Nasa Talks to Mars Rover Again

The NASA Deep Space Network (DSN) is an international network of antennas that provide the communication links between the scientists and engineers on Globe to the missions in space and on Mars.

The DSN consists of three deep-space communications facilities placed approximately 120 degrees apart around the world: at Goldstone, in California'due south Mojave Desert; nigh Madrid, Espana; and near Canberra, Commonwealth of australia. This strategic placement permits abiding observation of spacecraft as the Globe rotates on its own axis.

Acquire more about:

the size and forcefulness of the DSN Antennas
how the DSN prevents "busy signals"
how the DSN helps engineers navigate the spacecraft during cruise
special bespeak tones the DSN received during entry, descent, and landing
how the rover can communicate through Mars-orbiting spacecraft
10-band radio waves used by the rover to communicate
how fast and how much information the rover can send back

Size and Strength of the DSN Antennas

The DSN antennas are extremely large: 34 meters (virtually 37 yards) and 70 meters (about 76 yards). These enormous antennas enable humans to reach out to spacecraft millions of miles abroad. The larger the antenna, the stronger the signal and greater the amount of information the antenna tin ship and receive. The Mars Science Laboratory, while in its prowl phase configuration, communicated through low and medium-gain antennas. While Curiosity is roving on the planet, it is communicating with the Mars Reconnaissance Orbiter via its UHF antenna and to the DSN on Earth by way of its high-proceeds antenna.

Preventing Busy Signals

The Deep Space Network (DSN) communicates with well-nigh all spacecraft flying throughout our solar system. Many spacecraft are cruising in infinite, observing Saturn, the sun, asteroids and comets. In addition, the Mars Exploration Rovers are still decorated on the surface of Mars and NASA'south Mars Reconnaissance Orbiter has joined the other martian orbiters. The DSN antennas are extremely busy trying to track all of these space missions at one time. The Mars Scientific discipline Laboratory spacecraft must therefore share time on the DSN antennas. A sophisticated scheduling system with a team of hundreds of negotiators around the earth ensures that each mission's priorities are met.

During critical mission events, such as landing on Mars, multiple antennas on Earth and the Mars Reconnaissance Orbiter track the signals from the spacecraft to minimize risk of loss of communication. During the landed operations phase on the martian surface, the Mars Science Laboratory utilizes the Multiple Spacecraft Per Aperture (MSPA) capability of the DSN, which allows a unmarried DSN antenna to receive downlink from up to four spacecraft simultaneously, too as using the relay capabilities of the Mars Odyssey (ODY) and Mars Reconnaissance Orbiter (MRO) spacecraft.

The rover's downlink sessions (when the rover sends information dorsum to World) are generally roughly xv minutes each, with usually two downlink sessions per relay orbiter (ODY, MRO) per martian 24-hour interval (sol), with two sessions overnight and two sessions in the late martian afternoon. MSPA allows merely ane spacecraft at a fourth dimension to have the uplink, and Marvel commands early in each sol (martian mean solar day) for roughly 30 minutes to provide the instructions for that sol'southward activities.

Navigation

How the DSN helps engineers navigate the spacecraft during cruise

During cruise, the Deep Infinite Network antennas pick up signals from the spacecraft that tell navigators where the spacecraft are located. Engineers cannot physically see the spacecraft with the naked eye or a telescope, and they rely on radio "tracking" to know where the spacecraft are at whatever given fourth dimension. Similar a game of "Marco-Polo," the DSN listens for signals from outer space and tin can discover where the spacecraft is from where the sound comes from.

This navigation service is called "tracking coverage" and it includes Doppler, ranging and delta differential i-mode ranging, or "Delta DOR."

Doppler Data

In order to calculate the speed that a spacecraft is flight, engineers apply Doppler data to plot velocity along the line of sight between Earth and the spacecraft.

