Fundamental aspects of ion-beam debris mitigation and asteroid

Transcript

Fundamental aspects of ion-beam
debris mitigation and asteroid deflection Claudio Bombardelli Space Dynamics Group Technical University of Madrid (UPM) Seminar. Dipartimento di Scienze e Tecnologie Aerospaziali, Politecnico di Milano.
26e Tecnologie
MarchAerospaziali,
2015. Milan
“Seminar. Dipartimento di Scienze
PolitecnicoItaly.
di Milano. 26 March 2015. Milan Italy.
The Ion Beam Shepherd (IBS) Concept
“Seminar. Dipartimento di Scienze e Tecnologie Aerospaziali, Politecnico di Milano. 26 March 2015. Milan Italy.
§  Point the ion-‐beam of an ionic thruster towards a space object §  Ions reaching the debris surface penetrate the debris material substrate transferring their momentum (linear + angular) §  Need for a secondary propulsion system to prevent the shepherd from dri>ing away Key advantage: contactless momentum transfer Paradigm shiC: Electric propulsion as an ac#on force rather than a reac#on “Seminar. Dipartimento di Scienze e Tecnologie Aerospaziali, Politecnico di Milano. 26 March 2015. Milan Italy.
§  IBS method proposed by Technical University of Madrid (UPM) in 2009 §  Patented by UPM on March 11-‐2010 §  Studied by the European Space Agency for debris removal applicaJons (ARIADNA), asteroid deflecJon (SysNova, SSASN-‐VII) and in-‐orbit demonstraJon mission (IBS-‐IOD) §  Studied by DARPA Orbital Debris Removal in 2011 (Poulos Air & Space, USA) §  JAXA working on it for acJve debris removal in GEO (Dr. Kitamura) §  Under study by Russian R&D centers (Prof V. A. Obukhov, MAI, Russia). §  FP7 LEOSWEEP project currently at month 18/36 (more details in a dedicated slide) §  Interest from JPL (John Brophy) as enabling technology for asteroid retrieval “Seminar. Dipartimento di Scienze e Tecnologie Aerospaziali, Politecnico di Milano. 26 March 2015. Milan Italy.
§  “MOVE OBJECTS AROUND” Change the orbit of a space object from a safe distance using the ion beam linear momentum without docking. Enabling technology for debris removal, asteroid deflecJon and in orbit transportaJon §  “TURN OBJECTS AROUND” Use the ion beam to modify the angular momentum of a space object without docking. Enabling technology for debris despin, in orbit manipulaJon and assembly “Seminar. Dipartimento di Scienze e Tecnologie Aerospaziali, Politecnico di Milano. 26 March 2015. Milan Italy.
Fundamental parameters
• 
Near field beam divergence
= half cone angle containing 95% of the
(Gaussian-distributed) beam density at reference section R0
• 
Specific impulse (ions axial velocity)
• 
Nominal thrust magnitude
(n0= avg plasma density at R0; mi= ion mass)
• 
Plasma electrons’ Mach number
quantifies the “funnel-like” expansion
of the beam in the far-field region due to electron temperature (TeV). For M0 →∞ (cold
beam limit) the beam is conical. (qe=electron charge).
The Ion Beam Shepherd
(IBS)influence
Concept
Electron pressure
on beam profile
It doesn’t look so advantageous to limit the initial divergence when electrontemperature effects are strong.
• 
Define beam momentum transfer efficiency as the ratio between the force
transmitted to the target along the thruster direction and the thrust provided by
the ion engine:
• 
Low beam divergence measured at target location (δ) is key in order to allow high
efficiency at large separation
• 
Cannonball model:
Sputtering is the process by which material atoms or atom clusters are knocked off
from the target surface following ion impingements.
The sputtering yield, Y, is a statistical variable that quantifies the mean number of
atoms removed from a solid target per incident ion. It depends on many factors
including material properties, ion energy, ion incidence angle.
Backsputtering is a critical aspects of IBS technology due to:
§  Target erosion. Need to make sure that the target structural integrity is not
compromised.
§  Contamination. The flux of backsputtered atoms released from the target can
reach sensitive surfaces on the shepherd spacecraft (e.g. optical sensors, solar
panels, thermal coatings,...) and degrade their performance.
Thickness of the deposited contamination level should be kept below
200-300 nm [Tribble, et al., SPIE,vol 2864, pp 4-15,1996.]
