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  • Writer's pictureMatt Russell

#151 - Space line and Massive Neutron Stars

This week we're looking at two papers, one based around a space elevator concept called Space line and the other the uncovering of a massive Neutron Star. We chat about some films and the latest launch of crew to the ISS this week.

Photo by Daily Mirror via Getty Image

“The fact that we live at the bottom of a deep gravity well, on the surface of a gas covered planet going around a nuclear fireball 90 million miles away and think this to be normal is obviously some indication of how skewed our perspective tends to be.”

Douglas Adams

Illumination of Earth by Sun on the day of equinox (vernal and autumnal). Image by Przemyslaw "Blueshade" Idzkiewicz.

Monday 23rd Autumnal Equinox

The autumnal equinox is one of two points in Earth's orbit where the sun creates equal periods of daytime and nighttime across the globe. Many mark it as the first day of the fall. See what it looks like from space here:

OTD - 21 sep 2003 – The Galileo spacecraft is terminated by sending it into Jupiter's atmosphere.

An artist's concept of Galileo burning up in Jupiter's atmosphere. Credit: David A. Hardy

Mission Mangal in cinemas

Mission Mangal is the incredible true story behind India’s mission to Mars. It shows how Rakesh Dhawan (Akshay Kumar) and Tara Shinde (Vidya Balan) together with a team of brilliant scientists successfully sent a satellite to Mars in their very first attempt, a mammoth feat achieved by no other nation. This is a tale of inspiration which shows how dreams transform into reality with a vision, the courage to pursue it and fulfill it with sheer determination


The Space Line

Scientists are forever trying to get around the tyranny of the rocket equation, essentially that a rocket has to launch and carry the fuel to use to carry the payload, then needs to carry more fuel to carry that fuel, then needs to carry more fuel to carry that fuel etc etc. Many ideas have come to light and probably the most popular is the space elevator which allows the payload to climb into space, not requiring you to take any fuel up with you.

A simple sketch of the space elevator, in a frame co-rotating with the Earth. Drawn to scale with the Earth and the radius of geostationary orbit.

But boy oh boy that is some infrastructure required and a broken space elevator is a very dangerous object indeed , a mega strong cable smashing down and whipping and wrapping itself around the world ...carnage.

However a couple of brainboxes think they have uncovered a solution, or at least put the numbers to a solution, The Space Line, making them think that perhaps this idea has been underestimated, overlooked but actually has some legs and needs serious consideration.

The Space Line is a concept that is very similar to the space elevator and other concepts before. However, the authors of the paper do go into quite a bit of detail regarding the feasibility using the raw maths. The paper written by Zephyr Penoyre and Emily Sandford from Cambridge and Columbia University respectively appears in preprint at Cornell Universty arXiv

So what is the concept. Well instead of a space elevator - a cable going up from earth with a huge counterweight at the other end, much like a child on the end of a parent’s arms swinging them around on the beach. The cable dangles from the moon into the earth gravity well to about the depth of the geostationary orbits. This is sufficient that it pulls the cable taught, but because of the slow spin, the centrifugal and Coriolis effects are minimal.

A simple sketch of the Spaceline, with the Earth (radius R), Moon (radius r), Earth-Moon distance (D), and height of geostationary orbit (Rgeo) drawn to scale.

Due to the earth’s gravity, the space elevator - a cable going from earth up to a counterweight in space, the cable itself would have to be incredibly strong just to hold it’s own weight. And although we have some indication that carbon nano-tubes are capable of the tensile strength required, we are many decades away from the ability to manufacture it into a large cable, and we struggle with tiny microscopic lengths, On top of this the carbon nano-tubes would have to be faultless as recent studies show that the strength required is not reached with imperfect cables, this is extra hard when we are talking about down to the molecular level of perfection. However, the Space line would not be required to be strong as the paper goes into the maths required concluding that the carbon fibre products like Kevlar, Dyneema and Zylon would actually be strong enough.

Of course a it’s not as good as a space elevator, in fact nowhere near as good, because you still have to launch with roughly the same fuel problems as you have to get to Geostationary orbit, that still requires some of the worlds biggest working rockets. However, it’s considerably better than launch to the moon as you still have a significant climb to get out of the gravity well of the earth after geostationary orbit. Once you are at geostationary orbit you can use solar power to climb up the cable out of the gravity well to the Lagrange point, and then slide down the cable to the surface of the moon.

