Reverse-engineering the Globus INK, a Soviet spaceflight navigation laptop
One of the crucial attention-grabbing navigation devices onboard Soyuz spacecraft was the Globus INK,1 which used a rotating globe
to point the spacecraft’s place above the Earth.
This electromechanical analog laptop used an elaborate system of gears, cams, and differentials
to compute the spacecraft’s place.
The globe rotates in two dimensions: it spins end-over-end to point the spacecraft’s orbit, whereas
the globe’s hemispheres rotate based on the Earth’s each day rotation round its axis.2
The spacecraft’s place above the Earth was represented by the fastened crosshairs on the plastic dome.
The Globus additionally has latitude and longitude dials subsequent to the globe to point out the place numerically, whereas the sunshine/shadow dial beneath the globe indicated when the
spacecraft would enter or depart the Earth’s shadow.
The INK-2S “Globus” area navigation indicator.
Opening up the Globus reveals that it’s full of sophisticated gears and mechanisms.
It is superb that this mechanical know-how was used from the Sixties into the twenty first century.
However what are all these gears doing? How can orbital features be carried out with gears?
To reply these questions, I reverse-engineered the Globus and traced out its system of gears.
The Globus with the case eliminated, exhibiting the complicated gearing inside.
The diagram beneath summarizes my evaluation.
The Globus is an analog laptop that represents values by rotating shafts by explicit quantities.
These rotations management the globe
and the indicator dials.
The circulation of those rotational alerts is proven by the traces on the diagram.
The computation is predicated round addition, carried out by ten differential gear assemblies.
On the diagram, every “⨁” image signifies one among these differential gear assemblies.
Different gears join the elements whereas scaling the alerts by means of varied gear ratios.
Difficult features are carried out with three specially-shaped cams.
Within the the rest of this weblog put up, I’ll break this diagram down into practical blocks and clarify how the Globus operates.
This diagram reveals the interconnections of the gear community within the Globus.
For all its complexity, although, the performance of the Globus is fairly restricted. It solely handles a hard and fast orbit at a particular angle, and treats the
orbit as round.
The Globus doesn’t have any navigation enter similar to an inertial measurement unit (IMU).
As an alternative, the cosmonauts configured the Globus by turning knobs to set the spacecraft’s preliminary place and orbital interval.
From there, the Globus merely projected the present place of
the spacecraft ahead, basically dead reckoning.
A closeup of the gears contained in the Globus.
The globe
On seeing the Globus, one would possibly marvel how the globe is rotated.
It could appear that the globe should be free-floating so it may rotate in two axes.
As an alternative, a intelligent mechanism attaches the globe to the unit.
The secret’s that the globe’s equator is a stable piece of steel that rotates across the horizontal axis of the unit.
A second gear mechanism contained in the globe rotates the globe across the North-South axis.
The 2 rotations are managed by concentric shafts which might be fastened to the unit.
Thus, the globe has two rotational levels of freedom, regardless that it’s hooked up at each ends.
The picture beneath reveals the body that holds and controls the globe.
The dotted axis is fastened horizontally within the unit and rotations are fed by means of the 2 gears on the left.
One gear rotates the globe and body across the dotted axis, whereas the gear prepare causes the globe to rotate across the
vertical polar axis (whereas the equator stays fastened).
The axis of the globe is at 51.8° to help that orbital inclination.
The angle above is 51.8° which is essential: that is the inclination of the usual Soyuz orbit.
Because of this, merely rotating the globe across the dotted line causes the crosshair to hint the orbit.3
Rotating the 2 halves of the globe across the poles yields the completely different paths over the Earth’s floor
because the Earth rotates.
An essential consequence of this design is that the Globus solely helps a round orbit at a hard and fast angle.
Differential gear mechanism
The first mathematical aspect of the Globus is the differential gear mechanism, which might carry out addition or subtraction.
A differential gear takes two rotations as inputs and produces the (scaled) sum of the rotations because the output.
The picture beneath reveals one of many differential mechanisms.
Within the center, the spider gear meeting (crimson field) consists of two bevel gears that may spin freely on a vertical shaft.
The spider gear meeting as an entire is hooked up to a horizontal shaft, known as the spider shaft.
On the proper, the spider shaft is hooked up to a spur gear (a gear with straight-cut tooth).
