Preliminary Design and Validation of the Navigation Framework for Albedo’s VLEO Constellation
Ryan Watson and Kevin Kloster, Albedo Space
Date/Time: Friday, Sep. 20, 9:20 a.m.
Albedo is constructing a constellation of imaging satellites that will operate in very low earth orbit (VLEO). The payload is designed to capture 10-centimeter visible and 2-meter thermal imagery. This resolution represents a significant leap from existing commercial systems, opening numerous applications. The VLEO orbit is crucial for achieving this high resolution, but it also presents several navigation and mission design challenges. In this paper, we will discuss these challenges and our approach to addressing them.
For navigation of Albedo’s constellation, a commercially available off-the-shelf (COTS) GNSS receiver will be the primary sensing modality. Thus, as a starting point, we’ll provide a literature review of the plethora of excellent literature on GNSS-based high-accuracy orbit determination. This literature review will provide an excellent foundation before delving into the adaptations necessary for high-accuracy GNSS-based orbit determination in the VLEO regime.
Given the literature review, we can discuss the navigation architecture, which can divided into two modules: an on-orbit (moderate-fidelity) module and a ground-based (high-fidelity) module. The on-orbit navigation module operates in real-time on-board the satellite, balancing computation complexity and estimation accuracy. This design introduces interesting trade-offs, such as which states can be maintained within the estimator's state space and the fidelity of a given model, which will be discussed in detail in the full manuscript. The ground-based orbit-determination module is not constrained by real-time requirements. Instead, our primary objective is to estimate the vehicle's state with the highest fidelity possible so that the state can be propagated sufficiently into the future while maintaining accuracy requirements, enabling the scheduling of future data collection and planned orbital maintenance maneuvers. In the ground-based orbit determination section, we will discuss how we enable high-accuracy orbit determination via a discussion of the selected models, the estimation framework (i.e., a novel factor graph-based estimation scheme), and the known inadequacies and path forward for given models and estimator
As mentioned earlier, operating in the VLEO regime necessitates a tight integration between mission design and navigation. One aspect of Albedo’s mission where this is readily apparent is concerning orbit maintenance, as the high drag environment necessitates regular maneuver activities. The final paper will detail how the integration between navigation and mission design is instantiated, and the considerations and impact the ubiquitous thrusting has on the performance of the navigation framework.
Finally, to validate the proposed approach, we will follow a two-stage process. First, we will validate the approach detailed in this paper using a moderate-fidelity simulation environment. This will allow us to assess the robustness of the proposed approach to perturbations over the assumed envelope. Following the simulation results, we will proceed to validate the approach using flight-collected data. For this validation, we will leverage the several years of available data from the Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) mission, which operated in a similar orbital regime.
In summary, within this paper, we will present several key results, as outlined below.
1. An overview of a navigation framework capable of high-accuracy orbit determination of a constellation of VLEO satellites using commercially available off-the-shelf (COTS) sensors and limited computation resources.
2. A discussion on the intricacies of coordinating mission design and navigation for VLEO missions with high accuracy requirements.
3. A novel factor graph-based formulation for high-accuracy orbit determination.
4. A discussion of the current limitations and validation of the proposed approach, including results from simulation and flight data collected data.
5. A discussion on the ongoing efforts necessary for high-accuracy navigation in VLEO.
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