Resiliency of Electronics
Prior to this proposal, no cubesats have left Earth orbit, let alone being sent to Jupiter [1], [2]. A cubesat on Earth can still remain operational after 9 years [3], [4]. However Jupiter’s conditions are so harsh that throughout the 6 year or 33 orbits around Jupiter, the Galileo spacecraft received 4 times the maximum design limit of radiation [5]. Fieseler [5] stated that most spacecraft have the upper limit of 150 kRads.
According the graph that Fieseler [5] provided, the Galileo spacecraft received a culumative 150 kRads at only 2 years of the 6 years that it was orbiting Jupiter. Even NASA could not fully predict the effects that Jupiter had on the Galileo mission, which had various malfunctions [5]. However, since the Galileo was planned to have only 11 orbits of observations instead of the 33 actually done, satellites can still work even if some individual parts do not [5].
The mission time will be 2 years, because that is when Galileo spacecraft reached the typical upper limit of a satellite radiation tolerance [5]. During the project, individual cubesats will fail, although not all at once. Since there are 12 cubesats, one or two failures are minimized damage to the system.
Since cubesats are cheaper and less protected than the Galileo spacecraft, so they have to be fortified with additional materials to last long as possible [1], [2]. The fully completed spacecraft and all the cubesats will be sent to the Jet Propulsion Laboratory to be tested if it is space-hardened enough to travel to Jupiter [6], [7]. The probability curve of failure that is used is the Bathtub curve [7]. According to the Bathtub curve, the Shake-and-Bake tests will detect many failures at the beginning of the lifetime [7].
The likely points of failure are the Mother Ship, the individual cubesats. Since the Mother Ship is based on Juno, but with less equipment, the Mother ship will not be as likely to fail as the Juno mission. The cubesats will have redundancy to increase reliability [7]. By having twice the number of essential operations components, if one fails the other can take over.
Prob(a single failure) = q <= 1.
Prob(both fail) = q^2<= q.
The more cubesats there are, the more likely at least 1 cubesat will fail. However, just as the probably of at 1 failure increases, the chances that all cubesats failing decreases. Thus, it is not very likely that all 12 cubesats will fail.
Pr(chance of a least one failure) = 1- P(chance of no failure) = 1 – (1-q)^number of parallel unit
Pr(chance of all fail) = q^number of units that rely on each other <= q
The radioisotope generators are known for lasting for years and even decades, and almost never fail [8]. Because of the reliability of the radioisotope generators, the practical value of failure is zero. The radioisotope generators are the only devices that do not need a redundant part to increase reliability [7].
References:
[1] M. Wall. (2013, July 10). New Space Engine & 'CubeSats' Could Help Cut Cost Of Planetary Exploration, Scientists Say [Online]. Available: http://www.huffingtonpost.com/2013/07/10/cubesat-space-engine-interplanetary-flight-cost_n_3561531.html
[2] V. Kane. (2013, Oct. 24). The Potential of CubeSats. [Online]. Available: http://www.planetary.org/blogs/guest-blogs/van-kane/20131023-the-potential-of-cubesats.html
[3] Satview. (2014). CUBESAT XI-V (CO-58) [Online]. Available: http://www.satview.org/?sat_id=28895U
[4] Clyde Space. (2014). Some useful information about CubeSats [Online]. Available: http://www.clyde-space.com/cubesat/som_useful_info_about_cubesats
[5] P. D. Fieseler et al. (2014) The Radiation Effects on Galileo Spacecraft Systems at Jupiter [Online Report]. Available: trs-new.jpl.nasa.gov/dspace/bitstream/2014/11661/1/02-0220.pdf
[6] M. B. Murrill. (1996, Oct. 15). CASSINI SPACECRAFT READIED FOR "SHAKE AND BAKE" TESTS [Online]. Available: http://www.jpl.nasa.gov/news/releases/96/csshake.html
[7] T. Pratt et al., “Satellites,” in Satellite Communication, 2nd ed. Danvers, MA: John Wiley & Sons, Inc., 2003, ch.3, sec. 7, pp.87-89.
