46th Lunar and Planetary Science Conference (2015) 2925.pdf Surface Investigations of Asteroids: Science Justification and the Need for Instrument Development. K. K. John 1, P. A. Abell 1, and L. D. Graham 1, 1NASA Johnson Space Center, 2101 NASA Parkway, Houston, Texas 77058, [email protected] , [email protected] , [email protected] Introduction: One of NASA’s current objectives stating that technology development is necessary includ- is to send humans to an asteroid. To make this goal ing instrumentation for in-situ study [5]. feasible, it is critical to perform in-situ measurements to characterize these surfaces in order to understand the environment that astronauts, vehicles, and equipment will be exposed to while exploring. Currently, there is very little knowledge about the geophysical and ge- otechnical properties of asteroids. There is a lack of scientific data on the properties of regolith, as well as a lack of understanding of how regolith responds in its Figure 1: Surfaces of Itokawa showing rough terrain on the left and unique microgravity environment [1]. To truly under- smooth terrain on the right (Image: JAXA) stand the data from remote sensing, surface interaction is key. Characterizing the surface, the regolith, and its Past and Current Asteroid Missions: This section properties all feeds into obtaining ground truth. provides a brief description of relevant missions and instruments. Several of these missions were limited to Need For Surface Interaction and In-Situ Inves- remote sensing. tigations: Near-Earth asteroids come within 121 million NEAR : NASA and Johns Hopkins’ Near Earth As- miles of the Sun [2]. Asteroids are of scientific interest teroid Rendezvous (NEAR) Shoemaker spacecraft ren- largely because of the information they will provide dezvoused with asteroid Eros in 2001, becoming the about the origins of the Solar System. Asteroids are first spacecraft to land on the surface of an asteroid. It also important for exploration, particularly carbona- used innovative sensors and detection equipment to take ceous asteroids that could provide opportunities for in- images of the surface and collect information on Eros’ situ resource utilization. Asteroid detection capabilities structure and composition [2]. NEAR made several are being improved and missions like NEOWISE are discoveries, including the presence of a layer of debris identifying more reasonable targets for future robotic resulting from a long history of impacts. and human missions. However, technology develop- Hayabusa : JAXA’s Hayabusa mission to near- ment is needed to enable these future missions to per- Earth asteroid Itokawa was the first to land on, take off form meaningful science objectives. from, and return samples from an asteroid. Hayabusa’s Understanding the Effects of Regolith: The surfaces mini-lander called MINERVA (Micro/Nano Experi- of airless planetary bodies are covered with a layer of mental Robot Vehicle for Asteroid) was unsuccessful, dust particles, rock fragments, and glass particles called but would have used its three small color cameras to regolith. When NASA sends missions to an asteroid, relay images of the surface of the asteroid [6]. and eventually to Mars, many of the subsystems could Dawn: NASA’s Dawn visited Vesta in 2011, be- be affected such as instruments, spacesuits, airlocks, coming the first spaceraft to visist a main-belt asteroid. vehicles, hardware, robotics, and the crew. It is critical Dawn will arrive at Ceres in 2015. However, its capa- that regolith studies be done in order to understand the bilities are limited to remote sensing [7]. environment that astronauts and equipment will face. Rosetta: ESA's Rosetta rendezvoused with Comet Consensus in the Planetary Science Community: In 67P in August 2014. In November, it became the first a Planetary Science Decadal Survey (PSDS) white pa- spacecraft to land on a comet. The 100 kg lander, Phi- per, the planetary science community agrees that “future lae, detected “dust and debris ranging from millimeter to missions should focus more on in-situ investigations” meter sizes” [8]. Comets, like asteroids, will reveal stating that “at present, we do not have enough new in- information about the formation of the Solar System. struments” and that “basic laboratory research with po- Hayabusa 2 : JAXA successfully launched their tential in-situ instrument development even at laboratory second asteroid mission in December 2014, which is set scale (TRL0) should be strongly supported” [3]. An- to arrive at a carbonaceous near-Earth asteroid, 1999 other PSDS white paper on asteroids states that “for in- JU3, in 2018. JAXA will send the Mobile Asteroid situ science, probes and small landers need to be devel- Surface Scout (MASCOT) lander to the surface. oped that can accommodate a range of instrumentation” MASCOT will in-situ map the asteroid’s geomorpholo- [4]. Several Small Body Assessment Group (SBAG) gy, the intimate structure, texture and composition of the proceedings also confirm the need for asteroid missions, regolith [6,9]. Hayabusa 2 will also have three MINERVA mini-landers. 