• International Journal of Aeronautical and Space Sciences
• /
• v.13 no.2
• /
• pp.154-169
• /
• 2012

This paper presents a comprehensive review of spacecraft guidance algorithms for asteroid intercept and rendezvous missions. Classical proportional navigation (PN) guidance is reviewed first, followed by pulsed PN guidance, augmented PN guidance, predictive feedback guidance, Lambert guidance, and other guidance laws based on orbit perturbation theory. Optimal feedback guidance laws satisfying various terminal constraints are also discussed. Finally, the zero-effort-velocity (ZEV) error, analogous to the well-known zero-effort-miss (ZEM) distance, is introduced, leading to a generalized ZEM/ZEV guidance law. These various feedback guidance laws can be easily applied to real asteroid intercept and rendezvous missions. However, differing mission requirements and spacecraft capabilities will require continued research on terminal-phase guidance laws.

• The Bulletin of The Korean Astronomical Society
• /
• v.40 no.1
• /
• pp.61.3-62
• /
• 2015

Remote-sensing observation is one of the observation methods that provide valuable information, such as composition and surface physical conditions of solar system objects. The Hayabusa spacecraft succeeded in the first sample returning from a near-Earth asteroid, (25143) Itokawa. It has established a ground truth technique to connect between ordinary chondrite meteorites and S-type asteroids. One of the scientific observation instruments that Hayabusa carried, Asteroid Multi-band Imaging Camera(AMICA) has seven optical-near infrared filters (ul, b, v, w, x, p, and zs), taking more than 1400 images of Itokawa during the rendezvous phase. The reflectance of planetary body can provide valuable information of the surface properties, such as the optical aspect of asteroid surface at near zero phase angle (i.e. Sun-asteroid-observer's angle is nearly zero), light scattering on the surface, and surface roughness. However, only little information of the phase angle dependences of the reflectance of the asteroid is known so far. In this study, we investigated the phase angle dependences of Itokawa's surface to understand the surface properties in the solar phase angle of $0^{\circ}-40^{\circ}$ using AMICA images. About 700 images at the Hayabusa rendezvous phase were used for this study. In addition, we compared our result with those of several photometry models, Minnaert model, Lommel-Seeliger model, and Hapke model. At this conference, we focus on the AMICA's v-band data to compare with previous ground-based observation researches.

• The Bulletin of The Korean Astronomical Society
• /
• v.46 no.2
• /
• pp.57.2-57.2
• /
• 2021

An asteroid is important for understanding the condition of our solar system in early-stage because an asteroid, considered as a building block of the solar system, preserves the information when our solar system was formed. It has been continuously flowing into the near-Earth space, and then some asteroids have a probability of impacting Earth. Some asteroids have valuable minerals and volatiles for future resources in space activity. Korean government clarified, in the 3rd promotion plan for space activity, an asteroid sample return mission by the mid-2030s. However, it is almost impossible to do so based on only a single experience of an exploration mission to the Moon, Korea Pathfinder Lunar Orbiter, which will be launched in mid-2022. We propose a Rendezvous Mission to Apophis(RMA), beneficial in terms of science, impact hazardous, resource, and technical readiness for the space exploration of Korea.

• Journal of Astronomy and Space Sciences
• /
• v.38 no.2
• /
• pp.105-117
• /
• 2021

In this study, a preliminary trajectory design is conducted for a conceptual spacecraft mission to a near-Earth asteroid (NEA) (99942) Apophis, which is expected to pass by Earth merely 32,000 km from the Earth's surface in 2029. This close approach event will provide us with a unique opportunity to study changes induced in asteroids during close approaches to massive bodies, as well as the general properties of NEAs. The conceptual mission is set to arrive at and rendezvous with Apophis in 2028 for an advanced study of the asteroid, and some near-optimal (in terms of fuel consumption) trajectories under this mission architecture are to be investigated using a global optimization algorithm called monotonic basin hopping. It is shown that trajectories with a single swing-by from Venus or Earth, or even simpler ones without gravity assist, are the most feasible. In addition, launch opportunities in 2029 yield another possible strategy of leaving Earth around the 2029 close approach event and simply following the asteroid thereafter, which may be an alternative fuel-efficient option that can be adopted if advanced studies of Apophis are not required.

• The Bulletin of The Korean Astronomical Society
• /
• v.46 no.1
• /
• pp.43.4-44
• /
• 2021

99942 Apophis is an Sq-type Aten group Near-Earth Asteroid (NEA) with an estimated size of 370 m. It will approach the Earth to come within the geostationary orbit during the upcoming encounter on April 13, 2029 to offer a unique chance to study its 1) global properties, 2) surface arrangements, and 3) their detectable changes expected to happen, in sub-meter scale. What measurable scientific goals for the asteroid in this "once a millennium" event could transform our knowledge of planetary science and defense? The Apophis rendezvous mission aims to understand the characteristics of the small solar system body's nature. It also prepares for potential threats from natural objects by measuring in-situ surface, shape, rotation, and orbit changes expected to occur when the target asteroid passes close to the Earth in 2029. We will present an overview of the mission scheduled to be launched from late 2026 to early 2027 and introduce scientific objectives.

