Considerations on DOR Considerations on DOR Tone Frequency and - - PowerPoint PPT Presentation

Considerations on DOR Considerations on DOR Tone Frequency and Tone Frequency and Structure Structure

James S. Border James S. Border Jet Propulsion Laboratory Jet Propulsion Laboratory

Fall 2007 CCSDS Meeting Fall 2007 CCSDS Meeting Heppenheim Heppenheim, Germany, October 2, 2007 , Germany, October 2, 2007

• J. S. Border
• J. S. Border

Jet Propulsion Laboratory

California Institute of Technology

CCSDS Meeting, CCSDS Meeting, Heppenheim Heppenheim, Germany, Oct. 2, 2007 - , Germany, Oct. 2, 2007 - 2 2

Topics to be Covered Topics to be Covered

• Purpose

Purpose

• Description of

Description of ∆ ∆DOR DOR

• Projected Navigation Requirements

Projected Navigation Requirements

• Limiting Error Sources by RF Band

Limiting Error Sources by RF Band

• Error Dependence on DOR Tone Frequency and

Error Dependence on DOR Tone Frequency and Structure Structure

• Example:

Example: MRO X/Ka Results MRO X/Ka Results

• Proposed DOR Tone (Flexible) Specifications

Proposed DOR Tone (Flexible) Specifications

• Spectrum Management Issues

Spectrum Management Issues

• Ground Station Compatibility Issues

Ground Station Compatibility Issues

• J. S. Border
• J. S. Border

Jet Propulsion Laboratory

California Institute of Technology

CCSDS Meeting, CCSDS Meeting, Heppenheim Heppenheim, Germany, Oct. 2, 2007 - , Germany, Oct. 2, 2007 - 3 3

Purpose Purpose

• This

This is not is not a request to revise CCSDS 401 a request to revise CCSDS 401 (2.5.6B) (2.5.6B) (i.e. DOR Tone Specification) (i.e. DOR Tone Specification)

• The intended purpose

The intended purpose is to continue a is to continue a discussion within the DDOR SIG (WG) discussion within the DDOR SIG (WG) about whether we should request a about whether we should request a revision to revision to CCSDS 401 (2.5.6B) CCSDS 401 (2.5.6B)

• J. S. Border
• J. S. Border

Jet Propulsion Laboratory

California Institute of Technology

CCSDS Meeting, CCSDS Meeting, Heppenheim Heppenheim, Germany, Oct. 2, 2007 - , Germany, Oct. 2, 2007 - 4 4

Delta Differential One-way Range Delta Differential One-way Range

• ∆

∆DOR complements line-of-sight DOR complements line-of-sight range and Doppler measurements range and Doppler measurements

• ∆

∆DOR uses interferometry to DOR uses interferometry to directly measure spacecraft angular directly measure spacecraft angular position in the radio reference frame position in the radio reference frame

• Accuracy of 2 nrad is being used

Accuracy of 2 nrad is being used today today to support targeting for Mars to support targeting for Mars missions missions

• Tighter accuracy requirements may

Tighter accuracy requirements may be imposed by future missions be imposed by future missions

• The measurement is a group delay

The measurement is a group delay

• Measurement precision scales with

Measurement precision scales with signal spanned bandwidth signal spanned bandwidth

τ

Correlator

Baseline B θ

τ = B⋅cos(θ)/c

spacecraft delay τ

Spacecraft Quasar

• J. S. Border
• J. S. Border

Jet Propulsion Laboratory

California Institute of Technology

CCSDS Meeting, CCSDS Meeting, Heppenheim Heppenheim, Germany, Oct. 2, 2007 - , Germany, Oct. 2, 2007 - 5 5

Projected Navigation Requirements Projected Navigation Requirements

• Navigation community has developed draft DSN

Navigation community has developed draft DSN tracking system requirements to support future tracking system requirements to support future mission set mission set

• Year 2010:

