Space Settlement the Easy Way

Al Globus, San Jose State University Stephen Covey, DSI

Theodore Hall, University of MichiganJoe Strout, Luminary Apps, LLC

make it closemake it smallbuild up to it incrementally

The first one is the hardest, so

The Short Story

• Mother Earth has given us a small slice of space with little radiation. Equatorial LEO.

• Evolution has given us rotational tolerance, at least to 4-6 rpm, meaning 50-100 m diameter.

• This is hundreds of times closer and vastly less massive than we’ve thought the first settlements must be.

• Civilization has given us a tourism industry to pay for incrementally larger and larger space hotels.

• Caveat: this is preliminary! Verification necessary.

What is a ‘space settlement’?

You go to a space station to workYou go to a space hotel to play

You go to a space settlement to live*

*and raise your kids

Free-space vs Moon/Mars: Consider Bases

Skylab1970s

ISSnow

Lunar base2020s?

Martian base??????

Better for raising kidsKiller trade: kids raised on the Moon (⅙ g) or Mars (⅓ g) grow up weak. Kids raised in free space will experience 1g artificial gravity via rotation and grow up strong.

Other advantages:• Great views of Earth• Rapid resupply• Service Earth markets• Reliable abundant solar energy, short nights• Weightless recreation• Easier construction• Much greater growth potential

Early Settlement Designs

Shrink to 50-100 m diameter, no radiation shielding and place in equatorial LEO!

Enormous Engineering Challenge• Big

– 450 – 1,790 m diameter (1-2 rpm)• Reduce by 4x or more going from 2 to 4 rpm

– 1-20 million tons• Reduce to 1-10 ktons 4x smaller radius; no shielding

• Far away– Lunar distance (384,400 km)

• Reduce by 760 x by placing in equatorial LEO• Reduce by 100,000 x compared to closest Mars approach

• Harsh unfamiliar environment– Incremental development of space hotels

Radiation in Space Settlements● Decades, not years (Mars missions)● Not just adults!● Major types

○ Solar storms: mostly protons ■ high level but short and rare

○ Trapped protons and electrons○ GCR (galactic cosmic rays) most dangerous are

heavy (iron) nuclei at relativistic speeds■ Low level, always■ Omnidirectional■ Secondaries from inadequate shielding■ If shield for these, others taken care of

Adult Threshold: 20 mSv/year

● US average background 3.1 mSv/year● Large parts of Europe: > 10 mSv/year● Parts of Iran, Brazil, elsewhere much higher

○ up to 132 mGy/year in one case● ICRP occupation threshold: 20 mSv/year● Fukushima return threshold: 20 mSv/year● Astronauts: 500 mSv/year, 10-30K lifetime● Major caveat: different kind of radiation!

Pregnancy Threshold: 6.6 mGy/year

● Equals 5 mGy/pregnancy● No additional malformation or cancer risk at 5 mGy -- but

some at 10 mGy● Pregnancy only recommended for termination with > 100

mGy medical exposure● Occupational recommendation 1 mGy above background● Identified threats usually have 100-200 mGy threshold

○ Nuclear bomb victims mental retardation only > 200 mGy

● Major caveat: different kind of radiation!● Data and recommendation by the ICRP, International

Commission on Radiological Protection

Radiation Shielding in Deep Spacepolyethylene water lunar regolith

tons/m2 mSv/yr mGy/yr mSv/yr mGy/yr mSv/yr mGy/yr

1 193 85 199 86 274 109

2 136 52 146 54 261 82

3 90 31 100 34 221 62

4 57 18.5 66 21 172 48

5 35 10.8 42 12.5 126 37

6 20.9 6.3 26.3 7.5 89 28

7 12.2 3.6 16 4.4 61 20.9

8 40 15.1

9 26.1 10.5

10 16.6 7.1"Orbital Space Settlement Radiation Shielding," Al Globus and Joe Strout, June 2015.

