Author Topic: ITS spaceship solar panels  (Read 21101 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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Offline 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.

Offline 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 »

Offline 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 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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Offline 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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Offline 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 »

Offline 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.

Offline meekGee

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Re: ITS spaceship solar panels
« Reply #20 on: 11/06/2016 12:05 pm »
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.
The thermal radiation is isotropic.   (Well, depending on the surface) and so what the fin cares about is "how big an angle of the sky is "space".

As someone notes above, the ribs are backwards anyway.

I still don't understand why deploy at 90 degrees.

Btw, since this is a fast transit, did anyone figure out how much would ice sublimation weigh?



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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Offline Jim

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Re: ITS spaceship solar panels
« Reply #21 on: 11/06/2016 12:19 pm »

The thermal radiation is isotropic.   (Well, depending on the surface) and so what the fin cares about is "how big an angle of the sky is "space".

As someone notes above, the ribs are backwards anyway.


And the ribs are a large portion of that "space"

They can't be backwards, otherwise the vehicle would be in the view too.

Offline meekGee

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Re: ITS spaceship solar panels
« Reply #22 on: 11/06/2016 12:32 pm »

The thermal radiation is isotropic.   (Well, depending on the surface) and so what the fin cares about is "how big an angle of the sky is "space".

As someone notes above, the ribs are backwards anyway.


And the ribs are a large portion of that "space"

They can't be backwards, otherwise the vehicle would be in the view too.
Yes, you can keep the edge-on orientation pretty accurately and therefore also eliminate shading.

So this supports the idea that the ribs may be radiators (or else they would be on the back side so that shading isn't a problem even if pointing is a little bit off).

So maybe you also understand why deploy tangentially and not straight towards the back and pivot forward?   Counter rotating rings seem complex.

The deployment occurs after TMI, so it'd better be reliable...

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Offline Robotbeat

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Re: ITS spaceship solar panels
« Reply #23 on: 11/06/2016 02:25 pm »
The back of a solar panel must be high emissivity as a solar panel is basically its own radiator. It must reject heat like any other power conversion device and like other power conversion devices it works better and lasts longer if it can be kept cool.

I don't think the ribs are radiators.

I disagree with Jim because the body of the ITS should be capable of rejecting hundreds of kilowatts HOWEVER I kind of also agree with him that other radiators may be needed since the body needs to protect against some reentry heat, and I think integrating a radiator that can also operate at high temperatures and be insulating to those temperatures would be a big challenge such that you're probably better off just using deployable radiators.
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Online matthewkantar

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Re: ITS spaceship solar panels
« Reply #24 on: 11/06/2016 02:33 pm »
As said above, the area the solar panels deploy out of seems way too full of other gear to squeeze the panels and deployment mechanism into. Does anybody have any idea why they would be way back there instead of between upper most tank and cargo? Center of gravity issues? Does not make sense to me.

Matthew

Offline MikeAtkinson

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Re: ITS spaceship solar panels
« Reply #25 on: 11/06/2016 02:56 pm »
As said above, the area the solar panels deploy out of seems way too full of other gear to squeeze the panels and deployment mechanism into. Does anybody have any idea why they would be way back there instead of between upper most tank and cargo? Center of gravity issues? Does not make sense to me.

Matthew
If the solar panels are 40 m long x 10 m wide and 1mm thick then they take up 0.4 m3 double that for the ribs and add some more for the deployment mechanism and we get of the order of 1 m3.

I don't think the panels are going to have significant mass or volume compared to the overall spaceship mass and volume.

Offline meekGee

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Re: ITS spaceship solar panels
« Reply #26 on: 11/06/2016 03:16 pm »
What if the panels have those ultra flexible carbon rods in them, full length.  The rods spread out like a fan, but can be pulled back into the ship.

Deployment from a folded state would work well, but I can't see how stowing would work.
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Offline LMT

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Re: ITS spaceship solar panels
« Reply #27 on: 11/06/2016 04:10 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.