Smaller divergence allows operating from higher distance for equal
momentum transfer efficiency
Divergence reduction vs.
backsputtering flow reduction
Dependency is slightly more
than quadratic
e.g. one order of mag in going
from 16 deg to 6 deg
Average backsputtering flow reaching the IBS spacecraft from an
aluminum spherical target with constant momentum transfer
efficiency and varying beam divergence.
The number of objects in orbit is rapidly growing due to new launches, explosions and collisions. Even if we stop launching the growth will conJnue. à We have to start to acSvely remove what is already there Credits: J.C. Liou
NASA JSFC
Answer: big-‐size debris from crowded orbits in LEO: ·∙ Higher catastrophic collision probability ·∙ Higher post-‐collision debris mass yield Liou , J. C., Adv. Space Res, Vol 47, No 11, June 2011, pp 1865-‐1876. Kosmos-‐3M (SL-‐8) ~1.5 tons (upper stage) More than 260 of them in LEO ! European Remote Sensing Satellite (ERS-‐1) ~2.4 ton, 747-‐796 km orbit alt, 98.2 deg incl ESA Envisat ~8.2 tons 766-‐767km alJtude 98.5 deg inclinaJon “Seminar. Dipartimento di Scienze e Tecnologie Aerospaziali, Politecnico di Milano. 26 March 2015. Milan Italy.
SL-8 (Kosmos-3M) + SL-3 (Vostok)
ERS-1
Envisat + Zenith-2
• Overall, upper stages make up about 47% of the total LEO debris mass • 64% of the total LEO upper stage mass (i.e. 30% of the total LEO mass) grouped into only three rocket families: • No “confidenJality issues” • If you can remove one kind you can get the whole family “Seminar. Dipartimento di Scienze e Tecnologie Aerospaziali, Politecnico di Milano. 26 March 2015. Milan Italy.
• 
• 
• 
• 
Chemical/solid-‐propellant-‐based targeted reentry from original alJtude unsustainable (e.g. 850 kg of fuel just for a single Zenit target) Even with reusable high-‐Isp electric propulsion the mass cost for full removal rapidly escalates in Sme and may become overwhelming just a>er a few years. Consider reposiSoning to lower alJtude uncrowded orbital regions Learn from history: -‐ Cosmos-‐Iridium collision(789 km): 90% of fragments out by 2024 -‐ Fengyun collision (865 km): 90% of fragments out by 2090 !!! -‐ what if the next collision occurs at 950 km ? “Seminar. Dipartimento di Scienze e Tecnologie Aerospaziali, Politecnico di Milano. 26 March 2015. Milan Italy.
Tons of debris
70 tons of Zenit-2 moved from 800-850
to 700-750 km altitude (ΔV≈52 m/s)
95 tons of Cosmos-3M moved from
950-100 to 900-950 km (ΔV≈25 m/s)
Reduction of collision probability by
erasing dangerous density peaks
Tons of debris
Dramatic cost reduction when
compared with full removal
Later targeted reentry still possible at a
lower ΔV price
§  High deorbit efficiency. Uses high specific impulse electric propulsion.
§  Comparatively low risk. Because no mechanical contact is required to transfer
the deorbiting impulse and the IBS can work at a safe distance from the debris
§  Adaptability. An impinging ion beam transfers its momentum independently of the
particular debris shape or material as long as the target lays in the beam envelope
§  Reusability. Neglecting spacecraft parts degradation, the IBS has only one
expendable element: propellant. But thanks to the high specific impulse fuel
expenditures are drastically reduced and multiple removal operations are possible. §  Manoeuvrability. Unlike other deorbiting concepts the IBS has full and efficient
manoeuvrability in all directions, as it hosts high efficiency ion thrusters that
facilitate all types of orbital changes. Enables secondary payload opportunities
and collision avoidance during removal.
§  Technology readiness. Altogether the IBS spacecraft is of conventional design
except for the propulsion system (which is employed in a different way than usual) “Seminar. Dipartimento di Scienze e Tecnologie Aerospaziali, Politecnico di Milano. 26 March 2015. Milan Italy.
• 
Of interest for the dynamics and control of the target-shepherd relative position is
the dimensionless beam gradient matrix:
Where F=beam force on the target, r= target-shepherd rel position, req = nominal
equilibrium position for efficient (= coorbital) shepherding, RT= target radius.
• 
Cannonball model:
• 
Beam acts as a stabilizing spring along the x-axis (beam axis) but is distabilizing
along the other two.
