orbit manoeuvres

Question 1

what is orbital manoeuvring based on?

Answer 1

the principle that an orbit is uniquely determined by position and velocity at any point

Question 2

what is needed to undertake a transfer or manoeuvre?

Answer 2

change in velocity vector using an external force

Question 3

define burn time

Answer 3

finite time for which thruster is required to burn to achieve necessary change in velocity vector

Question 4

why can we assume an impulsive burn?

Answer 4

if the burn time < orbit period

Question 5

define single burn transfer

Answer 5

single impulsive burn of thruster, enabling transfer from one orbit to another

Question 6

where do burns occur?

Answer 6

intersection of orbits

Question 7

define general co-planar manoeuvre

Answer 7

non-tangential burn from an initial orbit velocity, to an intersecting co-planar orbit with final velocity

Question 8

how many burns does a hohmann transfer require?

Answer 8

2

Question 9

describe process of hohmann transfer

Answer 9

• first burn: required to change from initial circular orbit to elliptical transfer orbit
• second burn: made at apoapsis of transfer to give spacecraft sufficient energy to remain in final circular orbit

Question 10

what are hohmann transfers used for?

Answer 10

used to reduce or increase orbit altitudes

Question 11

define three-burn transfer

Answer 11

consists of three separate burns

Question 12

when are three-burn transfers used?

Answer 12

when there is a large difference between intitial and final orbit radius

Question 13

define fast transfer and when it is used

Answer 13

‘one tangent burn’, used when time is major constraint and fuel efficiency can be sacrificed

Question 14

define rendezvous manouevre

Answer 14

spacracraft intercepts another spacecraft in the same orbit but a different true anomaly, intercepting spacecraft either speeds up or slows down

Question 15

what orbit type is used to adjust the period of the spacecraft so it can meet the target spacecraft?

Answer 15

elliptical

Question 16

to intercept a spacecraft which is ahead, should the inner or outer ellipse be used and why?

Answer 16

inner ellipse provides faster orbit to catch up with spacecraft ahead

Question 17

how can we find the time required to synchronise with the target spacecraft?

Answer 17

difference in periods of the two orbits

Question 18

what is a plane change orbit?

Answer 18

manouevre where a simple plane change is done or both inclination and plane change occur in a combined manoeuvre

Question 19

why is it not favourable to change the plane of a low earth orbiting satellite?

Answer 19

very costly in energy terms, velocity in orbit increases as orbit altitude decreases, therefore energy required to make changes in a lower altitude orbit are higher than in a higher altitude orbit

Question 20

when do we use a combined plane change and hohmann transfer?

Answer 20

when spacecraft transferring from from initial launcher parking orbit to final mission orbit