Proposal for a Multiple-Asteroid-Flyby Mission with Sample Return

Available online at www.sciencedirect.com

Advances in Space Research 50 (2012) 327–333 www.elsevier.com/locate/asr

Proposal for a multiple-asteroid-ﬂyby mission with sample return

Dong Qiao ⇑, Pingyuan Cui, Hutao Cui

Key Laboratory of Dynamics and Control of Flight Vehicle, Ministry of Education, School of Aerospace Engineering, Beijing Institute of Technology, Beijing 100081, China

Received 22 November 2010; received in revised form 15 March 2012; accepted 13 April 2012 Available online 21 April 2012

Abstract

Asteroid exploration provides a new approach to study the formation of the solar system and the planetary evolution. Choosing a suitable target and designing of feasible profile for asteroid mission are challenging due to constraints such as scientific value and technical feasibility. This paper investigates a feasible mission scenario among the potential candidates of multiple flybys and sample return missions. First, a group of potential candidates are selected by considering the physical properties and accessibility of asteroids, for the sample return missions. Second, the feasible mission scenarios for multiple flybys and sample return missions to various spectral-type asteroids are investigated. We present the optimized design of preliminary interplanetary transfer trajectory for two kinds of missions. One is the single sample return mission to asteroids with various spectral types. The other is the multiple flybys and sample return mission to several asteroids. In order to find the optimal profiles, the planetary swing-by technique and Differential Evolution algorithm are used. Ó 2012 COSPAR. Published by Elsevier Ltd. All rights reserved.

Keywords: Asteroid exploration; Multiple ﬂybys; Sample return; Planetary swing-by; Diﬀerential Evolution algorithm

1. Introduction during the asteroid flyby and deliver the sample to the Earth. Morimoto et al. proposed two types of sample return Asteroid exploration provides a new approach to study missions and investigated the feasible mission scenarios the origin of the solar system and the formation of the plan- (Morimoto et al., 2004). Sears et al. introduced the Hera ets, because the asteroids hold key information for under- mission concept that involves multiple near-Earth asteroid standing these problems. They are often called the ‘‘fossil” sample return (Sears et al., 2004). Dachwald et al. investi- of the solar system. In the past, asteroid and comet missions gated the feasibility of multiple rendezvous and sample such as NEAR, Hayabusa, Deep Impact, ROSETTA, return missions to the near-Earth objects using solar sail- DAWN have been carried out, and gained plenty of valu- craft (Dachwald et al., 2006), and discussed main-belt aster- able experience and scientific data. With many new asteroid oid sample return missions by using the solar electric missions in various stages under development (Hayabusa II, propulsion (Dachwald et al., 2008). Don Quijote, Hera), our understanding of these celestial In this paper, we have primarily aimed this study at two bodies could be further improved in the future. aspects. On one hand, by considering physical properties, The sample return missions are able to obtain more phys- potential scientific value, and accessibility of asteroid, a ical details of the asteroids. Thus they attract more and more group of candidates are selected for the sample return mis- attention. Sukhanov et al. proposed main-belt asteroid sam- sions. On the other hand, we investigate the feasible mission ple return without landing on the asteroid (Sukhanov et al., scenarios for the sample return missions with multiple-aster- 2001). The proposed mission aims to collect the sample oids flybys. Two kinds of missions are considered: the single sample return missions to various spectral-type asteroids ⇑ Corresponding author. and the multiple-flybys and sample return missions to E-mail address: [email protected] (D. Qiao). several asteroids.

