SPACE AGE ARCHAEOLOGY: An area junk bestiary: yo-yo de-spin weights

Among the many oldest items of house junk in Earth orbit are de-spin weights from the US sequence of TIROS climate and TV satellites. I have been noticing them in particles catalogues for years, and determined it was time to seek out out what they had been actually all about.  

TIROS 1 was launched in 1960 – simply three years after Sputnik 1. The satellite tv for pc is now 60 years previous! TIROS stands for Tv Infrared Remark Satellite tv for pc Program. One purpose of the satellite tv for pc was to see if Earth commentary from house would work, and may very well be used for climate reporting and prediction. The opposite was to check tv broadcast potential – so you’ll be able to see that it is likely one of the progenitors of two very vital satellite-based industries right now.

The satellite tv for pc was a cylindrical drum lined in photo voltaic panels with brief, angled antennas. It returned one of many earliest photos of Earth from exterior.

Picture courtesy of NASA

There have been 10 satellites within the first TIROS sequence, after which they continued as TIROS-N in collaboration with the US Nationwide Oceanic and Atmospheric Administration (NOAA). Of those 10, 5 are nonetheless in Low Earth Orbit as items of house junk.

So what about these de-spin weights?

When rockets are launched, a key consideration is maintaining them stabilised in order that they do not pitch, roll or yaw, and find yourself in a crater within the floor as an alternative of in orbit. One option to stabilise them is to spin them perpendicular to their lengthy axis. This methodology of stabilisation was regularly used for the launch of small, light-weight spacecraft (Cornille 1962:1). The issue with that’s when the satellite tv for pc is launched, it has the identical spin because the rocket, which is mostly too excessive for it to perform. So it’s a must to cut back the spin and reset the satellite tv for pc. That is what the de-spin weights are for. There is perhaps one or two weights. Two weights are known as yo-yo weights, and one is only a yo-weight. 

Luckily, I didn’t must determine this out all on my own, because the Sensible Engineer has finished a reasonably nice job of explaining the ideas, as you will note within the video.

This can be a description of the mechanism from Fedor (1961:1):

The yo-yo de-spin mechanism is actually two items of wire with weights on the ends …  These wires are symmetrically wrapped across the equator of the satellite tv for pc and the weights are secured by a launch mechanism. At a pre-selected time after satellite tv for pc spin-up and launch from the launching automobile, the weights are launched, thus discarding sufficient momentum to scale back the spin of the satellite tv for pc to the specified worth.

The weights should not solely launched, however discarded as mission-related particles. This sort of discard is now discouraged in tips for mitigating house particles. 

One thing I ponder about is whether or not the weights nonetheless in orbit belong to the TIROS satellites remaining in orbit, or whether or not they belong to a re-entered TIROS? Did the de-spin weight are likely to re-enter with corresponding satellite tv for pc? Is the orbit an indicator? 

So many questions! Did the USSR use this mechanism for satellite tv for pc stabilisation? There are actually no USSR de-spin weights catalogue from this era that I might discover.

And what did they appear to be? These illustrated in Fedor (1961) look (from the grainy picture) to be rectangular, possibly about an inch lengthy. Fedor (1961) additionally makes use of a unit of measurement known as the slug-ft/2 and I do not even know what it’s. OK, I seemed it up and this is what it’s.

The place else can we discover de-spin weights? The Explorer sequence used them. Here’s a marvellous illustration of them engaged on Explorer 11, launched in 1961 (from Cornille 1962).

This can be a de-spin weight from 1962 British satellite tv for pc Ariel 1. Observe that this one would not have a inflexible wire, however a tightly coiled spring (additionally from Cornille 1962). The ‘stretch’ yo-yo design was patented by Cornille and Fedor in 1970. This instance has, to my thoughts, a reasonably sinister snake-like aura as if it’d out of the blue spring to life and begin searching for you out with its eyeless head and whipping tail.