The spider gear meeting, the spider shaft, and the spider’s spur gear rotate collectively as a unit.
Diagram exhibiting the elements of a differential gear mechanism.
On the left and proper are two finish gear assemblies (yellow).
The tip gear is a bevel gear with angled tooth to mesh with the spider gears.
Every finish gear is locked to a spur gear and these gears spin freely on the horizontal spider shaft.
In complete, there are three spur gears: two linked to the tip gears and one linked to the spider meeting.
Within the diagrams, I am going to use the image beneath to symbolize the differential gear meeting: the tip gears are symmetric on the highest and backside, with the
spider shaft on the facet.
Any of the three spur gears can be utilized as an output, with the opposite two serving as inputs.
The image for the differential gear meeting.
To grasp the habits of the differential, suppose the 2 finish gears are pushed in the identical path on the identical price, say upwards.4
These gears will push on the spider gears and rotate the spider gear meeting, with the complete differential rotating
as a hard and fast unit.
Then again, suppose the 2 finish gears are pushed in reverse instructions.
On this case, the spider gears will spin on their shaft, however the spider gear meeting will stay stationary.
In both case, the spider gear meeting movement is the common of the 2 finish gear rotations, that’s, the sum of the 2 rotations divided by 2.
(I am going to ignore the issue of two since I am ignoring all of the gear ratios.)
If the operation of the differential remains to be complicated, this vintage Navy video has an in depth rationalization.
The controls and shows
The diagram beneath reveals the controls and shows of the Globus.
The rotating globe is the centerpiece of the unit. Its plastic cowl has a crosshair that represents the spacecraft’s place above the Earth’s floor.
Surrounding the globe itself are dials that present the longitude, latitude, and the time earlier than getting into mild and shadow.
The cosmonauts manually initialize the globe place with the concentric globe rotation knobs: one rotates the globe alongside the orbital path
whereas the opposite rotates the hemispheres.
The mode change on the prime selects between the touchdown place mode, the usual Earth orbit mode, and turning off the unit.
The orbit time adjustment configures the orbital time interval in minutes whereas
the orbit counter beneath it counts the variety of orbits.
Lastly, the touchdown level angle units the gap to the touchdown level in levels of orbit.
The Globus with the controls labeled.
Computing the orbit time
The first movement of the Globus is the end-over-end rotation of the globe exhibiting the motion of the spacecraft in orbit.
The orbital movement is powered by a solenoid on the prime of the Globus that receives pulses as soon as a second and advances a ratchet wheel (video).5
This wheel is linked to a sophisticated cam and differential system to supply the orbital movement.
The orbit solenoid (inexperienced) has a ratchet that rotates the gear to the best. The shaft connects it to differential gear meeting 1 on the backside proper.
Every orbit takes about 92 minutes, however the orbital time might be adjusted by a couple of minutes in steps of 0.01 minutes6
to account for modifications in altitude. The Globus is surprisingly rigid and that is the one orbital parameter that may be adjusted.7
The orbital interval is adjusted by the three-position orbit time change, which factors to the minutes, tenths, or hundredths.
Turning the central knob adjusts the indicated interval dial.
The issue is the right way to generate the variable orbital rotation pace from the fastened pace of the solenoid.
The answer is a particular cam, formed like a cone with a spiral cross-section.
Three followers experience on the cam, in order the cam rotates, the follower is pushed outward and rotates on its shaft.
If the follower is close to the slim a part of the cam, it strikes over a small distance and has a small rotation.
But when the follower is close to the broad a part of the cam, it strikes a bigger distance and has a bigger rotation.
Thus, by shifting the follower to a specific level on the cam, the rotational pace of the follower is chosen.
One follower adjusts the pace primarily based on the minutes setting with others for the tenths and hundredths of minutes.
A diagram exhibiting the orbital pace management mechanism. The cone has three followers, however solely two are seen from this angle. The “transmission” gears are moved out and in by the outer knob to pick which follower is adjusted by the interior knob.
After all, the cam cannot spiral out endlessly.
As an alternative, on the finish of 1 revolution, its cross-section drops again sharply to the beginning diameter.
This causes the follower to snap again to its unique place.
