Spacecraft control - Perigrine / ULA mission

A very brief thought here, in the context of the poorly-contrlled "Perigrine" spacecraft recently launched by the ULA/Vulcan mission.

wouldn't the most likely place for a leak be, in the isolation/ throttling valves from tank to motor, which would restrict the possible (plausible) thrust vectors a lot, and hence the acceleration vectors on the spacecraft? Or are they thinking that launch vibration has fractured a piece of pipe (or a fitting) somewhere, with an unpredictable vector? In which case, venting the tank through the (more predictable vector) nozzle would at least reduce the uncontrolled vector available from the uncontrolled leak?

I don't really want to get into spacecraft design, but having had to design and build more than a few plumbing systems for [multiple] gases from [multiple] tanks to [multiple] consumers, the obvious (to me design is to have an isolation valve on each tank, leading to a manifold for each gas, then a line from each manifold to each consumer, with an isolation valve on each of those lines. Throttle valve downstream of each isolation valve.

So, anything other than a break in the tank-to-[1st isolation valve] is controllable by at least one valve. And even a leak in that section can be mitigated by using all the consumers, throttled to counterbalance the uncontrolled leak, and depressurising the tank as fast as is safe. The list of "consumers" (attitude thrusters) includes counteracting pairs, so you can ramp those to the maximum, to negligible effect on the overall directional vector.

I guess I'm either going to have to get into spacecraft design (is my design's component count too high?), or drop this. But it intrigues me, and takes me back to designing gas plumbing networks for mud logging units 36 years ago.

Update - 2024-Jan-17

Last night I noticed a couple of messages on MPML: (Minor Planets Mailing List, https://groups.io/g/mpml/topics)

From: [redacted]
Date: Mon, 15 Jan 2024 03:22:13 GMT

It seems peregrine has stopped leaking and is following a (mostly) newtonian 
orbit. My slightly-over-2-hour arc suggests an impact somewhere in South America 
in the morning of January 17 UTC (around 10:00 give or take a couple hours). The 
orbit is currently too uncertain to even say if it will impact in the Atlantic, 
Pacific, Brazil, or Peru, but it seems it's definitely somewhere around there 
along a line at 10-12 degrees south.

Orbital elements:  Peregri
[SNIP Orbital elements and observations]
  
Re: Peregrine observations?
From: [Redacted]
Date: Mon, 15 Jan 2024 04:41:53 GMT

Hi Sam,
Good to see some more data.
Astrobotic has posted about the upcoming re-entry :
https://www.astrobotic.com/update-17-for-peregrine-mission-one/
Based on the data I've seen (combined with yours), I expect it to come in about a 
day later, somewhere around latitude 10 south. It does still show a bit of odd 
motion. I'm reluctant to say much about longitude until we see more data and the 
fuel runs out. The uncertainty in re-entry time and longitude are linked; if 
you've got a one-hour uncertainty in time, the earth gets to rotate 15 degrees 

more or less. However, it shouldn't take much more data to get a precise 
re-entry time/location.

Not living in the area, and having no exceptionally tall hats ... has anything happened? I'm not seeing anything on the news. The operating (and owning) company's website has an update that the lander has passed apogee (furthest point, "apo-" from Earth ("-gee") and is currently 183,000 miles from Earth. (That's a bit over a quarter million km in real money.) So I guess the second estimate for impact - Friday-ish is looking more likely. So I'll takem my extra-tall hat off then.

The Press Release doesn't estimate a landing date.

Hmmm, the [code] tag on Blogger doesn't do what I expected. Ah, I should have been using a [pre] tag pair. [pre] also being block-level, not inline. ... now I need to force line-breaks.

Update - 2024-Jan-19

On Wednesday, Astrobotic published an update describing their mission-terminating strategy combining a series of short main engine burns, and attitude adjustment to control the drift induced by the leak. This resulted an a landing ellipse between New Caledonia, Fiji and Vanuatu. (For the geographically challenged, that's in the south west Pacific.) Quoting a landing ellipse to 6σ sounds a touch optimistic for a spacecraft with an attitude-affecting leak.

On Thursday (2024-01-18) they published another update with an image taken of their target :

(They describe some of the issues involved in planning imaging, when the spacecraft is no longer on it's planned trajectory : The first attempt to take this photo yielded an oversaturated image, with the Sun making the image too bright to see the Earth. As a result, the team precisely slewed the spacecraft to reposition the Sun to be hidden behind the thin payload deck strut just to the left of Earth, which produced the starburst effects on the vehicle and revealed the Earth’s crescent. This image is completely unaltered.) And just for entertainment, I'm trying the "rotate" option. If that works on Blogger. It did. So why did I have a note that it didn't?