§  IBS co-orbiting with the Debris with same semimajor axis (i.e. bounded
separation)
Control Strategy Beam-‐Debris InteracJon Debris-Shepherd
Relative Dynamics
Shepherd Orbit Dynamics
Debris Attitude Dynamics
Control Strategy Beam-‐Debris InteracJon §  Generic orbit eccentricity can be handled. §  Control part (FS) is fully from Shepherd RCS “Seminar. Dipartimento di Scienze e Tecnologie Aerospaziali, Politecnico di Milano. 26 March 2015. Milan Italy.
§  Quasi-circular orbit + spherical target + linearization of beam force around
nominal equilibrium position (no control, for now):
(*)
Dimensionless time: τ=ωt. Dimensionless displacements from nominal coorbiting
configuration: δx=x/RT (R-bar) δy=(y-ρnom)/RT (V-bar) δz=z/RT (H-bar)
Added term compared to Clohessy-Wiltshire is the beam-stiffness coefficient:
Beam-dominated regime: γ>>1 (GEO)
Gravity-dominated regime γ<<1 (LEO)
§  Control strategy needed in order to eliminate real-posiive eigenvalue along R-bar
(destabilizing gravito-centrifugal gradient + beam gradient)
§  RCS acts on shepherd CoM to control relative position in R-V-H-bar directions
§  Assume perfect metrology for preliminary design (navigation errors to be
handled later)
§  Adopt simple control strategy: linear LQR-tuned PD controller designed on a
cannonball model for the beam-target interaction
§  No cross-coupled control terms for simplicity
§  Analytical expression for optimal gains (m∈ℜ):
Non-linear true optimum controller is under
development
Baseline target (Kosmos-3M upper stage or “SL-8”)
§  Cylinder 6.5m hight by 4.8m diameter ; mass~1.5 tons
§ Nominal target orbit: e=0, i= 82 deg, h=700 km
Nominal equilibrium position:
§  On axis at 15 m distance from shepherd
Thruster
§  Nominal tangential thrust 100mN
§  Near field divergence 6 deg half angle
§  Plasma Mach number =20
Shepherd Spacecraft
§  mass= 300 kg, RCS saturation (at 30 mN)
LEOSWEEP:
improving Low Earth Orbit Security
With Enhanced Electric Propulsion
• Three-year Research and Innovation project funded by the EU under the FP7
programme FP7-SPACE-2013
• 2 million euros EC contribution
• Participants: SENER (coordinator Spain), UPM (Spain), Inst. of Tech. Mechanics
(Ukraine) , Yuzhnoye (Ukraine), Int. Space Law Center (Ukraine), TransMIT
(Germany) , DLR (Germany), DEIMOS (Portugal), U. of Southampton(UK), CNRS
(France)
• From Nov 2013 until Nov 2016
• Development of the ion beam shepherd (IBS) technology to deorbit rocket upper
stages in LEO
• Website: leosweep.upm.es
Should we learn how to deflect an asteroid?
•  Near Earth Objects (NEO): low impact probability but extremely severe effects •  Very limited pracJcal knowledge on NEO threat and the best technology approach to tackle it •  Large public awareness of the issue Meteor Crater, Arizona
Dast~ 50 m (NiFe asteroid)
Dcrat ~ 1.2 km
50,000 years
Tunguska event, Siberia
Dast~ 60 m
Blast wave (no crater)
June 30, 1908
Chelyabinsk, Russia
Dast~ 20 m (L-chondrite)
Exoploded at ~30 km altitude
(no main crater)
Feb 15, 2013
Manicouagan crater, Canada
Dast~ 5 km (C-type ?)
Dcrat ~ 100 km
~200 Myears
28 What do we need to (be able to) deflect?
CHELYABINSK
Possibly, asteroids in the range of 50 to 500 metersà different strategies available ExcepSonally, asteroids in the 0.5-‐10 km range à nuclear explosion (likely) the only opJon Asteroid size follows a
power-law distribution
due to homogeneous
fragmentation.
