Can I put a sphere around my asteroid?

Question

A different form and function of a Dyson sphere.

It is fairly far in the future and the residents of a D-type spherical asteroid (similar in size to Deimos, ~6km radius). They've been living in habitats and small domes dotted across the surface, with material shipped in and out. Instead of living underneath the ground, the mayor decided to investigate building a sphere around the whole thing, and pumping in atmosphere and materials to make the surface liveable.

Can this structure be built within reasonable expectations of the advancement of materials sciences and engineering as well as speculative materials? Will it be an impossible structure?

Dome: 100m above the surface, wrapping the entire asteroid with support structures as necessary and airlocked ports of entry/departure. With a 6.1km radius, it would have a surface area of 468km².

I can set aside the mechanism for filling this thing up with atmosphere, etc., but can I put a sphere around my asteroid? Keep in mind that it will have 1bar of pressure after it is completed. It can be closed (artificially lit inside/not glass).

Answer 1

Project Proposal for providing an atmosphere to Mikey's Asteroid

This proposal describes the product design, work to be done, materials required, and cost benefit analysis. All plans described here in are confidential and for the use of Mikey's Asteroid's government only.

Known Requirements

• Ingress and egress from the asteroid interior. This means that your airlocks/space ports will need to go through the bubble.
• Redundancy in the envelope to control the inevitable leaks. As this is a space-faring group, the hazards of outer space are well known so a small puncture is unlikely to be fatal, but getting that much air in one place is sure to be expensive.
• Radiation protection for whoever is walking around in the envelope.

Envelope Design

The naive approach would be to build a single giant balloon that wraps the entire asteroid. As experience has shown there will be the inevitable leaks and in a single giant bag controlling those leaks will require constant maintenance. So, let's not put all our air in one "basket".

Instead, let's construct a series of air domes with the edges of the dome hermetically sealed to the asteroid surface. On top of these domes, we shall place an asteroid wide envelope. This proposal shall assume that Mikey's Asteroid is composed of nickel/iron.

Basically, Mr. Mayor, we're going to wrap your fair asteroid in double layer bubble wrap.

Construction Sequence

1. Site preparation crews will lay out a hexagonal grid across the surface of the asteroid then mill the asteroid exterior with our patented Mill-A-Roid(TM) to a smooth finish. This milling process ensure that when the edges of each bubble is attached to the asteroid that there will be minimal air leakage between the bubble skirt and the asteroid. An additional lining of Bubble-Foam (TM) self-sealing foam between the skirt and asteroid adds an extra layer of leak protection.

2. Once the grid has been laid down and the edges milled, our army of skirt laying robots will place the skirt sections and affix them to the asteroid.

3. A second set of teams will then lay out and affix the bubble membrane to the skirt. Once the membrane has been attached to the skirt, a small amount of air will be introduced into the new bubble to ensure there are no leaks. Each skirt section is equipped with an airlock for rapid ingress and egress from each section. The membrane is specially constructed to block harmful ionizing radiation such as UV, and X-ray light while letting in normal visible light.

4. The hex grids surrounding the asteroid landing areas will not be covered by a bubble or the larger asteroid-wide membrane. The outer layer membrane will be attached to the skirt sections surrounding the landing areas. This will be the only places where the outer membrane will touch the asteroid directly though additional partitions between outer membrane and the asteroid are possible.

5. Sufficient atmosphere will be introduced within the outer membrane sufficient to lift it off the bubbles. Pressure in the outer membrane will intentionally be kept lower than within the bubbles to minimize air losses when the inevitable puncture occurs.

Materials

• Sufficient skirt sections to cover the asteroid in a hexagonal grid.
• Sufficient hex membrane to cover each hex grid with a bubble.
• Approximately 468km^2 of outer layer membrane.

Cost/Benefit Analysis

While the Double Layer Bubble technique is more costly in terms of materials and labor it offers some significant benefits over the less costly single-bubble approach. They are:

• Greater Fault Tolerance An unpartitioned single-layer bubble stands to lose all atmosphere in the event of a catastrophic puncture. A catastrophically punctured partitioned outer membrane only stands to lose 50% of the failed partition plus whatever bubbles were punctured as well. This poses significantly less risk to asteroid dwellers who may be on the surface during the event.
• Greater Safety Each skirt section is completely self-contained so should atmospheric seals fail, airlocks provide safe egress routes for anyone inside. Because of the outer membrane, atmospheric loses in a bubble can be recaptured.
• Greater Atmospheric Flexibility Because of the modular nature of this approach, some bubbles may be made larger or smaller depending on changing needs. Also, the atmosphere of a given bubble may be made significantly different than other bubbles providing flexibility unavailable with a single-layer bubble.

Answer 2

That would be a relatively easy construct to make. You wouldn't even need to make it that rigid: 1 atmosphere of pressure may be enough to turn a cloth sheet into a bubble, and we have plenty of materials which can withstand that atmosphere. I'd be more worried about making certain you can handle the inevitable leak.

I would, however, shy away from calling it a Dyson sphere. The order of magnitude difference in the orders of magnitude means anyone who sees the word will get an unrelated idea of your construction. Your structure has 468 sq. km. of area. A typically rendered Dyson sphere at 1AU is 280,000,000,000,000,000 sq. km. in area. At some point, the nature of the construction task shifts slightly, and there's also the difference in goals (a Dyson sphere captures the energy of the star)

Answer 3

Building from Cort Ammon's answer, we can use a pressurized "bubble" as the conceptual model, but severe refinements need to be made for this to be fully functional.

