Prospect for UV observations from the Moon. II. Instrumental design of an ultraviolet imager LUCI

Abstract

We present a design for a near-ultraviolet (NUV) imaging instrument which may be flown on a range of available platforms, including high-altitude balloons, nanosatellites, or space missions. Although all current UV space missions adopt a Ritchey-Chretain telescope design, this requires aspheric optics, making the optical system complex, expensive and challenging for manufacturing and alignment. An all-spherical configuration is a cost-effective and simple solution. We have aimed for a small payload which may be launched by different platforms and we have designed a compact, light-weight payload which will withstand all launch loads. No other UV payloads have been previously reported with an all-spherical optical design for imaging in the NUV domain and a weight below 2 kg. Our main science goal is focussed on bright UV sources not accessible by the more sensitive large space UV missions.Here we discuss various aspects of design and development of the complete instrument, the structural and finite-element analysis of the system performed to ensure that the payload withstands launch-load stresses and vibrations. We expect to fly this telescope -Lunar Ultraviolet Cosmic Imager (LUCI) -on a spacecraft to the Moon as part of the Indian entry into Google XPrize competition. Observations from the Moon provide a unique opportunity to observe the sky from a stable Joice Mathew · Ajin Prakash · Mayuresh Sarpotdar · A.G. Sreejith · Nirmal K. · S. Ambily · Margarita Safonova · Jayant Murthy Indian Institute of Astrophysics, Koramangala 2nd block, Bangalore, 560034, India E-mail: joice@iiap.res.in Noah BroschThe Wise Observatory and the Dept. Of Physics and Astronomy, Tel Aviv University, Tel Aviv 69978, Israel platform far above the Earth's atmosphere. However, we will explore other opportunities as well, and will fly this telescope on a high-altitude balloon later this year.

The Near Ultraviolet Transient Surveyor (NUTS): An ultraviolet telescope to observe variable sources

“…Despite its scientific potential, time domain astronomy in the UV has not been studied extensively (Sagiv et al, 2014;Mathew et al, 2017). Traditionally, transient observations from space are carried out in the high energy domains of X-Rays and gamma rays.…”

“…The instrument is attached to the spacecraft with an interface flange at the center of gravity (CG) for better mechanical stability. From our vibration analyses and launch provider specificatios (Mathew et al, 2017;Kumar et al, 2012), we have determined that the natural frequency must be above 100 Hz, and the instrument should be able to withstand shock loads of up to 5 g.…”

“…The assembly, alignment and initial calibration of the instrument were performed at the M. G. K. Menon Laboratory (MGKML) for Space Sciences at IIA. We have employed the procedures and techniques described in Mathew et al (2019) for the assembly and calibration of the Lunar Ultraviolet Cosmic Imager (LUCI, Mathew et al (2017)). This facility was also used by the UVIT payload on AstroSat (Kumar et al, 2012) and includes the necessary equipment for calibrating NUV instruments while ensuring cleanliness.…”

“…We, the small-payloads group at the Indian Institute of Astrophysics (IIA), have been working on building and testing payloads targeted at astronomical and atmospheric observations in the UV (Mathew et al, 2017;Chandra et al, 2020). We have used high-altitude balloons to test the sub-system prototypes and later develop them into full-fledged space payloads (Sreejith et al, 2016;Mathew et al, 2018a).…”

Prospect for UV observations from the Moon. III. Assembly and ground calibration of Lunar Ultraviolet Cosmic Imager (LUCI)

“…The original design of the instrument was the FUV re-orientable telescope (Safonova et al (2014), hereafter paper I); however challenges due to constraints on weight, volume, and power placed by the spacecraft team forced us to significantly reduce the size and weight of the payload as well as change the wavelength band from FUV to NUV. The mechanical constraints along with budgetary restrictions, availability of space-qualified components (detector & optics) and time-bound development resulted in the new instrument, where it was the design concept that defined the science goals (Mathew et al (2017), hereafter paper II). LUCI is proposed to be mounted on the Team Indus lander at fixed angle ( Fig.…”