2. Target selection for sample return missions on basis of the radar observation data. Among the C-type asteroids, Nereus is a well-known asteroid and was selected It is generally believed that a large number of small as the target for NEAP missions. bodies including asteroids and comets were left over as D-type and P-type asteroids have low albedo and are remnants of the formation of the solar system. Asteroids redder than the C-type ones. Their properties are thought represent a large part of these primordial objects and reside to be of the most primitive origin. D-type asteroids such throughout the solar system since its formation. Therefore, as (3552) Don Quixote and 1997 SE5 show some charac- asteroid exploration, especially the sample return, can teristics of extinct comets (Hicks et al., 1998, 2000). From obtain more mineralogical composition details of asteroids the hazard assessment and the resource utilization points and greatly enhance our understanding of the planetary of view, M-type asteroids that may have high metallic con- formation and evolution process. tents by virtue of high radar albedo are perhaps the most Asteroids are categorized into many populations. Among practical interests among the NEAs (Tedesco et al., these populations, the Near-Earth Asteroids (NEAs), whose 1987). Two most notable asteroids among the M-type dynamic characteristics allow close approaches to our pla- NEAs are (3554) Amun and (6178) 1986DA. net, are gaining increasing attention. The attention to NEAs V-type asteroids are widely believed to be the fragments is due to not only their apparent scientific value and technical of the basaltic surface of the large main-belt asteroid 4 feasibility, but also their potential risk of collision with the Vesta, and are thought to be possible parent bodies of Earth. For selecting the target for an asteroid mission, it is the Howardite–Eucrite–Diogenite meteorites. Therefore, undoubted that the NEAs should take priority of the poten- V-type objects, such as (3361) Orpheus, (6489) Golevka, tial candidates. and (3908) Nyx, are also regarded as the primary targets. The NEA population consists of several sub-categories, E-type asteroids show appear both compositional and such as Atens, Apollos, Amors and Apohele. The Aten aster- dynamical relation to the Hungaria region (high incli- oids have a semimajor axis a less than that of the Earth and nation objects) of the inner asteroid belt (Gaffey et al., aphelia Q larger than Earth’s perihelion distance (a <1 1992). Among the E-type objects, (3103) Eger, 1989ML, AU, Q > 0.983 AU). The Apollo asteroids have a semi-ma- 1998WT24, and 1991VH are well known. jor axis greater than that of the Earth and perihelia q inside Q-type asteroids have spectra similar to that of the the aphelion distance of the Earth (a > 1AU, q < 1.017 ordinary-chondrite meteorites in laboratory (Bus et al., AU). The Amor asteroids are those with perihelia 2002). S-type asteroids have higher albedo and their approaching from outside of the orbit of our planet reddish spectrum are characterized in the near-infrared side (A > 1 AU, 1.017 < q < 1.3 AU). In addition, the Apo- by the absorption bands of pyroxene and olivine. The rela- hele (or Inner-Earth Objects, IEOs), whose orbits reside en- tion between these two types of asteroids and the ordinary- tirely inside that of the Earth (Q < 0.983 AU), has been chondrite meteorites has been debated for decades. The also proposed for one additional group of NEAs, although exploration and sample return of Q-type and S-type aster- in practice the Aten group could be extended to include oid can help solving the controversial problems. Among these objects. these Q-type and S-type objects, there are a quantity of The physical properties of asteroid, such as taxonomy, notable Q-type asteroids such as Akka, 1991VK, 1998PG, shapes, rotations, and optical properties, may provide and well-known S-type objects such as Toutatis, McAuliffe, important clues for the evolution of the planetary dynam- Seleucus, Geographos, Ivar, Anteros. ics, the origin of the solar system, and other significant In addition, other physical properties, such as the exotic topics. Among them, the taxonomic classifications and rotation states, the binary system, and the elongated shape, the mineralogical interpretations provide evidence for are also significant factors influencing scientific target selec- understanding the origin and the formation of the solar tion because these properties can help us understand some system. Almost all the taxonomic classes of the main-belt important problems, notwithstanding the fact that these asteroids are represented among the NEAs, including some properties alone are not sufficient to conclusively reveal peculiar types in the outer asteroid belt. The spectral type the origin of an individual NEA. For example, 1996FG3, and the mineralogical characterization may be extremely Dionysus, Didymos, and 1998PG show the double light- useful information for pinpointing source regions of NEAs curve binary. and their dynamical evolution. When selecting candidates for mission, the accessibility For instance, the low-albedo primitive C-type bodies of asteroids need to be considered, as it happens that some would represent samples of the pristine material character- objects are ‘‘the best candidates” from a scientific point of izing the outer main-belt asteroids. Among the C-type view but don’t satisfy the technical requirements. The mea- targets, we choose Wilson-Harrington, 1996 FG3, Nereus sure of accessibility is generally the minimum total velocity asteroids as candidates. Wilson-Harrington appears to be increments for two-impulse transfer to rendezvous with the consistent with the primitive solar-system materials pre- target body. In previous literature, some classical methods sumed to dominate in comets (Fernandez et al., 1997). for evaluating accessibility of asteroid, such as the Hoh- 1996 FG3 asteroid may be composed of the primitive mann transfer (Perozzi et al., 2001; Binzel et al. 2004), main-belt composition and is double light-curve binary the global optimal two-impulse transfer (Hulkower et al., D. Qiao et al. / Advances in Space Research 50 (2012) 327–333 329