The "bubble" can be made out of virtually anything, and the asteroid itself can provide most of the raw materials for the basic bubble structure. Elements like Silcon, Aluminum, Iron or even carbon are all available on asteroids in various amounts, so depending on what is easily accessible, the membrane can be as simple as a huge aluminum foil bubble or a complex silicon based material.

The refinement comes from the various other parameters that need to be met. A huge balloon will have a great deal of internal pressure distributed across the surface, so a reinforcing structure will have to be added to reduce the amount of tension per unit area. A mesh or net made of a high tensile strength material will need to be on the outside of the bubble, and designed to be tightly fitted to the bubble when it is pressurized. Materials like titanium or carbon fibre will provide sufficient strength for this task (If the bubble itself is made out of woven carbon nanotubes or is a single sheet of graphine, then it might be strong enough on its own, but the belt and suspenders approach is always better with engineering).

Since you are in deep space, radiation needs to be blocked from the surface, otherwise the exercise is pointless. A second "bubble" with similar reinforcement is needed with a gap between the two bubbles. A gap of 5m filled with water provides a fairly simple, low tech radiation and impact shield and has added benefits like providing a thermal buffer (heat from direct sunlight will diffuse through the water and excess heat will radiate from the shaded side). If the "bubble" material is transparent or translucent, then you also get filtered sunlight on the surface of your asteroid. A platoon of mirrors in formation around the asteroid can be used to moderate or modulate the sun (artificial sunrises and sunsets can be arranged by this means, if desired). The outer surface will have platoons of small robots constantly patrolling (perhaps clinging to the fibres of the net), looking for and patching small leaks caused by micrometeorites.

Since you will want access to space, there are several options. The bubble could be pierced by "towers" which rise from the asteroid to the airlock structure. For safety and redundancy, I would suggest that the actual entry to the airlock tower is well below the ground, so if the airlock malfunctions, the "surface" is protected. I would actually suggest the bubble be "off centre" with the asteroid touching the bubble at the axis of rotation, and that point serves as the entry/exit point. Once again, there should be no direct communication between the inflated "surface" and the airlock, all the communication to the vacuum is to chambers drilled into the depths of the asteroid.

Since we are in space, the bubble will always be vulnerable, so the subsurface should be a honeycomb like structure. If the bubble is damaged and a leak detected, an alarm sounds on the surface, and people will always be reasonably close to an audit or emergency door that leads to the safe area below "ground". The subsurface will be divided into multiple chambers much like a submarine with lots of sealable doors and spaces, so there should never be a 100% casualty rate from accidental breakdown or natural disaster.

Answer 4

Green describes the general setup quite well.

Let's look a bit deeper into the issue of breaches of the hull, materials, and support, as well as protection from radiation and micrometeors.

we may want a magnetic field to ward off energetic particles, the way our own planet provides it. That, though, is not part of the current project, so we leave that aside.

While we could build a metallic bubble structure, and that would keep a lot of radiation out, it would also mean we would block the view, as well as any incoming light, which would otherwise be uite handy, givn that humans rely a lot on sight for almost anything we do.

So we may want a transparent shell for our habitat. After all, what would be the point of roaming the surface if it still felt like travelling in tunnels and caves? So transparent it must be.
We will use a multi-layered apploach, where the entire shell of every bubble is created from layers of the same polymers we use today for UV-blocking sunglasses. As a nice side effect, we can even have different colours for the individual bubbles, which gives beautiful artistic effects. We pay a fortune for that project, so it might as well be beautiful.

Obviously, a single layer of plastic won't withstand the impact of a very fast stone. So we have multiple layers, and inbetween the layers we inject a polymer gel. The pressure of the gel strengthens the structure and helps maintain the bubble's shape. also the gel not only slows down any impacting object, it also hardens when in contact with the atmosphere, or when illuminated with ultraviolet radiation. This way, not only are micrometeorites slowed down significantly while travelling through the layers of the bubble, often slowed down enough to be contained in the lower layers, the gel also works at closing small punctures automatically, resulting in next-to-zero loss of atmosphere.

The setup from a large number of individual bubbles provides additional protection, even if a larger breach should occur, much as described in Green's answer above.

Walling off each of the sections is an option. It can be done, but it would me more beautiful to have large open surfaces, so let's look how that can be provided.
Resting the bubbles on six points each, the corners of the proposed hexagons, should suffice. The pressure both inside the membrane structure as under the bubbles will take care of holding things up. The pillars will mostly provide anchoring points, and make sure the whole structure doesn't wobble around.

Expect spacing the pillars betwenn 100 and 500 meters apart.

The pressure inside the membrane system is provided from the ground, through tubes or hoses inside the pillars. Sensors will notice a drop in pressure, thus indicating a larger breach. Upon detection, around the borders of the section in question airbag-like structures can be inflated quickly, to wall off the compromised section.

Fear of a complete loss of atmosphere should be unjustified. A pressure of 1 bar is not that much, and air takes time to escape through any hole, so even a complete loss of several sectors will do less damage to the atmosphere than it will do tho the asteroid itself. The drop of pressure may be noticeable, even unpleasant, but never life threatening, unless one found oneself in the sector that got hit, but even there the damage from the impact will most likely pose a much bigger threat than the loss of atmospheric pressure.