Aerocapture Orbit Insertion System for Mars CubeSats!

Robert D. Braun!Zachary R. Putnam!

Georgia Institute of Technology!!

November 21, 2014 !

Motivation!•  Propulsive requirements for Mars orbit

insertion present a challenge for cubesat missions not attached to a host orbiter!

•  Aerocapture is an attractive option!– Orbit insertion via single atmospheric pass!– Drag modulation may be used to control

energy; provides freedom to select science orbit and means to manage risk posture!

– Requires only small, single-use, low-cost rocket motor to raise periapsis out of atmosphere!

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Aerocapture Maneuver!

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Mars!

Transfer orbit!

Science orbit!

Delta-V to correct apoapsis error!

Atmospheric pass!

Aerocapture interface (AI)!

Delta-V to raise periapsis!

Atmospheric exit!

Mars!

Transfer orbit!

Science orbit!

Delta-V to correct apoapsis error!

Atmospheric pass!

Aerocapture interface (AI)!

Delta-V to raise periapsis!

Atmospheric exit!

Host vehicle orbit insertion maneuver!

Jettison from host s/c prior to final targeting event!

Jettison from host s/c prior to final targeting event!

Host vehicle EDL!

From Lander Host Vehicle! From Orbiter Host Vehicle!

Drag Modulation is Well Aligned with Smallsat Mission Concept!

Vehicle utilizes changes in β (via changes in drag area) to manage terminal energy state and achieve desired orbit.!

Ballistic Coefficient!

Atmosphere!

Mars!

Initial state:!high-energy orbit!

Exit state: !lower-energy orbit!

Reduce drag area via jettison or other means!

Pre-deploy !drag area!

β1!

β1!

β2!

Low-β deceleration!

(β = β1)!

High-β deceleration!

(β = β2)!

Example: Discrete-event drag-modulation system is the simplest possible system; terminal state is controlled by a one-time change in drag area!

Ratio of β2/β1 is control authority metric for drag-modulation trajectory control systems (analogous to L/D for MSL or Orion).!

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Drag modulation system eliminates need for:!•  3-axis RCS!•  CG offset!•  Sophisticated guidance

and aero database!while significantly reducing aerothermal environment!

Putnam, Z.R.; and Braun, R.D.; “Drag-Modulation Flight-Control System Options for Planetary Aerocapture Missions,” Journal of Spacecraft and Rockets, Vol. 51, No. 1, pp. 139-150, Jan-Feb, 2014.!

Single-Event Drag Modulation Aerocapture Flight Performance!

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0 20 40 60 800

0.5

1

1.5

2

2.5

Transfer orbit period, hr

Cor

ridor

wid

th, d

eg β2/β1 = 10!

β2/β1 = 5!

β2/β1 = 3!

β2/β1 = 2!

Transfer orbit targeting: !•  Drag-only trajectory control with a modest β

ratio allows targeting of specific transfer orbits!•  Corridor widths comparable to or better than

untargeted, unguided systems!

MER req.: ±0.25 deg!

MSL req.: ±0.2 deg!

0 20 40 60 800

10

20

30

40

50

60

70

80

Transfer orbit period, hr

Peria

psis

rais

e de

lta−V

, m/s

Propulsive requirements:!•  Nominal required delta-V is a strong function of

transfer orbit apoapsis altitude and a weak function of β"

•  Short-period transfer orbits require larger delta-V!

Delta-V to raise periapsis altitude to 200 km!

β ratio (β2/β1) is control authority metric for drag systems!

System Definition and Key Trades!

Host s/c impacts!

Control authority!

System!mass!

Design complexity!

Rigid OML (unguided)!

Discrete Drag Skirt!

Attached HIAD!

Trailing HIAD!

Rigid Deployable!

Relative evaluation of different smallsat drag-modulation aerocapture concepts!

