5-1 design of uav systems concepts of operationc 2002 lm corporation lesson objective – to discuss...

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Design of UAV Systems

Concepts of operationc 2002 LM Corporation

Lesson objective – to discuss

Concepts of operationincluding …

• Basic concepts• Area coverage• Combat air patrol• Response time• Example problem

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Review

Concept of operations (ConOps) definition(s)

1. How something is used or operated• Typically associated with military systems but

also applicable to commercial systems. 2. The name of a document used to describe how

a system should be operated, e.g.

…describes the approach to deployment, employment, and operation of a new or upgraded system or capability being advocated to meet identified tasks or missions. CONOPS are not limited to single systems but can rely on other systems and organizations, as required.

http://www.fas.org/spp/military/docops/afspc/i10_606.htm

We will use the first definition – determining how something is used or operated vs. a ConOps document

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How UAVs are used

• Although it is tempting to consider UAVs as straight-forward replacements for manned aircraft, this does not take advantage of their inherent capabilities• No physical constraints

• Size, endurance, maneuvers, etc.• No mental/physiological constraints

• Memory, errors, training, etc.• No work rules, arguments, sick days or vacations• Fewer survivability concerns

• But they also have inherent limitations (today) • On board intelligence is either simple or easily spoofed• Off board intelligence is bandwidth limited

• UAV missions, therefore, tend to require or involve• Small size• Long endurance, high altitude or physiological constraints• Simple rules of engagement and ConOps

• High risk • Continuous operations

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Examples

Helios – Altitude record holder (air breathing aircraft)

MicroStar

Lockheed Martin Aeronautics Company

Global Hawk - 38 hour endurance

http://www.auvsi.org/members/us.cfm

Predator A – Hellfire missiles

HeliWing

www.fas.org/irp/program/collect/vtuav.htm

DarkStar

www.fas.org/irp/program/collect/docs/97-0230D.pdf

Tom Cat

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Air operations

Whether, manned or unmanned, there are two general types of missions, preplanned and on-demand• Preplanned missions are scheduled well in advance• On demand missions can be launched quickly (within minutes) if an aircraft is ready and a crew is on site- The military does “strip alert” and “standby alert” missions

- Strip alert pilots are in the cockpit, ready to go There are two basic types of loiter missions - standoff and over flight (or “penetration”)• Standoff missions generally are flown when over flight is not allowed or is considered too risky- Exceptions are missions flown with sensors that do not

look straight down such as synthetic aperture radar (SAR)Although missions can takeoff from one base and land at another, typically we design for fixed base operations

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Typical mission profile

0 Engine start1 Start taxi2 Start takeoff3 Initial climb4 Initial cruise5 Start pre-strike refuel6 End pre-strike refuel

Start cruise 7 Start loiter8 End loiter, start cruise9 Start ingress

10 Combat11 Weapon release 12 Turn13 Start egress14 End egress, start cruise15 Start post-strike refuel16 End post-strike refuel17 End cruise18 Start hold19 End hold

Notation

Border - Standoff

Border - Loiter/Penetrate

Border -Penetrate/Loiter

0

2 3

4 5 6 7 810 11

12 13151617

18

19

Standoff - Distance from loiter or combat to border (+/-)

Standback - Distance from refuel to border

Ingress - To target at penetration speed

Egress - From target at penetration speed

Range (Rge) = 2*Radius(R)

Terminology

1

14

9

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Target area coverage from base

Platform only

Ap = (p)*Rp^2 -Tan(p)*Db^2 (10.1)

where

p (radians) = ArcCos(Db/Rp) (10.2)

Rp = Platform radius

Db = Distance to border

Target area

Rp

Rp

Target coverage Area (Ap)

Base

Db

p

Xmax

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Coverage area example

For

Db = 250 nmRp = 500 nm

Platform only coverage

p = ArcCos(250/500) = 60 deg

Xmax = 433 nm

Ap = (60*/180)*500^2-250*433 = 153549 nm^2

Rp

Rp = 500 nmTarget coverage Area (Ap)

Base

Db

p

Int’l waters

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Lesson Concepts of operationc 2002 LM Corporation

UAV vs. manned operations

• Military UAV missions can be planned and operated like manned aircraft if they stay in military air space- Flights can be scheduled one day and flown the next or, in time critical situations, launched on demand

- But manned aircraft operations sometimes cease during UAV launch and recovery operations

• If UAVs have to fly in non-military airspace, flights may have to be planned days to weeks in advance - To allow time for coordination with local civilian air traffic control and VFR traffic

• Most manned military missions are for training- Pilots need proficiency flying (20+ hrs/month)

• Reconnaissance UAVs operate differently, after initial training, most missions are operational

• UCAVs are more different, plans are to keep most in storage until needed for combat (train on simulators)

