7
$\begingroup$

Tesla's Roadster is somewhere above us taking sunlight directly part of the time, then very cold on the next half of the orbit. Or when it rolls, one side gets hot, the other is cold.

Why don't the panels and other sensitive plastic things melt? Or at least degrade?

$\endgroup$
  • $\begingroup$ As for degradation: yes, that will probably happen over time. But not so much due to temperature as to ionising radiation. $\endgroup$ – MichaelK Feb 7 '18 at 13:35
  • $\begingroup$ Plastic will degrade much faster than on Earth. There is very intensive UV light not filtered by the atmosphere of the Earth. And the Sun shines 24 hours a day. Temperature cycles between hot and cold side will degrade the car too. $\endgroup$ – Uwe Feb 7 '18 at 13:51
  • $\begingroup$ This is not a primary technical source, but at least a discussion of some of the materials on Roadster versus what's used in real spacecraft: newatlas.com/tesla-roadster-fate/53317 $\endgroup$ – uhoh Feb 10 '18 at 7:51
  • $\begingroup$ Related What is that haze on Starman's windshield? $\endgroup$ – James Jenkins Feb 13 '18 at 18:19
10
$\begingroup$

Not close enough to the Sun

The Roadster's orbit has a perihelion (closest distance to the Sun) of 0.98 AU, that is to say only very slightly closer than Earth orbit.

From Elon Musk's Twitter:

enter image description here

At Earth Orbit, the influx of energy from the Sun is about 1300 Watts per square meter. This is not far from the maximum we can have on the Earth surface. The atmosphere does dampen a bit, but at most we can get 1000 W per square meter at the equator when the Sun is at zenith.

The temperature of an object depends the flow of heat to it, and the flow of heat from it. If there is more heat coming in than is going out, the object heats up. When more heat is going out than is coming in, the object cools down. When these things are in balance, the temperature is stable.

On Earth, there are (chiefly) two things that brings heat to an object: the convection/conduction of the atmosphere, and radiation from the Sun. The atmosphere is a huge contributor there, at a balmy 300+ K in regions where we would even begin to consider melting plastics on an automobile. So the "baseline temperature" of an object in the Earth's atmosphere is 300 K.

Add to that another 1000 Watts per square meter from the Sun and you can have so much energy going into an object that it heats up and can eventually achieve temperatures that can melt plastic in/on a car. This is especially so if it is a coupé car, that traps warm atmosphere inside.

But in space, you do not have that atmosphere, and this was not a coupé but an open top car. Hence the baseline temperature of the car when in space is not 300+ K but 0 K.

enter image description here

Note the distinct lack of an airtight enclosure around any plastic details

So while the second contributing factor — solar radiation — is indeed 30% higher in space than it is on Earth, the lack of the first one — a warming atmosphere — completely negates that. The car will most likely freeze over time.

As for degradation: yes, that will happen over time. But not so much due to temperature as to ionising radiation. We are fortunate here on Earth to be living under a protective blanket that is the atmosphere that keeps away most of such nastiness. In space... no such luck. As the Roadster coasted around in the Van Allen belts for a few hours before being sent off for good, some people reported already seeing radiation damage on the windscreen, I assume some "yellowing" of the plastic laminate.

$\endgroup$
  • 1
    $\begingroup$ A warming atmosphere is not needed for an object in space to be heated by the intensive sunlight. The Moon has no atmosphere, its surface gets hot during the Moon day and cold during the night. $\endgroup$ – Uwe Feb 7 '18 at 13:44
  • 1
    $\begingroup$ @Uwe Yes but for this we must consider the convection of heat from the ground below the surface that provides a "baseline" for the Moon's surface temperature in the same way that the atmosphere does for the Roadster on Earth. The Moon's surface temperature peeks at 127°C and dips to -173°C. So the median temperature is about -20°C, and if we ignore the Moon's hot core of about 1600-1700 K, we can assume that in this neighbourhood is where the balance point is, where the Moon's blackbody radiation balances the Sun's radiation. $\endgroup$ – MichaelK Feb 7 '18 at 13:54
  • 1
    $\begingroup$ Heat transfer in fluids or gases is called convection, in solids it is called conduction. In the vacuum of space heat is transfered only by radiation. There are no liquids or gases within the ground below the surface of the Moon. The hot core of the Moon might be partially liquid. $\endgroup$ – Uwe Feb 7 '18 at 14:52
  • 1
    $\begingroup$ What does "The car will most likely freeze over time." mean? The Roadster is not currently a liquid, so... Also, re "...s to ionising radiation...", significant degradation will happen due to non-ionizing longer UV radiation from the Sun as well. The Sun has a nasty flux of UV, and much of it is non-ionizing yet really rough on polymers. $\endgroup$ – uhoh Feb 10 '18 at 7:58
  • 2
    $\begingroup$ @uhoh "Freeze" as in "become a lot colder than it is now". And regarding degradation... yes, that is mentioned in the last paragraph. $\endgroup$ – MichaelK Feb 10 '18 at 9:29
6
$\begingroup$

The roadster will radiate the additional heat away.

Radiation is proportional to the fourth power of the temperature, so a slight increase in temperature massively increases the amount of outgoing heat radiation, and (with no atmosphere) there is nothing to stop it just disappearing into space.

