Geoffrey A. Landis Habitats 1 Geoffrey A. Landis Habitats in Space Launchpad Workshop Laramie, WY...

Geoffrey A. LandisHabitats

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Geoffrey A. Landis

Habitats in Space

Launchpad WorkshopLaramie, WY

July 2012


• Immediate needs:• Pressure• Oxygen• Thermal control (not too cold, not too hot)

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What do humans need to survive?

• A habitat is a pressure vessel containing breathable gas, and with a thermal control system


• Oxygen

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• Something has to regenerate the oxygen• In the short term, you can remove the CO2 and

discard it, and simply replace oxygen from stores• In the medium term, you can regenerate the CO2

with physical means• In the long term, you need full regeneration

– Photosynthesizing Plants, or very good technology– Need to remove trace contaminants as well


Pressure

• Humans need pressure.• We don’t need sea level pressure (14 PSI)– lower

pressure is OK if oxygen is increased• Spacecraft have run as low as 3.5, with pure oxygen

– Nobody actually knows if the nitrogen in the air we breath has long-term health effects, but in the short term, we don’t need it

– But high oxygen increases fire hazard

• More commonly seen is 8-10 PSI

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For the metric among you, 14 PSI = 1 bar = 100 kPa = 10 tons/meter2


Pressure

• Humans need pressure.• Atmospheric pressure is a huge force-- ten tons per square

meter. Big domes require enormously strong materials! – “Empty space” in a vacuum are very expensive to pressurize.

Habitats won’t have big empty volumes that aren’t serving an essential purpose

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“Silent Running”…why are these domes flat on the bottom? They are balloons: air pressure tends to make them spheres


NASA moonbase artist’s conception

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Note the dome continues in a sphere underground.Assuming the dome is 10 meter radius and pressurized to one atmosphere, the force due to air pressure blowing the hemispheres apart is 3,000 tons


• A short term habitat (eg., a ship) may bring these as consumables (from Earth, or some other base)

• For a permanent settlement, this must be a closed life support system– everything recycled.

• Closed life support systems typically run from sunlight• Outer solar system and beyond requires power source!

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Longer term: “life support system”:•Water•Oxygen•Food•Waste disposal


Power

• Habitats, and spaceships, need a power source.

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Your life support needs power. What’s powering your habitat? Solar arrays are big. Nuclear power supplies need radiators. Either way, you’re going to need big areas.

Pretty space colony… but where’s the power source?


International Space Station

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From this view, most of it is solar arrays!


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For Health:•Gravity (or equivalent)•Radiation protection


Gravity

• Humans need gravity• For all the talk about the wonders of zero gee

(technically, “freefall”)– humans lose bone and muscle mass in freefall (about 1% loss of bone mass per month). Astronauts returning from a few months in orbit are weak!

• Fortunately, you can get the effects of gravity from centrifugal force.

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Example of spin artificial gravity: “Pilgrim Observer”

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Example of spin artificial gravity: tether

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A tether is a long cable connecting one part of a spacecraft to another, for example, empty fuel tanks connected to a habitat. Spin the collected pieces around the center of gravity, and you get artificial gravity.

20-kilometer long tethers have been flown, so you don’t even need to spin very fast.

Right: tether satelliteLeft: “Mars Direct” mission


Example of spin artificial gravity:the Von Braun “wheel”

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What you need to know:How much gravity do you get from a given

spin?The larger the radius, the slower you can spin

Acceleration from spinning:•a = 39.5(RPS)2*r

– RPS = revolutions per second– r is radius from the center of gravity– a is effective gravity meters per sec2 – One Earth Gravity = 10 m/sec2

– Revolutions per Second = RPM / 60

In terms of time per revolution,• a = 39.5r/T2

– T is time to revolve once, in seconds

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What you need to know: How Fast do you need to spin to achieve a desired gravity?

The larger the radius, the slower you can spin

•RPS needed = 6.3*SQRT (a/r)

– RPS = revolutions per second– To get one Earth gravity, set a to 10– radius is in meters

In terms of time per revolution,• T = 0.16*SQRT(r/a)

– T is time to revolve once, in seconds

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Spin Gravity: exampleHow fast does a habitat need to rotate to

achieve an effective 1-G interior?

