I have been trying to find information on Hubble's gyros. So far all I have found is that they are rotating mass rate gyros with gas bearings and that the were the most accurate available when installed (according to NASA).

Does anybody know what organization manufactured the Hubble gyros? And anything about their heritage? Are they still manufactured (just curious, it seems unlikely there will be a chance to replace the ones onboard)? As far as I know, nobody still makes rotating mass gyros for space applications. I have checked websites for Honeywell and Northrup Grumman and found nothing.

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    $\begingroup$ Scott Manley just made a video about Hubble's gyros, and he mentioned the reason you can't find much info on them: these are ITAR controlled items. $\endgroup$
    – Hobbes
    Commented Jun 15 at 19:31
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    $\begingroup$ @Hobbes I was reading some presentations on Trick and JEOD this week, both of which are available open source, but one part of one (JEOD iirc, I think JEOD 4) is ITAR restricted and so not publicly available. The presentation went on to say "but F=ma would be ITAR if they could" $\endgroup$
    – Erin Anne
    Commented Jun 16 at 1:38
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    $\begingroup$ Well, yes, almost everything space related is ITAR. But it's OK to publish information like who makes the gyro, what its flight heritage is, and its performance specs. blobbymcblobby's answer below is all public domain, and even if it weren't, the only bits that are even close to ITAR-restricted are the details about the little wire (what it's made of, how it failed). $\endgroup$ Commented Jun 16 at 20:59

2 Answers 2


Does anybody know what organization manufactured the Hubble gyros?

Erin Anne's answer is on the money

Originally, Bendix Guidance Systems Division of Bendix Corporation built the RSU's. As of 2009, they were replaced entirely with newly manufactured units made by L-3 Communications.

(To clarify, of the three RSU's installed in 2009, each containing two gyros, two were newly manufactured by L-3, and a backup Bendix-manufactured unit, refurbished by L-3 was installed instead when one of the new ones failed to seat properly)


So I would like to add to that, the following notes (and not as an answer):

Found on page: https://asd.gsfc.nasa.gov/archive/sm4/multimedia/gallery2_gyro.html

A rectangular box with white handles on top, some circular connectors on one end and a black metal etched/embossed label on the side, captioned "Rate Sensor Unit. Each RSU houses 2 gyros"

The label is partially visible, and with the title "Space Telescope Rate Sensor Unit", is the logo for Bendix (Guidance Systems Division) bottom left:

Zoom on the label, rotated to make the text horizontal, still difficult to read

Bendix GSD product photo of the unit for HST:

Bendix Guidance Systems Division logo and label, legible, clearly the same as what's printed less-legibly in the previous image

Contractors for HST (From: NASA Hubble Space Telescope Reference Guide):

Table 5-2 "Space Telescope Equipment Responsibilities" from the linked document, showing (among many other pieces of equipment on the Hubble) the Rate Gyro Assembly's prime contractor is Bendix

Equipment: Rate Gyro Assembly, Contractor: Bendix

And finally, a ref for Bendix: https://en.wikipedia.org/wiki/Bendix_Corporation

And anything about their heritage?

research has shown the heritage goes back to Saturn, and at least looking to build upon Skylab's CMG experience. In general Bendix's involvement, with guidance systems, has an even longer history that predates the modern space industry.

Recommendations for improvements over Skylab CMG's:

During the 4 year period from 1970 to 1973 the Bendix Guidance Systems Division (BGSD) of the Bendix Corporation developed and delivered to Marshall Space Flight Center (MSFC) several items of advanced Control Moment Gyro (CMG) prototype and breadboard equipment for MSFC evaluation


1985, "Accommodation of Astrophysical Instruments in the Space Station System"


(through mergers in the 1980s, Bendix became a Honeywell brand; following further changes, the Bendix name is now related to the automotive industry only)

Are they still manufactured ? As far as I know, nobody still makes rotating mass gyros for space applications.

Specific to the HST RSU's, at some point L-3 Communications took over the contract for responsibility of the RSU's. Under this company, they manufactured new RSU's with modifications, for the 2009 SM4 STS-125 mission. Following a merger, this company became L3Harris Technologies, Inc.

It seems that technology has marched on, with spinning mass mechanical gyros having given way to ring laser gyros (and other types) for the space industry. Honeywell still list mass mechanical gyros as one of their key technologies.



Modern RGA:

A long white ribbed box with five connectors at one end and four feet with bolt holes protruding from the sides

The ISS for example mounts two (one a spare) Honeywell GG1320AF RGA's with three RLG's inside each.

Additional (RE: STS-125, SM4):


slide with CAD views showing where the RSUs are located on Hubble









after successfully installing the replacement RSU2, RSU1 failed to seat and bolt into position. While RSU3 successfully took the place of RSU1, the plan moved to placing the new RSU1 in RSU3’s position also proved to be problematic.

With the issue confirmed to be with RSU1 itself, the spacewalkers were informed to move to a backup plan of installing an old unit from the Contingency ORU Protective Enclosure (COPE), into the remaining postion. This also seemed to be “wobbling” on the installation plate, before success was finally forthcoming via a successful attempt to bolt the spare RSU in place. Hubble now has two new RSUs, and one spare, successfully installed.


