View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Institute of Transport Research:Publications Small Spacecraft in Planetary Defence Related Applications – Capabilities, Constraints, Challenges Jan Thimo Grundmann Caroline Lange DLR Institute of Space Systems DLR Institute of Space Systems Robert-Hooke-Strasse 7 Robert-Hooke-Strasse 7 28359 Bremen, 28359 Bremen, Germany Germany +49-421-24420-1107 +49-421-24420-1159 [email protected] [email protected] Bernd Dachwald Christian D. Grimm Faculty of Aerospace Engineering DLR Institute of Space Systems FH Aachen University of Applied Robert-Hooke-Strasse 7 Sciences 28359 Bremen, Hohenstaufenallee 6 Germany 52064 Aachen, +49-421-24420-1266 Germany [email protected] +49-241-6009-52343 / -52854 [email protected] Aaron Dexter Koch Stephan Ulamec DLR Institute of Space Systems DLR Space Operations and Astronaut Robert-Hooke-Strasse 7 Training – MUSC 28359 Bremen, 51147 Cologne, Germany Germany +49-421-24420-1183 +49-2203-601-4567 [email protected] [email protected] Abstract— In this paper we present an overview of the TABLE OF CONTENTS characteristics and peculiarities of small spacecraft missions related to planetary defence applications. We provide a brief 1. INTRODUCTION……………………………….1 overview of small spacecraft missions to small solar system MBRACING ONSTRAINTS bodies. On this background we present recent missions and 2. E C …………………..3 selected projects and related studies at the German Aerospace 3. GETTING SMALL ……………………………..5 Center, DLR, that contribute to planetary defence related 4. GETTING THERE ……………………………10 activities. These range from Earth orbit technology OING HINGS demonstrators to active science missions in interplanetary 5. D T ……………………………...13 space. We provide a summary of experience from recently 6. CONCLUSIONS ………………………………13 flown missions with DLR participation as well as a number of REFERENCES …………………………………..14 studies. These include PHILAE, the lander recently arrived on BIOGRAPHY……………………………………17 comet 67P/Churyumov-Gerasimenko aboard ESA’s ROSETTA comet rendezvous mission, and the Mobile Asteroid Surface Scout, MASCOT, now underway to near-Earth asteroid NTRODUCTION (162173) 1999 JU3 aboard the Japanese sample-return probe 1. I HAYABUSA-2. We introduce the differences between the Planetary defence related spaceflight missions come two conventional methods employed in the design, integration and testing of large spacecraft and the new approaches developed categories: by small spacecraft projects. We expect that the practical experience that can be gained from projects on extremely First, science missions to investigate the properties of small compressed timelines or with high-intensity operation phases solar system bodies in general prior to any recognized on a newly explored small solar system body can contribute threat. significantly to the study, preparation and realization of future planetary defence related missions. One is AIDA (Asteroid Second, missions to characterize and possibly deflect one Impact & Deflection Assessment), a joint effort of ESA, specific object become a recognized threat to such a degree JHU/APL, NASA, OCA and DLR, combining JHU/APL’s and confidence that exclusively dedicated missions are DART (Double Asteroid Redirection Test) and ESA’s AIM warranted. (Asteroid Impact Monitor) spacecraft in a mission towards near-Eath binary asteroid (65803) Didymos. 978-1-4799-5380-6/15/$31.00 ©2015 IEEE 1 The main difference between those categories is that nature In the aftermath of this event, the size-frequency distribution picks target and timeline for the latter, while for the former of natural impactors at Earth and their potential for careful deliberation in scientific committees usually does. destructive effects on the ground, and technical options for near-Earth object (NEO) deflection were revisited Since science missions do not fly frequently, the aim is to extensively [8]. maximize science output and consequently launch mass to the limit of accessibility of any suitable target object for The first wave of attention to the NEO threat had about affordable launchers within the space agency mission class. three decades earlier recognized the rare but potentially In threat-related missions the only constraint is the target globally catastrophic impacts of km-scale near-Earth object itself including getting there in time. asteroids (NEA) based on the observations of early photographic asteroid surveys and the emerging geological For science missions the target object can become a cratering record of the Earth. It drew strongly on the constraint on the scientific mission concept. Many discovery of prehistoric indicators of impact such as the interesting objects are difficult to reach without