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• 10 RPM may make your astronauts nauseated. There are both physical and psychological effects of high rotation speeds.

• This is radius: the diameter of your wheel is twice this radius.• For a tether, the spin is around the midpoint only if it has equal mass on both

ends. If the habitat is heavier than the counterweight, a longer tether is needed.


Spin Gravity: websites

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After I made this slide, I found a calculator online: http://www.artificial-gravity.com/sw/SpinCalc/

The wikipedia article has some interesting information on spin and some other methods of artificial gravity:http://en.wikipedia.org/wiki/Artificial_gravity

UH article on artificial gravity:http://www.uh.edu/engines/epi2638.htm


Example of spin artificial gravity:the Von Braun “wheel”

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Eyeballing this, the wheel looks like it has a radius of about 10 meters, so it has to spin at 10 RPM to give one gravity. (But they may be assuming a lower G level is sufficient for astronaut health.)


Radiation

• Humans need radiation shielding if you spend a long time out from under Earth’s magnetic field.

• Space is really a pretty hostile place.

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Artist’s conception of a Lunar basewith no evident radiation shielding

OK for a short stay, but you might not want to live here for many years

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Radiation

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• Three types of radiation:• Radiation belts (in Earth or Jupiter orbit)• Solar protons

• (“Coronal Mass Ejection”, sometimes called [inaccurately] “solar flares” or “solar cosmic ray”)

• A crew can get warning about a coming CME and take shelter

• Galactic cosmic rays• Hard to shield

• Long term cumulative damage


Ways to Shield from Radiation

• Mass– Earth is protected partly by our atmosphere

– Relatively easy to shield from solar protons, harder to shield from cosmic rays

– Lighter elements shield better– hydrogen shields best (water)

– Moon colonies often suggest shielding by burying habitat under lunar soil (“regolith”)

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NASA artist’s conception of lunar habitats shielded by being covered by lunar soil


Ways to shield from Radiation

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• Magnetic field– Magnetic fields cause charged particles to curve

Low energy particles curve most

high energy particlescurve least



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• Magnetic field– Magnetic fields cause charged particles to curve

– Earth’s magnetic field protects us


Magnetic Radiation Shield

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– Could protect a habitat by emulating the Earth’s magnetic field

– A big superconducting loop could produce such a fields• A magnetic field is produced by a loop of wire that has a current flowing in• Current flows in a superconductor with no power needed• The higher the magnetic field, the more the particle trajectory curves• Thus, it takes higher magnetic fields to shield a small volume, and lower magnetic

fields to shield a large volume• So magnetic shielding works best on big objects (space colonies!) and is hardest

on small objects (spaceships)

– Superconductors need to be kept cold• Liquid nitrogen temperature needed for today’s superconductors• Can be kept this cold by shielding the superconductor from both the sun and also

the reflected light from nearby planets or moons• Future technology: room temperature superconductor?

– You probabably want to shield the humans from high magnetic fields• This is relatively easy– put a smaller magnetic coil inside the big field that cancels

out the main field in the small volume of the havitat


Magnetic Radiation Shield

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• Electric field– Positive charge repels positive charge (e.g., protons)– attracts the

other charge (e.g., energetic electrons) which will short out the field.

– Possibly a combination of electric and magnetic fields could protect spacecraft or colonies (“plasma shield”)


Mixed (electric & magnetic) shielding

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Plasma radiation shield proposed by Eric Hannah. Cosmic rays are repelled from the colony, which is charged to 10 billion volts with an electron gun. The magnetic coils channel electrons from space into the central region, and prevent them from reaching the walls, which would neutralize the charge. (Courtesy Eric Hannah)

From http://www.nss.org/settlement/ColoniesInSpace/colonies_chap12.html


Summary

• Humans are fragile• Many systems are needed to

keep humans alive and active in space

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Geoffrey A. Landis Habitats 1 Geoffrey A. Landis Habitats in Space Launchpad Workshop Laramie, WY...

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