MISSION PLAN - PDS Small Bodies Node

5.0 Earth Gravity Assist Phase (EGA-60 to EGA+30 days)
5.1 Overview
The Earth flyby is performed to provide a gravity assist to the STARDUST spacecraft
and reduce the ∆V requirements of the mission. The flyby changes the orbital period
from 2 years to about 2.5 years. The spacecraft approaches Earth with a velocity of 6.5
km/s from the dark side and recedes back into the dark side having flown by the sunward
side. At closest approach, the altitude, for a 02/06/99 launch, will be 5965 km, but could
be as low as 1649 km depending on the actual launch date of the mission. During the
flyby the Sun-Earth-Probe angle cycles from ~130° to 28° at closest approach to a
minimum of 19° (8 minutes after closest approach) and back up to ~90° toward the end
of the EGA phase. The Earth flyby time is also dependent on the actual launch date. For
planning purposes, the first launch date is assumed which results in a flyby date and time
of 15 January 2001 11:01:24 (ET), or L+708.5 days.
Three special activities are planned for the Earth Gravity Assist (EGA) phase. The first
is a rehearsal or demonstration of the navigation processes required during return to
Earth. This activity is envisioned to be a ground activity only and will not involve the
spacecraft or require any increase in DSN resources. The second is an opportunity to
take Earth-Moon images. The third and final activity is a Dust Flux Monitor Instrument
experiment. Its objective is to collect data on dust particles near Earth perigee, within the
near-Earth magnetosphere. Support of this activity will require the DFMI to be turned on
and for the spacecraft +x-axis to be oriented parallel to the spacecraft velocity vector as
the spacecraft flys through perigee.
As previously mentioned, the Earth flyby contributes substantially to the reduction of ∆V
requirements for STARDUST. As such, an accurate execution of this event is important.
The JPL navigation team has successfully navigated Earth flybys twice for the GALILEO
project and will have done it again for the CASSINI project. No difficulties are
anticipated.
The spacecraft trajectory, again for a 02/06/99 launch, in Earth-sun fixed coordinates for
this phase is shown in Figure 5.1-1. Subphases are defined in Table 5.1-1. A trajectory
data set containing the following parameters can be found in Section 9.3:
Earth-Probe Range
Sun-Earth-Probe Angle
Sun-Probe-Earth Angle
Moon-Probe Range
Sun-Moon-Probe Angle
Sun-Probe-Moon Angle
Table 5.1-1 Earth Gravity Assist Phase Subphase Definition
Mission Phase Subphases Time (L+days) Duration
(days)
Earth Gravity Assist 649 - 739 90
65