The 2009 replacement of the RSU's:

crop of the top of a slide titled "Rate Gyro Assemblies (RGA)" stating "Consists of Electronics Control Unit (ECU) and the Rate Sensor Unit (RSU) (manufactured by L-3 Communcations (then Bendix)) / Each RSU contains 2 Rate Integrating Gyros; HST has a total of 6 Gyros / 3 Gyros are routinely in control loop" and a picture of a box with a white handle on top and two connectors on the end

The new RSU's were manufactured by L-3 Communications, and differed from previous RSU's in mainly two areas: the first with regards to a component that facilitates the transfer of electricity and data inside the gyro. Over time, the flex leads begin to corrode and can physically bend or break. Over three decades, Hubble had eight out of 22 gyros fail due to a corroded flex lead. With the new Enhanced Flex Leads (EFL), the flex lead is coated with a protective barrier to slow degradation caused by the fluid in which it floats. From this point on, the previous components were referred to as Standard Flex Leads (SFL).

The second area was that in previous gyros there was a build-up of particles and lubricant between the shaft and the rotor resulting in a transient load torque and a momentary disruption in the spin motor phase. Gyros that failed due to rotor restriction tended to have shaft-to-rotor spacing on the low end of tolerance. Tolerance was modified to ensure greater spacing.


HST Gyro Run Times through 2015/Sep-30

RGA Anomalies – Flex Lead Failure

gas gyro diagram and expanded components labelled

This is from 2015. Beyond this point it is difficult to find further info on new, if any, construction of such units.

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    $\begingroup$ You guys are crazy -- and awesome. $\endgroup$ Commented Jun 15 at 13:31
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    $\begingroup$ If you can find any information on Servicing Mission 4 in 2009 when all six gyroscopes were replaced that might provide some additional information and confirmation. The replacements were supposed to last longer than the originals so presumably there was something different about them, whether they were made by the same manufacturer, I would think so but that would need to be confirmed also. $\endgroup$ Commented Jun 15 at 13:37
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    $\begingroup$ I did find some but tossed it as it didn't have what I was looking for - it tends to be that the contractors themselves tell you what they made, whereas NASA less so. $\endgroup$ Commented Jun 15 at 13:40
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    $\begingroup$ blobbymcblobby - I don't remember what the differences were, seems like it was the lubrication or the bearings or something, presumably the rest of the package was pretty much the same, but I don't know that for sure. I have always been interested in knowing what the differences were between the current gyros and the originals. $\endgroup$ Commented Jun 15 at 13:59
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    $\begingroup$ @StevePemberton - so updated with info that might be of interest to you. New RSU's were made by L-3 Communications (now HarrisL3 Technologies Inc), and differed to earlier RSU's with silver plated flex leads to alleviate corrosion issues and tolerance modifications to avoid rotor restriction failures. The original Bendix facility that made the original RSU's was sold off and demolished. And then I ran out of leads.. $\endgroup$ Commented Jun 15 at 15:09

I think they were made by Bendix. Here's why:

Performance Characterization of the Hubble Space Telescope Rate Gyro Assembly has two authors, Weinstein and Slater, attributed to Allied Bendix Aerospace Corp, Guidance Systems Division, Teterboro NJ.

That prompted me to look to see if Bendix claimed them anywhere, and I got Scale Factor and Noise Performance Tests of the Bendix Corporation Rate Gyro Assembly, a 1980 report from the 6585th Test Group at Holloman Air Force Base, NM. Quoting the foreward:

This report documents the results of scale factor and noise performance tests of the three Bendix Corporation Rate Integrating Gyroscopes which were part of a Rate Gyro Assembly (RGA) to be used on the Space Telescope Pointing and Control System. Two gyros were standard Bendix models, while the third used a low-viscosity rotation fluid.

It's not airtight but the overlapping terminology, timeframe, and the contributions of the Bendix authors to the Hubble Space Telescope document are all quite suggestive.

The gyro assemblies must be bespoke, because Enhanced versions were provided to deal with some of the ongoing issues. I can't find any evidence that they were manufactured for further space telescopes, though obviously that isn't conclusive.

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    $\begingroup$ I was coming here to say the same thing, so I think its probably the right track. $\endgroup$ Commented Jun 15 at 6:54
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    $\begingroup$ @blobbymcblobby maybe you can write a firmer answer? I was hoping I could find a high-res photo of one of the rate sensing units because the photos I've seen make it clear they have a label on the side, but I haven't seen a photo where the label is legible. $\endgroup$
    – Erin Anne
    Commented Jun 15 at 7:00
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    $\begingroup$ Your answer is fine. Only other thing was that I did find some RGA package product photos and could work out information from the label. Eventually found a contractor list that confirms Bendix as contractor for the RGA. $\endgroup$ Commented Jun 15 at 10:22
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    $\begingroup$ I seem to remember that the gyros installed on the final 2009 servicing mission (they replaced all six of them) were different than the originals, and were expected to last longer, which in spite of the recent failures they have done quite well. Presumably the replacements were made by the same manufacturer as the originals but that would need to be verified. $\endgroup$ Commented Jun 15 at 13:31
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    $\begingroup$ Erin Anne - interestingly, there was a manufacturer change - for the 2009 STS-125, SM4, the Bendix-manufactured RSU's were replaced with units made by L3 Communications. $\endgroup$ Commented Jun 15 at 15:11

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