Spaceships With More Volume Without Lots of Extra Mass..

[Spacescifi]

 

Provided we never figure a way to cheat gravity, spaceships will always favor lower mass on launch.

That said, you can still get scifi looking spaceships!

Send a rocket looking spaceship up to orbit, and have it inflate the habital section that can look like a scifi vessel of your choice. Preferably any with curves (saucers, eggs, spheres, etc).

If money were no object, are there ANY good reasons not to stuff rockets with inflatables to expand space inlnfrastructure and volume for less mass?

 

Are hard modules better than inflated? Seems not to be the case to me, since inflated modules can be designed to self-repair (like scabs on skin). Try doing that with solid metal.

[Xd the great]

The biggest trouble with inflating space station modules is probably keeping it from getting punctured and destroyed from space debris.

[kerbiloid]

Just send an astronaut with soap for bubbles, spray foam, and duct tape, and he will do the rest.

[Toonu]

The issue can probably be also mitigated by all the expandable sections sealed by and internal airlock door of some sort inside the rigid core of ship to make repairs if needed and not endanger the whole ship when punctured? But then there is the issue of so much air being lost in case of big particle in the inflatable section you cannot replace properly until supply mission to the ship or near some planet...

[KSK]

If your spacecraft design allows for a separate habitation module which can be readily attached to the rest of the ship, and if there are volume constraints on your launch vehicle such that you need to pack a lot of eventual volume into the confines of a payload fairing or cargo bay, then an inflatable would seem to be a good choice, everything else being equal. Otherwise, whether a hard module is 'better' than a soft one will entirely depend on your ship design.

A couple of points to consider:

1.    At present levels of development, the weight saving from inflatables is relatively low.

Genesis II:    pressurised volume 11.5 cubic metres, mass 1.36 tons, so 8.45 cubic metres per ton.
BEAM:  pressurised volume 16 cubic metres, mass 1.41 tons, so 11.35 cubic metres per ton.

Compare to:

Destiny ISS laboratory module:  pressurised volume 104.77 cubic metres, mass 14.52 tons so 7.21 cubic metres per ton.

I haven't had time to look up equivalent data for the other ISS modules although I'm sure it's out there somewhere.

2.   Money usually is an object. The reason why present day spacecraft are optimised for lower mass on launch is because of the cost of that launch. Reduce launch costs and there's less need to optimise for mass in favour of optimising for cost using cheaper but more convenient materials that may be heavier.

And finally, a thought exercise. Parts of the ISS were made of steel. Why wasn't a lighter material used?

 

Edited December 9, 2019 by KSK

[kerbiloid]

25 minutes ago, KSK said:

Genesis II:    pressurised volume 11.5 cubic metres, mass 1.36 tons, so 8.45 cubic metres per ton.
BEAM:  pressurised volume 16 cubic metres, mass 1.41 tons, so 11.35 cubic metres per ton.

Compare to:

Destiny ISS laboratory module:  pressurised volume 104.77 cubic metres, mass 14.52 tons so 7.21 cubic metres per ton.

The Destiny total mass includes the equipment, while the named inflatables are empty.

It's 4.3 m in diameter and 8+ meters long. Made of aluminium and somewhere of steel.
Surface area = pi * 4.3 * 8.5 + 2 * pi * 4.3² / 4 ~= 140 m².
Thickness is unknown, but say 5 mm, density 2700.
Envelope mass ~= 140 *0.005 * 2700 ~= 2 000 kg.
Plus inner beams, so its total empty hull mass is ~5 t.
And as unlike the inflatables, it doesn't need additional inner structures to attach the equipment, the inflatables will mass ~2 t more when they mount metal trusses inside.

So, in fact the inflatable modules gain just ~10% of mass but significantly complicate the construction.

For a Martian flight you anyway need a thick radiation and meteoroid protection, so the mass economy will be totally negligible, because you must have a mass around the inhabited part of the ship.

So, inflatables are for personal projects like "me and cat in a space tent".

Edited December 9, 2019 by kerbiloid

[KSK]

Yes - I didn’t want to dig too deeply into the details since I didn’t have enough information about Destiny’s construction to hand. However, I think that the decrease in volume per mass for an inflatable spacecraft module (BEAM) to a free-flying inflatable spacecraft (Genesis 2) is quite instructive. 

 

 

[KSK]

8 hours ago, Xd the great said:

The biggest trouble with inflating space station modules is probably keeping it from getting punctured and destroyed from space debris.