• The Bulletin of The Korean Astronomical Society
• /
• v.40 no.2
• /
• pp.45.1-45.1
• /
• 2015

Hayabusa is the JAXA's space mission that succeeded in sample-return from S-type asteroid (25143) Itokawa. During the rendezvous phase, more than a thousand of images were taken with the Asteroid Multi-band Imaging Camera (AMICA). It is valuable to study the regional variation of the optical properties on the asteroid using these images to know the generality and uniqueness of the returned samples. In addition, AMICA images are important in that they provide unique data set at low phase angle (i.e Sun-Itokawa-AMICA's angle) that have not been explored in the previous asteroidal missions. At the previous conference (2015 KAS spring meeting), we introduced our preliminary data analysis of AMICA data without considering the shape model of Itokawa and mentioned. In this study, we present a new result obtained through further analysis, taking account of the shape model of the asteroid. We thus utilized "plate_renderer" tool to derive Hapke model parameters at different terrains. It is found that the opposition amplitude (parameter B0) is consistent with those of the other S-type asteroids while the opposition width (parameter h) is significantly narrower than those of the other S-type asteroids. At this conference, we plan to describe the regional variation of photometric properties on Itokawa.

• The Bulletin of The Korean Astronomical Society
• /
• v.37 no.1
• /
• pp.98.1-98.1
• /
• 2012

The Hayabusa mission successfully rendezvoused with its target asteroid 25143 Itokawa in 2005 and brought the asteroidal sample to the Earth in 2009. This mission enabled to connect the S-type asteroids to ordinary chondrites, the counterpart meteorites which exist in near Earth orbit. Recent finding of a fragment from 25143 Itokawa [1] suggested that the asteroid experienced an impact after the injection to the near-Earth orbit. In this presentation, we investigated the evidence of the recent impact on 25143 Itokawa using the onboard camera, AMICA. AMICA took more than 1400 images of Itokawa during the rendezvous phase. It is reported that AMICA images are highly contaminated by lights scattered inside the optics in the longer wavelength. We developed a technique to subtract the scattered light by determining the point spread functions for all available channels. As the result, we first succeeded in the determination of the surface spectra in all available bands. We consider a most fresh-looking compact crater, Kamoi, is a possible impact site.

• The Bulletin of The Korean Astronomical Society
• /
• v.46 no.1
• /
• pp.44.1-44.1
• /
• 2021

We plan to visit the Apophis, a Potentially Hazardous Asteroid (PHA). Apophis will have an extremely close encounter with the Earth on April, 2029. At the closest position, Apophis approaches 0.1 lunar distances from the Earth. The science goals are 1) mapping the surface of the asteroid before and after the encounter, 2) measuring surface roughness before and after the encounter, and 3) measuring interplanetary space environments such as magnetic field and dust particles. For the science goal, we are planning to employ five instruments for this mission, which are Polarimetric Asteroid Camera (PolACam), Asteroid Terrain Mapping Camera (MapCam), Laser Altimeter, Dust Particle Detector (DPDetector), Magnetometer (Mag). In this presentation, we plan to give a talk on the instruments.

• The Bulletin of The Korean Astronomical Society
• /
• v.46 no.2
• /
• pp.59.1-59.1
• /
• 2021

The Korean spacecraft for the exploration of Apophis will be equipped with an optical navigation camera with a wide-angle lens. The major purpose of the wide-angle camera is to capture imagery during the rendezvous phase in order to determine the spacecraft's position and the pointing direction relative to the asteroid Apophis. Two potential sciences, however, can be achieved by the wide-angle camera: (1) to measure the high-order gravity terms, and (2) to capture possible ejecting small particles. In this presentation, we will discuss instrument specification and operation scenario required to accomplish the given science objectives.

• The Bulletin of The Korean Astronomical Society
• /
• v.46 no.2
• /
• pp.57.3-57.3
• /
• 2021

99942 Apophis is an Sq-type Potentially Hazardous Asteroid (PHA) with an estimated diameter of 370 m. It will approach the Earth down to 31,000 km from the surface during the encounter on April 13, 2029 UT, which is closer than geostationary satellites. This once-in-a-20,000 year opportunity would further expand our knowledge on the physical and dynamical processes which are expected to occur due to the gravitational tidal forces when an asteroid encounter with a planet. It will also provide an opportunity to promote great knowledge of the science of planetary defense. The science goal of the Apophis mission is to global-map the asteroid before and after the Earth's approach. In this talk, we will present scientific objectives, and briefly introduce instruments and operation scenarios of the mission.