Pointing and control system performance and improvement strategies for the SOFIA Airborne Telescope

We describe the Faint Object infraRed CAmera for the SOFIA Telescope (FORCAST) which is presently operating as a facility instrument on the Stratospheric Observatory For Infrared Astronomy (SOFIA). FORCAST provides imaging and moderate resolution spectroscopy capability over the 5–40[Formula: see text][Formula: see text]m wavelength range. In imaging mode, FORCAST has a 3.4[Formula: see text] field-of-view with 0.768[Formula: see text] pixels. Using grisms, FORCAST provides long-slit low-resolution ([Formula: see text]–300) and short-slit, cross-dispersed medium-resolution spectroscopic modes ([Formula: see text]–1200) over select wavelengths. Preceded by both Spitzer and Herschel, the discovery phase space for FORCAST lies in providing unique photometric bands and/or spectroscopic coverage, higher spatial resolution and exploration of the brightest sources which typically saturate space observatories.

“…9. Further information on SOFIA image quality and plans for improvements can be found in Lampater et al (2010Lampater et al ( , 2011; Temi et al (2014); Graf et al (2016).…”

Section: Image Qualitymentioning

confidence: 99%

FORCAST: A Mid-Infrared Camera for SOFIA

Herter

Adams

Gull

et al. 2018

“…This section summarizes the implemented improvements in SOFIA's control system since early 2015. They have been published in more detail in Graf et al (2016) and Graf et al (2017). Future upgrades are introduced in Sec.…”

Section: Upgradesmentioning

confidence: 99%

“…Although, the main goal of the FBC is the compensation of quasi-static deformations, it unfortunately has also introduced some higher frequency noise into the loop which resulted in an increased jitter in that range. This is described in more detail in Graf et al (2016). After some investigation, the problems were identi¯ed to be mostly a sensor issue and high frequency disturbances on the power source in the gyro unit which have been found and eliminated.…”

Section: Sensor Change and Optimization Of The Image Motion Estimationmentioning

confidence: 99%

“…The elevation angle is also connected to the amount of disturbances on the telescope. More details about those in°uences are discussed in Lampater (2014) and Graf et al (2016). In addition, there are other factors whose e®ect is signi¯cantly more di±cult to assess.…”

Section: Measurement Proceduresmentioning

confidence: 99%

“…Early ideas on compensation methods have been published in Kaercher (2002). They have been adopted later on as described in Harms (2009) and are part of an ongoing development and upgrade e®ort (refer to Reinacher et al (2016a) and Graf et al (2016)). In Sec.…”

Section: Introductionmentioning

confidence: 99%

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Image Size and Control System Developments of the Airborne Telescope SOFIA

Graf

Reinacher

Jakob

et al. 2018

Self Cite

The SOFIA telescope is a worldwide unique observatory that enables infrared astronomy aboard a Boeing 747SP at altitudes of up to 45[Formula: see text]kft. Contrary to any ground-based telescope, SOFIA is exposed not only to aerodynamic forces but also aircraft motion and excitation. Nevertheless, the ambitious scientific goals require a stable platform and very precise pointing. As of now, the telescope can be considered diffraction-limited in the far-infrared wavelengths beyond 50[Formula: see text][Formula: see text]m. A careful study of the different sources of blur revealed that image jitter is among the most influential. During the course of a flight, the telescope is exposed to various excitation levels, leading to deformation of its flexible structure and vibrations in a wide range of frequencies. Since SOFIA entered its operational phase, continuous efforts have been made to develop and implement upgrades in the pointing and control system. The original design was a robust and conservative structure aimed to ensure safe operations with several different science instruments and many unknown parameters. In recent years, more and more agile system components have followed to tackle the residual image motion. This paper introduces the telescope control system followed by a summary of recently installed upgrades and ends with an outlook on future developments on our way to diffraction-limited imaging beyond 25[Formula: see text][Formula: see text]m.

The SOFIA Telescope in Full Operation

Reinacher

Graf

Greiner

et al. 2018

Self Cite

The SOFIA telescope is a 2.5[Formula: see text]m class Cassegrain telescope with Nasmyth focus. It is the largest telescope ever integrated into an aircraft. The telescope is exposed to the stratospheric environment during the observations and the fact that the telescope’s foundation, which is a Boeing 747 SP, is vibrating and moving in all degrees of freedom (DoF) requires a highly specialized and sophisticated design. Based on the telescope of its predecessor, the Kuiper Airborne Observatory (KAO), the SOFIA telescope design had to evolve to accommodate a telescope 2.5 times the size of KAO. In several hundred successful observation flights, the telescope proved that it performs not only as specified, but is also extremely reliable. Nevertheless, the telescope’s software and hardware are continuously upgraded to optimize its performance without interfering with the observation schedules to reach even more ambitious image size and pointing jitter goals to enable additional science cases. In addition, manufacturing of the line-replaceable units is in process to ensure that the SOFIA telescope can perform without any major interruptions for the envisioned 20 year lifetime. Some of the main features of the SOFIA telescope are its suspension assembly (SUA), which decouples the telescope from SOFIA’s fuselage with air springs and a spherical oil bearing, the extremely stiff Nasmyth tube (NT), which connects cavity and cabin mounted components of the dumbbell design, and the Secondary Mirror Assembly (SMA), which is used for chopping and fast pointing corrections. This paper aims to give an overview of these and all other major telescope subsystems in operation today. In addition, some of the upgrades, either implemented recently or slated for implementation shortly, are introduced.