[8] NASA. (2014, Feb 4). RPS Technology [Online]. Available: https://solarsystem.nasa.gov/rps/types.cfm
Prior to this proposal, no cubesats have left Earth orbit, let alone being sent to Jupiter [1], [2]. A cubesat on Earth can still remain operational after 9 years [3], [4]. However Jupiter’s conditions are so harsh that throughout the 6 year or 33 orbits around Jupiter, the Galileo spacecraft received 4 times the maximum design limit of radiation [5]. Fieseler [5] stated that most spacecraft have the upper limit of 150 kRads.
According the graph that Fieseler [5] provided, the Galileo spacecraft received a culumative 150 kRads at only 2 years of the 6 years that it was orbiting Jupiter. Even NASA could not fully predict the effects that Jupiter had on the Galileo mission, which had various malfunctions [5]. However, since the Galileo was planned to have only 11 orbits of observations instead of the 33 actually done, satellites can still work even if some individual parts do not [5].
The mission time will be 2 years, because that is when Galileo spacecraft reached the typical upper limit of a satellite radiation tolerance [5]. During the project, individual cubesats will fail, although not all at once. Since there are 12 cubesats, one or two failures are minimized damage to the system.
Since cubesats are cheaper and less protected than the Galileo spacecraft, so they have to be fortified with additional materials to last long as possible [1], [2]. The fully completed spacecraft and all the cubesats will be sent to the Jet Propulsion Laboratory to be tested if it is space-hardened enough to travel to Jupiter [6], [7]. The probability curve of failure that is used is the Bathtub curve [7]. According to the Bathtub curve, the Shake-and-Bake tests will detect many failures at the beginning of the lifetime [7].
The likely points of failure are the Mother Ship, the individual cubesats. Since the Mother Ship is based on Juno, but with less equipment, the Mother ship will not be as likely to fail as the Juno mission. The cubesats will have redundancy to increase reliability [7]. By having twice the number of essential operations components, if one fails the other can take over.
Prob(a single failure) = q <= 1.
Prob(both fail) = q^2<= q.
The more cubesats there are, the more likely at least 1 cubesat will fail. However, just as the probably of at 1 failure increases, the chances that all cubesats failing decreases. Thus, it is not very likely that all 12 cubesats will fail.
Pr(chance of a least one failure) = 1- P(chance of no failure) = 1 – (1-q)^number of parallel unit
Pr(chance of all fail) = q^number of units that rely on each other <= q
The radioisotope generators are known for lasting for years and even decades, and almost never fail [8]. Because of the reliability of the radioisotope generators, the practical value of failure is zero. The radioisotope generators are the only devices that do not need a redundant part to increase reliability [7].
References:
[1] M. Wall. (2013, July 10). New Space Engine & 'CubeSats' Could Help Cut Cost Of Planetary Exploration, Scientists Say [Online]. Available: http://www.huffingtonpost.com/2013/07/10/cubesat-space-engine-interplanetary-flight-cost_n_3561531.html
[2] V. Kane. (2013, Oct. 24). The Potential of CubeSats. [Online]. Available: http://www.planetary.org/blogs/guest-blogs/van-kane/20131023-the-potential-of-cubesats.html
[3] Satview. (2014). CUBESAT XI-V (CO-58) [Online]. Available: http://www.satview.org/?sat_id=28895U
[4] Clyde Space. (2014). Some useful information about CubeSats [Online]. Available: http://www.clyde-space.com/cubesat/som_useful_info_about_cubesats
[5] P. D. Fieseler et al. (2014) The Radiation Effects on Galileo Spacecraft Systems at Jupiter [Online Report]. Available: trs-new.jpl.nasa.gov/dspace/bitstream/2014/11661/1/02-0220.pdf
[6] M. B. Murrill. (1996, Oct. 15). CASSINI SPACECRAFT READIED FOR "SHAKE AND BAKE" TESTS [Online]. Available: http://www.jpl.nasa.gov/news/releases/96/csshake.html
[7] T. Pratt et al., “Satellites,” in Satellite Communication, 2nd ed. Danvers, MA: John Wiley & Sons, Inc., 2003, ch.3, sec. 7, pp.87-89.
[8] NASA. (2014, Feb 4). RPS Technology [Online]. Available: https://solarsystem.nasa.gov/rps/types.cfm