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NASA's Deep Space Network (DSN) has some very immediate problems

  1. NASA DSN science data is being continuously lost with Voyager I & II missions at the Madrid, Goldstone and Canberra signal intercept sites due to rain fades and decay of reception equipment.

  2. NASA (unlike SETI @ Home) has failed to innovate by using software to decode telemetry from Deep Space Missions -- famous for their very weak signals.

  3. NASA uses hardware (and hardware only) decoding technology. Thus NASA loses DSN data all the time.

  4. DSN @ Home can fix most (but not all) of the Deep Space Network’s problems relating to the Voyager missions -- and New Horizons.

  5. The US economy is operating under difficult conditions caused by the role debt now plats in the economy. Many US science projects will suffer unless radical new ways of thinking about how these projects are run (and in some cases how the core science is done).



 Voyager I & II solar system path versus termination shock




SETI Radio Telescopes Track New Horizons

07 NOV 2008 (JPL)

The New Horizons spacecraft has a new “audience” for the electronic signals it beams back to Earth.

http://pluto.jhuapl.edu/news_center/news/110708.php

In a successful September demonstration of its growing capabilities, the Allen Telescope Array (ATA) detected transmissions from New Horizons while the spacecraft was more than a billion miles from home. The ATA is a radio interferometer used for astronomical research and searches for signals of intelligent, extraterrestrial origin. A joint effort of the SETI Institute and the Radio Astronomy Laboratory at the University of California, Berkeley, it’s being constructed at the Hat Creek Radio Observatory in Northern California.

The SETI Institute routinely observes spacecraft such as New Horizons, which serve as an excellent test signal for confirming the correct functioning and effectiveness of the SETI signal-detection systems.

“We look forward to checking in with New Horizons as a routine, end-to-end test of our system health,” says Jill Tarter, director of the Institutes's Center for SETI Research. “As this spacecraft travels farther, and its signals grow weaker, we will be building out the Allen Telescope Array from 42 to 350 antennas, and thus can look forward to a long-term relationship.”

For the New Horizons observation, made Sept. 10, operators used a synthesized beam formed with 11 of the array’s 6.1-meter (20 foot) antennas – a method called “beamforming” that electronically combines the antennas into a single virtual telescope. The 8.4-GHz spacecraft carrier signal was then fed into the SETI Prelude detection system.

“We’re happy to be the ATA’s new friend in the sky, helping SETI to verify the operations of their electronics,” says New Horizons Principal Investigator Alan Stern. “It’s also nice to know that someone else is checking in on us during our long voyage to Pluto and beyond.”

Read more about SETI’s spacecraft-observation efforts at:
http://www.space.com/searchforlife/081024-seti-telescope-firstlight.html




Use the SETI @ Home and Astropulse source codebase to detect and decode Voyager I & II telemetry, and later on or simultaneously the telemetry of the New Horizons Pluto-Charon mission. Once the software codebase for doing so has been perfected move on adapting the codebase to the New Horizons mission that has similar transmission complexities.

The Deep Space Network antennas, especially the 70-m antennas, which provide most of the collecting area, are getting older and are becoming less reliable than desired. Further, it is difficult for the 70-m antennas to provide reliable operation at 32 GHz (Ka-band), where there is a 500-MHz-wide spectrum allocation compared to only 50 MHz at 8 GHz (X-band).

In future there may be a need for support for more deep-space missions, and also a need for increasing data rates from these missions. This means there may be a need for more sensitivity [A/T, where A is antenna effective collecting area and T is system temperature] at both X and Ka space communication bands. Therefore, it may be necessary not only to replace the aging antennas but also to increase the overall sensitivity (A/T) of the DSN.




All you need to know about the Voyager Downlink path




The High Gain Antenna transmits data to Earth on two frequency channels (the downlink). One, at about 8.4 gigahertz (8,400 million cycles per second), is the X-band channel and contains science and engineering data.

    • The X-band downlink science data rates are as high as 7.2 kilobits per second.

    • The other S-band channel, around 2.3 gigahertz transmits only engineering data on the health and state of the spacecraft at the low rate of 40 bits per second.

