The Indian public watched the rocket launches
On August 12, India's strongest reconnaissance satellite GISAT-1 failed to launch, and the cryogenic engine of the third stage of the carrier rocket failed to ignite, resulting in the satellite not being put into orbit and scrapped. Today, the class leader will give you a good introduction.
A resolution of 0.1 meters is enough, and no matter how high it is, it is not necessary for military satellites
Speaking of reconnaissance satellites, we all know that the Americans are the most powerful, and they launched the "KH-12" more than 30 years ago. The resolution of the pictures taken by satellites has reached the level of 0.1 meters, but such high-resolution satellites are basically working in low Earth orbit, the shooting range is small, and it is necessary to take pictures of specific areas, either satellite orbit change maneuvers, or wait for the earth to turn to its own lens, so people think, can you send a satellite to the geostationary orbit on the equator, because the object in this orbit is relatively geostationary, so that you can stare at a certain area for 24 hours without interruption? And because the orbit is as high as 36,000 kilometers, this satellite can be said to stand tall and wide, and China's Gaofen-4 was developed in this context.
The CG image of the Gaofen-4 satellite is essentially a space HIGH-definition camera
Gaofen No. 4 is China's first geostationary orbit optical observation satellite, it has an orbit altitude of 36,000 kilometers, with a maximum optical resolution of 50 meters, which of course can not be compared with the resolution of low-orbit satellites 0.1 or even a few centimeters, but this is also easy to understand: the same telescope, I see that things 100 meters away are definitely not the same as things 10 kilometers away. For example, if you want to shoot the entire 10 million square kilometers of the western Pacific Ocean, it only needs to take 60 photos, 4-12 minutes to complete the photo and transmission, 50 meters of resolution can roughly display the aircraft carrier such as a large sea target, and then by other low-orbit reconnaissance satellites to focus on reconnaissance, so as to achieve the purpose of determining the position of the aircraft carrier. In layman's terms, High Score IV is strategic, while low-orbit reconnaissance satellites are tactical.
Gaofen No. 4 accompanies satellite images, and the resolution is not enough
Of course, the resolution of 50 meters is still too low, and the 100,000-ton aircraft carrier is only 6-7 pixel blurry dots on its photos, so can the imaging effect of the same resolution on the 36,000 km orbit be achieved with the same resolution as on the hundreds of kilometers of orbit? The answer is yes, and the method is extremely "simple", just make the telescope lens larger. But the reason is understood, it is difficult to do it (in fact, this is the ascension), in order to achieve a resolution of 2.5 meters in the geostationary orbit, then the diameter of the lens needs to reach more than 4 meters, what is this concept, Hubble telescope lenses are only 4.03 meters.
India's GISAT-1 satellite, the lens caliber is smaller than Gaofen IV, and the weight is only half of Gaofen IV
Back to the Indian launch of the failed GISAT-1 satellite, its lens diameter of 700 mm, ground optical imaging resolution and Gaofen IV is the same as 50 meters, originally planned to launch in 2017, which and the launch of Gaofen IV at the end of 2015 is almost on the same starting line, it can be said that if India can really achieve the launch in 2017, they can catch up with China's footsteps, in the field of space strategic optical reconnaissance and China's equality, unfortunately, like other key projects in India, the traditional procrastination has been committed again. First in 2017 said that the satellite had technical problems to postpone the launch, this push is 3 years, planned to launch in 2020, coincidentally and caught up with the epidemic and could not be postponed to 2021, waiting for 4 years the result was rocket crater, and at this time, Gaofen IV has entered the late life (design life of 8 years).
China's 4.03-meter monomer silicon carbide mirror, if it can be successfully launched, it will not be a problem to find an aircraft carrier in the future
It is reasonable to say that the gap between India and China in this field should be 6 years from 2015, but in these 6 years, China has not been idle, and its progress has been faster, with a diameter of 4 meters. Ground resolution 2.5 meters of super lens, has been developed, is installed on the satellite platform experimental debugging, India to catch up with China is more difficult, from 700 mm to 4 meters, which is not three years and five years can be done, and first of all there must be a launch vehicle that can launch a satellite with a diameter of more than 4 meters (China only long march 5 is in line, India is not so thick rocket), so conservatively speaking, India alone in the satellite this piece of gap with China is about 10 years, plus the rocket gap, the overall 15-20 years or so, this is still based on normal conditions, if India commits procrastination again, it is another story.
Long March 5 rocket
India also has a backup satellite GISAT-2, which should continue to be launched in the short term, and if it fails again, it will be a disaster for India's geostationary orbit optical reconnaissance field, and it will be more difficult for those who want to catch up with China.