Smaller asteroids collision
are much more frequent
à We need to be able to
deflect small to medium
size asteroids
29 Deflection requirements
First paper highlighting the feasibility of asteroid deflection:
Aherns & Harris,
Nature, 1992
Main conclusions of Ahrens & Harris:
1)  Deflecting an asteroid is technologically feasible
2)  If the asteroid is not too large (say ~100 m) and the deflection action is initiated well
in advance (a few years) you do not need a nuclear bomb. Just hit it with a spacecraft
at high relative velocity (10-20 km/s) à (Kinetic Impactor)
3)  For very large and/or last-minute-discovered asteroids, nuclear bomb the only option
30 Deflection kinematics
A deflecJon acJon generally has two main consequences: 1)  It produces a change in the asteroid posiSon (δr) at impact angular posiJon (θc) 3)  It produces a Sme delay (δt) of the asteroid at impact angular posiJon (θc)
asteroid
nominal trajectory
asteroid
deflected trajectory
δr
θc
“Last-‐minute” deflecSon (less than one orbit before impact) à what maqers more is the posiSon change (δr)
“Early” deflecSon (a few orbits before the predicted impact) à what maqers is the Sme delay (δt) “Seminar. Dipartimento di Scienze e Tecnologie Aerospaziali, Politecnico di Milano. 26 March 2015. Milan Italy.
31 The ‘early’ deflection
•  Asteroids travel at typically vast~ 20-‐40 km/s. •  Suppose you delay the arrival of the asteroid at the “meeJng point” by δt ~ 10 minutes •  The asteroid misses the Earth by an amount of the order of vastδt ~10,000 km •  Earth radius is ~6,378 km. impact
vearth
vast
deflection
vae
vearth
vast
vae
32 The “early” deflection (ctd.)
•  How do you produce a delay at the asteroid/Earth meeJng point? -‐ If you have a lot of Jme (a few years) by changing the asteroid velocity deflection
impact
Example: 1)  Change the asteroid orbit velocity by 4 cm/s (say ~1.3 ppm) 2)  Orbit period changes by roughly the same % (1.3 ppm over, say, 1 year = 40 s) 3)  The Jme delay δt accumulates at about 40 seconds/year 4)  A delay of a few minutes is possible a>er ~10 years “Seminar. Dipartimento di Scienze e Tecnologie Aerospaziali, Politecnico di Milano. 26 March 2015. Milan Italy.
33 Impulsive vs. Slow push deflection
Changing the velocity of an asteroid by a few cm/s and a few years in advance is enough to avoid an impact. IMPULSIVE METHODS. Impulsive change of the asteroid momentum 1.a) Momentum is transferred from a spacecra> colliding at high speed (a few km/s) with the asteroid: KINETIC IMPACTOR 1.b) Momentum is transferred from the shock wave of a nearby (standoff) NUCLEAR EXPLOSION “SLOW-‐PUSH” METHODS. ApplicaJon of a Jny but conJnuous force on the asteroid along the tangent to its orbit 2.a) Force originates from a low thrust engine: ION BEAM SHEPHERD 2.b) Force originates from laser ablaJon: LASER METHODS 2.c) Force originates from spacecra> gravity: GRAVITY TRACTOR “Seminar. Dipartimento di Scienze e Tecnologie Aerospaziali, Politecnico di Milano. 26 March 2015. Milan Italy.
34 Most popular deflection methods*
Explosive strategy
Kinetic impact
(stand-off)
strategy
deflection
Gravity tractor
Ion beam shepherd
*Credit: JL Cano, DEIMOS
35 Comparison between IBS and GT
The GT performance
rapidly decreases the
smaller the asteroid, in
which case you need to
load S/C mass to get
enough gravity
One order of magnitude
difference for a typical
200 m diameter asteroid
Total deflection impulse
Total spacecraft mass at rendezvous
36 The PDC 2015 impact scenario
•  Hypothetical asteroid impact scenario proposed for the 2015 planetary
defense conference (PDC) in Frascati, Rome
•  The fictitious 150-500 m diameter asteroid, discovered on April 13
2015 and named 2015PDC, was found to have several potential impacts
with the Earth, the earliest and most likely on September 3, 2022
•  The impact probability, estimated in mid-June 2015, would reach 1% and
would continue to rise with the rest of the scenario to be played out at the
conference
•  Asteroid Ephemerides provided by JPL (but no covariance matrix)
•  Very interesting exercise to clarify several threat mitigation issues
including what is the best deflection approach
37 The impact path of risk
Path of risk stretching from eastern Turkey until the middle of Pacific and
passing through heavily populated areas such as Northern India.
