Elective 3 | Topic 6-8 Terms

Orbital Maneuver

A planned action taken to change the orbit or position of a spacecraft in space, usually achieved by firing onboard thrusters or engines to adjust its velocity and direction , allowing it to move to a different altitude, inclination, or orbital period as needed for its mission objective

Burn

A period when a spacecraft’s engines are fired to change its motion — specifically its velocity (Δ v ), which then changes its orbit

Prograde Burn

Performed in the direction of motion, increasing velocity and raising the orbit.

Radial Burn

Directed inward or outward from Earth, altering the orbit’s shape or orientation

Retrograde Burn

Performed opposite the direction of motion, decreasing velocity and lowering the orbit

Normal / Antinormal Burn

Executed perpendicular to the orbital plane, changing the orbit’s inclination.

Orbital Transfer

• a specific type of orbital maneuver where an object moves from one orbit to another in a planned and controlled way.

• It can be from a lower orbit to a higher orbit or vice versa

Parking Orbit

• Instead of going directly to its final orbit, the rocket first places the satellite into a low Earth orbit (LEO)

Transfer Orbit

From the stable orbit (parking orbit), the spacecraft performs a burn to enter this orbit.

Artemis I

An uncrewed flight test launching the Orion spacecraft on a 1.4 million mile journey beyond the Moon and back. It was launched last Nov. 16, 2022 and ended later on Dec. 11, 2022.

Artemis II

NASA’s first mission with crew aboard the SLS (Space Launch System) rocket and Orion spacecraft.

Artemis III

Scheduled for 2027, this new demonstration mission in low Earth orbit will test one or both commercial landers from SpaceX and Blue Origin, respectively

Artemis IV

NASA continues to target early 2028 for the first Artemis lunar landing. After reaching lunar orbit, the crew will transfer from Orion to a commercial lunar lander for their descent to the Moon’s surfac

Artemis V

Using the standard SLS (Space Launch System) rocket configuration, NASA expects to launch this lunar surface mission by late 2028, with subsequent missions planned roughly once per year

James Webb Space Telescope

• On December 25, 2021, it was launched through Arian 5 . Its target Lagrange Point was on Sun Earth L2.

• It was inserted into a transfer trajectory and was intentionally under speed to avoids risk of overshooting

Major Course Correction 1a

• 12 hours after launch, early in transfer trajectory

• Corrects most of the launch injection error

• Sets the correct overall path toward L2

• First critical double-check point before proceeding further

Major Course Correction 1b

• 2.5 days after launch, midway along the Earth-L2 transfer path

• Refines trajectory after MCC-1a

• Adjusts small residual errors

• Confirms spacecraft is still on the correct long-range path

Major Course Correction 2

• 29 days after launch, near Sun-Earth L2

• Final fine-tuning before orbit insertion

• Achieves very high precision (cm/s level)

• Ensures proper entry into halo orbit around L2

Impulsive Maneuver

• A quick burst of thrust that changes the velocity of a spacecraft.

• This maneuver is used to change the orbit of the spacecraft

Phasing Maneuver

• Used to adjust a spacecraft’s position along its orbit by changing its orbital period.

• By moving to a slightly higher or lower orbit, the spacecraft can speed up or slow down relative to a target.

• This is commonly used to align with a space station before rendezvous

Chase Maneuver

• Involves actively guiding a spacecraft to intercept and rendezvous with another object in orbit.

• It combines multiple burns to match orbit and reduce relative distance and velocity.

• This is used in missions where spacecraft dock with the International Space Station

Hohmann Transfer Orbit

• A fuel-efficient method for moving between two circular orbits using two burns.

• The first burn places the spacecraft into an elliptical transfer orbit, and the second circularizes it at the target altitude.

• It is widely used for transferring satellites from low Earth orbit to higher orbits like GEO

Escape Velocity

• The speed at which a spacecraft’s energy is sufficient that it never achieves orbit.

• In other words, it is how fast a spacecraft need to travel such that it continues into space and never returns to Earth under the effects of its gravitational field.

∞ (Infinite)

To escape the Earth’s gravity, the spacecraft must fly so far away that R𝑓 is ___

11174.2766 m/s

The value of escape velocity from the surface of Earth

Gravity Assist or Gravitational Slingshot

A maneuver in which a spacecraft gains or loses heliocentric velocity by passing close to a moving planetary body, i.e., a flyby maneuver

Heliocentric (Inertial) Frame

Planet-centric (Non-inertial) Frame

The analysis of a gravity assist maneuver involves two reference frame.

Planet Centric Frame

The planet is stationary, and the spacecraft approaches with velocity 𝑣_𝑖𝑛 with velocity and exits 𝑣_𝑜𝑢𝑡 such that the magnitudes are equal because of conservation of energy

Hyperbolic

The spacecraft’s trajectory is _____ relative to the planet.

Deflection Angle

A hyperbola is the angle by which a trajectory is “turned” as it passes around a central body when following a hyperbolic pat

Heliocentric Frame

There will be a change in velocity since they are on opposite direction

Heliocentric Speed

Although the spacecraft’s speed relative to the planet does not change, the change in direction of ^→𝑣 leads to a change in the _______

Voyager 1 and 2 Spacecraft

Used a series of gravity assists from Jupiter and Saturn to accelerate out of the solar system.

Orbital perturbation

Refers to the deviation of a celestial body’s actual path from its idealized orbit

Nudge or Disturbance

It causes an object in space to stray from its perfect, mathematically described orbit.

Third-body Perturbation

It refers to the gravitational influence exerted on an object’s orbit by a third celestial body, causing deviations from a two-body gravitation system.

Tidal Forces

Caused by the difference in gravitational pull across an object. Instead of pulling equally on the entire planet/spacecraft, a distant body (like the Moon or Sun) pulls slightly more on one side than the othe

Planetary Alignments

• When multiple celestial bodies line up, their gravitational effects combine and may affect another object.

• The net gravitational pull on a spacecraft can become stronger or more directionally consistent.

Asteroids and Comets

It can act as additional perturbing bodies, especially in regions like the asteroid belt or during close encounters

Solar Radiation

• Its pressure significantly perturbs the orbits of satellites, particularly those with high area-to-mass ratios.

• This can cause changes in orbital elements like eccentricity and perigee height

Outgassing

• It is the release of trapped gases from materials in a vacuum environment.

• This released gas molecules can create disturbances, like forces acting on the instrument, due to radiation pressure, and even temperature fluctuations

Atmospheric Drag

It causes orbit perturbation by slowing a satellite and causing it to lose altitude, essentially de orbiting it.

J₂ Perturbation

• It caused by Earth's oblateness.

• It introduces a non uniform gravitational field which is slightly stronger at the Earth's poles than at the equator

Active Control System

• It mitigate perturbations by continuously correcting deviations in a spacecraft’s motion and orientation.

Thrusters

It is used for station keeping maneuvers to adjust the orbit when it drifts due to forces like drag or gravitational irregularities.

Reaction Wheels

Spinning wheels inside the spacecraft. They are mainly used to counter any torques in a spacecraft

Control Moment Gyros (CMGs)

also use spinning wheels, but instead of just changing their speed, they tilt (or “gimbal”) the spinning rotor

Ground based tracking systems and onboard sensor

• It continuously measure the spacecraft’s position and velocity.

• Then discrepancies from the intended orbit are identified, planned corrective maneuver