Near Earth Asteroid (NEA) Deflection Mission
Ad Astra Rocket Company has evaluated the applicability of its 400 kW solar electric propulsion (SEP) “space tug” concept, Viento™ to successfully deflect an imaginary medium-sized asteroid in a direct impact scenario with Earth. Viento™ is equipped with two dual-core, VF-200-class engines operating at 200 kW each in: 1) additive translation mode to provide high speed translation capability to the target asteroid and 2) deflection mode with its two nacelles oriented in opposing tandem to utilize the plasma exhaust of one of the engines to gently “blow” on the asteroid to impart momentum and alter its trajectory, while the other engine, with proper gimballing and auxiliary spacecraft attitude control, maintains the spacecraft in a stable position, hovering adjacent to the asteroid without actually landing.
Ad Astra’s Viento™ spacecraft is configured in 2 modes: additive propulsive mode for fast transit to asteroid (left) and opposing tandem mode (right). The 400 kW solar electric propulsion spacecraft is equipped with 2, VF-200-class VASIMR® engines.
The imaginary asteroid, which we call “Khan,” is a 7 million ton, 150 m diameter body in an Apophis-like orbit, slightly modified to set up a direct impact with Earth on April 13, 2029, versus the near-miss that will actually occur with Apophis (99942 Apophis is a 270 m diameter boulder weighing approximately 40 million tons and discovered on June 19, 2004). Khan is in a nearly circular orbit with a period of 323 days. Each year, Earth crosses Khan’s orbit on April 13 as Khan heads inbound toward perihelion. Khan is large enough to pose a major threat to our planet and, in our imaginary scenario, if not deflected, Khan will impact Earth with an energy release of 131 megatons, causing a major regional disaster.
Ad Astra’s Viento™ carries out the deflection campaign in four phases: 1) departure on August 13, 2019 from Earth-Moon L1 (EML1) and a 305 day propulsive translation to a rendezvous with Khan on June 13, 2020; 2) a five-year active deflection period, ending on June 13, 2025, where the spacecraft is configured to hover adjacent to the asteroid while pushing on it with the other engine; 3) a four-year passive loiter period at Khan, ending on March 19, 2029, while Viento™ awaits an optimal return opportunity and 4) a 40 day return maneuver, which brings Viento™ back to its point of origin a the EML1.
The high power scalability of the technology forms the basis of an attractive mission. The VASIMR® propulsion system is electrodeless (expected to reduce component wear and increase lifetime) and has an inherent high power density and high specific impulse (Isp), with no thruster scalability concerns at total power of up to 1 MW. VASIMR® systems use more efficient, economical propellants, such as argon (~$5/kg) and krypton (~$300/kg), than conventional Hall and ion thrusters, which operate with much rarer and expensive xenon (~$1000/kg). Such flexibility results in significant operational cost savings. The 200kW VASIMR® engine is in a high state of technical maturity. A full scale prototype running with argon propellant and called VX-200 has executed more than 10,000 reliable high-power firings to date with greater than 70% thruster efficiency [B. Longmier, et al.] in Ad Astra’s 150 m3 Houston vacuum chamber.
The VASIMR® deflection capability is determined by the power level, the deflection time, and the size/mass of the asteroid. At the 400 kW level used in this study, the deflection of a 7,000,000 t asteroid is readily facilitated within the time frame from discovery to impact deflecting out to distances several times Earth's radius. Larger asteroids, up to ~15,000,000 t mass, may be deflected just enough to avoid a collision.