Itokawa (ISAS/JAXA)

Science and the

Human Exploration of Asteroids

1999KW4 (Ostro/JPL)

Erik Asphaug, Arizona State University

Space Studies Board, National Academy of Sciences

Fall Meeting, Nov 4, 2015

“Out there on an asteroid, there’s nobody

to boss you around. You’re free!”

Humans in the loop?

• Human scientific exploration is expensive and accommodates risk

• Asteroids are very unlike the Moon, perhaps more like exploring a deep oceanic abyss

• Great asteroid science can be done robotically – Why put humans

in the loop?

Asteroid Eros (NASA/APL)

Time is money • Humans figure things out fast in novel environments and get on to the next problem – Make quick assessments,

find the cool stuff, register the ‘same old’ stuff, and redefine the science goals (fast iterations)

• Human missions may cost ~10x more, but may achieve ~10x more science in a similar timeframe as a robotic mission – If time = money then human

missions are by far the better deal!

On Apollo 17, eight explosive charges

containing from 57 to 2722 g of high

explosive (!) were deployed at

distances between 100 m and 3.5 km

from an array of 4 geophones.

Acceptable risk

Example: seismology at an asteroid • Honeymoon phase: it seemed so easy at first!

– In the 1990s-2010s teams in US, Europe and Japan have proposed asteroid seismology experiments

– Identified as a primary objective of hazardous asteroid mitigation (‘know your enemy’)

• Mission concepts studies expose the need for detailed knowledge of the surface conditions...

– Landers? Not easy (Philae on Rosetta at 67P/C-G)

– Pods? Must show they would land in a suitable configuration, not buried in a hole or beneath regolith where you can’t communicate and where thermal runaway fries the batteries

– Penetrators? These require knowledge of surface conditions

• Then you have to worry about what the seismometer is coupled to… – Resting on surface rocks where there is no signal? How packed is the regolith in milli-gravity?

• Lastly you have to worry about whether the source event will displace the seismic array, given that a cell phone buzzing on an asteroid would go into orbit

– Don Quixote mission concept (ESA) got derailed at this juncture

Walker & Huebner (2004) Asphaug & Scheeres (2005)

We can learn a lot about the

NEO gravity environment

(~10-3-5 G) by studying the

microgravity (~0-10-6 G)

environments of space.

But asteroids have some

gravity, and this makes a

world of a difference for

science operations

Itokawa/Phobos/Moon are

approximately a geometric

progression (x100) in gravity

would you use lunar lander

heritage, or Hayabusa/OREx

heritage, in sample return from

Phobos?

SSB 1990

Itokawa (0.3 km) Phobos (22 km) Moon (3500 km)

Human science activities in the ‘flexible path’

2009 Augustine Commission

Human science opportunities at NEOs

– Search for remaining evidence of planetary

accretion and satellite formation • Sample return; petrographic and geologic record

of formative collisions

– In-depth basic studies of the most common planetary bodies in the universe

• Discover the unknown: basic exploration

– Understanding of the asteroid hazard

– Probe the subsurface conditions of small bodies as transient abodes for life

• Is transfer of life possible from planet to planet?

– Assays of resource potential in space • Lewis & Clark type missions

• Can we use NEOs to get to Mars and beyond?

1998 KW4 (Ostro/JPL)

Rogue’s Gallery: NEOs are a random sampling

…and the

problem of chaos

Newton: God

as the divine

clock maker,

Earth passing through the Geminid meteor shower

average flux of meteoroids is 40,000 tons per day

(photo: F. Bruenhes)

Asteroid Apophis:

a 300 m S-class

asteroid that gave

us a good scare

Meanwhile, on the same

day as Chelyabinsk…

2012 DA14 was coming inside of GEO to great fanfare

Near-Earth Asteroids are one of the richest

scientific treasures in the solar system

The potential immediacy of the impact hazard

compels us to go out and meet our future!

The Future Is Now!

Hazard or

Treasure?

