Over the last 50 years, remarkable planetary missions significantly expanded our knowledge of bodies throughout the Solar System. International cooperation has been an essential factor for maximizing the scientific output of many of these missions. In the past decades, Korea has made considerable progress in space research and technological development through cooperation with other countries.
Another opportunity for international cooperation in space science will occur on April 13, 2029 when the asteroid (99942) Apophis passes close to Earth. Objects as large as Apophis (340 m) only pass this close to Earth (with 0.1 lunar distances, closer than the orbit of geosynchronous satellites) every thousand years, on average. This event thus represents an incredibly rare natural "experiment" of subjecting the physical body of Apophis to Earth's tidal torques, altering its orbit, and potentially also producing observable internal or surficial changes, as indicated in "Apophis 2029: Decadal Opportunity for the Science of Planetary Defense".
The importance of this event and its sigificance for science, planetary defense, and general public engagement was recently highlighted on higly-successful "Apophis T-9 Years: Knowledge Opportunities for the Science of Planetary Defense" workshop with 300 participants and 60 presentations, representing 10 countries. In particular, a need for close-up characterization of asteroid Apophis prior, during, and after its fly-by was highlighted at several occasions. Among the mission concepts presented on the meeting was the "Rendezvous Mission to Apophis" (RMA) by our Korean colleagues. Currently, Dr. Young-Jun Choi is leading together with Dr. Hong-Kyu Moon the mission study in Korea, and is scheduled to present the concept to the Korean government for possible selection in autumn of this year.
We are convinced that the upcoming Apophis close pass to Earth represents a unique opportunity for asteroid exploration providing direct knowlege for the science of Planetary Defense. History demonstrates that investigation of the Apophis 2029 encounter will benefit from joint international cooperation rather than competition, just as the AIDA collaboration will lead to a better science return than either the DART or Hera missions alone would return. There is wide range of practical steps through which such cooperation can evolve – from wider science community support, joint data analysis, through possible hardware contributions or mission operations support, to the possibility of tandem missions performing complementary investigations.
In the spirit of Asteroid Day 2021, we invite members of the wider international scientific community to express your interest in RMA and support its adoption by the Ministry of Science and ICT of Korea.
Young-Jun Choi (KASI), mission PI
Hong-Kyu Moon (KASI), mission Co-PI
Richard Binzel (MIT) and Patrick Michel (CNRS), organizers of Apophis T-9 Years workshop
Tomas Kohout (Univ. Of Helsinki), international support coordinator
99942 Apophis
99942 Apophis is a silicate Potentially Hazardous Asteroid (PHA) with an
estimated size of 340 m [1]. Shortly after its discovery, the prediction
suggested a maximum probability of 2.7% that the PHA could be sent into a
collision course with the Earth on April 13, 2029 [2]. However, coordinated
follow-on observations with ground-based telescopes and radars to track this
object provided significantly improved predictions over the subsequent years,
and the possibility of impact was removed [3].
Science with Apophis
Apophis will approach the Earth to come within the geostationary orbit during the encounter in the year 2029. Thus, it is expected to offer a unique opportunity to study either its 1) global properties (shape, surface topography, internal structure, and rotation and spin states), 2) the surface arrangements (regolith and boulder distributions, distributions of space weathered and newly exposed un-weathered regolith on the surface), or 3) their detectable changes that are expected to occur on the body during the approach [4]. The tidal encounter is expected to trigger varying degrees of observable changes in the dynamics, spin-states, and the surface arrangements of Apophis due to tidal forces caused by Earth's gravity field. The encounter in 2029 is expected to alter its surface topography with material movement such as landslide and mass ejection [5]. Hence, the only possible way to quantitatively study tidally induced effects is in-situ measurement by a dedicated space mission aimed at the encounter. This is why KASI proposes the proposed mission, Rendezvous Mission to Apophis (RMA). The Rendezvous Mission to Apophis (RMA) is based on the third revision of the Basic Plan for Promotion of Space Development (2018) of the Korean Government. The science and a number of proposed missions, including RMA [6], were presented at the "Apophis T-9 Years: Knowledge Opportunities for the Science of Planetary Defense" [7] workshop and "Apophis 2029: Decadal Opportunity for the Science of Planetary Defense" white paper submitted to the Planetary Science and Astrobiology Decadal Survey 2023-2032 [8].
References
[1]
Brozović M. et al. (2018) Icarus, 300, 115-128.
[2]
Giorgini J. D. et al. (2008) Icarus, 193, 1-19.
[3]
JPL Small-Body Database Browser: 99942 Apophis.
[4]
DeMartini J.V. et al. (2019) Icarus 328.
[5]
Lauretta D.S. et al. (2019) Science 366, 1192.
[6]
Moon H.-K. et al. (2020) Apophis T–9 Years 2020 (LPI Contrib. No. 2242) .
[7]
http://www.hou.usra.edu/meetings/apophis2020/
[8]
Binzel R. P. et al. (2021) Apophis 2029: Decadal Opportunity for the Science of Planetary Defense.
Spacecraft Platform
There are several options for the spacecraft platform
for the mission, including a small scientific satellite bus system with compact
and modular designs developed by KAIST and local companies in Korea. The other
options include a standard bus system for low earth orbit satellites developed
by domestic commercial partners in Korea.
Science Payloads
KASI established scientific goals for the proposed mission as described in
'Science with Apophis'; the study of 1) the global properties, 2) the surface
arrangements, and 3) their detectable changes predicted to occur on Apophis
before, during, and after the encounter on April 13, 2029. To achieve the
goals, the science definition team (SDT) is currently drafting the science requirements
for candidate payloads. Our list includes wide/narrow-angle cameras, a
polarimetric camera (a heritage from PolCam, Wide-Angle Polarimetric Camera)
[9] to be onboard the KPLO (Korea Pathfinder Lunar Orbiter) [10], an imaging
spectrograph, [11], and a laser altimeter.
Launch Windows
KASI conducted a preliminary
mission analysis for the RMA, and found that the launch windows in mid-2027 and
mid-2028 are the most probable opportunities. Our tentative plan is to 1)
design (2022-2023), 2) build, integrate, and test (2024-2026), 3) launch
(2027/28), and perform 4) science operations (2027/28-2029) with universities,
research institutes, and companies in Korea. However, it
is open to overseas institutes for joint scientific
studies and operations. One of our current options for the launcher is to use
the KSLV (Korea Space Launch Vehicle) series rocket in development.
[9]
Sim C. K. et al. (2020) PASP, 132, 015004.
[10]
Ju G. et al. (2013) 64th IAC, Abstract IAC-13.A3.2C.10.
[11]
Kohout. T (2018) Advances in Space Research, 62, 8, 2239-2244
