Talk:Atmospheric reentry

From Wikipedia, the free encyclopedia

You have new messages (last change).
WikiProject Space
Portal:Space
 Space Portal
This article is within the scope of WikiProject Space.
B This article has been rated as B-Class on the assessment scale.
Related projects:
WikiProject Space exploration WikiProject Space exploration Space exploration-Importance: High

This article has been rated but has no comments. If appropriate, please review the article and leave comments here to identify the strengths and weaknesses of the article and what work it will need.
Former FA This article is a former featured article candidate. Please view its sub-page to see why the nomination failed. For older candidates, please check the archive.

Contents

[edit] Sphere/Cone vs Blunt Body

One comment I'd like to make... the current (2006-01-16) article seems to conflate sphere-cone and blunt body type reentry vehicle shapes, which isn't entirely accurate based on the common usage. There are really three variations here... sphere-cone, with the sphere having a large radius compared to the base radius (0.5 or greater ratio); blunt body, with a smaller nose radius than that, and with a large body angle (45 deg or greater); and conical, with a smaller nose radius than that (typically 0.1 or less), and a small body angle (typically around 20 degrees). The defining examples would be say a Discovery film return capsule for Sphere-Cone, oh... Viking, say for Blunt Body, and any modern ICBM RV for Conical.

The article has improved tons over the last couple of months, and that's much appreciated, but the more we can do the better 8-)

Now back to Acusil-I, writing some 6 DOF entry code, and International Space Station visiting vehicles specs. Groan. Georgewilliamherbert 07:30, 16 January 2006 (UTC)

You're point about blunt bodies is well made. I need to make it clear that there are two classes of entry vehicles, i.e. military RVs and space exploration entry vehicles. The concept of a blunt body for a military RV was abandoned with the Mark-2 RV. Carbon phenolic nose tips made high ballistic coefficient RVs practical. The faster transit time through the atmosphere made RVs more difficult targets for ABMs.

Egg plant 17:46, 17 January 2006 (UTC)

I'm not sure that all earth atmospheric re-entrys heat up to 7800 K. The space shuttle can only take 2300 F on the most heat resistant parts. There has got to be an equation here with the surface area, weight, and speed . cc

Hi. For your information, you can sign comments by typing four ~ characters in a row without any spaces.
The great innovation behind blunt reentry vehicles in the 1950s was that by making it blunt, the shockwave and peak heat are pushed back away from the skin of the vehicle. Since they aren't in direct contact, the actual heating of the vehicle is lessened. Most of the heat energy stays in the shocked gas that just moves around the vehicle, so the heat is mostly just dissipated into the atmosphere. If it wasn't, the vehicles would all melt as they were coming back in. Georgewilliamherbert 03:00, 29 January 2006 (UTC)
Thanks 24.137.78.34 16:15, 29 January 2006 (UTC)
George, I reworded your above explanation and included it in the section about blunt body theory. Egg plant 17:13, 16 February 2006 (UTC)


[edit] RVs in current times

~~MV~~

The RVs of today's nuclear weapons (Minutemen, SLBMS) seem to use ablative TPS. Were the heat sink types abandoned as well as the blunt body shape with the early RVs? It could be pointed out in contrasting military Rvs to non-military space vehicles.

Yes, the heat sinks were abandoned. In terms of energy absorbed or redirected per unit mass of thermal protection system, the ablative options are superior to any of the alternatives. Reusable lightweight TPS is heavier than ablatives, and heat sinks are considerably heavier. Ablatives also can deal with higher heat fluxes. The older blunt body RVs slowed down a lot during their reentry; modern ones stay hypersonic down to ground level, to improve accuracy and make interception harder, and going mach (many) at sea level is incredibly high heat flux. Georgewilliamherbert 19:03, 4 February 2006 (UTC)
I've never worked on military RVs and don't have access to classified information. However reports concerning the Mk-6 and Titan-II have been declassified. From those reports it is possible to reconstruct the trajectory of the Mk-6 to the altitude of its fuze setting. The speed of the Mk-6 at that altitude was 560 m/sec or Mach = 1.7 .
There is a movie floating around the web showing RVs from a Peacekeeper missile coming into Kwajalein. The RVs were white hot but looked like they were going low supersonic. I don't have a clue how they would fuze the nuclear warheads in an RV. The fuze would have to be very reliable but not spoofed by the significant G forces experienced by the RV or by buffetting and over pressure from an ABM near miss. A radar altimeter based fuze would not work if the RV's shocklayer was ionized. I see the technological limitations of the fuze forcing the RV to be low supersonic when it reached its target altitude.
Egg plant 00:51, 12 February 2006 (UTC)