Most people are familiar with the phenomenon of a car horn or train whistle changing its frequency as information technology moves towards or away from them. Electromagnetic radiation (e.g. low-cal waves or radio signals) also feel this effect. The size of the frequency shift, or "Doppler shift," depends on how fast the light source is moving relative to the observer. Astronomers often refer to the "redshift" and "blueshift" of visible light, where the light from an object coming towards united states is shifted to the blue finish of the spectrum (higher frequencies), and calorie-free from an object moving abroad is shifted towards the red (lower frequencies).

The Mars Scientific discipline Laboratory spacecraft commmunicates with controllers on the ground past radio signals. Ground controllers know the frequency of the signal that is emitted from the spacecraft. However, since the spacecraft is moving abroad from (or towards) us, this frequency is being Doppler shifted to a different frequency. So, engineers (or, more accurately, computers) compare the received frequency with the emitted frequency to get the Doppler shift. Information technology's and so straightforward to notice the velocity that would cause the resulting Doppler shift.

Ranging

Ranging is sending a code to the spacecraft, having the spacecraft receive that code and immediately send it back out the spacecraft's own antenna, and finally receiving that lawmaking back on Earth. The time betwixt sending the code and receiving the code, minus the delay in turning the bespeak around on the spacecraft, is twice the light fourth dimension to the spacecraft. Then that time, divided past two and multiplied by the speed of low-cal, is the distance from the DSN station to the spacecraft. This altitude is accurate to nigh five to ten meters (16-33 feet), fifty-fifty though the spacecraft may be 200 billion meters away!

Delta Dor

Delta DOR is similar to ranging, but it also takes in a tertiary signal from a naturally occurring radio source in space, such equally a quasar, and this additional source helps scientists and engineers gain a more accurate location of the spacecraft.

Quasars are a few billion light years away and a few billion years in the by. Quasars are used as extremely well known positions in the heaven to provide a scale for the aforementioned measurements fabricated inside a few tens of minutes of each other on a spacecraft. Being able to exercise quasar and spacecraft ranging well-nigh the same time and subtracting the answers cancels a lot of errors that are the same in both measurements from the temper and the equipment.

The "ranging" is non really ranging, simply differenced ranging. What is measured is the difference in the distance to the source between two complexes on Earth (for instance, Goldstone and Madrid or Goldstone and Canberra). From that an bending in the sky can be determined relative to the stations. The bending for the quasar is subtracted from the angle of the spacecraft, giving the athwart separation of the quasar and the spacecraft. That angle is accurate to about five to ten nanoradians, which means when the spacecraft is nearly Mars, say 200 million kilometers away, information technology can determine the position of the spacecraft to within i kilometer (0.6 miles).

Tones

Special signal tones the DSN received during entry, descent, and landing

During the entry, descent and landing phase of the Mars Exploration Rover mission, engineers listened anxiously for 128 distinct tones that indicated when steps in the process were activated; one sound indicated the parachute deployed, while another signaled that the airbags had inflated. These sounds were a series of bones, special individual radio tones.

The Mars Science Laboratory spacecraft transmitted in 10-band during its entry, descent and landing process, which was the expected path for confirmation of the initial events in the process. Due to signal strength constraints, these transmissions were elementary tones, comparable to semaphore codes, rather than full telemetry. The Deep Space Network listened for these direct-to-Earth transmissions. However, World went out of view of the spacecraft, "setting" below the Martian horizon, partway through the descent, so the X-ring tones were not available for confirming the final steps in descent and landing. Past then, the aptitude-pipe relay via Odyssey had begun.

Communication

How the rover can communicate through Mars-orbiting spacecraft

Non only does the rover send messages straight to the DSN stations, but information technology is also able to uplink information to other spacecraft orbiting Mars, utilizing mainly the Mars Reconnaissance Orbiter and Mars Odyssey (if necessary) spacecraft as messengers that pass along news to Earth for the rover. The respective spacecraft mainly "talk" via their UHF antennas. The Mars Reconnaissance Orbiter carries an Electra UHF payload with the adequacy of helping navigate the Mars Scientific discipline Laboratory safely toward Mars. The Ka-Band package aboard the Mars Reconnaissance Orbiter can serve as another possible pipeline to "talk" to the Mars Science Laboratory (read more nigh the Mars Reconnaissance Orbiter Engineering Instruments).

