BINARY CODED SEQUENTIAL ACQUISITION RANGING SYSTEM

• US 3,659,292 A
• Filed: 08/13/1970
• Issued: 04/25/1972
• Est. Priority Date: 08/13/1970
• Status: Expired due to Term

• Current Assignee: Low George M Deputy Administrator of The National Aeronautics and Space, N/a,, Richard M. Goldstein, Warren L. Martin
• Original Assignee: Low George M Deputy Administrator of The National Aeronautics and Space, N/a,, Richard M. Goldstein, Warren L. Martin
• Inventors: Goldstein, Richard M., Low, George M. Acting Administrator of the National Aeronautics and Space, N/a,, Martin, Warren L.
• Primary Examiner(s): Hubler, Malcolm F.
• Application Number:
  US05/063,532
• Time in Patent Office: 621 Days
• Field of Search: 343/6.5,6.5LC,12,14
• US Class Current: 342/98
• CPC Class Codes: G01S 13/36 with phase comparison between the received signal and the contemporaneously transmitted signal
• CPC Class Codes: G01S 13/84 for distance determination by phase measurement

Abstract

A binary coded sequential acquisition ranging system for determining the distance of very distant objects, such as extraterrestrial probes, is disclosed. A ground transmitter essentially including a phase modulator and a digital coder is employed to sequentially transmit a plurality of code components to a probe transponder for retransmission to a ground ranging circuit which serves to compare the returned code components with locally generated doppler-compensated reference code components. The ranging circuit includes a receiver digital coder, that is a counterpart of the transmitter digital coder, and an adder circuit which serves to effectively doppler compensate the receiver digital coder in accordance with detached doppler shift frequencies to provide the reference code components. A ranging receiver is employed to detect the relative phase difference between reference code components and returned code components. The detected relative phase difference is directly proportional to the range of the distant target and thereby provides a basis for the accurate calculation of range.

Claims

1. A ranging system of the type wherein binary coded compOnents are sequentially transmitted to a transponder-bearing space target for the purpose of resolving the range of said space target with respect to said ranging system which comprises:

a ranging transmitter including;

first coder means for generating a plurality of related first binary code components, and means for transmitting ranging signals including said binary code components to said space target for retransmission to said ranging system;

means for receiving retransmitted ranging signals, including received binary code components, and adapted to provide in response thereto a doppler frequency signal and a modulated carrier signal;

a ranging circuit including;

second coder means for generating a plurality of related second binary code components that are identical to said first binary code components generated by said first coder means, and which are provided on a first output lead and a quadrature output lead, means responsive to said doppler frequency signal, for controlling said second coder means to generate modified second binary code components which are identical to said received binary code components, and ranging receiver means for comparing the phases of said modified second binary code components with said received binary code components and providing a pair of analog signals having an amplitude representative of the phase difference between said received binary code components and each of said modified second binary code components, said ranging receiver means including a pair of phase comparison channels for receiving one of said modified binary code components, each of said phase comparison channels having demodulation mixer means for demodulating said modulated carrier signal, and means operatively coupled to said demodulation mixer means for providing one of said analog phase signals; and

utilization means operatively coupled to receive said analog phase signals for determining the range of said space target, wherein the phase delay between said received binary code components and said second binary code components is representative of a distance to said space target in excess of a first known distance but less than an additional known distance beyond said first known distance.

2. The apparatus defined by claim 1 further including a frequency source for applying an alternating current signal having a stable frequency to said first coder means and said second coder means.

3. The apparatus defined by claim 2 wherein said first and second coder means each comprise a binary counter having a plurality of stages each having an individually selectable output lead, said counter operating to provide a different code component in the form of a square wave output signal at each of said output leads in response to alternating current signals applied to said counter, the frequency of successive ones of said square wave signals being reduced by a factor of two.

4. The apparatus defined by claim 3 wherein said means responsive to said doppler signal comprises an adder circuit for varying the frequency of said alternating current signals applied to said second coder means in accordance with said doppler frequency signals.

5. The apparatus defined by claim 4 wherein said utilization means comprises:

means for converting said analog signals to digital signals; and

means, operatively coupled to receive said digital signals, for determining the phase delay between said received binary code components and said second binary code components.

