Faults & Safe Mode
How spacecraft notice problems and protect themselves.
Course
The heart of this site's mission: detecting faults, isolating them and recovering safely, with redundancy, safe mode and bounded, supervised autonomy.
Before you start
- Spacecraft Systems foundation recommended
Learning objectives
- Give examples of spacecraft faults and their effects
- Explain what safe mode is and why it exists
- Explain why distant spacecraft cannot wait for instructions from Earth
- Describe redundancy with an everyday example
By the end you can
- Can explain safe mode and redundancy
- Understands why spacecraft must sometimes act before the ground can reply
Before you start
- Foundation level of this track
- Probability basics
- Sensors & Telemetry advanced recommended
Learning objectives
- Describe the Fault Detection, Isolation and Recovery (FDIR) loop
- Use hysteresis and dwell time to avoid mode chattering
- Calculate the reliability benefit of redundancy
- Explain why autonomy is introduced in bounded, supervised steps
By the end you can
- Can explain FDIR in engineering terms
- Can design mode logic that is stable and safe
Lesson plan
Lessons · Ages 14–16
What can go wrong
- Power, thermal, sensor and communication faults
Safe mode
- Switch off what is not essential
- Point to the Sun
- Wait for the ground
Distance and delay
- Light-time to the Moon and Mars
- Why autonomy matters
Redundancy
- Spare units
- Voting between sensors
Hands-on activities
- Play Survive the Eclipse, inject a fault and watch safe mode protect the battery
- Design a 'safe mode' for your phone: what would you switch off first, and why?
Challenge: Survive the Eclipse
Size the battery and set safe mode so the CubeSat survives three orbits, then repeat with a fault switched on.
Pass criteria
- A sustainable power plan: more energy in than out over each orbit
- Battery never falls below the 20% floor
- The design survives with at least one fault injected
Physics and mathematics
Show the 2 equations
t = d ÷ c
t in s, d in km, c ≈ 300,000 km/s
The Moon is about 384,400 km away: about 1.3 seconds each way. Mars is between about 3 and 22 light-minutes away.
E = P × t
Wh
Safe mode lowers P so the battery lasts through the eclipse.
3D models
- CubeSat in orbit with eclipse and safe-mode states (available: Survive the Eclipse)
Lessons · Ages 17–18
FDIR
- Detection
- Isolation
- Recovery
- Verification
Mode logic
- Thresholds
- Hysteresis
- Dwell time
Reliability
- Independent failures
- Parallel redundancy
- 2-out-of-3 voting
Bounded autonomy
- Advisory, supervised, bounded
- Why generative AI must not close a safety-critical loop
Hands-on activities
- Play Survive the Eclipse at the Advanced level: set the safe-mode entry and exit thresholds yourself
- Write the FDIR table for one subsystem: symptom, check, isolation, response, verification
Challenge: Survive the Eclipse (Advanced)
Choose battery size and safe-mode thresholds so the mission survives three orbits with battery ageing and a solar string failure injected together, while still delivering most of the planned imaging.
Pass criteria
- Battery never falls below the 30% floor
- At least 80% of the planned imaging time delivered
- No more than two battery packs
- Safe mode on, with the exit threshold above the entry threshold
Physics and mathematics
Show the 2 equations
R_sys = 1 − (1 − R)²
probabilities from 0 to 1
Two independent units each 90% reliable give 99%, if failures really are independent.
enter safe mode below L; leave only above H, with H > L
percent state of charge
The gap stops the spacecraft switching back and forth around one threshold.
3D models
- CubeSat EPS with fault injection and safe-mode thresholds (available: Survive the Eclipse)
Classes and workshops
Online
Interactive mission and tutorials now; live online classes planned.
In person
No offline workshop is planned for this track yet; its activities can be done at home or in a school lab.
Existing tutorials for this track
Eligibility, independence and privacy
- Independent initiative. Space Academy is part of an independent ISHAVASYAM.ORG education initiative. It is not affiliated with, endorsed by, or run on behalf of ISRO, IN-SPACe, NSIL or the Department of Space.
- No competition eligibility. Learning here does not register anyone for, or make anyone eligible for, any national or international competition. Each competition's organisers set its rules and eligibility.
- Simulated and illustrative. Interactive missions use simplified models and simulated, illustrative values. They are labelled as such and are not flight data.
- Ages. Written for learners aged 14 to 18. Anyone may play the self-paced missions; enquiries from under-18s need a parent or guardian.
- Privacy. Missions never ask for a name, school, age or contact details. Progress is stored only in this browser and can be cleared at any time. This site uses Google Analytics to count page visits and mission steps. Some of the site's existing tutorials ask visitors to sign in with a Google account. If you are under 18, check with a parent or guardian before signing in.