This area will cover relevant news of the threat to the planet from Near Earth Objects (NEOs) including concepts and designs for mitigation. All opinions are those of the author.

28 April 2009

2009 IAA Planetary Defense Conference: Day 2 (Sessions 2 and 3)

2009 IAA Planetary Defense Conference: Day 2 (Session 2)

Session 2 Mission and Campaign Design
Session Chairs: Mariella Graziano, Ian Carnelli, Andreas Rathke

- R. Tremayne-Smith
Discussion of orbital debris problem, vide of U.S. recent AST-like event / Iridium impact, conception of LEO not the same as before, not about mitigation, checking for debris done casually, in low earth orbits need to have propulsion/maneuver, A-Train set of satellites has to move through this region, even more disciplines, getting more difficult to get space open for business, going to need same mechanisms for the orbit area,

Announcement of poster papers
- MAAT: NASA Ames research study, ESPA ring variant of NASA ARC Common bus, secondary payload, 10 month long launch opportunity, 3.1 km/s Delta-V (includes margin), ability to vary launch site, 2014 science mission for 6 months, modified LCROSS instrument suite
- Optimal control of gravity tractor spacecraft near arbitrarily shaped asteroids (M. Gehler, et al), see the influence of arbitrary gravity field on control forces, how GT could be optimally controlled, Discrete Mechanics and Optimal Control applicable to hovering control for very close to asteroids, solar sail size should be matched to asteroids, used 1 asteroid radius (about 500 meters),
- PANIC – mission concept study for mini autonomous lander (NASA Ames summer study), a micro scale lander (three instruments), total mass (9kg for 48 hours, $25M)
- Evolutionary optimization in a conceptual design of a NEA mission, what is netter of a single impacts or multiple kinetic impactor
- Small Solar System Body mitigation (J.T. Grundman), a realist approach, when down the list, and looked at all the problems

- Didymos Explorer and PANIC: Asteroid Concept Studies of the S4P Program at NASA Ames
Rozitis, B.1; Bellerose, J.2; Cook, A.3; Fahnestock, E.4; Mester, C.5; Murdoch, N.6; Olds, P.7; Reddy, V.8; Schindler, K.9; Thomas, C.10; Yamaguchi, T.11; Asphaug, E.12 ; Marchis, F.13 1The Open University (United Kingdom); 2JAXA/JSPEC (Japan); 3Rensselaer Polytechnic Institute (United States); 4University of Michigan (United States); 5Stanford University (United States); 6ESTEC/ESA (Netherlands); 7UARC/NASA Ames (United States); 8University of North Dakota (United States); 9University of Dresden (Germany); 10Massachusetts Institute of Technology (United States); 11The Graduate University for Advanced Studies (Japan); 12University of California (United States); 13SETI (United States)

Develop 1-2 concept studies for small spacecraft, integrate small spacecraft exploration, train the next generation of scientists/project leaders, 11 students from various backgrounds, no NEA binary and no M type asteroid has been visited yet, decided on Didymos (1996 GT), a Mars crossing Amor binary, also a PHO, low delta V, 750 m diameter (primary), accomplish the first in-situ investigation of binary asteroid, science objectives: asteroid geology, shapes and gravity fields, Yarkovsky effect, Yorp effect (if enough force then potential to make a secondary object), asteroid composition (link asteroid and meteorite classes), six instruments, use of Delta II vehicle (launch on 12 Nov. 2014), mission duration of 2 years, flybys at 5km and 3km, perform close approach, minimize eclipse time so hovering becomes a better approach and allow for secure deployment for lander, 151.8 kg (dry) /. 307.9 kg, cost ($136.5 M with 30% contingency), 207.6 W, Didymos explorer mission will allow thorough study, Q/A

- Foresight: Designing a Radio Transponder Mission to Near Earth Asteroid Apophis
Charania, A.1; Olds, J.1; Koenig, J.2 1 SaceWorks Engineering, Inc. (SEI) (United States); 2SpaceDev, Inc. (United States)

- The Challenge of Navigating Toward and Around a Small, Irregular NEO
Gil-Fernandez, J.; Prieto-Llanos, T.; Cadenas, R.; Corral, C.; Graziano, M. (GMV, Spain)

Examined multiple types of missions, impact missions and rendezvous missions, proximity operations, need high accuracy for navigation (around one meter), new sensors, requirements for NEO missions are highly demanding for GNC, robust GNC system, result shows impactor only could potentially do mission without specific shape model (not relying on shape information)