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Sensor coverage

• Some sensors are fixed (called “staring” sensors)- Photo reconnaissance cameras are often fixed- Staring sensors also used for self defense

• Others are essentially fixed (e.g. “line-scanners”)- The sensor rotates, target coverage is in thin strips which can be integrated over time to form an “image”- They can provide horizon-to-horizon coverage

• Some sensors are fixed in one direction and can be “slewed” in another (e.g. side looking radar) - Horizontal coverage controlled by vehicle flight path, elevation controlled independently

• Other sensors can be slewed in azimuth and elevation but only within limits (e.g. SAR)

• The most flexible sensors are fully “gimbaled”in azimuth and elevation and can cover an entire hemisphere (or more)

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Weapon coverage

• There are a wide variety of weapons types, both powered and unpowered - Powered weapons can extend target coverage from a little (free fall bombs) to a lot (cruise missiles)

• Almost all weapons are launched forward - Sonabouys and parachute delivered weapons are exceptions

• Guided weapons can attack targets well off of the flight patch axis

• Some weapons can be aimed like sensors- Machine guns and grenade launchers

• Some future weapons will also be aimed- Lasers

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Loiter missions

Manned military reconnaissance missions loiter over friendly territory- Sensors can look into neighboring territory without endangering the crew (in general)

Manned strike missions are flown both ways- Stealth aircraft are designed for over flight but they seldom loiter over hostile territory

Unmanned military reconnaissance (and strike) missions are also flown both ways- Global Hawk is designed to loiter over friendly territory- Dark Star was stealthy and designed to fly over hostile territory (UCAV will also operate this way)

- Predator is not a stealthy design but often loiters over hostile territory

- It takes a calculated risk (and is sometimes lost)

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Standoff vs. over flight

Sensors

- Sensors on penetrating platforms can look down and all around

- Inherently, they can cover more target area than a standoff sensor

Weapons

- Weapons on penetrating platforms have the same advantages

RSensor Coverage Capability Unusable

sensor coverage

Border

Standoffdistance

Penetrate Standoff

RUAV

Border

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Loiter patterns

Plus many others and combinations thereof

Figure 8Circle SearchRacetrack

Threat avoidance

Elongated 8

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Search area coverage

Straight line coverageArea = SwathSpeedTime

Equivalent range = Area/Swath

Search pattern coverageKArea = SwathSpeedTime

Typical factor (K) = 1.3?or

Ou

tsid

e ar

ea

Overlap

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Combat Air Patrol (CAP)

• Target area coverage (and response time) from a CAP type mission is a bit complex and not well understood- In this type mission, the air vehicle loiters over an

area until it receives and order to observe or attack an area of interest- Assumed to be at maximum fly-out distance

- Upon arrival over the target area, the air vehicle performs its mission and then returns to base

• The flight path, therefore, is triangular consisting of:- An outbound segment to the CAP location - Another segment to maximum distance- A third segment back to base

• Typically the CAP location is over friendly territory and we will call it a loiter/penetrate mission

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Loiter/penetrate geometry - optional

Base

Db

Dso

D1

D2min

Loiterlocation

D2max

D3min

XmaxPlatform only

Border

D3max

Note - Dso is negative here

2max

Definitions • D1+D2+D3 = 2*R - LED = 2R’ (10.7)where

D3 = Distance back to base R = Mission radiusLED = Loiter equivalent distance 2max = ArcCos(Dso/D2max) (10.8)

From geometry

• D1+ D2min = D3max (10.9)

• (D1-Dso)^2+Xmax^2 = D3min^2 (10.10) • Dso^2+Xmax^2 = D2max^2

therefore• (D1+Dso)^2- D3min^2 = Dso^2-D2max^2

andD2max = [Dso^2-(D1-Dso)^2+(2R’-D1)^2]

2(2R’-D1) (10.11)

Not optional

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Platform only coverage

Define LEDSolve for D2min (10.9)Solve for D2max (10.11)Solve for 2max (10.8)Solve for D3min (10.10)

• Numerically integrate sector area

from 2 = 0 to 2max where 2 = 2max/nn = number of integration steps

noteD2' + = 2*R -LED - D1 - D3’ (10.12)

andD3’ can be solved using the same approach used to solve for D2max

• Subtract triangular area defined by Dso, Xmax and D2max

Solution approach

D2max

Base

Db

Dso

D1

D2min

D3'

D2'

Loiterlocation

D3min

x

2

Xmax

Optionaltopic

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Solve for maximum area coverage (LED = 300nm) where

R = 650nmDb = 250 nmDso = -125nm

Solution steps

D2min = 375nm D2max = 410.7nm2max = 72.3 deg D3min = 464.3 nm

• Numerically integrate sector area from 2 = 0 to 72.3 deg (n=10)

