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The Teslarati article SpaceX’s third Block 5 rocket heads to Texas test site as launch marathon nears includes the image and caption below.

Is this an unused rocket body being transported for launch, wrapped in protective black plastic? Any reason for it to be black versus white or transparent? Would there be things that are meant to be hidden by opacity? Wouldn't heating from the hot Texas and Florida Sun be an issue with the choice of black?

enter image description here enter image description here

Images from Teslarati; click for full size view.

above left: Caption: "Falcon 9 B1047 spotted in Florida just a short trip away from Cape Canaveral, where it will likely launch Telsat 19V in mid-July. (Reddit /u/fatherofzeuss) (https://www.reddit.com/r/spacex/comments/8n950t/block_5_this_one_is_headed_south_parked_at_the/)".

right: Caption: "What is likely B1048 spotted heading to McGregor, Texas for static fire testing, June 11. (TeslaMotorsClub /u/nwdiver) (https://www.reddit.com/r/spacex/comments/8q2lkd/core_spotting_booster_seen_heading_to_mcgregor/)".

Awkward, unwieldy https links appear explicitly in the captions; I've quoted without alteration.

UPDATE: Here's a photo of a Falcon 9 wrapped tightly in black plastic and exposed to the Sun. While it may be moving and cooled by air at the time of the photograph, presumably Sandra Bullock isn't driving to keep it in constant motion at all costs.

enter image description here

From SpaceX Falcon 9 booster spied on highway as triple-satellite launch moves right

Reddit user INTAMIN1 spotted a Falcon 9 Booster Northbound between Hawthorne and Vandenberg on Jan. 22. (REDDIT /U/INTAMIN1)

EDIT: quick look to see how much heat we're talking about:

Let's do a back of the spherical cow calculation, assuming complete absorption of 3 hours of sunlight without any radiation or convective cooling (which is too extreme to be realistic) gives a temperature rise of about 100 K, assuming the good thermal conductivity of aluminum is sufficient to evenly spread the heat throughout the rocket's mass.

Conclusion: It's actually a substantial amount of heat and potential temperature rise, so the question "Why black?" is a reasonable one! 

                             3 hours  ~ 10800 s
                            3.6 x 45  ~ 162 m^2
      10800 s x 162 m^2 x 1360 W/m^2  ~  2.4 GigaJoules
                           25000 kg   ~  25000000 g aluminum
                       Specific Heat  ~  0.9 J/g K
2400000000 J/(25000000 g x 0.9 J/gK)  ~  107 K change
uhoh
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  • Perhaps they want to avoid people on the internet speculating about their rockets? :-) – Diego Sánchez Jun 14 '18 at 06:06
  • @DiegoSánchez I suppose it's possible. See photos in What support equipment is necessary to maintain a falcon 9 booster during transport after recovery? and the NYTimes article and YouTube video linked there. Maybe they're staring to keep their new Block 5 rockets "under wraps" literally. – uhoh Jun 14 '18 at 08:42
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    Black plastic foil is more resistant to UV radiation than colorless or white. – Uwe Jun 14 '18 at 10:16
  • @Uwe considering there are many kinds of plastic and many ways to add color to it, I'm sure no such generalization is possible. However, can you prove me wrong with a reference for that? – uhoh Jun 14 '18 at 10:29
  • Black cable binders may be used outdoors, white ones will get brittle very soon. – Uwe Jun 14 '18 at 10:40
  • Some information about black plastic and UV: 1, 2, 3. – Uwe Jun 14 '18 at 20:21
  • So, you've calculated the radiative heating, without calculating the radiative cooling from about three times the surface area (discounting that which faces the trailer bed –  Jun 14 '18 at 22:13
  • @JCRM that's correct. It's just a quick check to see if the amount of heat involved is in the right ballpark for the question to be worth asking. An answer might include convective cooling, thermal coupling of the plastic to the metal, maybe radiative cooling though that's probably not the major effect here, as well as points already covered. – uhoh Jun 15 '18 at 02:06

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The fabric sleeve used (not plastic) is deliberately black to increase internal temperature and with it pressure which helps maintain the stage's shape during transport (or rather, prevents it from bulging)... there's also two large compressors front and back of the transporter which do the same thing, pump air into the stage and keep it at relatively high pressure.

tl;dr the first stage, when empty, isn't strong enough to support its own weight and lateral forces during transport as it's designed for structural loads along its long axis.

