KOT window 3 '

KOT window 2

EOT window 1

Tape viewed from tape back side (inactive). Deck Plate

Oxide and carbon back coat are removed to form windows.

Figure 155.- Magnetic tape map (transport frontal profile). Dimensions except tape width are given in m (ft).

The DSE record electronics selected the proper data source and conditioned the data for transfer to the DST. VIS data from the FDS came to the DTR on seven separate lines and was simultaneously recorded on tracks 1 to 7. The data rate of each line was 301 714 2/7 bps. The VIS bit sync was divided by two and used to convert the data input from NRZ to Manchester code format. Manchester code is formed by the exclusive or combination of the NRZ data and the square-wave clock (at data rate frequency). The seven lines of Manchester data were routed to the TMEM where they were divided by two to form Miller code such that data and B/S information were recorded on each track. VL data were recorded on track 8 while the tape was running at speeds corresponding to either 4000 or 16 000 bps. FDS data were received at a 2000-bps data rate but were symbol encoded to a 4000-bps rate and recorded at the 4000-bps tape speed.

The purpose of the DSE playback electronics was to recover the playback data signal and derive a bit sync clock. The DTR could be operated at any one of five selectable tape speeds during the playback mode. Data were played back one track at a time by turning on one of the eight preamplifiers in the TMEM. The playback data signal from the TMEM was further amplified, filtered, gain compensated, and peak detected. The peak detector sensed both positive and negative peaks such that its output represented the Miller code form of the data previously recorded. The output of the peak detector was sampled by a one-half bit period integrating amplifier. The timing pulses to initialize the integrating amplifier and to store the output level were derived from the bit synchronizer PLL. The detected data were converted to NRZ format and sent to the data buffer. The bit synchronizer PLL locked to the playback data and generated the B/S timing signals. The PLL allowed the B/S information to be recovered from the playback data in the presence of moderate drop-outs and flutter. The bit synchronizer PLL determined the location of the Miller code data transition and reset the integrating amplifier so that each data transition would be coincident with the reset pulse. After the detected Miller code data had been converted to NRZ format, they were routed through a buffer. The buffer transferred the data from the bit sync clock to a stable external clock from the FDS. This removed the flutter from the data, that was inherent in the system when operating the motor under servo control.

The tape position logic was a counter which divided the tach clock by a count of 10 000. This resulted in either an increment or a decrement pulse to CCS for every 8 cm (3 in.) of tape, depending on whether the tape was moving in the forward or reverse direction. The increment and decrement pulses were used by the CCS to maintain current tape position and identify where each group of data was recorded. With this information it was then possible to command the tape to a known position to play back a particular group of data.

The telemetry coder assembled and transmitted to the FDS two 7-bit digital status words: mode word and playback word. The mode word contained mode, rate, and tape direction information and the playback word contained track, buffer counter position, and PLL lock status.

DSE-DST interfaces.- The DSE-DST interfaces consisted of the record and playback signals, the motor driver voltages, and the BOT/EOT signals. The TMEM, while functionally a part of the DSE, was physically located within the DST. The TMEM provided the DSE to tape head interface circuitry and contained the record head drivers and the playback preamplifiers for the 9 tape tracks. The record circuitry consisted of a Manchester-to-Miller encoder and a record head driver for each of the 8 data tracks. The same circuitry was provided for recording the tachometer signal, but this circuitry was not used during flight. The playback circuitry consisted of a separate preamplifier for each data track and a single common amplifier as the second stage for the playback signal. Only one of the preamplifiers was enabled at any one time. A separate two-stage amplifier was provided for the tachometer signal.

The tape reels were driven by a two-phase motor in the transport. The direction of motor rotation was determined by the relative phase (±90°) of the signals to the motor windings. The motor speed was controlled by modulating the amplitude of the control phase motor voltage with the servo error signal. A constant voltage was applied to the reference phase winding at all tape speeds.

The DSE supplied current to each light source and monitored the photocon-ductive transistors within the DST. When BOT or EOT was reached, the light source transmitted through the transparent tape window activated the phototransistor. The signal was conditioned to logic level amplitude with a pulse width dependent on tape speed. The DSE was activated by the trailing edge of the pulse. The signals were routed to the control logic of the DSE and buffered to the CCS.

Operational Performance

The total data storage capacity of the DTR on 8 tracks was a minimum of 6.4 x 108 bits or 8 x 107 bits per track. The bit packing density, on tape, was 2625 ± 20 percent bits/cm (6667 ± 20 percent bits/in.). The magnetic tape transport was designed to operate at six different tape speeds. The highest record speed was accomplished by operating the motor at synchronous speed. Other speeds were accomplished by operating the motor at asynchronous speed with servo control. The mean tape speeds were as follows:

VIS record 301 714 2/7 bps 114.7 cm/sec (45.16 in/sec)

The bit error rate for the DST was less than 1 x io~4 at 16 000, 8000, 4000, and 2000 bps. Run-up time was the time from the instant that motor power was applied until the average VIS record speed was attained. Run-up time did not exceed 8.5 sec. The total start time plus stop time did not exceed 17.5 sec. The DTR mechanical devices, for example, bearings, belts, tape, and magnetic head surfaces, were consumable in that they possessed a limited lifetime before degradation began to appear. The design life requirements after delivery for assembly into the flight VO were

45 7 km (1.5 x 106 ft) of tape across the heads

6500 tape passages of any given section of tape across the heads

10 000 start/stop cycles. The following were counted as start/stop cycles:

any velocity change was equal to 1/2 start/stop cycle, a direction reversed at any speed was equal to 1 start/stop cycle, and a single start or stop was equal to 1/2 start/stop cycle.

S/X Band Antenna Subsystem Purpose

The SXAS was the means by which the VO transmitted and received the S-band rf signals to and from the Earth and transmitted only X-band rf signals to the Earth. The SXAS consisted of an LGA designed for S-band only and an HGA designed for both S- and X-bands , two DFRJ's, and associated waveguides and cabling. Figure 156 is a drawing illustrating the antennas, rf cabling, and the waveguide plumbing. Figure 31 is a pictorial view of the HGA support structure and shows the DFRJ's and part of the rf cabling and waveguide assemblies.

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