Shutterstock / Andrey Armyagov ” src=”https://s.yimg.com/ny/api/res/1.2/N3RpzFZoAlTPZwrp0lBVQQ–/YXBwaWQ9aGlnaGxhbmRlcjt3PTk2MDtoPTYzMi42NjY2NjY2NjY2NjY2/https://s.yimg.com/uu/api/res/1.2/2.nEotBL68NyvsV2UHpcbQ–~B/aD05NDk7dz0xNDQwO2FwcGlkPXl0YWNoeW9u/https://media.zenfs.com/es/the_conversation_espa_a/422feb0f02bb24918b1544aeb9490834″ data-src=”https://s.yimg.com/ny/api/res/1.2/N3RpzFZoAlTPZwrp0lBVQQ–/YXBwaWQ9aGlnaGxhbmRlcjt3PTk2MDtoPTYzMi42NjY2NjY2NjY2NjY2/https://s.yimg.com/uu/api/res/1.2/2.nEotBL68NyvsV2UHpcbQ–~B/aD05NDk7dz0xNDQwO2FwcGlkPXl0YWNoeW9u/https://media.zenfs.com/es/the_conversation_espa_a/422feb0f02bb24918b1544aeb9490834″/>
Humans are capable of feats that were once typical of science fiction, such as speaking through a screen or stepping on the moon, but we still cannot accurately anticipate natural disasters. Thanks to continuous technological development, the news will be able to give news like this in a few years:
“The satellite images helped the emergency services to predict the development of the floods so that the citizens were evacuated safely before the rise of the water. Meteorologists were able to predict the path of the storm that caused the damage, and were able to see in time the first signs of the landslide that buried a residential area after the evacuation.
To achieve this, the satellite must monitor our planet from space in near real time. This is possible thanks to the same orbit that was used, in 1964, to broadcast the Tokyo Olympics from Japan to the US The first major sporting event transmitted via satellite: the Syncom 3.
How does satellite television work?
The television signal is not strong enough to reach the whole world; therefore, we transmit it using repeaters. A repeater receives a weak signal, amplifies it, and delivers it with more power to us. Finally, at home we put an antenna pointing towards the repeater so that it receives the signal and takes it by cable to the TV.
We can imagine the television signal as a beam of light. Since it does not pass through walls or mountains, the transmitting and receiving antenna must see each other. For this reason, the repeaters are very tall structures located in high places and the antennas at home are placed on a roof or terrace that does not have obstacles in front. Still, rugged and mountainous areas can have trouble receiving the signal.
The higher the repeater, the more places the television will reach. Where will we put the highest repeater in the world? Of course, in space.
But how are we going to put a repeater in space? Won’t it fall off? If we leave it still, yes, it will fall and smash on the ground. How is it possible? If there is no gravity in space, right? Why do astronauts float then?
The reality is very different from the popular belief of zero gravity. If we drop a ball from space (white path in the image that follows this paragraph), it will do so vertically, in free fall. If we give it a little horizontal speed (blue trajectory), it will go into free fall again, but it will land at a different point on the planet. If we launch it faster (green trajectory) it will go further. And if we throw it fast enough, it will never hit the ground because the ball will go into orbit.
Free fall of a ball on the Earth.
Imagine going in an elevator and the cable breaks: during the fall, your body will float through the air as if there were no gravity. It will enter a state known as microgravity. For this reason, astronauts do not float because there is no gravity in space, but because they are in orbit and an orbit is an eternal free fall.
So if the repeater is circling Earth, will we only watch TV when it passes overhead? The rest of the time we won’t see anything? We have the solution: the geostationary orbit.
The geostationary orbit
The force of Earth’s gravity decreases as we move further away. The further we are from the center of the Earth, the less speed we will need to stay in orbit. Therefore, the longer it will take to complete a trip around the planet. For example, astronauts living on the International Space Station at an altitude of 400 km go around the Earth every 90 minutes or so. Come sunrise 16 times a day!
If we go up to 35,786 km of altitude, we will go around the planet every 23 hours, 56 minutes and 4 seconds. This is a sidereal day: the exact time it takes for the Earth to turn around itself.
Since the satellite rotates at the same speed as the Earth, it will appear to us that it is practically still; drawing a small ellipse as if it had been pinned in the sky. Thus, the repeater will be able to illuminate large areas of the planet continuously and we will be able to watch satellite television without interruptions.
Radar satellite in geostationary orbit. Jorge Nicolás-Álvarez ” src=”https://s.yimg.com/ny/api/res/1.2/y63ptzY7YeViI8Q3BGv4Vw–/YXBwaWQ9aGlnaGxhbmRlcjt3PTk2MDtoPTkwNA–/https://s.yimg.com/uu/api/res/1.2/Wl0Xx6z.tGBawIX80WM0tg–~B/aD0xMzU2O3c9MTQ0MDthcHBpZD15dGFjaHlvbg–/https://media.zenfs.com/es/the_conversation_espa_a/35f0ae0e933ecbc97819f284478639de” class=”caas-img”/>
Radar satellite in geostationary orbit. Jorge Nicolas-Alvarez
Geostationary orbit can do much more than just watch TV. Radar satellites send a signal from space that bounces off the Earth and generates an echo. These echoes are processed by radar to obtain images of the planet with resolutions of tens of meters that can be used to detect small movements and thus predict natural disasters from space.
The problem is that, to date, all radar satellites orbit at low altitudes. This means that if they pass over us today they will not do it again for ten or fifteen days. Enough time for a catastrophe to occur without the satellite knowing.
The solution is to operate them from geostationary orbit, but the difficulty of this is equivalent to taking a photo from 35 786 km with the camera moving and hoping it is not blurry. The precise determination of the trajectory of the geostationary satellites will allow to know this movement to focus the images. Thus, they will be able to monitor large areas of the planet to predict natural disasters and evacuate the population in time.
This is how the same technology that keeps us staring on a screen will have its eyes on us to protect us at all times from the threats of our planet.
This article was originally published on The Conversation. Read the original.
Jorge Nicolás-Álvarez receives funds from the State Plan for Scientific and Technical Research and Innovation (MINECO), project codes TIN2014-55413-C2-1-P and TEC2017-85244-C2-2-P; and the María de Maeztu Excellence Unit (MDM-2016-0600) funded by the State Research Agency.
Antoni Broquetas Ibars receives funds from the State Plan for Scientific and Technical Research and Innovation (MINECO), project codes TIN2014-55413-C2-1-P and TEC2017-85244-C2-2-P; and the María de Maeztu Excellence Unit (MDM-2016-0600) funded by the State Research Agency.