Earlier this month, the Psyche spacecraft succeeded in sending a message to Earth via a laser beam at a distance of 16 million kilometers. The successful test is an important step towards fast Internet in space.
Psyche is onderweg naar een gelijknamige ruimterots tussen Mars en Jupiter. Daarvoor moet de ruimtesonde in de komende zes jaar 3,6 miljard kilometer afleggen. NASA gebruikt zijn lange reis ook om wat andere experimenten, waaronder communicatie via een laserstraal, uit te voeren.
Dat lukte op 14 november, liet ruimtevaartorganisatie NASA afgelopen weekend weten. De laserstraal met data legde een afstand van 16 miljoen kilometer af. Dat is ruim veertig keer de afstand tussen de aarde en de maan. Het laserlicht deed er vijftig seconden over om de aarde te bereiken.
“Zowel laserstralen als radiosignalen reizen met ongeveer de snelheid van het licht”, vertelt hoogleraar signaalbewerking en communicatie Jean-Paul Linnartz van de Technische Universiteit Eindhoven. Het is dus niet zo dat laserstralen vanuit een ruimtevaartuig sneller op aarde zijn dan een radiosignaal.
“Maar met een laserstraal kun je meer data in één keer versturen”, legt Linnartz uit. Je hebt daardoor als het ware een hogere downloadsnelheid dan wanneer je data via een radiosignaal ontvangt.
Fast internet in space
This development is particularly interesting for the upcoming manned Moon and Mars missions. The first manned space flight to the Moon in more than fifty years is scheduled to take place in November 2024. The first Mars mission with humans on board is scheduled to take place after 2033.
In addition to communicating via radio signals, future Moon and Mars missions also aim to communicate with Earth via laser beams. This makes it possible to send scientific information, high-resolution images and video broadcasts to Earth from space. Therefore it is also called “fast internet in space”.
The successful test is a real milestone according to NASA. “It supports the next big step for humanity: sending humans to Mars,” said NASA’s Trudy Curtis.
You have a higher “download speed” over a laser connection
The main advantage of lasers is that you can send more data at the same time, Lennarz says. This is because you can direct the laser beam better.
“A normal radio signal spreads more and more when it is transmitted over a large distance,” explains the professor. “So the signal becomes weaker, which means you can send less data.”
You can direct the laser beam better. But light from a laser beam also spreads over large distances. You can see this if, for example, you point a laser pointer at something. The further away this object is, the larger the area of the laser spot.
“But the signal propagates less than radio signals,” Lennarz says. “This allows you to send larger amounts of data at once.”
The laser beam must be precisely directed
But it’s definitely not easy. “The Earth is rotating and the spacecraft is moving through space at a great distance,” Lennartz explains. “In addition, it takes a certain amount of time for the laser beam to reach the Earth.”
All these factors must be taken into account, otherwise the laser beam will shoot through the ground. That is why, during the test, the so-called beacon signal was first sent from Earth to the Psyche spacecraft.
The spacecraft was able to direct its laser with the beacon signal to the point where the Earth will be in fifty seconds. According to NASA, a package containing the test data was then sent. The laser light containing the data was captured fifty seconds later by a special telescope in California.
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