Year 2010: 2 nrad 2 nrad ∆ ∆DOR accuracy DOR accuracy

  To support Mars missions

To support Mars missions

  Requirement can

Requirement can be met today using X-band be met today using X-band

• Year 2020: 1 nrad

Year 2020: 1 nrad ∆ ∆DOR accuracy DOR accuracy

  To support precise landing and/or sample return

To support precise landing and/or sample return

  Will be difficult using X-band

Will be difficult using X-band

• Year 2030: 0.5 nrad

Year 2030: 0.5 nrad ∆ ∆DOR accuracy DOR accuracy

  To support precise landing and/or sample return

To support precise landing and/or sample return

  Need to use Ka-band

Need to use Ka-band

• J. S. Border
• J. S. Border

Jet Propulsion Laboratory

California Institute of Technology

CCSDS Meeting, CCSDS Meeting, Heppenheim Heppenheim, Germany, Oct. 2, 2007 - , Germany, Oct. 2, 2007 - 6 6

∆ ∆DOR Error Models DOR Error Models

• The accuracy of the measurement

The accuracy of the measurement τ τS/C

S/C - (

• (τ

τQSR1

QSR1 +

+ τ τQSR2

QSR2 )/2

)/2 [for a QSQ sequence]

[for a QSQ sequence]

depends on signal strength, spanned bandwidth, depends on signal strength, spanned bandwidth, receiver specifications, media calibrations, receiver specifications, media calibrations, baseline knowledge, baseline knowledge, … …

• Equations have been developed to model

Equations have been developed to model measurement errors measurement errors

• Limiting error sources have been identified

Limiting error sources have been identified

• Error budget has been developed and checked

Error budget has been developed and checked using data (X-band) from several missions using data (X-band) from several missions

• J. S. Border
• J. S. Border

Jet Propulsion Laboratory

California Institute of Technology

CCSDS Meeting, CCSDS Meeting, Heppenheim Heppenheim, Germany, Oct. 2, 2007 - , Germany, Oct. 2, 2007 - 7 7

Limiting Error Sources by RF Band Limiting Error Sources by RF Band

• S-Band

S-Band

  DOR Tone frequency

DOR Tone frequency is 4 MHz is 4 MHz

  Charged particles limit accuracy for most cases

Charged particles limit accuracy for most cases

• X-Band

X-Band

  DOR Tone frequency is 19 MHz

DOR Tone frequency is 19 MHz

  Limiting errors are spanned bandwidth (effect on precision and

Limiting errors are spanned bandwidth (effect on precision and instrument dispersion), charged particles, quasar structure instrument dispersion), charged particles, quasar structure

• Charged particle errors reduced x13 relative to S-band (+)

Charged particle errors reduced x13 relative to S-band (+)

• Ka-Band

Ka-Band

  DOR Tone frequency is

DOR Tone frequency is 76 MHz 76 MHz

  Limiting error is spanned bandwidth (effect on precision and

Limiting error is spanned bandwidth (effect on precision and instrument dispersion) instrument dispersion)

• Charged particle errors reduced x15 relative to X-band (+)

Charged particle errors reduced x15 relative to X-band (+)

• Quasar cores tend to be more compact relative to X-band (+)

Quasar cores tend to be more compact relative to X-band (+)

• Quasar flux reduced

Quasar flux reduced x(2-3) relative to X-band (-) x(2-3) relative to X-band (-)

• System temperature increased x(2-3) relative to X-band (-)

System temperature increased x(2-3) relative to X-band (-)

• J. S. Border
• J. S. Border

Jet Propulsion Laboratory

California Institute of Technology

CCSDS Meeting, CCSDS Meeting, Heppenheim Heppenheim, Germany, Oct. 2, 2007 - , Germany, Oct. 2, 2007 - 8 8

Key Errors Scale with Spanned Key Errors Scale with Spanned Bandwidth Bandwidth

• For a given phase measurement

For a given phase measurement signal-to- signal-to- noise ratio, delay error scales noise ratio, delay error scales linearly with linearly with (Spanned Bandwidth) (Spanned Bandwidth)-1

• 1
• For a given instrumental dispersion (i.e.