Notably, recent heat pipe designs can reject spacecraft heat with a capability exceeding 50 W/cm2, which is a remarkable efficiency.  I think this frees the wing booms from that job, potentially saving much complexity in wing design.

Offline Oersted

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Re: ITS spaceship solar panels
« Reply #28 on: 11/06/2016 08:20 pm »
As said above, the area the solar panels deploy out of seems way too full of other gear to squeeze the panels and deployment mechanism into. Does anybody have any idea why they would be way back there instead of between upper most tank and cargo? Center of gravity issues? Does not make sense to me.

Well, my idea was dual-use, in space and on the surface. Deploying from near the main engines would mean deploying close to the ground.

Offline Llian Rhydderch

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Re: ITS spaceship solar panels
« Reply #29 on: 11/06/2016 09:11 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.

Notably, recent heat pipe designs can reject spacecraft heat with a capability exceeding 50 W/cm2, which is a remarkable efficiency.  I think this frees the wing booms from that job, potentially saving much complexity in wing design.

While were discussing thermal waste heat radiators, might there be room to design a heat radiator that opens up in space behind "doors" that would open from the topmost of the three hull protrusions? The one without any PICA-X surface, and shown all white in the drawings?

Once opened up, it perhaps could do heat radiation using some sort of equipment deployed from under the covers, on in the covers themselves like I believe was done with the Space Shuttle?, or some creative use of the space that is not needed for the landing gear.

Plus, for a really crazy idea, if there is sufficient volume external to the tank circumference extending up to one of the cargo decks, there might be a way to get a human-sized EVA portal worked in there.  Such an EVA opening might be used for a planned EVA option on some future mission, or for contingency access to the outside of the ship on multi-month passages when humans (or EVA droids?) are aboard.
« Last Edit: 11/06/2016 09:13 pm by Llian Rhydderch »
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Offline LMT

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Re: ITS spaceship solar panels
« Reply #30 on: 11/07/2016 04:58 am »
Wings on the Ground

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.

The ITS wing booms appear to be slightly tapered.  Does anyone else see that in the ITS renderings?

Boom tapering is unusual for a zero-g application, and is not seen, for example and to best of my knowledge, in any recent solar sail boom designs.  To my mind the ITS boom tapering, if real, suggests a secondary use of the booms as cantilever beams on the planetary surface.

Tapering reduces beam bending under gravity dead load.  Conceivably, on the surface, an Elgiloy boom's triangular cross-section could be supported by the deployment ring's spooling flange.  With optimized tapering, this boom configuration might carry the wing's dead load.



(This would also explain the positioning of booms between engines and PV panels.  This configuration can put some PV cells in shade during cruise phase, with engines oriented protectively toward the sun.  A more efficient configuration would place booms on the opposite side of the panels.  However the less efficient configuration is required if an Elgiloy boom's triangular base is to be supported by the spooling flange on the planetary surface, with PV panels hanging above.)

The pair of stacked 1.5 m deployment rings would be positioned ~8 meters above the surface, allowing even the largest cargo containers or vehicles to pass beneath the wings.  Also the wings are positioned to deploy between the extended landing legs, as would be expected for wings used on the surface. 

However each wing would block a crane overhead, so one wing would have be retracted during hours with cargo offload or crew access activity.
« Last Edit: 12/14/2016 06:40 pm by LMT »

Offline Chris_Pi

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Re: ITS spaceship solar panels
« Reply #31 on: 11/07/2016 06:34 am »
What if the panels have those ultra flexible carbon rods in them, full length.  The rods spread out like a fan, but can be pulled back into the ship.

Deployment from a folded state would work well, but I can't see how stowing would work.

Wind the stiffeners, Don't fold them. The thin-film panels could fold up between the stiffeners to keep the whole thing nice and narrow.

I'm thinking something kinda like like a tape measure, But with multiple tapes and the thin-film panels between all wound on top of itself on one spool. Use a couple comb-shaped guides on the sides of the slot the array deploys through to spread the stiffeners apart and pull the whole thing flat on the way out and to re-fold the film as it's wound back up.

