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Laboratory for Atmospheric and Space Physics

CUTE Design

About CubeSats

CubeSats are small satellites that are usually designed to perform scientific measurements and observations in space. The original specifications for CubeSats were released in 1999 by Cal Poly and Stanford University in an effort to standardize design to allow for reduced cost and increased accessibility to space. They come in multiples of a standard cube size of 10 cm x 10 cm x 10 cm, called units (U). They are launched as a “guest” on a host rocket carrying much larger spacecraft.

Fig. 1: Ray trace of CUTE telescope.

About CUTE

CUTE is a 6U CubeSat whose bus and primary subsystems (including the attitude control system, GPS receiver, communication systems, electrical power system, and solar array) are provided by Blue Canyon Technologies.

CUTE contains a novel rectangular reflector that increases collection area by a factor of 3 over a standard circular aperture. It was designed by Co-I Brian Fleming and will be fabricated by Nu-Tek. With the exception of the grating, all mirrors will be coated in aluminum (Al) with a protective overcoat of magnesium fluoride over (MgF2). MgF2 helps prevent the formation of an oxide layer that can absorb UV light.

Here’s how light travels through the CUTE instrument, as shown in Fig. 1

  • Light travels in from the left and is collected by a 20 cm x 8.5 cm rectangular Cassegrain telescope. The rectangular design provides more than three times the collecting area of conventional circular apertures that fit into a 1 U tall spacecraft.
  • The incident beam is reflected off a small fold mirror (1st Fold Mirror) and passes through the spectrograph entrance slit, which has a projection of 23 arcminutes (23′) on the sky.
  • Light is dispersed by an ion-etched diffraction grating (from Horiba J-Y) that builds off the heritage of the Cosmic Origins Spectrograph on the Hubble Space Telescope.
  • The dispersed beam is then reflected off of a second fold mirror (2nd Fold Mirror) before being recorded on a UV-optimized 2048 x 515 pixel e2v CCD array (Detector).

 

ig. 2. The CUTE science instrument.

Fig. 2 shows the CUTE science instrument. The CUTE primary acts as its own optical bench, supporting the secondary mirror in front of it and the spectrograph housing behind it. Two flexures mount the telescope to the bottom of the CUTE CubeSat bus. A heat strap comes off the back of the CCD detector and is attached to a radiator on the side of the CubeSat bus.

 

Fig. 3. Internal close-up rendering of the CUTE spectrograph enclosure. A cover closes the enclosure and acts as the CCD mount.

Fig. 3 displays the inside of the spectrograph. A shutter is used to block light from the CCD. The cylindrical fold mirror sits on a tip/tilt stage that will be used to align the spectrograph. The CCD is mounted on the outside of a panel that closes the spectrograph enclosure. A lamina emergent mount (LEM) will help absorb any thermal expansion and contraction that occurs on the CCD mount, and a heat strap is mounted to the LEM and attached to the side of the CubeSat bus.

 

Fig 4. Solid render of the closed spectrograph enclosure with the
CCD and a lamina emergent mechanism (LEM) heat strap
mount. The flexure on the left has a vertical cylinder nested
inside the horizontal cylinder that is bonded into the telescope.

Fig. 4 displays the back of the telescope + spectrograph enclosure. The width of the telescope is only 20 cm. The flexures are used to mount the science instrument to the bottom of the CubeSat.

 

Fig. 5 Final CUTE design rendering, with top and sides not shown.

Fig. 5 displays the final CUTE design. The top and sides of CUTE are not displayed to illustrate the orientation and fit of the science instrument. The BCT CubeSat bus will be delivered including the sun sensors, GPS patch, S-band transmitter, an ultra high frequency (UFH) antenna (not shown), and star tracker and attitude control and determination system (ADCS).

 

CUTE is scheduled to launch in the second quarter of 2020 into a sun-synchronous orbit. NASA’s CubeSat Launch Initiative (CSLI) will provide the launch opportunity.