For a given instrumental dispersion (i.e. bias) between spacecraft and quasar bias) between spacecraft and quasar phase measurements, delay error scales phase measurements, delay error scales linearly with (Spanned Bandwidth) linearly with (Spanned Bandwidth)-1

• 1

• J. S. Border
• J. S. Border

Jet Propulsion Laboratory

California Institute of Technology

CCSDS Meeting, CCSDS Meeting, Heppenheim Heppenheim, Germany, Oct. 2, 2007 - , Germany, Oct. 2, 2007 - 9 9

Key Key ∆ ∆DOR Error Terms at X-band DOR Error Terms at X-band and Ka-band and Ka-band

• Precision of

Precision of better than 1 better than 1 nrad at Ka nrad at Ka will require will require high high frequency frequency DOR tone DOR tone and high and high sample rate sample rate

(SNR)

• J. S. Border
• J. S. Border

Jet Propulsion Laboratory

California Institute of Technology

CCSDS Meeting, CCSDS Meeting, Heppenheim Heppenheim, Germany, Oct. 2, 2007 - , Germany, Oct. 2, 2007 - 10 10

Example: Dual Band X/Ka Example: Dual Band X/Ka ∆ ∆DOR DOR Measurements of MRO Measurements of MRO

• ∆

∆DOR measurements were made at both X- DOR measurements were made at both X- band and Ka-band for 7 passes during MRO band and Ka-band for 7 passes during MRO cruise cruise

• One pass (Jan. 20, 2006) included 40

One pass (Jan. 20, 2006) included 40 spacecraft spacecraft and quasar observations and quasar observations

• These data allow for direct comparison of X-

These data allow for direct comparison of X- band and Ka-band results band and Ka-band results

• Ka-band spanned bandwidth was x4 and Ka-

Ka-band spanned bandwidth was x4 and Ka- band sample rate was x2 relative to X-band band sample rate was x2 relative to X-band

• J. S. Border
• J. S. Border

Jet Propulsion Laboratory

California Institute of Technology

CCSDS Meeting, CCSDS Meeting, Heppenheim Heppenheim, Germany, Oct. 2, 2007 - , Germany, Oct. 2, 2007 - 11 11

∆ ∆DOR Measurement Residuals for DOR Measurement Residuals for MRO at X-band and Ka-band MRO at X-band and Ka-band

• Performance

Performance is comparable is comparable

• Less precision

Less precision is obtained at is obtained at Ka-band even Ka-band even though DOR though DOR tone is x4 and tone is x4 and sample rate is sample rate is x2 x2

• J. S. Border
• J. S. Border

Jet Propulsion Laboratory

California Institute of Technology

CCSDS Meeting, CCSDS Meeting, Heppenheim Heppenheim, Germany, Oct. 2, 2007 - , Germany, Oct. 2, 2007 - 12 12

Geometry for Extended Geometry for Extended ∆ ∆DOR Pass DOR Pass

• n Jan. 20, 2006
• n Jan. 20, 2006
• 40 delay

40 delay measurements of measurements of MRO and angularly MRO and angularly nearby quasars nearby quasars made at X-band made at X-band and Ka-band and Ka-band

• Data used to

Data used to examine examine components of components of error budget error budget

• J. S. Border
• J. S. Border

Jet Propulsion Laboratory

California Institute of Technology

CCSDS Meeting, CCSDS Meeting, Heppenheim Heppenheim, Germany, Oct. 2, 2007 - , Germany, Oct. 2, 2007 - 13 13

