Why Would Someone Want to Put an Asteroid in Orbit Around

the Moon?

Joseph A. Nuth IIISolar System Exploration Division

NASA’s Goddard Space Flight Center

Why an Asteroid Orbiting the Moon?• If something goes wrong, it does not hit Earth.• The Moon is close. Manned missions to the

asteroid can be <10% transit, >90% operations.• What can be done at the asteroid?– Piloted proximity operations and remote sensing – Manned interactions with the surface including

dealing with dust, grappling with the surface, etc.– Prospecting for and extraction of resources

• If something goes wrong, get home fast.

What is feasible with current technology?

(Image Credit: Rick Sternbach / KISS)

What Size Asteroid Can be Returned? • A 40KW Solar-Electric Power System could

retrieve a 500 ton asteroid in < 10 years.• A 500 ton asteroid is ~ 7m in diameter.• A 500 ton, carbonaceous C-type asteroid may

contain up to 200 tons of volatiles (~100 tons water and ~100 tons carbon-rich compounds), 90 tons of metals (approximately 83 tons of iron, 6 tons of nickel, and 1 ton of cobalt), and 200 tons of silicate residue (aka: shielding).

• At $10K/kg the asteroid “value” is $5B.

What “Challenges” Exist? 1.9 g/ cm3 2.8 g/ cm3 3.8 g/ cm3

2.0 7,959 11,729 15,917 2.5 15,544 22,907 31,089 3.0 26,861 39,584 53,721 3.5 42,654 62,858 85,307 4.0 63,670 93,829 127,339 4.5 90,655 133,596 181,309 5.0 124,355 183,260 248,709 5.5 165,516 243,918 331,032 6.0 214,885 316,673 429,770 6.5 273,207 402,621 546,415 7.0 341,229 502,864 682,459 7.5 419,697 618,501 839,394 8.0 509,357 750,631 1,018,714 8.5 610,955 900,354 1,221,909 9.0 725,237 1,068,770 1,450,473 9.5 852,949 1,256,977 1,705,898 10.0 994,838 1,466,077 1,989,675

Diameter(m)

Asteroid Mass (kg)We will not know the mass of the asteroid we are trying to capture until we get there: visible photometry plus Infrared can determine the size but not the density of a target NEO.

What “Challenges” Exist?

Rotation Period vs. Diameter for all Asteroids

Small bodies are more likely to be rapidly rotating: they are strongly affected by both the YORP and Yarkovsky effects that increase their rotation rate and perturb their orbit. Small bodies are therefore most likely to be “lost” after initial discovery.

How many targets are available?

Time Since Discovery Rate(#/day) Rate (#/year) Follow-Up 12 hrs 10 3,600 Astrometry 24 hrs 0.5 180 Astrometry, colors 48 hrs 0.2 70 Lightcurves 48 hrs 0.1 36 Spectroscopy 72 hrs 0.06 20 RadarNet Rate of Target Discovery 0.013 5

Note that we are looking for targets less than 10m in diameter. They can only be detected as they approach the Earth. The albedos of carbonaceous objects are typically very low (<5%) so spectroscopy is only possible at close range with most ground based telescopes. On the positive side, an ideal candidate is in almost the same orbit as the Earth and so it passes very slowly and there will be ample time to launch the mission.

Are there alternatives to tiny bodies?

Yes: all small bodies have regolith of about the right size. “Pick up a rock” Scenario

“Pick up a rock” Scenario• Advantage:– Allows a well planned mission to a target with a

precisely determined orbit.• Disadvantages: – Unless previously visited by a spacecraft, we can’t

be certain that the body has appropriately-sized boulders for the taking.

– Near surface operations with large solar arrays can be complex and risky.

– Is the boulder we want easily retrieved?

Mission Scenario to a Small Body

10.7 m

15.0 m

10.0 m

35.7 m

5.8 m

36 deg

2.7 m

5.9 m

Solar Array Wing

Spacecraft BusStructure

Capture BagDeployed

Hall Thrusters

Conceptual design of the Single Spacecraft Architecture in the deployed configuration.

Asteroid Return Mission Concept

407 km LEO Circular Orbit

Moon’s Orbit

Atlas V 551

3. Spiral Out to Moon (2.2 years)

Asteroid Orbit

2. Separation & S/A Deployment

4. Lunar Gravity Assist

5. Cruise to Asteroid (1.7 years) 7. Return to

Lunar Orbit(2 to 6 years)

6. Asteroid Operations(90 days: Deploy bag, captureand de-tumble asteroid)

1. Launch

Earth

8. Lunar Gravity Assist

9. Transfer to high Lunar orbit

Mission Design Parameters & TargetsC Value Comments

SEP Power 40 kW

Specific Impulse, Isp 3000 s

EP System Efficiency 60%

Spacecraft Dry Mass 5.5 t

Atlas V 521-class LV

Launch Mass to LEO 13.5 t

Spiral Time 1.6 years No shadowing

Spiral Xe Used 2.8 t

Mass at Earth Escape 10.7 t

Atlas V 551-class LV

Launch Mass to LEO 18.8 t

Spiral Time 2.2 years

Spiral Xe Used 3.8 t

Mass at Earth Escape 15.0 t

Spiral DV 6.6 km/s LEO-intersect Moon

Escape/Capture C3 2 km2/s2 Lunar assisted

NEA Stay Time 90 days

Target Returned Mass, t

Xe, t (no

Spiral)

