Author: Saqib ali
Today I’m going to explain what is the Deep Space and how do we communicate with spacecrafts in Deep space as well as near space. According to International Telecommunication Union (ITU) the term Deep space is defined as a region that lies outside the 2 million kilometers from the Earth and assign frequency bands i.e. S, X or Ka-band for communication with spacecrafts travelling into deep space. But, NASA and JPL not really restricted to the 2 million limit. NASA defines the limit as any region that lies outside from 16000km to 32000km.
How does NASA and other space agencies command and control their spacecrafts, get telemetry data, control attitude, send software updates, and get the science data back to earth. How NASA communicates with ISS, Hubble space telescope, Voyagers (Voyager 1 and 2), and recently launched science marvel the James Webb Space Telescope (JWST). In this article we are going to explore all this and especially the Deep Space Network (DSN).
Deep Space Network
Millions of kilometers away from Earth in a far distant place in space, NASA communicates with spacecrafts like Voyager 1 & 2, James Webb Space telescope and all the earlier outer space missions using its DSN. DSN is network of ground based parabolic dish antennas located in three places 120 degrees apart. One is in Goldstone California (USA), second in Madrid (Spain), and third in Canberra (Australia). Three stations at 120 degree apart makes at least one of them always facing deep space for communication.
These stations are built in a semi-mountainous region to avoid any radio frequency interference. Apart from NASA, other countries like Russia, China, Japan, India, and Europe have their own Deep space networks. They often assist each other on demand of emergency.
Antennas of DSN:
There are many sizes of antennas in DSN, the biggest is 70m, then 34m, and 26m. Only one 70m antenna is installed in each site and more than three 34 antennas. Most of the time 34m antennas are used to send and receive data to and from the spacecrafts in deep space. 70m antennas had been used only for emergency purposes i.e. Apollo 13 mission rescue, ESA’s SOHO mission rescue because the spacecraft gets into safe mode or low power mode in case of any fault. DSN was not primarily designed for Mercury (NASA space program), Gemini, Apollo, or Skylab but to assist them in case of emergency. Communication facility for these missions was provided though MSFN (Manned Space Flight Network) in which 26m antennas are used to send/receive signal. 26m antennas of DSN surely could assist the MSFN.
Hubble Space Telescope Communication:
Hubble is not in Deep space that’s why DSN cannot be used for Hubble communication. For Hubble, NASA uses the Tracking and Data Relay Satellite (TDRS) a type of geosynchronous satellites that communicates with ground stations in White Sands Ground Terminal (WSGT) in Las Cruces, New Mexico, 2nd in Guam (GRGT) and 3rd in Greenbelt, Maryland. Total of 9 TDRS satellites are present in orbit but 3 of them can provide full support.
James Webb Space Telescope Communication:
JWST has two antennas, one is High gain (600mm dish) and other is Medium gain (200mm is dish). JWST communicates with DSN ground stations using these HGA (High Gain Antenna) and MGA (Medium Gain Antenna). S band and Ka-band are used for data download and upload. How much data can be downloaded from JWST in 24 hours is surely less than the data rates available for Hubble. I will explain data rates and limitation of JWST vs Hubble in a future article.
Challenges and Future:
The 70m antennas at all three locations of DSN will be decommissioned by 2025 as they are reaching their end of life, moreover with new technology these are no longer necessary. More 34m antennas are being installed because these antennas can be used in array formation to enhance the basic capabilities.
New spacecrafts are being designed in a way that DSN only needed for bulk data transfer or in case of any emergency. This is “beacon mode service”, a new telecommunication technology for spacecrafts that are not tracked and communicated on daily bases by DSN. Only the health information or telecommunication status of the craft is relayed using a simple signal that can detected by any moderately sized antennas at ground. In this mode spacecrafts can communicate with each other too for relay purposes. This mode was used by the NASA’s New Horizons (Launched 2006) mission towards Pluto, almost all the Mars rovers are using this mode to communicate with Mars orbiters.
There is a need for a relay facility between ground stations and spacecrafts so that data transfer rates can be enhanced to support data intensive missions like JWST (moon could be a relay station). JWST can only transfer continuously for 4 hours two times a day with limited data rates that can cost the overall gains from the project. MRO (Mars Reconnaissance Orbiter), Mars Express (ESA) are being used as data relay stations for Mars rovers. There was a proposed project named Mars Telecommunication Orbiter (MTO) cancelled in 2005 that was a dedicated relay station for Mars rovers and spacecrafts in deep space. It was cancelled because the primary purpose of relaying data from Mars rovers to the Earth fulfilled by the MRO and Mars Express orbiters. MRO and Mars Express has a dedicated telecommunication package “Electra” a UHF software defined radio (SDR) for communication with Rovers. Mars Rover and Mars Express uses DSN and X-band at 8 GHz for communication.