ballistic missiles and getting into orbit

Ballistic Missiles and Getting Into Orbit

Unit 2, Chapter 7, Lesson 7: Ballistic Missiles and Getting into Orbit 2

Ballistic Missiles and Getting Into Orbit

Intercontinental Ballistic Missiles (ICBMs) Understanding Ballistic

Missiles and Trajectories Conic Sections ICBM Trajectories ICBM Development The Anti-Ballistic Missile Treaty

Launch Windows and Times Getting Into Orbit Launch Windows Launch Time

Unit 2, Chapter 7, Lesson 7: Ballistic Missiles and Getting into Orbit SECTION 7.1

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Understanding Ballistic Missiles and Trajectories

Not all spacecraft launched into space stay there.

Ballistic missiles only travel through space.


Conic Sections

All objects moving under the influence of gravity must follow paths that form conic sections.

Circles, ellipses, parabolas and hyperbolas are all conic sections because they are all ‘slices’ of a cone.

Parabolas and hyperbolas are useful only for interplanetary motion.

Circular and elliptical paths are for near Earth work.


Conic SectionsBallistic Trajectories

The shape of a Ballistic Trajectory is an ellipse that intersects the Earth at two points


ICBM Trajectories

Ballistics: Science dealing with motion, behavior, and

effects of projectiles—especially bullets, bombs, rockets, and missiles.

Science or art of designing and hurling projectiles to achieve a desired effect.


ICBM Trajectories (cont’d)

Ballistic trajectories Paths followed by non-thrusting objects Objects moving under the influence of

gravity Most of the trajectory is outside Earth’s

atmosphere (ignore all other forces except for gravity).


ICBM Trajectories (cont’d)Trajectory Example

As the man in the figure tries to squirt the dog, he has three basic options similar to the options with ballistic trajectories of rockets:

He can squirt the stream of water directly at the dog (low trajectory).

Aim the stream of water at a 45 degree angle (maximum range or accuracy).

Or, squirt the stream high into the air (high trajectory).


ICBM Trajectories (cont’d)Ballistic Trajectories

Define ballistic trajectories by: Rocket’s position (radius from the Earth’s center) at

burnout Rocket’s velocity at burnout Flight-path angle at burnout Direction of flight at burnout Latitude at burnout Longitude at burnout

Shape of ballistic trajectory: ellipse intersecting Earth’s surface at launch and impact


ICBM Development

ICBMs are long-range missiles using a ballistic trajectory.

ICBMs differ little technically from other ballistic missiles.

Ballistic trajectories have focused on being able to throw things farther and faster.


ICBM Development (cont’d)

V2 was first real intermediate range ballistic missile.

After the war, U.S. and USSR began race to develop ICBMs.

Key players in global space program also took part in developing ICBMs.


ICBM DevelopmentModern ICBMs and MIRVs

Modern ICBMs typically deliver multiple independently targetable re-entry vehicles (MIRVs). Each Re-entry Vehicle (RV) carries a nuclear-

weapon warhead. Allows a single missile launch to strike a handful of

targets. Proved to be an “easy answer” to deploying anti-

ballistic missile (ABM) systems: adding more warheads to a missile costs less than building the missiles to shoot down the additional warheads.


ICBM DevelopmentMinuteman

Minuteman I and II were U.S. ICBMs in service from 1960 to 1997.

Minuteman III entered service in 1978. Minuteman had two innovations that

gave it a long practical service life. Solid-rocket fuel technology. Earliest use of integrated circuit for digital

flight computer.


ICBM DevelopmentMinuteman (cont’d)


ICBM DevelopmentMinuteman (cont’d)

Early trajectory of a Minuteman Missile shown on it’s way to a test range


ICBM DevelopmentPeacekeeper

First deployed in 1986. Canceled, modified, and

reinstated over several administrations.

U.S. had to remove it from service to meet SALT II treaty.


ICBM DevelopmentPeacekeeper (cont’d)


ICBM DevelopmentICBM Missile Silos


The Anti-Ballistic Missile Treaty

Between U.S. and USSR to limit use of anti-ballistic missile systems in defending against missile attack.

Only two nuclear powers—kept both from believing they could avoid a counter-strike.

In force for 30 years from 1972-2002. U.S. withdrew from treaty in 2002.


ABM Treaty (cont’d)Arguments for Withdrawal

Allow U.S. to develop a ballistic missile-defense system to protect against rogue nations developing weapons.


ABM Treaty (cont’d)Arguments against Withdrawal

“Fatal blow” to the Nuclear Non-Proliferation Treaty.

Would lead to a world without effective legal limits on nuclear growth.

