34  UAV Energy-Aware Mission Planning

Battery Records, Reserve Gates, Route Choices, and Traceable Mission Scope

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34.1 Start Simple

Start with a mission that moves, loses energy, and changes its radio path while it works. In UAV Energy-Aware Mission Planning, the practical question is what the aircraft must sense, relay, decide, and prove before the flight or network role is safe enough to trust.

In 60 Seconds

Energy-aware mission planning decides whether a UAV should fly the whole mission, shorten it, split it, hand off work, or return early. The planner should use measured records from the actual aircraft and payload: pack energy, battery health, temperature and wind conditions, route distance, climb and descent work, hover or dwell time, payload draw, return-to-home demand, and fallback behavior. A defensible plan records the energy budget, the reserve gates, the route assumptions, the abort trigger, and the records that will be checked after the flight.

Phoebe the physics guide

Phoebe’s Why

A pack’s mAh rating is charge, not energy – multiply by pack voltage to get watt-hours, the number that actually predicts flight time. A real pack is also not a perfect voltage source: it has an internal resistance, so the moment the motors draw current the terminal voltage sags below the open-circuit reading, and it sags more during a hard climb than a level cruise because climb current is higher. That is exactly the “voltage sag under load” this chapter’s pack-record checklist already asks the reviewer to log – it is not a vague caution, it is a specific, computable number, and the segment with the highest current is also the segment with the least voltage headroom above a low-voltage cutoff.

The Derivation

Energy from charge and voltage:

\[E = V \times Q\]

Terminal voltage under load, internal resistance \(R_{int}\) (Thevenin model):

\[V_{term} = V_{oc} - I R_{int}\]

Remaining charge after self-discharge over time \(t\) at rate \(r\) per interval:

\[Q(t) = Q_0(1-r)^t\]

Derated usable pack energy behind a design reserve fraction \(k\):

\[E_{usable} = k \times V \times Q_0\]

Worked Numbers: A Catalog-Typical Mapping-Drone Pack

  • Catalog-typical 6S LiPo (this chapter deliberately avoids fixed platform numbers, so these are stated design-typical values): \(V=22.2\) V nominal, \(Q_0=10.0\) Ah, \(R_{int}\approx40\ \mathrm{m}\Omega\) pack. Energy: \(E=22.2\times10.0=222\) Wh.
  • Cruise segment, catalog-typical \(I=25\) A: \(\Delta V=25\times0.040=1.00\) V, terminal \(=21.2\) V (4.50% sag).
  • Climb segment, catalog-typical \(I=45\) A: \(\Delta V=45\times0.040=1.80\) V, terminal \(=20.4\) V (8.11% sag) – the climb segment \(E_c\) costs more than its share of \(E_m\) not only in energy but in instantaneous voltage headroom, which is exactly why the segment gate should check the worst-current point, not only the worst-distance point.
  • Self-discharge, catalog-typical LiPo \(r\approx2\%\)/month: over a 2-week gap between charge and flight, \(10{,}000\times\sqrt{0.98}=9{,}899\) mAh remains – a 101 mAh (1.00%) loss, small but not zero, which is why the “source of the estimate” line in the pack record matters even for a short turnaround.
  • Derating: a catalog-typical 20% design margin gives usable capacity \(E_{usable}=0.80\times222=178\) Wh – the number the mission’s \(E_{req}\) inequality should be checked against, not the full 222 Wh nameplate.

34.2 Learning Objectives

By the end of this chapter, you will be able to:

  • Build a UAV energy budget from measured pack, route, payload, dwell-time, climb, and return records.
  • Separate usable mission energy from reserve energy and return-to-home energy.
  • Explain why the farthest reachable point, not just the final waypoint, controls the return reserve.
  • Choose energy-aware route adjustments without hiding safety, payload, or data-collection trade-offs.
  • Create a traceable mission record that supports repeatable improvement across flights.

34.3 Protect Reserve Before Work

If you only need the operating rule, this layer is enough: plan the required mission, protect return reserve from the worst active point, then add optional work only when measured records leave enough margin.