But the ROTATEd DIV has a bad effect of laying out beyond the area of the post.

But will it lay out beyond these paragraphs? YES, it overprints them. I need to figure that out properly. I turned the ROTATE off. They're still flag-washing, I see. As if one's nation were anything to be proud of.

2024-01-05 Hydrides in Sub-Neptune Exoplanets

Last week I noticed a paper about the "Outcomes of Collisions between sub-Neptunes", noting that sub-Neptunes (not defined in that paper, but around 5~10×M_⊕ and < 3×R_⊕) have rather different collisional properties to terrestrial properties, due to their thick, gaseous atmospheres.

This paper ("Stability of Hydrides in Sub-Neptune Exoplanets with Thick Hydrogen-Rich Atmospheres") reveals another aspect of these planets, which have no analogues in the Solar system.

The question might be asked, why are these called "sub-Neptunes", not "sub-Uranuses"? After all, Uranus is less massive than Neptune (86.8 vs 102 ×10²⁴kg). But Neptune is smaller than Uranus (R_≆=49528 km vs R_≅=51118 km). There is clearly an interior-compression process going on (described as a "radius cliff"), and Neptune is well inside the effect, while Uranus may or may not be. (Another "radius cliff" is thought to occur in planets larger than Jupiter, going up into the "brown dwarf" star range, though the "turn-over" radius is somewhat uncertain.)

This paper describes another effect which probably does not happen in the Solar system. At least, not outside diamond-anvil high pressure machines on Earth. The bottom of the hot hydrogen-helium atmosphere can interact with silicate minerals in the planetary core, potentially reducing some of the silicates (and their component metal ions) to release metals. Iron (present as Fe²⁺ in fayalite (iron-olivine) can be directly reduced to Fe⁰_metal by interaction with the hydrogen. It is less clear if the magnesium in forsterite (magnesium olivine) can be reduced to magnesium metal, but it seems that a magnesium-iron hydride Mg₂FeH₆ is possible. Water (H₂O) is a minor byproduct, which might accumulate at the top of the rock/ metal core, or might diffuse up to the atmosphere to freeze out at a high level.

The work is experimentally difficult, because at these temperatures (3000 K +) and pressures, the hydrogen makes the diamond cells brittle, while also making it interfere with X-ray diffraction to identify the products before they decompose on decompression. Raman spectroscopy does support the presence of Mg-H bonding though.

The new "hydride" phases, and possibly water-derived compounds in the hdyrgen could lead to a more gradual radial change in properties in these planets, which further work on Neptune might detect, in the same way that Juno's recent close orbiting of Jupiter has suggested it has a "diffuse" core-atmosphere boundary.

Sub-Neptunes are an interesting type of planet - sufficient justification in themselves to go out into the galaxy.

2024-01-08 The Implications of Oumuamua on Panspermia

ʻOumuamua. So much to extract from so little.

That initial mark isn't a diacritic "backtick", though it's often presented as such, but a distinct Hawaiʻian letter ʻokina, Unicode U+02BB, decimal 699. To a linguist, it's a "phonemic glottal stop"., and the recommendation in new work is to use the UNICODE character in preference to the apostrophe or "backtick" diacritics. The correct (HTML) orthography is (all one word) "& #x2bb ; Oumuamua".

We have 1I/ʻOumuamua from 2017, and 2I/Borisov from 2019. So why not 3I/XXX? Yet. I maintain a watching brief on the Minor Planets Mailing List (MPML, and have done since ʻOumuamua. There hasn't even been a pulse of excitement with a first-report suggesting a significantly hyperbolic trajectory, even if it were later dis-confirmed. Nada. Zip. Zilch. Which isn't suspicious - yet - but it is getting just a touch nervous-making, because ... well, how did Fermi put it? "Where is everyone?"

This sounds like it's an advance in panspermia theory. It is - but not in a good way if you think that panspermia is a useful idea. The authors use the number (1) and size of ʻOumuamua (≈ 100m) to estimate numbers for the total number of impact events, and the total collision mass, then re-work that to estimate the number of (potentially) life-bearing particles to impact Earth between it's origin and the palaeontological origin of life, and from that to it's importance on a galcatic scale. Which is basically, a bog-standard panspermia argument. And their figure : assuming 10⁹ Earth-like planets in the Galaxy, order of 10⁵ of them might have been seeded by panspermia. One in ten thousand. I stil think that might be a bit optimistic, but it's a lot more realistic than some of the calculations done by other panspermia fans.