Not as much as you’d think. They’re built from pretty thick laminate fabrics which include Kevlar and a whole bunch of other layers designed to slow and entrap debris and any fragments caused by the initial collision between that debris and the module. On that basis they’re probably as safe as a metal skin plus Whipple shield design.

I think the bigger trouble is getting them to inflate reliably and safely. That’s where BEAM ran into problems as I recall and BEAM is a fairly simple (for space grade versions of simple) inflatable module.

[kerbiloid]

1 hour ago, KSK said:

They’re built from pretty thick laminate fabrics which include Kevlar

Kevlar protects from the air drag pressure (supersonic chutes) and bullets (vests).
It's pierceable by knives, spears, other slow sharp things, because its protection is based on the kinetic energy mass dissipation.
When a bullet hits the vest, the local part of kevlar transfers its energy to the neighboring fibers, all of them get hot and dissipate the heat. Against a slow penetration it's much more vulnerable.

Against rifle or even machine-pistol bullets you need ceramic or metal plates in your kevlar vest pockets.

And all those composite things being damaged in just one place like to loose their protective features completely, unlike the metals.

At the same time any classic metallic module is covered with insulation blankets made of same polymers.

So, the kevlar is not that tough. It's just better than nylon, and a metal hull is not that bare.

Edited December 9, 2019 by kerbiloid

[wumpus]

20 minutes ago, kerbiloid said:

So, the kevlar is not that tough. It's just better than nylon, and a metal hull is not that bare.

I worked for a company that made drones in the early 90s (unfortunately they were out of business before drones really took off), and they made one of their prototypes out of kevlar.  Thing once ran into a tree (they were fixed wing "aircraft", not quadcopters) and only the propeller (and possibly engine) was damaged.  On the other hand, cutting the fabric was so hard (even with the special shears) that they weren't interested in making more.

I have to wonder if you can laser-cut those things...  So kevlar isn't as tough as steel.  But if you have to accelerate the mass to orbit, you might prefer kevlar.

[kerbiloid]

1 minute ago, wumpus said:

But if you have to accelerate the mass to orbit, you might prefer kevlar.

Until you want to attach 450-kg racks to the walls.

[farmerben]

If you want inflatable storage space, it could be built far lighter than a habitation.

The rigid hull can be crammed full of gear initially, if we plan to put that gear in the shed once in space.

Do you have experience with bad air mattresses?  It takes less than 1 psi to establish the fully inflated shape.  Micrometer sized holes leak noticeably over periods of hours.   Over brief periods of time they seem to work well.  If you leave it on the floor without weight for many days, the shape is still somewhat expanded.  

 

A space shed works well in conjunction with an airlock.  A very tiny amount of air pressure would allow an astronaut with a breathing mask and a flight suit to work in there.  Deflation equipment allows us to recover most of the air before it escapes into space.  We will not disrupt the shape of the inflatable by sucking air out of it.  Only shadows are going to change the shape of our inflatable from now on. 

 

 

 

[farmerben]

10 hours ago, kerbiloid said:

Just send an astronaut with soap for bubbles, spray foam, and duct tape, and he will do the rest.

 

This is actually genius!  Soap bubbles would get sucked toward any leak.  The part that doesn't outgass or freeze becomes like wax.  While glue is attractive, just plain soap has the advantage of being able to easily decontaminate the equipment and recycle the soap.  

[KSK]

4 hours ago, kerbiloid said:

Kevlar protects from the air drag pressure (supersonic chutes) and bullets (vests).
It's pierceable by knives, spears, other slow sharp things, because its protection is based on the kinetic energy mass dissipation.
When a bullet hits the vest, the local part of kevlar transfers its energy to the neighboring fibers, all of them get hot and dissipate the heat. Against a slow penetration it's much more vulnerable.

Against rifle or even machine-pistol bullets you need ceramic or metal plates in your kevlar vest pockets.

And all those composite things being damaged in just one place like to loose their protective features completely, unlike the metals.

At the same time any classic metallic module is covered with insulation blankets made of same polymers.

So, the kevlar is not that tough. It's just better than nylon, and a metal hull is not that bare.