UAV energy-aware planning loop showing mission scope, measured energy records, route estimate, reserve gates, execution with live checks, and post-flight log updates feeding the next mission scope.
Energy-aware planning accepts, trims, splits, or returns from measured energy records, route estimates, reserve gates, live checks, and post-flight updates.

Mobile summary: Protect return reserve first; optional work only stays in scope while measured energy, route, payload, weather, and fallback records still pass.

Measure

Use logs from the actual aircraft, battery condition, payload mode, weather window, route, climb, dwell, and communication behavior.

Gate

Separate mission energy, return energy, uncertainty, and reserve so optional work cannot spend the energy needed for fallback.

Learn

Use live and post-flight records to update route cost, dwell cost, retry cost, wind sensitivity, and future scope gates.

34.4 Roof Inspection Scope Record

For the roof-inspection example, the record should make the scope decision obvious to the next operator: what must be collected, what can be skipped, and which gate protects return.

Required workFive photo waypoints and two short dwell points are mandatory because they satisfy the inspection service.
Worst return pointThe middle roof edge, not the final waypoint, creates the largest return requirement.
Optional workThe thermal sweep is accepted only if reserve still passes after route, dwell, payload, wind, and uncertainty costs are counted.
Post-flight updateThe next plan records measured dwell energy, wind penalty, payload draw, retry time, skipped work, and reserve at return.

34.5 Under the Hood: Why Energy Debt Hides

Energy plans fail when several small costs are treated as harmless extras. The controller may still show a healthy percentage while the mission has already spent the margin needed for return or handoff.

  • Dwell debt: hover, slow passes, photo retries, and weak-link retransmission turn time-on-task into propulsion and payload cost.
  • Route debt: detours, repeated climbs, wind exposure, and a farthest active point can dominate the final waypoint distance.
  • Payload debt: sensors, radios, compute, gimbals, lighting, storage, and live transfer modes change both draw and duration.
  • Fallback debt: waiting too long to skip, split, hand off, loiter, or recall can spend the reserve that made fallback possible.
Quick Check: Energy Planning Boundaries
Minimum Viable Understanding
  • Flight time printed in a specification sheet is not a mission plan. Use measured logs from the actual aircraft, payload, weather window, and battery condition.
  • Reserve is a gate, not spare energy to spend at the end of the route.
  • Return-to-home must remain feasible from every active part of the mission area.
  • Hover, slow passes, climbs, retransmissions, and repeated route corrections can matter as much as straight-line distance.
  • A good plan explains what will be skipped, shortened, handed off, or recalled when the energy gate tightens.

34.6 Prerequisites

Revisit these chapters if the terms are unfamiliar:

34.7 How This Chapter Fits

Trajectory control asks how the aircraft should move. Energy-aware mission planning asks whether the aircraft should keep accepting that motion plan. It sits between mission design and in-flight control: the planner sets the budget and reserve gates, while the controller checks those gates whenever route, link, weather, payload, or safety records change.

The overview depth layer shows the energy-aware planning loop that anchors mission scope, measured energy records, route estimate, reserve gates, execution with live checks, and post-flight updates.

34.8 Energy Budget Record

An energy plan should be written as a record, not as a single remaining-battery number. The record separates what the mission is allowed to spend from what must remain available for return, uncertainty, and fallback.

Let \(E_m\) be mission energy, \(E_t\) transit, \(E_d\) dwell, \(E_c\) climb, \(E_p\) payload, \(E_{ctrl}\) control overhead, \(E_{ret}\) return, \(E_u\) uncertainty, and \(E_{res}\) protected reserve.

\[E_m = E_t + E_d + E_c + E_p + E_{ctrl}\]

\[E_{req} = E_m + E_{ret} + E_u + E_{res}\]

The plan is acceptable only when the measured usable pack energy is greater than the required energy for the current mission scope. If the inequality is close, the correct action is not to hope that the battery lasts. Reduce the mission, change the route, split the flight, or hand off work.