46th Lunar and Planetary Science Conference (2015) 2925.pdf OSIRIS-REx: NASA’s OSIRIS-REx will launch in terization and works its way down to surface and sub- 2016 to carbonaceous, near-Earth asteroid Bennu, arriv- surface characterization. ing in 2018. It will use imagers and spectrometers to gather information about the topography, mineralogy, Table 1: Asteroid Science and Associated Instrumentation Asteroid Science Associated Instrumentation and chemistry [10]. Several of these capabilities are Global properties: mass, shape, Radioscience measurements, limited to remote sensing. The in-situ capabilities such density, rotation, porosity LIDAR, imagers, spectrometers as the SamCam will help to document the samples ob- Presence of volatiles Spectrometers, hyperspectral im- tained from the sample acquisition mechanism. agers, micro-GPR (ground penetrat- Fly-by missions: In the last 25 years, several mis- ing radar) Local magnetic field detection Micro-magnetometer sions observed asteroids remotely [7]. The Galileo Interior and surface structure Passive/active seismic measure- spacecraft took images of asteroids Gaspra and Ida. ments, radar Rosetta, on its way to Comet 67P, took images of as- Topography Imagers, optical cameras, LIDAR, teroids Steins and Lutetia. NEAR, on its way to Eros, radar flew by asteroid Mathilde. Similarly, Stardust, Mineralogical composition Visible, near-IR, x-ray, gamma-ray spectrometer; hyperspectral imagers Chang’e 2, Deep Space 1, Vega 2, and Deep Impact Radiation characterization Dosimeter have all encountered asteroids or comets. None of Temperature, thermal inertia Hyperspectral imager, RFID surface these missions visited the surface. A review of these acoustic wave (SAW) sensors, IR heritage missions involving asteroids further supports detector that surface interaction is considerably lacking. Surface roughness Hyperspectral imager, LIDAR Dust environment characterization Imagers, optical camera, Langmuir The Need to Visit the Surface: As useful as these Probe missions have been, they fail to produce the type of Surface mobility: granular flow, Imagers, optical camera, RFID data that can only be acquired on the surface. Ground regolith movement, particle levita- SAW sensors observations, rendezvouses, and fly-bys can provide tion information on rotation rates, asteroid taxonomic class, Particle size distribution Micro-imagers Particle properties: structure, tex- Visible imager general composition, shape, and size. However, we ture, shape, thickness must investigate the surface to determine internal struc- Cohesion, friability, surface Penetrometer, imagers, load cell, ture, detailed composition, surface topography, colli- strength, compaction physical interaction tool sional history, particle size distribution, particle behav- Mechanical properties of surface: Penetrometers, gages, specialized compressive strength, tensile tests ior, and mechanical properties of the particles. strength, shear strength, toughness, Interacting with the Surface: The missions dis- hardness cussed above did/will not all involve surface interaction. Albedo of particles Imagers, optical camera, IR detector In fact, the only tools used for asteroid surface interac- Subsurface environment characteri- Penetrometers, micro-GPR, thermo- tion to date are for Hayabusa, where a slug fired into the zation: voids, clumps, mass concen- couples trations, temperature, thermal regolith was meant to disturb the surface and collect inertia samples. In contrast, on the Moon, the astronauts used a number of manual tools, as well as rover wheels to dis- Conclusion: A review of past and current missions turb the surface. Martian tools include the MSL, Vi- illustrates that surface investigations at asteroids are king, and Phoenix rover arms. Lessons learned from needed. The planetary science community has ex- Apollo and Mars experiences can be applied to the next pressed the need for robotic precursor missions to inter- generation of tool development. act with and characterize the surface. Technology de- velopment is needed for instrumentation to perform the Asteroid Science and Associated Instruments: desired science. If we are to send astronauts to an aster- The planetary science community has detailed what sci- oid in the coming decades, it is necessary now to begin ence should be investigated on the surface. For each of development of in-situ instruments that can characterize