  The far-infrared (IR) region is rich with information needed to characterize
interstellar dust and to investigate the cold outer planets of the solar system
and their icy moons. The proposed sub-orbital observatory the Balloon
Experiment for Galactic INfrared Science (BEGINS) will utilize cryogenic
instruments to map spectral energy distributions (SEDs) of interstellar dust in
the Cygnus molecular cloud complex. A future high priority flagship mission
Uranus Orbiter and Probe carrying a net flux radiometer (NFR) will study the in
situ heat flux of the icy giants atmosphere to 10 bar pressure. These
instruments require far-IR filters to define the instrument spectral
bandwidths. Our ultimate goal is to define the instrument bands of BEGINS and
the NFR with linear-variable filters (LVFs) and discrete-variable filters
(DVFs). The LVFs and DVFs will be made of metal mesh band-pass filters (MMBF)
comprised of a 100 nm thick gold film with cross-shaped slots of varying sizes
along a silicon (Si) substrate with cyclic olefin copolymer (COC)
anti-reflection (AR) coatings. We present our progress towards LVFs and DVFs
with simulated and measured transmission of a room temperature, non-AR coated,
single-band 44 $\mu$m MMBF filter. We have successfully fabricated, measured,
and modeled a non-AR coated, room temperature 44 $\mu$m MMBF. The transmission
at room temperature and non-AR coated was measured to be 27\% with a resolving
power of 11. When COC-AR coated on both sides the transmission is expected to
increase to 69\% with a resolving power of 10.