~~MV~~

If I have understood your explanation correctly, heatsinks and radiative cooling could not be even low supersonic and slowed down greatly during re-entry.The ablation type is the only TPS that can protect the bomb can effectively and keep the speed supersonic or over Mach 1.2,making it superior in accuracy to heatsinks or other form of TPS, therefore its use in modern RVs such as Minutemen and Tridents.

Did I get that right?

[edit] RV shapes and Ablative materials

~~MV~~

I think the comment mentioned about RV's shapes nowadays is well made. The current RVs as the ones present in the minutemen and trident missiles are conical in shape, not quite a sphere-cone. Could I make a change in this mention and probably an specification that current military RVs are ablative types?

The article also seems to hint that ablative materials are not metals, but instead based on carbon materials. Is there a reason why the ablative materials of modern RVs (as minutemen and trident missiles) are not metals? Or is the weight of the metals the only reson why they are not used as ablative materials?

to be a good ablative material, it needs to burn or ablate...metals do not behave this way...they just heat up.Anlace 06:09, 7 February 2006 (UTC)

Modern RVs as used in the Minuteman and Trident missiles are sphere-cones with small nose radii. Carbon-phenolic or carbon-carbon is typically used for the nose tips because they get really hot (convective heat flux scales with the reciprocal of the square root of nose radius).
We take carbon for granted because it's so common (carbon is a major component of our bodies). However carbon is the most refractory substance in the universe. Carbon has a higher melting point than tungsten. Normally carbon never gets a chance to melt because it burns before it reaches its melting temperature which is also a good thing if carbon is being used as an ablator.
Egg plant 05:43, 10 February 2006 (UTC)
There's also been some work with low-regression stable refractory metal tips, some of which have some slight porosity and an ablative filler (or small holes drilled and an ablator inserted). The tip ablating slightly unevenly can otherwise cause slight flightpath changes. That seems to be an advance in reducing accuracy dispersion down into the 100m range. Georgewilliamherbert 06:01, 10 February 2006 (UTC)

[edit] Disambiguation and bypassing redirects

Hi there, Variable. It seems you and I disagree on whether the link to Reentrant dysrhythmia (which is a subtopic redirect page) should be bypassed by linking to Cardiac arrhythmia directly. While bypassing redirects is a general waste of time anyway (see Don't fix redirects that aren't broken, Can/should redirects be cleaned up?, and About fixing directs if you're not convinced), subtopic redirects should never be bypassed since they will eventually be fleshed out into real articles. There are several reasons for this, not the least of which is that it creates a great deal of work for us later: when the subtopic redirect is replaced with real content, every link that was bypassed to point to the main topic will have to be updated to point to the original subtopic page.

So I've replaced the bypassed link once again with a link to the subtopic redirect, i.e. Reentrant dysrhythmia. If after you've read the pages I referenced above, you still feel compelled to bypass the redirect, please discuss it before reverting my change. Thanks and best wishes, David Iberri (talk) 00:31, 16 February 2006 (UTC)

