Software Defined Radio in viaggio verso Marte

Il JPL di Pasadena ha recentemente comunicato che le prove in volo del radar e dell'impianto di comunicazione UHF della navicella Phoenix, attualmente in transito verso il pianeta Marte, hanno dato esito positivo.

Phoenix Mars Lander Status Report: Radar and Other Gear Pass Checkouts
September 04, 2007

Two crucial tools for a successful landing of America's latest mission to Mars, the radar and UHF radio on NASA's Phoenix Mars Lander, have passed in-flight checkouts.

The ultra-high-frequency radio won't be turned on again until landing day, May 25, 2008, when it will relay communications from Phoenix to orbiters already in service around Mars. Since launch on Aug. 4, 2007, and until the day it reaches Mars, Phoenix is communicating directly with Earth via even higher frequency X-band radio, mounted on a part of the spacecraft that will be jettisoned shortly before Phoenix hits the top of the Martian atmosphere.
The radar will monitor the spacecraft's fast-shrinking distance to the ground during the final three minutes before touchdown on Mars, triggering descent-engine firings and other necessary events during the most challenging moments of the mission.
The Phoenix flight operations team tested the radar and UHF radio on Aug. 24. Four days earlier, the team ran the first in-flight checkout of a Phoenix science instrument.

Sono andato ad approfondire e ho trovato sul sito ufficiale della missione questa descrizione delle modalità di contatto radio con la terra. Il link generale occupa le frequenze della X-Band, mentre il modulo di atterraggio comunicherà in UHF con le postazioni orbitanti (ma potrà anche essere captato a terra nel West Virginia dal Green Bank Telescope del National Radio Astronomy Observatory.

How will the Phoenix spacecraft communicate with engineers on the Earth?
Like all of NASA’s interplanetary missions, Phoenix will rely on the agency’s Deep Space Network to track and communicate with the spacecraft. The network has groups of antennas at three locations: at Goldstone in California’s Mojave Desert; near Madrid, Spain; and near Canberra, Australia. These locations are about one-third of the way around the world from each other so that, whatever time of day it is on Earth, at least one of them will have the spacecraft in view. Each complex is equipped with one antenna 70 meters (230 feet) in diameter, at least two antennas 34 meters (112 feet) in diameter, and smaller antennas. All three complexes communicate directly with the control hub at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. Phoenix will communicate directly with Earth using the X-band portion of the radio spectrum (8 to 12 gigahertz) throughout the cruise phase of the mission and for its initial communication after separating from the third stage of the launch vehicle. The cruise stage carries two copies of its communications equipment, providing redundancy in case of a problem with one of them. The mission will use ultra high frequency (UHF) links (300 megahertz to 1,000 megahertz), relayed through Mars orbiters during the entry, descent and landing phase and while operating on the surface of Mars. A UHF antenna on the back shell will transmit for about six minutes between the time the cruise stage is jettisoned and the time the back shell is jettisoned. From then on, a UHF antenna on the lander deck will handle outgoing and incoming communications. The UHF system on Phoenix is compatible with relay capabilities of NASA’s Mars Odyssey and Mars Reconnaissance Orbiter, and with the European Space Agency’s Mars Express. Phoenix communication relays via orbiters will take advantage of the development of an international standard, called the Proximity-1 protocol, for the data transfer. This protocol was developed by the Consultative Committee for Space Data Systems in an international partnership for standardizing techniques used for handling space data. The Phoenix spacecraft’s UHF signal might also be receivable directly via the Green Bank Telescope in West Virginia. Data transmission is most difficult during the critical sequence of entry, descent and landing activities, but communication from the spacecraft is required during this period in order to diagnose any potential problems that may occur. An antenna on the back shell will transmit during entry and descent. Another, on the lander deck, will transmit and receive during the final moments of descent and throughout the surface operations phase of the mission.

Per le comunicazioni dati la NASA ha fatto sviluppare dal CCSDS un protocollo ad alta velocità, Proximity-1 capace di trasmettere in UHF a 256, una velocità undici volte superiore ai 22 kilobit raggiungibili da precedenti missioni.

CCSDS Proximity-1 Communications Protocol Enables High-Speed Communication at Mars

