Payload Assessment

Applicable Phases

• Primary: Phase A (payload trade, first-order sizing), Phase B (preliminary design)
• Supporting: Phase C (performance verification), Phase D (calibration planning)

Analysis Workflows

1. Optical Payload Sizing

• Ground Sampling Distance (GSD): $GSD = h \cdot p / f$ where $h$ = altitude, $p$ = pixel pitch, $f$ = focal length.
• Diffraction limit: $\theta = 1.22 \lambda / D$ where $D$ = aperture diameter.
• Swath width: $W = 2h \tan(FOV/2)$ or $W = N_{pixels} \times GSD$.
• SNR estimation: Signal-to-noise ratio depends on solar irradiance, surface reflectance, atmospheric transmission, detector quantum efficiency, and integration time.
• MTF (Modulation Transfer Function): Budget for optics, detector, motion blur, and jitter (from gnc-assessment).

2. RF Payload Sizing

• SAR: Resolution = $\delta_r = c/(2B)$ (range) and $\delta_{az} = L_{ant}/2$ (azimuth). Power-aperture product drives overall system size.
• Radiometer: Sensitivity $\Delta T = T_{sys} / \sqrt{B \cdot \tau}$ where $B$ = bandwidth, $\tau$ = integration time.
• Communication relay: Size transponders, antennas, and link budget per communications-assessment.

3. In-Situ Instruments

• Mass spectrometer: Mass, power, and data rate estimates. Heritage instruments provide reference.
• Drill / Sample handling: Depth, torque, sample volume, contamination control requirements.
• Seismometer / magnetometer: Sensitivity, noise floor, deployment requirements.

4. Payload Resource Requirements

Derive the payload's demands on the bus:

• Mass: Instrument mass + optics + baffle + electronics + harness.
• Power: Continuous and peak power during observation modes.
• Data rate: Raw data rate = pixels × bits/pixel × frame rate (for imagers) or bandwidth × bits/sample (for RF).
• Data volume: Data rate × observation time per orbit. Feed to communications-assessment for downlink sizing.
• Thermal: Instrument dissipation and temperature limits. Feed to thermal-assessment.
• Pointing: Required accuracy, stability, and knowledge. Feed to gnc-assessment.

Output Format

1. Payload Sizing Report (payload_report.md): Instrument parameters, mass/power/data estimates, key performance metrics.
2. Bus Requirements Flowdown: Table of payload-driven requirements for each bus subsystem (mass, power, thermal, pointing, data).
3. Trade Notes: If multiple instrument options were considered, document the trade rationale.

Interface

• Reads from: /requirements/ (mission objectives, performance requirements)
• Writes to: /analysis/payload-assessment/
• Consumed by: systems-engineering-assessment (mass/power budget), thermal-assessment (dissipation), gnc-assessment (pointing requirements), communications-assessment (data volume), structural-assessment (CG impact), power-assessment (payload power)