Don D

avis

• Water,

metal, fuel

• Shelter from

radiation

• Training for

deep space

Bryan Versteegm, DSI

A Space Odyssey

First things first:

go find them and

determine their

precise orbits

LSST

Sentinel

Spacewatch

Human Voyages

"We'll start by sending astronauts to an asteroid for the first time in history” - President Obama, 2010

• NEOs are a sensible path to Mars – Testing human voyages in deep space

– Stepping stones to the asteroid-like Martian satellites

• We are way behind schedule to do this by 2025 – No chance for a precursor mission…

Effort to find large targets, with excellent orbital

knowledge, with short travel time, and low delta-v

D. Landau (in Planetary Science Decadal Survey)

Most known l0w-

delta-v asteroids are

small (~1-10 m) with

inadequate orbital

knowledge to plan a

mission…

Hence the original

ARM mission

concept, to ‘bag’ one

of these and make it

accessible to

astronauts

Early NEO Explorers

Meanwhile… interest in Phobos as a ‘gateway to Mars’ has never waned

Phobos and Deimos… A journey to the

asteroid-like moons

Phobos and

Deimos could solve

half the equation of

getting humans to

Mars.

A crew living on

Deimos could pilot

equipment on the

planet in real time,

to prepare habitats,

greenhouses, and

fuel/water/oxygen

factories and

depots.

Honey, I’m home!

No successful mission yet to either Martian moon

Image from Phobos-2 mission, which was lost

shortly after MOI (1989)

Left, artist’s sketch of what would have been

Summary so far • Asteroids are attention-getting and potentially

hazardous; we need to ‘do something’

• Important science can be greatly accelerated by human missions – More costly, but more effective and versatile

• In-situ resource utilization (ISRU) will enable future human exploration through deep space – Water, radiation shielding, propellant

• NEOs are a logical step forwards: – The Moon is a better place to practice living on Mars

– NEOs are a better place to practice getting to Mars

ESA/DLR

Reality sets in

Space art by Nick Stevens Radar image 1998 KW4

Despite appearances, most

asteroids are not mountainous:

Only 5% of Eros is steeper than 30°

NEAR Team (2000)

Are NEOs really accessible

to humans? – Lunar-like (pros, cons)

• Airless; extreme temperatures;

dusty; disorienting

– Spinning, perhaps tumbling

– Microgravity geophysics

• Everything happens real slow!

– or else it escapes

• How would you apply force to a drill or shovel?

• Can you anchor to the surface?

• How can you avoid kicking up a dust “atmosphere”?

– Potentially unstable landforms; ionized dust…

Radar image of Golevka

Final descent image of Eros, one of the largest NEOs (20 km, gravity

1/1000 of Earth) showing granular (electrical?) collapse in a dust pond

Abyssal plain (5 km deep)

Underwater analogy is

perhaps better than

the lunar analogy…

Eros: Sediment-filled landscape

Coming In for a Crash Landing, the NEAR Shoemaker orbiter impacts Eros at 4 m/s

67P/C-G (Rosetta mission)

Good news: smaller asteroids have less surface dust

because the solar wind has already picked it away

Itokawa

(JAXA/Hayabusa)

Scale Comparison

~30 km

Eros

~0.5 km

Itokawa

Human operations: pluses and minuses

• You don’t need an ascent vehicle

– Vesc (in m/s) equals the radius (in km)

• Milli-gravity is ‘easy’ but weird – Easier than zero-G: there is a ‘down’

• By the time you wake up, your stuff is on the floor…

– A huge rock weighs as much as a cricket, so you can move it

• But you only weight as much as a flea, so don’t get too excited

– A lander may sink/topple or be smothered in loose or cohesive dust; bedrock may not exist

• Ambient dust will be worse than the Moon – Like the bottom of a lake bed: don’t stir it up!

– Cohesive forces can dominate G-forces (like packing peanuts)

– Power concerns: dust covering solar panels, battery life, thermal…

Practice run: ACRM & ARRM

Grab a small asteroid, or pick up a ~3-6 m boulder, and use SEP to

transport it to DRO where humans can interact with it.

Has a programmatic advantage of aligning with the path to the Moon.

Conclusions

• Science is enabled by human exploration together with robotic exploration

• Asteroids possess resources that can enable future deep-space science missions, but they are complex objects

• Human voyages to NEOs can be aligned with the Moon-path to Mars: – The Moon is where we will

practice living on Mars

– An NEO is where we will practice getting to Mars