ESA Advanced Concepts Team (ACT) Analysis of Potential Asteroids to Visit

 Figure 1: Orbits of the best 10 asteroids for human missions (Source: ESA ACT).

The Advanced Concepts Team (ACT) of the European Space Agency (ESA) has been looking at potential asteroids to visit. From their news release...

Human missions to asteroids (as recently announced by US President Obama* on April 15 at the Kennedy Space Centre) are in several aspects different from those to Mars or to the Moon, among others because of the wide choice: there are millions of them in the Asteroid belt between the orbits of Jupiter and Mars and thousands in the Near Earth vicinity (NEAs). Not all of these are equally easy and safe to reach – and return from.

The team has taken up the challenge of filtering the good ones out finding possible return trajectories to all known asteroids.

For a first human mission to an asteroid after 2020, one can assume some basic requirements in order to help downselecting a list of interesting asteroids:

• The asteroid should be not too small in order to be able to eventually land and take samples;
  
• A minimum stay on the asteroid should be guaranteed to allow for a useful scientific return.
  

Furthermore, it is reasonable to assume some further human-related constraints, such as:

• The trajectory should allow for a safe way to return rapidly to Earth in case of problems up to half way to the target asteroid.
• The overall mission duration should not be too long in order to keep the journey bearable for astronauts.
  

As well as some technical constraints such as:

• No new revolutionary propulsion system by 2020 - thus delta V values within the range of current capabilities.
  
• A maximum hyberbolic excess velocity relative to Earth of 4.5 km/s for the return leg so as to allow for a safe landing of the return capsule.

The technical parameters used for the selection are:
Table 1: Baseline for asteroid selection

Apparent magnitude (corresponding to roughly 200m)	H ≤ 22
Time of flight	< 1.5 years
Stay time on the asteroid	> 5 days
Relative velocity at Reentry	4.5 km/s
Propulsion	Chemical, with 1 deep space manoeuvre per leg
Launch V infinity	6 km/s

Table 2 lists those asteroids considered as the prime candidates for such a mission.

Table 2: Preliminary list of best suited asteroids for a human mission

Id	Designation	Nominal  deltaV (km/s)	Nominal return time of flight (days)	Emergency return time of flight (days)	Emergency return deltaV (km/s)	Asteroid orbit's semi major axis a (AU)	Asteroid orbit's eccentricity e
323	2000 EA14	6.590	405	195	6.022	1.11	0.2
1365	207945 (1991 JW)	6.937	414	70	3.167	1.03	0.12
1109	2002 TD60	8.776	365	110	5.107	1.20	0.08
434	998 HG49	7.141	405	80	2.654	1.20	0.11
853	2001 QC34	7.428	379	85	2.349	1.12	0.19
1000	2002 OA22	8.675	389	90	2.803	0.94	0.24
1595	2000 OK8	8.931	500	90	4.043	0.98	0.22
515	2006 YF	8.217	448	195	6.677	1.11	0.19
1109	2002 TD60	8.776	365	110	5.107	1.20	0.08
209	65717 (1993 BX3)	8.505	248	120	1.808	1.39	0.28
1527	2006 HR29	9.187	500	120	3.613	0.98	0.26
173	2006 SU49	7.197	230	170	1.019	1.41	0.31
1491	2006 KL21	8.015	373	170	1.836	1.2	0.12
222	2004 KE1	8.561	320	130	2.256	1.30	0.18
66	25143 Itokawa	7.274	261	140	1.945	1.32	0.28
304	2006 QQ23	8.155	249	145	6.167	0.80	0.29
1685	1999 RA32	7.959	369	175	2.160	1.03	0.09
122	2002 TC70	8.714	405	150	2.839	1.37	0.20
1444	2007 SQ6	7.428	369	180	6.629	1.04	0.14
468	10302 (1989 ML)	7.701	351	165	3.622	1.27	0.14

Link: ACT News Item