CTIM-FD (Compact Total Irradiance Monitor-Flight Demonstration)
July 2022: A very small instrument has a big job ahead of it: measuring all Earth-directed energy coming from the Sun and helping scientists understand how that energy influences our planet’s severe weather, climate change and other global forces. With a size of an 8U CubeSat, CTIM is the smallest satellite ever dispatched to observe the sum of all solar energy Earth receives from the Sun — also known as TSI (Total Solar Irradiance). 1)
Total solar irradiance is a major component of the Earth radiation budget, which tracks the balance between incoming and outgoing solar energy. Increased amounts of greenhouse gases emitted from human activities, such as burning fossil fuels, trap increased amounts of solar energy within Earth’s atmosphere.
Figure 1: CTIM-FD is an eight-channel, 6U CubeSat that will spend one year in orbit to see if small satellites can be as effective at measuring Total Solar Irradiance as larger sensors like the Total Irradiance Monitor instrument used aboard the SORCE and TSIS-1 missions (video credit: NASA, Willaman Creative)
“By far the dominant energy input to Earth’s climate comes from the Sun,” said Dave Harber, a senior researcher at the University of Colorado, Boulder, Laboratory for Atmospheric and Space Physics (LASP) and principal investigator for CTIM. “It’s a key input for predictive models forecasting how Earth’s climate might change over time.”
NASA missions like the Earth Radiation Budget Experiment and NASA instruments like CERES (Clouds and the Earth’s Radiant Energy System) have allowed climate scientists to maintain an unbroken record of total solar irradiance stretching back 40 years. This enabled researchers to rule out increased solar energy as a culprit for climate change and recognize the role greenhouse gases play in global warming.
Ensuring that record remains unbroken is of paramount importance to Earth scientists. With an unbroken total solar irradiance record, researchers can detect small fluctuations in the amount of solar radiation Earth receives during the solar cycle, as well as emphasize the impact greenhouse gas emissions have on Earth’s climate.
For example, last year, researchers from NASA and NOAA relied on the unbroken total solar irradiance record to determine that, between 2005 and 2019, the amount of solar radiation that remains in Earth’s atmosphere nearly doubled.
“In order to make sure we can continue to collect these measurements, we need to make instruments as efficient and cost-effective as possible,” Harber said.
CTIM is a prototype: its flight demonstration will help scientists determine if small satellites could be as effective at measuring total solar irradiance as larger instruments, such as the Total Irradiance Monitor (TIM) instrument used aboard the completed SORCE (Solar Radiation & Climate Experiment) mission and the ongoing TSIS-1 (Total and Spectral Solar Irradiance Sensor-1) mission on the International Space Station. If successful, the prototype will advance the approaches used for future instruments.
CTIM’s radiation detector takes advantage of a new carbon nanotube material that absorbs 99.995% of incoming light. This makes it uniquely well suited for measuring total solar irradiance.
Reducing a satellite’s size reduces the cost and complexity of deploying that satellite into low-Earth orbit. That allows scientists to prepare spare instruments that can preserve the TSI data record should an existing instrument malfunction.
CTIM’s novel radiation detector – also known as a bolometer – takes advantage of a new material developed alongside researchers at the National Institute for Standards and Technology (NIST).
“It looks a bit like a very, very dark shag carpet. It was the blackest substance humans had ever manufactured when it was first created, and it continues to be an exceptionally useful material for observing TSI,” Harber said.
Made of minuscule carbon nanotubes arranged vertically on a silicon wafer, the material absorbs nearly all light along the electromagnetic spectrum.
Together, CTIM’s two bolometers take up less space than the face of a quarter. This allowed Harber and his team to develop a tiny instrument fit for gathering total irradiance data from a small CubeSat platform.
A sister instrument, the Compact Spectral Irradiance Monitor (CSIM), used the same bolometers in 2019 to successfully explore variability within bands of light present in sunlight. Future NASA missions may merge CTIM and CSIM into a single compact tool for both measuring and dissecting solar radiation.
“Now we’re asking ourselves, ‘How do we take what we’ve developed with CSIM and CTIM and integrate them together,’” Harber said.
Harber expects CTIM to begin collecting data about a month after launch, currently scheduled for June 30, 2022, aboard STP-28A, a Space Force mission executed by Virgin Orbit. Once Harber and his LASP colleagues unfold CTIM’s solar panels and check each of its subsystems, they will activate CTIM. It’s a delicate process, one that requires diligence and extreme care.
“We want to take our time and make sure that we’re doing these steps rigorously, and that each component of this instrument is working correctly before we move on to the next step,” Harber said. “Just demonstrating that we can gather these measurements with a CubeSat would be a big deal. That would be very gratifying.”
Funded through the InVEST program in NASA’s Earth Science Technology Office, CTIM launches from the Mojave Air and Space Port in California aboard Virgin Orbit’s LauncherOne rocket as part of the United States Space Force STP-S28A mission.
Another NASA graduate from the InVEST technology program, NACHOS-2, will also be aboard. A NACHOS (Nanosat Atmospheric Chemistry Hyperspectral Observation System) twin, NACHOS-2 will help the Department of Energy monitor trace gases in Earth’s atmosphere.
