08-12-2012, 05:26 PM
AN EYE IN THE SKY
[attachment=43125]
ABSTRACT
Mars is not going to give its secrets, but we have the tools to get them. NASA’s Deep Space Network (DSN), succeeded in making the communication possible with the rovers landed on Mars. NASA’s scientific investigations of the solar system are accomplished mainly through the use of robotic spacecraft. The Deep Space Network (DSN) provides the two-way communications link that guides and controls spacecraft and brings back images and other scientific data they collect. The Deep Space Network encompasses complexes strategically placed on three continents. The largest and most sensitive scientific telecommunications system in the world, it also performs radio and radar astronomy observations for the exploration of the solar system and the universe. It is managed and operated for NASA by the Jet Propulsion Laboratory (JPL). In this paper titled ”AN EYE IN THE SKY (Communicating with rovers)” we will be dealing with antennas used in the DSN, the arraying of antennas, the deep space communication complexes (DSCC)and the data flow in the DSCC.
INTRODUCTION
The radiation environment on the surface of Mars is unknown but probably poses a similar risk, even though the planet's tenuous atmosphere would provide some shielding. It still remains to be seen what the hazards are on the surface. The main worry for astronauts on Mars would be the periodic bursts of charged particles that stream outward from the sun. On Earth, a global magnetic field and a substantial atmosphere protect against that radiation. Observations made last year show bombardments of solar radiation can last more than a week. Presumably, astronauts on Mars would have to remain confined in some sort of shelter during such blasts of radiation. Without taking these risks NASA scientists, succeeded in landing “Rovers” to continue their research on Mars.
What is a Rover?
A “ROVER” is nothing but a robot.
The current mission to Mars involves a pair of robotic rovers that are known as the Mars Exploration Rovers (MER).The MER (Fig. 1) robots are the largest rovers to ever successfully land on another planet. On this mission NASA has designed the MER robots to act as robotic geologists.
Arraying:
A powerful technique for obtaining higher sensitivity in support of distant spacecraft is arraying. Arraying (Fig.4) means electronically combining the signals coming in from two or more DSSs, either at the same DSCC, at two different DSCCs, or with a non-DSN radio telescope. This increases the effective aperture, strengthens reception of the spacecraft's weak signal, and permits the spacecraft to be able to downlink data at a higher rate.
Full-Spectrum Arraying of Receiving Radio Antennas:
In the original DSN application, the signals received by as many as eight geographically diverse antennas are processed by full-spectrum receivers (FRS) followed by a full-spectrum combiner (FSC) (shown in Fig.6). The analog signal from each antenna is first down-converted to an intermediate-frequency (IF) band centered at 300 MHz. Then in an FSR, the IF signal is subjected to a combination of analog-to-digital (A/D) conversion and frequency down-conversion that yields an in-phase (I) and a quadrature-phase (Q) data stream, each consisting of 8-bit samples at a rate of 16 mega samples per second. The delay and phase of the I and Q streams from each antenna are altered by use of a delay line and a phase rotator. Adjustment is made first by using delay prediction, followed by a feedback measurement of residual delay and phase by the FSC. In the FSC, cross-correlations of upper and lower sidebands from different antennas (e.g., of the upper sideband received by antenna 1 with the upper sideband received by antenna 2) are computed. The correlations contain information on frequency-dependent and frequency-independent phase offsets related in known ways to differential delays and Doppler shifts. The correlations are processed to generate phase and a delay offset for feedback to each FSR. The I and Q data streams from the FSRs are weighted and summed; the sum signal is then subjected to digital-to-analog (D/A) conversion and frequency up-conversion to obtain the desired enhanced IF signal.
CONCLUSION
Research continues on ways to improve the communications capabilities of the DSN. Going to a higher frequency range than that currently in use would provide several benefits. So capabilities are under development to enable use of the Ka-band at frequencies as high as 31 to 35 gigahertz. Ka-band allows much more data transfer without the need for more ground antennas, which are very expensive to build.