No-panel UAV energy budget record showing measured battery state, derating records, mission loads, return requirement, reserve gate, and decision outcome.
Figure 34.1: UAV energy budget record showing measured battery state, derating records, mission loads, return requirement, reserve gate, and decision outcome.

34.8.1 Pack records

Record pack energy, state of charge, battery health, temperature condition, voltage sag under load, and the source of the estimate.

Weak records: assuming a rated flight time.

Strong records: recent flight logs from the same aircraft, payload, and operating profile.

34.8.2 Route records

Record planned distance, climb and descent segments, no-fly detours, expected wind exposure, and the farthest reachable point from base.

Weak records: endpoint distance only.

Strong records: route cost checked at each waypoint or mission segment.

34.8.3 Payload records

Record sensor, radio, compute, gimbal, lighting, and storage behavior. Payload draw may be smaller than propulsion, but dwell and retransmission time can make it mission-critical.

Weak records: one generic payload number.

Strong records: measured draw and time-on-task for the selected collection mode.

34.8.4 Fallback records

Record the recall rule, skipped-task rule, handoff target, loiter limit, and data-loss risk if the mission cannot continue.

Weak records: “return if battery is low.”

Strong records: a named gate that triggers a specific fallback action.

34.9 Reserve Gates

Reserve gates convert an energy estimate into a decision. They prevent the mission from spending return energy on optional work.

  1. Launch gate: the aircraft does not launch unless the route, reserve, return, and uncertainty budget all pass.
  2. Segment gate: each new segment must leave enough energy to return from the worst reachable point after the segment starts.
  3. Dwell gate: hovering, slow passes, repeated photos, and link retries have a time limit tied to the energy budget.
  4. Scope gate: low-priority tasks are skipped before the return gate is threatened.
  5. Return gate: the aircraft returns or hands off when the current reserve is no longer enough for safe continuation.
  6. Post-flight gate: the measured energy use updates the next planning record.
No-panel UAV route reserve gates showing launch, segment, dwell, scope, return, and post-flight update checks along a mission route.
Figure 34.2: UAV route reserve gates showing launch, segment, dwell, scope, return, and post-flight update checks along a mission route.

34.10 Route Planning Decisions

Energy-aware routing is not just shortest-path routing. A shorter route can still be worse when it forces repeated climbs, slow passes in poor wind, long hover periods, or weak-link retries.

34.10.1 Waypoint order

Visit nearby tasks together when this reduces route length and repeated climb. Do not blindly sort by task number or by final destination.

Check question: does this order keep return feasible from the farthest active point?

34.10.2 Dwell and collection mode

Choose hover, slow fly-by, fast fly-by, or deferred collection based on data need, link quality, and energy reserve.

Check question: what is the maximum dwell time before the task is skipped or handed off?

34.10.3 Altitude profile

Avoid unnecessary up-and-down profiles. Keep altitude changes tied to payload need, link geometry, terrain clearance, or safety constraints.

Check question: which climb is essential, and which is only a habit from a previous mission?

34.10.4 Split or handoff

Split the mission when one flight would spend too much reserve on distant or low-priority work. In a multi-UAV mission, hand off only when the receiving aircraft also has a valid reserve record.

Check question: does the handoff reduce risk, or just move hidden energy debt to another aircraft?

34.11 Worked Example: Inspection Mission Scope

Consider a roof-inspection mission with five waypoints, two photo dwell points, and one optional thermal sweep. The planning team has recent measured logs from the same airframe and payload. The numbers below are not universal platform values; they are the team’s measured planning inputs for this specific setup.

Measured usable energy The battery record shows usable pack energy after health and weather adjustment. The planner keeps a separate reserve instead of treating the whole pack as spendable.

Base route The base route includes outbound travel, waypoint-to-waypoint travel, return distance from the farthest reachable point, and a small route-uncertainty allowance.

Dwell tasks Two photo points require short stable dwell. The thermal sweep is useful but optional, so it is placed behind a scope gate.

Decision If the launch and segment gates pass, the aircraft flies the required photo route. If live energy drops faster than expected, the thermal sweep is skipped before return energy is threatened.