If the whole spool assembly isn't more than a few meters across it looks like it should fit in between the combustion chambers on the vacuum motors. Probably going to need an insulated compartment to keep from melting when motors are running. Plugging a spool into a built-in compartment could make panel swaps (Or removal for ground use) fairly simple either in space or on the surface. The insulated box and exterior hatch/TPS stays with the ship and the spool with the deployment motor and the guide comb gets swapped out.

No huge ship-circling moving parts and if they're oversized enough cargo ships might be able to get along with just one for the return trip and leave the other on Mars. If the whole array packs down small enough to squeeze in between motors.

Offline envy887

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Re: ITS spaceship solar panels
« Reply #32 on: 11/07/2016 12:45 pm »
A tape measure is very thin, while those spars appear to have substantial thickness. Perhaps a better analogy is a common spooled self-extending inflatable structure:

Offline docmordrid

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Re: ITS spaceship solar panels
« Reply #33 on: 11/07/2016 03:52 pm »
Which would fit in with Musks inflatable roll-out array statement.
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Offline LMT

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Re: ITS spaceship solar panels
« Reply #34 on: 11/07/2016 04:32 pm »
Which would fit in with Musks inflatable roll-out array statement.

?  Ref.?

Offline Robotbeat

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Re: ITS spaceship solar panels
« Reply #35 on: 11/07/2016 04:35 pm »
There's a video on YouTube of Musk saying that one option they're looking for is solar arrays that roll out like party tube noise maker things.
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Offline docmordrid

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Re: ITS spaceship solar panels
« Reply #36 on: 11/07/2016 04:42 pm »
And one of the items NASA is working on is ROSA - Roll Out Solar Arrays.

ROSA....

Quote
Technology testing

The U.S. Air Force has funded a test flight of the ROSA mechanism, now scheduled for a SpaceX launch in Spring 2017 to the International Space Station, where it will be deployed in space.

Of course another option is a roll-out hand fan-like framework with thin film areays between the segments.
« Last Edit: 11/07/2016 04:54 pm by docmordrid »
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Offline Robotbeat

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Re: ITS spaceship solar panels
« Reply #37 on: 11/07/2016 05:16 pm »
ROSA uses STEM booms, not inflatables, for deployment.

But NASA has done a lot of low TRL work on inflatables for solar array deployment. In hard vacuum, the difficulty is punctures by micrometeorites and the gvt you have to bring and replacement gas with you and that the array must remain inflated. None of these really apply on Mars. The atmosphere protects against all micrometeorites and also provides unlimited replenishment gas. Besides, inflation is just needed for deployment. Later on, you could have a rover anchor the end of the array with a rock or something.
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Re: ITS spaceship solar panels
« Reply #38 on: 11/07/2016 05:27 pm »
I was thinking it would work like a paper fan, with thin CF stays. One reason to make the stays tapered would be to keep the thickness of the packed fan more uniform.

storage and unfurling example images attached.

Offline LMT

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Re: ITS spaceship solar panels
« Reply #39 on: 11/08/2016 12:39 am »
Accordion Fan

I was thinking it would work like a paper fan, with thin CF stays. One reason to make the stays tapered would be to keep the thickness of the packed fan more uniform.

I think your paper fan = my wing-ring accordion fold.  Either way, we'd be looking at 2 folds per boom.

re: tapering:  In the ITS renderings it's not boom thickness that appears to taper, but boom height ("up" toward ITS cabin).  If as I suppose the wing is being wrapped 360 degrees around a deployment/retraction ring, the thickness of the wrapped wing would be uniform around the ring, with or without that taper.  A tapered boom would just decrease the height of the wrapped booms, toward the outer edge.  Height of the wrapped PV panels would increase toward the outer edge.  Max height of all wrap:  1.5 m.

That tapering would make sense if SpaceX plans to open the wings when the ITS is landed on the martian surface, where a tapered cantilever beam would reduce the wing's bend.  Otherwise the tapering serves no purpose that's obvious to me.

