Design of an innovative observer based feedback enabling faster telescope control in SOFIA

Graf, Friederike; Reinhart, Johannes; Reinacher, Andreas; Fasoulas, Stefanos

doi:10.1117/12.2306089

Cited by 2 publications

(3 citation statements)

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“…An optimized controller structure using an observer in the feedback loop is currently under development to achieve a higher bandwidth in the near future [refer to Graf et al (2018)]. The TA angular rate is measured with¯ber-optical gyroscopes, situated in the gyro unit close to the centerof-mass of the telescope.…”

Section: Pointing and Control System Structurementioning

confidence: 99%

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Image Size and Control System Developments of the Airborne Telescope SOFIA

Graf

Reinacher

Jakob

et al. 2018

J. Astron. Instrum.

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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.

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Section: Pointing and Control System Structurementioning

confidence: 99%

“…Even better results can be expected after adapting the current controller gains to that delay. Several approaches to achieve that have been studied in Reinhart (2018) and summarized in Graf et al (2018).…”

Section: Reduction Of Delay In The¯ne Drive Control Loopmentioning

confidence: 99%

Image Size and Control System Developments of the Airborne Telescope SOFIA

Graf

Reinacher

Jakob

et al. 2018

J. Astron. Instrum.

Self Cite

View full text Add to dashboard Cite

show abstract

“…While the performed work was highly successful, increasing demand on the pointing stability requires a continuation of the e®ort. The pointing stability improvements achieved in recent years and a brief outlook on planned work are summarized in Graf et al (2018a) with more detailed descriptions given in Graf et al (2016Graf et al ( , 2017Graf et al ( , 2018b. Figure 15 shows the power spectral density of a point source in cross elevation measured with the FPIþ.…”

Section: Pointing Controlmentioning

confidence: 99%

The SOFIA Telescope in Full Operation

Reinacher

Graf

Greiner

et al. 2018

J. Astron. Instrum.

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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.

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Design of an innovative observer based feedback enabling faster telescope control in SOFIA

Cited by 2 publications

References 4 publications

Image Size and Control System Developments of the Airborne Telescope SOFIA

Image Size and Control System Developments of the Airborne Telescope SOFIA

The SOFIA Telescope in Full Operation

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