarines were rudimentary at

the time• The only way to hit the U.S. was with

missiles• Thus, the Russians poured efforts into

building huge rockets