Hot answers tagged

75

+1 Good question! It's not actually gold, but I think this is a common misconception, so allow me to elaborate for a bit. The stuff that you see satellites covered in is not normal foil, its just the outer layer of so-called "Multi Layer Insulation" or MLI. That means that there are several layers of foil, each separated by a spacer, so that transfer ...


62

I've done a lot of work on this subject with researchers and engineers at JPL, NASA Langley, and NASA Ames. There are some interesting things that come out of high-fidelity CFM (Computational Fluid Mechanics) modeling of entries or re-entries, and also from flight experience. This FAA tutorial segment is a good general reference for the principles involved. ...


22

According to Wikipedia launch windows to Venus occur every 19 months. In some cases multiple successful probes were launched with the same design at the same time so I'll group those together (the Soviets launched two similar/identical missions per launch window they actually used to ensure mission success through redundancy). I'll label each mission with ...


18

Direct measurement is difficult; I've seen some optical methods used but can't put a hand on them at the moment. Here are some calculated inner and outer wall temperatures for the Space Shuttle Main Engine, a regeneratively-cooled booster engine. The X axis is axial distance from the throat. I am pleased to see that both metric and English units are provided....


16

Yes, you would like to conserve the energy, but sadly that is not possible. The problem is: The energy you have is heat. The second law of thermodynamics states that entropy always increases, and that means that while every process in the spacecraft produces heat, going in the opposite way is impossible. You can produce energy from heat if you have a ...


12

Astronaut spacesuits use gold (thin layer) Gold coating protects eyes from harmful sunlight Gold is also used by NASA in the construction of spacesuits. Because of its excellent ability to reflect infrared light while letting in visible light, astronauts’ visors have a thin layer of gold on them to protect their eyes from unfiltered sunlight. Satellites ...


11

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: 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 ...


10

Don't convert it into heat in the first place, and then don't dissipate it fast. MSL used an electromagnetic brake to slow the descent of the rover from the skycrane. It dissipated the energy into a resistor. Here, instead store the energy in a superconducting magnet. It can remain there as long as you can keep the magnet cold, and you can then either use ...


10

You are missing something basic here, which is that the Sun's corona is rather sparse. To take matters to an even greater extreme, consider the intergalactic medium. The temperature of the extremely sparse intergalactic medium can be in the hundreds of millions of kelvins. However, a macroscopic thermometer in this hot medium would not get anywhere close to ...


10

There is a fixed amount of energy which has to be dissipated. You can, to some extent, choose how fast this is done -- more air resistance (either by getting into thicker air or having a bigger surface) dissipates it faster, with higher g forces. Less air resistance dissipates it slower, but you do have to make sure to get rid of it all before you hit the ...


9

They tend to be a combination of a highly reflective material, aluminized mylar usually, with a thin mesh in between the layers. The goal is to reflect as much light as possible (specifically those wavelengths emitted by objects at human-body temperature), and keep direct contact between elements to a minimum. Wikipedia has a great picture, shown below.


8

Apparently, black was chosen despite its thermal properties. This 2005 paper was written at the end of the assessment phase where technical feasibility of the mission has been demonstrated. It shows several options were studied, including a white shield. Materials with a/e (absorption/emission constant, ed.) close to 1 could also be used. Typically ...


7

There are many ways to control the temperature of a satellite and the distribution of heat within a satellite. Often they are wrapped in multi layer insulation, which gives them their typical golden shine, or other surface treatments like white paint are applied. Other measures include retractable blinds, orienting the satellite in a specific way to the sun, ...


7

All objects in a vacuum will have a decreasing temperature, unless new heat is supplied. The reason for that is energy lost to thermal radiation, which is electromagnetic radiation carrying energy away. In fact, this is the same thing that allows the Sun to emit light even though surrounded by vacuum. The magnitude of the radiated energy is proportional to ...


7

Relevant information can be found in this patent of the company: https://www.google.com/patents/US6481670 The plan seems to be to circulate coolant in tubes positioned between the inflatable layers. The tube segment substantially enclose the spacecraft, and in particular, the critical layers that are desired to be protected. This protective barrier ...


