PROCYON update: Asteroid 2000 DP107 target selected, ion engine stopped
PROCYON (PRoximate Object Close flYby with Optical Navigation) is a microsatellite that launched on December 3 as a secondary payload with Hayabusa2. The mission has now selected their asteroid flyby target -- a binary asteroid named 2000 DP107 -- but is reporting a problem with their ion engines.
PROCYON (PRoximate Object Close flYby with Optical Navigation) is a 50 kg-class microsatellite developed by the University of Tokyo (UT) and JAXA/ISAS (Japan Aerospace Exploration Agency/Institute of Space and Astronautical Science). Launched with Hayabusa2, its goal is to perform a close flyby of an asteroid in early 2016.
The target of PROCYON is now set to "2000 DP107" which is a [binary asteroid]. 800m and 300m. [After the encounter], PROCYON will not be able to return to near Earth orbit to perform a [second] swingby. So [200 DP107 is the] only chance of asteroid approach. The Earth swingby is December 3, 2015 and asteroid passby is May 12, 2016.
The nominal mission has been accomplished. Solar panels are OK, temps are OK, triaxial control is OK. It is very much alive.
The ion engine stopped in mid-March 2015, trying to restart, but no indication yet of recovery at the moment. The cause of this has not been identified yet, but the most likely reason is thought to be that a minute metal piece has migrated into the gap between the 2 ion grids of the ion source.
Therefore, several options have been identified, as follows.
Give this grid a thermal cycle of expansion and contraction.
Give the probe an acceleration and rotate, stop, rotate, stop etc.
Apply high voltage and burn out the meal piece.
These options will be tried carefully. However, the deadline for recovery is currently end of April 2015 in time for the Earth swingby in December 2015. This deadline is also being re-evaluated for accuracy.
In the meantime, geo-corona image acquisition has been successful. The image has not been made available as [papers] are being written at the moment.
In these delay-Doppler radar images, the primary appears to be much larger than the satellite, but actually the satellite is more than a third as large as the primary. The reason that the primary appears so large in the radar image is that spread along the horizontal axis in a radar image is a function of the spin rate, and the primary is spinning very fast, once every 2.8 hours. The satellite is probably locked in spin-orbit resonance, spinning once with every 1.77-day revolution, so it appears quite small.
Naidu et al. 2015
Observations of binary asteroid 2000 DP107
2000 DP107 was the first asteroid discovered by radar to be a binary. It was observed in both October 2000 and September 2008. The data show that it is composed of an ~800 meter diameter primary and a ~300 meter diameter secondary revolving around their common center of mass. The primary rotates much faster than the secondary.
The high-quality observations in 2008 permitted Shantanu Naidu and coworkers to develop a shape model for both components of 2000 DP107. Here is the shape model for the primary:
Naidu et al 2015
Radar-derived shape model of the primary component of 2000 DP107
Shape model of the primary as seen along the three principal axes x, y, and z. Yellow regions have radar incidence angles of more than 60 degrees and hence are not well constrained. The effective surface resolution is about 57 meters. It measures 990 by 940 by 960 meters along its principal axes; its volume is equivalent to a sphere of diameter 860 meters.
You might notice that this asteroid is pointy at its poles and bulgy at the equator. That's a common feature of fast-spinning near-Earth asteroids. Other asteroids known to have this shape include 2008 EV5 (the current leading target for the asteroid retrieval mission) and Bennu (the target for OSIRIS-REx).
The shape has a simple physical cause: it's spinning so fast that the force of gravity at its equator is almost perfectly canceled by the centrifugal acceleration caused by its spin. Objects on its equator could float into space with the tiniest kick. So it's considered quite likely that a chance encounter with a passing asteroid delivered just such a kick that launched a bunch of material (at extremely slow speed) off of the primary's surface, which eventually coalesced into a satellite. Spin-up followed by rotational fission is the likely cause of all those near-Earth asteroid binaries.