Author Topic: ITS spaceship solar panels  (Read 13443 times)

Offline Llian Rhydderch

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ITS spaceship solar panels
« on: 11/05/2016 11:11 AM »
The images Musk presented of the ITS spaceship have a very particular solar panel design shown.

Now he said that the ships were rendered from actual CAD models of what they plan to build.  Taking that as a given, and not using this thread to try and design some new/better/my-favorite-type-of solar panels, let's start examining the engineering of spaceship internals required to support such a design.

First question: extension and retraction.  How might one design the spaceship internals necessary to make such panels possible: launch secure, reliable extension, sufficiently strong for the loads encountered in some ship maneuvers, with straightforward and robust panel retraction at Mars?  Where would the panels fit inside the ship and around the tankage/engines that were shown in the image?



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Online docmordrid

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Re: ITS spaceship solar panels
« Reply #1 on: 11/05/2016 12:49 PM »
My first thought was thin film arrays as a layer of an inflatable structure. Which begs, how do you deflate for storage in a vacuum? Shape memory? How do you patch it?  Self-sealing layer?
« Last Edit: 11/05/2016 12:52 PM by docmordrid »
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Offline guckyfan

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Re: ITS spaceship solar panels
« Reply #2 on: 11/05/2016 01:03 PM »
My first thought was thin film arrays as a layer of an inflatable structure. Which begs, how do you deflate for storage in a vacuum? Shape memory? How do you patch it?  Self-sealing layer?

Maybe inflated only for deployment. Some minor stiff components to keep shape when deployed. Maybe pressurize to some extent during use of the RCS and for trajectory corrections. Roll it back for retracting.

Edit typo
« Last Edit: 11/05/2016 01:03 PM by guckyfan »

Offline Jim

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Re: ITS spaceship solar panels
« Reply #3 on: 11/05/2016 02:21 PM »
Don't forget (which Spacex has) that a large radiator is also required.

Online meekGee

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Re: ITS spaceship solar panels
« Reply #4 on: 11/05/2016 02:30 PM »
I read the design as having the radiator fins as the stiffeners, and the PV array stretched between them.

How it deploys and stows is beyond me.  An EVA?!  :o
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Offline Jim

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Re: ITS spaceship solar panels
« Reply #5 on: 11/05/2016 02:59 PM »
The fins see each other so that isn't so efficient.  More acreage is then required

Offline Robotbeat

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Re: ITS spaceship solar panels
« Reply #6 on: 11/05/2016 04:53 PM »
Radiators could be fitted into the skin, like they are in Dragon's trunk. Also, with emissivity management, radiators may not even be required.
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Offline Jim

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Re: ITS spaceship solar panels
« Reply #7 on: 11/05/2016 05:20 PM »
Radiators could be fitted into the skin, like they are in Dragon's trunk. Also, with emissivity management, radiators may not even be required.

Dragon not relevant.  It is has low power consumption and not manned. Radiators will be required.  And more than the body surface area.

Offline Oli

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Re: ITS spaceship solar panels
« Reply #8 on: 11/05/2016 06:21 PM »
Now he said that the ships were rendered from actual CAD models of what they plan to build.

I find that doubtful. Musk also said the vehicle would have split body flaps, far from a minor detail, but they're nowhere to be seen.

Offline jpo234

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Re: ITS spaceship solar panels
« Reply #9 on: 11/05/2016 06:30 PM »
Radiators could be fitted into the skin, like they are in Dragon's trunk. Also, with emissivity management, radiators may not even be required.

Dragon not relevant.  It is has low power consumption and not manned. Radiators will be required.  And more than the body surface area.
Somebody did some maths on this: https://thephysicsofspacex.wordpress.com/2016/10/31/thermal-management-aboard-the-its/

Don't know, whether the calculations are correct.
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Offline LMT

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Re: ITS spaceship solar panels
« Reply #10 on: 11/05/2016 06:38 PM »
Wings & Rings

I read the design as having the radiator fins as the stiffeners, and the PV array stretched between them.