Earth Escape

Flight Time, yr (no spiral)

Arrival C3,

km2/s2

2008 HU4 250 5.0 4/27/2022 4.0 1.8

2008 HU4 400 5.2 4/27/2021 5.0 1.7

2008 HU4 650 6.5 4/27/2020 6.0 1.6

2008 HU4 950 8.9a 4/28/2019 7.0 1.6

2008 HU4 1300 9.1a 4/28/2018 8.0 1.6

2008 HU4 200 8.7a 8/15/2017 8.0 0.0b

1998 KY26 30 4.9 11/11/2019 4.7 2.0

1998 KY26 60 4.2 7/19/2020 5.3 2.0

2000 SG344

1800 1.8 3/8/2027 2.6 2.0

2000 SG344

3600 1.5 2/14/2027 2.6 2.1

2000 SG344

100 6.3 4/20/2024 6.5 0.0b

Capturing the Asteroid

Put the Target into High Lunar Orbit• Trajectory calculations

indicate that a high lunar orbit is stable for at least 20 years.

• Missions to this target can proceed at leisure.

• Dust and Debris that is generated by asteroid operations will fall to the Moon.

Example mission returning 1300 t of a small (~7 m) NEA with a radar opportunity in 2016.

Backup Slides

Authors and Study ParticipantsJohn Brophy Co-Leader / NASA JPL Fred Culick Co-Leader / Caltech Louis Friedman Co-Leader / The Planetary SocietyCarlton Allen / NASA JSC David Baughman / Naval Postgraduate School Julie Bellerose NASA ARC/Carnegie Mellon Univ.Bruce Betts / The Planetary Society Mike Brown / CaltechMichael Busch / UCLA John Casani / NASA JPL Marcello Coradini / ESA John Dankanich / NASA GRC Paul Dimotakis / Caltech Martin Elvis / Harvard-Smithsonian Center

forAstrophysicsIan Garrick-Bethel / UCSC Bob Gershman / NASA JPL Tom Jones / Florida Institute for Human and Machine

Cognition

Damon Landau / NASA JPL Chris Lewicki / Arkyd AstronauticsJohn Lewis / University of Arizona Pedro Llanos / USC Mark Lupisella / NASA GSFCDaniel Mazanek / NASA LaRC Prakhar Mehrotra / Caltech Joe Nuth / NASA GSFC Kevin Parkin / NASA ARC/Carnegie Mellon Univ.Rusty Schweickart / B612 FoundationGuru Singh / NASA JPLNathan Strange / NASA JPL Marco Tantardini T/ he Planetary SocietyBrian Wilcox / NASA JPL Colin Williams / NASA JPLWillie Williams / NASA JSCDon Yeomans / NASA JPL

Sponsor: Keck Institute for Space Studies

Meeting a National Goal

• The Manned Space Program was tasked with sending astronauts to rendezvous with a Near Earth Asteroid by 2025 along the Flexible Path.

• Unfortunately, humans are quite fragile and have a tendency to develop various cancers when exposed to space radiation for the times required to reach most NEOs (>180 days).

• In going to a NEO, >90% of the mission is spent in transit with <10% at the asteroid.

Why Do We Want to Visit NEAs?• As part of the Flexible Path, NEAs were a deep

space target to demonstrate new capabilities.• As part of long term plans to expand humanity

into the Solar System, they contain all of the resources needed to sustain life without any reliance on terrestrial materials (@ $10K/Kg).

• Can we tweek the rules in order to achieve most of the HSF goals and add some new ones as well? That was the purpose of the study.

One-time Stunt or Long-term Facility? • At a minimum, several missions to an orbiting

lunar asteroid can be done for the cost of a single manned mission to a deep space target and much more can be accomplished.

• Begin “bootstrap” construction of a long-term space manufacturing facility that can produce water, fuel, structural metals and shielding.

• Bring additional asteroids to lunar orbit at regular intervals for processing.

• Practice moving asteroids (Hazard mitigation)

Why now?• Asteroid retrieval and industrial-scale processing is

enabled by three key technology developments: • the ability to discover and characterize an adequate

number of sufficiently small near-Earth asteroids for capture and return;

• the ability to implement sufficiently powerful solar electric propulsion systems to enable transport of the captured NEA to the vicinity of Earth;

• the planned human presence in cislunar space in the 2020s, enabling exploration and exploitation of the returned NEA.

Number of Known Asteroids• 1980 < 10,000• 1985 < 12,000• 1990 < 15,000• 1995 ~ 25,000• 2000 ~ 125,000• 2005 ~ 325,000• 2010 ~ 525,000

• “The Near-Earth Object Surveys and Hazard Mitigation Strategies: Interim Report” from the NAS estimates that we have found only about 10% of the >140 m class objects as of 2010.

We have only classified about 5000 of the known asteroids.

Why do we care about classification?If the goal of a manned mission is making specific measurements or emplacement and testing of specialized equipment, then that equipment will be designed for a specific set of requirements and will only work on certain types of material (e.g. spectral classes).

Asteroid classification is the basis for the exploration of the solar system

Commercial exploitation of nearby asteroids, as well as the far future selection of asteroid resources to support independent habitats , will require prior knowledge of their composition and structure before retrieval.

Outline of the Presentation• Why might we want to put an

asteroid in orbit around the Moon?• What size asteroid would we be

able to relocate to lunar orbit with our current technology?• How would this be accomplished?