This answer to How exactly did Cassini provide rock-solid attitude control to enable high resolution low light imaging? (1.2 arcsec/pixel for narrow angle camera) says:

Cassini was the first spacecraft to use a Litton Hemispherical Resonator Gyro (HRG)

but specifies "Litton". Linked in that answer is Hemispherical Resonator Gyro: an IRU for Cassini Proc. SPIE 2803, Cassini/Huygens: A Mission to the Saturnian Systems, (7 October 1996) which says in the abstract:

The JPL Inertial Reference Unit (IRU) is the single most sophisticated assembly on the Cassini spacecraft. At the core of the IRU is the state-of-the-art, Litton Hemispherical Resonator Gyro (HRG).


The Cassini mission is the first use of an IRU for a deep space planetary mission that does not use a spun-mass sensor.

I don't know what a "spun-mass sensor" means exactly; uncertain if "spun" refers to part of a manufacturing process (e.g. spin casting which could certainly be used to make metal hemispheres, see also Acme Metal Spinning1) or to the sensor being based on a mass that is spinning.

But here I'd like to ask:


  1. What was the first hemispherical resonator used in spaceflight?
  2. What was the first used on a deep space mission?

The following may be helpful (hat tip to Ng Ph):

1no affiliation; "ACME" anything is reminiscent of the rocket-based Wile E. Coyote & Road Runner Warner Brothers cartoons. Another example of a metal-spinning company.


1 Answer 1


The answer to both questions appears to be the same mission, depending on how you define a "deep space mission".

Image showing that the first NRG in space was the NEAR mission

If you don't consider NEAR deep space, then it's Cassini.

Its first mission was the NEAR program which launched the first HRG based system into space in 1996. This was quickly followed by a commercial communications satellite then the CASSNI (sic) mission to Saturn.

Source: The Hemispherical Resonator Gyro: From Wineglass to the Planets

  • 1
    $\begingroup$ The paper is really interesting! "The HRG 130P Gyro: 91 systems launched (89 satellites) 12 million operating gyro hours in space with 100% mission success" $\endgroup$
    – uhoh
    Nov 16, 2021 at 1:13

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