Categories
applied science astrophysics

Are Wrinkled Lightsails Less Efficient?

Just watched a small explanatory video by Bill Nye on the Planetary Society’s LightSail 2 spacecraft (not exactly the same one as the one attached to this post but essentially the same). And by the end some voice in my head was shutting out Bill.

This is what it was saying.

  • 1 – That lightsail material in the demo looks ‘crinkled’ as in – the foil is not stretched taut at all.
  • 2 – The actual momentum of photons is quite small so a maximal energy received => propulsion produced ratio would be desired. Er=>Pp as close to 100 % as possible.
  • 3 – A small force impressed on different parts of an uneven, and not taut, surface might get spent simply rearranging the flatness of that surface with a consequent reduction in actual delivered momentum to the spacecraft itself. Let’s call that Mechanical absorption. So Pp = Er – Ma
  • 4 – A stiff surface might reduce losses due to Ma.
  • 5 – How to produce a very light, large, stiff surface in space?

Would there be enough delivered momentum to actually stretch a foil sail taut?

And if that was possible would a flexible material like a foil surface not also be subject to mechanical waves due to continuous driving inputs of momentum due to photon impacts?

If the wave length of any induced acoustical/mechanical phenomena approached some integer fraction, or multiple, of a major surface dimension it could result in destructive (or wasteful) harmonics.

In the video Bill says

and so we found that the sales do billow a little bit just like sales on a sailboat

From the video at about 2:20

My guess is that billowing would come from either unspent mechanical vibrations in the structure or induced mechanical impulses unevenly distributed. If the latter then that energy used up in material deformation (billowing) is energy not used for propulsion. Much like the sound coming from a motor represents energy lost from the system.

How do you make a surface that is acoustically immune to momentum sucking vibrations and stiff and light and properly able to absorb as much photon momentum as possible and transfer that into propulsion momentum as efficiently as possible?

There’s a lot of ‘and’s in that question . . .

Please don’t misunderstand me – I’m not criticizing Bill or the Planetary Society or any researchers hoisting lightsail powered craft into space. Bravo to them all – I applaud their efforts immensely.

But I just wonder if the system could be made more effective with better applied materials science from the start.

Categories
astrophysics Uncategorized

300+ years to solve Newton’s 3 Body Problem

A few decades back I wrote a screen saver for Windows that relied on Newton’s laws of gravity to drive things around the screen.

It was the bouncing line with a difference: the ends of the line had ‘mass’ and velocity. There was an unseen gravity well, a black sun if you will, that had gravity but a fixed position. The motion of the line ends followed Newton’s gravity equation.

As I worked on this and watched how it developed multi-body gravity systems I was amazed at how complex it could be but then I learned about Newton’s 3 body problem. And saw how crazy it became when I allowed all 3 ‘bodies’ in my little system move.

Well the problem has apparently been solved

Categories
astrophysics rambling social commentary

Stretching Conventional Wisdom Too Far

Today found me reading an article (https://phys.org/news/2019-10-giant-radio-galaxies-defies-conventional.html) about research into the far distant universe.

In this case the research was “New research on giant radio galaxies defies conventional wisdom”.

The article begins with this summation:

Conventional wisdom tells us that large objects appear smaller as they get farther from us, but this fundamental law of classical physics is reversed when we observe the distant universe.

https://phys.org/news/2019-10-giant-radio-galaxies-defies-conventional.html

Now I understand conventional wisdom (CW) and why it would tell us that: CW operates within the scope of human scale thinking that has obtained since time immemorial to us humans. And yes things that are further away do appear smaller.

But CW appears to have suffered arrested development sometime in the 19th century (the era of Classical Physics) – before we discovered:

  • that light takes time to cover distances.  So the further away something is from us the light we see from it comes from further back in time.
  • that almost everything in the universe is moving away from us at increasing rates of speed the further it is.
  • that this universe we live in was once a small thing that experienced a Big Bang and expanded enormously (and still appears to be expanding)

My own version of CW knows these things and takes them into account. So when I read that opening paragraph I was a bit perplexed – why would anyone with the same basic cosmology education I got think that the things we see very far out there, from very long ago, would not appear to be larger?

