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«Korolev’s Planet» keeps publishing cosmonauts reports from the International Space Station.

The sixth story is Roman Romanenko’s talk about the technology of Earth remote sensing from onboard the International Space Station.

Dear visitors to the Korolev’s Planet web site, greetings from Roman Romanenko onboard the Russian Segment of the International Space Station.

Earth remote sensing is one of the important experiments or studies that we are conducting here onboard the Russian Segment of the International Space Station. Why is it so important? Because the basis of our space studies is the study of Earth, its surface, as well as water expanses of our planet. What is Earth remote sensing, and how do we perform it here onboard?

For this purpose we have at our disposal a series of windows in the Service Module of the Russian Segment, which allow us to do this. As well as some software programs – applications which are at our disposal on our onboard computers.

Some historical background. Earth remote sensing, or, to put it in simple terms, taking pictures of the Earth surface began as early as the first missions into space. As far as I can remember, Titov, who was the second cosmonaut after Yuri Gagarin, took the first pictures (it was back in August of 1961) of the Earth surface during his one-day mission. From that moment on, cosmonauts have been doing it every day. The only difference is that the hardware has been getting improved, the software’s been getting improved, the amount of data downlinked to Earth from the International Space Station has been expanding.

I believe that a very serious kind of hardware for its time was employed by the cosmonauts who flew onboard our space station, back then it was still Soviet space station called Mir, the orbital space station Mir. And that hardware, pretty serious piece of hardware, was considered the best. It was located in the Priroda module. What we have now, I’m going to tell you about it and show it. So. In order to consider this question and delve into the subject of Earth remote sensing, we need to have a look at what we have here. First of all, we have a very good large-diameter window. There is only one such very special window here. Its specialty consists in the fact that it’s the largest window on the Russian Segment, and, secondly, it is transparent to ultraviolet. This could be dangerous. And that’s why it has covers on both sides. The first cover is the internal one, and it provides the window with protection against mechanical damage from the inside, and the second cover is outside. It protects the window against damage from micro-particles and various objects flying around in the outside atmosphere of our station.

At present moment the covers are open and you can see through the Earth surface moving past the window. Right now beneath us is the ocean, and, as our program Sigma tells us, we are now approaching South America. In a couple of minutes we will reach the coast of South America. That’s what the ocean looks like from the altitude of 420 km. Since we started talking about where we are flying and how we are flying, I would like to say: very important conditions for taking pictures of earth surfaces, features, oceans and Earth in general are the altitude, the attitude in space, the attitude of our station with respect to the Earth surface, as well as orbital inclination. So. As I already mentioned, we fly at the altitude of about 400 km. The orbital inclination, that is, the angle between the equator and the plane of our orbit is about 51 degrees. If I had held the station in my hand, it would have looked like this. We fly from here. Here we have the upper point of our orbit, and here is the lower point. That is, it would have looked like this: The Earth is rotating in this direction, we, accordingly, fly like this. And then we go down. And that goes on and on. 16 times per day we reach the northern latitude of 52 degrees and then descend to our lowest point of 52 degrees of southern latitude.

Attitude. What is required in order to be able to see Earth through these windows at all times? For this we need special attitude called orbital attitude. The orbital attitude is the attitude where the station axis, the center of mass of the station connects with the Earth center of mass along a radius vector. This is the Y-axis. The X-axis lies in the orbital plane pointing toward the velocity vector and is perpendicular to the Y-axis, and Z-axis completes the right-hand coordinate system. This coordinate system enables us to continuously view the underlying terrain through our windows on the Russian Segment. That’s very convenient. Sometimes this coordinate system is changed in order to perform some maneuver, or during docking or undocking of transportation spacecraft. But mostly, 90% of the time, the station maintains this attitude. And this helps us to conduct Earth remote sensing. And so, I’ve just told you about the window. Yes, this window, our largest and most interesting window with covers is also used for serious experiments to study the surface of the oceans, sunlight reflections, natural resources, as well as the Earth surface – various natural disasters, hurricanes, etc., and, generally speaking, all kinds of events happening on Earth.

Here we place special equipment: The frame, the bracket, install the camera with other hardware, which can take pictures not only in the optical spectrum, but in the entire spectral range, that is including visual spectrum and all the other spectral ranges, we can take pictures in all of these spectral ranges. In principle, we could close it so as not to damage it eventually. A little later I’ll close it – I’ll send a command to control laptop, and the cover below will automatically close the window to protect it against the damage from other objects or meteoroids.

We have at our disposal some other windows, which we use on a continuous basis. In order to use the windows, their covers must be opened. We only use them for certain experiments. These five windows we use just for day-to-day imaging of various features which the Earth prescribes up photograph in the course of our workday, and on days-off as well.

