Design Drivers

Related: Spacecraft Design Overview

Spacecraft Design Drivers	Mission Source	Impact	Thresholds
Mass	Payload mass	Launch vehicle	<250 kg, <1,000 kg, <7,000 kg
Power Consumption	Payload design	Power sys, solar array config	Beyond Mars or <2 weeks
Cost	Funders	Ripples throughout system	<$5M,<$100M, <$500M
Schedule	Funders	Development process	<3 yrs, <5 yrs, >5 yrs
Lifetime	Mission design	Redundancy, quality of parts	<1 yr, <3 yrs, <5 yrs, >5 yrs
Reliability	Mission design	Redundancy, quality of parts, margin	Experimental, operational, human rated
Delta V	Mission design	Propellant load	0, 100, 1,000, 2,000
Orbit	Mission design	Solar array, thermal, radiation reg, launch vehicle	<1,000 km, high-Earth, planetary
Payload Accommodation — Data Rate, Vol, Latency	Mission purpose	Comm, data storage, ground	Thresholds changing fast
— Pointing Requirements	Res or antenna beam	Attitude control system	<5 deg, <0.5 deg, <20 arcsec
— Mass, Volume, FOVs	Payload constraints	Mechanical design	Diameter: <1 m, <5 m
— Other		Data system, master oscillator, cost of ground processing	Mission specific

1. Mass

Primary Cost Driver

Launch costs scale roughly with mass.

Limits or Thresholds:

• Exceeding certain mass thresholds can force switching to a larger launch vehicle (huge cost jump) → cost for launch can be a step-function.

Cascading Effect:

• Larger mass → more propellant → bigger rocket → higher cost.

2. Power

Power Considerations

Determines size of solar arrays (or need for RTGs).

• Larger arrays → higher mass, structural complexity, thermal load.

Power Demands Mainly Come From:

• Payload operations (e.g., high-power instruments).
• Communication system (high data rates over large distances).

3. Cost

Cost Influencers

• Mass & Power strongly influence cost.
• Constrained schedules can increase cost due to overtime, parallel testing, or more robust hardware.

Trade-offs:

• Saving mass may cost more in advanced materials or tighter manufacturing tolerances.

4. Schedule

Schedule Impacts

• Short Schedule: Fewer design iterations, higher risk of failures, potential for cost overruns.
• Long Schedule: Potentially better optimization, but higher overhead and risk of technology becoming obsolete.

5. Reliability & Lifetime

Reliability Requirements

• Desired mission duration dictates how robust subsystems must be.
• Redundancy Strategies (single-string, block-redundant, cross-strapped) increase both reliability and mass.

Human-Rated Missions:

• Demand highest reliability → significantly higher complexity and cost.

6. Total ΔV

ΔV Considerations

Defines how much propellant and what propulsion system is needed.

• Orbit changes, station-keeping, or planetary transfers can greatly increase ΔV demands.

7. Orbit Selection

Orbit Impact Factors

• Thermal Design: Altitude, inclination, and orbit shape affect sun exposure.
• Communication Systems: Altitude and orbit shape affect link budget.
• Attitude Control: Altitude and orbit shape affect atmospheric drag, which affects station-keeping.

Orbit Types:

• LEO, GEO, or interplanetary → each has unique design implications (radiation environment, link budget, etc.).

8. Payload Accommodation

Data Rate & Storage

• High data rate payloads (e.g., imaging instruments) need larger data storage and higher bandwidth for downlink.

• Latency requirements may dictate how frequently data must be transmitted to Earth.

Pointing & Stability

• Precision payloads (e.g., telescopes, cameras) require tight attitude control for accurate targeting.
• Stability is crucial to maintain the field of view (FOV) and prevent image distortion.

Physical Constraints

• Payload size (volume) and mass must fit within the spacecraft’s structural and launch constraints.
• FOV considerations ensure no obstructions block the payload’s sensors or instruments.

Contamination & Temperature

• Optical and UV payloads are highly sensitive to contamination, requiring special handling and clean environments.
• Temperature control is critical to protect delicate instruments.