Panspermia remains a practically useless idea. Given that even with panspermia, somewhere has to be the origin of life, all that panspermia does is move the question of how life originated from here, under conditions compatible with the history of Earth's environment to an unknown location, with an unknown history of environmental conditions. Which, as useful ideas go, is damned-all a useful idea.

I propose Optimi-Panspermia : wherever your organism proposing panspermia lives today, the planet where it's panspermia origin is had conditions like the worst planet in the system (for Earth/ Solar system, would that be Neptune, Eris, or Mercury?), and then the dispersed panspermia seeds had to get to the Earth-analogue planet, then immediately adapt to the new conditions and take over. That sounds a credible panspermia to me. And it has no more evidence for it than any other panspermia proposal.

Sorry, did I sound like a fan of panspermia for a few femtoseconds there? Sooooo misleading.

2024-01-05 HTML learnings for this month

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Contents

HTML notes and learnings

Table alignment

Item 2

End of document

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HTML notes and learnings

So, I'm getting a bit ... ticked off with clicking the "open in new window" option on Blogger's "add link" dialog. So ... I should be able to put ' target="_blank" ' into the CSS style header for my "a" link. No? Need to check on a different page!

OK, well I tried that - at least simplistically with 'a {target:"_blank";}' in the "style" header block . Didn't work ; page opened in the same tag.

Now, why didn't it work?

Table fidding

Do I have unstructured ways to add a comment to a table. Or would a caption do? I've got "caption-side: bottom;" set in the style sheet.

I set up a TFOOT line below the TBODY section, including a TR with COLSPAN set to occupy the whole table.

I need to find a better way to set columns to R-align - better than cell-by-cell, at least. (Stack-Overflow suggests CSS of ... Which looks workable. But it's complicated. It's easier to change the default to , because that's what I'm going to use most often. And it's mucking up updating. Or is the system just broken? This is getting horribly complex - and not working with the big table in the MOND post.

Nope, I don't understand this. Yet.

Back to Contents.

This post is probably going to grow "Contents" and sections. It's a more incremental concept.

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Table Column styling

Working on the MOND table, I realised that I hate the (default) left-alignment of tables. I need to find a way to make this.column left-aligned, that.column right-aligned, and other.column centered. Something better and more manageable than setting EVERY cell.

So, what I'm wanting is something like :

H1	H2	H3	H4
1	2	3	4
2,1	2,2	2,3	2,4
3,1	3,2	3,3	3,4
4,1	4,2	4,3	4,4
F1	F2	F3	F4

But every line is of the form : ..tr....td style="text-align:right"..4,1../td....td..4,2../td.. ..td style="text-align:center"..4,3../td.. ..td style="text-align:left"..4,4../td..../tr..
which is undesirably verbose.

StackOverflow has a question that suits, and an answer:

<colgroup> <col> <col style='text-align:right'> </colgroup> <tbody> <tr [...] then "if you look at the MDN [Mozilla Developer Network] docs for <col>, you find this: "Do not try to set the text-align property on a selector giving a <col> element. Because <td> elements are not descendant of the <col> element, they won't inherit it."

So, I think I need to go down the "define my own classes" route : HTML isn't rendered by column, it's rendered by rows. That's why there ,,tr..,,/tr.. (table rows) exist, but ..tc,,../tc,, (table columns) do not. That being said, the easiest way to style a column in HTML, is by applying the same CSS class to every ..td,,../td,, in the given column. You can type in the same class to every one manually, or you could write it programmatically, via javascript or a server-side script.

So I need a worked example of defining, say, three derived classes : td.l, td.c, td.r (TableData.Left, etc). This multiply-linked solution seems specific for 4-column tables, with the 3rd column R-aligned. Ungood, I think.

What I think I'm going to try is

1. define an extension to td (possibly also to th, for completeness?) "td.l", which inherits td's properties but adds "text-align: left;"
2. similarly "td.r" and "td.c"
3. then set up rows of [blah] td.r td.r td.c [blah]
4. Which isn't as elegant as I'd like, but if the alternative is having to write whole new sets of table definitions for every instance, may be good enough.

Testing (pretty-aligned)

Right	Centre	Left
r	c c	llll
rRRRR	c CCCC	LLLll
rRR	c cCCC	lLLL
rR	c cCC	lLLll

OK - I'm getting somewhere now. I need my own class in the STYLE header (wol.td.c etc), then have my own "td class=..." in each row. Which is still 8 more characters than I'd like per element, but it's getting better. Unfortunately, while it seems to be legal, it's not having the desired effects.

