Project Lyra: Sending a Spacecraft to 1I/’Oumuamua (former A/2017 U1), the Interstellar Asteroid Andreas M. Hein 1, Nikolaos Perakis 1, T. Marshall Eubanks 1,2 , Adam Hibberd 1, Adam Crowl 1, Kieran Hayward 1, Robert G. Kennedy III 1, Richard Osborne 1 Contact email: [email protected] 1 Initiative for Interstellar Studies, Bone Mill, New Street, Charfield, GL12 8ES, United Kingdom 2 Asteroid Initiatives LLC Abstract The first definitely interstellar object 1I/’Oumuamua (previously A/2017 U1) observed in our solar system provides the opportunity to directly study material from other star systems. Can such objects be intercepted? The challenge of reaching the object within a reasonable timeframe is formidable due to its high heliocentric hyperbolic excess velocity of about 26 km/s; much faster than any vehicle yet launched. This paper presents a high-level analysis of potential near-term options for a mission to 1I/’Oumuamua and potential similar objects. Launching a spacecraft to 1I/’Oumuamua in a reasonable timeframe of 5-10 years requires a hyperbolic solar system excess velocity between 33 to 76 km/s for mission durations between 30 to 5 years. Different mission durations and their velocity requirements are explored with respect to the launch date, assuming direct impulsive transfer to the intercept trajectory. For missions using a powered Jupiter flyby combined with a solar Oberth maneuver using solid rocket boosters and Parker Solar Probe heatshield technology, a Falcon Heavy-class launcher would be able to launch a spacecraft of dozens of kilograms towards 1I/’Oumuamua, if launched in 2021. An additional Saturn flyby would allow for the launch of a New Horizons-class spacecraft. Further technology options are outlined, ranging from electric propulsion, and more advanced options such as laser electric propulsion, and solar and laser sails. To maximize science return decelerating the spacecraft at ’Oumuamua is highly desirable, due to the minimal science return from a hyper-velocity encounter. Electric and magnetic sails could be used for this purpose. It is concluded that although reaching the object is challenging, there seem to be feasible options based on current and near- term technology. 1. Introduction On October 19 th 2017, the University of Hawaii’s Pan-STARRS 1 telescope on Haleakala discovered a fast- moving object near the Earth, initially named A/2017 U1, but now designated as 1I/’Oumuamua [1]. It is likely that this object has its origin outside the solar system [2–9], with a velocity at infinity of 26.33 km/s, an eccentricity of 1.20, and an incoming radiant (direction of motion) near the solar apex in the constellation Lyra [10]. Due to the non-observation of a tail in the proximity of the Sun, the object seems to be an asteroid [11]. However, it has been hypothesized that either a cometary tail was present for a brief moment but was not observed [12], as 1I/’Oumuamua was discovered post perihelion, or that an organically rich surface, resulting in an insulating mantle prevented a cometary tail from forming [13]. Such a mantle could be the result of long-term cosmic ray exposure, although Jackson et al. argue against this possibility [14]. The comet hypothesis has been supported by the observation of non-gravitational acceleration, which can be explained by cometary outgassing [15]. However, the question is still far from resolved [16]. Spectroscopic results [12,13,17–21] indicate that the object is reddish, with a distribution similar to Trans-Neptunian objects [18,19,21]. The rapidly changing albedo has also lead to the assumption that the object is rotating and is highly elongated [19,22,23] with estimated dimensions of 230m x 35m x 35m [21]. The axis ratio of is larger than for any small solar system body [21]. Its orbital features have been analyzed by . ≥ 6.3.: 1 1 [10,24,25]. Hypotheses for its origin range from a star of the Local Association [4] to a more distant origin in the galactic thin disk, with the ejection dating back several billion years [7,20]. Estimates for the abundance of interstellar objects with a similar size are wide-ranging. Feng and Jones [4] estimate an abundance of interstellar objects larger than 100 m as . The steady state population of interstellar objects with a size of the order of 100 m inside6.0 the 10 orbit of Neptune has been estimated as on the order of 10 4 by [21]. As 1I/‘Oumuamua is the nearest macroscopic sample of interstellar material, likely with an isotopic signature distinct from any other object in our solar system, the scientific returns from sampling the object are hard to understate. Detailed in-situ studies of interstellar materials at interstellar distances is likely decades away. For example, Breakthrough Initiatives’ Project Starshot, which is developing a laser-propelled