The important learning point is the decision structure. The team does not ask, “Can the UAV probably finish?” It asks:

  1. What energy records are measured rather than assumed?
  2. Which tasks are mandatory, optional, or handoff candidates?
  3. Which segment contains the worst return demand?
  4. Which gate will shorten the mission before return reserve is spent?
  5. What post-flight data will update the next plan?

34.12 UAV-WSN Data Collection

In UAV-assisted wireless sensor networks, the aircraft may act as a data mule, temporary gateway, or emergency collector. Energy planning must balance route efficiency with data urgency.

34.12.1 Buffer urgency

Sensors with full or time-critical buffers may need earlier collection. The route should record why urgency justifies extra travel.

34.12.2 Contact quality

A weak link can turn a brief pass into a long dwell. The plan should include a retry limit and a fallback, such as collecting a smaller summary or returning later.

34.12.3 Cluster collection

Dense deployments can reduce flight cost by collecting through a cluster head or temporary relay, but this shifts energy and reliability assumptions to the ground network.

34.12.4 Mission scope

When reserve tightens, the aircraft should drop low-priority nodes before risking the return gate. The skipped-node list becomes part of the mission record.

34.13 Common Pitfalls

UAV Energy Planning Pitfalls

Planning from rated flight time. Rated endurance is useful for screening platforms, but mission planning needs measured logs for the actual aircraft, payload, route, battery condition, and weather window.

Treating reserve as a percentage only. A percentage can be a policy, but the operational question is whether the aircraft can return from the worst active point while still preserving required margin.

Optimizing distance while ignoring dwell. Data collection, retries, inspection holds, and station-keeping can consume more budget than the extra distance saved by a clever route.

Letting optional work consume mandatory return energy. Optional sweeps, extra photos, and extended relay service should have explicit scope gates.

Failing to update the next plan. Post-flight logs should update route cost, dwell cost, wind sensitivity, battery health assumptions, and fallback timing.

34.14 Readiness Checklist

Before a mission is accepted, verify these items:

Measured records The budget is based on recent logs or controlled measurements, not only on a datasheet.

Worst return point The return requirement is checked from the farthest reachable point in the active mission, not only from the final waypoint.

Dwell limit Every hover, retry, slow pass, or station-keeping task has a maximum allowed time.

Scope order The plan clearly identifies which tasks are mandatory, optional, skipped first, or handed off.

Fallback action The return, loiter, handoff, or abort behavior is named and tied to a specific gate.

Post-flight update The team knows which log fields will update the next mission budget.

34.15 Concept Relationships

34.15.1 Energy budget and route scope

The energy budget limits which route segments, dwell tasks, and optional collections can be accepted.

34.15.2 Return reserve and safety state

Return reserve is a safety gate. It must survive optional work, link retries, and route detours.

34.15.3 Payload work and dwell time

Payload energy is not only watts. It is also the time spent holding position while the payload collects, transmits, or retries.

34.15.4 Post-flight logs and future planning

Energy planning improves when each flight leaves measured records about actual route cost, dwell cost, battery behavior, and fallback triggers.

34.16 Interactive Checks

Knowledge Check: Mission Feasibility

Label the Diagram

34.17 Summary

Energy-aware mission planning is the discipline of deciding what a UAV is allowed to attempt with its current battery, route, payload, weather, and fallback records. The central habit is to separate mission energy, return energy, uncertainty, and reserve instead of collapsing them into one remaining-battery number. The safest plans protect return feasibility from every active point, place optional work behind scope gates, and use post-flight logs to improve the next plan.

34.18 See Also

34.19 What’s Next

34.19.1 Mission patterns and avoidance

UAV Missions and Collision Avoidance

34.19.2 Multi-UAV trajectory coordination

UAV Swarm Coordination Trajectory

34.19.3 Trajectory implementation labs

UAV Trajectory Labs and Implementation

34.19.4 UAV production checks

UAV Networks: Production Checks

34.20 Key Takeaway

UAV energy planning must reserve capacity for flight, sensing, communication, return-to-home, and contingencies. A route that consumes the safety margin is not operationally viable.