Table 1 Potential candidates for sample return mission. Name NEA group Spectral type Diameter (km) Rotation period (hr) Nereus AP C; E; X 0.51 0.33 0.24 15.16 1996FG3 AP C; X 1.6 3.5942 + 16.14 Wilson-Harrington AP CF 3.46 3.556; 6.1 Dionysus AM Cb 1.0 1.5 2.7053 + 27.74 Eger AP E; Xe 1.78 5.7059 1989ML AM E; X 0.28 19 1991VH AP Sk, Sq 1.12 2.6236 + 32.66 1998WT24 AT E; Xe 0.415 3.6877 1986DA AM M 2.3 3.58 Amun AT M; X 2.1 2.53 1997SE5 AM D; T 3.8 9.0583 Don Quixote AM D 18.7 7.7 Didymos AM Xk 0.8 1.7 2.2593 + 11.91 (3908) Nyx AM V 1 4.4260 (6489) Golevka AP V; Sq; Q 0.35 0.25 0.25 6.02640 (3361) Orpheus AP V 0.5 3.58 Akka AM Q 0.8 7.283 1998PG AM Q; Sq 1.0–2.3 2.5162 + 14.01 Toutatis AP S; Sk 2.8 176 + 130 McAuliﬀe AM S; A 2.3–5.1 6 1991VK AP S; Sq; S 1.4 4.2096 Seleucus AM S; K 3.4 1.4 1.4 75. Geographos AP S 5 2 1.5 5.2233 Ivar AM S 9.12 4.795 Anteros AM S; L 2.43 2.8695 Information on the physical properties of our sample was retrieved from the NEODyS internet database (http://newton.dm.unipi.it/neodys/index.php).

1984; Lau et al., 1987), and the planetary swing-by method Earth. Here, the separate maneuver of the capsule is not (Qiao et al., 2006; Cui et al., 2010), were introduced. considered. As a result, the potential candidates and their relevant The work presented here is limited to the impulsive physical parameters are summarized and listed in Table 1. maneuver. In this section, we only consider single sample return. It is assumed that two trajectory sequences are proposed to design the transfer trajectories of sample return mis- 3. Mission design of sample return for various spectral-type sions. They are: (a) Launch from the Earth ! Rendezvous asteroids with the target ! Stay and sample ! Return to the Earth; (b) Launch from the Earth ! Swing-by ! Rendezvous with In this section, we investigate the preliminary design of the asteroid ! Stay and sample ! Return to the Earth. feasible transfer trajectories for sample return missions. It is assumed that, when collecting sample, the velocity and 3.1. The transfer trajectory of sample return mission the position of the spacecraft relative to the target asteroid both should both be zeros. After accomplishing sam- Based on the assumptions above, the objective function of ple mission, an impulse velocity is required for departing primary mission design can be given as the sum of velocity from the asteroid. When arriving at the Earth, a sample increments including impulses for escape from the Earth- return capsule will be released from the spacecraft. The parking orbit (circular, 200 km altitude) DtL, for rendezvous capsule will reenter the atmosphere and land on the with the asteroid Dtrend, and for departure from the asteroid

