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Orbital instruments

Interactive engineering collection

Collection 01 / Analog computation

Evidence & limits

Voskhod-era electromechanical navigation

Globus IMP

An orbit calculated in brass, steel and motion.

ИМП · Review v2

Drag to rotate · Shift + drag to pan · click to inspect

Exterior view
Photo-informed · not a verified 1:1 replica

Assembling the instrument…

Initial conditions & calibration

Analytical period Not a recovered IMP calibration

min

Orbital phase · О

Reference longitude · Э

Fixed demonstration inclination

Circular-orbit model. Settings are illustrative, not a reconstruction of a particular flight.

Ground trackNominal ±½ orbit

● Present nadir○ Landing preview

Instrument power Exhibit control

Exhibit control. Power off freezes both the pulse actuator and the preview motor.

Review v2 · repaired mechanisms and state handling. Exact hardware calibration and hidden transfer stages remain unverified.

Read the reconstruction notesSources, confirmed principles and modeled assumptions

Voskhod IMP · not the later Soyuz INK

This is a functional educational reconstruction, not a metrologically verified digital twin. The representative reduction now drives the reference orbital accumulator through an explicitly exposed ideal gain. This is still not a complete recovered IMP gear train. The optional later-INK cam example is hidden by default, not counted as verified IMP hardware. The model must not be used for spacecraft navigation, deorbit planning or hardware manufacture.

What this model reproduces

The early instrument’s front arrangement, Russian legends, globe, combined coordinate display, counter and correction controls are interpreted from François Guay’s IMP photographs. A single pulse actuator and a separate landing-preview motor are retained. The later INK’s second solenoid, separate coordinate scales and light/shadow display are intentionally absent.

Element	Evidence level
Front-panel arrangement & component types	Photo-informed; proportions are estimated
Coordinate calculations and globe/readout agreement	Analytical circular-orbit model; tested numerically
Individual gears, cam outlines & exact internal placement	Representative geometry; original tooth counts and dimensions not established by the reference set
65° inclination, 90 min initial period	Fixed educational scenario, not a flown unit’s calibration
1 or 5 second pulse, 60-tooth ratchet	Teaching choices, not verified IMP specifications
Landing lead of 120° and motor transition rate	Illustrative preview, not a ballistic re-entry model
Hammertone coating, brass, steel, acrylic & paper	Procedural visual approximations; no measured PBR scans
Globe cartography	Re-authored from Natural Earth coastlines; not the original Soviet printed map

Operating the reconstruction

Drag to orbit; use Shift-drag or the right mouse button to pan. Click the model to capture the wheel, then scroll or pinch to zoom. The front-view button aligns the camera with the fixed crosshair. The Э and О knobs advance the longitude reference and orbital phase by 5° when clicked; Shift-click reverses. The correction grip edits a numeral drum; click its center to select the decimal digit. The historical description identifies a period indicator, but its exact scale and correction transfer are unrecovered. The analytical period is therefore kept separate. The small counter handwheel adds one displayed revolution; Shift-click subtracts one (the step size is a teaching choice). The exhibit has a separate zero-counter button.

While the model holds keyboard capture, Space pauses or runs the orbital clock, as the transport does. The step button advances one assumed sequencer pulse. X changes the X-ray view; E changes the exploded view; R restores the camera; Escape releases the capture. Landing mode uses the separate simulated preview motor, even while the orbital clock is paused. Power-off freezes both actuators. The annunciator identifies the selected mode; the display explicitly marks motor transit, which is not a settled landing result. The orbit counter excludes the added preview angle. The exploded view separates assemblies for inspection and is not a connected working configuration.

Review v2: connection ledger

Motion path	Implemented / unresolved
Pulse → ratchet → compound spur train	60-tooth reconstructed ratchet; 24:96, 20:100, 20:92 pairs. Matched modules, centers and phase. Ratchet stroke is kinematic, not a force/contact simulation.
Terminal shaft → orbit	Explicit ideal gain +92 × pulse interval / period(min). Original variable transfer is unrecovered; no hidden claim of mechanical completeness.
Earth branch → equatorial ring	Matched ring/pinion ratio and a declared concentric-shaft cancellation. Hidden transfer geometry is not reconstructed.
Coordinate cams → drums	Finite-roller envelope profiles; analytic lever calibration. Original cam traces and rack/levers not recovered.
Preview motor → worm wheel → phase adder	32:1 reconstructed worm ratio; absolute travel and corrected differential planet signs. Worm-wheel tooth surface is a visual approximation, not a hob-generated conjugate surface.
Numeral display	Real textured rotating cylinders. Counter carry is kinematic; its original carry train is not reconstructed.
Optional INK comparison	Closed conical cam, finite-radius follower envelope and non-reversing outputs. Isolated from the IMP correction transfer.
Radio-visibility circle	Purpose documented for Voskhod. Its radius is illustrative, not a calibrated radio-coverage solution.

