January 15, 2016

Proposed Proto space colony

At Centauri Dreams, Gregory Matloff has some thoughts on the kind of space facility we can build with our current technologies.

The Bigelow B330 expandable station has been proposed for quite while. The new analysis is about the exact location of a base and using two stations for spinning for simulated gravity.

We need to answer some fundamental questions regarding human life beyond the confines of our home planet. Will humans thrive under lunar or martian gravity? Can children be conceived in extraterrestrial environments? What is the safe threshold for human exposure to high-Z galactic cosmic rays (GCRs)?

To address these issues we might require a dedicated facility in Earth orbit. Such a facility should be in a higher orbit than the International Space Station (ISS) so that frequent reboosting to compensate for atmospheric drag is not required. It should be within the ionosphere so that electrodynamic tethers (ETs) can be used for occasional reboosting without the use of propellant. An orbit should be chosen to optimize partial GCR-shielding by Earth’s physical bulk. Ideally, the orbit selected should provide near-continuous sunlight so that the station’s solar panels are nearly always illuminated and experiments with closed-environment agriculture can be conducted without the inconvenience of the 90 minute day/night cycle of equatorial Low Earth Orbit (LEO).

Initial crews of this venture should be trained astronauts. But before humans begin the colonization of the solar system, provision should be made for ordinary mortals to live aboard the station, at least for visits of a few months’ duration.

Another advantage of such a “proto-colony” is proximity to the Earth. Resupply is comparatively easy and not overly expensive in the developing era of booster reuse. In case of medical emergency, return to Earth is possible in a few hours. That’s a lot less than a 3-day return from the Moon or L5 or a ~1-year return from Mars.

A Possible Orbital Location

An interesting orbit for this application has been analyzed in a 2004 Carleton University study conducted in conjunction with planning for the Canadian Aegis satellite project. This is a Sun-synchronous orbit mission with an inclination of 98.19 degrees and a (circular) optimum orbital height of 699 km. At this altitude, atmospheric drag would have a minimal effect during the planned 3-year satellite life. In fact, the orbital lifetime was calculated as 110 years. The mission could still be performed for an orbital height as low as 600 km. The satellite would follow the Earth’s terminator in a “dawn-to-dusk” orbit. In such an orbit, the solar panels of a spacecraft would almost always be illuminated.

Two Bigelow B330 could be launched with one Falcon Heavy

The study of the adjustment of humans and other terrestrial life forms to intermediate gravity levels might be one scientific goal of the proposed 600-km habitat, the habitat should consist of two (Bigelow B330) modules arranged in dumbbell configuration connected by a variable-length spar with a hollow, pressurized interior. The rotation rate of the modules around the center could be adjusted to provide various levels of artificial gravity. Visiting spacecraft could dock at the center of the structure.

Image: The pressurized volume of a 20 ton B330 is 330m3, compared to the 106m3 of the 15 ton ISS Destiny module; offering 210% more habitable space with an increase of only 33% in mass. Credit: Bigelow Aerospace.

An Al Globus and Strout preprint demonstrates that, for a 600-km circular equatorial orbit, elimination of all shielding increases radiation dose projections to about 2X that of the habitat equipped with a 250 kg/m2 water shield. If shielding is not included and this scaling can be applied to the high-inclination orbit, expected crew dose rates will be less than 0.8 Sv/year. This is within the annual dose limits for all male astronauts and female astronauts older than about 45

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