How scientists doubled data transfer rates with New Horizons
At the end of last year, the New Horizons interplanetary station, which was sent to explore Pluto and its satellite Charon in 2006, awoke . The station made images for optical navigation, but they will reach Earth in two weeks. Why so long? After all, the LORRI camera makes only ten images every day. The answer is simple: Pluto from the Earth is at a distance equal to thirty distances from our planet to the Sun. Therefore, the radio signal is weak: New Horizons can transmit one kilobit per second. And only three seventy-meter plates of the NASA Deep Space Network are receiving data.
But the station team has a trump card up its sleeve - a trick that allows you to increase the transmission speed almost twice.
New Horizons uses an antenna and one radio amplifier to transmit data to Earth. The speed is 1 kilobits per second. Three 70-meter plates from NASA's Far-Space Network are capable of receiving data from such a distance, and you have to fight for work with them - at best, the team will receive one eight-hour communication session per day. During this time, you can send 28.8 megabits of data. While the New Horizons station is directed to Earth, it does not look at Pluto, so it has to choose between transmission and data collection.
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The LORRI camera sensor, which the station uses, is a square with a side of 1024 pixels of 12 bits each, we get a file of 12,582,912 bits in size. The image can be shrunk to 2.5 megabits without loss, especially when its part is occupied by the blackness of space. You can shrink more in JPEG, but for optical navigation you need more accuracy. In 8 hours we will receive 11 images if we transmit only them. But this is not the only type of data New Horizons collects.
All this means that during the active collection of information, the station fills up the disks, which then cannot release - it does not have time to send information to Earth. How to transfer all the data? Need to increase the speed.
70-meter plate in Canberra, Australia.
The New Horizons communications system includes two almost identical TWTA radio amplifiers in case one of them fails. The difference between them - versatile circular polarization. Thanks to this, TWTA can transmit the same data synchronously, and special equipment on NASA’s remote space communications network will receive and combine them. This will amplify the signal by 1.9 times compared to using one TWTA.
Researchers came up with this hack after launching the station and tried it at the beginning of the mission, but amplifiers need a lot of energy, and the radioisotope energy source New Horizons has degraded in almost ten years of use. Its capacity is not enough for the simultaneous operation of two amplifiers along with the provision of other station systems. Therefore, you need to turn off "something unnecessary." For example, navigation and control systems. The following question arises:
To keep the antenna station-oriented to the Earth, you need energy for a positioning system. But scientists have figured out how to get around this limitation. Before starting a long communication session using two transmitters, the station twists around its axis. The gyroscopic effect stabilizes its direction. For the promotion of the station you need to spend fuel - hydrazine. Although at the same time take pictures with LORRI will not.
To make room for data, the team plans to hold two long-term communication sessions. The first - from March 10 to April 4, the second - from 15 to 27 May. At this time, the station will not take photos, but some other systems - SWAP, PEPSSI, SDC - will continue to work.
This trick can only be used if both transmitters are in service. In any case, it will take more than a year before all the data arrive on Earth: there are too many of them. Soon the energy is not enough for simultaneous operation of TWTA. By the time the Kuiper belt is examined, only one transmitter will probably work, so the New Horizons will be a lesson for everyone.
But the station team has a trump card up its sleeve - a trick that allows you to increase the transmission speed almost twice.
How does the station transmit data now?
New Horizons uses an antenna and one radio amplifier to transmit data to Earth. The speed is 1 kilobits per second. Three 70-meter plates from NASA's Far-Space Network are capable of receiving data from such a distance, and you have to fight for work with them - at best, the team will receive one eight-hour communication session per day. During this time, you can send 28.8 megabits of data. While the New Horizons station is directed to Earth, it does not look at Pluto, so it has to choose between transmission and data collection.
')
The LORRI camera sensor, which the station uses, is a square with a side of 1024 pixels of 12 bits each, we get a file of 12,582,912 bits in size. The image can be shrunk to 2.5 megabits without loss, especially when its part is occupied by the blackness of space. You can shrink more in JPEG, but for optical navigation you need more accuracy. In 8 hours we will receive 11 images if we transmit only them. But this is not the only type of data New Horizons collects.
All this means that during the active collection of information, the station fills up the disks, which then cannot release - it does not have time to send information to Earth. How to transfer all the data? Need to increase the speed.
70-meter plate in Canberra, Australia.
How to increase the speed?
The New Horizons communications system includes two almost identical TWTA radio amplifiers in case one of them fails. The difference between them - versatile circular polarization. Thanks to this, TWTA can transmit the same data synchronously, and special equipment on NASA’s remote space communications network will receive and combine them. This will amplify the signal by 1.9 times compared to using one TWTA.
Researchers came up with this hack after launching the station and tried it at the beginning of the mission, but amplifiers need a lot of energy, and the radioisotope energy source New Horizons has degraded in almost ten years of use. Its capacity is not enough for the simultaneous operation of two amplifiers along with the provision of other station systems. Therefore, you need to turn off "something unnecessary." For example, navigation and control systems. The following question arises:
How to keep the station directed to Earth?
To keep the antenna station-oriented to the Earth, you need energy for a positioning system. But scientists have figured out how to get around this limitation. Before starting a long communication session using two transmitters, the station twists around its axis. The gyroscopic effect stabilizes its direction. For the promotion of the station you need to spend fuel - hydrazine. Although at the same time take pictures with LORRI will not.
To make room for data, the team plans to hold two long-term communication sessions. The first - from March 10 to April 4, the second - from 15 to 27 May. At this time, the station will not take photos, but some other systems - SWAP, PEPSSI, SDC - will continue to work.
This trick can only be used if both transmitters are in service. In any case, it will take more than a year before all the data arrive on Earth: there are too many of them. Soon the energy is not enough for simultaneous operation of TWTA. By the time the Kuiper belt is examined, only one transmitter will probably work, so the New Horizons will be a lesson for everyone.
Source: https://habr.com/ru/post/376119/
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