- PROBA-IP: An ESA Technology Demonstration Mission Targeted to Apophis
Cano, J.L.1; Peñín, L.F.1; Cornara, S.1; Santandrea, S.2; Marcos, F.3; López, A.3; Jentsch, C.4; Bernhardsdotter, E.5; Taylor, M.6; Page, O.7; 1DEIMOS Space S.L. (Spain); 2ESA / ESTEC (Netherlands); 3EADS CASA Espacio (Spain); 4EADS Astrium Satellites (Germany); 5SSC (Sweden); 6SSTL (United Kingdom); 7SciSys (United

Follow-on to Don Quixote orbiter (Sancho), consortium performing for ESA, related to in-orbit demonstration of autonomous technologies, PROBA-2 (Sept. 2009 launch): solar observatory, PROBA for formation flying, PROBA-IP take technologies to interplanetary field, need to determine a cost specific mission, scientific goals only if margins will allow for it, current study is a preliminary concept evaluation, launch before 2015,choose asteroids close to the Earth, count on cheap launchers, use of low thrust propulsion, reuse an upper stage design (use of LISA Pathfinder’s propulsive stage being developed for ESA already), initial filter sin asteroids resulted in 60 asteroid (Apophis was promising and choose as primary) – choose 1989 UQ selected as a back-up launch in 2017, VEGA launcher, need for active control during to high unstable dynamic orbit, analysis of a Phto-Gravitationally Stable Orbit, consideration of different types of SEP engines, arriving with low velocity, departing in Jan 2015, 1.892 km/s departure velocity, arrival date in in 2017, 435 kg wet mass / 350 kg dry mass, delta-V of 3.9 km/s, GNC technologies (autonomous GN&C in cruise/approach/operations, use of DTU’s advanced stellar compass used as DTR/NAVCAM/WAC), power (two wing arrays, HEMP 3050 engine, easy to control – control mass flow rate – good for autonomous control), ACS (three axis stabilize, X-band, in middle of the study, study ends in summer, provide ESA with design concept at that point, potential for accurate determination of Apophis orbit and features, orbiter acting as beacon for deflection techniques

- Exploration of Near-Earth Objects via the Orion Crew Exploration Vehicle: A Planetary Defence Rationale
Abell, P.A.1; Korsmeyer, D.J.2; Landis, R.R.3; Jones, T.D.4; Adamo, D.5; Morrison, D.6; Lemke, L.6; Gonzales, A.6; Gershman, B.7; Sweetser, T.7; Johnson, L.8 1NASA Johnson Space Center / Planetary Science Institute (United States); 2Intelligent Systems Division, NASA Ames Research Center (United States); 3Mission Operations Directorate, NASA Johnson Space Center (United States); 4Association of Space Explorers (United States); 5Trajectory Consultant (United States); 6NASA Ames Research Center (United States); 7Jet Propulsion Laboratory (United States); 8NASA Headquarters (United States)

Paul Abell, feasibility study within Constellation program office at JSC, led out of Ames Research Center, Rob Landis/Ed Lu, a few folks at JPL (for trajectory analysis), Tom Jones, Bret Drake – sponser, this is only a Phase I feasibility study, NASA has not endorsed this yet, work done to date based on 4.5 month effort, a phase 2 study is as yet to be determined, proposed since 1966 (Eugene Smith) – “A Manned Flyby Mission to Eros”, no changes to Constellation element performance, established 4 misison concepts (2 bookends) based upon planned Cx launch system, at mid term considered mid-volume concepts (Ares V concepts), determine mission length options, Lower bookend (EELV for Centaur upper stage) + Ares I, Upper bookend (ARES V for EDS + LSAM) + Ares I, mid-volumes (use Ares V concept for Orion launch), for mid-volume (EDS and Orion SM perform rendezvous for 7-14 day visit with 20-75 outbound segment, which NEOs are a good target of opportunity with Earth-like orbits with low eccentricity and inclination, used JPL HORIZONS database, analyzed 90-120-150-180 day options, 9 NEOS founds within 2020-2035, 1999 AO10 is one potential target (2025/2206 mission) – 11.2 km/s reentry speed, value of human exploration to NEOs (exploration, science, and general public), expand human capability beyond low Earth orbit, asses resource potential for NEOs, gain operational experience for complex tasks (human/robots), assess psychology of crew autonomy at 10-20 second round trip for deep space, help indentify most efficient deep space exploration architectures, sample return, perform unprecedented deep-space voyage experience, would be a stepping stone type mission, demonstrate the way to Mars, understanding NEOs helpful for future impact threat, Can ye do this (Yes we can do it, Constellation program elements can support crew of 2-3), need to leverage next generation survey to find more targets, in depth Phase 2 mission analysis (applicable innovative technologies, radiation shielding, etc,), question: need to balance cost and missions (we have not done any cost estimate, not going to be a science mission/exploration mission/) – many communities, high cost – similar in cost to a lunar sortie (not the same as space station) – not the same as lunar outpost, question – chances to continue the study and do the mission- a lot of interest at NASA HQ, liked to do Phase 2 – interest at HQ leads to believe that Phase 2 will happen, holding pattern because of not permanent administrator

