Voskhod Spacecraft "Globus" IMP navigation instrument
[2][3] The design objectives for the IMP were to compute and display the geographic coordinates at the spacecraft's nadir, i.e. which point on Earth's surface it was overflying.
[citation needed] The Soyuz TMA spacecraft and its successors now provide similar functions to the Globus using a computerized world map on a computer display.
The spacecraft essentially controlled itself, and the cosmonauts were expected to initiate maneuvers or corrections only after approval from the MCC and according to its data and parameters.
The readings from the IMP were primarily intended to help cosmonaut pilots confirm that the automated flight sequencer was operating normally.
The data would also keep the crew aware of their position when they were orbiting over the nighttime part of the Earth, or when the spacecraft's viewports and Vzor periscope couldn't be pointed toward the ground.
[citation needed] However, the IMP would become crucial if manual retrorocket activation became compromised by failure of either the flight sequencer or communications with mission control, as did happen on Voskhod 2.
[1][7][8] By contrast, the US crewed space programs used a similar, mechanical positional indicator only during two of its early Mercury missions before discarding it.
[citation needed] Like most of early spacecraft's cockpit instruments, the IMP Globus was designed and tested to remain operative in a complete vacuum, in case of an accidental depressurisation of the cabin.
The moving terrestrial globe was protected by a hemispherical transparent plastic dome, on which was engraved and printed a cross-shaped sight.
A second mode of operation, activated by the cosmonauts, advanced the globe to a position where the spacecraft would land should the retrorockets be fired at that moment to effect the reentry sequence, which also lit the место посадки indicator.
[citation needed] When the critical operation of deorbit retrorockets burn was approaching in preparation for atmospheric entry, the crew monitored the automatic orientation of the spacecraft (a function of the attitude control system), then toggled the proper switch on the Control panel to "fast-forward" the IMP instrument in order to display the projected point of landing.
From the sole solenoid actuator's incremental motion, the horological mechanism derived irregular oscillating functions which in turn rotated the globe and varied its axis, and also moved its two cylindrical indicators for longitude and latitude.
The only other electric actuator used in the IMP instrument was the motor used to fast-forward the mechanism from the actual point-to-nadir to the expected landing point, some 120 degrees further east.
The Smithsonian Institution's National Air and Space Museum in Washington DC (US) exhibits several Soyuz spacecraft whose Globus are still in place, but their instrument panels are not visible to visitors.
