3 ms·
Ok, I have a very rough number for the possible size if launched on a fully reusable BFR with payload based on a talk Elon gave in late 2017 [1]. I'm assuming t
by sq_ 9y ago
Ok, I have a very rough number for the possible size if launched on a fully reusable BFR with payload based on a talk Elon gave in late 2017 [1]. I'm assuming that internal space scales roughly linearly and that deflated width isn't a factor when flying on the BFR, so I could be way off.
Here's the math:
Fully reusable BFR can do ~150,000 kg to LEO, Bigelow B330 weighs ~50,000 lbs or ~22,676 kg [2]
B330 has 330 m^3 of space [3], and the BFR could lift roughly 6.6 B330's
330 * 6.6 = 2,178 m^3
So, with my assumptions, a fully reusable BFR would be able to lift a Bigelow module with about 2,178 cubic meters of internal space.
Of course, I'm probably forgetting something and my assumptions are probably off; however, I think that it's safe to assume that a fully reusable BFR could lift a very big module to LEO.
[1] http://www.spacex.com/sites/spacex/files/making_life_multiplanetary_transcript_2017.pdf http://www.spacex.com/sites/spacex/files/making_life_multipl...
[2] http://www.bigelowspaceops.com/b330.php http://www.bigelowspaceops.com/b330.php
[3] https://en.wikipedia.org/wiki/B330 https://en.wikipedia.org/wiki/B330
Edit: based on what @hughes said below, it looks like I did forget something: volume scales at a different rate than surface area. So it looks like the internal volume would be more like 5600 m^3.
- hughes 9y agoApproximating the station as a hollow shell of constant thickness, the mass would scale with the surface area. The volume would scale proportional to the surface area to the power of 3/2. So 6.6x the mass gets you 6.6x the surface area, which gets you about 17x the volume, or ~5600m^3
- sq_ 9y agoAh, figured I was forgetting something. Editing my comment to reflect what you said. Thanks for the correction!
- avmich 9y agoEven though volume grows with 3rd power of size and area with 2nd, you'd still better calculate volume here as 2nd power. The reason is that you usually want to have progressively thicker walls when the size of the object grows, and that - linear with diameter - growth of thickness reduces available weight, so the volume still grows as 2nd power. But even then FH would deliver huge volumes on orbit.
- j-pb 9y agoOk, here's the kicker! I spun heh this a bit further, and imagined an inflatable torus with the same surface area and thus weight. With an inner radius of 30m you get a comfy diameter of ~2.5m. [1] If we throw this into spincalc [2] and ask it to compute the rotation rate of such a station to get mars gravity levels of 0.376g. Then we get ~3.2 revolutions per minute, which is well within human comfort levels according to this study [3]. (4 is the max) So yeah this would basically allow you to shoot up a retrofuturistic rotating space station with comfortable gravity levels for future martians in one shot. Wow! [1] http://www.wolframalpha.com/input/?i=outer+radius+of+a+torus+with+1525+square+meters+surface+and+inner+radius+of+30m http://www.wolframalpha.com/input/?i=outer+radius+of+a+torus... [2] http://www.artificial-gravity.com/sw/SpinCalc/ http://www.artificial-gravity.com/sw/SpinCalc/ [3] http://www.spacefuture.com/archive/artificial_gravity_and_the_architecture_of_orbital_habitats.shtml http://www.spacefuture.com/archive/artificial_gravity_and_th...
- sq_ 9y agoThat is really cool. Outside of cool space stations, that could definitely be a useful addition for interplanetary spacecraft (like the spinning component of the Hermes from The Martian).
- j-pb 9y agoYeah, but attaching two spacex interplanetary spaceships nose to nose via a tether and giving the pair spin with the maneuvering thrusters would probably give you a s*load more space with much more comfortable artificial gravity. Still the scifi character of the ring is neat :D