According to this Wikipedia list, the rockets Delta IV Heavy and Proton can launch the same mass payload to LEO, 23 tons. But the capacity, according to Wikipedia, is dramatically different when it comes to what mass payload those same rockets can launch to GEO geostationary orbit, or to TLI trans lunar injection. (13 and 7, or 9 and 5.7 tons for DIVH and Proton).

Why is this? Are public tables like this practically useless for comparison of different launch systems? Or does the launch capacity to different altitudes depend on what upper stage is compatible with the launch system? Or what else?

  • $\begingroup$ Would launch site be a factor in the table's values? i.e. GTO becomes difficult/energy expensive or impossible for launch sites away from the equator. So if a launch system is, for whatever reason, constrained to a site some distance from the equator, it may be usable for GTO but inefficient...? $\endgroup$ – Anthony X Sep 6 '14 at 15:17

The numbers on the Wikipedia page are a little messed up, so you can't do apples-to-apples comparisons. You'd need to go to the actual payload planner's guides to see what the performance is to what orbits. Here are the guides:

Delta IV Launch Services User's Guide

Proton Launch System Mission Planner's Guide

A Proton launch to a LEO with the launch site inclination (51.5°) is 23 t. A Delta IVH launch to a LEO with the launch site inclination (28.7°) is 28.79 t. Quite a bit more. The 23 t on the Wikipedia page is for a Delta IVH launch to a polar orbit (90°), at 23.56 t. So you would expect the Delta IVH to also deliver quite a bit more to GTO or TLI.

(You said GEO, but you must mean GTO, since launch vehicles rarely if ever deliver a spacecraft all the way to GEO -- they drop off the spacecraft in GTO, Geosynchronous Transfer Orbit, which has an apogee around GEO and a low perigee).

What's more, the Proton is handicapped with a launch site so far to the North. Large plane change maneuvers are required to reduce the inclination of the orbit to drop off the spacecraft closer to (but still not at) the GEO inclination of 0°. This figure from the guide shows how large the plane change is:

Proton Mission Profile from SC injection into GTO from Parking Orbit

The 6.92 t GTO figure for the Proton is a drop off to a 31.1° inclination orbit, with a perigee at 2175 km. That leaves 1800 m/s to the spacecraft to get to GSO.

The Delta IVH delivers 14.22 t to a 27° orbit, requiring essentially no plane changes to get there, with a 185 km perigee leaving 1804 m/s to the spacecraft to get to GSO.

The Proton is even further handicapped by a lower Isp upper stage (the Бриз-М or Breeze-M) using storable propellants, as compared to the Delta IVH upper stage using LH2/LOX. So there will be lower performance for the Proton as compared to the Delta IVH when boosting past LEO, even if they were at the same starting point in orbit and mass.

  • $\begingroup$ Yup, that's the explanation. It's also the reason why the Russians are paying us Europeans rent for our well-positioned launch site in Kourou/French Guiana to launch GTO Soyus missions. $\endgroup$ – Rikki-Tikki-Tavi Sep 7 '14 at 22:27

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