Psyche Probe on Its Way to Asteroid Belt

Image credit: NASA/JPL-Caltech/ASU/Peter Rubin

Powered by a Hall thruster producing "250 millinewtons of force — about the amount of force that you would feel from the weight of holding one AA battery." 

Newton's first law of motion states that an object continues in its state of rest or uniform motion in a straight line, unless acted on by an external force. So once you give something a push in space, it keeps going. That doesn't happen on Earth because the external force in this case is drag, due to friction from the air. That slows an object down. Newton's second law of motion basically says that acceleration is proportional to force, so while the quarter-newton propulsion force is small and provides little acceleration, velocity increases over time. So unlike conventional rocket propulsion which generates high acceleration for a short period of time, Hall thrusters gently accelerate spacecraft for periods of months or years, to slowly build up velocity.

You can read more about the Psyche mission in this article on the NASA website. 

The Abolition of the Leap Second

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You may have heard Dr Shane Bergin speaking about this on Today with David McCullagh this morning. Leap seconds are being abolished and replaced by a system that will eventually allow a leap hour to be added, although that is unlikely to happen for thousands of years.

Leap seconds were introduced because a day isn't exactly 86,400 seconds long. Billions of years ago, a day was only about five hours long. According to a research article published in the academic journal Paleoceanography and Paleoclimatology, a day lasted approximately 23.5 hours during the Cretaceous Period, around 70 million years ago.

The gravitational interaction between the Earth and the Moon produces tidal effects that gradually slow the Earth's rotation. Leap seconds were added at irregular intervals to keep the time shown on our clocks closely aligned with the Earth's rotation and, consequently, the apparent motion of the Sun across the sky.

The last leap second was added on 31 December 2016, at 23:59:60 UTC. It was the 27th leap second added since 1972. The adjustments can cause problems for computer systems and other digital infrastructure, so international timekeepers have now agreed to phase them out in favour of a system that allows a much larger difference between atomic time and time based on the Earth's rotation.

In contrast, we will still need leap years because the Earth takes approximately 365.25 days to orbit the Sun, rather than exactly 365 days. Adding an extra day to February in leap years keeps our calendar aligned with the seasons. Without this adjustment, the dates of the seasons would gradually drift through the calendar, and Christmas would eventually fall in summer.

 

You can read more about the changes here on Scientific American. 

Scientists just voted to redefine how the world keeps time 

My Telemetry Software Didn't Control Voyager 1

Credit: NASA/JPL-Caltech

NASA's decision to switch off an instrument on Voyager 1 to keep the spacecraft operating reminded me of my much less glamorous work in a past life, when I wrote telemetry software to control pumps and other equipment in sewage and water treatment plants.

The Andromeda Galaxy: "It's Big, And Also Faaarrr Away"

The apparent size of the Andromeda Galaxy, compared to that of the Moon. AI image created by Grok.

At a distance of 2.5 million light-years, or 24 million trillion km, the Andromeda Galaxy is the most distant object visible to the naked eye. We can see it because space is mostly empty, and light from the stellar object reaches us relatively unchanged, unlike what happens when we view distant objects on the horizon on Earth.

How Much Thrust?

SLS rocket. Image credit: NASA

8.8 million pounds, 4.0 million kilos or 17.3 million newtons (the SI unit of force). That's 15% more thrust than the Saturn V rocket, used for the Apollo missions to the Moon in the late '60s and early '70s.
The SLS or Space Launch System is the rocket that's being used for the Artemis missions that will once again carry astronauts to the Moon. (Artemis was Apollo's twin brother in Greek mythology).
Huge amounts of thrust are needed to accelerate spacecraft, so that they can escape Earth's gravity. The escape velocity of planet Earth is 11.2 km/s or 25,000 mph. We can't simply use rockets to travel point-to-point to the Moon as it would be inefficient and require continuous rocket firing and fuel use. By travelling fast enough initially, hence the massive engines and fuel tanks, we can "coast" there, like a car with one's foot on the clutch. The principle is based on Newton's first law of motion—so once an object starts moving, it keeps moving uniformly, unless another force acts on it, Earth's gravity in this case. (That's why the Voyager spacecraft are still moving out beyond the Solar System). Technically, a spacecraft is falling back to Earth under the influence of the latter's gravity, but in the case of lunar missions, the Moon and its gravity "take over" when the craft is close enough, allowing it to be injected into lunar orbit. 