Reaction from Russia and China would hinder other arms negotiations (but offsetting pluses have made that reaction milder than expected).

Unit 2, Chapter 7, Lesson 7: Ballistic Missiles and Getting into Orbit SECTION 7.2

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Launch Windows and Times

Above: September 1997—The Shuttle Endeavour waits for launch time.Left: April 1998—The Columbia Shuttle propels off the launch pad and accelerates into orbit.


Getting into Orbit

To meet the conditions of a space mission, launch-team members need to: Launch the spacecraft from a specific

place. Launch the spacecraft at a specific time. Launch the spacecraft in a specific

direction.


Launch WindowsDefinition

An opportunity to launch a satellite from Earth directly into the desired orbit from a given launch site.


Launch WindowsConcept

A launch window is an opportunity to launch a satellite from Earth directly into the desired orbit from a given launch site. We can always launch into parking orbit and then

perform a Hohmann Transfer to put a spacecraft in the desired orbit, but this is complicated and requires more fuel.

A launch window means getting directly into the desired orbit without having to maneuver.


Launch WindowsConcept (cont’d)

Launch windows are like bus schedules.

Launch windows normally cover a period of time.

Launch vehicles must follow trajectory rules by Newton’s Laws of Motion.


Launch Windows and Launch Time

Endeavour clears the tower on STS-47

Columbia accelerates into orbit on STS-87


Launch Time

To determine what time a launch site passes into a launch window, we need a new definition of how to tell time.


Orbital Racetrack

If the car is one mile past the starting line, and the pit is one-half mile past the starting line, then the car must be one-half mile from the pit.

Given the car’s speed, we can figure out how long before the car reaches the pit.

Knowing this rate allows us to determine the best time to launch a spacecraft directly into orbit, or the launch window.


Launch TimeSolar Time

The spacecraft must launch in a specific direction: The vernal equinox direction is the main direction

we use to describe the motion of spacecraft that orbit the Earth.

Because the Earth and the launch site rotate, it’s an easy reference from which to measure the angular distance between the orbital plane and our launch site.

Knowing this angular distance and Earth’s rotation rate, we can figure out the best times to launch.


Launch TimeSolar Time (cont’d)

Greenwich Mean Time (GMT)— is the basis for the time kept on watches to handle daily business. GMT is the mean solar time for the Prime

Meridian (Greenwich, UK). All other time zones are GMT plus or minus

a certain number of hours.


Launch TimeSolar Time (cont’d)

The Royal Observatory in Greenwich, England


Launch TimeSolar Time

Apparent Solar Day An Apparent Solar Day is the time between

successive passages of the Sun overhead, which is from noon one day to noon the next day.

Apparent solar day’s length varies throughout the year (Earth’s orbit around the Sun is elliptical).

Average of the lengths for one year gives us a mean solar day.


Launch TimeSidereal Time

Because there is a problem using solar time, the reference point for GMT rotates with the Earth, we seek an inertial (fixed) reference point: We use the same reference point as the

geocentric-equatorial coordinate frame—vernal equinox direction.

A sidereal day is the time between the subsequent passings of the vernal equinox direction overhead a particular longitude line.


Launch TimeSidereal Time (cont’d)

Because the inertial reference vernal equinox is so far away, the length of a sidereal day corresponds to exactly 360° of Earth rotation.

A sidereal day is slightly shorter than an apparent solar day: 23 hours, 56 minutes, 4 seconds in solar time.


Launch TimeSidereal Time (cont’d)

We can tell sidereal time in degrees.

Earth rotates 360° in 24 hours.

So, 3 a.m. (0300) is 45° of Earth’s full rotation.

Similarly, noon (1200) is 180° and 6 p.m. (1800) is 270°.


Launch TimeLocal Sidereal Time (LST)

Time since the first point of constellation Aries was last overhead.

Can be expressed in time or angle If Earth has rotated 90° since the local

longitude line was aligned with the vernal equinox direction, LST is: 90° 0600 hrs

Mission planners mathematically convert LST back to GMT for launch timing.


Launch TimeLocal Sidereal Time (LST)


Launch Time Solar Time versus Sidereal Time


Summary Intercontinental Ballistic Missiles (ICBMs)

Understanding Ballistic Missiles and Trajectories Conic Sections ICBM Trajectories ICBM Development The Anti-Ballistic Missile Treaty

Launch Windows and Times Getting into Orbit Launch Windows Launch Time


Next

For some payloads, the mission requires us to get a payload into orbit and get it back to Earth from space.

On the next lesson we’ll tackle the last part of a space journey: atmospheric re-entry.

ballistic missiles and getting into orbit

Documents

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dog low trajectory

air high trajectory

orbiticbm development

influence of gravity

stream of water