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<\/p>\nLaunched in 2012, NASA\u2019s twin Van Allen radiation belt probes have been swinging through the hazardously charged-particle region around Earth while returning valuable scientific data that has not only helped scientists better understand this protective region around Earth but also plan for future missions of exploration that will travel beyond the Van Allen belts. <\/p>\n
More than six years after launch, controllers have begun the process of ending the Van Allen probes mission by lowering their orbital perigees from 385 miles (619 km) to 190 miles (305 km) \u2013 a change that will set up an end to the probes\u2019 mission in early 2020 and a controlled re-entry roughly 15 years from now.<\/p>\n
The coming end:<\/b><\/p>\n
It might seem odd that the Van Allen Probes mission has begun taking steps for a destructive reentry to Earth\u2019s atmosphere 15 years from now.<\/p>\n
But in the world of close-to-Earth space travel, it all comes down to ensuring that the probes do not contribute to the large population of space junk and potentially hazardous debris in Earth orbit.<\/p>\n
And this, for the Van Allen probes, is something that requires action now for an event that won\u2019t occur until 2034.<\/p>\n
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The Van Allen probes orbit through Earth\u2019s radiation belts. (NASA Goddard\u2019s Scientific Visualization Studio)<\/p>\n
\u201cIn order for the Van Allen Probes to have a controlled reentry within a reasonable amount of time, we need to lower the perigee,\u201d said Nelli Mosavi, project manager for the Van Allen Probes at the Johns Hopkins Applied Physics Laboratory. \u201cAt the new [perigee], aerodynamic drag will bring down the satellites and eventually burn them up in the upper atmosphere.\u201d<\/p>\n
To lower their orbital perigees (point of closest approach to Earth), controllers will command the probes through a 10-day series of engine burns one at a time that will lower their perigees from 385 miles (619 km) to 190 miles (305 km).<\/p>\n
Aerospace & Defense (adsbygoogle = window.adsbygoogle || []).push({});<\/p>\n This process began for Van Allen probe-B two days ago on 12 February 2019 and will culminate on 22 February. The second spacecraft, Van Allen probe-A, will perform the same set of maneuvers from 11-22 March 2019.<\/p>\n The perigee lowering operations themselves are a series of five, two-hour burns of each probes\u2019 engine. But lowering the Van Allen probes\u2019 perigees was not simply a matter of aligning each probe\u2019s engine for a retrograde burn at orbital apogee (farthest point in orbit of Earth). [NOTE: Burning retrograde at apogee will lower an orbit\u2019s perigee.]<\/p>\n Because the probes spin as part of their operation, mission controllers had to calculate when each spinning probe\u2019s engine would align in the needed direction at just the right point in the orbit so that burning the engine would lower the spacecraft\u2019s perigee.<\/p>\n When calculated, NASA noted that the needed geometry for the burns only happens once or twice every year.<\/p>\n<\/p>\n