Have you ever wondered why we aren't able to receive cellular signals 10 feet under the ground, yet we are able to connect to satellites hundreds of miles away from our Earth? How come we are constantly connected to all these space stations and satellite, yet we are not able to get service in NYC subway stations?
Today NASA’s Curiosity rover is exploring Mars, Juno is orbiting around Jupiter and Cassini is visiting Saturn. But still, we are continuously connected with them. Even the nearest satellite to the Earth is NASA’s Aqua satellite which is about 705 KM from the Earth, while the weather satellite is about 36,000 KM from our Earth surface. All of these satellites are constantly sending data back to earth. But how?
It’s all because of NASA’s DSN(Deep Space Network).
Earth rotates around its orbit, and it rotates around the sun at the same. So the distance from all these planets keep changing and we weren’t able to connect to space stations all the time. Since Earth is oblate spheroid (kinda round /oval) there isn’t an exact point to send data 24/7. To solve this problem the DSN has three ground stations located approximately 120˚ degrees apart on Earth (120 ˚+ 120˚ + 120˚ = 360˚). They are located at Goldstone California, Madrid Spain, and Canberra Austalia. Together all three of them cover the entire 360-degree angle of Earth. Means we can send a signal anywhere on Earth from outer space and an antenna from one of these locations will catch the signal. These ground stations also communicate with satellites to initiate course corrections, provide software updates, and alter the way scientific observations are made.
Quote (nasa.gov) “The diameter of the Deep Space Network antennas ranges in size from 34 meters (111feet) to 70 meters (230 feet) — equivalent to the height of a 20 story building! The dishes need to be so large in order to capture the faint signals sent from millions, even billions, of miles away. With its sophisticated equipment, the 70-meter antenna is able to capture a 20 watt signal from the depths of space, which is less powerful than the energy emitted by a refrigerator light bulb”.
Due to launch weight limits engineers have to use low power transmitters. These antennas are so powerful, quote “they can hear a whisper from billion of miles”. It can even hear the most distant man-made object from space. You guessed it right!, Voyager 1 and 2. Voyagers have already entered in the interstellar medium and passed the Solar system. So by the time Voyager’s signal travel back to earth they are 20 billion times less than what used to power a digital watch. These antennas are perfectly designed to receive and amplify these signals. But it also means radio static emission emitted by basically everything gets amplified too. So astronomers encoded the signals in such a way it can distinguish satellite signals from noise. There is another trouble, equipment so strong also makes noise and not to mention heat waves too. So to avoid this disturbance, amplifiers are designed to work at very cold temperatures within a few degrees above absolute zero. Another way DSN amplifies these signals is by using the multiple antennas at the same source is called Arraying. It works really well for radio waves.
What’s cool about it is NASA lets you see the real-time data these antennas are receiving and which spacecraft is sending that data.
Deep Space Network Now
The real time status of communications with our deep space explorers
Satellites communicate by using radio waves to send signals to the antennas on the Earth. The antennas then capture those signals and process the information coming from those signals.
uplink and downlink
The communication going from a satellite to ground is called downlink, and when it is going from ground to a satellite it is called uplink. When an uplink is being received by the spacecraft at the same time a downlink is being received by Earth, the communication is called two-way. If there is only an uplink happening, this communication is called upload. If there is only a downlink happening, the communication is called one-way.
The Deep Space Network provides back up to the other two networks:
1: The Near Earth Network (NEN): Formerly known as the Ground Network, the Near Earth Network (NEN) provides telemetry, commanding, ground-based tracking, data, and communications services to a wide range of customers. E.g Geo satellites
2: Space Network (SN): The Space Network consists of:
- Ground systems that operate as a relay system between satellites
- Satellites in low Earth orbit (LEO) above 73 km
- Ground facilities
So the way DSN is designed on earth and satellite position on the globe at least one of these antennas will hear the broadcast. Signals from NEN are stronger so they get picked up really easily. For deep space missions, it’s a bit harder. So to strengthen the signals we use both low and high gain. low gains antennas spread their signals everywhere while high gain antennas are more focused so the signal strength is stronger when it reaches the earth. The ability to focus makes them really efficient but remember the station on Earth are moving too so even if they are no focused these antennas can still pick them up too.
NASA is developing a trailblazing, long-term technology demonstration of what could become the high-speed internet of the sky.
— The Laser Communication Relay Demonstration(LCRD) will help NASA
understand the best ways to operate laser communications systems. They could enable much higher data rates for connections between spacecraft and Earth, such as scientific data downlink and astronaut communications.
— Laser Communications Relay Demonstration (LCRD) could revolutionize the way mission-critical data is transmitted to and from spacecraft. The mission is a technology demonstration to verify the longevity of optical communications systems in space, which can provide data rates 10 to 100 times better than traditional radio-frequency systems.
Internet on Mars
Mars is so far away in fact that it takes radio signals quite a long time to get from the spacecraft back to Earth. During Curiosity EDL, this delay will be 13 minutes, 48 seconds, about mid-way between the minimum delay of around 4 minutes and the maximum of around 24 minutes.
LCRD will be a great step towards fast internet but there will always be a time delay between earth and mars due to their orbit around the sun.