I looked into this in a bit more detail. Turns out that Kevlar isn't used for its puncture resistance but for its tensile strength. From the Wikipedia article on TransHab:

The key to the debris protection in the design and prototype units was successive layers of Nextel,  a material commonly used as insulation under the hoods of many cars, spaced between several-inches-thick layers of open cell foam, similar to foam used for chair cushions on Earth. The Nextel and foam layers cause a particle to shatter as it hits, losing more and more of its energy as it penetrates deeper.

Many layers deep in the shell was a layer of superstrong woven Kevlar to hold the module's shape. The air was held inside by three bladders of Combitherm, a material commonly used in the food-packing industry. The innermost layer, forming the inside wall of the module, was Nomex cloth, a fireproof material that also protected the bladder from scuffs and scratches.

Jumping back to my original post, the reason this post caught my eye is because I've been looking into inflatable modules as part of my own sci-fi ship design.  Putting details in spoilers because its kinda long and... well because spoilers for anyone reading First Flight.

 

Spoiler

 

The blob in Richlin’s rendezvous window grew steadily larger, acquiring shape and definition as it drew closer. At one kilometre the colony ship was impressive, at point one kilometre it was simply immense. The bridge module loomed in front of them; the four symmetrical petals of the docking port cover already open, strips of running lights on their undersides glowing brightly. Above the port, the ship’s name was stencilled across the hull plates in neat Kerba script:

KSV 0001

Richlin stared at the bridge crew silhouetted behind their windows and shook his head in amazement. “Unbelievable. From kerbal-in-a-can Moho capsules to that!”

“It’s something,” Wilford agreed. 

The edges of the forward crew shelter were visible behind the bridge, hub for the eight great pressurised spokes linking it to the main habitation and cargo modules running the length of the ship. Amidships, the rearward crew shelter and its spokes provided a second supporting hub, both shelters threaded on the great main truss that formed the spine of the ship and supported the propellant tanks and other vital systems. Aft of the shelters, a lattice of open girders secured the far ends of the habitation and cargo modules to the spine. Beyond that, at a carefully calculated distance from the rest of the ship, the convex disk of the shadow shield blotted out the stars, slicing a dark oval from the blue glow of Kerbin's horizon.

And beyond the shadow shield...

Wilford shivered. Wernher's masterpieces.

The LV-Ns. 

As far from the bridge and crew compartments as the KSA engineers could put them and the reason why all docking operations with a colony ship were undertaken from a strictly cabin-to-cabin approach. A muffled clang interrupted his thoughts followed by the familiar ripple-bang of docking latches snapping shut. Wilford unstrapped from his couch and picked up his helmet. Camrie tapped him on the shoulder. "I'll pass that through in a minute along with your EVA suit. Time you two were aboard." To Wilford's surprise she threw her arms around himself and Richlin. "Good luck boys - and for Kerm's sake be careful out there!"

"We will," said Wilford, hugging her back. "Keep an eye on Sherf for me - and don't let Jeb do anything that James wouldn't do."

Camrie snorted. "I'll let Gene take care of that. Now go on - or do I have to kick you through that hatch myself?"

 

Those spokes are built from an inflatable tube supported by a girder section. This was for two reasons: firstly it let the ship designers optimise both parts separately rather than trying to build an inflatable module that would be structurally rigid enough and could resist all the various forces caused by spinning-up (and spinning down) the ship. No idea how realistic that is (I'm a writer dammit not a mechanical engineer) but it seemed at least plausible. Secondly, there were volume constraints when launching all the ship components to orbit. Much more efficient to launch one fairing full of girder sections stacked in parallel, followed by one fairing full of deflated tubes stacked atop each other and put enough parts on orbit in two flights to build three spokes, than to take three flights to launch each spoke already assembled and inflated.

And if you think that's a little bit crazy, you're in good company

“Good afternoon, Director. As Roncott said, I’m in charge of the Stratus Portable Systems Division and - as you might expect - we have considerable experience in designing, manufacturing and manufacturing with, space-grade fabrics.” Halnie gestured at the spoke module behind her. “Naturally, we’ve prepared a full technical specification for the KSA, together with details of our test protocols and outcomes of those tests. To cut a long story short, Director, we were able to devise suitable laminate materials which combine the requisite air-tightness, tensile strength and impact resilience.”

“We fully appreciate that it’s not an easy idea to get to grips with.” Halnie offered Lodan a faint smile, “even Jeb dismissed it out of hand the first time he heard about it, but we believe that our fabrics offer some significant advantages over conventional spacecraft construction materials."

Edited December 9, 2019 by KSK