1. In 2015 NASA launched the Magnetic MultiScale mission (MMS). One of the goals
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1. In 2015 NASA launched the Magnetic MultiScale mission (MMS). One of the goals of the spacecraft was to measure the magnetic field in the near-Earth space environment to within 0.25nT (nanotesla). To avoid the noisy magnetic environment of the spacecraft, the magnetometer (magnetic field sensor) was placed on a 5m boom. The boom was stowed initially and was designed to deploy after launch. Unfortunately after launch the boom only deployed 2.6m and became stuck. The mission engineers determined the magnetometer would measure a max signal of 0.1 0nT at 0.26m resulting from the unwanted spacecraft background. The magnetometer itself has a range of 1256nT and outputs a voltage (10V) that's passed to a preamplifier The preamplifier increases the signal by 10x, but it also introduces an uncertainty of 0.01%. After the preamplifier, the signal is passed to a 12 bit ADC. The FSI of the ADC can be assumed to be the max (in magnitude) output of the preamplifier. Prior to launch, the team found a precision uncertainty of 0.10nT for the system when calibrating in the lab. A. In June 2015, congress asked NASA if the MMS mission goals had been met. What should they say? B. In the first mission results from space, the team published a paper with the spacecraft measuring a magnetic field of 6.00nT. What voltage was the ADC outputting?Explanation / Answer
A. yes the goal is achieved.
after the boom is deployed the error in the signal is
0.1nT for a full range of 256nT
% error = 0.1*100/256 = 0.039 %
now the amplifies adds uncertianity of 0.01% at full scale.
GTotal uncertinity after pre-amplfier = 0.039% +0.01% = 0.049%
ADC do not add any further uncertainity in the measurment.
Uncertianity in measurment at full range = 256*0.049/100 = 0.125 nT , achieved
which is better than the goal of 0.25 nT
B) ADC 12 bit
10 V *10 = 12 bit = 0xfff corrosponds to 256 nT
100 V -> 256 nT
measument 6.0nT = (6/256)*100 = 2.34375 V
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