SOFIA Science Instrument Development FAQs

Please note that after an instrument solicitation is published, as is the currently the case for the Next Generation Science Instrumentation, all questions about science instrument development will be answered publicly on this FAQ.

Atmospheric Transmission (ATRAN) plot / data file with atmospheric transmission information from 1 to 5 microns
Small File in Flexible Image Transport System (FITS) format (16 MB)
Large File in Text format (307 MB)


What NASA Procedural Requirements(NPRs) are applicable to the Science Instrument(SI) developer?

For the convenience of the SI developer, the SOFIA program has flowed down and captured all applicable NPRs in the documents provided in the SOFIA Science Instrument Development Library. If SI developers meet the requirements within these documents, then the NPR requirements will be met.

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What factors need to be considered when designing an instrument to be airworthy?

The primary purpose of a SOFIA science instrument airworthiness certification is safety. Receiving an airworthiness certification significantly reduces the likelihood that either the aircraft or the personnel onboard will be harmed. Airworthiness requirements can be found within the SOFIA Science Instrument System Specification,
SOF-AR-SPE-SE01-2028, located in the SOFIA Science Instrument Development Library.

The following are topics that pertain to the airworthiness of a science instrument:

  • Anything that can cause injury to personnel
  • Anything that can cause a fire
  • Commands by one system to others that result in hazardous conditions
  • Anything that affects the aircraft pressure boundaries
  • Foreign Object Damage (FOD) and equipment security
  • Pressure systems
  • Cryogens
  • Toxic substances
  • Radiation, both ionizing and non-ionizing

Additional information concerning airworthiness can be found within the Science Instrument Developers’ Handbook,
SCI-AR-HBK-OP03-2000, located in the SOFIA Science Instrument Development Library.

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Can you tell us more about Phase 1 of this solicitation?

Phase 1 is designed to be all about the science and is one of the most significant changes to this call. It gives us a way to meet with the scientific community and actually change the way we have done things in the past. One of the things that we are very excited about for this call is the significant changes we have made in how we engage with the community. No longer is this a call for a particular technology at a particular level of readiness to do a particular observation.

The first phase of this call is all about science.

We have the observatory as a known quantity and from there, well, even the sky isn’t a limit in our case. We are truly working to go to the scientific community and ask with no preconceived notion or limitation: What is the science that we can complete together?

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We are using ATRAN to determine atmospheric transmission, but we are curious if there is a similar tool (just a plot or data file would be fine too) that contains the typical sky background for SOFIA from 1-5 microns?

There is no specific tool available for this calculation, however it is fairly straightforward to model a typical sky emission background spectrum using the ATRAN tool, with some reasonable assumptions re: typical temperatures for blackbody sky and telescope emission. Emissivity = 1.0 – Transmission (from ATRAN).

An assumed sky temperature of 240 K (~ -33 C) is typical for the altitudes at which SOFIA observes, and it is reasonable to assume the same temperature for the SOFIA telescope. Per the SOFIA FLITECAM Instrument Scientist / Senior Science Advisor, 15% represents a good estimate for telescope emissivity in this regime.

The contributions from OH emission lines have been included in the posted theoretical sky + telescope background spectrum for SOFIA observing at 41,000 ft. and a telescope elevation angle of 45 degrees, based on the temperature and emissivity assumptions cited above.

Note that this plotted sky + telescope emissions spectrum is not based on actual on-sky observations, however these same assumptions are presently incorporated into the grism mode exposure time calculators that are used to plan observations and flights.

The wavelength range of 1-5 μm has thus far been covered only by the 1st gen. SOFIA Science Instrument (SI) First Light Infrared Test Experiment CAMera (FLITECAM).  FLITECAM is no longer among the suite of SIs offered for SOFIA Observing Campaigns, but when it was still being flown for observations, it did command the SOFIA telescope to perform a maneuver known as a “sky dip” to determine the local sky background during observing flights.

Spectroscopy results presented in the FLITECAM Commissioning Report indicate a good fit with the posted model output included with this response.

SOFIA typical background emission (1-6 µm) (pdf)

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Is it possible to get the Zemax file of the SOFIA telescope?

Yes, the Zemax prescription file (OS01-697.zmx) for the SOFIA telescope is available below. Additional documentation of the as-built SOFIA telescope optical design may also be found in the following documents.

SOF-SPE-KT-1000-0-01, Issue No. 2, Rev. – , Optical Assembly Design Definition (pdf)
SOF-TAN-KT-1000-0-02, Issue No. 1, Rev. – , As Built Ray-Tracing Analysis (pdf)

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