This is not necessarily saving us work later, given that Reentrant dysrhythmia is not an article on its own and may, or may not, ever become one, and that even if it does the redirect will likely be removed altogether as it will likely result in reentry becoming a disambiguation page. That is, either way it will have to be altered on this page once the article for Reentrant dysrhythmia is written, as atmospheric reentry is not by far the most common meaning of reentry (this, of course, is IMHO). Therefore, I thought (and think) it better to have the redirect here be directly to the target page in the case that its ever moved (ICD diagnoses might come under different names in future revisions, for example). In short, I don't disagree with the general principal that it's not important to fix redirects that aren't "broken", but in the case of disambiguation link to a subtopic it's a bit different because the creation of the article will change the dab link anyway. siafu 01:26, 16 February 2006 (UTC)
I know I'm biased, but I think that atmospheric reentry is by far the most common meaning of reentry... Georgewilliamherbert 04:31, 16 February 2006 (UTC)
Given that the vast majority of topics for which an encyclopedic article could be written generally do receive entries on Wikipedia, it's reasonable to assume Reentrant dysrhythmia will one day have its own article. It's therefore natural to treat a link to Reentrant dysrhythmia or any other subtopic redirect as a bona fide article. So if you feel that Reentry should be a disambig page, then it would be appropriate to turn it into one now, listing Atmospheric reentry and Reentrant dysrhythmia for starters. I would have done that originally except that I think atmospheric reentry is the more common meaning of the term reentry. Cheers, David Iberri (talk) 04:56, 16 February 2006 (UTC)
I've discussed this with George Herbert. Following his advice, I'm not going to take any further action concerning this disambiguation. Based on what George tells me, there is no attractive way to disambiguate in the Wikipedia format. Egg plant 16:39, 16 February 2006 (UTC)
Most topics that could be written generally have not received entries on wikipedia, and given the nature of the advance of human knowledge it is likely to stay that way. It is not useful to assume that an article will "one day" be written simply because it could; wikipedia is not being prepped to be used by readers "one day" off in the future-- it is being used now. It could be months, years, or eternity before Reentrant dysrhythmia is turned into an article (unless you know something I don't there), so all else being equal, the link should put the article its linking to directly and not through a redirect because (and it happens) articles do sometimes move around, leaving redirects behind. The original page you pointed to in this argument, however, says: Some editors are under the mistaken impression that fixing such links improves the capacity of the Wikipedia servers. But because editing a page is thousands of times more expensive for the servers than following a redirect, the opposite is actually true. Since not only was the change reverted, but we've gone ahead and posted multiple times here on the talk page, this is all essentially moot. siafu 19:36, 16 February 2006 (UTC)

[edit] Sphere-cone paragraph

~~MV~~

It is mentioned in this paragraph that the MK-2 Rv used a radiatively cooled TPS based upon a metallic heat shield, but the Mk-2 used the heat-sink concept. It seems that unlike the ablative or thermal soak TPS, the heat-sink does not work as a protector of heat to the aeorshell or the payload, it only conducts the heat away form the shell of the RV. Was the mention of a metallic heatshield referring to the heatsink or does the heatsink concept also have a heatshield besides the copper heatsink?

FYI, You can sign your comments by typing four ~ characters in a row with no spaces...
There was usually some internal insulation between the heatsink TPS and the main body of the entry vehicle; keeping that heat out of the main body of the vehicle was the point. There usually isn't any sort of external coating or heatshield; the heatsink (copper, beryllium copper) is usually exposed straight to the entry gasflow, and though you hope and design that the shock will carry most of the heat away and around, dissipating in the atmosphere, radiant heating and residual frictional and hot gas contact heating will directly heat up the heatsink material.
There's no effect such as the outgassing in ablative TPS systems, where the gas being sublimed out of the surface pushes the hot atmospheric shock heated gas back and away from the ablative surface.
There doesn't seem to be a happy medium where you mix the two approaches. Either your application optimizes all for one way of doing it, or all for another.
Georgewilliamherbert 08:47, 19 February 2006 (UTC)

[edit] Heatsink in modern times

Was the heatsink ever improved to be used in high-beta missiles or current space shuttles or did the weight make them impossible to use in such way? It seems like radiative cooling is still used in space technology, but all MIRVS seem to make use of ablative TPS nowadays. Why couldn't heatsinks be used im MIRVS?

Mario Lopez 22:16, 10 April 2006 (UTC)

Heatsinks were too heavy. Ablators are much more mass efficient. Every gram wasted on an inefficient thermal protection mass could have gone instead to payload mass.

Egg plant 06:59, 2 May 2006 (UTC)

[edit] History dispute?

The intro is now the "History" section, but I still think it has some problems. No one ever considered human spaceflight until the soviets decided they could have propaganda, well after ICBMs?