interstellar probe along with a beaming infrastructure for example, currently aims at a launch date in the 2040s [26]. Hence, an interesting question is if there is a way to exploit this unique opportunity to study interstellar material by sending a spacecraft to 1I/‘Oumuamua to make observations at close range. The Initiative for Interstellar Studies, i4is, has announced Project Lyra on the 30 th of October to answer this question. The goal of the project is to assess the feasibility of a mission to 1I/‘Oumuamua using current and near-term technology and to propose mission concepts for achieving a fly-by or rendezvous. The challenge is formidable. According to current estimates, 1I/‘Oumuamua has a heliocentric hyperbolic excess velocity of 26 km/s. This is considerably faster than any object humanity has ever launched into space. Voyager 1, the fastest object humanity has ever built, has a hyperbolic excess velocity of 16.6 km/s. As 1I/‘Oumuamua is already leaving our solar system, any spacecraft launched in the future would need to chase it. However, besides the scientific interest of getting data back from the object, the challenge to reach the object could stretch the current technological envelope of space exploration. Hence, Project Lyra is not only interesting from a scientific point of view but also in terms of the technological challenge it presents. This paper presents some preliminary results for a mission concept to 1I/‘Oumuamua. 2. Trajectory Analysis In the following, we first provide a first order trajectory analysis assuming one or more impulsive transfers in the vicinity of the earth and a free trajectory to 1I/‘Oumuamua. Subsequently we present results for a more complex trajectory that combines a Jupiter flyby and a solar Oberth maneuver. 2.1 Trajectory Analysis without Gravity Assist Given the hyperbolic excess velocity and its inclination with respect to the solar system ecliptic, the first question to answer is the required velocity increment (DeltaV) to reach the object, a key parameter for designing the propulsion system. The DeltaV for a mission without gravity assist is calculated by determining the transfer hyperbola from Earth orbit with respect to the position of 1I/‘Oumuamua at a certain point in time. Using the vis-viva equation (1), the orbital velocity v of a body on a hyperbolic trajectory can be computed. (1) 2 1 = − Where is the standard gravitational parameter, r is the radial distance of the object from the central body, and a the semi-major axis. With a few arithmetic manipulations, the relationship (2) between the orbital velocity , the escape velocity from the Sun, and the hyperbolic excess velocity ∞ can be obtained. (2) ∞ 2 = + 2 ∞ can be understood as the velocity at infinity with respect to the Sun. Note that the earth’s orbital velocity can be exploited for reducing the required DeltaV. Nevertheless the high inclination of 1I/‘Oumuamua relative to the ecliptic requires significant additional DeltaV. (3) ∞ 2 = − ! " cos & cos ' = + − ! " cos & cos ' Where i is the inclination of the trajectory with respect to the ecliptic and the angle between the velocity vector of the trajectory and the velocity vector of the Earth. ' Obviously, a slower spacecraft will reach the object later than a faster spacecraft, leading to a trade-off between trip duration and required DeltaV. Furthermore, the earlier the spacecraft is launched the shorter the trip duration, as the object is closer. However, a launch date within the next 5 years is likely to be unrealistic, and even 10 years could be challenging, in case new technologies need to be developed. A third trade-off is between launch date and trip time / characteristic energy C3. The characteristic energy is the square of the hyperbolic excess velocity ∞. These trade-offs are captured in Figure 1. The figure plots the characteristic energy for the launch with respect to mission duration and launch date. An impulsive propulsion system with a sufficiently short thrust duration is assumed. No planetary or solar fly-by is assumed, only a direct launch towards the object. It can be seen that a minimum 3 exists, which is about 703 km²/s² (26.5 km/s). However, this minimum value rapidly increases when the launch( date is moved into the future. At the same time, a larger mission duration leads to a decrease of the required 3 but also implies an encounter with the asteroid at a larger distance from the Sun. A realistic launch date (for a probe would be at least 10 years in the future (2027). At that point, the hyperbolic excess velocity with respect to the Earth is already at 37.4km/s (1400 km²/s²) with a mission duration of about 15 years, which makes such an orbital insertion extremely challenging with conventional launches in the absence of a planetary fly-by.