X-Band Delay Residuals X-Band Delay Residuals

• Error drift similar

Error drift similar for spacecraft for spacecraft and quasar and quasar

• QSQ points are

QSQ points are accurate to 1.1 accurate to 1.1 nrad for either nrad for either close quasar close quasar pair or quasar pair or quasar pair at larger pair at larger angular angular separation separation

• J. S. Border
• J. S. Border

Jet Propulsion Laboratory

California Institute of Technology

CCSDS Meeting, CCSDS Meeting, Heppenheim Heppenheim, Germany, Oct. 2, 2007 - , Germany, Oct. 2, 2007 - 14 14

Ka-Band Delay Residuals Ka-Band Delay Residuals

• Performance is

Performance is similar at Ka- similar at Ka- band band

• Some Ka-band

Some Ka-band measurements measurements are too weak to are too weak to make a direct make a direct comparison with comparison with X-band X-band

• J. S. Border
• J. S. Border

Jet Propulsion Laboratory

California Institute of Technology

CCSDS Meeting, CCSDS Meeting, Heppenheim Heppenheim, Germany, Oct. 2, 2007 - , Germany, Oct. 2, 2007 - 15 15

Why Should DOR Tone Why Should DOR Tone Specifications Be Flexible ? Specifications Be Flexible ?

• Ground systems can generally make VLBI

Ground systems can generally make VLBI measurements using various frequency measurements using various frequency channels channels

• Measurements are being made today at

Measurements are being made today at various DOR Tone frequencies to support various DOR Tone frequencies to support legacy missions legacy missions

• Different missions will have different

Different missions will have different navigation and telemetry requirements navigation and telemetry requirements

• J. S. Border
• J. S. Border

Jet Propulsion Laboratory

California Institute of Technology

CCSDS Meeting, CCSDS Meeting, Heppenheim Heppenheim, Germany, Oct. 2, 2007 - , Germany, Oct. 2, 2007 - 16 16

Proposed Specifications for Ka- Proposed Specifications for Ka- band DOR Tones band DOR Tones

• Let each mission choose highest frequency

Let each mission choose highest frequency DOR Tone needed to meet navigation DOR Tone needed to meet navigation requirements (e.g. 19 MHz to 160 MHz) requirements (e.g. 19 MHz to 160 MHz)

  Perhaps two options (76 MHz or 160 MHz) would

Perhaps two options (76 MHz or 160 MHz) would suffice for all missions suffice for all missions

  This will be more practical if transponder design

This will be more practical if transponder design allows for flexibility allows for flexibility

• Must also have lower frequency signal

Must also have lower frequency signal components for ambiguity resolution components for ambiguity resolution

  Lowest frequency required depends on how well

Lowest frequency required depends on how well angular spacecraft position is known angular spacecraft position is known without without using using ∆ ∆DOR DOR

• J. S. Border
• J. S. Border

Jet Propulsion Laboratory

California Institute of Technology

CCSDS Meeting, CCSDS Meeting, Heppenheim Heppenheim, Germany, Oct. 2, 2007 - , Germany, Oct. 2, 2007 - 17 17

Proposed Specifications for Ka- Proposed Specifications for Ka- band DOR Tones - cont band DOR Tones - cont

• Instrumental bias between narrowband

Instrumental bias between narrowband spacecraft phase measurement and wideband spacecraft phase measurement and wideband quasar phase measurement could be reduced if quasar phase measurement could be reduced if DOR Tone is spread DOR Tone is spread

  Ranging

Ranging PN code might be used for this PN code might be used for this

• Less important if extra wideband DOR Tones

Less important if extra wideband DOR Tones are used are used

• More important if quasar sampling bandwidth is

More important if quasar sampling bandwidth is increased to improve quasar signal-to-noise ratio increased to improve quasar signal-to-noise ratio

• This will be more practical if transponder design

This will be more practical if transponder design allows for flexibility allows for flexibility

• J. S. Border
• J. S. Border

Jet Propulsion Laboratory

California Institute of Technology

CCSDS Meeting, CCSDS Meeting, Heppenheim Heppenheim, Germany, Oct. 2, 2007 - , Germany, Oct. 2, 2007 - 18 18