MISSION&OVERVIEW&

Entry&&(150&km)&

E+7min&

M2020&Site,&E+4min&

E+9min&

P1&(Orbit&#2)&

P0&&E+3min&

Periapsis((

Entry&73) Entry)

Enable)Aerocube)Controller)Ini5alize)IMU,)Temp)Sensors)Record)Telemetry)

&72) &71) &70)

Eject)Aerocube,)Beacon)Tones)Deploy)Aero&skirt)

Hibernate)

Wake)from)Hiberna5on)Acquire)ALtude)Knowledge)Warm)Cat&bed)Heaters)Transmit)Beacon)Tones)

Turn)to)Entry)ALtude)Aeropass)

JeLson)Aeroshell)

Earth)Occulta5on)Sun)Eclipse)

Deploy)Solar)Arrays)

Periapsis)Raise)Maneuver)(PRM))

&2) &1) +1) +2) +3) +4) +5) +6) +7) +8) +9) +10) +11) +12)

Periapsis)#1)(P1))Start)Orbit)#2)

MRO)Visibility)

Release(from(Mothership(

Deploy'Aeroskirt'E/71'hrs'

Eject'Aerocube'on'Divert'Vector'E/72'hrs' Aeropass(

7min(

Eclipse(75min(

Earth(Occulta5on(38min(

PRM(E+6(hr(

Sun(Earth(

MRO(

Divert@Deploy(E@72(hrs(

Wake:(Entry(AFtude(Transmit(Beacon(E@2(hrs(

tumbling(Deploy(HGA((in(Orbit(#2)(

Deploy(Solar(Arrays(and(UHF(antennas(

Discrete(Event(Drag(Modula9on(for(Aerocapture((

Vehicle'u)lizes'changes'in'β'(via'changes'in'drag'area)'to'manage'terminal'energy'state'and'achieve'desired'orbit.'

Space&

Atmosphere&

Planet&

AI'state:'high=energy'orbit'

Exit'state:''lower=energy'orbit'

Reduce'drag'area'via'jeCson'or'other'

means'

Pre=deploy''drag'area'

β1

β1

β2

Low=β'decelera)on'

(β = β1)

High=β'decelera)on'

(β = β2)

Ballis)c'Coefficient'

Example:'Discrete=event'drag=modula)on'system'is'the'simplest'possible'system;'terminal'state'is'controlled'by'a'one=)me'change'in'drag'area'

Divert:& E"1$day$ E"2$days$ E"3$days$ E"4$days$ΔV&Divert&(m/s)& 3.51$ 1.83$ 1.23$ 0.94$3σ&Expected&ΔEFPA&(°)! 0.09$ 0.1$ 0.11$ 0.11$Corridor&forβ2/β1&=&5& 0.4$ 0.4$ 0.4$ 0.4$Corridor&forβ2/β1&=&10& 0.6$ 0.6$ 0.6$ 0.6$

Source& Affects& ~3σ&Value& Units& ΔEFPA&M2020$B"plane$Errors$ M2020$EFPA$ 0.05$ °$ 0.05&M2020$A>tude$Knowledge$ Divert$DirecHon$ 0.25$ °$ 0.0005&Spring$K"constant$ Divert$Magnitude$ 2%$ $$ 0.101&Release$Timing$ Release$θ$ 100$ ms$ 0.01&RSS&Total& $$ $$ $$ 0.11&

Divert(ΔV(&(Corridor(Width(

Targe9ng(Error(Budget(

Timeline(

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Rigid OML!

Discrete Drag Skirt!

Rigid Deployables!Trailing HIAD!Attached HIAD!

Preliminary Sizing!Entry Mass, kg ! !25!Orbiter Dry Mass, kg !10!Rigid Dia, m ! ! !0.5 !Drag Skirt Dia, m ! !1.2!β, kg/m2 ! ! !15/85!ΔV capability, m/s ! !35!Attach/deploy h/w, kg !5!

Anticipated System Development Challenges!

•  Interface with host spacecraft!•  Deployment from host spacecraft!•  Deployment of cubesat after aerocapture

maneuver!

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Summary: Drag-Modulation Aerocapture Benefits!

•  May provide “standard” cubesat orbital insertion system for hosted missions!– Enables orbital cubesat missions for lander host!– Allows insertion into different orbit than targeted by

orbiter host!–  Likely carried on cruise stage!

•  Demonstrates feed-forward technologies:!– Flight demonstration of aerocapture and hypersonic

drag-modulation trajectory control!– Potential test-bed for novel TPS materials!

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