Based on OLTARIS calculations

shielding tons/m2 500 km mSv/yr mGy/yr 600 km mSv/yr mGy/yr

~0 16.7 10.2 23.4 1,559

0.01 16.3 3.6 21.7 101

0.025 15.6 3.7 19.8 50.6

0.05 14.6 3.9 17.5 21.8

0.075 13.9 4 16.1 12.5

0.1 13.3 4 15 8.9

0.15 12.5 4.1 13.6 6.1

0.2 11.9 4.2 12.9 5.3

0.25 11.6 4.3 12.5 4.9

0.5 12 4.6 12.6 4.9

0.75 12.8 4.8 13.4 5.1

1 13.3 4.9 14.2 5.2

1.25 13.7 5 14.4 5.2

1.5 13.8 4.9 14.5 5.2

1.75 13.7 4.8 14.4 5.1

2 13.5 4.7 14.1 4.9

Equatorial LEO

Radiation Shielding

With 20 mSv/yr for the general population and 6.6 mGy/year for pregnant women limits mean space settlements in equatorial LEO may not require any dedicated shielding.

Circular equatorial orbits,Polyethylene shielding

Why Equatorial Orbit?

Mass (tons/m2)

0° (mSv/yr)

15° (mSv/yr)

30° (mSv/yr)

45° (mSv/yr)

60° (mSv/yr)

75° (mSv/yr)

90° (mSv/yr)

0.25 14.6 262.8 636.0 424.1 345.0 335.5 334.0

0.5 12.1 112.1 253.5 178.2 164.0 168.7 170.3

1 13.2 43.4 88.7 79.1 90.3 100.2 102.7

2 14.0 21.6 36.7 45.5 58.9 66.4 68.3

3 12.6 16.4 25.1 33.2 42.4 47.1 48.3

4 10.3 12.3 17.6 23.5 29.4 32.2 32.9

5 7.9 8.9 12.1 16.1 19.6 21.3 21.7

6 5.7 6.3 8.2 10.7 12.7 13.7 13.9

Inclination comparison, water shielding, 600 km circular orbit

South Atlantic Anomaly

Image credit: NASA

Shielding Mass from 1975 Study

NOTE: mass model does not include internal furnishings, solar arrays, and many other items that are not significant compared to shielding mass, but are important if no shielding is required.

Mass model based on 1975 study mass tons

name struct mass air mass shielding mass total/non-shielding

multiple dumbbells 75,000 37,000 9,900,000 89

multiple torus 100,000 10,400 9,700,000 89

banded torus 112,000 13,200 7,000,000 57

single torus 4,600 1,900 1,000,000 155

cylinder 775,000 299,000 19,400,000 19

sphere 64,600 35,200 3,300,000 34

dumbbell 400 200 1,400,000 2,334

Moon-L5/Earth-LEO Energy Distance Comparison

● Moon -> L5 2.3 km/sec● Earth -> LEO 10.0 km/sec● Energy scales as the square of delta-v

○ 100 / 5.29 = 19 x○ Eliminating shielding saves 19 x of mass!

● Energy to deliver materials to site is the same● However

○ Lunar: raw materials, and not all of those○ Earth: any product we can manufacture

● NOTE: comparison using rocket equation more complex, similar outcome (21x) for isp = 450

Rotate Faster to Reduce Size

● To get 1g, radius scales as inverse square of rotation rate

○ Double rpm reduces radius by factor of 4

● Structural mass scales as cube of radius

○ Surface by square

○ Pressure shell stress linearly

● Atmosphere scales as cube of radius

● Furnishings scale as square

● 2 -> 4 rpm reduces mass by 16-32 x

Negative Effects of Rotation

● Motion sickness○ fatigue○ stomach awareness○ nausea ○ vomiting

● Inaccurate limb motion● Difficulty in throwing accurately

Graybiel’s Rotation Room

"In brief, at 1.0 rpm even highly susceptible subjects were symptom-free, or nearly so. At 3.0 rpm subjects experienced symptoms but were not significantly handicapped. At 5.4 rpm, only subjects with low susceptibility performed well and by the second day were almost free from symptoms. At 10 rpm, however, adaptation presented a challenging but interesting problem. Even pilots without a history of air sickness did not fully adapt in a period of twelve days."

