History of telescopesand Earth Observation
Humans have always been curious about the world; there was a desire to learn. Starting with observing the world around them from ground level, then from balloons and airplanes, and finally from orbit. In this article, we will briefly delve into the history of telescopes and then move on to the famous or breakthrough telescopes that observe our world from orbit.
Origins of aerial photography
The first ever aerial photograph was taken by Gaspard-Félix Tournachon in 1858 from a balloon. He photographed the town of Bievre in France using the wet plate collodion process photography.
Thirty years later, in 1888, Arthur Batut using a camera hooked up to a kite, took aerial photos of the town of Labruguiere. Interestingly, the photos were taken only after the kite had reached a certain assumed altitude; an altimeter was attached to the system.
The next milestone can be defined as aerial photos taken from the aircraft. One of the pioneers of aviation, Wilbur Wright, piloted a plane equipped with a camera in 1909.
War always accelerates the development of technology. During the First and Second World Wars, there was a strong technological development; both sides in the war took a lot of aerial photos for reconnaissance purposes.
The first photo from space was taken on October 24, 1946, from a V-2 rocket that was originally developed by the Third Reich armaments industry, but after the war ended, it was transferred with scientists (including Wernher Von Braun, who later became one of the fathers of the Apollo program) to the United States, which used it (in upgraded versions) as a research platform. The launches took place from a training ground located in the White Sands desert of New Mexico. The picture below was taken using a DeVry 35 mm black-and-white movie camera that was set to take photos every 1.5 seconds.
The first images taken by the satellite from orbit were taken on August 14, 1959, by the U.S. Explorer 6 using a spot scanner television system. The main purpose of this satellite, however, was to study radiation, magnetism, radio wave propagation in the atmosphere, and micrometeorites.
Telescopes in space
Mentioned at the end of the previous chapter, the images taken from the V-2 rocket or the Explorer 6 satellite were certainly important, but nevertheless, it cannot be said that the platforms from which they were taken allowed a continuous influx of images and scientific data. In this section, we will look at telescopes that were intentionally sent into space to continuously collect data. Today, let’s talk only about the telescopes that make Earth observations possible.
The first satellite from the US Landsat program was launched in July 1972. To date, nine satellites have been launched, with the last one in 2021. Images taken from orbit as part of this program are used to analyze changes and observe the current state in many fields, such as agriculture, cartography, geology, and the like.
Imaging of the Earth is currently done with two Landsats – 8 and 9, from the Sun Synchronous Orbit (read more about it here), and the sensors collect data in multiple spectra: panchromatic, multispectral and thermal.
These are large satellites, weighing nearly 3 tons (~6,000 pounds) at launch. The dimensions of the latest satellite are 4.5 m x 3 m x 3 m (15.1 ft x 9.8 ft x 9.8 ft).
The European counterpart to the U.S. Landsat project is the European Copernicus program, which aims to globally and continuously collect data from orbit. As part of this program, a series of Sentinel satellites have been developed. The first of these reached orbit in April 2014. The premise of the program is to revisit the same locations frequently in order to have the ability to take comparative images that could show changes in a dynamic way.
The program allows the collection of data to analyze weather, agriculture, natural disasters, and also data on the oceans.
Of course, there are also many other satellites and constellations for Earth observation, but it is impossible to list them all. More and more countries want to have their own constellations; Poland, for example, is planning the PIAST constellation. Nevertheless, leaving aside government projects, over the past few years a number of commercial companies have emerged to create their own constellations of satellites dedicated to Earth observation. For example, one of them is the company MAXAR, which operates a constellation of four satellites, providing coverage of almost 4 million square kilometers per day.
How does it look today?
Over the past two decades, the cost of sending a payload into orbit has declined incredibly. It used to cost $54,500 to lift a kilogram using the Space Shuttle, while the same kilogram sent today by Falcon 9 costs only $2,720. The emergence of a multitude of „new space” companies such as SpaceX, RocketLab and Firefly makes it possible for smaller companies that are not government agencies to send multiple satellites into orbit at favorable prices. Affordable costs and frequent launches allow smaller companies, like Scanway, access to space.
Currently, the highest resolution that is commercially available is provided by the Finnish company ICEYE. Their satellites are capable of imaging terrain using synthetic-aperture radar (SAR) with a resolution of 25 cm.