7

The Tesla Roadster is not experiencing 250°C temperatures. This answer to another question shows that in Earth orbit it will be just over 0°C, similar to you and me: What's the typical temperature of a satellite orbiting the Earth? The key plot from that answer shows that out near Mars it will be around -80°C


6

In a vacuum, there are only two ways to get rid of the heat, radiators and sublimators. You can not simply get the energy in the heat back to useful forms like electricity, due to the laws of thermodynamics. The efficiency of both is dependent on the temperature they operate at. For radiators, we have the Stefan-Boltzmann law, that says that the power ...


6

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 ...


6

Partial answer to a very cool question! While the pun was not intended, I'll take credit for it anyway. (see also this answer) One of the functions of the nozzle† is indeed to "remove" as much of the heat as is practical and convert that kinetic energy from random to ordered motion.† Same mechanism has been hypothesized for water plumes released to space ...


5

In the general case of "spacecraft" meaning any satellite, manned or otherwise, or upper stage the hierarchy for thermal control looks like this: Passive systems materials chosen for their radiative finish (paint, mirrors etc) materials chosen for solid conductivity or insulating properties (aluminium face-skins on honeycomb panels, interface filler, CFRP ...


5

There are space radiators, and then there are space radiators: https://en.wikipedia.org/wiki/Liquid_droplet_radiator Spraying droplets of your thermal fluid through space before collecting and recirculating them effectively creates a radiator of large surface area without the mass. Plans were drawn up to fly a Liquid Droplet radiator demonstration unit on ...


5

If you want to minimize heating, you need to spend time at high altitudes (>100 km) gradually losing speed. This means you need wings to provide lift. So for now I'm going to ignore the heating issue and just look at what kind of wing you'd need. This question arrives at a wing loading of 20 kg/m2 for an aircraft that can fly at 100 km altitude at ~8 km/s. ...


5

There would be thrust but it is going to be very slight. This is basically a rocket where there is no nozzle, so looking at specific impulse the exhaust velocity would be defined by velocity of the evaporating molecules (100s of meters per second)*sin45 due to the random departure direction time the mass per second of ablation. If you wanted to improve this,...


5

New Horizon's Integrated Electronics Modules are not pressurized. The spacecraft's thermal control system works by managing radiant and conductive heat transfer, not by convection. The approach taken by New Horizons is to retain heat like a thermos bottle – New Horizons is already in the vacuum of space where no conductive and convective heat will be lost ...


5

Summary: The time will depend on how the inside of the spacecraft is insulated, but if we assume that you are in contact with the metal shell of a spacecraft similar to the lunar module (and make a lot of approximations regarding convection in the Venusian atmosphere), you will get serious burns within 15 minutes. The assumptions I make break down as the ...


4

You can infer the state of the art from the following quote from Gilmore's 2002 handbook: Most spacecraft radiators reject between 100 and 350 W of internally generated electronics waste heat per square meter. The upper end of this range is typical of a radiator that runs at a fairly high temperature (say 40°C) and experiences a relatively modest heat ...


4

Unfortunately telemetry readings aren't shown on ISSLive.com (Tristan has actually pointed out to me there is no telemetry, which to me is a surprise, but there you go). See this analysis for the ISS. It is an analysis rather than a measurement and was performed in 1997 and so take it with a pinch of salt. Headline is -100 degF (-73°C) in eclipse to +150 ...


4

It doesn't crack or break, because it's made of inorganic material. Chemist Richard Sachleben states in this article from Life Science Will SpaceX roadster survive Space that it will take a long time for 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 ...


4

The answer belies the common misconception that getting to and from space is merely a matter of going up and down through the atmosphere. At this phase of re-entry, the velocity of the spacecraft is mostly in the direction across the atmosphere, not down through the atmosphere. You can see that the hottest points on both spacecraft are actually along the ...


4

A Detra-Kemp-Riddell model for stagnation heating. Detra, R. W.; Kemp, N. H.; and Riddell, F. R.: Addendum to "Heat Transfer to Satellite Vehicles Re-entering the Atmosphere." Jet Propulsion, vol. 27, no. 12, Dec. 1957, pp. 1256-1257. published online Equation 32 (page 20) and Ref 6 in NASA TM X-2058 A General Transient Heat-Transfer Computer Program for ...


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