  The Debris Disk Explorer (DDX) is a proposed balloon-borne investigation of
debris disks around nearby stars. Debris disks are analogs of the Asteroid Belt
(mainly rocky) and Kuiper Belt (mainly icy) in our Solar System. DDX will
measure the size, shape, brightness, and color of tens of disks. These
measurements will enable us to place the Solar System in context. By imaging
debris disks around nearby stars, DDX will reveal the presence of perturbing
planets via their influence on disk structure, and explore the physics and
history of debris disks by characterizing the size and composition of disk
dust.
  The DDX instrument is a 0.75-m diameter off-axis telescope and a coronagraph
carried by a stratospheric balloon. DDX will take high-resolution,
multi-wavelength images of the debris disks around tens of nearby stars. Two
flights are planned; an overnight test flight within the United States followed
by a month-long science flight launched from New Zealand. The long flight will
fully explore the set of known debris disks accessible only to DDX. It will
achieve a raw contrast of 10^-7, with a processed contrast of 10^-8. A
technology benefit of DDX is that operation in the near-space environment will
raise the Technology Readiness Level of internal coronagraphs, deformable
mirrors, and wavefront sensing and control, all potentially needed for a future
space-based telescope for high-contrast exoplanet imaging.