- Navigation and Guidance of Hayabusa around the Tiny Asteroid Itokawa
Yoshikawa, M.1; Kawaguchi, J.1; Hashimoto, T.1; Kubota, T.1; Terui, F.1; Ogawa, N.1; Ikeda, H.1; Kominato, T.2; Matsuoka, M.2; Uo, M.3 1JAXA (Japan); 2NEC Aerospace System (Japan); 3NEC Toshiba Space System (Japan)

Hayabusa changed the concept of small NEOs, before we thought many craters on Itokawa – surface covered with boulders, the study for Hayabusa is also important for spaceguard,June 2010 Earth reentry, have a brief history, first gravity swingby with low thrust propulsion, ground based operation was limited during Hayabausa touchdown (delay of 32 minutes and low bit rate of 8 kbps), intelligent GN&C is required, discussion of touchdown marker, during first touchdown maneuver - an obstacle was encountered and then went into feeefall near asteroid (unexpected), believe during the first touchdown may have captured some pieces of asteroid, mass estimation based upon using R&RR and LIDAR data, bulk density of 1.0 g/cm^3, Itokawa may be a rubble pile object, movie : "Hayabusa - Back to Earth" , next mission would like to know information inside the small bodies

- A Dawn-based Gravity Tractor and Kinetic Impactor Mission Concept Study
Wie, B. (Iowa State University, United States); Lam, Q. (Orbital Sciences Corporation, United States)

Changed name: NEO Deflection Systems Design, Dawn-based gravity tractor, multiple gravity tractor option also examined, NEO Deflection alternatives, three options (nuclear standoff or surface, kinetic impactor, gravity tractor, basic system (TII + Upper stage + 1400 kg payload – Dawn 900 kg GT or 1400 kg kinetic impactor or 900 kg interceptor with 500 kg nuclear explosive device), option 1 (Delta IV Heavy + Upper stage of Star + 6000 kg – multiple GT) , Option 2 (Ares V + Upper stage + 55 MT payload), Dawn spacecraft not designed for GT mission, use existing S/C bus technology, Dawn system to be presented at IAC 2009, two launch windows for Dawn based GT (2020 and 2021) for Apophis, delta-V from GTO is 3.45 km/s, Delta-IV heavy concept (three GTs/impactors/interceptors), GT mass = 2823 kg (wet mass, 1233 dry mass) for each GT, reason for multiple gravity tractor due to single point failure – more GTs allow for larger delta-V and more robust and reliable, do not need active station-keeping with multiple GTs – need more launch vehicles for such a system, paper in Journal of Guidance/Nav. Control, examined advanced low thrust propulsion, also a crewed 180 day NEO mission to Apophis – departure 10 September 2028, 160 days to Apophis – thought Ares I and Ares V is not enough (having trouble using design) – one page summary of ongoing project to be done during the summer, another poster paper on examining nuclear standoff for NEO deflection – estimation of optimal standoff of about 200 m (not 20 m as usual value) for a 1 km “solid” NEO, if GN&C control system has to meet 20 m optional standoff distance (this is too difficult for GN&C system) – we have to make decision (standoff explosion during fast flyby or rendezvous), position accuracy than 50cm (3 sigma), collaborative research with GMV aerospace for NEO terminal guidance, need large scaled funded R&D program for developing, testing, and deploying)

2009 IAA Planetary Defense Conference: Day 2 (Session 3)
Session 3 Deflection Technologies & Simulations
Session Chairs: Dario Izzo, Patrick Michel