Earth Speeding Through the Universe and How is Speed Measured in Spacecraft

AI image generated by ChatGPT

Did you know that we're travelling at 600,000 km/hr on planet Earth as our home galaxy, the Milky Way, orbits the Local Group, a group of neighbouring galaxies? That's somewhat faster than the mere 1000 km/hr velocity of a point on the island of Ireland, due to the Earth turning on its axis. We don't experience the effects of constant velocity on our bodies, only acceleration and deceleration. So we can't tell whether we're stationary or moving.

Top 100 Cool Science Facts for Kids!

Photo courtesy Geralt on Pixabay. Text overlay © Eugene Brennan

Why is the sky blue? 

What is air made of? 

How many stars are there? 

World of wonder fun science facts that every child should know! This article covers space, nature, technology, engineering, elementary mathematica, chemistry, physics and biology.
Science is fascinating and tries to explain how everything in the world and outer space works. Science gives us the answers to questions like "What is electricity?" and "How does an aeroplane fly?" Read on and learn 100 more cool science facts! 

Artemis II On Schedule

Artemis II crew. Image credit: NASA/Kim Shiflett

The Artemis I mission, launched in 2022, involved sending an uncrewed Orion spacecraft into orbit around the Moon and bringing it back to Earth. Artemis II will be a crewed mission, launching four astronauts into a free-return orbit around the Moon and back to Earth, the first time humans will have been in lunar orbit since 1972. The mission had been delayed until September 2026 due to technical problems, but has now been brought forward to April of next year or possibly earlier. NASA's Orion spacecraft comprising of a command and service module sits on top of the unimaginatively-named Space Launch System (SLS), the equivalent of the Saturn V rocket used for the Apollo program. The 8.4 m (27.6 ft) diameter, 98 m (322 ft) tall SLS is a two-and-a-half-stage rocket, powered by engines that burn liquid hydrogen and liquid oxygen, assisted by two solid rocket boosters.

How Much Does the Length of a Day Vary By?

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Every four years we have a leap year and an extra day is added to the calendar in February. That's because the time it takes for the Earth to orbit the Sun is approximately 365.25 days. Considering the Earth's orbit as approximately a circular path around the Sun, If we didn't compensate for the extra quarter day, the Earth would end up being a little short of a full 360 degrees of its way around the Sun on the 31st December (a quarter day short). Eventually 31st of December would fall earlier and earlier in the seasons until it ended up in the summer. By adding an extra day every four years, the Earth is allowed to "catch up" in its orbit. Similarly, a day, or the time it takes the Earth to revolve on its axis isn't exactly 24 hours long and is influenced by environmental and geological events. In fact in 2025, the length of time between the longest and shortest day was approximately 1.6 mS. It mightn't seem like a lot, but to keep everything in sync, leap seconds have to be added onto Coordinated Universal Time (UTC) every so often. The leap second was introduced in 1972. The most recent leap second adjustment was in December 31, 2016. However leap seconds are controversial and cause issues with critical systems that rely on accurate timekeeping. 

More info here.

UN Planetary Defence Slightly Worried

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A 1.3% chance of hitting Earth according to this BBC article. But Earth should really be called "Water", because when viewed from the Pacific side, there's little land to be seen other than New Zealand and Australia. So even if it hits Earth, there's a high probability of it ending up in the ocean, just like spacecraft that are decommissioned and re-enter Earth's atmosphere. Even if the odds of it hitting our planet increase, and something has to be done about it, deflection technology has been proven to work. In 2022, the Double Asteroid Redirection Test or DART spacecraft, launched in 2021, collided with the asteroid Dimorphos, nudging it and adjusting its orbit.

