The Dawn mission, part of NASA's Discovery Program, has as its goal the scientific exploration of the two most massive main-belt objects, Vesta and Ceres. The Dawn spacecraft was launched from the Cape Canaveral Air Force Station on September 27, 2007 on a Delta-II 7925H- 9.5 (Delta-II Heavy) rocket that placed the 1218-kg spacecraft onto an Earth-escape trajectory. On-board the spacecraft is an ion propulsion system (IPS) developed at the Jet Propulsion Laboratory for the heliocentric transfer to Vesta, orbit capture at Vesta, transfer between Vesta science orbits, departure and escape from Vesta, heliocentric transfer to Ceres, orbit capture at Ceres, transfer between Ceres science orbits, and orbit maintenance maneuvers. Full-power thrusting from December 2007 through October 2008 was used to successfully target a Mars gravity assist flyby in February 2009 that provided an additional AV of 2.6 km/s. Deterministic thrusting for the heliocentric transfer to Vesta resumed in June 2009 and concluded with orbit capture at Vesta on July 16, 2011. From July 2011 through September 2012 the IPS was used to transfer to all the different science orbits at Vesta and to escape from Vesta orbit. Cruise for a rendezvous with Ceres began in August 2012 and completed in late December 2014. From December 2014 through June 2016 the IPS was used for transiting the spacecraft to the Approach phase, survey orbit, the high altitude mapping orbit (HAMO), and the low altitude mapping orbit (LAMO) with arrival to LAMO on December 13, 2015, almost eight years after the start of deterministic thrusting to Vesta. The LAMO orbit, at a mean altitude above Ceres of approximately 385 km, is the spacecraft's final destination and there are no plans to move the spacecraft from LAMO once science operations there are completed. Since arrival at LAMO Dawn's IPS has been used for occasional orbit maintenance maneuvers while the spacecraft performs scientific investigations. Dawn has successfully completed its science goals and Dawn's primary mission is scheduled to end June 30, 2016. To date the IPS has been operated for approximately 48,458 hours, consumed approximately 401 kg of xenon, and provided a delta-V of over 11.0 km/s, a record for an on-board propulsion system. The IPS performance characteristics are close to the expected performance based on analysis and testing performed pre-launch. Dawn's IPS continues to be fully operational as of June 2016. This paper provides an overview of Dawn's mission objectives and the results of Dawn IPS mission operations from Survey orbit through the completion of Dawn's primary mission.
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机译：作为美国国家航空航天局（NASA）发现计划的一部分，“黎明”计划的目标是科学探索两个最大的主带物体维斯塔（Vesta）和谷神星（Ceres）。黎明号航天器于2007年9月27日从卡纳维拉尔角空军基地发射，并搭载了Delta-II 7925H- 9.5（Delta-II重型）火箭，将1218 kg的航天器置于逃生轨道上。航天器上装有由喷气推进实验室开发的离子推进系统（IPS），用于向Hesta的日心传输，在Vesta处的轨道捕获，在Vesta科学轨道之间的传输，从Vesta出发和逃逸，日心传输到Ceres，轨道捕获在谷神星处，在谷神星科学轨道之间进行转移，并进行轨道维护演习。从2007年12月到2008年10月的全功率推力被成功用于2009年2月的火星重力辅助飞越，提供了2.6 km / s的额外视音频。确定性向日心向维斯塔转移的推力于2009年6月恢复，并于2011年7月16日在维斯塔捕获了轨道。从2011年7月至2012年9月，IPS被用于转移至维斯塔的所有不同科学轨道并逃离维斯塔轨道。与谷神星会合的巡航始于2012年8月，并于2014年12月下旬完成。从2014年12月至2016年6月，IPS被用于将航天器转移到进场阶段，勘测轨道，高空测绘轨道（HAMO）和低高度制图轨道（LAMO），并于2015年12月13日抵达确定性推力Vesta，开始将近八年。 LAMO轨道是塞莱斯的最终目的地，其平均高度在谷神星上方约385公里，因此没有计划将航天器从LAMO中移出。自从到达LAMO以来，Dawn的IPS已用于航天器进行科学调查时的偶尔轨道维护演习。 Dawn已成功完成其科学目标，Dawn的主要任务定于2016年6月30日结束。迄今为止，IPS已运行约48,458小时，消耗了约401千克氙，并提供了超过11.0 km / V的V值s，这是机载推进系统的记录。根据发布前进行的分析和测试，IPS性能特征接近预期的性能。截至2016年6月，Dawn的IPS仍将全面投入运营。本文概述了Dawn的任务目标，以及从调查轨道到Dawn的主要任务完成，Dawn IPS任务的成果。
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