How it deploys and stows is beyond me.  An EVA?!  :o

If the ITS radiator loops are as efficient as the Dragon's, they'll reject ~100 kW of heat over 200 m2.   Higher heat rejection rates are possible.  Radiator loops could be integrated into the ITS airframe / hull at multiple locations.  The open hull between PV wings and engines is suggestive just because it would allow for double-sided, high-efficiency heat rejection.  However that location might be too rough-and-tumble for a radiator mounting.

Image: Dragon trunk, with radiator visible as flat checkerboard. 



The booms of each ITS wing would then be simple guide structures, akin to booms of the LightSail 2 nanosat.



The ITS animation suggests, to me at least, that a wing's booms are deployed and retracted on a ring ~14 m in diameter.  In retraction the thin-film PV accordion-folds loosely in the space between the 14 m ring and the 17 m hull.  Each wing is attached to its own ring, one stacked above the other, operating in counter-rotation.
« Last Edit: 12/14/2016 06:42 PM by LMT »

Online meekGee

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Re: ITS spaceship solar panels
« Reply #11 on: 11/05/2016 07:46 PM »
The fins see each other so that isn't so efficient.  More acreage is then required
They see each other, but over a relatively small angle, judging by the proportion.  They mostly see space, and the PV skin, whose back side can be low emissivity.

They are though, by definition, shaded in this configuration.

The total area, in relation to the total PV area, is not too far off from what you see at the ISS, especially since you can expect the PV panels to be a lot more efficient than ISS, but the radiators, not so much.

That said - who knows.  Deployment/stowage is hard enough without the coolant loops in there.
« Last Edit: 11/05/2016 09:13 PM by meekGee »
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Offline Oersted

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Re: ITS spaceship solar panels
« Reply #12 on: 11/05/2016 08:07 PM »
Just a thought: The solar array positioned at the base of ITS makes me think that SpaceX perhaps considers dual-use, i.e. en route and on the surface. How that could be done I don't know, but deployment by inflation could be part of the solution I guess.

Offline Llian Rhydderch

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Re: ITS spaceship solar panels
« Reply #13 on: 11/05/2016 10:13 PM »
Wings & Rings

The ITS animation suggests, to me at least, that a wing's booms are deployed and retracted on a ring ~14 m in diameter.  In retraction the thin-film PV accordion-folds loosely in the space between the 14 m ring and the 17 m hull.  Each wing is attached to its own ring, one stacked above the other, operating in counter-rotation.

The SpaceX-provided animation (at 2:45) shows the extension, but obfuscates the causal mechanism.  Your theory is interesting.  I'm not quite groking how your postulated ring mechanism would work.  Could you sketch it?
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Online meekGee

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Re: ITS spaceship solar panels
« Reply #14 on: 11/05/2016 11:02 PM »
Wings & Rings

The ITS animation suggests, to me at least, that a wing's booms are deployed and retracted on a ring ~14 m in diameter.  In retraction the thin-film PV accordion-folds loosely in the space between the 14 m ring and the 17 m hull.  Each wing is attached to its own ring, one stacked above the other, operating in counter-rotation.

The SpaceX-provided animation (at 2:45) shows the extension, but obfuscates the causal mechanism.  Your theory is interesting.  I'm not quite groking how your postulated ring mechanism would work.  Could you sketch it?

Just single-framed it, and still confused.

If the closed accordion would should straight back and then pivot forward, I'd say it is as long as the ship, and stored in side-scabbards on the outside of the hull.

But it emerges almost tangential, which is I guess where the counter-rotating stowage mechanism comes in, but why....
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Online oiorionsbelt

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Re: ITS spaceship solar panels
« Reply #15 on: 11/06/2016 12:13 AM »
I'm confused.
The arrays look to facing the wrong way.
Wouldn't the engines be facing the sun, for solar radiation protection? Therefore shouldn't the solar panels also be facing reward with any radiators facing forward?
« Last Edit: 11/06/2016 12:14 AM by oiorionsbelt »

Offline LMT

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Re: ITS spaceship solar panels
« Reply #16 on: 11/06/2016 03:55 AM »
Wings & Rings

The ITS animation suggests, to me at least, that a wing's booms are deployed and retracted on a ring ~14 m in diameter.  In retraction the thin-film PV accordion-folds loosely in the space between the 14 m ring and the 17 m hull.  Each wing is attached to its own ring, one stacked above the other, operating in counter-rotation.