Selected Posters:
Gary Johnson (Texas State Technical College), “An Electrostatic Variation of the Gravity Tractor “, Add an equipment kit to charge up the asteroid ans use the force of the electrostatic attraction (electrostatics as upgrade), “it smells good”, encourages community to take idea and run with it
Sanchez, J.P (Univ. og Glasgow): Consequences of fragmentation due to a NEO mitigation strategy
Pete Swan (from the space elevator community), NEO community, space elevator will be here for launch in 20-30 years, where do you park a space elevators, elevated parking structure for planetary defense pre-positioned assets
Adriano Campo Bagatin , “Response to collisions by NEA with gravitational aggregate internal structures”, study of collision outcomes depends on target’s number of components, the detailed internal structure of the impact region seems at least as important as the overall internal structure (texture) of the target

Antoni Perz-Poch, “Multi-spacecraft Electrostatic Tractor with Swarm Optimization”, real time coordination among satellites with an 4-6 satellites each 10 kV
Andrew Bacon, A Method for Fragmentation for Apophis, low cost fragmentation by using two or more Fregat Soyuz as smart impactors at resonant seismic frequency of Apophis to create an even distribution

- Methods for the Deflection of Threatening Asteroids: Some Problems, Theoretical
Considerations and a Few Myths
Keith Holsapple (University of Washington, U.S.)

Overview of some of the proposed methods for deflection, what do we need to do? After the astronomers say what we do, deflect (around 1-3 cm/s 10 years prior), disrupt or disperse it, or destroy it, a myth (destroy it): to vaporize a small 100 m asteroid requires about 30 Mtons of energy, you only change state, myth (“deflection is not possible in space”), danger of breaking it up is overestimated, delta momentum for deltaV for 1cm/s is 10^7 for H (momentum), table of mass for 100 m object: solid rocket (130 tons), gasoline (90 tons), dry cow dung (80 tons), bipropellant liquid rocket (70 tons), 10 km/s impactor (30 tons), 50 km/s impactor (6 tons), Fusion nuclear bomb (0.1 tons), E/C = c^2 ( 0.7 kg), things less than 30 tons could be considered, disrupt and dispersing it: needs 10^2 J/kg of asteroid, at or just under the surface, nuclear bomb (buried, surface, standoff), impacts unlikely to do except for smallest bodies), another myth: destruction energy might worsen the situation, there are neverl several large pieces in an impact disruption, typical fragment disruption velocities are several m/s, escape velocities are cm/s, tnes of cm/s are enough to miss the earth on the scale of a year, disruption would not be a problem if a year out or more, blowing it up at the last minute may work, how (bombs, bullets, gravity tractor), not good ideas (attached, surface landing, Yarkovsky, e-mag forces, tether), ones to focus on (nuclear, solar, laser), nukes are the last resort, is a method works better simply crashing its mass into the asteroid compared to its design method, forget it..unless there is a compelling reason, gravity tractor (10-100 factor just to impact), GT requires large mass/long time, no good ideas with interaction with surface for laser ablation (need to know dynamics), nice picture (MADMEN) – real surface tie it down, some methods have political problems (nukes in space, moving something slowly over the course of the earth –liability/weapon), composition problems (impacts, nukes, mass drivers, lasers, solar), porous materials are very good at absorbing energy shock, the forces on any stake in a rubble pile scale linearly with gravity (10^-5 to 10^-6 probability) – fastening with biggest item may not work, controllability/precision, robust mission with multiple instantaneous times, further analysis of nuclear (for porous material need to move into 20 m close), bullets (beta factor – due to blow back, do not know how much), B=1 (perfectly plastic impactor), other value it becomes a cratering problem, porous materials very little of beta (experiments would be good), with a single impact (200 m), multiple impact could do a km, an approach along the trajectory is not required, can hit it off center, no going to disrupt it, traj accuracy (mass, shape, spin, thermal inertia), kinetic impactor (just need mass) – thus Don Quixote would be preferred mission.

- Asteroid Deflection by Means of Electromagnetic Forces During an Earth Fly-by
Sanjurjo-Rivo, M.; Peláez, J. (Universidad Politécnica de Madrid, Spain)
Few works devoted to the analysis of deflection maneuver during Earth flyby (magnetic field and enhancement of gravitational interactions), uses a patched conic approximation (objective: avoid keyhole), electrostatic interaction (charge asteroid, electrodynamic tether (rigid attached to the asteroid)l – not feasible, can use these forces in indirect way, e-d tether modify the shape, electrodynamic tether, tether length of 350m E-d effect will be greater than the gravitational one, developed some techniques for electrostatic and E-D tethers

- Simulations of the Deflection of an Apophis-like Object
Jutzi, M.1; Michel, P.2; Benz, W.1 1University of Bern (Switzerland); 2University of Nice-Sophia Antipolis, Côte d'Azur Observatory (France)

