Transcript Rocket Science and Orbital Mechanics

Rocket Science and
Orbital Mechanics
Academic Decathlon Preparation for
San Fernando HS by
Dr. Muller
Action and Reaction
• One of the basic principles of rocketry is that a
force creates an equal and opposite force in the
other direction.
• F=m•a
• “pounds of thrust” in British units
• Newtons in metric
• 4.45 N = 1 lb of thrust
Ramifications
• The Space Shuttle has a massive weight to get a 65,000
lb payload into space: 20x more fuel by weight than the
Orbiter!
Pounds
Empty
Fuel
Orbiter
165,000
NA
Ext. Tank
78,100
1,359,000 + 226,000
Boosters
185,000 x2
1,100,000 x2
SRBs
• Burn for 2 min and generate 3.3M lb of thrust
• Fuel made of ammonium perchlorate (69.6%), aluminum (16%),
iron oxide (.4%)
• Also contains a polymer binder (12.04%) + a curing agent
(1.96%)
• By changing the mixture, you change explosion to high-thrust
burn (see p23)
• Has an 11-point star inside to increase burning area; evens out to
circle as it burns
• SRB +: simplicity, low cost, safety
• SRB -: thrust not controllable, burn can’t be stopped
Liquid-Propellant Rockets
• Fuel tanks contain a fuel and an oxidizer, which
is pumped at controlled rates into a combustion
chamber; gases have high acceleration.
• Typical liquid fuels include liquid gases; the
cooled gases are used to cool the combustion
chamber as they head to it.
• Combinations for different rocket experiments
appear on p24-25.
Next-Generation Rockets
• Small rocket thrusters use pressurized nitrogen
to correct orbital decay.
• Current experiments seek to use highacceleration ions or atomic particles at high
acceleration to drive rockets; dangerous for use
on Earth.
Physics
• Thrust = mass • exhaust velocity (T = mC)
• By extension, C = T/m
• Impulse = how long a pound of propellant can
deliver a pound of thrust (Isp)
• C = g • Isp
• ∆V is the change in velocity.
• Mass ratio of a fuel-laden vehicle is (M + P)/M,
where M is empty vehicle weight and P is
propellant weight.
More Physics
• Rocket equation:
(M+P)/M = e∆V/C
• Increasing ∆V means that the mass ratio will go
up – this makes the combined mass heavier,
which is bad.
• Increasing C means that the mass ration will go
down – this makes the combined mass lighter,
which is good.
Satellites
• Orbit is a circular or eliptical path: apogee, perigee, geosynchronous
• Sputnik was first in 1957. Lasted 92 days.
• Laika was launched in 1958. Lasted 30 days.
• Difference of Earth’s rotation at equator makes shots
from there easier.
• Escape velocity is to get into space: 25,039 mph.
• Orbital velocity is required to create circular orbit:
17,000 mph at 150 mi.
• Geosynchronous orbit is 7,000 mph at 22,223 mi.
• Polar orbits are lower and are used for photography.