The benefits of using the orbiting spacecraft are that the orbiters are closer to the rover than the DSN antennas on Earth and the orbiters have Earth in their field of view for much longer fourth dimension periods than the rover on the footing.

Considering the orbiters are simply between 160 and 250 miles (257 and 400 kilometers) above the surface of Mars, the rover doesn't have to "yell" as loudly (or use as much energy to send a message) to the orbiters every bit it does to the antennas on Earth.

X-band Radio Waves

10-band radio waves used past the rover to communicate

The rover communicates with the orbiters and the DSN through radio waves. They communicate with each other through 10-band, which are radio waves at a much higher frequency than radio waves used for FM stations.

The radio waves to and from the rover are sent through the orbiters using UHF antennas, which are shut-range antennas that are similar walkie-talkies compared to the long range of low-proceeds and high-gain antennas. All three orbiters agile at Mars — NASA's Mars Odyssey and Mars Reconnaissance Orbiter and the European Space Agency'south Mars Express — were at positions where they could receive transmissions from the Mars Science Laboratory spacecraft during its entry, descent and landing. Only Odyssey relayed the information immediately, however. The other two orbiters recorded Mars Scientific discipline Laboratory data from the Mars Science Laboratory spacecraft, belongings information technology onboard, and sending it to World hours later. Mars Reconnaisance Orbiter even captured images of the spacecraft on its parachute during entry, descent and landing.

The prowl stage had 2 antennas that were used to communicate with the Earth. The low-gain antenna was omni-directional and was used when the spacecraft was near the Earth. Because it radiated in all directions, the low-proceeds antenna did not need to exist pointed at the Earth to enable a communications link. The medium-gain antenna was a directional antenna that had to exist pointed toward the Earth for communications, but had more power to communicate when the spacecraft was farther away from the Earth. The medium-proceeds antenna acted like a floodlight and could direct the free energy into a tighter beam to attain Earth. But like a floodlight directs more lite into a focused area than a normal light seedling does out of a lamp, the medium-gain antenna could direct the information from the spacecraft into a tighter beam than the low-gain antenna.

When the rover speaks directly to Earth (from the surface of Mars), it sends messages via its loftier-proceeds antenna (HGA). The high-proceeds antenna can send a "beam" of data in a specific direction and it is steerable, so the antenna can move to point itself direct to whatever antenna on World. The benefit of having a steerable antenna is that the entire rover doesn't necessarily have to change positions to talk to Earth. Like turning your neck to talk to someone beside y'all rather than turning your entire trunk, the rover tin save energy by moving only the antenna.

Data Rates/Returns

The data charge per unit direct-to-Earth varies from most 500 bits per 2d to 32,000 bits per second (roughly half as fast equally a standard domicile modem). The data rate to the Mars Reconnaissance Orbiter is selected automatically and continuously during communications and tin be every bit high as two million bits per second. The information rate to the Odyssey orbiter is a selectable 128,000 or 256,000 bits per 2nd (4-8 times faster than a home modem).

An orbiter passes over the rover and is in the vicinity of the heaven to communicate with the rover for about eight minutes at a time, per sol. In that time, between 100 and 250 megabits of data can exist transmitted to an orbiter. That same 250 megabits would take up to 20 hours to transmit straight to Earth! The rover tin can merely transmit direct-to-Earth for a few hours a day due to power limitations or conflicts with other planned activities, even though Earth may be in view much longer.

Mars is rotating on its ain axis so Mars often "turns its back" to Earth, taking the rover with information technology. The rover is turned out of the field of view of Earth and goes "night," just similar nighttime on Earth, when the lord's day goes out of the field of view of Earth at a certain location when the Globe turns its "back" to the lord's day. The orbiters can meet Globe for about 2/iii of each orbit, or about 16 hours a day. They can send much more data directly-to-Earth than the rover, not just because they can see World longer, but as well because they accept a lot of power and bigger antennas than the rover.

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Source: https://mars.nasa.gov/msl/mission/communications/