This works best in direct sunlight, obviously, which is when compressors will have the hardest time. And even in cloud it will work well.

Interestingly, @Hobbes also mentions this pressurisation in his Aug 2015 answer but I can't find if @kimholder actually did ask the follow up question.

Rory Alsop
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  • And a clouded sky stops the transport waiting for sunshine? If there are compressors to keep pressure high, why use black foil to increase the temperature and pressure only under intensive sunshine? – Uwe Jun 14 '18 at 21:05
  • This makes a lot of sense, but I'd love to see a reference. – Organic Marble Jun 14 '18 at 23:14
  • +1 This is a really interesting point! The flying noodle monicker for a design necessarily long and thin for transport on a wide variety of US highways is a real thing! We'd have to establish that unlike what's shown in these photos, black plastic was used consistently, both before and after flight for any rocket that might be used again. – uhoh Jun 15 '18 at 02:14
  • I mentioned pressurization there in reference to the Atlas Centaur stage. AFAIK, the Falcon uses flight pressurization, ie it's designed to be transported without pressurization, but can't withstand flight loads without pressurization. – Hobbes Jun 15 '18 at 07:42
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    If the F9 is pressurized, the black foil will reduce the load on the compressor but the compressor will have enough capacity to keep up even at night. Compressor loads won't be high because the tanks are airtight. – Hobbes Jun 15 '18 at 07:43
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    references for flight pressurization in https://space.stackexchange.com/questions/18332/is-the-pressurization-of-propellant-tanks-necessary-for-structural-integrity/18349#18349 – Hobbes Jun 15 '18 at 07:51
  • @Hobbes that's one of my favorite answers, thanks! – uhoh Jul 10 '18 at 01:51
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They have been wrapping the boosters in transport (and second stages, though those are smaller and thus rarely noticed by passerbys) all along.

The question, is this a booster being transported for launch is easy to answer. It is on its way for testing in McGregor, before being then shipped to a launch site. (The article speculates this is core 1048 and it is assigned to Vandenberg to launch an Iridium mission in July as its first mission).

All the pictures I have seen until now have shown the booster wrapped in black, the white front bit is new in this one.

As for the temperature, recall that these stages launch to 60+ miles, and reenter, so they experience some mighty high heat loads, are covered in heat insulation so the local heat, of a black wrap should be inconsequential.

Looks like the white-caps are possibly the new way of the world. The 1050 core was caught on the road with white caps on the end.

Core 1050 - 4th B5 core - in transit, white capped

geoffc
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  • They are also filled with cryogenic coolant on the inside when they do that, and various systems are running to deal with issues. These look sealed up and powered off, unless there's a hidden air conditioner. Something that's black with no ventilation can get pretty hot, but it's possible thermal inertia moderates any heating in this case. – uhoh Jun 14 '18 at 10:13
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    When they land they are empty for the most part. You might be asking about presurization like an older Atlas balloon body needed, but Falcon 9 does not need that to support its own weight. – geoffc Jun 14 '18 at 13:42
  • Cold is cold. 100 tons of LOX at it's bp is the same temperature as 1 ton of LOX, and I'm pretty sure they have some LOX up until the last second, for successful landings at least. Temperature of the RP-1 is a different matter. – uhoh Jun 14 '18 at 14:30
  • added photo to question, no "white cap" if I understand what that refers to. I'm not sure of the significance of it though. – uhoh Jan 28 '19 at 04:00
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Let's apply Occam's Razor:

The plastic is there to protect the stage against the elements (rain, sand, dirt blowing around). Black plastic is easy and cheap to make (see bin liners).

The number of times a non-wrapped stage has been photographed makes "they want things to be hidden" an unlikely reason to wrap the stage.