Pensacola Slow Rotation Room at the Naval Aerospace Medical Research Laboratory (Pensacola, Florida). 4.57 m (15 ft) diameter, 2.1 m (7 ft) high, could rotate within 2.5% of any desired speed up to 10 rpm

Summary of Rotation Tolerance Synthesis

Rotation Rate Caveats

The studies● have very few subjects, usually 10 or less.● show great variability in rotation tolerance from person to person.● sometimes chose subjects for higher than normal rotation tolerance.● have only adult subjects.● are only a few weeks or less in duration.● use rotational experiment environments with very short radii of rotation,

typically under 3 m (there is one exception). This means the effects observed in these experiments are likely much more severe than in a settlement as most effects attenuate with larger radii.

● are almost all on the surface of the Earth and there is evidence that the negative effects of rotation are much less in an otherwise weightless environment (Skylab, Vomit Comet).

Space Settlement Rotation Rate

● Recommendations○ Up to 2 rpm should be no problem for residents and require little

adaptation by visitors.○ Up to 4 rpm should be no problem for residents but will require some

training and/or a few hours to perhaps a day of adaptation by visitors.○ Up to 6 rpm is unlikely to be a problem for residents but may require

extensive visitor training and/or adaptation (multiple days). Some particularly susceptible individuals may have a great deal of difficulty.

● “Space Settlement Population Rotation Tolerance,” Al Globus and Theodore Hall preprint June 2015

Rate (rpm)

1 2 3 4 5 6 7 8 9 10

Radius (m)

895 224 100 56 36 25 19 14 11 9

Kalpana One Mass Reduction

Measure Kalpana One

Rotation (RPM) 2 4 6

Shielding (t/m2) 6 0 0

Radius (m) 224 56 25

Length (m) 325 77 35

Hull (kT) 5,450 11.5 1

Radiators (kT) 39.1 6.7 0.9

Air (kT) 50.2 0.7 0.07

Total Mass (kT) 5,539.3 19 2

Mass ratio 1 292 2,717

Measure Kalpana One

rotation (rpm) 2 4 6

radius (m) 224 56 25

Hull (kT) 194 3.8 0.5

Internal Struct (kT)

65 3.8 0.8

Shield (kT) 4,026 0 0

Non-struct (kt) 23 1.4 0.3

Air (kt) 42 0.66 0.06

Total Mass (kT) 4,351 9.6 1.6

Mass ratio 1 453 2,812

Stephen Covey Joe Strout

Stanford Torus Mass Reduction

MeasureRotation (RPM) 1 4 6Shielding (t/m2 ) 6 0 0Major Radius (m) 900 49 21.5Minor Radius (m) 65 7 4Hub Radius (m) 100 10 5Spoke Radius (m) 10 3 3Spokes 6 4 2Hull (kT) 14,500 0.435 0.062Air (kT) 81.1 0.051 0.007Total Mass (kT) 14,581 0.486 0.070

Mass ratio 1 30,002 209,408

Measure

rotation (rpm) 1 4 6

outer radius (m) 895 56 25

tube radius (m) 65 7 4

Hull (kT) 14.5 0.1 0.03

Internal Struct (kT)

102 0.7 0.2

Shield (kT) 12,727 0 0

Non-struct (kt) 74 0.5 0.1

Air (kt) 88 0.07 0.01

Total Mass (kT) 13,196 1.43 0.35

Mass ratio 1 9,245 38,208

Stephen Covey Joe Strout

Extraterrestrial Mining

● Assumed to be necessary due to massive radiation shielding requirements and huge size

