NASA GSFC/CIL/Adriana Manrique Gutierrez
The James Webb Space Telescope (JWST), which costs $10 billion and will be launched at the end of 2021, must have the most advanced storage? Somewhat surprisingly, according to IEEE Spectrum, there’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. First, the JWST is located about 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 about 28.6GB of data each day, so the upper limit of one day is about 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 after 10 years of service life, a 68GB SSD will have about 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 after 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…