N.B.: The covariance ellipsoid is expected to be much larger than the Earth
size and chance of impact is still low
38 Zooming on Northern India…
39 The first and most important action
•  Due to the asteroid orbit geometry with respect to the Earth there appear to
be no significant opportunities to increase the accuracy of the
asteroid orbit by future ground-based observations.
•  A rendezvous mission will be absolutely necessary and should be
launches ASAP because
1)  It will permit to confirm / rule out an impact
2)  It will allow estimating where on Earth it will strike to (probably) within
a few tens of kilometer
3)  It will provide an estimate of the asteroid size and mass
4)  It will be necessary in order to accurately measure the deflection
whatever method is used
40 Estimated ellipsoid size at impact (1-sigma)
After tracking by rendezvous S/C
Start from Itokawa-like covariance matrix (actually obtained by Arecibo radar observ
but likely achievable with in-situ tracking) and propagate linearly starting from a
hypothetical rendezvous date in 2019
Projecting onto Earth geoid surface will yield an estimated 60 km semimajor axis (1
sigma) at impact
41 Consequences of a possible impact
Need to carefully study possible impact effects. Check literature on the subject:
“Calculations of Asteroid Impacts into Deep and Shallow Water” GALEN GISLER, ROBERT WEAVER,2 and
MICHAEL GITTINGS, Pure Appl. Geophys. 168 (2011), 1187–1198
•  Impact in the open sea: not critical enough to warrant deflection as asteroids
smaller than 500 m lack the capability of generating tsunami-like impact waves
•  Impacts on the ground: catastrophic consequences if within about 100 km
from coastlines or densely populated areas.
CONCLUSIONS:
•  If the asteroid falls in the ocean or in a deserted region it should probably not be
deflected
•  If the asteroid falls in a populated area it may be enough to just change his path
so that it strikes a deserted region…
42 A case for IBS deflection
Key design tradeoff : should the rendezvous mission have a deflection capability?
•  If yes, it is definitely not going to be a nuclear bomb:
-  It would greatly complicate the mission and slow down its development
-  a nuclear deflection mission could be implemented later if needed
•  IBS deflection capability would comfortably fit in the mission
-  Ion thrusters can be efficiently exploited for both the interplanetary transfer
trajectory and the contactless deflection with no major expected increase in
technological complexity.
-  The cost of the added propellant mass required for deflection can be largely
justified by the criticality of a possible impact event.
43 A possible rendezvous+deflection S/C design
•  Dawn-type 10 kW(1AU) power subsystem with an estimated 150 kg mass
•  Two redundant sets of (3+3) ionic thrusters , 3500 s specific impulse, 70%
electrical efficiency, and a 200mN + 200mN maximum thrust capability at 1AU.
•  A preliminary estimate for the total spacecraft mass at interplanetary orbit
insertion is of 1200 kg including 400 kg of Xenon.
Optimum Interplanetary trajectory found:
•  Dep on May 28 2017 (Soyuz, C3=10km2/s2)
•  Arr on Sep 30 2019
•  Total of 200 kg fuel spent
44 Full deflection vs. Impact retargeting
ASSUME IMPACT IN NEW DELHI
Full deflection is problematic because
1)  Limited time available increases momentum transfer requirements
2)  It involves the asteroid impact point passing over at least 5 countries
- India, Pakistan, Afghanistan, Iran, Turkey (westward deflection)
- Bangladesh, Myanmar, Thailand, Laos, Vietnam and Philippines (eastward)
Consider impact point retargeting to the nearest unpopulated region
1)  Much cheaper and easier to achieve (especially for large asteroids)
2)  Probably much easier to solve politically
45 Saving New Delhi with an IBS
Start deflecting in November 2019 and track deflection month by month.
40 (185) mN transmitted force for 33 month enough to retarget a 150 (250) m
asteroid into unpopulated Afghan territory
46 Turning a hot-potato into a win-win situation
At first sight the asteroid retargeting case seems politically very complex
- hot-potato kind of situation: nobody wants an asteroid threat in their backyard
How do you solve this?
•  India will pay an asteroid toll fee to Pakistan
•  India will also pay an asteroid impact fee to Afghanistan to use its territory to
absorb the impact
•  India may conduct the deflecting mission or pay a deflecting country/agency
•  The deflecting party will be liable of any miss-deflected asteroid damage
•  Afghanistan will end up owning the asteroid exploitation rights for various
purposes (science, mining, show biz, tourism, …) ….
47 Questions ?
48

Fundamental aspects of ion-beam debris mitigation and asteroid

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