To forestall this from jerking the globe backward, the follower is linked to the differential gearing by way of a slip clutch and ratchet.
Thus, when the follower snaps again, the ratchet holds the drive shaft stationary.
The drive shaft then continues its rotation because the follower begins biking out once more.
Every shaft output is accordingly a (principally) easy rotation at a pace that will depend on the place of the follower.
A cam-based system adjusts the orbital pace utilizing three differential gear assemblies.
The three adjustment alerts are scaled by gear ratios to supply the suitable contribution to the rotation.
As proven above, the changes are added to the solenoid output by three differentials to generate the orbit rotation sign, output from differential 3.8
This sign additionally drives the odometer-like orbit counter on the entrance of the Globus.
The diagram beneath reveals how the elements are organized, as seen from the again.
A again view of the Globus exhibiting the orbit elements.
Displaying the orbit rotation
For the reason that Globus does not have any exterior place enter similar to inertial steering, it should be initialized by the cosmonauts.
A knob on the entrance of the Globus offers handbook adjustment of the orbital place.
Differential 4 provides the knob sign to the orbit output mentioned above.
The orbit controls drive the globe’s movement.
The Globus has a “touchdown level” mode the place the globe is quickly rotated by means of a fraction of an orbit to point the place the spacecraft would land
if the retro-rockets had been fired.
Turning the mode change triggered the globe to rotate till the touchdown place was underneath the crosshairs
and the cosmonauts may consider the suitability of this touchdown web site.
This mode is carried out with a touchdown place motor that gives the fast rotation. This motor additionally rotates the globe again to the orbital place.
The motor is pushed by means of an electronics board with relays and a transistor, managed by restrict switches.
I mentioned the electronics in a previous post so I will not go into extra
particulars right here.
The touchdown place motor feeds into the orbit sign by means of differential 5, producing the ultimate orbit sign.
The touchdown place motor and its related gearing. The motor pace is geared down after which fed by means of a worm gear (higher middle).
The orbit sign from differential 5 is utilized in a number of methods.
Most significantly, the orbit sign offers the end-over-end rotation of the globe to point the spacecraft’s journey in orbit.
As mentioned earlier, that is completed by rotating the globe’s steel body across the horizontal axis.
The orbital sign additionally rotates a potentiometer to supply {an electrical} indication of the orbital place to different spacecraft methods.
The sunshine/shadow indicator
Docking a spacecraft is a tough endeavor, finest carried out in daylight, so it’s helpful to understand how a lot time stays till the spacecraft
enters the Earth’s shadow. The sunshine/shadow dial underneath the globe offers this data.
This show consists of two nested wheels. The outer wheel is white and has two quarters eliminated.
Via these gaps, the partially-black interior wheel is uncovered, which might be adjusted to point out 0% to 50% darkish.
This show is rotated by the orbital sign, turning half a revolution per orbit.
Because the spacecraft orbits, this dial reveals the sunshine/shadow transition and the time to the transistion.9
The sunshine/shadow indicator, seen from the underside of the Globus. The shadow indicator has been set to 35% shadow. Close to the hub, a pin restricts movement of the interior wheel relative to the outer wheel.
You would possibly count on the orbit to be at nighttime 50% of the time, however as a result of the spacecraft is about 200 km above the Earth’s floor,
it would generally be illuminated when the floor of the Earth beneath is darkish.10 Within the floor monitor beneath, the dotted
a part of the monitor is the place the spacecraft is within the Earth’s shadow; that is significantly lower than 50%.
Additionally notice that the tip of the orbit does not match up with the start, because of the Earth’s rotation throughout the orbit.
The latitude indicator
The latitude indicator to the left of the globe reveals the spacecraft’s latitude. The map above reveals how the latitude oscillates between
51.8°N and 51.8°S, similar to the launch inclination angle.
Despite the fact that the trail across the globe is a straight (round) line, the orbit seems roughly sinusoidal when projected onto the map.11
The precise latitude is a surprisingly sophisticated perform of the orbital place.12
This perform is carried out by a cam that’s hooked up to the globe. The various radius of the cam corresponds to the perform.
A follower tracks the profile of the cam and rotates the latitude show wheel accordingly, offering the non-linear movement.
A cam is hooked up to the globe and rotates with the globe.