6. The apparatus defined by claim 5 wherein the number of binary code components sequentially transmitted to said transponder-bearing space target and retransmitted therefrom is selected such that the cyclic period of only the lowest frequency binary code component exceeds said additional known distance, said analog signals having a maximum positive amplitude level when said received and second binary code components are in phase and having a maximum negative aMplitude level when said received and second binary code components are 180* out-of-phase, and wherein said phase delay is determined by a process including the steps of:

measuring the phase difference between the received and second binary code components having the highest frequency;

shifting all second binary code components by an amount equal to the measured phase difference between the received and second binary code components having the highest frequency such that said measured phase difference is reduced to zero and the analog signal corresponding to the highest frequency second binary code component is at a maximum positive amplitude level;

sequentially shifting successively lower frequency second binary code components, along with all other lower frequency second binary code components, by an amount necessary to have the analog signals corresponding to said lower frequency second binary code components sequentially brought to a maximum positive amplitude level; and

determining the total amount of shift required to have the analog signals, corresponding to all second binary code components, brought to a maximum positive amplitude level, said total amount being a measure of said phase delay.

7. In a ranging system adapted to resolve the range of a distant space target which is further than a first known distance but no further than an additional known distance, the ranging system including a transmitter for generating and sequentially transmitting a plurality of binary code components, each successively having a frequency that is decreased by a factor of two, to a transponder-bearing space target, a ground receiver for receiving code components retransmitted from said space target and adapted to provide a doppler signal representative of any doppler frequency shift in the frequency of received code components, the improvement comprising:

a ranging circuit including;

component means, coupled to receive said doppler frequency signal, for providing, at a pair of quadrature terminals, a plurality of model code components having a frequency identical to said received code components, and ranging receiver means, coupled to said quadrature channels and to said ground receiver, for developing a pair of analog signals respectively having an amplitude representative of the phase difference between said received code components and said model code components, said ranging receiver means including a pair of phase comparison channels, each channel having first mixer means for mixing the model code components provided over one of said quadrature terminals with said received code components, second mixer means operatively coupled to said first mixer means for developing one of said analog signals, and means for filtering said analog signals; and

utilization means adapted to receive said analog signals, for resolving the phase delay between said received code components and said model code components, said phase delay representing the distance beyond said known distance to said space target.

8. The apparatus defined by claim 7, said system further including a source of frequency signals for applying said frequency signals to said transmitter and to said component means, said component means including:

a binary counter having a plurality of stages each coupled to an individually selectable output lead, a plurality of model code components being provided at respective ones of said output leads, successive model code components having the frequency thereof reduced by a factor of two;

an adder circuit coupled to receive said frequency signals and selectively receive said doppler signals for selectively providing either said frequency signals or the sum of said frequency signals and said doppler signals at an output thereof;

switching means for selectively applying said doppler signals to said adder circuit; and

divider means for applying output signals from said adder means to said binary counter, said aDder output signals being reduced in frequency by a preselected factor wherein the model code components provided by said binary counter will be identical to received code components whenever said adder output signal represents the sum of said frequency signals and said doppler signals.

9. The apparatus defined by claim 7 wherein said utilization means comprises:

converter means for converting said analog signals to digital signals; and

computing means, coupled to receive said digital signals, for determining the phase delay between said received code components and said model code components.

10. The apparatus defined by claim 9, said system further including a source of frequency signals for applying said frequency signals to said transmitter and to said component means, said component means including:

a binary counter having a plurality of stages each coupled to an individually selectable output lead, a plurality of model code components being provided at respective ones of said output leads, successive model code components having the frequency thereof reduced by a factor of two;

an adder circuit coupled to receive said frequency signals and selectively receive said doppler signals for selectively providing either said frequency signals or the sum of said frequency signals and said doppler signals at an output thereof;

switching means for selectively applying said doppler signals to said adder circuit; and

divider means for applying output signals from said adder means to said binary counter, said adder output signals being reduced in frequency by a preselected factor wherein the model code components provided by said binary counter will be identical to received code components whenever said adder output signal represents the sum of said frequency signals and said doppler signals.

11. The apparatus defined by claim 9 wherein said analog signals have a maximum positive amplitude level when said model and received code components are in phase and have a maximum negative amplitude level when said model and received code components are 180* out of phase, and wherein said phase delay is determined by a process including the steps of:

measuring the phase difference between the received and model code components having the highest frequency;

shifting all model code components by an amount equal to the measured phase difference between the received and model code components having the highest frequency such that said measured phase difference is reduced to zero and the analog signal corresponding to the highest frequency model code component is at a maximum positive amplitude level;

sequentially shifting successively lower frequency model code components, along with all other lower frequency model code components, by an amount necessary to have the analog signals corresponding to said lower frequency model code components sequentially brought to a maximum positive amplitude level; and

determining the total amount of shift required to have the analog signals, corresponding to all model code components, brought to a maximum positive amplitude level, said total amount being a measure of said phase delay.