This article is about the proposed NASA mission. For asteroid mining and utilization, see Asteroid mining.
Grippers on the end of the robotic arms are used to grasp and secure a boulder from a large asteroid. Once the boulder is secured, the legs would push off and provide an initial ascent without the use of thrusters.
The Asteroid Redirect Mission (ARM), also known as the Asteroid Retrieval and Utilization (ARU) mission and the Asteroid Initiative, was a space mission proposed by NASA in 2013. The Asteroid Retrieval Robotic Mission (ARRM) spacecraft would rendezvous with a large near-Earth asteroid and use robotic arms with anchoring grippers to retrieve a 4-meter boulder from the asteroid.
The spacecraft would characterize the asteroid and demonstrate at least one planetary defense technique before transporting the boulder to a stable lunar orbit, where it could be further analyzed both by robotic probes and by a future human mission, ARCM (Asteroid Redirect Crewed Mission). If funded, the mission would have launched in December 2021, with the additional objectives to test a number of new capabilities needed for future human expeditions to deep space, including advanced ion thrusters.
The proposed 2018 NASA budget called for its cancellation, the mission was given its notice of defunding in April 2017, and NASA announced the "close out" in June 13, 2017. Key technologies being developed for ARM will continue, especially the ion thruster propulsion system that would have been flown on the robotic mission.
Astronaut on EVA to take asteroid samples, Orion in the background
The main objective of the Asteroid Redirect Mission was to develop deep space exploration capabilities needed in preparation for a human mission to Mars and other Solar System destinations per NASA's Journey to Mars flexible pathways.
Space tug missions, to disaggregate non-time-critical Mars logistics from crew, can reduce the costs by as much as 60% (if using advanced solar electric propulsion (ion engines)) and reduces overall mission risk by enabling on-site check-out of critical systems before the crew departs.
Not only would the solar electric propulsion (SEP) technologies and designs be applied to future missions, but the ARRM spacecraft would be left in a stable orbit for reuse. The project has baselined any of multiple refueling capabilities; the asteroid-specific payload is at one end of the bus, for possible removal and replacement via future servicing, or as a separable spacecraft, leaving a qualified space tug in cislunar space.
Expanded and sustainable deep space operations
The robotic and crewed missions would demonstrate capabilities past Earth orbit, yet within a few days' return contingency. Lunar Distant Retrograde Orbit (DRO), encompassing Earth-Moon L1 and L2, is essentially a node for Earth system escape and capture. This is more so if an Exploration Augmentation Module (EAM) is brought for extended human stays, possibly by an ARRM-like SEP module. On its return leg from Mars, a human mission may save tons of mass by capturing into DRO, and transferring to a parked Orion for Earth return and reentry.
Additional mission aims included demonstrating planetary defense techniques able to protect the Earth in the future - such as using robotic spacecraft to deflect potentially hazardous asteroids. Under consideration for deflecting an asteroid are: grabbing the asteroid and directly moving it, as well as employing gravity tractor techniques after collecting a boulder from its surface to increase mass ("enhanced gravity tractor").
The asteroid redirect vehicle would demonstrate the "gravity tractor" planetary defense technique on a hazardous-size asteroid. This method leverages the mass of the spacecraft (18 tons) and its 6m boulder cargo (at least 20 tons) to impart a gravitational force on the asteroid, slowly altering the asteroid's trajectory. (ogv; gif)
Asteroid grippers on the end of the robotic arms are used to grasp and secure a 6 m boulder from a large asteroid. An integrated drill would be used to provide final anchoring of the boulder to the capture mechanism.
Rendering of the Asteroid Redirect Vehicle departing the asteroid after capturing a boulder from its surface.
The vehicle would land on a large asteroid and grippers on the end of the robotic arms would grasp and secure a boulder from the surface of a large asteroid. The grippers would dig into the boulder and create a strong grip. An integrated drill would be used to provide final anchoring of the boulder to the capture mechanism. Once the boulder is secured, the legs would push off and provide an initial ascent without the use of thrusters.
The advanced ion engine uses 10% of the propellant required by equivalent chemical rockets, it can process three times the power of previous designs, and increase efficiency by 50%. It would use the Hall-effect, which provides low acceleration but can fire continuously for many years to thrust a large mass to high speed. Hall effect thrusters trap electrons in a magnetic field and use them to ionize the onboard xenon gas propellant. The magnetic field also generates an electric field that accelerates the charged ions creating an exhaust plume of plasma that pushes the spacecraft forward. The spacecraft concept would have a dry mass of 5.5 tons, and could store up to 13 tons of xenon propellant.