Sector area = 188767 sqnm

• Subtract triangular area defined by Dso, Xmax and D2max (48907sqnm)

• Total area = 139860 sqnm

Platform coverage example

D2max

Base

Db

Dso

D1

D2min

D3'

D2'

Loiterlocation

D3min

x

2

Xmax

2maxOptional

topic

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R = 650 nmLED = 300 nmDb = 250 nmDso = -125nm

thereforeD2min = 375nm D2max = 410.7nm2max = 72.3 deg D3min = 464.3 nm

• Circular sector area (2 = 0 to 72.3 deg)Average radius = 393 nmSector area = 194895 sqnm

• Subtract triangular area defined by Dso, Xmax and D2max (48907sqnm)

• Approximate area = 146078 sqnm (+4.5%)

Approximate solution

D2max

Base

Db

Dso

D1

D2min

D3'

D2'

Loiterlocation

D3min

Xmax

Circular segment approximation• Radius = (D2Min+D2max)/2• Center at loiter location

The approximation is valid for loiter penetrate only

2max

Optionaltopic

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Figures of merit

• During pre-concept and conceptual design, simple figures of merit are typically used• Examples:

• Operational time on station - Global Hawk goal = 24 hours at a distance of 1200 nm from base

• Target area coverage per unit time - Global Hawk wide area search goal = 40,000 sq.nm/day- With 10 km sensor swath width at 343 kts at 10% over lap (Area = SwathSpeed24 0.9)

• Number of targets per unit time - Global Hawk goal target coverage = 1900 2Km x 2Km spot images/day

• But some ConOps require different metrics• Increasingly the figure of merit of interest is area coverage within a given response time

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Response time example

Platform response time On alert (pre-assigned)

Tr = Tse+Ttto+Tcl+Tcr+TpenwhereTse = time to start engines (≈ 5 min)Ttto = time to taxi & takeoff (≈ 10 min)Tcl = time to climb = Dcl/VclTcr = time to cruise = Db/Vcr-TclTcr = time to penetrate = Dpe/Vpe

Response time (Tr) - The time required to respond to a request or order such as:

- Put platform overhead, put sensor on target or put weapon on target

On standby (not assigned)

Tr = Tr+TprepwhereTprep = additional preparation

times includingAircraft prep (1-2 hrs)Crew transit (2-4 hours)Mission planning (15-60 min)Flight plan coordination (45 min) ≈ Tr + 3 to 6 hrs (@ minimum)

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Response time effects

Sensors

• Sensors arrive on target before the platform (@ speed of light)

- Target coverage is increased by the range of the sensor at any given time

Weapons

• If a weapon is faster than the platform - the weapon will arrive over target first and response time improves

• If the weapon is slower – coverage area may increase but at a slower response time

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Figures of merit

Base

Platform only example • For a specific missions with specific response time requirements, a calculation that includes all of the individual time increments and shows that the requirement can be met, will be the primary figure of merit.

• For more generalized missions, target coverage as a function of time, can be a good figure of merit- For example, Xsqnm target

coverage within Y minutes

Border

Mission radius

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Operating distance effects

• The closer an air vehicle loiters to its target area, the more efficiently it can employ its sensors and the quicker it can respond to assignments or requests• It does, however, reduce target area coverage

- It is a simple matter of geometry for a vehicle with a fixed range or radius

Base

Loiter

Border

Radius = 500 nm

362 nm

438 nm487 nm

463 nm

200 nm

50 nm

Target coverage

area 148K sqnm130K sqnm

Border

Example

Total mission radius = 650 nm

LED = 300 nm

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Next subject

Lesson objective – to discuss

Concepts of operationincluding …

• Basic concepts• Area coverage• Combat air patrol• Response time• Example problem

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Surveillance UAV - review

• Predator follow-on type• Land based with 3000 foot paved runway

- Mission : provide continuous day/night/all weather, near real time, monitoring of 200 x 200 nm area

- Basing : within 100 nm of surveillance area- Able to resolve range of 10m sqm moving targets to 10m and

transmit ground moving target (GMT) data to base in 2 minutes - Able to provide positive identification of selected 0.5m x 0.5 m

ground resolved distance (GRD or “resolution”) targets within 30 minutes of detection

- Ignore survivability effectsMinimum required trades

- Communication architecture- Sensor(s) required- Control architecture- Operating altitude(s)- Time on station- Loiter pattern and location

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Surveillance UAV

200 nm

Loiter location(s)?

100

nm

Surveillance area

200

nm

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Our example – how to start?

• Analyze the problem - What is the customer really asking for?- What information is missing?

• Look at some potential solutions- What are the overall system design drivers?

