Thermal Modeling of the BLAST-TNG Balloon Telescope

by Nathan P. Lourie, University of Pennsylvania

BLAST-TNG (The Next Generation Balloon-borne Large-Aperture Submillimeter Telescope) is a telescope which will survey the origins of stars and planets, including systems similar to our own Solar System, from a high-altitude balloon flying through the stratosphere 35 km above Antarctica. The instrument features a cryogenically-cooled camera with extremely sensitive superconducting detectors, and a telescope with a 2.5-m-diameter carbon fiber composite mirror.  The camera observes the thermal emission from interstellar dust around galactic molecular clouds, the locus of star formation in the galaxy, and is polarization-sensitive, enabling observations of the structure of magnetic fields in these regions. BLAST-TNG is funded by NASA, its detectors were built by National Institute of Standards and Technology (NIST) in Boulder, Colorado, and nearly all the major instrument systems were designed, built, and tested by graduate students and post-doctoral researchers at the University of Pennsylvania, Arizona State University, Northwestern University, and the National Radio Astronomy Observatory

Accurate modeling of the thermal behavior of the balloon payload is a critical aspect of the instrument design, from the beginning stages of the project through the planned launch from McMurdo Station, Antarctica in December 2019. For BLAST-TNG, the most critical components to model are the electronics and the telescope optics, all of whose temperatures are controlled passively through careful design of large aluminized polyethylene Sun shields. The Sun shield design must manage the temperature of the entire payload and avoid direct illumination of the optics when observing all the required astronomical targets. 

BLAST

Figure 1: The BLAST-TNG experiment on the launch vehicle shown before its first launch attempt from McMurdo Station, Antarctica in January 2019, showing the extensive Sun shields.

During flight, the payload operates in a spacelike environment which is well-suited to modeling with Thermal Desktop and RADCAD, which simulates the radiative environment, orbital path around Antarctica, and the albedo from the ice sheets that the balloon passes over. However, the stratospheric environment presents unique challenges from the space environment which are harder to model “out of the box.” The conductive/convective cooling from the ~3 mbar ambient air pressure and low-velocity winds at the balloon altitude are especially hard to model. To ensure the model is accurate, all critical components are modeled through an iterative process of environmental testing in flight-like conditions to calibrate the component-level conductive links before simulating the performance of the full system in its stratospheric orbit. Further details of the Thermal Desktop model built for BLAST-TNG can be found in papers by (Soler et. al. 2014) and (Lourie et al, 2018).

Thermal Model Flow

Figure 2: Because the stratospheric environment is not a pure-radiative environment like space, critical components must be individually modeled and validated through an iterative process of environmental testing. The general approach is shown here, illustrated through the validation of the model for the detector readout electronics crate.

 

Advanced Pipes in FloCAD
Thursday November 14, 9-10am MT (8-9am PT, 11am-noon ET)
This webinar introduces advanced features for FloCAD pipes in addition to working with complex geometry. Complex geometry includes interior fins and surfaces for heat transfer, flow around enclosed objects, annular flow, concentric pipes, and more. FK Locators and TEEs as modeling objects will also be introduced.
Custom Heat Transfer and Pressure Drops
Tuesday November 19, 2-3pm MT (1-2pm PT, 4-5pm ET)
Do you know what the default assumptions are in FloCAD, and whether or not they apply in your situation? Do you know how far you can go past that starting point? The answer: pretty far. There are numerous mechanisms in FloCAD for adjusting factors, scaling uncertainties, and applying different or supplemental correlations. This webinar summarizes the options available to you to customize your flow models to make sure that they apply to each new situation you encounter.
Heat Exchangers: Detailed and System-level
Thursday November 21, 2-3pm MT (1-2pm PT, 4-5pm ET)
This is two webinars in one. The first explains the use and assumptions behind the FloCAD HX system-level modeling object. The second webinar describes detailed-level modeling of complex heat exchanger passages, including application of Compact Heat Exchanger (CHX) methods.
Starting in 2020, we will begin offering Introduction to Thermal Desktop and Introduction to RadCAD as either in-person training or online training, alternating between online and in-person every three months. The training uses lectures and demonstrations to introduce you to basic Thermal Desktop and RadCAD usage. Hands-on tutorials provide practice building models and interpreting results (tutorials are completed by students outside of the online class time).
 
The next training class will be an online format in January 2020:
  • Introduction to Thermal Desktop (and SINDA) - A three-part series on January 14, 16, and 21 from 9am to 12pm, Mountain time
  • Introduction to RadCAD - January 23 from 9am to 12pm, Mountain time
For up-to-date schedules, fees, and policies, visit our Product Training page. To register for the class above, complete our registration form and select "Online" for the Training Format.
 
If you are interested in product training for your company based on your schedule, please contact us to obtain a quote for training between 8-12 attendees. We can come to your facility or the lectures can be presented online. Descriptions of the available classes can be found in our course catalog.
 
To keep up with our training opportunities, take a look at our new Events and Training Calendar.