The melting point of plastic varies a lot, but I would be surprised if the plastic in cars melted at less than 200°C. At that temperature, a back-of-the-envelope calculation would show 6 or 7 times the outgoing radiation than at room temperature, whereas the radiation coming in is only slightly more than the maximum on earth.

In addition, part of the car will be in shadow and not receiving any direct heat, but still radiating away heat that has conducted from other parts of the car.

So, in summary, the heat radiated will exceed the heat received before it gets hot enough to melt.

$\endgroup$
  • $\begingroup$ Would you mind posting your back of the envelope calculation? Thanks. $\endgroup$ – ReactingToAngularVues Feb 14 '18 at 10:38
  • 1
    $\begingroup$ Room temperature = 293K, 200°C = 493K. 493^4/293^4 = 6.79. I am assuming all other components of the equation are constants. But I am not an expert on this, so I welcome any corrections, though I think the general argument is correct and I didn't mean to imply the calculation was exact (hence, the envelope). $\endgroup$ – rghome Feb 14 '18 at 10:49
3
$\begingroup$

The Tesla will most definitely degrade significantly on this mission. It is not designed in any way shape or form for this sort of mission.

SpaceX/Musk know this, and completely admit it was just a silly thing to launch for the sake of its silliness.

Musk in the post mission press conference said he expected it to not last very long.

People are already reporting that the windshield was showing damage, before the camera shut off.

$\endgroup$
2
$\begingroup$
  1. The Roaster is some 94M miles from the Sun. For contrast, Mercury is some 35M miles away from the Sun (almost 3x the distance away)
  2. There's nothing close to the Tesla to retain any heat. Mercury's maximum temperature is about 800F/425C. The Roadster shouldn't get even remotely that close, and even if it did, nothing would hold the heat near to the Roadster
$\endgroup$
  • 2
    $\begingroup$ Space is not cold. Temperature is a quality of matter. Space is the (near) complete absence of matter. Hence space has no temperature. And while there are tiny amounts of matter in space — the Interplanetary Medium — it is not dense enough to be of significance for this question. $\endgroup$ – MichaelK Feb 7 '18 at 13:34
1
$\begingroup$

The car will degrade (not melt),.. slowly. As stated in other answers, the roadster won't get close enough to the Sun to cause it to melt, however, it will in fact decay. Chemist Richard Sachleben states in this article from Life Science Radiation will Tear Roadster Apart that it will take a long time for parts like the windshield to discolor and come apart relative to any organic material in the car (leather seats, rubber tires) and will only start to do so as the plastic in the windshield starts to decay. He believes the organics will last around a year, but gives no specific guess on the glass. He believes the car will continue to decay until all the is left is the metal frame and probably the electric motor.

$\endgroup$
-5
$\begingroup$

Look, as far as I know, he should be melting. As much as it is "distant" from the sun, when there is more heat coming in than going out, warming occurs. and it does not automatically cool on the "shadow" side, because the absence of atmosphere causes the only possible heat loss (in the vacuum) to be by radiation; this is the same loss of heat that an ideal thermal bottle would lose, a thermos bottle in the earth can hold the temperature for days because it isolates the contact between the hot part with the cold part (atmosphere or something with a lower temperature) , in space there are no molecules to be the "cold part" so the shadow does not cool, it just "stops heating" ... until the radiation decay of the material gradually lose heat (which takes a lot of time).

Still the absurdity that "shadow cools in space" would create another problem, if a material does thermal expansion on one side, and contraction on another, it cracks, breaks, etc ...

$\endgroup$
  • 1
    $\begingroup$ Both of your basic assertions are correct in a qualitative sense -- thermoses do work mostly that way, and differential heating can cause damage -- but in practice neither is quite as dramatic as you're supposing. Thermoses need to not only be vacuum insulated, but also mirror-lined to stop radiation as well. $\endgroup$ – Nathan Tuggy Feb 10 '18 at 6:35
  • $\begingroup$ this topic has aroused a lot of controversy, we already have themes about it even on youtube. youtube.com/watch?v=FIjNzHDFHpA in this video, the point that I find interesting is that of mr. of the nasa that is explaining that some pieces of metal can reach 2000 ° ... even if we try to round off, ignore some factors, etc ... in the earth where the intensity of solar light (and radiation) is almost all absorbed by the atmosphere , we still have cars that have their melted panel left in the sun of a simple beach, nor do they have to be in the desert sun. $\endgroup$ – Pedro Jorge Feb 10 '18 at 14:23
  • 1
    $\begingroup$ The atmosphere does not absorb "almost all" the sun's intensity. It absorbs less than a quarter. Giving great weight to mistaken assumptions like that and ignoring other factors is bound to give wildly inaccurate results. $\endgroup$ – Nathan Tuggy Feb 10 '18 at 17:41
  • 2
    $\begingroup$ A thermos bottle has a silvered coat on the inside to reflect the heat back in, which helps it stays warm. The roadster will radiate heat away and the level of radiation rises with the fourth power of temperature. Plastic won't melt until 200 degrees C, at which point it will be radiating away 6 or 7 times the heat it would radiate at room temperature, while receiving only slightly more than it would on earth. So it will get no where close to melting. $\endgroup$ – rghome Feb 14 '18 at 9:45

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.