Geoffrey A. Landis Habitats 1 Geoffrey A. Landis Habitats in Space Launchpad Workshop Laramie, WY July 2012

Geoffrey A. Landis Habitats Immediate needs: Pressure Oxygen Thermal control (not too cold, not too hot) 2 What do humans need to survive? A habitat is a pressure vessel containing breathable gas, and with a thermal control system

Geoffrey A. Landis Habitats Oxygen 3 What do humans need to survive? 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

Geoffrey A. Landis Habitats 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 4 For the metric among you, 14 PSI = 1 bar = 100 kPa = 10 tons/meter 2

Geoffrey A. Landis Habitats 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 5 “Silent Running” …why are these domes flat on the bottom? They are balloons: air pressure tends to make them spheres

Geoffrey A. Landis Habitats NASA moonbase artist’s conception 6 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

Geoffrey A. Landis Habitats 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! 7 What do humans need to survive? Longer term: “life support system”: Water Oxygen Food Waste disposal

Geoffrey A. Landis Habitats Power Habitats, and spaceships, need a power source. 8 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?

Geoffrey A. Landis Habitats International Space Station 9 From this view, most of it is solar arrays!

Geoffrey A. Landis Habitats 10 What do humans need to survive? For Health: Gravity (or equivalent) Radiation protection

Geoffrey A. Landis Habitats 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. 11

Geoffrey A. Landis Habitats Example of spin artificial gravity: “Pilgrim Observer” 12

Geoffrey A. Landis Habitats Example of spin artificial gravity: tether 13 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 satellite Left: “Mars Direct” mission

Geoffrey A. Landis Habitats Example of spin artificial gravity: the Von Braun “wheel” 14

Geoffrey A. Landis Habitats 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 sec 2 –One Earth Gravity = 10 m/sec 2 –Revolutions per Second = RPM / 60 In terms of time per revolution, a = 39.5r/T 2 –T is time to revolve once, in seconds 15

Geoffrey A. Landis Habitats 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 16

Geoffrey A. Landis Habitats Spin Gravity: example How fast does a habitat need to rotate to achieve an effective 1-G interior? 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.

Geoffrey A. Landis Habitats Spin Gravity: websites 18 After I made this slide, I found a calculator online: The wikipedia article has some interesting information on spin and some other methods of artificial gravity: UH article on artificial gravity:

Geoffrey A. Landis Habitats Example of spin artificial gravity: the Von Braun “wheel” 19 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.)

Geoffrey A. Landis Habitats 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. 20

Geoffrey A. Landis Habitats Artist’s conception of a Lunar base with no evident radiation shielding OK for a short stay, but you might not want to live here for many years 21

Geoffrey A. Landis Habitats Radiation 22 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

Geoffrey A. Landis Habitats 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”) 23 NASA artist’s conception of lunar habitats shielded by being covered by lunar soil

Geoffrey A. Landis Habitats Ways to shield from Radiation 24 Magnetic field –Magnetic fields cause charged particles to curve Low energy particles curve most high energy particles curve least

Geoffrey A. Landis Habitats Ways to shield from Radiation 25 Magnetic field –Magnetic fields cause charged particles to curve –Earth’s magnetic field protects us

Geoffrey A. Landis Habitats Magnetic Radiation Shield 26 –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

Geoffrey A. Landis Habitats Magnetic Radiation Shield 27

Geoffrey A. Landis Habitats Ways to shield from Radiation 28 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”)

Geoffrey A. Landis Habitats Mixed (electric & magnetic) shielding 29 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

Geoffrey A. Landis Habitats Summary Humans are fragile Many systems are needed to keep humans alive and active in space 30