Date Released: Monday, May 3, 2004

Proximity-1, a communications protocol developed by the international Consultative Committee for Space Data Systems (CCSDS), was instrumental in the success of a recent first-ever demonstration of in-orbit communication between NASA's Mars Exploration Rover (MER) Spirit and European Space Agency (ESA) Mars Express (MEX) orbiter.
Proximity-1 is a short haul delivery protocol designed to establish a two-way communications link between a lander and an orbiter, negotiate data rate and communications mode, and reliably deliver data during short orbiter-to-surface contacts.
Supported by NASA, CCSDS is an international committee founded by the world's major space agencies dedicated to furthering interoperability in space through the development of standardized techniques for handling space data. NASA's Jet Propulsion Laboratory (JPL), working with its international partners in the CCSDS, led the development of Proximity-1.
On February 6, 2004, Proximity-1 performed flawlessly during the NASA and ESA sponsored demonstration of communications between the rover Spirit and MEX orbiter. The CCSDS protocol not only enabled the first in-orbit communication between NASA and ESA spacecraft, it also helped establish the first working international communications network around a planet other than Earth.
"I believe CCSDS protocols are the real 'story behind the story' of successful communications on the Mars missions," said Peter Shames of NASA's Jet Propulsion Laboratory (JPL), Pasadena, Calif. "Without them, trying to establish communication between the rovers and orbiters would be like trying to tune in an FM station on an AM radio."
Prior to the development of CCSDS' Proximity-1, earlier missions like Mars Pathfinder had to transmit data directly from the Martian surface back to Earth. With millions of miles between the two planets and Spirit's limited transmitter, the maximum data transmission rate from Mars to Earth was approximately 22 Kbps. Also, despite error correcting codes, very weak signal levels meant data reliability was limited.
Mars mission planners had long recognized the advantage of transmitting data from lander to orbiter, then from orbiter to Earth. The distance from lander to orbiter is only a few hundred miles, allowing energy-efficient communications using simple omni-directional antennas. This means that signals received from the lander are stronger and have fewer errors. The orbiter, less constrained by power, is able to then re-transmit the data to Earth at a high rate.
Planners estimated that the rover's data transmission rate using a shorter, Proximity-1-enabled communication path would be up to four times faster than one using a direct to Earth link. They also estimated data rates would be higher since Proximity-1's reliability features allow the protocol to immediately fill any data gaps. Regardless, because the path was largely untested, planners were unwilling to make it the primary path of communication on the project, that is, until Proximity-1's flawless performance on February 6th.
Today, utilizing CCSDS' Proximity-1, MER rovers Spirit and Opportunity are reliably sending data to the Mars Odyssey orbiter at 256 Kbps, twice as fast as the planned maximum transmission rate. Further, scientists are receiving an average of three times more data than originally estimated and relay links enabled by Proximity-1 are responsible for over 90 percent of all of the data returned from the rovers.
"Communication between the Mars rovers and orbiters has been so successful because of CCSDS-developed protocols," said Shames. "In fact, in recent years, all Mars spacecraft have implemented standard data communications protocols developed by CCSDS on their long-haul links back to Earth."
Proximity-1, CCSDS' most recent success, is the first space communications protocol to reliably operate in the proximate environment between a Mars bound asset and an orbiter. Coupled with long-haul CCSDS protocols already used to relay data from the orbiters back to Earth, CCSDS' Proximity-1 is yet another sign of a new era of successful international cooperation in space.
CCSDS will move forward in supporting the efforts of NASA, ESA, and other space agencies in using joint communications assets in future missions to the surface of Mars and, as it has for more than 20 years, will continue to develop new protocols to further both commercial and governmental interoperability in space.

About the Consultative Committee for Space Data Systems

In 1982, the world's major space agencies recognized that future data system interoperability would be enhanced through the development of standardized techniques for handling space data and established the Consultative Committee for Space Data Systems (CCSDS) as a forum where common space data system standards could be developed.
Over two decades later, CCSDS has grown into an organization of international cooperation and information-sharing comprised of 10 member agencies, 22 observer agencies and over 100 private industry associates from around the world. Data communications protocols developed by CCSDS now fly on over 280 international missions, including every spacecraft associated with the Mars mission.
For more information about CCSDS, please visit the CCSDS web site at http://www.ccsds.org.

Ma l'aspetto davvero affascinante per noi è lo sviluppo di ricetrasmettitori e ricevitori DSP a campionamento di media frequenza (IF sampling) capaci di analizzare una media frequenza di 70 MHz. Ecco una descrizione dei vari progetti per le attuali missioni dalle pagine del sito Marstech, sempre del JPL:

CMC Electronics Cincinnati (CMCEC) is developing a reprogrammable IF-sampling digital transceiver modem to support the next generation of reprogrammable, low-mass and low-power transceivers for future interplanetary missions requiring proximity links.
Previous developments by CMCEC in support of Mars Exploration Program missions include proximity transceivers for the Mars Climate Orbiter, Mars Polar Lander, Mars Odyssey and Mars Exploration Rovers. Within these transceivers, digital processing including the Proximity-1 protocol is implemented in VHDL, permitting reuse and enabling CMCEC to bring this technology forward to a reprogrammable modem.
CMCEC is developing and testing two IF-sampling receivers for space applications. The first is a Factory Reconfigurable S-Band Command Receiver and the second is a Multi-Mode Spread-Spectrum Factory Reconfigurable Receiver. Both of these receivers sample a 70 MHz IF, digitally demodulate and recover received data. All digital signal processing, control and interface functions are implemented in Field Programmable Gate Arrays (FPGAs) utilizing VHDL, making the designs portable, reusable and reconfigurable.
Additionally, CMCEC and JPL are jointly developing the Mars Electra UHF Proximity Transceiver. The Electra similarly samples a 70 MHz IF, digitally demodulates and recovers data. Electra is a fully software-reprogrammable transceiver implemented with FPGA and microprocessor technology. CMCEC and JPL are leveraging this large base of portable and reconfigurable digital signal-processing technology and Proximity-1 protocol implementation in the development of a Reprogrammable Transceiver Modem.
The Reprogrammable Transceiver Modem provides a very small, low-power transceiver modem solution utilizing advanced digital signal-processing techniques implemented in a RAM-based FPGA and a One-Time Programmable (OTP) FPGA. This modem will be capable of modulating and demodulating standard waveforms including FSK, BPSK, QPSK, CDMA, TDMA and FDMA, as well as other complex modulation schemes. Additionally, the modem will support navigation and radiometric observable techniques including Half-Duplex Navigation, and will interoperate with the Mars In Situ Sensor Web.
For further information, go to A Proximity Microtransceiver for Interoperable Mars Communications.

Non mancate di seguire l'ultimo link, puntato sulle pagine della Kansas State University che descrivono il nuovo microricetrans UHF, dove trovate anche alcune fotografie e un sacco di materiale descrittivo con misure. Basti pensare che se gli attuali ricetrasmettitori sono grandi come una scatola di scarpe, pesano due chili e consumano fino a 70 Watt, con l'SDR la sezione radio occupa una scheda di pochi centimetri quadrati che consumerà 100 mW!