Table 2 Optimal samples return proﬁles for potential candidates. 2 2 Asteroid Launch period Date of Rend. Stay time day Mission duration, yr Launch C3km /s Dtrend. km/s Dtdep .km/s t1Er. km/s Nereus Jan. 2018 Jan.08, 2020 180 4.09 30.9 1.18 0.11 5.77 Nyx Oct. 2015 Nov.15,2017 485 5.05 35.7 0.97 0.58 8.33 1989ML Jul. 2025 Jun.28, 2026 744 3.98 13.3 0.87 1.32 3.72 Toutatis Oct.2020 Nov.19,2023 535 8.10 61.2 0.80 0.31 10.7 Seleucus May2023 May24,2025 306 4.99 48.9 1.11 0.98 7.64 Anteros May2016 Aug.18,2017 196 2.99 32.2 1.20 0.96 6.95 1991VK Jan. 2022 Jun.24,2023 728 5.02 44.5 0.57 0.75 7.03 330 D. Qiao et al. / Advances in Space Research 50 (2012) 327–333

Dtdep.. Considering the chemical-propelled ballistic trajecto- 59.03%, respectively. The 2:1DV–EGA transfer profile for ries, a trajectory of the sample return mission can be divided Q-type 1991VK asteroid has 0.65 km/s and 19.04 km2/s2 into several trajectory segments. For a single trajectory decrease in the total velocity increments and the launch segment, the pork-chop plots method (Longuski et al., energy, respectively. In this paper, we just adopt the Earth 1991) can be used to get a quick estimation of the velocity swing-by to reduce total velocity increments and launch increments and the rendezvous/return opportunity. The energy. If the Venus swing-by or the Venus-Earth swing- obtained optimal sample return opportunities are listed in by is applied to the design of missions, there could be more Table 2. opportunities. In Table 2, C3, Dtrend., and Dtdep. are the launch energy, the velocity increments at rendezvous and at departure, 4. Mission design of multiple-asteroid-flyby and sample respectively. t1Er. is the hyperbolic Earth arrival velocity. As shown in Table 2, Nereus, Nyx, 1989ML and Anteros return asteroid have feasible sample return opportunities. The total flight time of the mission to S-type Anteros asteroid, In this section, we mainly investigate the preliminary which is about 2.99 years, is the shortest. From Table 2,it design of the feasible transfer trajectories for the sample can be seen that S-type Toutatis asteroid needs the maxi- return missions with multiple flybys. It is assumed that the mum launch energy, which implies that the planetary trajectory sequences are: Launch from the Earth ! Plane- swing-by technique should be used. Here, we just provide tary swing-by ! Multiple asteroids flybys ! Rendezvous the rendezvous opportunities on basis of the impulsive with another asteroid ! Stay and sample ! Return to the transfer. If the electric propulsion or the solar sail is Earth. applied to the interplanetary missions, there could be more To design a trajectory of such mission, the trajectory is opportunities. divided into several segments, and then a trajectory candi- date is found to satisfy many constraints and to connect each segment. The optimal and feasible transfer trajectories 3.2. The transfer trajectory of sample return mission with may be very sensitive to initial conditions. Using tradi- Earth swing-by tional optimization methods (such as the gradient search) to search from the initial conditions, it is difficult to find In Table 2, S-type Toutatis and Q-type 1991VK require an optimal result. Therefore, it is needed to perform a more launch energy for the rendezvous missions. This leads global search, i.e. searching over some given range of the us to adopt the planetary swing-by technique to reduce the permissible initial conditions. Here, the Differential Evolu- launch energy and extend the original two-impulsive trans- tion (DE) algorithm will be used. fer. Here, 2:1DV–EGA technique is used (Sim et al., 1997). The design parameters about S-type Toutatis and Q-type 1991VK with 2:1DV–EGA are listed in Table 3. 4.1. The problem statement As shown in Table 3, the total velocity increments Dttotal and the launch energy C3 required for rendezvous and sam- It is assumed that the trajectory consists of n legs. The ple return from the asteroid are reduced significantly by total velocity increments Dttotal of the mission are the sum using 2:1DV–EGA transfer technique. Compared with the of the velocity changes that are performed: at Earth escape direct two-impulsive transfer, the total velocity increments from the parking orbit (circular, 200 km altitude) DtL,at Dttotal and the launch energy C3 of 2:1DV–EGA transfer rendezvous with the target asteroid Dtrend, at departure for S-type Toutatis asteroid decrease by 15.59% and from the asteroid Dtdep., and the deep-space maneuver Dtmi

