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25 September 2013
Asteroid Initiative Idea Synthesis Workshop Asteroid Deflection Session
Prepared by:
Andrew E. Turner
3825 Fabian WayPalo Alto, CA 94303.4604USA
Affordable Spacecraft with Capabilities to Enable Multiple Deflection Schemes
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Four Diverse Asteroid Deflection Techniques
1. Gentle sustained push applied directly by the Asteroid Redirect Vehicle (ARV) via its robotic arms against a selected site on the asteroid, or against a robotically deployed fixture that distributes the push pressure over a wider area on the asteroid to demonstrate direct asteroid deflection
2. Electrostatic tractor technique using the technology developed at the University of Colorado
3. Gravity Tractor technique defined by the B612 Foundation also defined by NASA Ames Research Center (ARC). which we have augmented to include a robotically extracted boulder as a gravity multiplier
4. Kinetic impactors developed by ARC
These 4 techniques are applied when appropriate to the asteroid target, whose nature may not be known until it is approached. It may not be possible to select which type of asteroid is to be manipulated, but we have a flexible spacecraft system design that can handle any type
More than one of these techniques may be applied during a single mission So the “person in the street” understands the importance of this project, we would
demonstrate the capability to Move an asteroid large enough to constitute a threat to show we can “save the planet” Retrieve a boulder to distant Earth orbit so a sample can be brought home by U.S.
astronauts that people can touch
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Spacecraft Configuration
The versatile flight-proven, economical SSL bus can accommodate the specialized equipment for this mission, which has been commercially procured on a Firm Fixed Price basis more than 80 times (~5 launches/year)
Proposed equipment has sufficiently diverse functionality that it can handle any of the 4 deflection techniques
It will be discussed how even a single deflection technique involves multiple equipment types
40 kW of electric propulsion is sufficient to generate 2N of thrust using thrusters already available from SSL, can adapt new thrusters if needed
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SSL Has Full Access to MDA’s Robotics Technology
The robotics proposed for this mission already exist and reuse hardware and control software from the ISS robotics, Orbital Express Autonomous Satellite Capture Demonstration and the DARPA Phoenix Satellite Repurposing Demonstration
SSRMS captures HTV at ISS IDD engages the Martian surface
MSL Robotic Arm, Multi-Tool Turret13-m Hubble Telescope Capture Arm with Visual Servo Algorithms to Capture Free
Flyers (available for this mission)
This equipment now located at NASA-GSFC
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Asteroid Deflection/Retrieval Gravity Tractor Example
Propellant Budget accounting borrowed from heritage spacecraft mission analysis for this application
Masses of acquired 6-m boulder also 200-m diameter asteroid counted as spacecraft mass Propulsion: 8 SPT-140 with total 2N thrust, bi-propellant with total 80N thrust About 7% of total impulse applied to the 1 mm/s delta-V Deflection, this operation requires
about 2 months
EP Total System SystemDelta-V Efficiency Impulse Isp Delta-mass Final Mass
Thruster (m/s) (MN-s) (s) (kg) (kg)PSM 14,500.0SEPARATED MASS 300.0 14,200.0TRANS-LUNAR TRAJECTORY CORRECTION MANEUVERS BIPROP 10 0.95 300.0 50.7 14,149.3POST-LGA VELOCITY AUGMENTATION EP 800 0.95 11.6 1750.0 677.5 13,471.7RENDEZVOUS WITH ASTEROID EP 500 0.95 7.0 1750.0 406.9 13,064.9MANEUVERS NEAR ASTEROID EP 50 0.95 0.7 1750.0 40.0 13,024.9LANDING ON ASTEROID/APPROACH BOULDER BIPROP 10 0.95 298.3 46.8 12,978.1ACQUIRE BOULDER 160,000.0 172,978.1LIFTOFF FROM ASTEROID/INITIAL HANDLING OF BOULDER BIPROP 1 0.95 298.3 62.2 172,915.9DESPIN BOULDER BIPROP 0.95 0.0 172,915.8ACQUIRE ASTEROID FOR GRAVITY TRACTOR OPERATION 6,283,185,307.2 6,283,358,223.0GRAVITY TRACTOR OPERATION EP 0.001 0.70 9.0 1750.0 523.0 6,283,357,700.0DISENGAGE ASTEROID 6,283,185,307.2 172,392.8MANEUVER AWAY FROM ASTEROID BIPROP 0.0656 0.95 297.5 4.1 172,388.7SHAPE TRAJECTORY FOR LGA CAPTURE TO EARTH ORBIT EP 500 0.95 89.4 1750.0 5,206.6 167,182.1POST-CAPTURE MANEUVERS TO ACHIEVE STABLE ORBIT EP 50 0.95 8.8 1750.0 511.9 166,670.1EP MANEUVER RESERVE EP 30 0.95 5.3 1750.0 306.4 166,363.7BIPROP RESERVE 831.2 165,532.6BIPROP HOLDUP 5.0 165,527.6PRESSURANT 5.0 165,522.6COMBINED EP TOTAL IMPULSE 131.7DRY SPACECRAFT MASS 5,522.6TOTAL XENON MASS 7,672.4TOTAL BI-PROPELLANT MASS 1,000.0EXCESS BIPROP TANK CAPACITY 100.0EP XENON THROUGHPUT IF 4 EP USED 1,918.1
