L9 - Getting to Orbit

Question 1

What is a Launch Window?

Answer 1

It is the period during which we can launch directly into a desired orbit from a particular launch site.

Question 2

How many opportunities are there to launch form a particular launch site to a particular inclination?

Answer 2

• Orbit plane and launch site must intersect.
• Launch window exist only if i > Latitude or i < (180 - latitude)
• If latitude = i; one launch per day
• If latitude < i; two launches per day (ascending/descending nodes opportunities)

Question 3

What are the different launch phases?

Answer 3

• Vertical Ascent
• Pitch Over
• Gravity Turn
• Vacuum Phase

Question 4

Describe the Vertical Ascent.

Answer 4

• It simplifies the launcher and launch pad structures
• Minimises bending forces
• Gravity drag, acts against thrust to reduce vertical velocity
• Gain altitude quickly to minimise time spent in densest part of atmosphere
• A roll manoeuvre can align with launch azimuth

Question 5

Describe the Pitch Over.

Answer 5

• While velocity is low to reduce aerodynamic loads/torques
• Thrust gimballed (nozzle moved) to gain horzontal velocity
• Achieves correct entry angle for start of gravity turn
• Thrust gimballed in line with LV when complete

Question 6

Describe the Gravity Turn.

Answer 6

• Flight path no longer vertical
• Gravity acts to pull rocket back down
• If no thrust: parabolic trajectory back down
• Gravity turn guidance (pitch vs time value)
• 0 angle of attack until vacuum phase

Question 7

Describe the Vacuum phase.

Answer 7

• No more atmosphere
• Continued acceleration until orbit velocity
• Velocity, altitude and direction control system

Question 8

What are the components of launch vehicle design velocity.

Answer 8

• ΔV burnout: needed at burnout to be in correct orbit
• ΔV launchsite: due to Earth’s rotation
• ΔV Gravityloss: needed to overcome gravity
• ΔV Drag: extra needed to overcome atmospheric drag and other losses

ΔVDesign = ΔVBurnout - ΔVLaunchsite + ΔVGravityloss + ΔVDrag