Table 3 Samples return proﬁles with Earth swing-by strategy. S-type Toutatis Q-type 1991VK Direct transfer 2:1DV-EGA Direct transfer 2:1DV-EGA Date of Launch Oct. 31, 2020 Dec. 07, 2018 Jan.14, 2022 Feb.11, 2020 Date of Earth Swing-by – Oct. 29, 2020 – Jan.15, 2022 Swing-by altitude (km) – 1176 – 3459 Date of Rendezvous Nov. 19, 2023 Nov. 18, 2023 Jun. 24, 2023 Jun.24, 2023 Date of Departure May 07, 2025 May 07, 2025 Jun. 21, 2025 Jun.21, 2025 Date of Return Earth Dec. 04, 2028 Dec. 04, 2028 Jan.19, 2027 Jan.19, 2027

Dttotal(km/s) 6.84 5.77 6.41 5.76 2 2 C3 (km /s ) 61.2 25.1 44.5 25.5 Midcourse Dt (km/s) – 0.36 – 0.21

Dtrend.(km/s) 0.80 0.79 0.57 0.48 Dtdep.(km/s) 0.31 0.31 0.75 0.75 t1Er. (km/s) 10.7 10.7 7.04 7.04 Mission duration (yr.) 8.10 10 5.02 6.94 D. Qiao et al. / Advances in Space Research 50 (2012) 327–333 331

(i = 1,....,n - 1). So the total velocity increments can be addition, it patches the swing-by trajectories together by described as: the matching conditions, which involves matching the Xn1 magnitude of an incoming hyperbolic excess velocity Dttotal ¼ DtL þ Dtrend þ Dtdep: þ Dtmi i t1 with the magnitude of the outgoing hyperbolic excess velocity t1+. It is assumed that the matching error is For this problem, the launch time tL, the ﬂyby time tf, Dt1, and then the rendezvous time ta, the deep-space maneuver time tm, the departure time ta, the planetary swing-by time ts, Dt1 ¼jt1þ t1j and the deep-space maneuver position rm are chosen as the variables of the objective function. The planetary In this paper, the matching error Dt1 is less than 0.001 km/s. In order to obtain the trajectories that are clo- swing-by altitude hs, where hs deﬁnes the height over the planet atmosphere surface in order to avoid entering ser to the actual mission requirements, the JPL DE405/406 atmosphere, is regarded as the inequality constraints. In planetary ephemeris is used.

Table 4 The optimal results for transfer trajectories of multiple-asteroid-flyby with sample return mission. Sample return for Didymos Sample return for 1991VK Sample return for Nereus Sample return for Akka Date of Launch Oct. 26, 2018 Feb.13,2020 Dec. 23,2015 Jul. 25, 2018 Date of Earth Swing-by Nov. 09,2020 Jan. 14,2022 Jan. 8,2018 Jul. 04, 2020 Swing-by altitude (km) 61758 2861 41435 7982 Flyby asteroid I 8685 Faure 1900 Katyusha 16947 Wikrent C-type Nereus Date of flyby I Jan. 08,2022 Nov. 04,2022 Jul.21,2018 Apr. 22, 2022 Flyby asteroid II – – 6100 Kunitomoik. V- type Nyx Date of flyby II – – Jun. 29,2019 Feb. 06, 2024 Date of rendezvous Jul. 03,2022 Jun. 24,2023 Jan. 08,2020 Dec. 28, 2024 Date of departure Jun. 17,2023 Jun. 21,2025 Jul. 07,2020 Sep.11, 2027 Flyby asteroid III 17993 Kluesing 1653 Yakhonto. 5667 Nakhimovs. – Date of flyby III Nov. 11,2023 Aug. 04,2025 Jun. 20,2021 – Date of return Nov. 13,2024 Jan. 20,2027 Feb. 08,2022 Jul.17, 2029

