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.

11 May 2011

2011 IAA Planetary Defense Conference: Day 3 Session 5

Notes from Day 3 of 2011 IAA Planetary Defense Conference. Follow twitter feed for more information:

Day 3 (Wednesday 11 May 2011) Session 5
Campaign Planning

- J-T Grundman
AsteroidSQAUDS/iSSB - Synergistic NEO Deflection Campaign and Mitigation Effects Test Mission

reflection of past IAA 2009 conference white paper: campaign studies and focus on smaller objects
looking at desires of various missions: heavy launcher development, fast mission scenarios, low space debris generation, include amateurs,
small and smart interceptor design produced in advance of heavy launch vehicle development
launcher test schedule triggers search for suitable target (3-6 months to launch)
every month 8-20 known NEOs approach Earth within 0.2 AU
NEAs about the size of 100m chosen
instruments: ranger like camera bank, dust counters, plasma instruments
take the AsteroidFinder spacecraft
have a more modular approach to spacecraft development
using CEF (Concurrent Engineering Facility)
put a kit together
interceptor: 179 kg mass
fits in standard secondary payload volume
took a Ariane 5 model for heavy life (12 MT to GTO)
20 impactors on a launch vehicle
Use Shoemaker Levi 9 multiple impact scenario

Q: need for observer spacecraft for any deflection
A: not about a proper deflection (testing mission) - not a deflection

- A. Zimmer
"Target Selection and Mission Analysis of Human Exploration Missions to NEAs"
Univ. of Stuttgart

complex trade space, multiple NEAs too many filers, launch window investigation, mission abort options
better understanding of parameter space for trajectory options for human missions

accessibility model: pre-selection of asteroid, based on celestial mechanics rather than scientific gain
approach: based on upper stage performance, departure from LEO, two impulse round trip mission, termination condition: deltaV limit (first burn) <10k/s, mission duration <365 days

verification of model: used 7812 NEAs, size criterion (H<=25) and slow rotation rate, 6704 NEAS, then semi-major axis, eccentricity, inclination: 2567 NEAs, then termination condition:
left with 240 NEAs between 2010 and 2040
statisitics: most attractive tragets with deltaV<7.5 km/s left with 73 targets - most of PHAs, pre-dominantly Atens and Apollos, many targets require long missions and high DeltaV
absolute mag less than 22-only about 20 NEOs

170 launch windows between 2020 and 2040
gradually increase in mission duration and then increase time with 1 mission every 2 years
looking at anytime abort (duration of return to Earth minimized) and free return (delta V minimized)
only investigated outbound mission leg only (once at asteroid)
long missions (= 365 day return, free return possible, anytime abort is limited)

better understand of abort options and assessment of prx ops, and Near Earth Largrnage points
design a building block of architecture

- Sugimoto, Y.
"Effects of NEO Composition on Deflection Methodologies"
Univ. of Glasgow

Looking at short warning time cases
for small bodies mass is not always available and estimate from bulk density if highly unlikely
most abundant NEOs are S-type asteroids (about 50%)
evidence theory can quantify epistemic uncertainties without assuming a distribution function specific to asteroid composition
NEO properties: micro-density, micro-porosity, bulk porosity, and albedo (out dist. on those)

two measures of uncertainty: beliefs and plausibility
set scene, set a baseline composition: 40% bulk porosity and 3.6g/cm?^2, and 0m2 albedo
deviation required (1.66 Earth-radii and 2.5 Earth-radii safe distance)

three types of mitigation missions: kinetic, nuclear, and solar collector
Q: did listing of meteorite densities did it include all data: did not include data, only a fraction of data are usable since meteorites have been weathered and potential better samples needed that are less weathered and handled better
Q: what is important is physical properties

- Cyrus Foster
"Multiple Concepts and Operations for Asteroid Mitigation including Multiple Gravity Tractors"

Deflection campaigns uses more than gravity tractor
redundant gravity tractor for insurance against failure

how does deflection scale with use of multiple gravity tractors
three concepts: single gravity tractors at a time, simultaneously tractor GTs w/station keeping, simultaneously tracting with mechanical docking to form single gravity tractor
used Apophis
looking at six launch opportunities: sending single 1MT gravity tractor

Concept 1: single GT at a time
other GTs an acts are tracking and use as backup
simpler operational concept but poorer deflection, total deflection of 76.1 km

Concept 2: simultaneous GTs
station keep around single point (could also be interested in halo orbits)
enables simultaneous ops but
total deflection of 122.4 km

Concept 3: mechanical docking approach
eliminates strict station keeping requirements but requires mechanical interface and docking ops

Concept 3b: keep empty gravity tractor docked
total deflection of 134.6 km

for Apophis: docked stacking provided a 10% improvement,

Trajectory Browser Tool at NASA Ames (web based tool to search rendezvous opportunities)
transfer from Earth to 8k NEOs and user can access database and select constraints
database of 2 body ballistic trajectories for various missions configurations

