Understand the factors and requirements associated with a spacecraft launch

Understand the dynamics of Gravity Assist and the basic principles of placing a spacecraft into orbit

Understand the dynamics of spacecraft reentry in terms of the environment and spacecraft design considerations

Maneuvering/Traveling in Space I

Spheres of InfluenceA body’s sphere of influence (SOI)

is the surrounding volume in which its gravity dominates a spacecraft. In theory, SOI is infinite. In practice, as a spacecraft gets

farther away, another body’s gravity dominates.

The size of a planet’s SOI depends on:The planet’s massHow close the planet is to the

Sun (Sun’s gravity overpowers that of closer planets)

Gravity-Assist TrajectoriesProcess using a

planet’s gravitational field and orbital velocity to “sling shot” a spacecraft, changing its velocity (in magnitude and direction) with respect to the Sun.

Gravity-Assist TrajectoriesAs a spacecraft

enters a planet’s sphere of influence (SOI), it coasts on a hyperbolic trajectory around the planet.

Then, the planet pulls it in the direction of the planet’s motion, increasing (or decreasing) its velocity relative to the Sun.

Trajectories in Space TravelGravity-assist trajectories draw on a planet’s angular momentumSpacecraft use this angular momentum to speed up when behind

a planet, or slow down in front of a planet

Hyperbolic, Parabolic & Elliptical Paths

Elliptical path travels a trajectory similar to a racetrack, closed in on itself

Hyperbolic path takes the object much farther out into space

Parabolic orbit is the middle ground between the two

Space Shuttle Rendezvous Maneuvers

Space shuttle and Russian Soyuz capsules rendezvous with the ISS and then dock

Rendezvous maneuvers are tricky and dangerous

You speed up when you drop into a lower orbit where your velocity is higher and your orbital path shorter

Launch Windows: ConceptA 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.

X

Y

Launch WindowsDefinition

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

Getting into OrbitTo meet the conditions of a space mission,

launch-team members need to:Launch the spacecraft from a specific place.Launch the spacecraft in a specific direction. Launch the spacecraft at a specific time.

X

Y

But What Time To Use?

Launch Time: Solar 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.

However,….

Launch Time Solar Time versus Sidereal Time

http://www.youtube.com/watch?v=jiyQHPI_mFU

• The average time taken for the sun to return to its highest point is 24 hours (Solar Day)

• But as the Earth completes a rotation around its axis, it moves a short distance (approximately 1°) along its orbit around the sun.

• Therefore, the Earth still needs to rotate a small additional angular distance (beyond 360°) before the sun reaches its highest point.

• Hence since we are concerned with direction and distance given a 360° rotation of the earth, we use LST as launch time

Launch Time: Local Sidereal Time

LST is then converted to GMT for the Public “Launch Time”

LaunchAccounts for up to 30% of mission

costLaunch operation systems include:

The launch site and its associated rangeThe launch padPayload- and vehicle-processing facilitiesLaunch operations centers

Launch-Site Selection: Geography

Launch-site latitude determines the minimum orbital inclination available from a given siteThe Space Shuttle launches from

the Kennedy Space Center at 28.5 degrees latitude.

A launch site’s ideal geographical location is on the equator. European Space Agency’s

Kourou Launch Site Boeing’s Sea Launch System

Physical limits constrain the range of available inclinations, politics and safety also play a part.

The range must be clear of population centers and under the launch-site authority’s control.

Launch-Site Selection: Range Safety

Understand the factors and requirements associated with a spacecraft launch

Understand the dynamics of Gravity Assist and the basic principles of placing a spacecraft into orbit

Understand the dynamics of spacecraft reentry in terms of the environment and spacecraft design considerations

Maneuvering/Traveling in Space I