In their everyday life, cosmonauts, just like ordinary people, do not like to use demountable cameras or some brackets – this means that the hardware needs to be assembled and disassembled. That’s why it is very important, if you see some uncovered feature, without any cloud cover, you must take its picture immediately. Otherwise, we’ll fly past this feature at 8 meters per second. That’s it, we are not going to see it anymore, it will be covered with clouds. That’s why we have this piece of equipment called the ultrasonic platform. It lets us to take pictures using these two frames: the receiving frame with 6 sensors installed on this small window and the transmitting frame which transmits the ultrasonic signal to that frame. By means of these centers this signal is sent to a special control unit, where the coordinates of the position of my lens in this window are recorded and then sent by wire to the laptop. Running on that laptop is a program which tracks the position of the lens in that frame and recalculates the position of the lens in that frame from its own coordinates of that frame, that is, that platform, into the Earth coordinates. Obtained at the output as the result are conventional Earth coordinates, which are then fed into a high-data rate link downlinking data to Earth, to РСПИ. And that's it. All that’s left to do now is to take picture – point and shoot, and coordinates go to the program, and the program sends the coordinates to Earth. And after that I also downlink to Earth the picture using our communications equipment. And the Earth already has a complete knowledge of what I took the picture of with a fairly high degree of accuracy. This is a new piece of equipment. We are now using it in two experiments – the main experiments which we use to tune up this system. As yet, there have been no glitches, the system operates with precision and helps the Earth to determine the location. The two experiments are the Seiner experiment and the Visir experiment.

As I already said, the information is sent to Earth. But why is it so convenient for us? Because we don’t have to use various brackets and devices which help us track something. We can take pictures holding cameras simply with our hand. This is especially convenient, when we are flying and do not know where we are in relation to Earth and we cannot transmit our coordinates to the ground. On the ground, the specialists wouldn’t be able to figure out what it is that we took the picture of. For example, we are flying over an ocean. For example, we saw some ship. We took pictures of it. And using this system, the ground already knows the coordinates of the place where the ship is located. And everything becomes very simple. Also at night. During nighttime photography it allows us to transmit to the ground the exact coordinates of what we have just photographed at a specific moment in time. Well, if the Earth is hidden behind solid cloud cover, it’s also very interesting to have the data from the system in order to know what our camera photographs at the moment.

I’ve just told you about the way we use a conventional window together with an absolutely new system, which makes it possible to transmit not only photographs, but also the coordinates of the underlying surface, which we have just photographed. And yes, there is one more interesting thing. You can have a look. Displayed on this laptop is the position of the camera, of the lens axis. I’m now going to switch on the camera and show you. Here I’m turning the camera around, and here are the distances between sensors, which are then recalculated into angles. These angles are converted to normal coordinates which are received on the ground. Here I turn around the camera lens without thinking about what I’m taking pictures of, how do I take them and where do I take them. After some little time the Earth will already know where did I point at and what did I take pictures of.

And now let me tell you what nice software application we have onboard. So, we have onboard trajectory and navigation software Sigma. We use it on continuous basis – day, night, on workdays and on days-off. It always helps us to understand where we are currently located. Let’s say we are flying and see that there is an ocean. An ocean always looks like any other ocean. But if we look here, we can see that we are currently flying from South America towards Africa, towards the southern part of Africa. We can see a red dot. The red dot represents us, that’s our vehicle and we are moving. The white line is our orbit in which we are flying. In addition to this, we can also see the position of the Sun, a reflection of the Sun. We can see the position of the Moon and a reflection of the Moon. We can see - owing to the fact that our position is predicted 2 weeks in advance, we can fast-forward and see where we will be in 24 hours or in 2.5 hours. We can fast-forward or set some specific time and see where we will be and what we will be flying over at that moment. What else do we have? We have, as you can hear, a built-in voice assistant, which also tells us what we are flying into: whether we are flying into the Earth shadow or into the daylight, whether we have a communications session or not. We also know about the light and shadow conditions, we have all the communications zones plotted on the map as well as a number of lists of features which are provided to us from Earth, that is, those features we must work with during our mission – that is, take the pictures of the underlying surface. These are specific features, which the Earth proposed to us that we work on. This list can be called up and throughout all our activities this list will be displayed over our orbit – how much time is left till we reach that feature, from what side do we see it and through what window it will be easier to see it, what will be the Sun elevation above that feature. And also, based on statistical data, it says whether to expect clouds over that location at that particular time of year. In addition to the list uplinked from Earth and input into this program, we can ourselves select any feature on the ground we like. For example, I can now click on the lowest point of Africa. And we can see on display – «yes, the point will appear at 16.17.49». We’ll pass over it at 16.17.57 and leave the observation zone at 16.19.00. It takes into account the diameter of our window and tells us that I’ll be able to observe it at such and such time. And it also tells us that the reliability of imaging is 82% and average cloud cover is 6 points. In principle, this feature will be covered. Nevertheless, it’s better if we try and see, and take a picture if it is at all possible, that would be nice. How is this acheived? I already said that the program itself, having trajectory and navigation support, makes a two-weeks prediction. We also have the capability to go back several days in the archive, and look up where we were at such and such time, if we are studying some old photo and forgot when we took it. We can ‘rewind’, go back in time and see where we took this or that picture. It’s very convenient. Cosmonauts like it. Not only Russian cosmonauts, but also all our partners like it.

In order for the program to operate without glitches, and give us our exact position at all times, the ground, via our network, automatically continuously inputs into it updates uplinked from Earth, new trajectory data and settings. And we have a very exact map of our position above Earth surface.

Well, in principle, that’s all I wanted to tell you about today. I’ve told you about hardware, software, windows, and showed you the cameras which we use in order to perform Earth remote sensing, that is, the imaging of the underlying surface and various features on Earth. I hope that this is not our last session with you, so see you later. In the next communications session I’ll tell you some other things about life onboard the International Space Station. Good bye! 

Рассказ Романа Романенко
Рассказ Романа Романенко

 

 

 

 

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