Confused?

Let’s see if my basic logic can help you follow this . . .

We think the universe is about 13.6 Billion Years old (13.6 GY) .
This also means that the edge of the visible universe is 13.6 GLY (Billion Light Years) from us.
That means when we see some object or structure 10 GLY from us the light was emitted 10 GY ago when the universe was just 3.6 GY old.

Good so far? (if not go back, reread and rethink about that – we’ll wait for you 🙂

Okay – this is where it gets interesting.

The universe is expanding.
Hubble was the first to discover that there was more universe our there than just what we saw in our galaxy. That the nebulae were actually other galaxies outside our own Milky Way.
He measured the spectra of their light and found that these were shifted towards the Red end of the spectrum.
He noticed that when he measured the red shifts of objects at inter galactic scales the further the object was from us the more red shift it had.
Meaning not only that these things are moving away from us (otherwise there would be no shift in the spectrum) BUT the ones further away are moving away faster than the closer ones.

Eventually we worked out that this is because the universe is expanding and has been since the beginning it apparently had.
One way to think about it is that measuring stick that once crossed the universe is still there but the gradations on its scaling are getting smaller in size and larger in number. (much the same as a dollar from 50 years ago is still a dollar today but due to inflation how much you can buy with it has shrunk – in both case we call this inflation)

At a very very early stage of the universe the structures formed occupied a certain fraction of the size of the actual universe.

At the age of 3.6 GY the universe was 3.6G LY in radius.
And let’s say that a large galaxy of 500,000 LY in size had formed and a monster black hole at its centre had been spewing and feeding the huge polar lobe structures we now know that they form.

These lobes are typically larger than the galaxy that spawned them. So let’s say these grow to 750K LY in size. Two of them plus the galactic bulge between could span 2 Million LY.

In a 7.2 GLY diameter universe 2 Million LY is a fraction of 2/7200 or 2.78×10^-10. That is the size and fraction of the size of the universe it was when if formed 10 GY ago.

Moving forward in time to Now.

The universe has expanded to 27.2 GLY diameter. This is approx. 3.778 times the size it used to be 10 GY ago.

All the structures that existed 10GY ago that do NOT have a strong gravity well to hold all their parts close in have also expanded in size.

So the galaxies themselves might have enough mass within them to keep most of their masses within their gravity wells . . . the ejected stuff further outside the well’s mouth will be subject to this universal expansion.

In the cases of Radio Galaxies the lobes of radio emitting gases and plasma may well fit in this category.

So lobes that were 750K LY in diameter would have grown to 2,833 LY in diameter after 10G years of expansion.

If you buy into the expanding universe you have to also buy that structures evolved Billions of years in the past cannot fail to appear larger now than old-style Conventional Wisdom would suggest.

When you look at the Wikipedia article (https://en.wikipedia.org/wiki/Radio_galaxy) on radio galaxies you will find this: “The largest radio galaxies have lobes or plumes extending to megaparsec scales”

A parsec is just over 3.262 LY. A mega parsec is 3.262 Million Light Years.

If we took our example radio galaxy and moved its birth back to 1 Billion Years in the life of the universe (12.6 GY ago) the expansion by now would have been 27.2 times instead of 3.7. So the 750LY lobes would appear to be 10.2LY across now.

Back when I was 12 years old (mid 60s) I learned about Hubble and the Red Shift and the expanding universe. Without benefit of a calculator I could still come up with a size and age of 12.5 GLY size and 12.5 GY age. Admittedly rough calculations by a child but this is how I’ve learned to think about the universe.