160-ton boulder acquired
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Background to Example
1. Gravitational attraction between the 10-ton spacecraft and the 200-m asteroid is below 2N without the 160-ton boulder
2. Gravitational attraction is 7N at the asteroid’s surface when the 160-ton boulder is acquired so employ chemical thrusters
3. At 90m altitude the gravitational attraction is 2N which can be balanced by the electric thrusters. The asteroid subtends a total angle of about 90 deg. as seen from the spacecraft. This assists with avoidance of the asteroid’s shadow for full solar array power and avoidance of impingement of the thruster plumes on the asteroid’s surface
What if the asteroid is not a “rubble pile” but a coherent asteroid and we cannot extract a boulder? We might push
What if the asteroid is a “rubble pile” but contains only rubble far smaller than 6m (160 ton) boulders? We might scoop
What if 90 m is too close to the asteroid for continuous operation? We might reduce thrust, operate from a greater distance and spend more time but not more propellant performing the deflection demonstration
1 2 3
23
Asteroid is spherical with a density of 1500 kg per cubic meter
7 Use or disclosure of the data contained on this sheet is subject to the restrictions on the title page.Proprietary
25 September 2013
Hip Pocket Slides
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Background: Coherent, Fractured, or “Rubble Pile” Asteroids
Example of a “rubble pile”: Asteroid Itokawa, hundreds of meters across, from which Japanese spacecraft Hayabusa returned samples in 2010 from a 2005 visit
Small asteroids, only a few meters across, may tend to be coherent boulders A coherent asteroid is more amenable to being pushed or acquired for captive-carry, a
“rubble pile” is more amenable to being pulled using the gravity tractor, once a coherent boulder has been acquired from its surface
Source: What We Have Learned from the Asteroid Itokawa Samples Returned by the Hayabusa-1 Mission’, The 10th IAA International Conference on Low-Cost Planetary Missions 18 June 2013
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The Path to the Asteroid, and The Way Back, via The Moon
New generation of commercial LVs: 10-15 tons into trans-lunar trajectories
A lunar gravity assist (LGA) is used to eject the spacecraft into interplanetary space with nearly enough impetus to reach Near-Earth Asteroids
An LGA can provide a delta-V on the order of 1 km/s
Later maneuvers using electric propulsion speed the spacecraft on its way
This avoids spending considerable time in the Van Allen belts near the Earth, thus minimizing radiation exposure
Barycentric Orbits Spacecraft Launch Mass
Apogee at Lunar Altitude
A lunar gravity assist (LGA) is essential for bringing home the 160-ton boulder
Even with electric propulsion spacecraft has insufficient total impulse to achieve capture with this heavy mass
Lunar gravity acts on every atom within the spacecraft and the boulder, so there is no stress created as it operates
The spacecraft carrying the boulder is constrained not to be significantly nearer to Earth than the moon
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A Second (Much Smaller) Moon …
YouTube video http://www.youtube.com/watch?v=3KG3kHWLSZo supplied by the Keck Institute for Space Studies displays injecting the captured asteroid into a distant retrograde lunar orbit following a low perigee pass by Earth
An alternative strategy would be to use an LGA only and inject into an orbit of roughly the same size and the same period as the orbit of the moon This orbit would be inclined to the lunar orbit with a wedge angle of about 50°, but
both orbits could be inclined about 23° to Earth’s equator, therefore captured asteroid is reachable from a Cape Canaveral launch
The asteroid would be maintained on the opposite side of its orbit from the moon to limit perturbations due to lunar gravity, corresponding to a halo orbit about the Earth-moon L3 point, precise location to be evaluated
The boulder is now ready for astronauts to visit, study it and return samples
North
Wedge angle
Lunar orbitRetrieved
Boulder orbit
