- CZ-5 = Long March 5
- YZ-2 = Yuanzheng 2
- SJ-17 = Shijian 17
SJ 17 (Shijian 17) is a Chinese experimental satellite flown on the maiden CZ-5/YZ2 launch.
It is reportedly carrying out experiments with ion propulsion for station keeping.
The satellite will be directly inserted into geostationary orbit by the YZ-2 upper stage of the launch vehicle. (my emphasis)
CZ-5 has two stages according to Wikipedia, and second stage uses a pair of LH2/LOX restartable YF-75D engines. According to the Spaceflight 101 article China’s Long March 5 Heavy-Lift Rocket achieves full Success in Inaugural Mission:
The two engine nozzles began glowing bright orange again when the second stage re-started on a burn of just over four minutes to boost the stack into a highly elliptical sub-GTO-type orbit. Loud cheers emerged when the Yuanzheng-2 upper stage separated from the booster right at the half-hour mark into the flight, marking Mission Success for the Long March 5 rocket.
Assuming control of the flight, Yuanzheng-2 immediately fired its hypergolic main engine for a short supplementary burn to raise the high point of the orbit to Geostationary Altitude at around 36,000 Kilometers. Next was a coast phase of around five and a half hours to allow YZ-2 to climb to the apogee of the orbit so that its second burn can circularize the orbit and reduce its inclination to reach a Geostationary Orbit for spacecraft separation at 18:57 UTC.
The hypergolic-fueled Yuanzheng-2 seems to be considered an "upper stage", and yet, separation is considered the completion of the Long March 5's mission. Is the YZ-2 considered a 3rd stage?
How many stages does the Long March 5 actually have? Two, or three?
above: Long March-5 Rocket from here