The Daybreak mission to Vesta and Ceres, launched in 2007, used de-spin weights, because the launch rocket’s third stage was spin-stabilised. I needed to know the place the weights ended up. Luckily my pal Ady James knew the place to search for them and situated this weblog submit by Daybreak Mission Director and Chief Engineer Marc Rayman for me:

After the third stage has completed firing, it stays securely hooked up to Daybreak for one more 4 minutes 50 seconds. Though the stage is stabilized by spinning, the spacecraft doesn’t function that method; but by this time, they’d be spinning collectively at 46 rpm, too quick for the latter’s management system. Due to this fact, beginning 5 seconds earlier than separation, the third stage prompts a surprisingly easy system to gradual its rotation fee. Wrapped across the Delta are two cables, every 12.15 meters (39 ft 10 inches) lengthy. On the finish of every is a 1.44-kilogram (3-pound-3-ounce) weight fabricated from aluminum and tungsten. When the cables are launched, the spin causes them to unwind. As they carry the weights farther and farther out, the spin slows down due to the identical precept that makes an ice skater spin quicker by pulling her arms in or slower by extending them to her sides. After 4 seconds, when they’re totally unwound, the cables unhook from the spacecraft. With their weights nonetheless hooked up, they enter impartial orbits across the Solar; maybe one in all them can be studied by a future photo voltaic system archeologist.

Nicely there you go, he was proper as that is precisely what I am doing! This submit provides some attention-grabbing particulars. The load is let go by releasing the cable, so the cable continues to be hooked up to it. I ponder if it stays taut after launch? The cables are 12 metres, greater than the size of two tall girls end-to-end. No details about the form of the weights, however we do have supplies – aluminium and tungsten. Why tungsten, a metallic briefly provide on Earth? There isn’t a have to make these weights sturdy as their solely goal is to be heavy. Maybe tungsten provides the required weight for measurement. How does this alloy react to house climate, plasmas and bombardment? Is it contributing aluminium particles to the house setting? Might they mix with the atomic components so widespread within the house setting to kind new compounds? Al2O3 (aluminium oxide) or tungsten oxides?

The weights would, one presumes, behave like a meteorite as they’re strong. And extra like a metal-rich meteorite too. Would they be distinguishable via a telescope or by spectroscopy?

So many questions.

What number of of those weights are circulating amongst all of the house junk? Jonathan McDowell’s catalogue of house objects has 286 de-spin weights listed. What number of of those are nonetheless in orbit is one thing I am going to have to depart for a future calculation.

What in regards to the injury a collision with a de-spin weight would trigger? These are dense, heavy, strong objects, and I will guess for that purpose could be way more harmful than one thing of the same measurement, cross-sectional space or velocity, however made of various supplies. It also needs to be doable to mannequin how an affect crater from collision with one in all them would possibly differ from different items of house junk. This is able to assist determine legal responsibility for the injury, because the launching state is chargeable for this beneath UN treaties.

Comparatively, there should not that many de-spin weights, in contrast say to rocket our bodies, however maybe the larger injury they’ll do would benefit being selectively focused for lively particles elimination. 

As Fedor and Cornille are quickly turning into my yo-yo gurus, I assumed I ought to study just a little extra about them. Sadly Henry Cornille died in 2019 on the age of 80. He went on to work on the Apollo programme. I could not discover something about Fedor on-line so this clearly requires deeper archival analysis. If you concentrate on it, they’re the pioneers of right now’s house tether know-how.

I’ve received one other free finish to tie up right here – the relation to the favored youngsters’s toy known as the yo-yo. I realise I do not know something about its origins. *goes and appears up* Nicely, this was an eye-opener, as my assumptions that it was Sixties invention change into extraordinarily flawed! The yo-yo could be very historical know-how, originating in China (as certainly does rocket know-how). 

This can be a fetching pink determine vase displaying a boy taking part in with a yo-yo within the fifth century BCE, from the Antikensammlung museum in Berlin.

The yo-yo despin weights are a beautiful thread linking physics from the previous to the longer term. I’ve grow to be fairly captivated by them.


Cornille, Henry J.Jnr 1962 A way of precisely decreasing the spin fee of a rotating spacecraft. NASA Technical Observe D-1420 

Fedor, JV 1961 Principle and design curves for a  yo-yo de-spin mechanism for satellites. NASA Technical Observe D-708

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