CTIM-FD: Compact Total Irradiance Monitor-Flight Demonstration


CTIM-FD will help researchers develop new technologies for measuring Total Solar Irradiance (TSI), a “Most Important” measurement in the latest Earth Science Decadal Survey. This eight-channel, 6U CubeSat will spend one year in orbit to see if small satellites can be as effective at measuring TSI as larger sensors like the Total Irradiance Monitor (TIM) instrument used aboard the SORCE and TSIS-1 missions. On July 2, 2022, CTIM-FD was successfully deployed into orbit (~500km and 44.9deg inclination) by the Virgin Orbit LauncherOne.

Science Area

For four decades, scientists have used space-based remote sensors to measure TSI, which describes the amount of incident solar radiation that reaches the Earth from the sun. TSI is a major component of Earth’s radiative system, which impacts everything from local weather conditions to global climate change. Maintaining this unbroken record of TSI data is critical for preparing future generations of scientists to understand and mitigate the effects of climate change.


Lighter and more compact, CTIM features several improvements to the original TIM design. In particular, CTIM’s novel Vertically Aligned Carbon Nanotube (VACNT) bolometers mark a significant milestone in the quest to develop lightweight components for CubeSat-compatible instruments. These silicon-based bolometers will dramatically reduce the weight of the CTIM CubeSat without compromising its ability to measure the total irradiance of the sun (200 – 2400 nm) with an uncertainty of <0.01% and a stability of <0.001%/year. CTIM employs heritage technology previously developed on the ESTO project “Carbon Absolute Electrical Substitution Radiometers (CAESR)“.


  • Silicon-based VACNT bolometers are nearly ideal optical absorbers, exhibiting good thermal conductivity along their length and resistance to robust UV exposure. Also, the spatial extent of VACNTs can be very precisely controlled through fabrication techniques, enabling most of the key elements of the bolometer to be fabricated onto one piece of silicon.
  • A thermally integrated reflector recaptures light not absorbed on initial incidence and reduces reflectance changes in the VACNTs due to degradation. Thermal integration greatly simplifies the calibration and reduces uncertainties in the correction for reflective light lost.

Principal Investigator

David Harber Photo

David Harber, an instrument engineer at University of Colorado Boulder / LASP, is the principal investigator (PI) on the CTIM-FD mission. He received a PhD in Physics from the University of Colorado Boulder, an M.S. in Physics from the University of Washington, and a B.S. in Engineering Physics from the Colorado School of Mines.

On this project, Dave is assisted by co-investigators Greg Kopp and Peter Pilewskie, also at University of Colorado Boulder / LASP. NIST is also a partner of this project.



D. Harber, et al., “Compact total irradiance monitor flight demonstration,” Proc. SPIE 11131, CubeSats and SmallSats for Remote Sensing III, 111310D (2019). https://doi.org/10.1117/12.2531308