Spectrum Management Issues Spectrum Management Issues

• Procedure that is followed

Procedure that is followed

 

A project makes a request to use telemetry and DOR signals at certain A project makes a request to use telemetry and DOR signals at certain frequencies frequencies

 

A system review package is put together and analysis is done to check A system review package is put together and analysis is done to check for interference for interference

• Suggestion: Ask for guidelines before building a wideband Ka

Suggestion: Ask for guidelines before building a wideband Ka transponder transponder

• Potential for interference is low

Potential for interference is low

 

DOR Tones are DOR Tones are “ “off

• ff”

” most of the time most of the time

 

A DOR tone will only interfere with a carrier tracking loop when it falls A DOR tone will only interfere with a carrier tracking loop when it falls within loop bandwidth ( within loop bandwidth (≈ ≈10 Hz) 10 Hz)

• Interference with

Interference with subcarrier subcarrier or symbol tracking loop is unlikely

• r symbol tracking loop is unlikely
• Presence of

Presence of DOR Tone may impact carrier acquisition for a closed-loop DOR Tone may impact carrier acquisition for a closed-loop receiver receiver

 

Use of frequency and rate Use of frequency and rate predictions could lessen risk predictions could lessen risk

 

Other signals will only Other signals will only interfere with DOR interfere with DOR Tone Tone phase measurement if phase measurement if they stay within processing bandwidth ( they stay within processing bandwidth (≈ ≈ 0.01 Hz) 0.01 Hz)

• J. S. Border
• J. S. Border

Jet Propulsion Laboratory

California Institute of Technology

CCSDS Meeting, CCSDS Meeting, Heppenheim Heppenheim, Germany, Oct. 2, 2007 - , Germany, Oct. 2, 2007 - 19 19

Ground Station Compatibility Issues Ground Station Compatibility Issues

• Ground stations receive RF signals within specified

Ground stations receive RF signals within specified passbands passbands

  Extra wideband DOR

Extra wideband DOR Tones may fall outside passband Tones may fall outside passband

• Ground stations record frequency channels at specified

Ground stations record frequency channels at specified sampling rates sampling rates

  Extra wide modulation on DOR Tones may fall outside sampling

Extra wide modulation on DOR Tones may fall outside sampling rate rate

• Now is the time to plan for future Ka-band capabilities

Now is the time to plan for future Ka-band capabilities

  Wide

Wide bandwidths and high data rates will be driven by telemetry bandwidths and high data rates will be driven by telemetry as well as DOR requirements as well as DOR requirements

• All missions need to be aware of limitations if cross-

All missions need to be aware of limitations if cross- support is envisioned support is envisioned

  Likely impact is loss of one

Likely impact is loss of one sidetone sidetone, i.e. reduction to level of , i.e. reduction to level of performance that would have been obtained performance that would have been obtained from a lower from a lower frequency DOR Tone frequency DOR Tone

• J. S. Border
• J. S. Border

Jet Propulsion Laboratory

California Institute of Technology

CCSDS Meeting, CCSDS Meeting, Heppenheim Heppenheim, Germany, Oct. 2, 2007 - , Germany, Oct. 2, 2007 - 20 20

Summary Summary

• ∆

∆DOR is an efficient, accurate technique for DOR is an efficient, accurate technique for determining spacecraft angular position determining spacecraft angular position

• Future missions may require improved accuracy

Future missions may require improved accuracy that can only be that can only be met using wideband DOR met using wideband DOR Tones at Ka-band Tones at Ka-band

• Flexible DOR Tone specifications may

Flexible DOR Tone specifications may be be practical if transponder design can be flexible practical if transponder design can be flexible

• Spectrum management issues and ground

Spectrum management issues and ground station compatibility issues appear to be station compatibility issues appear to be workable workable