Assumptions: (Apophis like object) – impact energy will not cause, why is is difficult to model

- Dynamical Characterization, Control, and Performance Analysis of Gravity Tractor Operation at Binary Asteroids
Eugene Fahnestock (University of Michigan / NASA Jet Propulsion Laboratory, United States)

Extensive study done at the request of B612 for using the GT to deflect hypothetical impactor (2016 NM4) by group at JPL, no detailed study of using GT at the binary object, apply prior GT control to case of binary, what is the differential performance penalty for binary versus solitary, 2016 MN4 – shape models from 1999 KW4, small size binary in analysis (65-24 m), placement of GT such that avoid collision and to maximize towing effectiveness, assuming SEP system, cant main GT thrusters by some angle to avoid exhaust impingent, computed ideal values (static setup to maintain equilibrium, GT station-keeping approaches, can get better control using simpler control algorithm, teo regions with good performance metrics (interior region meaning inside secondary ~ 215m, exterior region d ~ 430 m), conclusions: delta-V accumulations more likely to be near the top of their spread, mass loss more likely to be near the bottom of its spread, in relative terms there is a performance penalty compared to GT operation at solitary NEO, penalty for being exterior, completing deflection operation a binary NEO still quite achievable in absolute terms (even with simple control approach). 1999 KW4 may be typical (average period around 24 hours, KW4 is less than, KW4 is much smaller than those one would study)

- The SHADOW Mission: Deflecting APOPHIS with a Flotilla of Solar Shields
Prado, J.-Y.1; Perret, A.2; Boisard, O.2; Bertrand, R.1 1CNES (France); 2U3P (France)

Increasing number of resonant orbit with time, about 1 in 50 chance for an impact with the earth between 2036 and 2130, attempt to define safe areas for one century, SHADOW is tow parts, one is observation, another is deflection mission, Part 1: observe and track for Yarkovsky effect, Part 2: Apophis deflection by canceling Yarkovsky effect – developed in parallel with flotilla of solar shields, high Delta-V needed – useful for solar electric propulsion, Yarkovsky thesis in late 1800s, 1987 : small variation in LAGEOS, 2003 first observed in GOLEVKA, YE is tiny (10^-10) – effect like a butterfly on an aircraft carrier, main effect on semi-major axis, shadow 2 mission: transfer module using SEP carries 4x200 kg solar shields, shields controlled by transfer module, sail hovers a few km over the asteroid, no direct link of individual sails to Earth, chemical propulsion needed for balancing photonic pressure, only effective is there is substantial YE, next approach 2012/2013 must not be missed, excellent opportunity for worldwide training, solar shield/sail technology not proven, in mythology: Sun always tried to destroy Apophis, question: disagree with keyhole analysis

- Asteroid Deflection Theory: Deflection Charts and some New Deflection Options
Izzo, D.; Chy, C.H.Y. (European Space Agency, Netherlands)

New title: Asteroid Deflection Theory (Orbital Mechanics), Delta-V models are a.) full n-body propagation and b. keplerian propagation, if libration cycle tied to resonance begins, analytical methods lose accuracy, closed form solution is a formation flying problem between nominal asteroid (mother) and its deflected image (daughter), for small DVs the linearized rendezvous equations hold, delta-V use in-plane, optimal direction is along the velocity vector, optimal angle is between 0 and 1 degree for most of orbit, issue with model - linearization/integration error grows with time / accounts for only instantaneous velocity change, disregards the asteroid-Earth phasing and does not account for system design, the deflection formula (equation for acceleration and miss geometry), deflection charts: push time and start time relationships – show trade-offs given a particular encounter, but these charts do not tell us the optimal deflections, crucial to understand the strategy for system design and requirement for amount of deflection, larger deflection distance may mean kinetic impactor may be superseded by other options.

- Ariadna Encounter 2029: Introduction to the three studies
Call from ESA for ideas and concepts.