Mission Design Center Small Body Missions at NASA Ames
currently a NASA internal website

Q: perhaps increase efficiency for concept 1 if one if to use expended GT is sent

Q: use kinetic impactor and GT to trim perhaps, that might be easier
A: for Apophis multiple gravity tractor is overkill for this example (just providing it for example)

Q: how robust is the scenario are, launching GT at different times, putting GT later

Q: Looked at refueling GTs
A: Have not considered

Q: is the NEO tool distinguish types of NEOs based upon quality of observations
A: Yes, have orbit condition code as user input

- Nahum Melamed
"Development of Handbook and an online tool on Defending Earth against potentially hazardous objects"

develop a handbook for kinetic impact
develop a web based resource center for first order deflection mission requirements
aid in KI design

characterize NEO, determine deflection maneuver by using Lambert solution, select launch vehicle, determine deltaV, determine B Plan position
currently development B plane position is finished, working on the determine the trajectory phase portion
available on JPL portal at future stage

Current state of the web tool (Phase 1a)

ongoing development, save and retrieve buttons, B-plan updates, add variable resolution on earth impacts, possibly to vary to DeltaV slides, show keyholes,

Phase 1b development:
integrate with launch capability and use LV payload planners guide, use Lambert solution to connect departure, get DeltaV to imparted NEO

tool ready in a could of months

- Andres Glavez
"ESA Asteroid Mission Studies: What we have learnt"

Don Quijote was an interesting exercise

how can a generic precursor be defined? complicated missions, many options, have freedom how to select a target (not like reality), multiple trade-offs in architecture

clever use of orbital mechanics (Don Q. Mission): dual launch with spacecraft separated into different trajectories
flexible mission timelines
orbit stability
be prepared for the unexpected
mission layer is related to the type of information mission is expected to gather

radio science experiment: requires iterative process with determination of position and computation of position of asteroid

- Sam Wagner
"Robotic and Human Exploration/Deflection Mission Design for Asteroid Apophis"
Human mission requirements for 180 and 365 day crewed mission
2028/2029 human mission
two launch windows for each close encounter
180 days is the max for most NASA missions
for 2028/2029 launch dates, very small launch windows (2-12 days)
180 day summary, need 12 km/s
365 day mission: lower Delta V required, 6 km/s deltaV needed, similar to Ares I with Orion
Use Apophis for NEO missions, similar to Lunar deltaV with 6.5-7 km/s

Fictional crewed 2036 deflection missions: minimum one year mission length, 8.5 km/s deltaV
launch window exactly one year prior to impact, arrival 15 days prior to impact (only one chance)
Apophis arrival, departures, Earth arrival in last 1.5 months

Fictional post 2029 Intercept mission
continuously launch from 2035-2036, max deltaV is 4 km/s
arrival velocities from 0.09 - 20 km/s

Human pilot Mission Conclusions:

180 day mission: 11-12 km/s
365 mission: 6.5-7 km.s

- Erik Ball
"NEO Object Interception Using Nuclear Thermal Rocket Propulsion"
in place of Steven Hoewe

Scenario: Need to deflect large long Period Comet (10 km)
deflection or destruction

minimum energy for example is 3300 terajoules, thermonuclear explosion
NTR is very useful for such applications, CSNR worked on such NTRs,
chose NTR since high specific impulse (engine T/W, 6:1) up to 1000s ISP

yield requirements for deflection: scales linearly with comet size (effect based on comet properties are unknown), effects of trapped volatiles
surface burst or close standoff
40km/s: penetration impossible
Beta assumption: 3X10-4 (kg*m/s)/J
hundreds of megatons for large comet

independent variables: time of launch, angle of launch, rocket delta-V

optimize trade off between high mission deltaV and high payload mass
choose best engine size (larger engine is more mass but more thrust reduces gravity drag)

how crucial is an early launch (fast mission: 50 days before impact): high deltaV, later launches (12-27 days before impact) have 20-40 days for launch windows
early interceptor have a high fuel mass, low fuel mass but high payload mass, optimal point at about 17 days before impact (0.25 T/W of interceptor rocket)
Chemical rocket not a feasible rocket because mass to LEO is very high for chemical
even low thrust is too massive and not enough thrust for short time
3600 MT in LEO (very massive

how big could we deal with (21 HLLV in 2-3 months, carrying 20 MT interception - 1 MT is engine, most if fuel mass), 9 MT of payload, arrive at comet within 2 days of each other (7-8 month flight time), mission deltaV is 7 km/s

perhaps may be able to get up to 5 km diameter in terms of mitigation with feasible approaches
need to have technology ready perhaps
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