Slingshotting Satellites Into Orbit

Only a third scale prototype at the moment and the company SpinLaunch has raised $150 million in investment. The centrifugal launcher spins the rocket in a vacuum to reduce drag and releases it at the right instant so it leaves the launcher at almost 7500 km/h. Once the rocket reaches a certain altitude, engines ignite to boost the projectile to an orbital velocity of 27,600 km/h. The advantage of the technology is that it dispenses with multistage rockets requiring enormous quantities of fuel, potentially reducing the cost of launching payloads into space.

Science Friday Podcast — Mars Sample Return Mission. It is Rocket Science

Image courtesy NASA/JPL-Caltech

On the program this week, the team discuss the retrieval of the Mars samples collected by the Perseverance rover. Some are ready for collection on the planet's surface and 30 samples in total will be returned to Earth. The return probably wont happen until late in the next decade. It's a difficult and complex project with many parts that have to work perfectly. A launch system has to be landed on the planet first (called the Mars Ascent Vehicle). An ESA spacecraft called the Earth Return Orbiter will then capture the launched sample capsule from orbit and transport it back to Earth where the samples can be analysed. The Perseverance rover has multiple analysis instruments on board, including two types of spectrometers (an instrument that can determine the chemical makeup of a substance). However more sophisticated analysis can only be done back on Earth.

More info on the retrieval project on the NASA website here.

Mars Curiosity Rover: Lessons Learned on Wheel Design

Public domain image courtesy NASA/JPL-Caltech/MSSS.

"The anomalous wheel wear suggests that loads and terrains representative of actual operational conditions were not adequately simulated during life testing"

 

The tyres are made from aluminium. According to this recommendation by JPL, metal fatigue and single event punctures caused by wind-eroded, immobile pyramidal shaped rocks was responsible for the damage.

The Curiosity rover has travelled over 20 miles on the surface of Mars since it landed on the red planet in 2011 as part of the Mars Science Laboratory mission. The robot is about the size of a small car and weighs around 900 kg.

5 Live Science Podcast — Jocelyn Bell Burnell and Pulsars

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In this 5 Live Science podcast, Northern Ireland native Jocelyn Bell Burnell talks with Dr Chris Smith about radio astronomy and her discovery of pulsars. These are rotating neutron stars that emit beams of electromagnetic radiation from their magnetic poles, the radiation sweeping the Universe like a lighthouse beam. Neutron stars are extremely dense. Atoms are mostly empty space, a simplistic model resembling our Solar System with electrons existing in outer orbitals and a nucleus at the centre. However just like the Solar System, there is lots of space between the electrons and nucleus. In a neutron star, gravity squeezes everything together so tightly that nuclei in adjacent atoms pack up against each other. The result is super-extreme density and according to Scientific American, a ping-pong ball sized piece of a neutron star would weigh over a billion tonnes.

https://www.bbc.co.uk/sounds/play/p0kds1xg

Linked content, courtesy the BBC. The BBC in no way endorses content on this blog.

Drag Acts

Image: Heavens-Above

The atmosphere doesn't end at a certain altitude, it just gets thinner and thinner. According to NASA however, the Karman line at an altitude of 62 miles is generally recognised as a boundary, and 99.99997 percent of Earth's atmosphere lies beneath this level. It's also speculated that a cloud of hydrogen atoms around the Earth, called the geocorona, may extend to over twice the distance between the Earth and the Moon.

The International Space Station (ISS) orbits at an altitude of 370–460 km.

How Do Spacecraft Get Their Power?

Rocket engines are used for propulsion on spacecraft, but the electronics has to be powered also. Frequently solar panels are used for generating electricity. But what happens if a space probe is so distant from the Sun that it's just a pinprick of light like any other star?