- Catastrophic Impact Energy Threshold for Disruption of Small Porous and Non-Porous
Asteroids: a Crucial Information for Deflection Strategies
Michel, P.1; Jutzi, M.2; Benz, W.2; Richardson, D.C.3 1University of Nice-Sophia Antipolis, Côte d'Azur Observatory (France); 2University of Bern (Switzerland); 3University of Maryland (United States)

Previous: NEOMAP at ESA (2004), how can we be sure that we will not destroy the body? The larger the rocks the weaker they are, at larger radius energy goes up, simulating a catastrophic disruption? Computing the fragmentation code, various types of internal structure, non-porous versus porous body fragmentation, reaccumulate to form family members, not so easy to destroy a body, first complete simulations of asteroid disruption (Science in 2001 and 2003), objects greater than 100m are rubble piles, disruption by impact of a 25 km asteroid (shape comes out similar to Itokawa), two regimes (strength and gravity) for disruption energy versus radius, for gravity regime no difference between porous or non-porous, for strength regime, porous a little more energy than on-porous, disruptive regime: largest output is 50% of target body, generate a lot of aggregate, characterized catastrophic disruption for targets of different sizes, etc., Marco Polo mission in assessment study for ESA Cosmic Vision 2015-2025 at ESA, proposed ESA-JAXA partnership, have not investigated macro-porosity of rubble piles in this same fashion, question: did we ever have an integrated small bodies (did we ever have monolithic bodies)

- Designs of Multi-Spacecraft Swarms for the Deflection of Apophis by Solar Sublimation
Vasile, M.1; Maddock, C.1; McInnes, C.2; Radice, G.1; Summerer, L.3 1University of Glasgow (United Kingdom); 2Strahclyde University (United Kingdom); 3ESA Advanced Concepts Team (Netherlands)

Years ago did a comparison of multiple deflection criteria (miss distance, warning time, spacecraft mass in orbit), found surface ablation was not as bad, nuclear blast led to in some cases unwanted fragmentation, moved on to surface ablation, first proposed by Lunan in 1992 and Melosh in 1993, Mirror Bees (media too concept), 4 month study supported by ESA ACT, study dynamics and mass estimates, solar pumped laser, if shoot are an angle – lose efficiency but avoid the plume of gas, cannot fire during the entire orbit, perturbations in orbit – required control authority, direct imaging with adaptive reflector, summary of two systems (laser and direct imaging), simulation of camera for observation, direct imaging: 1200 kg at TRL 2 including 40% propellant for the transfer (mirror diameter of 60m), laser (25% system efficiency) – mirror diameter 5m, done for Apophis, better to add more spacecraft than increase concentration ratio for same mirror size, various curves for warning times and size of bees, direct imaging required larger mirrors with adaptable shape, laser system requires smaller mirrors but more complex and requires efficiency above 20%, indirect laser pumping is more mature at his time, multiple spacecraft is better, many mirrors with low conversion factor appears to be more efficient than increasing the concentration factors of a few mirrors, question on impact of dust plume, experiments on simple rocks show that perhaps not 180 degrees of dust, Keith H.: has anyone done any calculations of absorption of that energy and verify the dynamics-concerned this is based on perfect gas models – when you have porous surfaces analysis may be more complicated, Melosh’s initial estimate indicates that effective at km sized body – will this work , perhaps competitive with 1km asteroid in terms of time to deviate and effect

- Apophis Encounter 2029: Differential Algebra and Taylor Model Approaches
Armellin, R.; Di Lizia, P.; Bernelli-Zazzera, F. (Politecnico di Milano, Italy)

Investigate differential algebra and Taylor models for 2029 Apophis encounters, , new algorithms (Improved Monte Carlo, and Close Encounter Algorithm), differential algebra: automatic differentiation technique, can be used for the nonlinear expansion of uncertainties of Apophis, third order expansion shows errors of 10 km in position, developed a DA Monte Carlo simulation, Close Encounter Distance (CED) Algorithm, a set of tools for NEO close encounters, attempt to develop faster and more efficient computational tools

- New Directions in Asteroid Deflection using Nuclear Explosives
Dearborn, D.1; Schultz, P.2; Ulrich, W1LLNL (United States); 2Brown University (United States); 3DTRA (United States)

