Selecting a Spectrometer for Solar Irradiance Data

The Boulder Project for Research at High-Altitude on Distributed Irradiance Aboard an iNexpensive CubeSat Experiment (RADIANCE), based at The University of Colorado (CU), is preparing for two-week test flight aboard the Arctic HiWind Gondola. The test flight is being sponsored by the University Corporation for Atmospheric Research (UCAR).

Spectrometer, Solar Irradiance, Stratosphere, RADIANCE Project


Senior students doing the Bachelor’s program in Aerospace Engineering at CU have the opportunity to work on projects for real world customers.

The High-Altitude Observatory (HAO), part of the National Center for Atmospheric Research (NCAR), initiated the RADIANCE project. Engineering Fellow, Jenny Kampmeier, who was selected from among the aerospace engineering student applicants, is leading the RADIANCE team.

The RADIANCE project involves developing a 3U CubeSat prototype, using entirely commercial off-the-shelf (COTS) components. The objective is to develop ways to offer climate scientists reliable continuous solar irradiance data that are inexpensive and easy to mass produce and calibrate, by employing CubeSats.

It is important for climate scientists to maintain a continuous record of solar irradiance data in order to study the effects of solar radiation on Earth’s climate. Irradiance data has been available since the launch of the Nimbus-7 spacecraft in November 1978. However, development and funding delays, instrument failure and launch schedules have created gaps in the historical record.

Moreover, the existing methods for determining solar irradiance employ active cavity electrical substitution radiometry. These methods involve heavily funded space missions such as the TIM instrument aboard the NASA SORCE spacecraft. Different agencies were involved in developing irradiance instruments, which were not similar to each other. There was a wide variation in calibration, and so available data is not consistent.

Design Challenge

Researchers and scientists use the 3U CubeSat program to deploy a standardized payload on a space flight mission. With dimensions of 10 cm x 10 cm x 30 cm, the 3U payload (one “U” denotes 1000 cm3) must accommodate the full complement of sensors, data handling, power supply and command processor for deployment on the HiWind Gondola flight.

Other than the strict size and weight constraints, this project was also mandated to use COTS parts within an equally strict budget. Operational requirements had to be met, despite these, and other, constraints.

Spectrometer, Solar Irradiance, Stratosphere, RADIANCE Project

Considering the environmental conditions aboard the HiWind Gondola, the team included thermal systems in order to maintain operational conditions during its flight as well as during its ascent and descent.

Other than capturing still solar images and taking irradiance measurements, the RADIANCE CubeSat will also measure humidity, temperature and other environmental data, besides measuring the off-sun angle to record attitude.

Spectrometer, Solar Irradiance, Stratosphere, RADIANCE Project

The main objective of the RADIANCE project is to take valuable solar irradiance measurements. To be successful in this effort, the minimum criterion is to obtain wide-spectra measurements between 250-1000 nm at the rate of 1 spectra/minute during the duration of the flight. The choice of spectrometers dictated the ability to perform wide-spectrum irradiance measurements, within the other limitations and parameters.

Spectrometer Selection

The RADIANCE team discovered Avantes spectrometers, thanks to peer recommendation and research. By closely working with Damon Lenski, General Manager of Avantes, Inc., the RADIANCE team opted for the AvaSpec-MINI, which has a back-thinned CCD linear array 2048 pixel detector, and provides resolution up to 0.1 nm. However, the team initially showed interest in the MINI because of the price.

We had a budget of $5000 to complete the entire project. Other companies that produce spectrometers small enough to fit inside our form factor quoted prices outside our budget.

Project Member, Jeremy Muesing

Although price was the initial deciding factor to select the Avantes’ AvaSpec-MINI spectrometer, the RADIANCE team is pleased with its performance. The MINI provides the full range of UV/VIS spectra of 200-1100 nm, although the project scope needed irradiance spectra measurements only in the 250-1000 nm range.

We are getting a slightly larger range, and our customer is always happy whenever we can provide more scientific data.

Project Member, Jeremy Muesing

Weighing just 174 g and roughly of the size of a deck of cards (94.5 x 67 x 19.5 mm), this ultra-low stray light device can be conveniently integrated. The RADIANCE team used the Avantes’ demo program for code development, and closely collaborated with Avantes engineers to perfect integration and calibration of the AvaSpec-MINI.

Arctic HiWind Gondola Mission

The prototype of 3U CubeSat RADIANCE project is now being tested after passing the design review. During the final phase of this project, the 3U payload will be deployed for a 2 week circumpolar high-altitude balloon flight aboard the HiWind Gondola, in order to circle the Antarctic continent at a height of 40 km.

The project requirements entail the payload to withstand and operate in harsh climatic conditions during ascent, flight, and descent, to successfully land, and to operate on its own power and not rely on that of the HiWind Gondola.

The payload shall collect solar irradiance data above the specified 1 nm resolution (AvaSpec-MINI offers a resolution of 0.1 nm), and surpass the 250-1000 nm spectrum target. All collected spectra and ambient environmental data will be stored by the RADIANCE CubeSat on a long-lasting data storage device for convenient retrieval.

The highly anticipated first flight of the RADIANCE CubeSat has been scheduled for the winter of 2017-2018, marking the completion of the current phase of the RADIANCE project.

RADIANCE Path to Space

The HiWind RADIANCE deployment is expected to surpass the expectations. The apparent progress of the CU design team in developing mass-producible Irradiance CubeSats, using COTS components, has encouraged NCAR and HAO to chalk out plans to continue development for space-readiness.

However, the path to space has its own challenges. The thermal system for a space-ready RADIANCE CubeSat must be reconfigured to cool the instrument and dissipate the heat from the payload, instead of heating the instrument at the time of ascent. A space payload should also have a minimum of three reaction wheels to control height - an adjustment controlled by the HiWind during high altitude testing.

However, it is expected that the RADIANCE project sponsors will have favorable results in the next phase of development of a lost-cost solar irradiance measurement standard, working toward a future where solar irradiance data will be comprehensible and accessible for further climate research.

Avantes is a Proud Advocate of Climate Research

The local distributor or sales engineer of Avantes can be contacted in order to learn more about irradiance applications, such as this project, or to find out the capabilities of Avantes’ OEM integrations. This will help a client to understand why Jeremy Muesing of the RADIANCE team said:

Working with Avantes was incredible! I cannot tell you how many times we've had conversations about what a great manufacturer Avantes is. We were impressed by how responsive their sales and support team was in our interactions. They have gone above and beyond helping us with this project.

Jeremy Muesing


This information has been sourced, reviewed and adapted from materials provided by Avantes BV.

For more information on this source, please visit Avantes BV.


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