Dttotal (km/s) 5.98 6.29 6.30 7.03 2 2 C3 (km /s ) 25.8 25.3 25.4 26.6 Dtrend (km/s) 0.83 0.63 1.23 0.67 Dtdep (km/s) 0.49 0.55 0.15 0.96 Midcourse Dt (km/s) 0.32 0.79 0.61 1.02 t1Er (km/s) 7.97 7.12 5.89 5.89 Mission duration (yr.) 6.07 6.93 6.21 11.0

Fig. 1. Flight path of Akka sample return mission with multiple diﬀerent spectral-type asteroid ﬂybys. 332 D. Qiao et al. / Advances in Space Research 50 (2012) 327–333

Table 5 vector exceed the corresponding upper and lower bounds, The mission parameters of multiple-asteroid-flyby with Nyx asteroid we randomly and uniformly reinitialize them within the sample return. prespecified range. Then, the objective function values of Event Parameters Remark all trail vectors are evaluated. After that, a pruning is Launch Nov. 19,2013 — performed. The objective function value of each trial vector Earth Swing-by Oct. 28,2015 13142 km (Swing-by altitude) is compared to that of its corresponding target vector in the Flyby asteroid I Jun. 20,2016 Flyby 10646 Machielalberts current population. If the trail vector has no greater objec- Flyby asteroid II Sep. 27,2016 Flyby 8644 Betulapendula Flyby asteroid III Jul. 03, 2017 Flyby 8775 Cristata tive function value than the corresponding target vector, Rendezvous Nov. 16,2017 Rendezvous with Nyx the trial vector will replace the target vector and enter the Departure Mar. 16,2019 Departure from Nyx population of the next generation. Otherwise, the target Flyby asteroid IV Feb. 07,2020 Flyby 2828 Iku-Turso vector will remain in the population for the next generation. Return Earth Nov. 13,2020 – It is known that the quality of solutions obtained with DE C (km2/s2) 25.2 – 3 algorithm is very sensitive to the selection of the routine’s Dttota l (km/s) 6.98 – Dtrend. (km/s) 1.04 – tuning parameters. By comparing various tuning parameter Dtdep. (km/s) 0.58 – combinations for a variety of complex interplanetary mis- Midcourse Dt (km/s) 1.04 – sion scenarios, a set of tuning parameters were identified as t1Er. (km/s) 8.59 – being superior for solving general interplanetary trajectory Mission duration (yr.) 6.98 – problem (Olds et al. 2007). In this paper, set of tuning parameters NP =28,CR = 0.8, F = rand [1,1] are selected. 4.2. The optimization technique

Differential Evolution is a stochastic direct search method 4.3. Search and optimal results that uses a set of parameter vectors that interact in a way that is inspired by the evolution of living species. The initial pop- In this section, various spectral-type asteroids are ulation should better cover the entire search space as much selected as sample return targets to design transfer trajecto- as possible by uniformly randomizing individuals within ries with multiple-asteroid-flyby, and search a lot of trans- the search space constrained by the prescribed minimum fer profiles. The optimal results are listed in Table 4. and maximum parameter bounds. After initialization, DE From Table 4, it can be seen that the transfer profile of employs the mutation operation to produce a mutant vector X-type Didymos (see the second column in Table 4)and with respect to each individual, so-called target vector, in the Q-type 1991VK sample return missions (see the third col- current population. For each target vector at the generation, umn in Table 4) include two asteroids flybys, respectively. its associated mutant vector can be generated via certain For these profiles, one flyby happens before the sample mutation strategy. After the mutation phase, crossover return, the other is after that. The profile of C-type Nereus operation is applied to each pair of the target vector and (see the fourth column in Table 4) and Q-type Akka sample its corresponding mutant vector to generate a trial vector. return (see the last column in Table 4) comprise of three If the values of some parameters of a newly generated trial asteroid flybys. In Table 4, the X-type Didymos profile

