RARR Antennas and Tracking

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	=== Range ===		=== Range ===
-	GRAAR VHF used six '''range tones''' in 5:1 frequency intervals from 20 KHz to 8 Hz. Two tones at a time were used according to spacecraft distance. The '''lower tone''' produced a coarse range reading and the '''higher tone''' a finer resolution. the highest tones were modulated dirctly onto the carrier bt those below 4 KHz were modulated onto a 4 KHz sub-carrier.	+	GRAAR VHF used six '''range tones''' in 5:1 frequency intervals from 20 KHz to 8 Hz. Two tones at a time were used according to spacecraft distance. The '''lower tone''' produced a coarse range reading and the '''higher tone''' a finer resolution. the highest tones were modulated directly onto the carrier but those below 4 KHz were modulated onto a 4 KHz sub-carrier.
	In addition S-band used two higher tones - 500 KHz and 100 KHz - for even more precise range measurement. A pseudo-random '''Ambiguity Resolving Code''' (ARC) was later retrofitted to the S-band system to extend non-ambiguous ranging to almost four times the distance to the Moon. This was modulated onto the 4 KHz sub-carrier at 4000 bps.		In addition S-band used two higher tones - 500 KHz and 100 KHz - for even more precise range measurement. A pseudo-random '''Ambiguity Resolving Code''' (ARC) was later retrofitted to the S-band system to extend non-ambiguous ranging to almost four times the distance to the Moon. This was modulated onto the 4 KHz sub-carrier at 4000 bps.

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Revision as of 07:56, 3 January 2007

The GRARR VHF and S-band antennas were driven by identical hydraulically-powered X-Y mounts with digital angle encoders accurate to ±0.1°.

The VHF antenna was a 8.4m (28ft) square array of cavity-backed slots operating at about 150Mc. The array was later upgraded to backward-scatter dipoles. The antenna had a beamwidth of 16° and was often used as an acquisition aid for the narrower beamwidth S-band antenna.

The S-band antenna consisted of twin 4.2m (14ft) parabolic dishes operating at around 2500Mc with a beamwidth of 2.5°. One dish transmitted and the other received; the separation of transmit and receive functions decreased noise feedback on the receive dish. Both VHF and S-band antennas had 10Kw transmitters.

Tracking was accomplished by a coherent (continuous) link from the ground station to the spacecraft and back to the ground station. The spacecraft transponder operated according to the international IFF standard – 240:221. Initially the frequency conversion was downwards but later, to be compatible with the Apollo USB transmissions, GRARR spacecraft frequency conversion was downwards.

Range

GRAAR VHF used six range tones in 5:1 frequency intervals from 20 KHz to 8 Hz. Two tones at a time were used according to spacecraft distance. The lower tone produced a coarse range reading and the higher tone a finer resolution. the highest tones were modulated directly onto the carrier but those below 4 KHz were modulated onto a 4 KHz sub-carrier.

In addition S-band used two higher tones - 500 KHz and 100 KHz - for even more precise range measurement. A pseudo-random Ambiguity Resolving Code (ARC) was later retrofitted to the S-band system to extend non-ambiguous ranging to almost four times the distance to the Moon. This was modulated onto the 4 KHz sub-carrier at 4000 bps.

A more precise position could be triangulated with up to three stations in common view using three independent VHF transponders carried by the spacecraft; each operating on a different frequency. The spacecraft carried only a single S-band transponder; triangulation being of lesser value at lunar distances.
(read more 'Range' detail)

Range Rate

After range had been determined, range tones were removed from the coherent link. Range was then maintained by integrating the measured range rate – the rate of change in the phase of the return signal (Doppler effect) – with previous range measurements.
(read more 'Range Rate' detail)

Angle

(read more 'Angle' detail)