A quick estimate of the heat load: let's look at the temperature inside a closed car on a sunny day. That reaches a temperature of 27 ºC (50 ºF) above ambient.

Hobbes
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  • I'm not sure if you've had any personal experience being wrapped in black plastic near the Tropic of Cancer in June, but it can probably get quite toasty. So had he lived in Florida or Texas, black would not be the first color that Occam would reach for in the summer. – uhoh Jun 14 '18 at 11:39
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    The heat load on the stage will be far lower during transport in black plastic than during launch and reentry. – Hobbes Jun 14 '18 at 12:05
  • During reentry the rocket is also filled with tons of cryogenic LOX, and there may be additional active cooling. Further, Occam asks "Does the rocket spend all afternoon reentering, or is heating only matter of minutes?" – uhoh Jun 14 '18 at 12:08
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    Inert rocket = aluminium and semiconductors with critical temperatures above 200 °C. Temperature in black plastic: 70°C. – Hobbes Jun 14 '18 at 12:36
  • I've never seen a lithium battery or an electrolytic capacitor happy at 200 °C Rockets have lots of parts. But an answer based on poor thermal coupling between overwrap and the rocket body plus thermal inertia might be good (the logic behind the 70°C) – uhoh Jun 14 '18 at 12:45
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    There's some evidence that the temperature caused by the black plastic is within the spacecraft's limits - they use it. Without apparent issues. Debating whether it's within limits when it's clearly within limits seems silly. SpaceX is surely capable of using white plastic if they needed it. – ceejayoz Jun 14 '18 at 16:13
  • @ceejayoz that makes sense, which is why nobody has debated that. I've added a quick estimate to the question showing that this is potentially a substantial temperature rise, and I don't think it's the cost of white plastic that would lead them to opt for lower cost black plastic. – uhoh Jun 14 '18 at 18:37
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    It may be a substantial temperature rise, but the fact that they haven't had rockets explode from an overheated part or re-engineered the material would seem to indicate it's not a significant temperature rise. – ceejayoz Jun 14 '18 at 18:38
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    just to point out, from the article, it isn't plastic - it's a fabric sleeve. – Rory Alsop Jun 15 '18 at 07:02
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    @uhoh I doubt they are using "laptop" lithium batteries. There are downhole lithium batteries (used in drilling) that routinely take 200C, and are shock and vibration resistant. https://excellbattery.com/industries/oil-industry/ As for capacitors, again they can be built to accommodate a wide range of environments. Ceramic capacitors can take more heat than the average capacitor (125C) and high temp ceramic capacitors operate easily in the 200C range. https://www.ttiinc.com/content/ttiinc/en/resources/marketeye/categories/new-technology/me-slovick-20140612.html – Edwin Buck Jul 09 '18 at 04:01
  • @EdwinBuck thanks for the info! The point of that comment was that silicon is not necessarily the only temperature sensitive aspect of electronics, not that it would be impossible. It's good for me to be reminded that there are other kinds of lithium batteries besides lithium-ion, and that just because the CEOs are the the same, a Falcon 9 rocket is not necessarily filled with liquid-cooled 18650 cells à la Tesla. As for electrolytic capacitors (or supercaps) with hundreds or thousands of μF for power filtering, there may not be ceramic replacements. This has got me thinking... – uhoh Jul 09 '18 at 04:56
  • @EdwinBuck ...and that often leads to a new question. In this case I've just asked Is there anything like a standard for maximum temperature for mission-critical electronics in spacecraft? An older and slightly related electronic component question is Is there a space-certification procedure used by commercial spacecraft manufactures for electronic components? – uhoh Jul 09 '18 at 05:11
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    @uhoh Having known a lot of engineers, and having learned a lot from them, their answers range from. "Yes", to "it depends on how much money you have", to the very rare "no". Seeing that we can launch computers into space (and have been doing so for nearly 50 years now) I imagine that most of the component answers are in the "yes, if you have enough money" and that all of the systems are designed for shock / heat tolerances which are within the estimated designs of the rest of the rocket. – Edwin Buck Jul 09 '18 at 21:04