● Not necessary for settlements proposed here● Settlements provide in-space market for materials

○ Key to lunar and asteroid mining● Settlements provide workshops and markets to

develop processing and manufacturing facilities● Raw materials important when settle beyond LEO

Killer App: Tourism

● Currently a sellers market○ $50 million for 7-10 days at ISS

■ Learn Russian, months at Star City■ Waiting list, but price probably too high

○ $26.25 million Falcon 9 visit Bigelow station○ $95-250 thousand for five minutes in space

■ Hundreds paid deposit

Crouch, G. I., “Researching the Space Tourism Market,” Presented at the annual Conference of the Travel and Tourism Research Association, June 2001

price/ticket (1994 $) passengers/year

1,000 20 million

10,000 5 million

100,000 400 thousand

250,000 1,000

500,000 170

Reusable Orbital Launch Vehicles

● Necessary to bring down cost○ May need 10-100 x

● Experience: 130+ shuttle flights● Work in progress includes

○ SpaceX Falcon 9/Heavy○ X37○ Blue Origin○ Skylon

● CATS prize (ASD) proposal○ $3.5 billion for four prizes○ Two flights within a week ($1G, $750M)○ Ten flights within ten weeks ($1G, $750M)

From ISS to First Settlement● ISS longest dimension almost 4 rpm diameter (112 m)● Bigelow inflatable space station in development

○ Target market: national space programs● ASD/NSS policy: augment or replace ISS with multiple

privately owned, commercially operated stations with NASA help and anchor tenant (ala COTS, CCDev)

● A hotel is simpler than a station○ NSS policy: allow CCDev to fly tourists in empty seats

● In time, hotels may rival size of 4 rpm settlement!○ Must develop efficient life support○ For high end, must grow food○ May rotate to minimize training

● Increase rotation to get 1g artificial gravity suitable for kids

Future Work● Verify

○ Radiation levels -- looks good○ Program to assess space radiation (GCR) on tissue

■ Ground experiments■ ISS

● needs rodent centrifuge■ Dedicated facility in correct orbit

○ Program to verify rotation findings■ Vomit Comet■ ISS crews

● Construction and maintenance techniques● Recycling● Clean up LEO debris● Determine minimum size

Conclusion

● Development of the first space settlements may be radically easier than the 1970s studies suggest by○ Placing them in equatorial LEO

■ Eliminates radiation shielding○ Rotating at 4 rpm to make them smaller○ Building incrementally larger space stations and

hotels starting with the ISS ● This approach

○ Distance from Earth reduced by 760 x○ Mass reduced by >300 x○ Extraterrestrial mining not necessary○ Technology and infrastructure developed

incrementally driven by tourism profits

Ad Astra Baby!

How Wide is the Window?inclination ovaries All GCR all radiation GCR Trapped Proton and Neutron Albedo

deg mSv/yr mSv/yr mSv/yr mGy/yr mGy/yr mGy/yr

0 16.77 17.68 16.78 10.23 3.194 7.036

1 16.77 17.68 16.78 10.23 3.194 7.036

2 16.8 17.75 16.81 21.97 3.201 18.77

3 16.83 17.89 16.84 51.31 3.208 48.1

4 16.86 18.25 16.87 97.74 3.215 94.52

5 16.93 18.97 16.91 161.7 3.221 158.5

6 17.22 20.56 16.98 274.2 3.247 271

7 17.88 22.95 17.06 427.1 3.274 423.8

8 19.48 26.96 17.14 656.9 3.292 653.6

9 21.88 31.89 17.27 897.1 3.311 893.8

10 27.34 40.49 17.39 1217 3.33 1214

11 26.58 42.69 17.49 1616 3.358 1613

12 39.55 70.7 17.66 2012 3.388 2009

13 68.8 94.39 17.85 2567 3.422 2563

14 88.04 118.3 18.04 2915 3.462 2912