Subject: Re: "Dawn" Achieves Ceres Orbit
From: Daniel Adamo <[email-masked]>
Date: Sat, 04 Apr 2015 12:11:40 -0700

ATIG Members-

Updating Dawn's approach to (1) Ceres, the attached plot of Ceres-centered
motion has SEP thrusting modeled into the mid-April time frame.  This plot
is viewed from Ceres' equatorial plane in a direction looking "up" in the
plot sent March 8.  From the updated trajectory, SEP thrusting to achieve
Dawn approach over Ceres' north rotational pole is evident.  Planned SEP
thrusting in late April (not modeled in this plot's ephemeris) will achieve
a circular "RC3" orbit at 13,500 km altitude on April 23.  You can read more
about Dawn's Ceres approach at http://dawnblog.jpl.nasa.gov/?p=2437.

-Dan

From: Daniel Adamo <[email-masked]>
Date: Sun, 08 Mar 2015 21:45:51 -0700
Conversation: "Dawn" Achieves Ceres Orbit
Subject: "Dawn" Achieves Ceres Orbit

ATIG Members-

About the time most of us in the U.S. were arising on Friday morning, March
6, the Dawn spacecraft was achieving orbit about dwarf planet asteroid (1)
Ceres.  Because Dawn uses solar electric propulsion (SEP), its thrust duty
cycles are highly flexible and equally uncertain because of the low
accelerations exerted.

The attached plot of Dawn's Ceres-centered motion depicts orbit capture, but
SEP thrusting doesn't appear to be modeled much after March in the
associated ephemeris posted March 6 to http://ssd.jpl.nasa.gov/?horizons.
According to http://dawnblog.jpl.nasa.gov/2015/03/06/dawn-journal-march-6/,
Dawn should be in its circular RC3 orbit about Ceres (13,500 km altitude,
polar inclination, ascending node at local midnight) on April 23.  I'll
attempt to pass along subsequent plots reflecting SEP thrusting leading to
RC3 as they become available.

-Dan