The Seebeck effect

If you heat the end of a piece of wire, it establishes a thermal gradient from the hot end to the cold end. This causes charge carriers (electrons or "holes") to move from one end of the wire to the other, resulting in a potential difference or voltage between the two ends of the wire. This is called the Seebeck effect. Devices that make use of this effect are called thermocouples and there's one in your oil or gas central heating boiler for measuring the temperature inside the burner chamber. A thermocouple is made of two wires of dissimilar materials twisted or bonded together at one end and can measure temperatures of over 1000 degrees C.

 

A thermocouple measuring circuit. Image courtesy Wtshymanski, CC BY-SA 3.0 via Wikimedia Commons

Thermopiles

Now as you may be aware, if you connect lots of batteries in series, e.g. AA cells end to end, the voltages add up. So for instance in a transistor radio, four AA, 1.5 V cells give 6 V for powering the radio. The electromotive force (EMF) or voltage generated by a single thermocouple is typically small, of the order of tens of microvolts per degree of temperature difference between its hot and cold end. If hundreds or thousands of thermocouples are connected together in series, they can generate useful voltages. This arrangement is called a thermopile. If all the junctions between the wires are made hot, and alternating junctions are kept cold, the device can generate electricity to power things. Thermopile powered radios, running on oil lamps, were used in remote areas of Russia in the past where electricity and batteries were unavailable.

 

Radioisotope thermoelectric generators (RTG, RITEG)

A radioisotope thermoelectric generator is a thermopile that uses a radioisotope source to heat the hot junctions of a thermopile while the other junctions are kept cool. The radioisotope source is typically materials such as uranium or plutonium. RTGs can generate hundreds of watts and were used in the Voyager 1 and Voyager 2 spacecraft, launched in 1977. The Perseverance Rover on Mars is powered by a 110 W RTG using Plutonium-238 as a heat source.

References

NASA. (n.d.). Mars 2020: Perseverance Rover - NASA Science. NASA. https://science.nasa.gov/mission/mars-2020-perseverance

Rowe, M. (2020, October 23). Thermocouples: Simple but misunderstood. EDN. https://www.edn.com/thermocouples-simple-but-misunderstood/ 

Thermo-electric generators. (n.d.). http://www.douglas-self.com/MUSEUM/POWER/thermoelectric/thermoelectric.htm

 

 

 

Hubble's Deep Field Images

Image Credit: NASA, ESA, R. Bouwens and G. Illingworth (University of California, Santa Cruz) https://hubblesite.org/.../news-releases/2006/news-2006-12

For 10 days in 1995, the Hubble Space Telescope stared at a tiny patch of space near the Plough constellation. It built up a time exposure image showing thousands of galaxies, some so distant it takes 10 billion years for light to reach us from them, travelling at almost 300,000 km per second. In subsequent years, Hubble created further deep field images.
You can read more about the observation on the Hubblesite here.

The Sun's Vital Role: How It Powers Life and Energy on Earth

© Eugene Brennan

 

As you probably know, the Sun is a giant nuclear reactor, the cosmological equivalent of a hydrogen bomb. It’s our nearest star and it would take 600 years to cycle there at a leisurely pace of 12 miles per hour, 24/7. That’s if there was actually a road we could travel on! Even at a distance of 93 million miles, we feel its heat, and it lights our world and has a huge influence on planet Earth. Without the Sun, the Earth would eventually become a cold, frozen place as the temperature of the planet continued to fall to hundreds of degrees below zero. The Sun drives the climate and it creates the energy necessary for crops to grow. Without sunshine, the chemical process known as photosynthesis can’t take place, since plants need light energy to turn CO₂ and water into sugar and starch in their roots, stems and leaves. Without plants, animals can’t survive either, because herbivores eat plants and carnivores in turn eat the herbivores that eat the plants. The Sun was also responsible for providing the energy that is now locked into fossil fuels. Refined oil products and gas originated from dead marine organisms which over millions of years metamorphosed into crude oil. Those organisms, such as plankton, algae and other sea creatures relied on the energy of the Sun for life. Similarly coal originated from trees in ancient forests, pressed into a rock-like material by huge pressures from above. Our renewable energy sources today all derive their energy from the Sun. Solar panels convert sunshine directly into electricity. Wind, wave, tidal and hydro power wouldn’t be possible without the motion of air and sea caused by solar energy heating the ground surface and oceans and generating air currents.