Why is that decades have passed – we’re even in a new millennium now – and that child has grown into a gray haired man but still our Conventional Wisdom is stuck somewhere before my grandparents were born?

Perhaps that is part of the problem our society appears to have in relating to science and technology. If you sound like you’re a scientist or know science you’re some kind of ‘elite’ and that’s a bad thing in the current political climate pervading society.

The idea that scientific fact and theory are being relegated to being ‘just another opinion with as much credence as the opinions of politicians and snake oil salesmen and charlatans’ scares the crap out of me.

Back when the Khmer Rouge emptied the cities they had a purge of \intellectuals’. Anyone who wore glasses was automatically branded an intellectual and sent to camps to be worked to death. Why? Because they could read . . .

When I see the wholesale discarding of science and scientists in favour of political expedience; denial of evidence based predictions because they prescribe hard-to-do solutions; I have to ask how did we come to this?

People want the world to make sense.

If the brightest brains tell them the world is so strange that they would not understand it even if they could understand the science all they hear is: you’re too stupid to understand this stuff – leave it to us. (which implies a classification-by-smarts system where the scientists are smarter and therefore in a higher class)

I know most scientists aren’t out to lord it over the normal people but that’s one possible take-away that non-science people get.

In better times they might get other, less negative, take-aways . . . but not now. Now there’s so many ‘alternative truths’ floating about being spouted by ‘truth tellers’ it would be very hard for the uneducated to filter out the crap from the facts. And most of those sources push some form of the negative take-away. Reinforce the idea that you cannot trust science and scientists. And most of those web denizens are engaged in reaching out to the non-science-people in the world. Like most media outlets they make money from the eyeballs and views and clicks they garner. So the more egregious and outlandish or scary the claims they make the more money they make. Truth is secondary.

A good education is pretty much free on the web as well . . . why most do not avail themselves of it is another issue.

I wasn’t trying to be preachy – just scratching an itch.

Categories
astrophysics

How Your Measuring Tool Was Made Makes A Difference In Cosmology

Last week I wrote about a dawning realization in Cosmology that White Dwarf stars may be older than previously thought. There are likely implications for how this might affect predicted values of distance and age of the regions they live in.

It turns out that there’s another aspect of those stars’ evolution that might throw off the calculation of age.

At a certain point in their aging process a White Dwarf will explode as a
Type Ia SuperNova. Specifically: “When the white dwarf reaches 1.4 solar masses, or about 40 percent more massive than our Sun, a nuclear chain reaction occurs, causing the white dwarf to explode. The resulting light is 5 billion times brighter than the Sun.”

Now the calculation of when that would happen used to be pretty straightforward because ‘we knew the process well’. But we don’t. As my previous post pointed out we are learning more about how these starts age and they aren’t exactly doing what we thought.

Now we find out that the Supernova event can be triggered by the White Dwarf’s companion . . . without having to wait until the WD reaches critical mass by itself.

More rejigging of those stellar measurements likely required . . .

Categories
astrophysics

Big News On Dwarf Stars Rejigs Stellar Clocks

Stars like our Sun get old and become Red Giants. Then they get older and eventually Shed Their Skins (outer layers) leaving behind a remnant which we call a White Dwarf.


White dwarf stars are some of the oldest stellar objects in the universe. They are incredibly useful to astronomers as their predictable lifecycle allows them to be used as cosmic clocks to estimate the age of groups of neighboring stars to a high degree of accuracy

In this article “Fading White Dwarfs Confirm the Age of the Universe” you can see what that means. That article is from 15 yeas ago and in it you will find this: ” The rate of white dwarf cooling is well understood “

I remembered that from my youth when I was more interested in cosmology. Cosmologists like standard candles and standard clocks. They make determining the age and size / distance of stars, galaxies and the universe possible.