Even at a destination, the SEP system can be configured to provide power to maintain the systems or prevent propellant boil-off before the crew arrives. However, existing flight-qualified solar-electric propulsion is at levels of 1-5 kW. A Mars cargo mission would require ~100 kW, and a crewed flight ~150-300 kW.
Originally planned for 2017, then 2020, and then for December 2021. The mission was given its notice of defunding in April 2017. The launch vehicle would have been either a Delta IV Heavy, SLS or Falcon Heavy. The boulder would have arrived in lunar orbit by late 2025.
The carbonaceous boulder that would have been captured by the mission (maximum 6 meter diameter, 20 tons) is too small to harm the Earth because it would burn up in the atmosphere. Redirecting the asteroid mass to a distant retrograde orbit around the Moon would ensure it could not hit Earth and also leave it in a stable orbit for future studies.
NASA Administrator Robert Frosch testified to Congress on "asteroid retrieval to Earth" in July 1980. However, he stated that it was infeasible at the time.
The 'Option A' was to deploy a container large enough to capture a free-flying asteroid up to 8 m (26 ft) in diameter.
The two options studied to retrieve a small asteroid were Option A and Option B. Option A would deploy a large 15-metre (50 ft) capture bag capable of holding a small asteroid up to 8 m (26 ft) in diameter, and a mass of up to 500 tons. Option B, which was selected in March 2015, would have the vehicle land on a large asteroid and deploy robotic arms to lift up a boulder up to 4 m (13 ft) in diameter from the surface, transport it and place it into lunar orbit. This option was identified as more relevant to future rendezvous, autonomous docking, lander, sampler, planetary defense, mining, and spacecraft servicing technologies.
The crewed portion to retrieve asteroid samples from the Moon orbit (Orion EM-3) was criticized as an unnecessary part of the mission with claims that thousands of meteorites have already been analyzed and that the technology used to retrieve one boulder does not help develop a crewed mission to Mars. The plans were not changed despite the NASA Advisory Council suggested on 10 April 2015 that NASA should not carry out its plans for ARM, and should instead develop solar electric propulsion and use it to power a spacecraft on a round-trip flight to Mars.
Under the 2018 NASA budget proposed by the Trump administration in March 2017, this mission was cancelled. In June 13, 2017 NASA announced a "closeout phase" following the defund. NASA has emphasized that key technologies being developed for ARM will continue, especially the solar electric propulsion system that would have been flown on the robotic mission.
^McElratht, T.; Elliott, J. (Jan 2014). "There and Back again: Using planet-based SEP tugs to repeatably aid interplanetary payloads". Advances in the Astronautical Sciences (152): 2279–2298.
^Price, Humphrey W.; Woolley, Ryan; Strange, Nathan J.; Baker, John D. (2014). "Human Missions to Mars Orbit, Phobos, and Mars Surface Using 100-kWe-Class Solar Electric Propulsion". AIAA SPACE 2014 Conference and Exposition. doi:10.2514/6.2014-4436. ISBN978-1-62410-257-8.
^Manzanek, D.; Reeves, D.; Hopkins, J.; Wade, D.; Tantardini M.; Shen, H. (April 13, 2015). "Enhanced Gravity Tractor Technique for Planetary Defense". Iaa-Pdc.
^NASA RFI: Spacecraft Bus Concepts to Support the ARM and In-Space Robotic Servicing- Section "Separable Spacecraft Architecture ARRM Concept".
^Kathleen C. Laurini and Michele M. Gates, "NASA's Space Exploration Planning: the Asteroid Mission and the Step Wise Path to Mars", 65th International Astronautical Congress, Toronto, Canada, Sept-Oct. 2014. This paper (and related papers from the 65 IAC) can be found on the NASA page Asteroid Initiative Related Documents (accessed 5 January 2014)
^Lee, P.; Hoftun, C.; et al. (2012). "Phobos and Deimos: Robotic Exploration in Advance of Humans to Mars Orbit". Concepts and Approaches for Mars Exploration 2012. 1679: 4363. Bibcode:2012LPICo1679.4363L.
^Price, H.; Baker, J.; et al. "Human Missions to Mars Orbit, Phobos, and Mars Surface Using 100-kWe-Class Solar Electric Propulsion". AIAA Space 2014 Conference and Expo Proceedings.
^Percy, T.; McGuire, M.; et al. "Combining Solar Electric Propulsion and Chemical Propulsion for Crewed Missions to Mars". Ntrs 20150006952.
^John Brophy; Fred Culick; Louis Friedman; et al. (2012-04-12). "Asteroid Retrieval Feasibility Study"(PDF). Keck Institute for Space Studies, California Institute of Technology, Jet Propulsion Laboratory. Table 1: Asteroid Mass Scaling (for spherical asteroids). Page 17.
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