Like most stars, the Sun formed when clouds of dust left over from the formation of the Universe coalesced under the influence of gravity into clumps. The process took millions of years and planets in our Solar System formed similarly. The swirling clumps slowly became more defined and spherical. Small clumps became planets, but the larger clump at the centre of the Solar System continued to become tighter and more compressed. Newton’s law of universal gravitation states that: 

 

“Every particle attracts every other particle in the universe with a force that is proportional to the product of their masses and inversely proportional to the square of the distance between their centres.”

 

The consequences are that the force of gravity is stronger if either or both particles have greater masses and are closer together.

In the case of the Sun, the sheer volume and weight (or more correctly mass in this context) of the clump at the centre of the Solar System meant that there was colossal gravity, and that gravity continued to pull everything together towards a common centre. As everything continued to get closer together, the “distance apart” in Newton’s law became smaller. The result was a runaway situation with distance getting smaller and gravity increasing because of the increasingly smaller distances between particles. Eventually atoms were squeezed into one another, ultimately sparking off a fusion reaction (something we've being artificially doing for decades in experiments on Earth in the quest for fusion power). The process didn’t continue however and eventually there was equilibrium between the heat of the thermonuclear reaction causing expansion and gravity pulling inwards.

Facts about the Sun

 

• It’s 93 million miles or 149 million km from Earth.

• The Sun is approximately 4.6 billion years old.

• It has a diameter of approximately 864,600 miles or 1,391,400 km.

• Eventually the Sun will become a red giant star, swallowing up the inner planets including Earth in 7.59 billion years time.

• Ultimately the Sun will become a white dwarf with 54% of its original mass.

 

Weight is something that changes depending where you are in the Universe. An astronaut weighs less on the Moon, but their mass is the same. Both mass and weight are measured in kg.

Many thanks to ChatGPT for making up the title!

References:

How does the Sun work? | High Altitude Observatory. (n.d.). https://www2.hao.ucar.edu/.../about-the.../how-does-sun-work
K.-P. Schröder, Robert Connon Smith, Distant future of the Sun and Earth revisited, Monthly Notices of the Royal Astronomical Society, Volume 386, Issue 1, 1 May 2008, Pages 155–163, https://doi.org/10.1111/j.1365-2966.2008.13022.x

What Came Before the Big Bang?

Image created on request by Bing Image Creator.

The general consensus is that space and time began with the Big Bang and everything expanded from a mathematical point. It wasn't as though there was a massive explosion and then everything expanded into a huge, pre-existing void. We couldn't identify a point in space today where the Big Bang occurred and put a plaque at it marking the event. In a sense it occurred everywhere. Before the Big Bang, there was no space, it was created, as was time. So there was also no "before" the Big Bang.

"Nothing was around before the Big Big(sic) Bang" according to Stephen Hawking in this interview where he discusses the concept of four dimensional "spacetime".

Cartoon created on request by Bing Image Creator. The Grammar Police were involved because BIC can't spell !

 

#scienceweek #ScienceWeek2024

Super Fast Spinning Star

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The disc on a 4 1/2" angle grinder spins at less than half this speed. Centripetal force is the force that pulls inwards on a rotating object, like when you turn round and round in a circle, holding a rope with a weight on the end and the weight flies outwards. In that scenario, you can feel the tension in the rope. That's the reaction to you pulling inwards (Newton's third law - "For every action there is an equal and opposite reaction"). For a rope or angle grinder disc, the material can withstand the tension and grinder disks are reinforced with nylon mesh to stop them exploding. In the case of a spinning neutron star reported in the article, the immense gravity is the force that prevents it flying apart.