The SpaceX-provided animation (at 2:45) shows the extension, but obfuscates the causal mechanism.  Your theory is interesting.  I'm not quite groking how your postulated ring mechanism would work.  Could you sketch it?

The notion is really just a tweaked scale-up of the LightSail 2 deployment methods.

Here's the deployment mechanism on LightSail 2:



Here are some engineering details of LightSail 2, at SpaceFlight101.



As imagined on the ITS:

Image attached:  2rings.png

2 wing deployment rings (blue) are stacked beneath the methane tank.

Each ring rotates 360 degrees to deploy its ~42 m wing booms.  Rings rotate independently and in opposite directions.

Image attached:  Deployed_and_Retracted.png

These are wing perimeter cross-sections. 

Deployed booms (blue) spread ~3 m apart at wing perimeter.  Thin-film PV panels (white) are held in tension by the booms.  Accordion tensioning wire (green) is relaxed and fully extended.

Retracted booms wrap around the ring.  Accordion tensioning wire is retracted in sync with boom retraction, and wound around a tensioned spool (green).  PV panels are now held in tension by the accordion wire.  At perimeter, the 3 m panel is tension-folded into 2 x 1.5 m accordion pleats, occupying 0.15 m between the sandwiching 1.5 m booms.  The retracted booms and panels form a layered wrapper 2 x ~1.2 m thick, filling most of the space between the deployment ring and the ITS hull.



Notionally.  The accordion tensioning mechanism is especially simplistic.  I'd think some more elegant mechanism could be integrated cleanly into the PV panels.  Elgiloy leaf springs?
« Last Edit: 12/14/2016 07:47 PM by LMT »

Online MikeAtkinson

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Re: ITS spaceship solar panels
« Reply #17 on: 11/06/2016 07:58 AM »
I think they are much more likely to be rolled up. Something like this:

http://www.surrey.ac.uk/ssc/research/space_vehicle_control/deploytech/mission/

I'm sure I've seen a better example somewhere, but my google-fu is not strong today.

Offline john smith 19

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Re: ITS spaceship solar panels
« Reply #18 on: 11/06/2016 09:02 AM »
The images Musk presented of the ITS spaceship have a very particular solar panel design shown.

Now he said that the ships were rendered from actual CAD models of what they plan to build.  Taking that as a given, and not using this thread to try and design some new/better/my-favorite-type-of solar panels, let's start examining the engineering of spaceship internals required to support such a design.

First question: extension and retraction.  How might one design the spaceship internals necessary to make such panels possible: launch secure, reliable extension, sufficiently strong for the loads encountered in some ship maneuvers, with straightforward and robust panel retraction at Mars?  Where would the panels fit inside the ship and around the tankage/engines that were shown in the image?
Indeed it does look odd. So they extend from the rear at 90deg to the body, then fan out and we can see the stiffening ribs from this PoV.

Logically the stiffening ribs should be behind the surface to avoid shadowing some of the array area.  Other points will be that since no PV array is 100% efficient where does the heat go and how big is the "hotel" load (from the people inside) those radiators have to dump as well. The panels are very long so one option is they are laying inside the skin of the vehicle and being bent through 90deg during deployment.

One idea would be if the panels are thin film the heat they cannot convert to electricity is directly radiated from the back surface, eliminating a specific radiator structure. likewise TF arrays make the stiffeners smaller.

A possible concept would be TF arrays between the ribs and the ribs being inflatable tubes. Keep in mind the inflatable rescue slides on aircraft for an idea of how strong quite lightweight low pressure structures can be.

The joker in the pack for inflatable systems is controlled re-packing for descent, which this system will also have to do.

There are a number of technologies for deploying long rigid spars from small containers (search "aerospace mechanisms" ). It helps if you can avoid having a heavy point mass at the far end of the structure away from the deployment mechanism. The sequence is also important. IIRC these go to full length, then fan out, not the other way around.
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Offline Jim

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Re: ITS spaceship solar panels
« Reply #19 on: 11/06/2016 11:57 AM »
The fins see each other so that isn't so efficient.  More acreage is then required
They see each other, but over a relatively small angle, judging by the proportion.


No, each individual fin (except for the end ones) is looking at two fins next to it.  And at the base, they are wider and closer.

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