The brilliant bit of the idea, which is in debt to the work of Pearson, Eubanks and Radley and others is the moon is tidally locked, this means that the same face of the moon is pointing to earth all the time, so the cable actually is not being swung by the moon rather it more like its dropped into a gently flowing river as the earth rotates once a month (slightly less, a lunar month) underneath.

The authors are most keen to point out that the Lagrange point L1 has some key benefits. Usually, the L1 Lagrange point is unstable and spacecraft require serious station-keeping to remain in this spot, but the presence of the cable could make this spot totally stable with a heap of benefits. This could turn out to be a centre of space manufacturing and rendezvous point for Earth-moon activity. So the authors expect to see considerable infrastructure built around this area of the cable. And knowing that this is a node into the Interplanetary Superhighway!!!

So how big is this initial cable?

Well, the authors try out a few designs, one straight, one tapered and one hybrid tapered. They propose a cable as thick as a pencil lead and estimate that the cable is only twice as heavy as the eagle lunar lander, so could actually be launched to the moon using current technology and deployed as such. The cable would cost billions to make and launch, but not in the undo-able billion range.

So, in short, the authors think that the cable would bring these benefits, bring down the cost of transport from geo to moon, Motion is easier via the line and simplifies navigation, haulage to and from the lunar surface, the technology payoff of such an undertaking, and this Lagrange base camp idea.

Many more details need ironing out, technological and sociological. But I’ve not seen too many objections that hold up to this work. And I love the idea that it would create a Lagrange Base Camp.

Largest Neutron star

Your average Neutron star is only about 1.4 times the mass of the Sun, but astronomers have discover one 2.17 times heavier.

Cross-section of neutron star. Densities are in terms of ρ0 the saturation nuclear matter density, where nucleons begin to touch. Robert Schulze

A Neutron star forms when a very big star 10-30 times bigger than the sun collapses, as it collapses, just like an ice skater pulling in their arms their spin becomes exaggerated due to the conservation of angular momentum. Sending out pulses of light first discovered by Jocelyn Bell. the linear speed of the surface of a neutron star can get up to about ¼ light speed and the gravity 10^11 x earth gravity.

But they collapse so far that they become pretty much the densest thing there can be. We are all familiar with the atoms of normal matter being made of a nucleus and a swarm of electrons whizzing around … in fact, if the nucleus was a football in the middle of a stadium these electrons would be whizzing around outside the stadium somewhere. Basically what we perceive as solid matter is barely even there. ….except in Neutron stars where the matter has been so compressed pretty much only the neutral neutrons from the original nuclei remain, the protons and electrons mostly gone, are all pushed next to one another only, only resisting further collapse by pressure theorized by the Pauli exclusion principle. If the mass gets too big the whole thing collapses into a black hole as the fabric of space-time is distorted beyond breaking point.

Another thing preventing further collapse is the spin of the neutron star that has gone from a massive spinning star to a dense super fast spinning ball the size of a city, the centrifugal force stopping it collapsing into a black hole. Slowly over time the loss of energy through gravitational waves probably means this bad boy will collapse into a BH.

This 2.89 millisecond Neutron star, J0740+6620 is about 19 miles across, 4600ly from earth or 27 million billion miles away. Discovered in 2012 And described by astronomers at the Green Bank Telescope Thankful Cromatie and Scott Ransom and a whole bunch of other researchers.

Left: unperturbed lightrays in a flat spacetime, right: shapiro-delayed and deflected lightrays in the vicinity of a gravitating mass Yukterez (Simon Tyran, Vienna)

It’s mass was calculated using the Shapiro Time Delay, because the science of time delays don’t care about your feelings. Luckily this pulsar is a binary with a white dwarf, and even luckier this white dwarf passes between us and the pulsar, a transit that effects the pulses of energy from the neutron star and using 5 years worth of data the scientists have used this slight disruption of the neutron star pulses to calculate the mass of the white dwarf and form this they are able to calculate the mass of the neutron star because it’s part of this binary system and they know the orbital periods etc. The Authors point out that the accuracy could be greatly increased using chime within a year doing daily measurements.

Paper is Relativistic Shapiro delay measurement of an extremely massive millisecond pulsar.

There are probably about 100 million of these things in the milky way.

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