    • The S-band transmitter has not been used since the last planetary encounter.

Damaged or malfunctioning downlink systems
In the case of Voyager 2, which began its tour of the outer planets in 1977, a failure in the transponder's phase-locked loop (PLL) capacitor while on its way to Jupiter left the spacecraft extremely sensitive to Doppler dynamics on the uplink, thus jeopardizing the link whenever coherent mode was selected. To prevent complete loss of telemetry data during critical encounters, Voyager was switched to noncoherent mode prior to the high Doppler dynamics of closest approach (even though the transponder remained locked to the uplink), thus sacrificing the most desirable data, from the standpoint of celestial mechanics researchers, at Saturn, Uranus, and Neptune.




How will the DSN software work?

Initial signal intercept parameters (based on ITU CCSDS parameters)

  • Sample rate: 64 kbs, 128 kbs. Note 32 kbs may be adequate. The sample rate has yet to be determined.

  • Sample depth (magnitude): 16 bits or 24 bits; SETI style 'phase sampling' will probably not be necessary as signal phase can be determined by post processing the signal in the software domain. It is assumed that 16 bit sampling must be tried initially, but it is also assumed that 24 bit sampling will probably be mandatory.

  • Antenna information: A very small amount will be included with the work units, probably in a different file. Probably an open source (open specification) file format like WAV or AU will be used. The work unit will not be compressed via psychoacoustic methods aka MP3, AAC, Ogg.




Initial work unit generation parameters

  • Work unit size: 4.01 mb, the 0.01 mb being for the dish or dishes parametric metadata

  • Work unit overlap: 3.2 seconds

  • Work unit sample modes: Single Dish (Probably CISRO Parkes)

  • Work unit sample modes (future implementation): 2 Dishes Cophased, 3 or 4 Dishes Cophased, VBLI Modes






Decoder algorithm (generalized)

  1. Use SETI @ Home algorithms to detect Voyager signals (carrier f(0) detection, decoder parameter programming).

  2. Use Astropulse @ Home algorithms to aid in secondary parameter programming of the decoder.

  3. Assume that for each 10% of progress, decoder may have to be reprogrammed to cope with changing reception conditions.

  4. Upon completed detection (CW_lock = True; software carrier_lock = true, carrier_sidelobe_lock = true), use Astropulse to do long run iFFTs to further characterize the signal when appropriate.

  5. Use a new codebase to decode Voyager's telemetry, storing processed data with XML wrapper, also returning the raw bitstream.

  6. Display on the screen the scientific data, coupled with the telemetry data. It will take many design tries to get this down.


Astropulse research project's contribution to the codebase

Not only does dedispersion allow us to see the true shape of the signal, but it also reduces the amount of noise that interferes with the signal's visibility. Noise consists of fluctuations that produce a false signal. There could be electrical noise in the telescope, for instance, creating the illusion of a signal where there is none. Because dispersion spreads a signal out to be up to 10,000 times as long, this can cause 10,000 times as much noise to appear with the signal. (There's a square root factor due to the math, so there's really only 100 times as much noise power, but that's still a lot.)

The amount of dispersion depends on the amount of ISM plasma between the Earth and the source of the pulse. The dispersion measure (DM) tells us how much plasma there is. DM is measured in "parsecs per centimeter cubed", or pc cm^-3.

This phrase "parsecs per centimeter cubed" probably sounds a bit meaningless ... here's the explanation: a parsec is about 3 light years. If a source is 1 parsec away, and the space between the Earth and that source is filled with plasma, with 1 free electron per cubic centimeter, then that's 1 pc cm^-3. To get the DM, multiply the distance in parsecs by the electron density in cm^-3. The density of free electrons in the ISM is about 0.03 per cubic centimeter.

