Skip to main content
U.S. flag

An official website of the United States government

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

Compact Spectral Irradiance Monitor

Illustration shows satellite in space with curve of Earth and distant Sun.
Illustration showing the Compact Spectral Irradiance Monitor cubesat
Credit: LASP

Instrument Details



Low Earth orbit (LEO), 575 kilometers above the Earth’s surface


The Compact Spectral Irradiance Monitor (CSIM) — a small instrument squeezed into a “CubeSat” the size of a shoebox, at a fraction of the usual cost and potentially offering greater accuracy — measures solar spectral irradiance, the distribution of solar energy input across a specific wavelength range, providing insight into how the Earth’s atmosphere responds to changes in solar output. CSIM was launched in December 2018. A successor instrument, the Compact Total Irradiance Monitor (CTIM), is scheduled for launch in late 2022.

NIST’s role:

A novel “NIST on a chip” detector provides periodic on-board calibrations for the CSIM. The NIST chips are radiometers, which measure light intensity, and they are smaller, faster, cheaper and equally if not more accurate than their predecessors. The chips consist of carbon nanotubes and metals patterned on silicon wafers. The chips were made under an agreement between NIST and the Laboratory for Atmospheric and Space Physics, which built the CSIM with support from NASA. NIST also designed and built a detector for CTIM.

Significant discoveries:

CSIM obtained “first light” results across its full scanning range with impressive accuracy. It is currently operational and measures daily top-of-the-atmosphere solar spectral irradiance. The CSIM mission has been highly successful in demonstrating new technologies. 

Other interesting facts:

Carbon nanotubes, the darkest material on Earth, efficiently absorb nearly all light across a broad span of wavelengths. 


The Laboratory for Atmospheric and Space Physics at the University of Colorado Boulder


a close up of a portion of a long rectangular chip resting on a quarter.
NIST light absorber made of carbon nanotubes
Credit: NIST
A flat disk has a black center and bronze around the outside.
NIST detector for CTIM 
Credit: N. Tomlin/NIST
Various devices are built into a piece of equipment shaped like a suitcase.
Compact Spectral Irradiance Monitor (CSIM)
Credit: CU/LASP
Created October 8, 2021, Updated November 16, 2021