Fig. 2. Flight path of Nyx sample return mission with multiple asteroid flybys. D. Qiao et al. / Advances in Space Research 50 (2012) 327–333 333 has the lowest total velocity increments Dttotal (5.98 km/s) 720000), National Natural Science Foundation of China and shorter flight time of mission (6.07 years) than others. (Nos. 10832004 and 11102020), Research Fund for the The Q-type Akka profile has smaller hyperbolic Earth Doctoral Program of Higher Education of China (No. arrival velocity than others, but its flight time of mission 20101101120001). China Postdoctoral Science Foundation exceeds 10 years. The flight path of Q-type Akka profile is (Granted Special Grade No. 200902049). In addition, the shown in Fig. 1. author also thank for Science and Technology Innovative In addition, the V-type (3908) Nyx asteroid is selected as the Research Team of Beijing Institute of Technology, and sample return target to design the transfer trajectories with four suggestion of Prof. Huang Fenglei. asteroids flybys and planetary swing-by. The optimal transfer profile and some key parameters are shown in Table 5. References As seen in Table 5, the spacecraft is planned to be launched from the Earth on Nov. 19, 2013. Then it will have Binzel, R.P., Perozzi, E., Rivkin, A.S., Rossi, A., et al. Dynamical and three asteroids flybys, the 10646 Machielalberts (Main-belt compositional assessment of near-Earth object mission targets. Mete- orit. Planet. Sci. 39 (3), 351–366, 2004. asteroid) on Jun. 20, 2016; the 8644 Betulapendula Bus, S.J., Binzel, R.P. Phase II of the small main-belt asteroid spectro- (Main-belt asteroid) on Sep. 27, 2016, the 8775 Cristata scopic survey: a feature-based taxonomy. Icarus 158 (1), 146–177, (Main-belt asteroid) on Jul. 03, 2017; and then rendezvous 2002. with the 3908 Nyx asteroid on Nov. 16, 2017. It will depart Cui, P.Y., Qiao, D., Cui, H.T., Luan, E.J. Target selection and transfer from the Nyx asteroid on Mar. 16, 2019, and then have a trajectories design for exploring asteroid mission. Sci. China Technol. Sci. 53 (4), 1150–1158, 2010. flyby the 2828 Iku-Turso (Main-belt asteroid) on Feb. 07, Dachwald, B., Seboldt, W., Loeb, H.W., Schartner, K.H. Main belt 2020. Finally, it will return to the Earth on Nov.13, 2020. asteroid sample return mission using solar electric propulsion. Acta The total flight time is about 6.98 years. The flight path is Astronaut. 63 (1–4), 91–101, 2008. shown in Fig. 2. Dachwald, B., Seboldt, W., Richter, L. Multiple Rendezvous and sample return missions to near-earth objects using solar sailcraft. Acta Astronaut. 59 (8–11), 768–776, 2006. 5. Conclusions Fernandez, Y.R., McFadden, L.A., Lisse, C.M., Helin, E.F., Chamberlin, A.B. Analysis of POSS images of comet-asteroid transition object In this work, we first propose a group of potential candi- 107P/1949 W1 (Wilson–Harrington). Icarus 128 (1), 114–126, 1997. dates of the asteroid flybys and sample return mission to be Gaffey, M.J., Reed, K.L., Kelley, M.S. Relationship of E-type Apollo launched in the future. After an extensive study of the phys- asteroid 3103 (1982 BB) to the enstatite achondrite meteorites and the Hungaria asteroids. Icarus 100 (1), 95–109, 1992. ical properties and the scientific value of asteroids, we select Hicks, M.D., Buratti, B.J., Newburn, R.L., et al. Physical observations of 25 potential candidates for the sample return mission. 