L6 - Orbital Maneuvering & Interplanetary Travel

Question 1

What is the the most energy efficient means of transferring between two points?

Answer 1

The Hohmann Transfer.

Question 2

What is the Hohmann Transfer?

Answer 2

It is the most efficient transfer between two circular coplanar and coapsidal (aligned major axis) orbits.

• ΔVp at perigee to put satellite on elliptical transfer orbit
• ΔVa at apogee to put satellite in final circular orbit
• Both ΔVs are tangential and impulsive

Question 3

What are the two types of plane changes?

Answer 3

• Simple
• Combined

Question 4

Describe a simple plane change.

Answer 4

It is when changes alter the inclination or position of the ascending node.

It is best performed as far as possible from Earth.

Question 5

What is a combined plane change?

Answer 5

It happens when the magnitude and the direction of the velocity vector change.

A Hohmann transfer can be used, it is more efficient in terms of ΔV.

Question 6

When should you apply a ΔV to change an inclination?

Answer 6

Ascending node or Descending node

Question 7

Where should you always perform a plane change?

Answer 7

At the apogee, when the velocity is at its lowest.

Question 8

What are all the aspects of plane changes?

Answer 8

• Simple
• Combined
• Inclination change
• Apogee burn (lowest velocity)
• Use of Hohmann burns

Question 9

What is an orbital rendez-vous?

Answer 9

It is getting two or more spacecrafts to arrive at the same point in an orbit at the same time.

Question 10

What are the two types of rendez-vous?

Answer 10

• Co-planar
• Co-orbital

Question 11

What must be done for success in a co-planar rendez-vous?

Answer 11

The interceptor must initiate a ΔV at a precise moment so as to arrive in the correct orbit at the same place and time than the target vehicle.

There can be a “waiting time” before this ΔV is performed.

Question 12

What must be done for success in a co-orbital rendez-vous?

Answer 12

Interceptor may be “leading” or “behind” the target.

• Behing: slow down to get to faster orbit
• Leading: Speed up to get to lower orbit

Question 13

What is the sphere of influence of a planet?

Answer 13

It is a sphere area around a planet within which any object can be considered under the sole gravitational influence of the planet.

Question 14

What is the sphere of influence dependant on?

Answer 14

It is dependant on the distance from the sun and the body’s mass.

Question 15

What is the sphere influence of Earth?

Answer 15

1 million kilometers.

Question 16

What is the main approximation made for interplanetary travel.

Answer 16

The patch-conic one. It breaks the interplanetary travel space into as many regions as they are influencial bodies. Each regions is then considered under the gravitational influence of one body.

The two body problem is recovered.

Question 17

What is the Sun-centred coordinate system used for interplanetary transfers?

Answer 17

The heliocentric-ecliptic system.

Question 18

What is the synodic period of two planets?

Answer 18

It is the time between successive launch opportunities.

Question 19

What is the time between successive launch opportunities for two planets called?

Answer 19

The synodic period.

Question 20

What are the steps involved in getting from one planet in the solar system to another.

Answer 20

Planet departure.

• Circular parking orbit with radius.
• ΔV to enter hyperbolic escape trajectory
• Coasted to the boundary of planet SOI
• Enter the helocentric elliptical transfer orbit
• Coast along interplanetary journey

Target Arrival

• Arrive at boundary of planet SOI
• Coast on hyperbolic arrival trajectory
• ΔV to enter circular parking orbit

Question 21

How can the gravitational pull of planets be used to get “free” velocity changes?

Answer 21

Gravity-assist technique uses a planet’s gravitational field and orbital velocity to “sling shot” the spacecraft.