Offline Chris_Pi

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Re: ITS spaceship solar panels
« Reply #40 on: 11/08/2016 01:00 am »

That tapering would make sense if SpaceX plans to open the wings when the ITS is landed on the martian surface, where a tapered cantilever beam would reduce the wing's bend.  Otherwise the tapering serves no purpose that's obvious to me.

IIRC the assumed sun-facing side of the array is the bottom - works with motors toward the sun. Deploying on the surface would have them upside-down. (Maybe they can be removed and flipped?) Only other time a stiff array would be needed is if the plan is to deploy them as soon as the ship gets to orbit and keep them that way all the way to Mars. Guaranteed deployed panels during cruise would be to nice to have. Some way to jettison the array quickly would be needed or re-entry could get interesting if one doesn't stow properly.

I don't have any idea if doing the TMI burn with the panels out is capital C crazy or just lower-case c. But two floppy solar arrays during wouldn't help any.

Offline lamontagne

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Re: ITS spaceship solar panels
« Reply #41 on: 11/08/2016 03:27 am »
The back of a solar panel must be high emissivity as a solar panel is basically its own radiator. It must reject heat like any other power conversion device and like other power conversion devices it works better and lasts longer if it can be kept cool.

I don't think the ribs are radiators.

I disagree with Jim because the body of the ITS should be capable of rejecting hundreds of kilowatts HOWEVER I kind of also agree with him that other radiators may be needed since the body needs to protect against some reentry heat, and I think integrating a radiator that can also operate at high temperatures and be insulating to those temperatures would be a big challenge such that you're probably better off just using deployable radiators.
The body of the ship should be insulated, and therefore the surface will be cold, and not a very good radiator.  But I don't really understand the solar panel arrangement either.

Offline lamontagne

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Re: ITS spaceship solar panels
« Reply #42 on: 11/08/2016 03:39 am »
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.

I did some work on power and cooling for the ITS, when it was the BFS.  A bit out of date since I expected radiators in the cargo bay doors, as per the space shuttle.
« Last Edit: 11/08/2016 03:43 am by lamontagne »

Offline LMT

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Re: ITS spaceship solar panels
« Reply #43 on: 11/08/2016 03:56 am »

That tapering would make sense if SpaceX plans to open the wings when the ITS is landed on the martian surface, where a tapered cantilever beam would reduce the wing's bend.  Otherwise the tapering serves no purpose that's obvious to me.

IIRC the assumed sun-facing side of the array is the bottom - works with motors toward the sun. Deploying on the surface would have them upside-down. (Maybe they can be removed and flipped?)

I suppose the panels could be designed for easy detachment from the booms, when wings are deployed on the ground.  A flexible thin-film panel could be twisted over in a quick helical zipper-flip.

Or the cells might be bifacial, and left in place, if efficiency justified.
« Last Edit: 12/14/2016 07:47 pm by LMT »

Offline Robotbeat

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Re: ITS spaceship solar panels
« Reply #44 on: 11/08/2016 04:37 am »
But the ITS's solar arrays would only supply ~1/20th of the power on Mars as would be needed for refueling a single ITS.
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Offline LMT

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Re: ITS spaceship solar panels
« Reply #45 on: 11/08/2016 05:46 am »
But the ITS's solar arrays would only supply ~1/20th of the power on Mars as would be needed for refueling a single ITS.

?  The crewed ITS wouldn't be expected to power everything of course.  As for "refueling", I'd expect an unmanned ITS, such as a propellant plant, to have some custom power config.  E.g., several ring-wings stacked upstairs around the plant.  Deployed to cover the full circle around the plant, they'd produce max ~600 kW, enough to power ~500 terrestrial homes. 

Enough for a propellant plant?

Offline Robotbeat

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Re: ITS spaceship solar panels
« Reply #46 on: 11/08/2016 05:54 am »
Need about 1MW of electricity average. So about 6MW of solar.
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Offline LMT

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Re: ITS spaceship solar panels
« Reply #47 on: 11/08/2016 06:00 am »
Need about 1MW of electricity average. So about 6MW of solar.

