Project goals

  • Development of a telescope system for spectroscopic analysis of space debris
  • Self-learning pointing model for high-precision static and dynamic pointing
  • High-precision debris tracking via orbit determination

Description

More satellites have been launched in the year 2023 than any year prior. 40% of all objects currently tracked within earth’s orbit have been sent there in the last four years. An unwanted side effect of this trend is a steady increase in the amount of space debris orbiting earth. Should the trend set in previous years continue, space debris will become an ever increasing threat to satellites. Until there is a global plan to prevent future as well as remove current space debris, an improvement in orbit prediction accuracy is vital. Thereby, unlikely collisions can be detected and the lifetime of satellites extended.

Night photo of the SpecTrackular ground station with geodesic dome opened, showing the large telescope inside on top of a container

Fig. 1: MPEI-OGS: Optical Ground Station

SpecTrackular aims to develop a telescope system capable of measuring the orbital path of space debris and allow spectroscopic characterization. Therefore, high-precision pointing and tracking of the telescope system, an improvement of the orbital path based on collected data and a spectroscopic measurement of the debris object are needed. Reflectance spectroscopy requires particularly precise tracking, because the light source, aperture and detector need to be aligned within a few arcseconds. Spectroscopic analysis of reflected sunlight can give information on the material, pose and rotation of the debris object, which, in turn, enables more accurate orbit propagation.

Illustration of space debris object in front of the night sky within pinhole of a spectrograph

Fig. 2: Optical properties of spectrograph dictate error budget

Pointing

The error sources contributing to the total misalignment of a telescope system have different time constants, depending on their physical origin. A self-learning pointing model, capable of adapting to changing conditions with minimal downtime, regardless of the time of day is being developed.

The current pointing model has the following characteristics:

  • Basic kinematic model + set of higher-order harmonics
  • Day-to-day update performed in < 6 minutes
  • Atmospheric refraction calculation based on environmental data
  • Hysteresis reduction either via pseudo-random grid (Fig. 3, left) or semi-active optics (Fig. 3, right)

At present, a pseudo-random pointing grid approach has been implemented and results in a pointing error of 2.8 arcsec RMS. A semi-active optics approach is currently in development to reach the targeted pointing error of <2 arcsec.

Polar plot of a 150 connected points on the left, illustration of semi-active optics for a telescope system on the right

Fig. 3: Hysteresis reduction via pseudo-random pointing measurements (left) or semi-active optics (right)

Orbit propagation

Using the updated telescope system, the angular position of a space object can be measured with an accuracy below 2 arcseconds. The resulting high-precision tracking data can then be used for orbit determination to correct an outdated orbit vector. The combination of these advancements will hopefully lead to a telescope system, capable of performing spectroscopic characterization.

Inverted images from two satellites on a white background with crosshairs

Fig. 4: Comparison between original (SGP4) propagation and improved orbital propagation (OD)

Coudé-Path

To enable high-quality spectroscopic measurements, the implementation of a Coudé optical path is foreseen as part of the telescope system. A Coudé path allows the collected light to be redirected through a sequence of mirrors to a fixed, mechanically stable location, where a high-resolution spectrograph can be installed on an optical table. This approach decouples the spectrograph from the moving telescope structure, enabling improved mechanical stability as well as the integration of larger and more complex instrumentation. Such a configuration is important for precise reflectance spectroscopy of space debris, because it allows long integration times, minimizes alignment errors, and supports the use of more sophisticated calibration and detection systems.

Use case

  • Space situational awareness (SSA)
  • Conjunction assessment

Project partners

  • ASA Astrosysteme GmbH

Funding

  • FFG – Research Promotion Agency, Austrian Space Applications Programme (ASAP), ID: 911962