Atto–femto scale planarsats: A power‑first design and feasibility framework for planar, surface‑limited spacecraft

Abstract

This thesis develops and demonstrates an early-phase, power-first design and feasibility framework for highly miniaturized planar spacecraft, referred to as ``PlanarSats'', with primary emphasis on femto- and atto-class missions. In these missions, subsystem functionality is concentrated onto a single thin substrate (typically a printed circuit board), and the same limited surface must be shared between electronics placement and solar-power generation. Planarity therefore introduces a direct competition between electrical integration and energy collection, and this competition couples to operations through illumination and attitude. As a result, feasibility is not well captured by isolated subsystem spreadsheets or by directly reusing assumptions common to CubeSat-scale missions. Instead, geometric allocation, uncertainty-aware power sizing, communications-driven duty cycle, and operational constraints must be treated as a coupled early-phase problem. The objective of the thesis is to make this coupled design-to-feasibility loop explicit, repeatable, and practical for a project team working under strict mass, volume, and resource limits. The thesis establishes PlanarSat as a geometry-first classification rather than a new standardized mechanical envelope. Mass-based classes (micro/nano/pico/femto/atto) and standardized form factors (CubeSat, PocketQube) are valuable for broad comparisons and launch integration, but they do not directly surface the dominant coupling introduced by extreme planarity. To ground the classification in evidence, the thesis reviews a diverse set of ultra-small spacecraft missions and credible concepts, comparing architectures, access-to-space strategies, subsystem choices, and operational dependence on host platforms. Satellite independence is defined in system terms (dedicated power, communications, and control), enabling consistent comparison across missions that may be physically deployed together yet remain operationally distinct. The survey shows that PlanarSat missions are frequently conditioned by external interfaces, deployment constraints, and the degree of autonomy granted by the host, and that these factors can dominate schedule, risk, and achievable operations. This landscape synthesis motivates early feasibility tools that expose the operational consequences of surface allocation and that keep host and interface dependencies visible rather than implicit. Building on the landscape synthesis, the thesis introduces a phase-aware power contingency and margin methodology tailored to PlanarSats and other surface-limited ultra-small satellites. Because heritage is limited and relative uncertainty can be high at very low power levels, contingency selection is treated as a primary design decision rather than a procedural afterthought. Agency practices and the AIAA framework are reviewed and then adapted with refined low-power subcategories and a log-linear selection method for choosing contingencies appropriate to both mission class and design maturity. Power is budgeted from a current best estimate (CBE) to a sizing value (maximum expected value, MEV) by applying justified contingencies; where bounding analyses are required, an explicit system-level margin yields a maximum possible value (MPV). A key contribution is the introduction of the Operational Power Envelope (OPE) as the operationally interpretable output of power sizing. Instead of reporting a single scalar budget, the OPE translates the sized power assumption into bounded feasible operating conditions, such as allowable Sun-incidence angles and mode duty cycles. This operational framing makes it clear which feasibility claims are driven by sizing assumptions, which are driven by geometry, and which are driven by operational choices. To complement operational interpretation, the thesis derives an analytical feasibility-screening framework for estimating the minimum feasible PlanarSat size (minimum installed area) for a given functional set. The framework couples the solar-cell area required to meet contingency-corrected peak-mode power demand with the electronics placement area implied by component footprints and integration constraints on planar faces. Closed-form expressions are provided for representative surface-allocation architectures, including separated and mixed electronics/solar layouts, and for the per-face sufficiency requirement that arises when attitude is uncertain and stored energy is limited. These expressions map power and placement requirements into a minimum-area bound, and then into an operational envelope through a cosine Sun-incidence model. Sensitivity analysis identifies the dominant parameters that govern further miniaturization: solar-cell efficiency and tiling fill ratio reduce required cell area; power-path efficiency reduces inflated mode sums; and contingency policy trades installed area against operational robustness and risk. The result is a rapid, transparent screening tool intended for early project phases, helping a project team avoid high-fidelity design effort before confirming that a concept is feasible in principle under explicit assumptions. The framework is demonstrated in an integrated mission-concept case study: EsTRACE (Es-layer TRAnsient Cloud Explorer), a PlanarSat concept for monitoring sporadic-E ionospheric layers that can strongly perturb HF/VHF propagation. EsTRACE transmits sequential beacons in the amateur bands using weak-signal digital and continuous-wave waveforms and leverages distributed amateur receiver networks for near real-time SNR mapping. The spacecraft is developed through bid/proposal, conceptual design review, and preliminary design review using the proposed power-first loop, explicitly coupling link-budget closure to duty cycle and solar-array tiling under a free-tumbling, batteryless constraint. Across the design evolution, per-mode bus power is decomposed and iteratively refined, contingency is applied to obtain MEV, and discrete commercial solar-cell formats constrain the achievable MPV. Architecture choices such as allocating cells across multiple faces, trading footprint against robustness, and enforcing per-face power sufficiency are evaluated to widen the batteryless operational envelope under attitude uncertainty. Interpreted through the OPE, the case study shows how continuous sunlit science operation is feasible only within bounded illumination conditions, while transmission modes with higher instantaneous demand require gated operation and favorable orientations. Beyond feasibility closure, the study also clarifies what must be validated to progress toward implementation, including RF/antenna characterization, mechanical and inhibit-chain closure to the deployment interface, and hardware verification of batteryless operation under representative illumination and attitude scenarios. The thesis also addresses how to retain traceability with model-based systems engineering (MBSE) without the overhead of a full-scale requirements--functional--logical--physical stack, which can be impractical for time- and resource-constrained PlanarSat projects. A tailored MBSE view stack is proposed in which a compact requirements and functional view is retained, but a combined Physical/Electrical view, centered on power-first sizing and the OPE, becomes the main driver. Operational and verification artefacts are intentionally reduced to a simple power-aware state machine and a small requirement-to-test matrix. The approach is demonstrated on a conceptual batteryless radiation-sensing PlanarSat, showing that meaningful traceability can be maintained using lightweight artefacts while keeping explicit power and operational constraints central. Overall, the thesis contributes a unified, uncertainty-aware framework that ties planar geometry, power budgeting, surface allocation, and operations into a coherent early-phase feasibility loop. By formalizing PlanarSat as a geometry-driven class, introducing operationally interpretable power sizing through the OPE, providing an analytical minimum-size screening method, and demonstrating integration on a realistic mission concept, the work enables more reliable early decision making for femto- and atto-class spacecraft. Future work is recommended to extend the framework to time-domain energy feasibility with storage, integrate thermal and link constraints more tightly, and validate the operational envelope with hardware and flight data.