1996 PW and 1997 SE5: extinct comets or D-type asteroids? Icarus 143 In addition, several feasible mission scenarios of single (2), 354–359, 2000. sample return and multiple-asteroid-flyby of sample return Hicks, M.D., Fink, U., Grundy, W.M. The unusual spectra of 15 near-Earth are investigated, respectively. One scenario is the single asteroids and extinct comet candidates. Icarus 133 (1), 69–78, 1998. Hulkower, N.D., Lau, C.O., Bender, D.F. Optimum two-impulse transfer sample return mission to various asteroids (such as C-type for preliminary interplanetary trajectory design. J. Guid. Control Dyn. Nereus, V-type Nyx, E-type 1989ML, S-type Toutatis, 7 (4), 458–461, 1984. Seleucus and Anteros and Q-type 1991VK). The other is Lau, C.O., Hulkower, N.D. Accessibility of near-Earth asteroids. J. Guid. the multiple flybys and sample return mission to several Control Dyn. 10 (3), 225–232, 1987. asteroids. The profiles of sample return with multiple-aster- Longuski, J.M., Williams, S.N. Automated design of gravity-assist trajectories to mars and the outer planets. Celest. Mech. Dyn. Astr. oid-flyby, whose target of sample return included X-type 52 (3), 207–220, 1991. Didymos, Q-type 1991VK, C-type Nereus, Q-type Akka Morimoto, M., Yamakawa, H., Yoshikawa, M., Abe, M., Yano, H. and V-type Nyx asteroid, are presented in detail. In order Trajectory design of multiple asteroid sample return missions. Adv. to find the optimal profiles, the planetary swing-by (DV- Space Res. 34 (11), 2281–2285, 2004. EGA) technique and DE algorithm are applied. Olds, A.D., Kluever, C.A., Cupples, M.L. Interplanetary mission design using differential evolution. J. Spacecraft Rockets 44 (5), 1060–1070, The DV–EGA technique is effective, but not the only 2007. approach to reduce the total velocity increments and the launch Perozzi, E., Rossi, A., Valsecchi, G.B. Basic targeting strategies for energy in the design of interplanetary mission. Some other tech- rendezvous and flyby missions to the near-Earth asteroids. Planet. niques, such as Venus-Earth, Venus-Venus-Earth or Venus- Space Sci. 49 (1), 3–22, 2001. Earth-Earth swing-by, are also adoptive. The minimum launch Qiao, D., Cui, H.T., Cui, P.Y. Evaluating accessibility of near-Earth 2 2 asteroids via Earth gravity assists. J. Guid. Control Dyn. 29 (2), 502– energy from Earth to Venus is about 8 9km/s . Therefore, 505, 2006. Venus used as swing-by planetary is attractive. In the future, Sears, D., Allen, C., Britt, D., et al. The hera mission: multiple near-Earth the techniques mentioned above may be studied and further- asteroid sample return. Adv. Space Res. 34 (11), 2270–2275, 2004. more, adopted to improve our work. Sim, J.A., Longuski, J.M., Staugler, A.J. V1 Leveraging for interplanetary mission: multiple revolution orbit technique. J. Guid. Control Dyn. 20 (3), 409–415, 1997. Acknowledgements Sukhanov, A.A., Durao, O., Lazzaro, D. Low-cost main-belt asteroid sample return. J. Spacecraft Rockets 38 (5), 736–744, 2001. This research was supported by the National Basic Tedesco, E.F., Gradie, J. Discovery of M class objects among the near- Research Program of China (973 program, No. 2012CB Earth asteroid population. Astron. J. 93 (3), 738–746, 1987.