The Earth’s rotation
The second movement of the globe is the Earth’s each day rotation round its axis, which I am going to name the Earth rotation.
The Earth rotation is fed into the globe by means of the outer a part of a concentric shaft, whereas the orbital rotation is supplied by means of the
interior shaft.
The Earth rotation is transferred by means of three gears to the equatorial body, the place an inner mechanism rotates the hemispheres.
There is a complication, although:
if the globe’s orbital shaft turns whereas the Earth rotation shaft stays stationary, the body will rotate, inflicting the
gears to show and the hemispheres to rotate.
In different phrases, preserving the hemispheres stationary requires the Earth shaft to rotate with the orbit shaft.
A closeup of the gear mechanisms that drive the Globus, exhibiting the concentric shafts that management the 2 rotations.
The Globus solves this downside by including the orbit rotation to the Earth rotation, as proven within the diagram beneath, utilizing differentials 7 and eight.
Differential 8 provides the traditional orbit rotation, whereas differential 7 provides the orbit rotation because of the touchdown motor.14
The mechanism to compute the Earth’s rotation round its axis.
The Earth movement is generated by
a second solenoid (beneath) that’s pushed with one pulse per second.13
This movement is easier than the orbit movement as a result of it has a hard and fast price.
The “Earth” knob on the entrance of the Globus permits handbook rotation across the Earth’s axis. This sign is mixed with the solenoid sign by differential 6.
The sum from the three differentials is fed into the globe, rotating the hemispheres round their axis.
This solenoid, ratchet, and equipment on the underside of the Globus drive the Earth rotation.
The solenoid and differentials are seen from the underside of the Globus. The diagram beneath labels these elements in addition to
different essential elements.
The underside of the Globus.
The longitude show
The longitude cam and the followers that monitor its radius.
The longitude show is extra sophisticated than the latitude show as a result of it will depend on each the Earth rotation and the orbit rotation.
In contrast to the latitude, the longitude does not oscillate however will increase.
The longitude will increase by 360° each orbit based on a sophisticated components describing the projection of the orbit onto the globe.
More often than not, the rise is small, however when crossing close to the poles, the longitude modifications quickly.
The Earth’s rotation offers a smaller however regular unfavorable change to the longitude.
The computation of the longitude.
The diagram above reveals how the longitude is computed by combining the Earth rotation with the orbit rotation.
Differential 9 provides the linear impact of the orbit on longitude (360° per orbit) and subtracts the impact of the Earth’s rotation (360° per day).
The nonlinear impact of the orbit is computed by a cam that’s rotated by the orbit sign. The form of the cam is picked up and fed into differential 10,
computing the longitude that’s displayed on the dial. The differentials, cam, and dial are seen from the again of the Globus (beneath).
A closeup of the differentials from the again of the Globus.
The time-lapse video beneath demonstrates the habits of the rotating shows.
The latitude show on the left oscillates between 51.8°N and 51.8°S.
The longitude show on the prime advances at a altering price. Close to the equator, it advances slowly, whereas it accelerates close to the poles.
The sunshine/shadow show on the backside rotates at a continuing pace, finishing half a revolution (one mild/shadow cycle) per orbit.
Conclusions
The Globus INK is a exceptional piece of equipment, an analog laptop that calculates orbits by means of an intricate
system of gears, cams, and differentials.
It supplied astronauts with a high-resolution, full-color show of the spacecraft’s place, means past what
an digital area laptop may present within the Sixties.
The disadvantage of the Globus is that its performance is proscribed.
Its parameters should be manually configured: the spacecraft’s beginning place, the orbital pace, the sunshine/shadow areas, and the touchdown angle.
It does not take any exterior steering inputs, similar to an IMU (inertial measurement unit), so it isn’t significantly correct.
Lastly, it solely helps a round orbit at a hard and fast angle.
Whereas a extra fashionable digital show lacks the bodily appeal of a rotating globe, the digital resolution offers
rather more functionality.
I lately wrote weblog posts offering a Globus overview
and the Globus electronics.
Comply with me on Twitter @kenshirriff or RSS for updates.
I’ve additionally began experimenting with Mastodon lately as @[email protected].
Many because of Marcel for offering the Globus.
I labored on this with CuriousMarc, so take a look at his Globus videos.