Launch: The CTIM-FD CubeSat, along with other payloads, was air-launched on the Virgin Orbit LauncherOne mission of the USSF STP-28A, called”Straight Up”, from the Mojave Air and Space Port in California on 02 July 2022 at 05:20 UTC (10:20 PDT on 01 July 2022). Virgin Orbit's carrier plane is a modified Boeing 747 called Cosmic Girl. 2)
This launch was particularly important for Virgin Orbit as it marks the first night mission for the responsive launch company.
Orbit: Near-circular orbit at an altitude of ~500 km and an inclination of 45º.
The mission carried seven payloads, primarily science and technology demonstrations, arranged by the Space Test Program: 3)
• Compact Total Irradiance Monitor (CTIM) is a 6U CubeSat funded by NASA and developed by the University of Colorado Boulder. It will test the ability of a CubeSat to measure total solar irradiance, the amount of solar radiation that reaches the Earth, with the same precision as larger spacecraft.
• GPX2 is a 3U CubeSat developed by NASA to test the use of commercial components for differential GPS, precision navigation that could be used for future in-space operations. The satellite will deploy a two-meter gravity-gradient boom to passively stabilize itself once in orbit.
• Gunsmoke-L features a pair of 6U CubeSats built by Dynetics for the U.S. Army Space and Missile Defense Command. The service describes the satellites as “tactical space support vehicles” that will “aid in all phases of joint force operations.”
• The Modular Intelligence, Surveillance and Reconnaissance B (MISR-B) mission will uses a CubeSat “to demonstrate various capabilities and mission effectiveness” of the U.S Special Operations Command.
• Nanosat Atmospheric Chemistry Hyperspectral Observation System (NACHOS) 2 is a 3U CubeSat funded by NASA to detect trace gases like sulfur dioxide in the atmosphere. The NACHOS-1 CubeSat, with the same instrument, deployed from a Cygnus cargo spacecraft June 28 after that spacecraft departed from the International Space Station.
• Recurve is a CubeSat mission developed by the Air Force Research Laboratory. It will test adaptive radio-frequency technology in a mesh network.
• Slingshot 1 is a 12U CubeSat built by The Aerospace Corporation using a bus from Blue Canyon Technologies. The spacecraft carries 19 technology demonstration payloads, including a modular plug-and-play interface.
Development status of CTIM-FD
• August 30, 2019: The long-term balance between Earth’s absorption of solar energy and emission of radiation to space is a fundamental climate measurement. Total solar irradiance (TSI) has been measured from space, uninterrupted, for the past 40 years via a series of instruments. The Compact Total Irradiance Monitor (CTIM) is a CubeSat instrument that will demonstrate next-generation technology for monitoring total solar irradiance. It includes novel silicon-substrate room temperature vertically aligned carbon nanotube (VACNT) bolometers. The CTIM, an eight-channel 6U CubeSat instrument, is being built for a target launch date in late 2020. The basic design is similar to the SORCE, TCTE and TSIS Total Irradiance Monitors (TIM). Like TSIS TIM, it will measure the total irradiance of the Sun with an uncertainty of 0.0097% and a stability of <0.001%/year. The underlying technology, including the silicon substrate VACNT bolometers, has been demonstrated at the prototype-level. During 2019 we will build and test an engineering model of the detector subsystem. Following the testing of the engineering detector subsystem, we will build a flight detector unit and integrate it with a 6U CubeSat bus during late 2019 and 2020, in preparation for an on-orbit demonstration. 4) 5)
1) Gage Taylor, ”Novel NASA Instrument Sets Sights on Earth-bound Solar Radiation,” NASA Feature, 1 July 2022, URL: https://www.nasa.gov/feature/esnt/2022/novel-nasa-instrument-sets-sights-on-earth-bound-solar-radiation
2) ”Virgin Orbit launches seven satellites into space on Straight Up mission,” Virgin Orbit, 2 July 2022, URL: https://www.virgin.com/about-virgin/latest/virgin-orbit-launches-seven-satellites-into-space-on-straight-up-mission
3) Jeff Foust ”Virgin Orbit launches Space Force mission,” SpaceNews, 2 July 2022, URL: https://spacenews.com/virgin-orbit-launches-space-force-mission/
4) David Harber, Zach Castleman, Ginger Drake, Samuel Van Dreser, Nat Farber, Karl Heuerman, Marc Miller, Joel Rutkowski, Alan Sims, Jacob Sprunck, Cameron Straatsma, Isaac Wanamaker, Wengang Zheng, Greg Kopp, Erik Richard, Peter Pilewskie, Nathan Tomlin, Michelle Stephens, Christopher Yung, Malcolm White, and John Lehman "Compact total irradiance monitor flight demonstration", Proceedings of SPIE, Volume 11131, 'CubeSats and SmallSats for Remote Sensing III, 111310D,' SPIE Optical Engineering+Applications' San Diego, CA, USA, 30 August 2019, https://doi.org/10.1117/12.2531308
5) The ”Compact total irradiance monitor: Flight demonstration,” in full length is also available at: https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=928470
The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: ”Observation of the Earth and Its Environment: Survey of Missions and Sensors” (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (email@example.com).