- ConOps- Communications- Payload

• Pick an initial approach (or starting “baseline”)- Define requirements- Analyze it- Estimate cost and effectiveness

• Analyze the other approaches- Compare results

• Select a baseline approach- Reasonable balance of cost, risk and effectiveness

Today

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What is the customer asking for?

• A system that can monitor a large area of interest- Conduct wide area search (WAS) for 10 sqm ground moving targets (GMT), range resolution 10m. Send back data for analysis within 2 minutes

• A system that can provide more data on demand- Based on analysis of wide area search information- Based on other information

• A system that can provide positive identification of specific operator selected targets• Within 30 minutes of request at a resolution of 0.5 m

• But what is positive identification?- Does it require a picture or will a radar image suffice?

• …and what happens to search requirements while the UAV responds to a target identification request?

• …and how often does it respond?• …and what is the definition of “all weather”?

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Getting answers

• Ask the customer- But don’t always expect a definitive answer

• Some typical responses – - Positive identification :

- “Visual image required”- Search while responding to target identification request: - “interesting question, what are the options?”

- ID response frequency – Assume 1 per hour- Weather definition : “Assume

- Clear day, unrestricted visibility (50% of the time)- 10Kft ceiling, 10 nm visibility (30%)- 5Kft ceiling, 5 nm visibility (15%)- 1Kft ceiling, 1nm visibility (5%).

- Threshold target coverage = 80%; goal = 100%”- Note: a measure of effectiveness just got defined!

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Some constraints

• WAS all weather sensors- Assume minimum look down angle () = 5- Assume maximum look down angle () = 60

• ID sensors- Assume nominal maximum slant range = 30 nm

- For reasonable resolution against typical ground targets

- Assume minimum look down angle () = 5

Max rangeMin rangeh = altitude

Slant range - minSlant range - max

hmin = RmaxTan()

Rmin = RmaxTan()/Tan()GMTI coverage area [Tan()/Tan()]^2

Strip coverage area [Tan()/Tan()]

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• If a UAV loiters over a fixed point in the middle of a square surveillance area, it can meet the 80% coverage, 2 minute moving target detection wide area surveillance (WAS) requirement if1. It makes 2 minute turns (assuming a nominal 45 degree WAS field of regard)

- And the image processing plus transmit time is held to 30 seconds or less

2. The WAS range is slightly larger than ½ the width of the surveillance area- Area of circlesquare = /4

= 0.7853. It has a 100% detection rate, 100 % of the time

WAS ConOps

Target

101 nm

200 nm x 200 nm

Target

Min range effects ignored

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• We have a threshold requirement for positive (visual image) target identification (ID) 80% of the time

• To design our baseline for the threshold requirement• We have to be able to operate at or below 10 Kft for 30% of the target identifications

• 50% of the time we can stay at altitude and 20% of the time we won’t see a target (unless we image at <= 5 Kft)

Positive ID ConOps

Cloud ceiling/visibility Clear day, unrestricted 10Kft ceiling, 10 nm 5Kft ceiling, 5 nm 1Kft ceiling, 1nm

Percent occurrence 50%30%15%05%

Atmospheric conditions (customer defined)

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ConOps assessment

• The WAS and ID mission requirements are in conflict- 80% WAS coverage is required (at a minimum)

- Assuming a uniform distribution of targets- This implies that minimum sensor range 100 nm for a single UAV WAS ConOps which drives the WAS sensor to operate at high altitude- Assume a minimum 5 degree look down angle and

calculate the altitude required for 100 nm range- Target ID, however, will be at 10Kft or less

- To meet the 80% visual ID requirement (weather) • One option for reducing the mismatch is to go to a

multi-UAV ConOps- A four (4) UAV WAS ConOps would reduce the WAS range requirement to 50nm (at a minimum)

- A Sixteen (16) UAV WAS ConOps would reduce the range requirement to 25 nm

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• We can design one (1) air vehicle or two (2)- A one air vehicle type solution will be a compromise

- Can’t optimize for both environments- But only one development program, production line and support system will be required

- A two air vehicle type solution will require 2 development programs, 2 production lines and 2 support systems-Cost will go through the roof

• We could do a trade study to determine which approach is most cost effective but historically a single, multi-capability design will be lower cost than 2 optimized single mission vehicles - Therefore, we will try to find a single system design solution for both missions

- If that doesn’t work, we can always fall back to the other option

Bottom line

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Homework

(1) Do a first order assessment of your selected system design project- Assume the answers in charts 30 and 31 apply

(2) Define at least two (2) ConOps that might work(3) What are the range and altitude implications for

the required WAS and ID sensors?(4) Do you think one air vehicle will be able to do

both missions?- If not, how many do you think will be required?

Submit your homework via Email your to Egbert by COB next Thursday

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Intermission

5-1 design of uav systems concepts of operationc 2002 lm corporation lesson objective – to discuss...

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