[attachment=43125]
ABSTRACT
Mars is not going to give its secrets, but we have the tools to get them. NASA’s Deep Space Network (DSN), succeeded in making the communication possible with the rovers landed on Mars. NASA’s scientific investigations of the solar system are accomplished mainly through the use of robotic spacecraft. The Deep Space Network (DSN) provides the two-way communications link that guides and controls spacecraft and brings back images and other scientific data they collect. The Deep Space Network encompasses complexes strategically placed on three continents. The largest and most sensitive scientific telecommunications system in the world, it also performs radio and radar astronomy observations for the exploration of the solar system and the universe. It is managed and operated for NASA by the Jet Propulsion Laboratory (JPL). In this paper titled ”AN EYE IN THE SKY (Communicating with rovers)” we will be dealing with antennas used in the DSN, the arraying of antennas, the deep space communication complexes (DSCC)and the data flow in the DSCC.
INTRODUCTION
The radiation environment on the surface of Mars is unknown but probably poses a similar risk, even though the planet's tenuous atmosphere would provide some shielding. It still remains to be seen what the hazards are on the surface. The main worry for astronauts on Mars would be the periodic bursts of charged particles that stream outward from the sun. On Earth, a global magnetic field and a substantial atmosphere protect against that radiation. Observations made last year show bombardments of solar radiation can last more than a week. Presumably, astronauts on Mars would have to remain confined in some sort of shelter during such blasts of radiation. Without taking these risks NASA scientists, succeeded in landing “Rovers” to continue their research on Mars.
What is a Rover?
A “ROVER” is nothing but a robot.
The current mission to Mars involves a pair of robotic rovers that are known as the Mars Exploration Rovers (MER).The MER (Fig. 1) robots are the largest rovers to ever successfully land on another planet. On this mission NASA has designed the MER robots to act as robotic geologists.
Arraying:
A powerful technique for obtaining higher sensitivity in support of distant spacecraft is arraying. Arraying (Fig.4) means electronically combining the signals coming in from two or more DSSs, either at the same DSCC, at two different DSCCs, or with a non-DSN radio telescope. This increases the effective aperture, strengthens reception of the spacecraft's weak signal, and permits the spacecraft to be able to downlink data at a higher rate.
Full-Spectrum Arraying of Receiving Radio Antennas:
In the original DSN application, the signals received by as many as eight geographically diverse antennas are processed by full-spectrum receivers (FRS) followed by a full-spectrum combiner (FSC) (shown in Fig.6). The analog signal from each antenna is first down-converted to an intermediate-frequency (IF) band centered at 300 MHz. Then in an FSR, the IF signal is subjected to a combination of analog-to-digital (A/D) conversion and frequency down-conversion that yields an in-phase (I) and a quadrature-phase (Q) data stream, each consisting of 8-bit samples at a rate of 16 mega samples per second. The delay and phase of the I and Q streams from each antenna are altered by use of a delay line and a phase rotator. Adjustment is made first by using delay prediction, followed by a feedback measurement of residual delay and phase by the FSC. In the FSC, cross-correlations of upper and lower sidebands from different antennas (e.g., of the upper sideband received by antenna 1 with the upper sideband received by antenna 2) are computed. The correlations contain information on frequency-dependent and frequency-independent phase offsets related in known ways to differential delays and Doppler shifts. The correlations are processed to generate phase and a delay offset for feedback to each FSR. The I and Q data streams from the FSRs are weighted and summed; the sum signal is then subjected to digital-to-analog (D/A) conversion and frequency up-conversion to obtain the desired enhanced IF signal.
CONCLUSION
Research continues on ways to improve the communications capabilities of the DSN. Going to a higher frequency range than that currently in use would provide several benefits. So capabilities are under development to enable use of the Ka-band at frequencies as high as 31 to 35 gigahertz. Ka-band allows much more data transfer without the need for more ground antennas, which are very expensive to build.