A GTO is a long, stretched orbit with its low point a few hundred kilometres up and its high point near geostationary height, used to carry satellites towards GEO.
Rockets usually do not carry a satellite all the way to geostationary orbit. Instead they release it on a stretched ellipse: the low point is a few hundred kilometres up, and the high point is near 35,786 km. This is a geosynchronous transfer orbit.
The satellite then fires its own engine near the high point to round the orbit out. That job is called orbit-raising.
The transfer orbit is usually tilted, too. ESA notes that a launch from Kourou, about 500 km north of the equator, leaves a slightly tilted transfer orbit, and the burn at the high point removes that tilt as well. Launches from Cape Canaveral can instead aim the high point above geostationary height — a "supersynchronous" transfer — to save fuel.
On 29 May 2023 a GSLV launched the 2,232 kg navigation satellite NVS-01 from Sriharikota. ISRO's target orbit was 170 km at the low point and 36,568 km at the high point, tilted 19.36° to the equator.
Today the catalogue shows NVS-01 at 35,751 × 35,820 km with an inclination of 1.84°. The satellite's own burns lifted its low point by about 35,600 km and took out most of the tilt.
In January 2025 a GSLV placed NVS-02 into its transfer orbit correctly. But when the satellite tried its first orbit-raising burn, the valves that let oxidiser into its thrusters did not open. Without that burn the satellite stayed on its stretched orbit.
Its catalogue orbit is still 214 × 37,251 km, with a period of 660 minutes — 11 hours, not one day.
Because GTO is the usual drop-off point for geostationary satellites, launch vehicles quote their capacity to it. ISRO's GSLV Mk II can carry 2,250 kg to GTO. The PSLV can carry 1,425 kg to a sub-GTO, a transfer orbit with a lower high point.
NVS-02's estimated height swings between about 214 km and about 37,251 km every 11 hours — a transfer orbit it never left. Track NVS-02 on its transfer orbit
The vis-viva equation gives the speed anywhere on an orbit: v² = GM (2/r − 1/a), where a is the semi-major axis.
Worked numbers for the GSLV-F12 target orbit (R = 6,378 km, GM = 398,600 km³/s²):
If the orbit were already in the equator's plane, one burn at apogee would need Δv = 3.05 − 1.57 = 1.48 km/s. But the GTO is tilted 19.36°. A plane change is cheapest where the satellite moves slowest, so it is folded into the apogee burn. By the law of cosines:
Δv = √(v_a² + v_c² − 2·v_a·v_c·cos 19.36°) = 1.68 km/s.
The tilt removal adds only about 0.2 km/s because it is done at apogee. Braeunig notes this is standard practice: a small plane change at perigee, most of it at apogee.
For NVS-02 the same arithmetic gives a = 25,111 km and T = 2π√(a³/GM) = 660 min — exactly the catalogue's period, confirming the satellite is still on its transfer ellipse.
The rocket reaches the high point only on a stretched ellipse. The satellite's own engine then makes the final burns at apogee to make the orbit circular, which is the standard way to reach GEO.
The valves that admit oxidiser to its thrusters did not open, so the planned orbit-raising burn could not be done. The satellite stayed in an elliptical transfer orbit.
The satellite moves slowest at apogee, so turning its direction there costs the least change in velocity, and it can be combined with the circularising burn.