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tahanson43206

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Registered: 2018-04-27

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Companion: Tutorial on the Nature of Heat as Applied to a Heat Shield

This topic is offered for contributions to all present and future members who would like to add to the primary topic, offer corrections, to to suggest related but perhaps slightly off topic readings.

This topic is a companion to the primary topic: Tutorial on the Nature of Heat as Applied to a Heat Shield

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tahanson43206

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Registered: 2018-04-27

Posts: 19,389

Re: Companion: Tutorial on the Nature of Heat as Applied to a Heat Shield

For GW Johnson re #221

Thank you for your continued interest in this topic!  I have started an investigation of the nature of quantum level interactions between gas particles and solid (bound by cohesive electron bonds) matter.  I've been too busy with other interests/duties to pursue it, but it is there waiting for someone to invest the time that will be needed.

The object of ** that ** topic is to try to understand (a) why elastic particles (molecules) bounce away from solid molecules instead of sticking to them, (b) to try to imagine a way to capture them.  It ** is ** intuitively obvious that since electrons repel each other, electron shells of atoms would repel each other, unless an atom has enough momentum to overcome the objections of the electron shells and penetrate far enough to dislodge the target atom from the matrix of which it is apart, as happens when solid material (ie, heatshield) is exposed to gas molecules at sufficiently high speed.

The Skylon approach ** appears ** to be to cool the metal of the funnel collecting gases so the arriving molecules do not dislodge the metal and (b) to absorb energy from the elastic molecules as they bounce around frantically in the confines of the tunnel where they are being collected.

The ** ideal ** situation (possibly not available in the ** real ** Universe) is for the gas molecules to quietly accept capture by the arriving heat shield, to accept acceleration to the velocity of the heat shield without frantically trying to escape, and to contribute to the momentum of the heatshield vehicle by decreasing that momentum by the amount of the mass of the molecule.

To my knowledge there is ** no ** way to achieve that ideal, but I think the topic is worth exploring.

If the ideal could be achieved, then the molecules in the path of the vehicle would pile up in front of it in an accumulating stack until the vehicle releases them, at which point they would have a velocity lower than was the case when the descending vehicle first showed up.

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tahanson43206

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Registered: 2018-04-27

Posts: 19,389

Re: Companion: Tutorial on the Nature of Heat as Applied to a Heat Shield

The analogy of a baseball caught in a mitt is the only model I have (at the moment) to try to envision a way/means/method of capturing a molecule of CO2 and preventing it from bouncing away, as is the case at present, in ** all ** landing/deceleration systems except for the Skylon concept, which I don't know much about.

A baseball has ** some ** elastic properties, which is illustrated by it's ability to take the impulse from a bat and subsequently remain intact during significant acceleration in a direction opposite to its original path from the pitcher.  A CO2 molecule has much superior elastic properties.  Those properties may even be as close to perfection as Nature allows, although there ** are ** limits.  At some point (well characterized by investigations of physics) the wall of resilience of electron shells is overcome by force greater than it's defenses, and the nucleus finds itself engaged in whatever activity occurs at that point.

However, the mitt (and it's support system) are able to accept the mass/momentum of the arriving baseball, absorb that energy without deforming, and gradually bring the baseball to a zero velocity with respect to the mitt.

What I'm looking for may not be available in Nature, but it is possible to imagine what it might "look" like ...

A capture mechanism would necessarily consist of more than a few atoms arranged for the purpose of trapping an arriving CO2 molecules.

An individual CO2 molecule has a mass/momentum that in itself is not very large.  It is the SUM of all the CO2 molecules in the path of a heat shield, or in the path of a collection funnel, that does observable damage to an arriving object.  Individual CO2 molecules can (and do) penetrate into the solid matrix of whatever substance is presented by the first layer of the arriving object, and even though the individual CO2 molecules may not be damaged by the encounter, they certainly can (and do) disrupt electron bonds between atoms that make up the solid surface of the arriving object.