Please give refs or calcs, to flesh out a realistic scenario.  (For propellant production, not for solar panel sunlight.)
« Last Edit: 12/14/2016 06:40 pm by LMT »

Offline Robotbeat

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Re: ITS spaceship solar panels
« Reply #48 on: 11/08/2016 07:03 am »
Need about 1MW of electricity average. So about 6MW of solar.

Please give refs or calcs, to flesh out a realistic scenario.  (For propellant production, not for solar panel sunlight.)
2000000kg of propellant with about 15MJ/kg of energy needed to produce each kg (including inefficiencies). So 3*10^13J. So in 365 days, it requires 1MW average power. If you want to wait an entire synod, you could halve that.
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Offline Llian Rhydderch

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Re: ITS spaceship solar panels
« Reply #49 on: 11/08/2016 02:18 pm »

I did some work on power and cooling for the ITS, when it was the BFS.  A bit out of date since I expected radiators in the cargo bay doors, as per the space shuttle.

Not really out of the question yet.  wstewart earlier suggested radiators that could achieve on the order of 50 W/cm2 of heat transfer, here:


Notably, recent heat pipe designs can reject spacecraft heat with a capability exceeding 50 W/cm2, which is a remarkable efficiency.  I think this frees the wing booms from that job, potentially saving much complexity in wing design.

It is within the ballpark of possibility that "doors" could open in the dorsal-side hull spine (the one that is solid white, with no PICA-X on it) of the spaceship that would expose sufficient area that thermal management might be handled there, with no need to complicate the solar panel "wings" with the radiator job.
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Offline Oersted

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Re: ITS spaceship solar panels
« Reply #50 on: 11/09/2016 08:09 pm »
Check out the DSS Roll-Out Solar Array (ROSA) which will fly in the trunk of a Dragon... - Seesm like just the right tech for the IST.

Offline envy887

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Re: ITS spaceship solar panels
« Reply #51 on: 11/22/2016 12:34 pm »

I did some work on power and cooling for the ITS, when it was the BFS.  A bit out of date since I expected radiators in the cargo bay doors, as per the space shuttle.

Not really out of the question yet.  wstewart earlier suggested radiators that could achieve on the order of 50 W/cm2 of heat transfer, here:


Notably, recent heat pipe designs can reject spacecraft heat with a capability exceeding 50 W/cm2, which is a remarkable efficiency.  I think this frees the wing booms from that job, potentially saving much complexity in wing design.
The 50 w/cm2 cited there is the heat flux through a heat pipe cross-section, not radiative heat rejection per radiator area.

Heat radiation is a function of temperature; to radiate 50 w/cm2 to a near absolute zero sink the radiator has to be over 1200 degrees C.

Offline LMT

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Re: ITS spaceship solar panels
« Reply #52 on: 11/22/2016 05:58 pm »

I did some work on power and cooling for the ITS, when it was the BFS.  A bit out of date since I expected radiators in the cargo bay doors, as per the space shuttle.

Not really out of the question yet.  LMT earlier suggested radiators that could achieve on the order of 50 W/cm2 of heat transfer, here:


Notably, recent heat pipe designs can reject spacecraft heat with a capability exceeding 50 W/cm2, which is a remarkable efficiency.  I think this frees the wing booms from that job, potentially saving much complexity in wing design.
The 50 w/cm2 cited there is the heat flux through a heat pipe cross-section, not radiative heat rejection per radiator area.

Heat radiation is a function of temperature; to radiate 50 w/cm2 to a near absolute zero sink the radiator has to be over 1200 degrees C.

Right, the pipe is not the finished panel, and 50 W/cm2 is flux measured at heat source.  Where source temperature is low, it's assumed that a heat pump increases working temperature, to use the pipe's full radiative capability.  Such a pump/pipe combo would allow many ITS hull surfaces to serve as radiators, regardless of sun orientation; as in this SSL patent:  "Spacecraft radiator system using a heat pump".

I noted heat pipe capability just to explain why I thought the huge ITS wing booms probably would not need to serve double-duty as radiators.  Agree/disagree?
« Last Edit: 12/14/2016 07:55 pm by LMT »

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