From : http://setiathome.berkeley.edu/ap_info.php




Voyager carrier wave as tracked by SETI based equipment

Voyager telemetry intercept at 109 AU, carrier wave integrated over 192 seconds




Comments of Voyager and New Horizons downlink decoding

  1. Voyager craft use [ ] as their base downlink modulation format, bandwidth = ; symbol rates = { } ; harmonics = {1st: 2nd}

  2. New Horizons uses [ ] as its base downlink modulation format, bandwidth = ; symbol rates = { } ; harmonics = {1st: 2nd}

  3. At least one of the Voyager craft has a transponder fault, so some noise filtering may have to be replicated in software




Target reception frequencies (f0)

Voyager I (Craft 31)

  • 8,414,995,272.530 Hz (Titan)

  • 8,414,995,272.376 Hz (Saturn)

both craft have a downward frequency trend

  • there are 2 downlink frequencies for each craft

Voyager II (Craft 32)

  • 8,420,430,593.447 Hz (Jupiter)

  • 8,420,430,462.000 Hz (Saturn)

  • 8,420,430,456.100 Hz (Uranus)

  • 8,420,430,398.420 Hz (Neptune)

  • 90 AU: (?)

New Horizons

  • 8436.895671 MHz

Bandwidth: 800 Hz, nominal

  • There may already be some deviation from the original f(0)

NOTE: The DSN does not disclose (on any of its websites) current known downlink and uplink frequencies for the Voyager Program. This policy of secrecy is not becoming of NASA or the DSN.

NB: Voyager I's f(0) data is unavailable at the time of posting for other encounters within the solar system. All f0 data here is from occultation experiments.

Note: The carrier wave is drifting at rate of -0.6 > Hz/second due to Doppler effects from Earth rotation and craft motion.




This software innovation will make it possible to improve the overall reliability of the Deep Space Network, and the deep space science platforms using the Deep Space Network.

This software innovation will allow the Voyager I & II, and any future spacecraft to have downlink data rates that will nearly reach the maximum rates specified by the "Shannon Limit" from information theory and the error correction schemes in place.

  • Download applicable NASA Deep Space Network research documents (ZIPPED PDFs)

  • This document set is subject to revision (and even deletion) and is intended for informational use only.




Other future mission optimizations possible with this research

  • Allowed f_Subcarrier_Frequency values too restrictive :  CCSDS%2091011R1/DispForm.aspx?ID=113

  • Some uplinks for flying spacecraft use subcarrier frequencies other than 8000 Hz and 16000 Hz. For example, Voyager I and Voyager II uses 512 Hz and Muses-C uses 4000 Hz.

  • The DSN Uplink is required to generate subcarriers for commanding over a much wider range of values (from 1 Hz to 16000 Hz), including values that take into account Doppler shifts.

  • Future implementations may require higher subcarrier frequencies.






Governmental and Intergovernmental Space Agency Websites

  1. European Space Agency (ESA)

  2. Australia CSIRO Space Research (CSIRO)

  3. Canadian Space Agency (CSA)


Space Agency Websites relating to Voyager or New Horizons or the DSN

  1. SETI Casper (signal processing research) : seti.berkeley.edu/casper/

  2. NASA's Deep Space Network (DSN)

  3. NASA's Planetary Data System (PDS)

  4. NASA Radio Science Research : http://radioscience.jpl.nasa.gov/

  5. NASA Voyager Mission : voyager.jpl.nasa.gov

  6. NASA Voyager Mission : NSSDC-84A, NSSDC-76A

  7. NASA New Horizons [1] : pluto.jhuapl.edu

  8. NASA New Horizons [2] : NSSDC Catalog: 2006-001A

  9. R & D New Horizons [3] : boulder.swri.edu/pkb/

  10. DSN Research Publications : http://tmo.jpl.nasa.gov/ipn_progress_report/issues.cfm?force_external=0 ; Site Search

Dataset Websites

  1. NASA Voyager Mission : pds-rings.seti.org/voyager/rss/ (datasets, misc)

  2. Instrument datasets for Voyager (magnetic, plasma) : cohoweb.gsfc.nasa.gov/cw.html

  3. Distributed Computing Links : boinc.berkeley.edu, SETI @ Home, Astropulse

  4. Planetary Society : planetary.org/explore/topics/new_horizons/



Important onward reference points, science and telemetry

Related websites

Initial Concept
02 FEB 2000

Initial Text Version
23 MAR 2000

Latest Revision
03 FEB 2010 (misc edits)