Sure, they considered it, just like people considered human flight well before the Wright brothers, they just didn't have a clue how to do it until the ICBM research.WolfKeeper 17:22, 7 May 2006 (UTC)

The history it lays out is pretty much contradictory to my understanding of the causes behind the space race, and it cites no sources, which means there's no way to verify the sequence of events it describes. I think it could stand to be trimmed and rewritten to focus on how people came to understand the problem itself, rather than colorful speculation about ending on dreary notes and a flawed description of the space race. Did von Braun consider reentry, for example? Night Gyr 08:23, 3 May 2006 (UTC)

The dispute tag has been misused. It is for use when:
  • it contains a lot of unlikely information, without providing references.
  • it contains information which is particularly difficult to verify.
  • in, for example, a long list, some errors have been found, suggesting that the list as a whole may need further checking.
  • it has been written (or edited) by a user who is known to write inaccurately on the topic.
(see: Wikipedia:Accuracy dispute). The facts are that reentry was made possible by Allen who was doing research on reentry for ballistic missile research. I've read the (now declassified) paper. The history section says this, and (IMO atleast shows little if any connection to your description above). Unless you can defend your description and show likelyhood of factual statements I have removed it.WolfKeeper 17:22, 7 May 2006 (UTC)

[edit] Definitions list cleanup

I think the list of jargon needs pruning, too. Several of the entries can be combined, for example, outer mold line doesn't need a separate entry from aeroshell, I think, and we don't need to include Mach number here, it has its own article. Night Gyr 08:32, 3 May 2006 (UTC)

I just put the IMU and RCS definitions back in; those have links back to the main articles on those topics, and the descriptions here are appropriately short and contextual IMHO.
Outer mold line defines the outside shape of the aeroshell; we might be able to combine those two entries, as long as both terms are listed (both are used individually and unambiguously in different areas of reentry analysis). I think that a short defining note and link to the Mach number article are still important. Georgewilliamherbert 18:02, 3 May 2006 (UTC)
I would argue that most vehicles intended to reenter the Earth's atmosphere are ICBM RVs and not orbiting spacecraft. Therefore the original introduction was factually incorrect and has been corrected. I tweeked the image arrangement to make it more tidy. I'm tempted to add more content (describe the chemistry of shocklayer radiative heat flux) but unfortunately the article has gotten too long. Egg plant 18:05, 6 May 2006 (UTC)
A lot of the size is the list of definitions, that seems to take up half the article. I think it might help to rewrite it in prose to cut down on redundancy and then just bold each term. I'm going to put the orbit example back in, also mentioning ICBMs, because while ICBMs are the most common RVs out there, deorbiting craft are the most common actual events. Night Gyr 20:20, 6 May 2006 (UTC)
How about an intermediate compromise? I don't like the idea of doing it as prose, but we could do a traditional list (* chars) and trim most of the definitions to one (or at most two) lines... Georgewilliamherbert 20:27, 6 May 2006 (UTC)
I revised the introduction again. The article describes entry vehicle's entering the atmospheres of nonterrestrial planets from heliocentric orbit. Using the language "Earth orbit" is too restrictive. Also the United States and presumably the English, French, Chinese, Iranians, North Koreans and Russians are doing ICBM readiness tests on a regular basis (also the more advanced ICBMs are typically MIRVed). I don't have access to the data but it's reasonable to assume that the "most common actual event" is in fact reentering ICBM RVs on a suborbital trajectory. The last two spacecraft reentering from orbit that I know about were Stardust from heliocentric orbit and a Soyus capsule returning astronauts from the ISS. Egg plant 04:54, 7 May 2006 (UTC)

Considering how long the article is and how the big list of terms breaks up the narrative flow, I've split it off into Glossary of atmospheric reentry. Bryan 01:23, 6 July 2006 (UTC)

[edit] Heights

This article has so much technical information but is missing basic information such as heights and speeds. Where does peak heating occur.. at treetop level? -Rolypolyman 14:50, 17 July 2006 (UTC)

Yes; it can do. There's an equation for it; for some bodies the peak heating is a ground level (or below).WolfKeeper 23:16, 21 July 2006 (UTC)

[edit] Individual astronaut re-entry systems and Reference Desk question

Could those who wrote this article please have a look at the Reference Desk question here:

If anyone here could answer the questions over there, that would be great. Carcharoth 11:49, 14 December 2006 (UTC)

