Rockets

Tuesday: RocketryWednesday: Meet in my room 601: hydrogen demo and Quiz over rocketry.Thursday: Satellites and Orbital MechanicsFriday: Satellites, Orbital Mechanics and Tsiolkovsky Quiz

What are the seven obstacles?

Vacuum of spaceHeatReentryOrbital mechanicsDebrisRestroomsGetting off the ground

Three Countries that have put people in orbit are…

Russia (USSR)ChinaUnited States

Rockets Overview

What type of energy does a motor use?How is that different from a rocket

engine?What principle does a rocket engine use?

Rocket Propulsion

Newton’s 3rd Law?

How do we overcome this problem??

Measured in Newton’s. WHY?

Thrust

Lets try a practice problem…

An elephant weighs 1 ton, how much thrust is necessary to hold its weight at a constant level but not send it into orbit?

1 TON

Is it really that easy?

In order to be launched however, the thrust must be greater than your weight. In other words you must have extra thrust.

That extra thrust make you ACCELERATE upwards.

In other words, “the greater the thrust the faster your rocket will accelerate.”

So which Newton’s law are we talking about now?

2nd Law: f = ma

When mass increases, acceleration decrease.

Another problem you say… Sure

On a frictionless surface you want to measure acceleration of a rocket moving horizontally. (we don’t want to fight gravity just yet).

If the rocket produces 50lbs of thrust and weighs 10 kgs, what is the acceleration?

Lets add gravity into the mix. This time the same rocket is launched upward. What is the acceleration?

The book’s example

So what must be done to change the thrust?

More ballsBigger ballMore acceleration

So what is the funny problem that rockets have?

The fuel, that they use to create thrust weighs something. (like adding an extra space suit to the rocket) but more of course.

Just some statistics…

How many main sections of the shuttle are there?

How much does the shuttle weigh at launch?

What is the shuttle’s main engine fuel?

For how many minutes did the Space Shuttle’s two solid boosters burn at launch?

3

4.4 millionLiquid oxygen and hydrogen

2

Lets compare and contrast the two types of rockets…

Solid Fuel Liquid Fuel

Now its time for the fun part…

The fundamentals of rocketry rest on Newton’s laws.

Thrust = (propellant mass flow) x (exhaust velocity)

T= mCPropellant mass flow = how much “fire”

come out.Exhaust velocity = It represents the force with respect to the amount of

propellant used per unit time

Lets explore exhaust velocity…

It is a way to describe the efficiency of rocket and jet engines

Measured in ISP = number of seconds a lb of propellant can deliver a lb of thrust.

C= g (ISP)C = Exhaust velocity g= gravity ISP= impulse

In order for all this to matter…

velocity = to get where you want to go.This is the fundamental currency of

astronauts.Measure in units of speed.The ROCKET EQUATION shows how big a velocity the system can generate.

The ROCKET EQUATION

(M + P) / M = e V/C

e= 2.71828(M + P) = M= DRY mass at lift off, P= Propellent

M = DRY mass in orbit

V/C = shows the velocity change a rocket can generate

.

Because of the exponent there small changes make big differences.

Increase in V or decrease in C can be bad. It is desired to have a have V down and C up.

Since the mass of tanks, engines and most other vehicles increase in proportion to the propellent load, it can be described as 1 factor.◦DRY MASS FRACTION = F◦Takes into account system design and lightness

of the materials used in construction.

F x Propellent mass = dry mass ** this is not counting payload***

For example:If F = 0.1 and it is carrying 90 tons of propellant what would the dry mass of the ship?

What if the mass ratio of the system had to be

10 to perform a certain V?

Then there would only be allowed a 1 ton payload. However, if the F increases to .12 the dry mass of the vehicle would be 10.8 and there would be no lift off!!

9 tons

How do we fix this?

We chop the V into stages and then drop the dry mass of that stage.