# Why are these Falcon 9 1st stage bodies (apparently) wrapped in black plastic for transport?

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?

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.

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

• Perhaps they want to avoid people on the internet speculating about their rockets? :-) Jun 14 '18 at 6:06
• @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 8:42
• 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

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.

• 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. 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 2:14
• 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. Jun 15 '18 at 7:43
• references for flight pressurization in space.stackexchange.com/questions/18332/… Jun 15 '18 at 7:51

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.

• 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
• 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. 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 4:00

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.

• The heat load on the stage will be far lower during transport in black plastic than during launch and reentry. Jun 14 '18 at 12:05
• Inert rocket = aluminium and semiconductors with critical temperatures above 200 °C. Temperature in black plastic: 70°C. Jun 14 '18 at 12:36
• 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. Jun 14 '18 at 16:13
• 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. Jun 14 '18 at 18:38
• just to point out, from the article, it isn't plastic - it's a fabric sleeve. Jun 15 '18 at 7:02