No issues with Keith’s conclusions about nuclear option (only if other methods are not available), new work follows up with NASA 2006 report – proposed kiloton or sub-kiloton explosives on surface, you can break up asteroid (1 kiloton or less below breaking up 1 km size), reason to consider nuclear explosives – most mass efficient methods of transporting energy, plenty of tests, have been used in space, application and consequence (decades to impact: standoff/push), sources have been demonstrated, suitcase size types, LLNL have experience in making craters (290m x 100 m , ~200 m asteroid of Nevada tough), information on kinetic impactors, LLNL has 3-D codes, but use 2-D code (Langrangian Eulerian 2-D code), can put different types of properties (strength – water no strength, gravel-sand – force puts in pseudo force, can also put in porosity, never done that for meteorite in terms of crush curve, something that has porosity – early on you exceed crush pressure, want to take energy and distribute it, how much material are you really throwing out, Nevada tuff (density -= 1.9 g/cm^3), after you push something – you care about where pieces go, even when you do an impactor or nuclear – there is material thrown off – some small amount that is near original speed, approaches (decades to impact: standoff or low yield – surface emplacement), years to impact – high yield impact), standoff calculations - you need to heat a lot of mass, would like to do with neutrons versus X-rays, X-rays come in - heat first layer – that layer bleaches out – put in energy into a thin amount of mass, neutrons go right on in – for this >50% is absorbed in column density 48 g/cm^2, neutrons does not carry about mixture of elements (except for hydrogen), Neutrons – enhanced fusion, US stockpile weapons optimized yield/weight, would like something that provides a lot of neutrons – need a lot of fusion – US did that part of Plowshare program (peaceful nuclear explosions) – 35 tests, recent work looked at setting things at surface, with 0.1 kt at surface (0.38% of mass ejected, 1kt too much, 0.5 kt, 270 m body with 0.1 kt is too much – mass too low to depend know what you will get, no need for nuclear tests, real uncertainty is material properties of surface – when that energy is placed on surface how does the surface respond? Provide a dependable source to transport energy – would like to use things that were tested but now weaponized, when time scale is short if 50m is coming in then can covert to powder if just outside the moon, we have the duty to tell them what is possible.

- Using a Gravity Tractor to Help Mitigate Asteroid Collisions with Earth
Yeomans, D.K.1; Bhaskaran, S.1; Broschart, S.R.1; Chesley, S.R.1; Chodas, P.W.1; Jones, M.A.1; Sweetser, T.H.1; Lu, E.T.2; Schweickart, R.L.2 1JPL/Caltech (United States); 2B612 Foundation (United States)

Completed recently for B612, using the leverage of pre-impact close Earth approach to deflect a hazardous NEO with very modest amounts of energy, using slow NEO trim maneuvers to avoid primary and secondary impact possibilities, using rendezvous S/C images and tracking, 610 meter keyhole in April 13, 2029. Apophis test case is predicted to pass through the 2036 keyhole – impact 4/13/2036, assume it will impact for test case, launch in 2021 spacecraft, to S/C tracking and spacecraft acts as a gravity tractor, S/C again tracks Apophis, Feb. 14 2022 start tracking 580 x 15 km uncertainty ellipse, ends with 360x180 km ellipse after 60 days of tracking, GT placed 250 m from the asteroid’s center of mass along the asteroid velocity vector, five thruster configuration, takes 10kg / month for S/c hovering, 1000 kg S/C provided 1.14 x 10^-12 m/s^2 acceleration, 60 days of tracking moves Apophis on b-plane, Apophis is a unique case gets close to earth very close prior to impact, a few tens of percent could likely take advantage for gravity tractor, secondary keyholes are cm to one meter, primary keyhole is 610 m wide, secondary keyholes are more dense to primary keyhole, safe harbor could be established at zeta + 2.5 km (safe harbor around keyhole), examine the risk corridor during a slow deflection moves slowly, assume a KE impactor for beta = 2, m = 2400 kg, V = 5 km/s, if done in April 2022, deflection is 200 km change, by far the most important requirement of any successful mission campaign is warning time for carry out mitigation mission, Apophis unusual since close approach prior to impact, a pre-impact close approach multiples the effect tof earlier deflection, a deflection to avoid impact just needs to move out of keyhole, gravity tractor is a high precision procedure, GT could provide a trim maneuver

Panel Discussion

Dave Morrison: agnostic when it come to nuclear or non-nuclear, need to take into account spacecraft transportation, what is doable if you had a choice between the two methods,

Dearborn: If you were doing the standoff approach, question on altitude (putting our tons of neutrons) – could approach with fast speed, would prefer if UN passed law that all asteroids are rounds, adjust standoff time so you have right face of asteroid, “physics package” of about 100 lbs – put a seeker to reduce speed (not that much mass)

K. Holsapple: What is the uncertainty ellipse, question of getting to the right place, would want something there ahead of time

Dave. M.: No one has looked at nuclear deflection option reaching options

Alan Harris: getting caught with Apophis, Apophis is slow with the return, rendezvous with Apophis is ok, average RMS velocity is 15-20km/s, would encourage non rendezvous options (potentially proximity fuze option)

Exactly how precise time is for your detonation?
Keith H.: how accurately do you know where you are so you can have proximity fuze, radar fuze have fast timescales,

Fly multiple fast flybys, should not too focused on single flight mitigation options,