A "mitt" for a CO2 molecule would be able to accept the molecule in an entrance, (somehow) deal with the momentum of the molecule to accelerate it to the velocity of the arriving vessel, and ** then ** trap it so it doesn't bounce away until the acceleration is complete.  At that point the CO2 molecule can be released to the "passenger" compartment (whatever that is) because it has been tamed and will no longer present a threat.

The Skylon cooling system ** seems ** to have an effect similar to that described above, but the molecules of air are not "captured" individually. They ** are ** (somehow) accelerated to the velocity (or near to the velocity) of the craft so they can be used as part of a subsequent combustion process.

(th)

SpaceNut

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From: New Hampshire

Registered: 2004-07-22

Posts: 29,431

Re: Companion: Tutorial on the Nature of Heat as Applied to a Heat Shield

The heat shield of pica x for a mars entry is of higher speed as compared to the take off to orbit cooling by the skylon system.
The shield burns off and becomes a hot plasma wake that passes around the ships capsule shape. Other than the shield material of glass we are left to that type since the glass ceramics are quite heavy.

Edit
Keep in mind that the co2 atmosphere is disassociated by the heat of friction such that the bonds of the co2 is being split as moxie has shown works at just 800C' approximate.

peak heat shield temperatures https://newscenter.lbl.gov/2017/02/22/b … rs-mission

During an actual atmospheric entry at Mars, there is substantial heat load on the shielding material, with surface temperatures approaching 4,000 degrees Fahrenheit.

why can we not work in one unit type?

https://www.bbc.com/news/science-environment-53129281

During this stage, its heat shield had to endure temperatures as high as 2,100C (3,800F). When it was about 11km (7mi) above the ground,

https://mars.nasa.gov/news/8859/sensors … tmosphere/

The data will show the increase in heating and pressure as the entry vehicle passes through the atmosphere of Mars. MEDLI2 will keep collecting data after the peak heating (maximum heat shield surface temperature of about 2,300 to 2,400 degrees Fahrenheit, or 1,200 to 1,300 degrees Celsius) …

tahanson43206

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Registered: 2018-04-27

Posts: 19,389

Re: Companion: Tutorial on the Nature of Heat as Applied to a Heat Shield

For SpaceNut re #4

Thank you for posting in the Companion topic ...

A discussion of traditional mass flows is valuable for contrast with the stated purpose of the Nature of Heat topic.

GW Johnson has ** just ** published a thorough analysis of traditional engineering concepts of gas flows encountered by re-entry vehicles.

Since ** this ** topic (and the primary member of the two-topic set) is about individual atoms/molecules, the traditional observation of mass flows around an object traveling through an atmosphere is highly relevant, because it shows the nature of the problem to be solved.

In his long post in the Ballistic Delivery topic, GW Johnson included an observation that the bow wave ahead of a heat shield becomes (or at least ** may ** become) ionized.  That tip may prove useful, as this topic attempts to address the problem of capturing individual molecules so they don't escape and contribute to disorder.  Disorder is what we observe when we watch a meteor (or a spacecraft) streak across the sky.

***
To your post ... thanks for the contrast of velocity for skylon in a flight to orbit compared to what that vehicle would be dealing with upon return from orbit, if it ever gets there.  In another topic, if memory serves, there is discussion that Skylon is intended to use purely rocket propulsion after it rises above the regions of the atmosphere where collecting oxygen makes sense.

***
To all ... if there is a reader of this forum who would care to make (or attempt) a contribution to this topic, or to the primary, please contact NewMarsMember * gmail.com.   This set of topics in intended to deal with a capability of physics >> engineering that does not exist, and which may in fact not be possible.

In that sense, it is patterned after the exploratory topics created by JoshNH4H while he was active with the forum.

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SpaceNut

Administrator

From: New Hampshire

Registered: 2004-07-22

Posts: 29,431

Re: Companion: Tutorial on the Nature of Heat as Applied to a Heat Shield

The wiki page that goes with this topic can make use of the information pertaining to the mars landers and rovers as they have quite a bit in them with regards to the geometry shape and other characteristics that are needed to safely land man....or goods unharmed.

First posts in the companion should point to the wiki development page that you, tahanson43206 own until further notice by you.... as well as the wiki first post should point to the companion topic that you want ideas and information posted to....