Mathematical scope

For argument of latitude u, fixed inclination i and east-positive reference λ₀: φ = asin(sin i sin u), λ = atan2(cos i sin u, cos u) + λ₀ − ω⊕t. The simulation uses a spherical Earth and a sidereal rotation period of 86164.0905 s. It omits orbital eccentricity, precession, perturbations, drag, gear backlash, friction and actual cam errors. The landing view advances both orbital phase and idealized Earth rotation during the assumed lead time.

Primary reference material

Yu. Tyapchenko · Vostok / Voskhod information-display systemsFigure 16: decimal period indication, digit selection, radio-visibility circle, Voskhod orbit counter and correction handwheel. Includes recollections of the original systems team.

François Guay · IMP front viewOriginal artifact photograph, 26 February 2009. CC BY-SA 3.0.

François Guay · IMP interiorOriginal artifact photograph. Brass chassis, red wiring and drum arrangement.

François Guay · Researching and exhibiting Voskhod GlobusFirst-hand teardown observations. Actuators, passive components, uncertainty in pulse timing.

Ken Shirriff · Inside the Globus INKUsed to distinguish the later instrument and explain the equatorial-drive principle; not treated as an IMP dimensioned drawing.

Ken Shirriff · Reverse-engineering the Globus INKComparative evidence for cam and differential principles, not an IMP gear inventory.

Natural Earth · Public-domain cartographyCoastline geometry only; the globe’s color, grid and typography are re-authored.

Build

Dependency-free WebGL 2. Geometry, shaders and textures are generated in the page; the coastlines and three machined plates load from this site’s own asset file. No CDN, account or upload is required. Reconstruction geometry and generated appearance: CC BY-SA 3.0. Original application and renderer code: MIT. Reference photographs are linked, not redistributed.

Saves the current rendered view as a PNG. It is an image of the reconstruction, not a photograph or a measurement.

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c. 1964 · Computing

Globus IMP Navigation Instrument

Set by hand and driven by sequencer pulses, this instrument predicted where a Voskhod crew was with gears, cams and a differential — it never measured it.

The crew of a Voskhod had no computer to ask where they were. They had this: a globe in a case, set by hand to a starting position and then driven by one input — pulses from the spacecraft sequencer — which it turned into a predicted position with gears, cams and a differential. The exhibit lets you assume a pulse every second or every five, because the original timing is not confirmed.

In this reconstruction a solenoid pulls a pawl into the next tooth of a sixty-tooth ratchet, and three matched gear stages reduce that by ninety-two to one. Between pulses nothing moves: step the sequencer and the instrument sits still, then jumps. Latitude comes off a cam cut to the arcsine of the orbit geometry; the longitude correction comes off a second cam, because an inclined ground track runs behind the orbit angle for half a revolution and ahead of it for the other half. The Earth's own rotation is added to that, which is why each revolution lands west of the last.

A separate landing-preview motor swings the globe ahead to an illustrative landing place. It has its own clock: pausing the orbit does not stop it, only instrument power does, and the display is marked in transit until the motor settles.

Two things this reconstruction refuses to invent. The variable transmission that set the orbital period was never recovered, so the exhibit applies the ratio as an openly labeled ideal gain rather than miming a mechanism. And the three-digit correction code is turned and reported as a code, because what it meant in minutes is not known. Every subsystem carries its own evidence note; the gear counts, cam outlines and wiring are representative, not recovered originals.

Specifications

Input: An assumed sequencer pulse every 1 or 5 seconds; one ratchet tooth each
Train: Reconstructed 60-tooth ratchet and 24:96, 20:100, 20:92 stages (92:1)
Functions: Latitude and the longitude correction, each cut as a cam
Clocks: Pulse-driven orbit clock and an independent landing-preview motor
Output: A time-based position prediction, not a navigation measurement
Scope: Photo-informed reconstruction; not manufacturer drawings or a verified 1:1 replica

All exhibits

Globus IMP

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