Dearborn: Aerospace did a scenario approach of hypothetical, every launch window advocated sending several options, launch them so approach at different times to see effect was sufficient

Rusty S.: Need to do a system level cost effectiveness analysis, ultimate questions- how do we best spend funds, if we look at cost effectiveness, it seems intuitive that if he takes Alan Harris size/freq. dist, most productive things I can do is to accelerate second generate of survey to the point that the unknown residual of any size NEO decreases as rapidly as possible, when invest in 2nd generation search, largest NEOS become known earliest. If we say nuclear device is needed for large object, three basic reasons for nuclear: big object at any time, smaller object getting to it rapidly – both of those disappear for all but comets – third issue does not disappear – geopolitical procrastination, geopolitical community cannot make a decision in time to use a non-nuclear method – one remain case that will not go away – ultimate geopolitical (audience claps)

K. H: most politically method is likely to be the one to be stuck with since politicians cannot decide to do anything else

Dearborn: if Tunguska sized object is going to fall in central Africa – people at UN would talk all the way down, if it were hitting for Paris – one nation might choose to do something, was not proposing to spend more money, what is the number one thing – send more money to Don Yeomans, if you want something to learn about asteroids – you need an impactor mission (Don Quixote),

Michel, P: comments by the people – most of people who want deflection mission, there is public fear of using weapons, may scientists do not want to come to this conference since they think it implies nuclear weapons, we have to be careful how we pronounce this

Dearborn: I do hear things that may scientists nuclear devices for excavation, information should be in the room, in the meeting with Tom Gehrles, the deflection dilemma – nuclear explosive – may indeed be facing larger risk to build such a system and have it ready – one needs to think very carefully whether the cure may be worse than the disease (SALT treaties, Chinese declared that they were not ready to turn in nuclear weapons for asteroids – never mind their weapons were not designed for asteroids)

Dearborn: did not advocate building anything

K.H: if anyone says we need to test a nuclear weapon, we need to understand response of the asteroid and can do that with an impactor

Clark C.: the porosity has been discussed a lot today, do not think asteroids look like piles of dust, Don David and Chapmen coined rubble pile, a rubble pile consists of hugh pieces to fine stuff (Itokawa), how are you going to kinetic or nuclear – how you are going to model the response of such a heterogeneous nody

K. H: ultimately how nigh is your event compared to the grains? Less effect than you might image (question of size scale)

Dave M.: comments on Rusty’s argument, statistically is we do survey or not, we are here that something could happen, you cannot just say statistically we cannot worry, a couple of people say nuclear is the system of choice, would think kinetic impactor is surely more easy to do – but several people said nuclear

Dearborn: if you can do it another way then do another way

K.H.: just a question of mission design, if you can do it with an impactor then do it with an impactor, perhaps solar collectors could be competitive – maybe could reach further,

Nothing like a deadline to focus, as soon as we do, everything kind of resolves, you always want a backup plan, nuclear will become less of a political liability

Alan Harris: let us not build it until we need it

K.H.: at some point someone would want to being up biggest “gun”

If you repeat the Tunguska event today, cost of real estate (300-400 M Euros over an unpopulated area) pay for a survey program,

Dearborn: with Tunguska like event, today the population is 12.5 people per square km, every few hundred years 25,000 dies, in an actuarial sense that is also the cost, with regard to where they put money, U.S./China/Russia have nuclear weapons for their own reasons – working their way down – at that point can extend out response time, keep nuclear weapons for political considerations and not for stopping asteroids,

Alan Harris: 20,000 per mean event, median = 0

A.Glavez: surprised debate is so polarized, you need several options, whenever this kind of things come, you have to have this knowledge, important to have working on a sustainable way

D. Izzo: for Apophis nukes may not the solution, coming up with different ideas

Michel, P: useful for having a demonstration mission like Don Quixote

K.H.: The engineering/mission questions are those that can be tested, what we do know for sure if we impact at certain velocity, deep impact (beta well over 100-200 perhaps), even calculations come up with ejecta velocities of beta of 30, need to know beta better, if we can hit it,

Michel, P.: we need a test

P. Gatterson: political leaders are ok are estimating risk, bit of fear mongering to talk about the cure is worse than the disease, even if you have a preference against using nuclear weapons, that is not prohibition against using it. Would add to Rusty’s case: you choose a softer touch approach and you fall back on redundancy but at least you thought through, not advocating a test mission.

No comments:

Post a Comment

Note: Any opinions expressed on the blog are solely those of the author. The site is not sponsored by, nor does it represent the opinions of, any organization, corporation, or other entity.