Nope, still too much burying data in presentation. Just stick to the long-winded method - it's little worse.

W3.CSS approach.

https://www.w3schools.com/w3css/w3css_tables.asp has a way of "classing" centre- or left- aligned table cells. But their implementation ends up with code like "<th class="w3-right-align"> Points</th>" ... which in itself isn't so great. BUT it does only need setting in the header they assert. OK, "imply" in the first level demonstration ; I checked and it's untrue. It needs setting on every cell. No benefit.

Back to Contents.

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Foot - I still need to fix the image size problem.

End of document

2023-01-04 First new, shorter post : the state of MOND research.

Short, single topic post.

These posts were getting really long - and therefore daunting to undertake. Maybe doing shorter, single topic posts will be easier.

New Year, New MOND data

A personal itch, being scratched in public

On a regular basis one hears assertions that "Big Science suppresses non-standard theories" - often followed up by "Free energy" schemes, Climate change scepticism, Anti-vaccination screeds and the like. It's a feature particularly of Slashdot, but more generally of the Internet. If I "did" Facebook, I'd probably cite them too. Kooks are everywhere and are vocal, and they love a "my voice is being suppressed" narrative.

So, a few months ago, I conducted an (admittedly crude) survey of a "controversial" idea in "non-standard" science using Arχiv. It was nothing complex (I searched for various terms ["Mordehai Milgrom", "MOND", "Non-Newtonian Gravity", "MOG", "Dark matter" in Arχiv's database (anywhere in article title, abstract, or body text, or figures) from Jan 01 to Dec 31 for each year, recording the counts. And now, it's time to update the numbers. They're not good reading for the conspiracy-of-suppression" theorists (well, is any reading good for them? It's not as if they like actual evidence).

Date of search	Mordehai Milgrom	MOND	Non-Newtonian Gravity	MOG	Dark matter
1991 - 2001-12-31	75	1072	735	180	43348
2001-12-31	4	38	46	16	3404
2002-12-31	2	12	13	2	693
2003-12-31	1	22	17	2	765
2004-12-31	1	12	20	2	885
2005-12-31	2	35	22	2	1005
2006-12-31	2	35	27	4	1068
2007-12-31	2	49	24	2	1179
2008-12-31	3	61	20	3	1329
2009-12-31	4	51	23	6	1635
2010-12-31	5	50	38	4	1586
2011-12-31	4	60	35	5	1643
2012-12-31	5	42	23	6	1765
2013-12-31	6	56	33	3	1802
2014-12-31	3	58	33	8	1986
2015-12-31	3	40	33	5	2123
2016-12-31	6	51	32	6	2150
2017-12-31	2	55	39	17	2239
2018-12-31	3	48	35	16	2231
2019-12-31	4	55	34	8	2419
2020-12-31	3	51	46	19	2525
2021-12-31	2	43	47	9	2651
2022-12-31	4	63	44	11	2836
2023-12-31	4	85	51	24	3429

How long is it since I made a snide comment about conspiracists and their data aversion? Too long. See table above. For those who aren't familiar with the field, "Mordehai Milgrom" is a prominent researcher in "modified gravity" ; "MOND" is a popular theory of "modified gravity" ; "MOG" is a different such theory ; "non-Newtonian Gravity" is more general term for the field ("Newtonian Gravity" being the "Big Science" conventional theory in favour of which all the other theories are being suppressed for (whatever) reason(s) ; "Dark Matter" is just there for a marker of overall theoretical activity in astronomy.

Lots of data. Would a picture help?

Much clearer. Publications in these two particular theories of non-Newtonian gravity have continued to happen at comparable rates to general astronomical activity, though the relative popularity of these two theories varies a little, "MOG" having picked up in the last few years. Mr (Professor? Probably.) Milgrom continues to publish at a fairly consistent rate - which isn't so surprising, since he's been doing so for about 40 years.

That's not the sign of a field of research that is being "suppressed", "forced underground", or even "harmful to researcher's careers". It's a sign of a relatively unpopular topic within a field. Now, "unpopular" may not be a particularly nice state to be in (anthropomorphising "theories"), but it's not a sign of effective suppression. Effective suppression is samizdat publication on midnight press runs, and the occasional publisher's head boiled in tar and spiked over the entry gates to Physics & Astronomy Departments pour encourager les autres (a short-form Voltaire-ism [Candide, ch.xxiii]; the long form is darker than many people realise.)

Having done the leg-work, I'll continue to update the data file yearly (until I get bored). If you think I should be looking at different data, that's what the "Comments" are enabled for.

Back to Contents List.

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