Asteroid Grand Tour Options

[nprev]

This article from JPL describes recent efforts to derive a main belt multi-asteroid mission trajectory...any of you orbitsmiths out there have some early thoughts/observations?

[elakdawalla]

Last year's was a very different challenge. From the Problem Description (PDF):

The main objective of the optimisation is to maximise the change in the semi-major axis of the asteroid 2001 TW229 subsequent to the impact of an electric propelled spacecraft.

1-The target
Consider the asteroid 2001 TW229 and its osculating orbital elements in the J2000.0 heliocentric ecliptic reference frame:

a (semi-major axis, AU): 2.5897261
e (eccentricity): 0.2734625
i (inclination, deg.): 6.40734
ω (argument of pericenter, deg.): 264.78691
Ω (Right Ascension of the Ascending Node, deg.): 128.34711
M (mean anomaly at epoch 53600 MJD, deg.): 320.47955

2-The spacecraft
Consider a nuclear electric propelled spacecraft with a wet mass of 1500 kg (dry mass can be considered to be zero) and equipped with a thruster with the following capabilities: specific impulse Isp=2500 sec., maximum thrust level T=0.04 N.

3-The mission
The spacecraft has to be transferred from Earth to the asteroid 2001 TW229 with a launch in [3653-10958] MJD2000 (Modified Julian Date 2000), corresponding to years 2010 to 2030. The maximum time of flight is 30 years. At arrival the quantity {equation: J = mf |U-rel dot v-ast|} has to be maximised, where mf is the final mass of the spacecraft, U-rel is the velocity of the spacecraft relative to the asteroid at arrival and v-ast
is the heliocentric velocity of the asteroid. The launcher available for the mission is able to provide a 2.5 km/sec escape velocity to the spacecraft with no constraint on the escape asymptote direction. Consider also a constraint on the minimum allowed heliocentric distance of 0.2 AU.

4-The dynamical models
Consider only the Sun gravity as an external force acting on the spacecraft. Planets may be used to perform swing-bys, in this case the effect should be modelled as an instantaneous direction change on the spacecraft velocity relative to the planet, subject to a constraint on the angle magnitude (a minimum pericenter radius has to be considered, see table below for details). The planet ephemerides used should have an accuracy equivalent to that of JPL DE405 ephemerides (http://ssd.jpl.nasa.gov/horizons.html). Use the numerical values given below and assume the astronomical unit equal to AU=1.4959787066e+008 km, and the Earth standard gravitational acceleration to g0=9.80665 m/s2.

CODE

Mercury Venus Earth Mars Jupiter Saturn Sun
Gravitational Constant, km^3/sec^2
22321 324860 398601.19 42828.3 126700000 37900000 1.32712428 e+011
Minimum pericenter radius allowed during fly-by, km 2740 6351 6678 3689 600000 70000 N/A

I'm more interested in this year's results...I'd love to see a multi-asteroid tour. Dawn will get two, but that's in part because it's aiming for two very specific ones, and is going into orbit at both. Another mission that was less constrained could surely survey more in shorter time.

--Emily