ISRO performs first orbit­raising manoeuvre of Chandrayaan­3

ISRO performs first orbit­raising manoeuvre of Chandrayaan­3

Subject : Science and technology

Section: Space technology

Concept :

• A day after the Indian Space Research Organisation (ISRO) successfully launched India’s third moon mission, Chandrayaan-3, the first orbit-raising manoeuvre was conducted on Saturday.
• The manoeuvre was performed by the ISRO Telemetry Tracking and Command Network (ISTRAC) in Bengaluru to place the Chandrayaan-3 spacecraft at the 41,762 km x 173 km orbit.
• This means that Chandrayaan-3 is now in an orbit, which when closest to Earth is at 173 km and farthest at 41,762 km.

Orbital Manoeuvre

• In spaceflight, an orbital maneuver (otherwise known as a burn) is the use of propulsion systems to change the orbit of a spacecraft.
• For spacecraft far from Earth (for example those in orbits around the Sun) an orbital maneuver is called a deep-space maneuver (DSM).
• An on-orbit burn (ie a delta-v, for change in velocity) can alter the shape of an orbit.
• Posigrade burns (forward in the direction of orbit) will raise the existing flight path, while retrograde burns (opposite the direction of orbit) will lower it.
• Left Posigrade burn results in higher orbital altitude and Right Retrograde burn lowers orbital altitude
• An interesting feature of orbital burns is that if no other burn occurs, the spacecraft will always pass again through the point of burn. These burns can be combined into orbital maneuvers that will change the size, shape, or orientation of the orbit

Hohmann transfer:

• An elliptical orbit used to transfer between two circular orbits in the same plane. The first posigrade burn stretches the circular orbit into an elliptical one. Then at the apoapsis of the elliptical orbit, another posigrade burn circularizes the orbit at a higher altitude. Two retrograde burns can be done in the same order if a smaller circular orbit is desired
• A Hohmann transfer orbit being used to increase orbital altitude

Bi-elliptic transfer:

• An alternate way to transfer between two circular orbits in the same plane. It takes a combination of three posigrade/retrograde burns (posigrade, posigrade, retrograde to increase, retrograde, retrograde, posigrade to decrease altitude), but despite the extra burn, it can actually be more fuel efficient than the Hohmann transfer if the ratio between the new and old altitudes is sufficiently high (~12x). A mathematical explanation for why is included in a later section.
• A bi-elliptic transfer being used to achieve a higher altitude circular orbit. Posigrade burns at points 1 and 2, retrograde burn at point 3
• Orbital inclination changes:
• The Hohmann and bi-elliptic transfers are useful for orbits in the same plane, but what if we want to increase orbital inclination? These require much more energy, but can be done with an upward or downward thrust perpendicular to the existing orbital plane at one of the nodes. This will rotate the orbital plane about the line of nodes