As promised, here is the next in my series on satellites that began with my previous post. Next, I’ll follow up with a post on satellite orbits.
There are four main types of satellites mentioned here: Earth Observation, Navigation, Communication and Universe Observation.
Earth Observation (EO)
The very first satellite sent into orbit was a simple radio transmitter, broadcasting a signal using four antennas. The Russians had intended to send a much more complicated instrument into space as its first satellite, but changed their plans to ensure they launched before the Americans. Sputnik 1 launched in 1957 and offered scientists an insight into the atmosphere. The drag of the satellite gave an idea of the density of the upper atmosphere and the journey of the radio signals back to the surface gave details of the ionosphere.
Since this first launch many hundreds of satellites have been used to study, learn and track changes on Earth and in our atmosphere. There is a very rich source of data now available above us and we are starting to see innovation in how we use the information from the EO satellites. This is known as a “downstream” application in the Space Industry and it is a very creative and technical field. By looking back down at the surface, we can get a broader view of how we live and by analysing the data provided by the satellites, we can perhaps improve the way we do things.
Disaster management is an area that is benefiting from satellite data. If an earthquake affects an area, then the images obtained from satellites can show where the response needs to be concentrated and can highlight blocked routes into the region that need to be dealt with to ensure supply of aid.
By monitoring the changing landscape of the Earth over time, we can see the change in the Polar ice caps and the level of de-forestation in areas such as South America. The level of detail available means that individual forests can be targeted and tracked allowing for improved management of our resources but we are also gathering huge amounts of information that could contribute to the understanding of climate change.
The Earth is constantly bombarded by radiation and one major source is the Sun. Satellites can be used to monitor the Sun’s weather and if there is a large sunspot and explosion of material towards the Earth we can also track the impact on the atmosphere. This tracking allows for protection of other satellites in orbit, as they can change position and attempt to shield themselves from the oncoming particles.
Weather monitoring and prediction has benefited from having access to a wealth of imaging and other data. The Met Office can run sophisticated computer models based on extensive real-time data. This doesn’t just impact on whether you need to take an umbrella out with you in the morning, but will affect shipping and aircraft routes and planning.
Navigation
How do you find your way around an unfamiliar place? You could ask for directions to your destination, but most likely you’ll take out your smartphone and use satellite navigation. To find your location your phone needs to know the time it takes for a signal to travel from a satellite to your phone. It then uses this to calculate the distance to the satellite. This is then repeated for a further 3 different satellites.
At the moment the satellites your phone connects to are free to use and are part of the Global Positioning System (GPS) owned by United States. From 2016 Europe will have its own network of satellites called Galileo. The current GPS system will give you a position accurate to 10 metres, whilst the Galileo system will eventually give up to 1 metre accuracy. Satellites for navigation have many different applications and implications.
Trains can be monitored using navigation satellites, meaning that the rail network can be managed efficiently with trains being re-routed or amendments to timetables made based on real-time incidents. The same can be applied to road traffic.
Commercial companies can monitor their fleet, whether they are road vehicles, trains, ships or planes. This makes managing logistics more cost-effective.
Personalised services are now being offered based on your location. Some smartphone apps allow you to have access to discounts based on your location, or your internet search results can be automatically tailored to where you are.
Navigation for cars, cycles and pedestrians is also available via smartphones or specialist devices. These use maps combined with GPS to give you route information. However, be careful! If your device can’t find four different satellites (for example if you’re in a built-up area) then it won’t be able to provide you with a route.
Communication
Arthur C. Clarke was one of the first to predict the use of satellites for the purpose of communication. Published in Wireless World in 1945, he specifically talked about the use of three geostationary satellites (satellites that orbit above the same point on the Earth) but it wasn’t until the early 1960s before this became reality. You can read the full text here.
Satellites are used to broadcast many different types of signals. They host streams to allow us to talk by mobile phone, but they also broadcast high-quality video of sporting events and news as they happen. There are many different owners of communication satellites, some will be commercial and others will be owned by governments for the sole use of their armed forces.
One key future use of satellites for communication will be bringing a high-speed internet connection to remote locations. As an example we can look at UK-based company Avanti. They are using their satellites to offer 100% coverage for broadband in a set geographical area. In the UK only 73% of households have access to broadband, whilst in the Netherlands this is 100%. There is a lot of existing infrastructure in the UK so the broadband coming into your house is most likely to be via a cable network rather than through a satellite signal. However, if you go to remote locations in Africa, the same infrastructure isn’t there but through companies like Avanti communities still have access to the internet using a connection with a satellite.
Universe Observation
Gazing up at the sky is an activity we humans have occupied ourselves with for thousands of years. As we have learned more about the universe as technology developed, the more we wanted to see. One barrier to what we can see has turned out to be our own, protective atmosphere. As light passes through the atmosphere its path is affected and what we see on the ground is a smeared out version of the actual image. In the giant telescopes that are being built and used in places like Chile have sophisticated electronically controlled mirrors that compensate for this effect of our atmosphere. However, we can get around this by having our telescopes and instruments above the atmosphere.
The Hubble Space Telescope is in orbit around the Earth and allows us to see wonderful detail of our universe. Since launching in 1990, it has allowed us to see stars forming in nebulas and the earliest galaxies in its “Deep Field” image. We have also seen evidence for black holes and extra-solar planets. Being above the atmosphere means we can see that much more. It is still operational and will be joined in 2018 by the James Webb Space Telescope. This satellite will take images in visible wavelengths (from orange) through to mid-infrared, whilst Hubble’s pictures are in the visible, ultra-violet and near infrared areas of the electromagnetic spectrum. We will be able to continue the detective work of unravelling the history of the universe with this telescope.
In addition to telescopes that have multiple targets, we have specialist satellites that observe either one target or investigate one type of object. One example is the Kepler mission. This is searching for extra-solar planets by observing the light curve from stars. If there is a regular dip in the curve, this could be caused by a planet moving between the star and the satellite. Kepler is not an Earth satellite, but orbits around the Sun every 372 days and this maximises the observations.