Handbook of Turbomachinery Second Edition Revised - Ventech!

shall see, contemporary rocket engine turbomachinery generally makes no
provision for lubrication of rolling element bearings per se, but rather
supplies to the bearing a quantity of the propellant being pumped to act as a
coolant. This design practice results in weight reduction due to the omission
of both the lubricating fluid supply and the required distribution system, but
also a reduced bearing DN capability for a given time period.
The turbopump for the Thor engine system, designed in the early to
mid-1950s, incorporates a two-stage impulse turbine similar to that shown
in Fig. 23. The turbine shaft is supported by acylindrical roller bearing for
radial load reaction and a ball bearing to react the axial thrust. Both of these
bearings are 35-mm bore diameter and operate at approximately 40,000 rpm
for a bearing DN number of 1:4610 6 . The twin centrifugal pumps are
supported on a common drive shaft by combination of a 70-mm ball bearing
and 70-mm cylindrical roller bearing. At a pump shaft speed of 6,800 rpm, a
bearing DN number of 476,000 results. The bearings in this turbopump are
lubricated by blending the kerosene fuel with an extreme-pressure additive
known as Oronite. The mixture of these two fluids results in a quite excellent
lubricant.
The F-1 engine employed a direct-drive turbopump that depended on
the largest set of rolling element bearings ever used in a production rocket
engine system. The large two-rotor turbine (35-in. pitch diameter) was
supported by a 170-mm bore cylindrical roller bearing, while a tandem 130mm
bore ball bearing reacted axial thrust. These bearings operated at an
angular velocity of 5,500 rpm, with a DN number of 935,000 and 715,000 for
the roller and ball bearings, respectively.
The advent of liquid hydrogen as a propellant seemed to mark the
general period where cooling/lubrication of a rolling element bearing was no
longer performed by either conventional oils or kerosene. There are a
number of reasons for this. Among them are the weight savings mentioned
earlier, as well as the substantial difficulty of prevention of freezing of the
lubricant due to exposure to cryogenic hydrogen. The Pratt and Whitney
RL-10 (Centaur) and the Rocketdyne J-2 engine marked the first production
use of hydrogen-cooled bearings, the RL-10 using GH2 as coolant, and the
J-2 using hydrogen in the liquid state as coolant. Bearing DN numbers
attained in the case of the J-2 engine were 1:6610 6 .
The Space Shuttle main engine makes the greatest demand thus far on
rolling element bearings in rocket propulsion systems. The high-pressure
fuel turbopump employs two pairs of 45-mm bore ball bearings at a shaft
speed of 37,000 rpm at maximum thrust, for a bearing DN number of
1:7610 6 . Likewise, the high-pressure oxygen turbopump employs two 45mm
bore ball bearings in concert with two 57-mm bore ball bearings. These
bearings are cooled by a supply of liquid oxygen obtained from the pump,
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