curtailing iridium anomaly at the cretaceous-tertiary boundary leading mission scope in favour of propulsion and/or greatly to the seminal Alvarez hypothesis [9], the recognition of extending flight time by planetary gravity-assists. However, Meteor Crater near Flagstaff, Arizona, and the Tunguska this only prevails as long as interest in a specific object or a event of 1908, and other historical data (e.g. [10] for a subset of possible targets outweighs more general summary) as related to meteoritic impacts. This recognition considerations of the scientific communities involved in the of the impact threat was formalized into the goal to discover mission. In most cases, a more easily accessible object of 90% of all NEAs larger than 1 km diameter, relatively the same or a sufficiently similar class would be selected. quickly followed up by the definition of Potentially There may however be missions for which just one object of Hazardous Asteroids (PHA) of at least 140 m diameter the vast number of solar system bodies discovered so far is which can approach Earth to within 0.05 AU. The ongoing of interest and accessible at the same time. [1] dedicated NEO surveys based on mass automatic exposure and processing of CCD images [11] confirmed the From Tunguska to Chelyabinsk: Bursts of Interest significant contribution to the threat of the much more The widely reported airburst of the Chelyabinsk bolide on frequent small impactors with regional or locally February 15th, 2013, returned the focus on planetary devastating effects [12]. NEAs in the sub-PHA size range defence. This 500 kt TNT-equivalent range event caused by have recently become accessible enough to observation to a 20 m diameter chondritic body [2] was just barely non- enable estimates of the population based on re-discovery lethal: early reports stated that 1491 people including 311 rates which indicate that their relative frequency is children were seen by medical staff in the region [3] and somewhat higher than expected from earlier extrapolations 112 people were treated in hospitals, two of them in serious down from the PHA size range [13][14][15]. Also, condition. One woman suffered broken vertebrae and was modelling of the effects of atmospheric entry and asteroid flown out for treatment, one man’s finger was cut off by fragmentation strongly suggests much higher yield to flying glass. [4] Most injuries were by glass shattered and ground-level damage efficiency than previously expected scattered about or accelerated by the blast wave [5]. from observations made e.g. at the 1908 Tunguska impact Property damage included massive destruction of window site. [16][17][18] U.S. government sensors recorded at least panes in the midst of the Siberian winter, mostly on 556 fireball events from 1994 through 2013, ranging from appartment blocks, and several collapsed structures. [6] about 5 t TNT-equivalent to the Chelyabinsk superbolide. [19] The distribution of injuries also clearly demonstrated the value of preparedness in natural disasters: At one school and The shift of focus towards the threat posed by smaller, more kindergarden site, 20 children were injured by flying glass frequent impactors also changed the approach towards as the blast wave hit during the break just after the first deflection. The impulse necessary to deflect an object on a lessons were over. At another, not regognizing the event for given orbit to a safe passage of Earth reduces with its mass what it was, Ms Yulia Karbysheva, a 4th-grade school – a substantial reduction of requirements for the expected teacher, ordered her students to exectute the there still likely next event: The now become unlikely case of a practised duck and cover drill – none of 44 was injured. She surprise civilization killer asteroid was replaced by impacts herself did not follow and suffered serious lacerations and a just slightly too large to be dealt with by practical tendon cut by flying glass in one arm. [4] application of preparedness and civil defence infrastructures but likely to occur on human timescales. For yet smaller It has to be noted that the main fragmentation occurred 31.8 impactors, the choice is to stand and stare or duck and km south of the city centre of Chelyabinsk approximately at cover. the minimum distance to the ground track [7] at an altitude of 29.7 km [2], or at about 44 km line-of-sight distance This reappreciation of risk based on the success of NEO between the largest release of energy in the event and a surveys and on likelihood of occurrence on human population of 1.13 million. timescales made deflection feasible within the present capabilities of the Earth’s spaceflight infrastructure. 2 However, smaller impactors are also much more difficult to agency