[edit] Expanding this article

Also, I found references in the article to less conventional astronaut re-entry systems such as the MOOSE and FIRST systems:

Could someone expand this section to include links to Rogallo wing, Paresev and also try and cover (or at least link to) the material in this astronautix article? I might try and do this myself, but hopefully someone who wrote this page will do a better job of it. Thanks Carcharoth 11:49, 14 December 2006 (UTC)

[edit] Secrecy controversy

There is a lot in this article about the supposed effects of secrecy and of what was secret at one point and etc. This should all be cited — as it is it verges on unsubstantiated polemic. It'd be very interesting if all of it were true but we need to actually cite that — there is a lot of junk out there on technologies which have supposedly been supressed by secrecy, and we need to have rather rigorous standards here. An article by someone alleging said secrecy hampering this work would be fine. --24.147.86.187 02:14, 12 January 2007 (UTC)

How do you cite this? Talk to any aerospace engineer about the effects of International Traffic in Arms Regulations (ITAR) on the American aerospace industry and he'll give you an earful. Do you know that formerly declassified documents have been reclassified? Formerly confidential NASA TM-X documents were declassified in the mid-1970s but have since been reclassified as "unclassified/limited". "Unclassified/limited" means that it is illegal for this information to be disclosed to non-US citizens. This same information could have been legally viewed and photocopied by non-US citizens in the 1980s. Also a new document can be declared ITAR if old information is recombined in a way that an ITAR censor finds questionable. Would an ITAR censor find this Wikipedia article objectionable? ITAR information may not be disclosed to non-US citizens.

[edit] Nations who have developed successful reentry

According to [1], only four nations have actually completed orbital reentry successfully; could we get some mention of this in the article? Night Gyr (talk/Oy) 02:24, 23 January 2007 (UTC)

A problem I see is, that the article is mixing up "manned orbital reentry" and "unmanned orbital reentry". While it's true that US, Russia, and China have recovered "manned orbital reentry craft", what India did is the recovery of an "unmanned orbital reentry craft" which has already been done by Japan (on May 30, 2003) and probably EU earlier than 2003. India's space program is aimed at a manned mission by 2014 and I don't really see any technological reason that India can fail to archieve this goal, still it's a bit premature to claim the "fourth nation" status. --Revth 03:08, 23 January 2007 (UTC)
Which spacecraft for japan? I can't find any entry for it. Night Gyr (talk/Oy) 03:20, 23 January 2007 (UTC)

ah got it [2]. Unmanned Space Experiment Recovery System Night Gyr (talk/Oy) 03:21, 23 January 2007 (UTC)

Yes, that's the one. The number of nations should be still less than ten though, as recovering is far more difficult than simply shooting up.--Revth 04:52, 23 January 2007 (UTC)

All I;m finding for ESA is Atmospheric Reentry Demonstrator, which is suborbital. Night Gyr (talk/Oy) 04:57, 23 January 2007 (UTC)

The Atmospheric Reentry Demonstrator (ARD) didn't get very hot and flew a boring trajectory (it was essentially ballast for an early Ariane V test launch). ESA did build the Huygens atmospheric probe that landed on Titan. NASA helped out a bit (behind the scenes) with Huygens. Never the less, Huygens was a significant technical achievement that should have been a major source of pride for the Europeans (most Europeans probably never heard of it). Egg plant 05:19, 25 January 2007 (UTC)

[edit] Article Title

It seems to me that the title should be "Atmospheric Entry". Reentry implies that the vehicle left the planet it is entering, which is clearly not the case with vehicles entering the atmosphere on Mars, Venus, or any other planet. The difference is small I know, but it is not trivial. anonymous6494 21:49, 23 January 2007 (UTC)

