James Webb Space Telescope
It costs $10 billion to build and will be launched by the end of 2021 James Webb Space Telescope (JWST), must have the most advanced storage, right?Somewhat unexpectedly, according to IEEE Spectrumthere’s only a 68GB SSD on the JWST, enough to store a day’s worth of photos, but not too much.
There are two main reasons behind this. The first is that the JWST is regarding 1.5 million kilometers from Earth and cannot be upgraded with subsequent maintenance missions like Hubble in low-Earth orbit. Therefore, JWST’s storage device was originally designed to withstand the ultra-low temperature of -223 degrees Celsius and to withstand the impact of cosmic rays in outer space. These requirements make it not as high-capacity production as a general household SSD, but a specially designed space-use SSD that has undergone a fairly rigorous certification process.
Another factor is limited communication. The 25.9GHz Ka band between JWST and the earth can theoretically reach a speed of 28Mbps, but there are only two 4-hour windows per day to communicate with the earth. These two windows can transmit regarding 28.6GB of data each day, so the upper limit of one day is regarding 57GB, which has become the bottleneck for JWST to collect data, even if the data control system inside the telescope itself can reach 48Mbps is useless. But having said that, 57GB is still much larger than Hubble’s 1~2GB a day, even if Hubble is 400 kilometers above the ground.
Therefore, JWST is designed to estimate that following 10 years of service life, a 68GB SSD will have regarding 60GB of free space left, which includes the daily requirement of 57GB, and a little space to store engineering and telemetry information. What to do following more than 10 years is not in the design consideration. At that time, it may depend on the actual remaining space, the damage of the primary mirror of the telescope (the primary mirror in outer space will often be hit by micrometeorites), the remaining fuel to maintain the orbit, and The overall health of the telescope, and how long the mission can be extended.
However, even if 68GB is the minimum requirement to get the job done, and it’s not an ordinary SSD, it shouldn’t be a bad idea to bring an extra spare, right? In addition to providing backup in case of SSD failure, if the communication technology can be improved in the future, maybe more data can be collected and sent back one day. 10 billion has been spent, it should not be less than this cost…
