Jeff Bezos Muses About Those Underappreciated Engine Components – Bearings

Finding its bearing: Orbit plot with starting shaft location (red dot) marking each revolution as shaft spirals to its center during propellant fluid film pressurization. (Credit: Blue Origin)

By Jeff Bezos

Although the BE-4 turbopump is smaller than your refrigerator, it generates 70,000 horsepower from a turbine running at nearly 19,000 revolutions per minute that pumps cryogenic propellants to pressures just under 5,000 pounds per square inch. To react the forces generated by the rotating turbine and impellers inside the pump, production rocket turbopumps to date have used traditional ball and roller bearings. For BE-4, we’re doing something different – we’re using hydrostatic bearings.

A hydrostatic bearing relies on a fluid film supplied by a high-pressure source to provide support for the shaft and cause it to float without contacting the static structure except at startup and shutdown. The BE-4 main turbopump uses hydrostatic journal bearings for radial support and hydrostatic axial bearings to carry axial thrust. The system is bootstrapped. The high pressure fluid films for the bearings are supplied by the propellants themselves – liquefied natural gas and liquid oxygen – tapped off from the pump discharge flows.

Material selection is a critical consideration for this approach, as there is physical contact between the bearing surfaces during the start transient before the fluid film is fully established and during the shutdown transient as the fluid film dissipates. With lab-scale tests and full-scale bearing rig tests using actual pump hardware, we evaluated over 20 material combinations in over a hundred tests, leading to our baseline material and coating choices.

Extensive rotordynamic and computational fluid dynamics analyses have shown the feasibility of this design, and recent powerpack tests confirmed that this approach works during the startup and shutdown transients – the most critical phases. The shaft orbit plot below shows that the turbopump lifts off smoothly and centers during a typical start transient, demonstrating a smooth ride on a film of propellant.

Why do we go to all this trouble instead of just using traditional bearings? Engine life. We’re relentlessly focused on reusability, and properly designed hydrostatic bearings offer the potential for longer engine life without refurbishment. This is one of the many engineering decisions we’ve made that we hope will lead to reusability – not just in principle – but to practical, operational reusability. If “reusability” requires significant refurbishment, inspection, and re-validation between flights, then it simply won’t lead to the far lower launch costs we need to achieve our vision of millions of people living and working in space.

We’ll keep you up to date as our testing progresses in the coming weeks.

Gradatim Ferociter!

Jeff Bezos

  • Mr Snarky Answer

    Plan was to employ this on LOX pre-burner of SSME. They never pulled the trigger and just did a bunch of research instead. Glad to see people pulling the trigger on stuff that has been researched but not employed. Rumor is Raptor uses hydrostatic bearings too, but I have no concrete source on this.

  • windbourne

    one thing about NASA is that they do all this wonderful research. We really need for CONgress to fund these kinds of operations to the point where it can show some use, as opposed to stopping it mid way without knowing end results.

  • No they don’t. Bush cancelled the Space Launch Initiative in 2002.

    They haven’t done a damn thing in propulsion since then.

    Well, I guess they prepared to dispose of the SSMEs.

  • WhoAmI

    They’ve lost their bearings!

  • duheagle

    Well, there was the J-2X. But, yeah, that doesn’t really seriously erode your point. Pretty much makes windbourne’s point too.

  • When I wrote that I knew I had forgotten something but I couldn’t pin it down, haha. Touche;, I love hydrogen.

  • Enrique Moreno

    Very interesting. “Babbitt” bearings are common in big powerful machines.


  • Jeff2Space

    SLI wasn’t research into new launch vehicle technologies. It used “throwback” technologies to minimize risk. NASA needs to get out of the launch vehicle development business and help others make their launch vehicles better. This is what NACA did for aviation, and it worked well for the US aviation industry.

  • Jeff2Space

    Except J-2X wasn’t research into new engine technologies, it was an engine development program. Today, US companies can develop engines without NASA running the program (e.g. AR-1, Merlin, Raptor, BE-3, and BE-4).

    Something useful NASA could do is fly the linear aerospike engines they developed for X-33. They’ve been test fired on the ground, but without actually flying them, we don’t have any real data on how they’ll perform in flight.

  • windbourne

    We really should have allowed X-33 to completion.
    There was a LOT of tech demonstration on that.
    Thankfully, they DID do the tanks.
    But, IIRC, the thermal skin was a nice re-usable design.

  • Paul Thomas

    Got to laugh. This is a Blue Origin story and every comment so far has been not about Blue Origin.

  • Dave Salt

    I guess it depends upon how you define ‘research into new launch technologies’ but SLI certainly aimed at what I’d consider to be new engine technologies with a focus on reusability…
    …which included the use of hydrostatic bearings on both LOx/LH and LOx/Kerosine engine turbopumps, though I’ll admit they didn’t manage to get very far 🙁

  • Please allow me to refresh your memory.

    The RS-84 was a bit of a throwback, like the AR-1.

  • Jeff2Space

    I stand corrected. I was clearly thinking of another program. SLI did try to push engine technologies, which was a good thing.

  • duheagle

    You fail to grasp that the purpose of most comments on these forums is to bitch about something. Blue Origin simply doesn’t supply much about which to bitch. So we improvise.