A satellite climbs by firing its engine forward: burning at the low point lifts the high point, and burning at the high point lifts the low point.
To climb, a satellite does not point its engine at the sky. It fires along its direction of travel, adding speed. The extra speed carries it farther out on the opposite side of the orbit.
NASA puts the rule simply. Adding energy at the low point (periapsis) raises the high point (apoapsis). Taking energy away at the high point lowers the low point. The same logic works in reverse to raise the low point: burn forward at the high point.
Chandrayaan-3 shows the rule in action. An LVM3 launched it on 14 July 2023 into an elliptic parking orbit of about 170 × 36,500 km. Then the spacecraft fired its engine near the low point again and again. ISRO's mission log records the steps:
The low point barely moved. The high point climbed about tenfold.
A satellite heading for geostationary orbit does the opposite. It fires near its high point to lift its low point. NVS-01 left its rocket on a 170 × 36,568 km transfer orbit in 2023. It now circles at 35,751 × 35,820 km.
The same engines are used again at the end of a satellite's life. ISRO raised GSAT-12 above the geostationary belt in 2023 with a series of seven burns.
The engine for these big burns is often called a liquid apogee motor. India's Mars Orbiter Mission carried a 440 newton one, and used it at Mars in 2014 to brake into orbit there.
NVS-02 could not raise its orbit in 2025 because valves feeding oxidiser to its thrusters did not open. It remains on its stretched transfer orbit.
The Chandrayaan-3 propulsion module is in a very high Earth orbit, listed at about 125,000 × 308,000 km; compare its estimated distance with ordinary satellites. See Chandrayaan-3 on the tracker
The vis-viva equation ties speed to orbit size: v² = GM (2/r − 1/a). At a fixed point r (the perigee), a larger speed means a larger semi-major axis a, and since r_p stays put, the apogee r_a = 2a − r_p must rise.
Worked numbers for Chandrayaan-3 (R = 6,378 km, GM = 398,600 km³/s²), using ISRO's orbit heights:
The whole climb from a 36,500 km apogee to beyond the Moon's distance took only about 0.56 km/s of extra perigee speed. Near perigee, a small speed change makes a large change at apogee. Escape speed at the last perigee radius is √(2GM/r) = 10.94 km/s, so the final orbit was still bound to Earth, just reaching far enough for the Moon to take over.
Why fire near perigee, not anywhere? The energy per kilogram added by a small burn is v·Δv. It is largest where v is largest, which is at perigee. This is the Oberth effect, and it is why orbit-raising burns cluster at the fast point.
Near perigee, pointing so the thrust is along its direction of motion. Adding energy at perigee raises the apogee.
Each burn near perigee raised the apogee step by step, from about 36,500 km to over 369,000 km. The final step on 1 August 2023 sent it on a path towards the Moon.
It fires forward near apogee, which raises the perigee until it matches the apogee height.