FIREBall-2: advancing TRL while doing proof-of-concept astrophysics on a suborbital platform

ABSTRACT

Here we discuss advances in UV technology over the last decade, with an emphasis on photon counting, low noise, high efficiency detectors in sub-orbital programs. We focus on the use of innovative UV detectors in a NASA astrophysics balloon telescope, FIREBall-2, which successfully flew in the Fall of 2018. The FIREBall-2 telescope is designed to make observations of distant galaxies to understand more about how they evolve by looking for diffuse hydrogen in the galactic halo. The payload utilizes a 1.0-meter class telescope with an ultraviolet multiobject spectrograph and is a joint collaboration between Caltech, JPL, LAM, CNES, Columbia, the University of Arizona, and NASA. The improved detector technology that was tested on FIREBall-2 can be applied to any UV mission. We discuss the results of the flight and detector performance. We will also discuss the utility of sub-orbital platforms (both balloon payloads and rockets) for testing new technologies and proof-of-concept scientific ideas.

1. INTRODUCTION

The development of new detector technology is a key component of NASA’s mission to advance our understanding of the universe around us. New advances in technology are always the precursors to discovery. Typically, NASA funds astrophysics technology development through the Astrophysics Research and Analysis (APRA) and Strategic Astrophysics Technology (SAT) programs, which are designed to take technology concepts from a low technology readiness level (TRL), up to a TRL of 6, at which point the technology can be included in proposals for space missions and are considered relatively low risk.

In addition to funding technology development, NASA funds sub-orbital science investigations under APRA, either using sounding rockets or balloon flights to provide access to a near-space environment. These sub-orbital science investigations are typically seen as both interesting in their own right, but also as pathfinders for future space missions. The ability to increase a technology’s TRL is just as important as the science goals of the missions. Because of the low cost of the sub-orbital program, riskier science can also be tested out. Additionally, these programs are not required to follow the more standard NASA management/risk mitigation program of a higher cost/profile mission, and so offer an opportunity for student and post-doc training that is not possible for Class-D or higher mission profiles. The ability to try out risky, interesting science, to test new technology, and to train future PIs is unique in NASA’s portfolio. The sub-orbital program is a crucial, but under-appreciated, gem of NASA.

Funded via the APRA program, the Faint Intergalactic-medium Redshifted Emission Balloon (FIREBall), is a perfect example of the benefits of building a sub-orbital program. The science is at the forefront of modern extra-galactic astronomy. The experiment has provided one for the first test flights of an important UV detector technology. The program as a whole has trained over 10 graduate students, with several becoming PIs in their own right.

FIREBall is designed to discover and map faint emission from the circumgalactic medium of low redshift galaxies (0.3<z<1.0). This payload is a upgrade of FIREBall-11 (FB-1), a path-finding mission built by our team with two successful flights (2007 Engineering, 2009 Science). FB-1 provided the strongest constrains on intergalactic and circumgalactic (IGM, CGM) emission available from any instrument at the time.2 FIREBall-2 significantly upgraded the spectrograph to increase the field of view, the number of targets observed, and most importantly, the overall system efficiency. The key component of FIREBall-2 was the use of a UV optimized, delta-doped, anti-reflection coated, electron multiplying CCD detector (EMCCDs), which has eight times better throughput that the FB-1 detector (a GALEX spare near-UV microchannel plate). FIREBall-2 had its first flight in the fall of 2018 from Fort Sumner, NM and acted as a pathfinder and test-bed for this new UV detector technology.