Q-PACE
CubeSat Particle Aggregation and Collision Experiment (Q-PACE), originally referred to as Cu-PACE, is a planned orbital spacecraft mission that will study the early stages of protoplanetary accretion by observing particle dynamical aggregation for several years.

Current hypotheses have trouble explaining how particles can grow larger than a few centimeters. This is called the meter size barrier. This mission was selected in 2015 as part of NASA's ELaNa program, and it is scheduled for launch in September 2019.

Overview

 
Observations of the collisional evolution and accretion of particles in a microgravity environment are necessary to elucidate the processes that lead to the formation of planetesimals (the building blocks of planets), km-size, and larger bodies, within the protoplanetary disk. The current hypotheses of planetesimal formation have difficulties in explaining how particles grow beyond one centimeter in size, so repeated experimentation in relevant conditions is necessary.

Q-PACE will explore the fundamental properties of low‐velocity (< 10 cm/s) particle collisions in a microgravity environment in an effort to better understand accretion in the protoplanetary disk. Several precursor tests and flight missions were performed in suborbital flights as well as in the International Space Station. The small spacecraft does not need accurate pointing or propulsion, which simplified the design.

It will be an air launch to orbit from Virgin Galactic's Cosmic Girl airplane above the Mojave desert in California.

Objectives
 
The main objective of Q-PACE is to understand protoplanetary growth from pebbles to boulders by performing long-duration microgravity collision experiments. The specific goals are: 
Quantify the energy damping in multi-particle systems at low collision speeds (< 1 mm/s to 10 cm/s)
Identify the influence of a size distribution on the collision outcome.
Observe the influence of dust on a multi-particle system.
Quantify statistically rare events: observe a large number of similar collisions to arrive at a probabilistic description of collisional outcomes.

Method

Q-PACE is a 3U CubeSat with a collision test chamber and several particle reservoirs that contain meteoritic chondrules, dust particles, dust aggregates, and larger spherical particles. Particles will be introduced into the test chamber for a series of separate experimental runs.

The scientists designed a series of experiments involving a broad range of particle size, density, surface properties, and collision velocities to observe collisional outcomes from bouncing to sticking as well as aggregate disruption in tens of thousands of collisions. The test chamber will be mechanically agitated to induce collisions that will be recorded by on‐board video for downlink and analysis. Long duration microgravity allows a very large number of collisions to be studied and produce statistically significant data.

Selection process

Q-PACE was selected for flight through NASA's CubeSat Launch Initiative which placed it on ELaNa XX. The development of the mission and science investigation was funded through NASA's Small Innovative Missions for Planetary Exploration (SIMPLEx) program. It was one of the first two missions selected in SIMPLEx. The other is called LunaH-Map and is led by Craig Hardgrove at the University of Arizona.