# Space missions, communications and measurement

> A mission trades measurement goals against mass, power, thermal control, communications and trajectory constraints. No single orbit is best for every goal.

Course: [Orbits, missions and exoplanets](https://studybrix.com/en/courses/orbits-missions-and-exoplanets/index.md)
Level: university
Prerequisites: Orbital basics, energy and signal travel time.

## Notes

### Mission design

A mission trades measurement goals against mass, power, thermal control, communications and trajectory constraints. No single orbit is best for every goal.

### Communications

Signals travel at finite speed. One-way delay differs from round-trip delay, and data rate differs from propagation speed.

### Remote sensing

An instrument measures a physical signal with finite resolution and uncertainty. Calibration converts measurements into interpretable estimates.

### Reproducibility

Keep instrument configuration, units, timing conventions and processing steps with the data. These are part of the scientific result.

## Practice questions

### 1. A spacecraft is 900000 km away. Use light speed 300000 km/s. Find one-way signal delay.

Answer: 3 s

Explanation: Delay=distance/speed=3 s.

### 2. A spacecraft is 900000 km away. Use signal speed 300000 km/s and neglect processing delay. Find round-trip signal delay.

Answer: 6 s

Explanation: A round trip covers twice the one-way distance.

### 3. Which statement distinguishes data rate from signal speed?

A. Data rate sets vacuum light speed
B. They are always identical quantities
C. Both are measured only in kilograms
D. Data rate counts information per time; signal speed controls travel time

Answer: Data rate counts information per time; signal speed controls travel time

Explanation: Bandwidth and propagation describe different aspects of communication.

### 4. An instrument uses 20 W for 15 s. Find energy consumed.

Answer: 300 J

Explanation: Energy=power×time.

### 5. Why can a spacecraft image not be interpreted fully without instrument metadata?

Sample answer / marking guidance: Exposure, wavelength band, calibration, geometry and processing can affect the signal. Metadata supplies the context needed to assess it.

Explanation: Credit several measurement-context factors.

### 6. Which is an engineering tradeoff rather than a universal improvement?

A. Communication has no delay
B. Every orbit meets every goal
C. All added hardware has zero cost
D. More instrument capability may require more mass and power

Answer: More instrument capability may require more mass and power

Explanation: Mission constraints must be balanced.

### 7. Propose a data-only student investigation using an existing spacecraft dataset.

Sample answer / marking guidance: Choose a documented dataset, define a measurable question, record calibration and units, analyse a subset, estimate uncertainty and compare results with the stated model.

Explanation: Credit a clear question, existing data and uncertainty; no hardware construction is required.

### 8. A downlink carries 8 megabits each second for 10 s. Ignoring overhead, find transferred megabits.

Answer: 80 Mbit

Explanation: Multiply rate by duration.

## Further reading

- https://science.nasa.gov/learn/

Original AI-assisted educational draft; not independently teacher-reviewed. References support further study, not copied exercises, affiliation or curriculum accreditation.