Most of the time, it's coming back to Earth after having been launched from here. There are a few exceptions (the Venus and Mars landers; Galileo and Huygens at Jupiter and Titan), but almost all atmospheric entries are re-entries. It wouldn't be bad to have a redirect from "Atmospheric entry" to here, but this is the most common usage in the field (and I do some spacecraft design and re-entry work... not full time, but I've designed entry vehicles). Georgewilliamherbert 21:52, 23 January 2007 (UTC)
The issue of "entry" versus "reentry" was debated ad nauseum by the ding-dongs who formerly edited this article (I'm glad they got bored with Wikipedia and left). They were more concerned about semantics than getting their facts right. I deleted all of that nonsense many months ago. Egg plant 07:29, 24 January 2007 (UTC)
Be nice... Georgewilliamherbert 08:02, 24 January 2007 (UTC)
Yes, of course, my apologies, must remember to be nice.... Egg plant 04:17, 25 January 2007 (UTC)
Understandable. I didn't know Ding Dongs could use Wikipedia, or even type for that matter... anonymous6494 03:08, 25 January 2007 (UTC)
Zippy the pinhead likes to eat them with taco sauce. Egg plant 04:20, 25 January 2007 (UTC)
Since there seems to be some activity on this talk page again, is it possible someone could take the challege posed in the section I posted a few sections up: #Expanding this article? I've linked the existing mention of Rogallo wing, but there is still lots of material in this article that could be used as a basis for carefully expanding the Wikipedia article. I'll add it as an external link for now, but I hope someone can do a timeline section on the history of re-entry vehicles, both planned and actual. That would be a good way to tie in the "first" dates being discussed above. Carcharoth 10:56, 24 January 2007 (UTC)
Rogallo wings have a very nasty stall characteristic which is why that particular wing isn't used anymore for hang gliding (killed a bunch of people). Most (all?) of those one man rescue reentry vehicles from the 1960s were little more than one page proposals (a single artist's conception) that never received any development funding. Also the ballute type entry vehicles may not be practical due to aeroelastic instability. People keep proposing ballutes anyway because they're sort of a "magic sword" (like skyhooks, anti-matter drives, suspended animation, etc.) for solving impossible aerospace problems (the fact that they're impractical is only a minor detail). Egg plant 04:38, 25 January 2007 (UTC)
Even a paragraph on a few of the failed or impractical proposals would be nice. Gives a bit of the history and background to the subject, to round out the technical engineering material. Carcharoth 17:33, 25 January 2007 (UTC)

[edit] Pictures added

Just added pictures of the Mir and Columbia break-ups during re-entry. Are there any other pictures of re-entry available? Would putting a picture of a meteorite shower, showing atmospheric entry by natural space debris, be outside the scope of the article? What about a picture of of what happens after a successful re-entry, with a return capsule parachuting down to the sea, or a space shuttle landing?

I had a look on Commons and found these:

Stardust re-entry

Skip-type re-entry trajectory

Soyuz re-entry

Design for a NASA re-entry vehicle

Space shuttle re-entry

Are any of these suitable for this article? Carcharoth 11:54, 24 January 2007 (UTC)

The picture of the Dynasoar should probably be included (The other pictures are less interesting). Dynasoar was a USAF vehicle (was to have been launched from a Titan-II) and not NASA. I don't know if a thermal protection system was ever designed for Dynasoar. NASA's Space Shuttle was partially a consequence of Dynasoar getting canned. One might argue that it was too bad the Dynasoar didn't fly before the Shuttle. The design mistakes that ultimately ruined the Shuttle program might have been discovered with the much cheaper Dynasoar and thereby avoided. Egg plant 05:04, 25 January 2007 (UTC)
You seem to be approaching this from an engineering persepctive. The Dynosoar picture shows an actual craft close up, but the actual pictures of what re-entry looks like from a distance, although they might not seem interesting, do give another perspective on the subject. And before I forget, would anyone be able to run with the idea (I think I suggested it above) for a timeline of milestones in atmospheric re-entry history. First Earth, first on another planet, first by different countries, first by different spacecraft programs, and so forth. Carcharoth 17:37, 25 January 2007 (UTC)
Actually, on second thoughts, those "bright white dot" re-entry pics are rather boring. But maybe use one of them? Carcharoth 17:42, 25 January 2007 (UTC)
I agree that the "bright white dot" pictures are not interesting. The Atmospheric reentry article already has too many pictures of "bright lights in the sky". The "skip reentry" picture is of interest but leads to a whole new line of discussion that I've started below. Egg plant 19:46, 28 January 2007 (UTC)
Retrieved from "http://en.wikipedia.org../../../a/t/m/Talk%7EAtmospheric_reentry_9404.html"