LARA design is based on proven satellite technologies to deliver a sophisticated 3U CubeSat instrument optimized for low-frequency radio observations in the 30–300 MHz range. Drawing inspiration from missions such as Radioastron and the China-Netherlands NCLE, LARA integrates a robust design with a modular, low-cost architecture suitable for both scientific and technological demonstration objectives.
The instrument’s data processing architecture employs an Analogue-to-Digital Converter (ADC) and Field Programmable Gate Array (FPGA) system, a proven approach in high-performance CubeSat missions, ensuring efficient signal acquisition, processing, and transmission within the CubeSat’s constrained power and volume limits.
As a technology demonstrator, LARA is engineered with a low-cost budget and a comprehensive development pipeline, moving through functional model, engineering model, flight model, instrumentation, and supporting infrastructure stages.
The main requirements guiding its design include:
- Observation Frequency Range: 30–300 MHz, covering key astrophysical signals such as Jupiter’s synchrotron radiation and solar bursts and epoch of reionization studies.
- Receiver Temperature: Less than 100 K, ensuring sensitivity to cosmic signals.
- Antenna: Single Helicoidal, deployable configuration with dual polarization, suitable for lunar orbit or L2 deployment (or pre-orbit deployment in LEO).
- Radiation Pattern: 45° beamwidth at 3 dB, with an antenna gain of 10 dBi, adjustable based on final antenna design iterations.
- Processing Capacity: Full instantaneous bandwidth coverage, producing raw spectral data and all four Stokes parameters for polarimetric analysis.
- Payload Power Consumption: Maximum of 6 W, accommodating peak operational demands.
- Payload Weight: Average of 4 kg, fitting within 3U CubeSat mass constraints.
LARA’s operating modes are tailored to diverse scientific targets and include:
- Radio Continuum Observation: Long integration times (e.g., minutes to hours) to capture steady-state emissions, such as Jupiter’s synchrotron radiation.
- Transient Observation: Shorter integration times (e.g., 100 ms) for detecting pulsars and fast radio bursts, requiring rapid sampling and event triggering.
- Spectral Emission Observation: Variable integration times to study RFI characteristics (in LEO) or solar burst spectra, supporting calibration and heliospheric analysis.
- Polarimetry: Generation of all four Stokes parameters (I, Q, U, V) to analyze polarized emissions from astrophysical sources.
- Onboard Processing: Event detection and data storage capabilities to prioritize high-value data within internal memory.
- Raw Data Acquisition: Capacity to retain raw spectral data for a set period, enabling post-processing flexibility.
- Communication Interface: Seamless interaction with the service platform for control commands and data transmission.
The instrument comprises four main hardware sections and one software module, integrated within a 3U CubeSat mechanical structure and thermal design, adhering to standard CubeSat principles. The thermal and power design will be finalized based on orbital analysis (e.g., solar flux radiation in lunar orbit or L2 for efficiency), ensuring operational stability across the 6–12 month mission lifetime.
Antenna Module
LARA design incorporates a quadrifilar helical antenna (QHA) intended to cover the 30–300 MHz range. Key design points to maintaining as close as we can to a high efficiency over such a 10:1 bandwidth. The current baseline calls for a ~1.5 m overall helix length (tip-to-tip when fully deployed), typically providing one to two turns depending on the chosen helix pitch.
Mechanical Configuration and Deployment:
- The helix is stowed in a ~0.5U volume and unfolds passively via stored strain energy in fiberglass supports. Once released, it extends to its full 1.5 m length. This length refers to the total physical extent of the structure, not just a single turn, though the final geometry (pitch, number of turns) will be refined through electromagnetic (EM) simulations.
- Thermal stability and rigidity are crucial to maintain polarization purity and a half-power beamwidth (HPBW) near 45° in the mid-band (e.g., 50–150 MHz). Preliminary mechanical models suggest the structure can remain stable without a ground plane, albeit with a slight gain trade-off.
Anticipated Performance:
- While LARA’s concept points to ~10 dBi nominal gain, this value is realistic primarily around the band center (e.g., 50–150 MHz). At the band edges (30–40 MHz, 250–300 MHz), actual gain may drop by several dB due to the antenna’s finite size relative to the wavelength. We will refine these estimates via full-wave simulations and vacuum-chamber tests before finalizing the flight model.
- Alternative designs—such as a conical log-spiral or a crossed-dipole extension—are under consideration if the mission demands stronger performance below 50 MHz. However, these approaches also scale in size/complexity, especially at the lowest frequencies (~30 MHz).
Analogue Front-End
The Analogue Front-End (AFE) module is the critical interface between LARA’s quadrifilar helical antenna and the digital processing subsystem, tasked with capturing, amplifying, and conditioning RF signals in the 30–300 MHz band for subsequent digitization and analysis. It employs a low-noise amplification chain, bandpass filtering to minimize signal degradation and reject out-of-band interference and a digital step attenuator to ensure the dynamic range needed between the different kind of radio sources, ensuring high-fidelity data delivery to the Digital Back-End for transmission to the service platform. The AFE includes an integrated calibration system with reference signals—such as a fixed resistive load to maintain stable gain and frequency response.
These LNAs drive a multi-stage amplification chain, achieving a total analogue gain of 90 dB (e.g., 20 dB LNA, 70 dB secondary amp) while maintaining a receiver temperature below 100 K. Key characteristics include:
- RF Bandwidth: 30–300 MHz, tailored to LARA’s science targets (e.g., Jupiter’s synchrotron radiation, solar bursts), with a 270 MHz passband enforced by a custom bandpass filter (insertion loss <1 dB, rejection >40 dB outside band).
- Total Analogue Gain: Approximately 90 dB, distributed across stages to provide a dynamic range >90 dB, accommodating diverse signal strengths without saturation, with option to be reduced by digital attenuation to compensate for different strength radio sources.
- Calibration: A fixed 50 Ω load (e.g., Vishay precision resistor, ±0.1 dB stability) to gain baseline checks for in-orbit tuning, ensuring sensitivity across operational conditions.
Digital Back-End
The Digital Back-End (DBE) module digitizes analogue signals from the AFE, processes them to extract scientific data, and formats the output for transmission to the service platform using standard protocols. It manages telemetry operations, controlling onboard electronics and monitoring environmental parameters (e.g., temperature, voltage, current) to ensure system health over the mission. The DBE’s ADC-FPGA architecture, adapted from high-performance CubeSat missions, supports LARA’s demanding data processing requirements.
Key characteristics of the DBE include:
- Analog-to-Digital Conversion: Dual channels at 600 MSPS (mega-samples per second), providing a 300 MHz acquisition bandwidth to fully capture the 30–300 MHz spectrum with Nyquist compliance.
- Spectral Processing: Polyphase Filter Banks (FFT+FIR Filters) with 512/1024 bins (~292 kHz resolution), producing raw spectral data and all four Stokes parameters (I, Q, U, V) for polarimetric analysis.
- Configurable Integration Time: Adjustable from 1 ms (transient detection, e.g., pulsars) to minutes (continuum sources), optimizing sensitivity and data volume.
- Internal Storage: NAND flash capacity to store raw data, with overflow managed by prioritization algorithms.
- Event Detection: The onboard logic identifies transients, triggering the storage and processing for downlink.
- Synchronization: Precision timekeeping synchronized with ground stations for accurate timestamping.
- Interfaces: CAN and UART interfaces for data output and control through FPGA Processors as communication interface with the instrument service platform.