This is how that works: When I was 12 I used what I knew of the the expansion of the universe and the Red Shift (the farther away a galaxy is the faster it is receding from us) to calculate the edge of the visible universe to around 12.5 Billion Light Years. At / after that point the stars are receding from us at the speed of light so we’d never see anything – a simplistic idea but that’s where the limit worked out to be. It was a fun exercise from before I had any access to a calculator. (PC’s didn’t show up for nearly 20 years.) And it you believe in the Big Bang that would also correlate with the approximate age of the universe.

But the nature of science is to push back the boundaries of our knowledge and understanding – to make the universe of our knowledge larger. And it’s not uncommon for the gains to show us where we were wrong or our understanding was incomplete. Which is a good thing.

So when I was reading “Thousands of stars turning into crystals” at Science Daily I got a smile when I read “This could make them potentially billions of years older than previously thought”. Cool (that’s a pun also)

What does that mean for the research in the article from 15 years ago?
Does it change the calculations that Richer used to determine an age of the universe?

I’ll confess that I’m not all that sure if it does or not because Richer’s team was looking for a thermal cutoff point in white dwarf populations – the older the stars the cooler the stars so when you run out of them you have found the coldest stars.

From that temperature you can reverse the clock and determine age because “the rate of white dwarf cooling is well understood ” as was believed back then. But if that rate isn’t what they thought it was back then, if the stars they could find are actually billions of years older than they had thought 15 years ago then it’s likely that this calculation will have be redone. And the best guesstimate of the age of the universe will have to be adjusted . . . again. (Steady State was so much simpler – there was no ‘beginning’ 🙂

Meanwhile another part of my brain is trying to figure out if there’s any SF material in mining White Dwarf cores for dense crystalline Oxygen . . . or Carbon. Maybe the Oxy cores are clad in Diamond or some other exotic variant of Carbon. And that there may be 15,000 of these within 300 light years from here . . . makes it feel like the Big Empty is kinda crowded. Which makes for more potential SF fodder.

Categories
astrophysics

Panspermia Gets Another Boost

Panspermia gets another boost.

For those who don’t know panspermia is the theory that life may not have started here on earth. It might have come on comets or meteoric dust particles that drift into the earth’s gravity well and then into the atmosphere.

The new boost is a test recently done where they applied plasmid DNA molecules to the outside of body panels of a spacecraft before launching. Then they checked after re-entry. All the panels they had painted with DNA still had salvageable DNA. And when they checked most of this DNA was still able to transmit genetic information to bacterial and connective tissue!

Now this was plasmid DNA, not a spore. It ‘survived’ launch, space and re-entry into the atmosphere. Not too shabby for a molecule.

Categories
astrophysics

Spacecraft Earth Has Another Shield

It would appear that Spaceship Earth has one more Shield against assault from space that we were not aware of.

We’ve known for 60 years about the Van Allen Radiation belt. And the Ozone layer. These protective layers absord and deflect charged particles from the Solar Wind and the more intense form of Ultra Violet radiation (light).

Well they have discovered a previously unknown shield between the two Van Allen belts. As described in the ScienceDaily article what this one protects us from are dangerously energetic electrons. These electrons are looping around the Earth at speeds of 100,000 miles per second. But they don’t get into the atmosphere because of this ‘transient storage ring’.

Congrats to Dr. Baker of CU-Boulder for carrying on his professor’s area of interest. That was Van Allen himself.

Categories
astrophysics

Now We Know Why the Dark Side of the Moon Is Different from the Earth Side

Did you know that the surface of the moon on the side we do not see is actually different from the side we can see?

When you look up and see the ‘man in the moon’ you are actually looking at the ‘maria’, or seas, that form the flat basins of major impact craters. In 1959 after we got to see the far side (courtesy of the Soviet space program) it was noted that there are far fewer of these ‘seas’ on that side. And no one knew why … and the Lunar Farside Highlands Problem was born.

Well now we think we know the hows and whys.

http://www.sciencedaily.com/releases/2014/06/140609122056.htm