Gunter's Space Page says:

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?

enter image description here

above: Long March-5 Rocket from here

  • $\begingroup$ @polygnome sounds good to me - consider bringing it back? $\endgroup$ – uhoh Nov 4 '16 at 13:17

A Honda Civic is a two axle vehicle. It can tow a trailer. When it's towing a trailer, Civic-plus-trailer is functionally a three axle vehicle.

There's no essential difference between a spacecraft with propulsion and a rocket stage.

In this case, Long March 5 is a two-stage rocket because it's designed and built separately from the YZ stage.

Long March 5 + YZ is functionally a three stage rocket.

  • $\begingroup$ A good point, though it would be interesting to distinguish whether the "upper stage" has some input into the control of events on the previous stages, such as separation, or is a pure passenger ejected by the previous stage. As an example, and please correct me if I am wrong, my understanding is that the Briz upper stage of the Proton follows the "control" model, delivered satellites follow the "passenger" model. $\endgroup$ – Puffin Nov 5 '16 at 15:09

Your Answer

By clicking "Post Your Answer", you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.