Friends, on Cosmonautics Day, our little server successfully flew into the stratosphere! During the flight, the server on board the stratospheric balloon distributed the Internet, filmed and transmitted video and telemetry data to the ground. And we can't wait to tell you how it all went and what were the surprises (well, how without them?).
A little background and useful links, for those who missed everything:
- Post about into the stratosphere (which we encountered in practice during launch).
- How did we do"Β» of the project - for lovers of geek porn, with details and code.
- a project where it was possible to monitor the movement of the probe and telemetry in real time.
- space communication systems that we used in the project.
- Text launch the server into the stratosphere.
Since we really wanted to launch on Cosmonautics Day and received official permission to use the airspace on that very day, we had to adjust to the weather. And so that the wind did not take the stratospheric balloon beyond the boundaries of the permitted zone, we had to limit the height of the ascent - instead of 30 km, we climbed by 22,7. But this is already the stratosphere, and about twice as high as passenger planes fly today.
The Internet connection with the stratospheric balloon was quite stable throughout the flight. Your messages were received and displayed, and we filled in the pauses with quotes from Gagarin's negotiations with the Earth 58 years ago π
According to telemetry, it was -60 0Π‘ outside, and inside the hermetic box it reached -22 0Π‘, but everything worked stably.
Graph of temperature changes inside (here and further on the X scale are tens of minutes):
Another experimental digital high-speed transmitter was installed on board. This is our attempt to make high-speed Wi-Fi, and we are not yet ready to reveal the details of its design. With this transmitter, we wanted to broadcast video online. And indeed, despite the cloudiness, the video signal from the GoPro on board the stratospheric balloon was received by us at a distance of up to 30 km. But having received the video in our MCC, it was not possible to transfer it to the Internet over the ground ... Now we will tell you why.
We will soon show the video recordings of the flight from the onboard cameras, but for now you can watch the online recording from the probe
The main surprise awaited us: the very poor performance of the 4G modem in our MCC, which made it impossible to transmit video online. Although the probe successfully received and transmitted messages via the Internet, they were received by the server - we received service confirmations from it and saw them displayed on the screen via video broadcast. We had concerns about communication with satellites and signal transmission to Earth, but no one expected such an ambush that mobile 4G Internet would be the weak link.
And not in some wilderness, but not far from Pereslavl-Zalessky, in an area that, according to the maps of MTS and MegaFon, is well covered by 4G. In our mobile MCC there was a heaped Kroks ap-205m1-4gx2h router, into which two SIM cards are inserted, and which had to summarize traffic over them so that we could fully broadcast video to the Internet. We even installed external panel antennas with 18 dB gain. But this piece of iron worked disgustingly. The Kroks support team was able to advise us only to upload the latest firmware, but this did not help, and the speed of two 4G SIM cards turned out to be much worse than the speed of one SIM card in a regular USB modem. So, if you can tell me which piece of iron next time is better to organize data transfer with the summation of 4G channels, write in the comments.
Our trajectory calculations turned out to be quite accurate, there were no surprises. We were lucky, the stratostat landed on soft peat soil 10 meters from the reservoir and 70 km from the launch site. GPS Distance Graph:
And this is how the vertical flight speed of the stratospheric balloon changed:
True, one of the two landing displays did not survive the landing (yes, there were two of them, like the GoPro cameras; duplication is a good way to increase reliability), the video shows how it went in stripes and turned off. But all other equipment survived the landing without problems.
Conclusions on the experiment and on the quality of the Internet connection.
The server operation scheme looked like this: on the landing page, you could send text messages to the server through the form. They were transmitted via the HTTP protocol through 2 independent satellite communication systems to a computer suspended under the stratospheric balloon, and he transmitted this data back to Earth, but not in the same way via a satellite, but via a radio channel. Thus, we understood that the server generally receives data, and that it can distribute the Internet from the stratosphere. On the same landing page, the stratospheric flight schedule was displayed, and the points of receipt of each of your messages were marked on it. That is, you could track the route and height of the βsky-high serverβ in real time.
In total, our participants sent 166 messages from the landing page, of which 125 (75%) were successfully delivered to the server. The range of delays between sending and receiving turned out to be very large, from 0 to 59 seconds (average delay 32 seconds).
We did not find any noticeable correlation between height and delay level:
This graph shows that the delay level did not depend in any way on the distance from the launch site, that is, we honestly transmitted your messages via satellites, and not from the ground:
The main conclusion from our experiment is that we can receive and distribute the Internet signal from stratostats, and such a scheme has the right to exist.
As you remember, we promised to compare Iridium and GlobalStar communications (we never received the Gonets modem on time). The stability of their work in our latitudes turned out to be almost the same. Above the clouds, the reception is quite stable. It is unfortunate that representatives of the domestic system "Gonets" checked something there, prepared, but could not provide anything for testing.
Plans for the future
Now, we are planning the next project, even more complex. Now we are working on various ideas, for example, whether we can organize a high-speed laser communication between two stratospheric balloons in order to use them as repeaters. In the future, we want to increase the number of access points and ensure a stable Internet connection speed of up to 1 Mbps within a radius of 100-150 km, so that in the next launches there will be no more problems with transferring online video to the Internet.
Source: habr.com