Universe Today

September 14, 2010May 16, 2016 by Fraser Cain

What Is Terminal Velocity?

The higher you are when you jump, the more it hurts when you hit the ground. That’s because the Earth’s gravity is constantly accelerating you towards its center. But there’s actually a maximum speed you reach, where the acceleration of the Earth’s gravity is balanced by the air resistance of the atmosphere. The maximum speed is called terminal velocity.

The terminal velocity speed changes depending on the weight of the object falling, its surface area and what it’s falling through. For example, a feather doesn’t weigh much and presents a very large surface area to the air as it falls. So its terminal velocity speed is much slower than a rock with the same weight. This is why an ant can fall off a tall building and land unharmed, while a similar fall would kill you. Keep in mind that this process happens in any gas or fluid. So terminal velocity defines the speed that a rock sinks when you drop it in the water.

So, let’s say you’re a skydiver jumping out of an airplane. What’s the fastest speed you’ll go? The terminal velocity of a skydiver in a free-fall position, where they’re falling with their belly towards the Earth is about 195 km/h (122 mph). But they can increase their speed tremendously by orienting their head towards the Earth – diving towards the ground. In this position, the skydiver’s velocity increases to more than 400 km/h.

The world skydiving speed record is held by Joseph Kittinger, who was able to fall at a speed of 988 km/h by orienting his body properly and jumping at high altitude, where there’s less wind resistance.

The gravity of the Earth pulls at you with a constant acceleration of 9.81 meters/second. Without any wind resistance, you’ll fall 9.81 meters/second faster every second. 9.81 meters/second the first second, 19.62 meters/ second in the next second, etc.

The opposing force of the atmosphere is called drag. And the amount of drag force increases approximately proportional to the square of the speed. So if you double your speed, you experience a squaring of the drag force. Since the drag force is going up much more quickly than the constant acceleration, you eventually reach a perfect balance between the force of gravity and the drag force of whatever you’re moving through.

Outside the Earth’s atmosphere, though, there’s no terminal velocity. You’ll just keep on accelerating until you smash into whatever’s pulling on you.

We have written many articles about the terminal velocity for Universe Today. Here’s an article featuring the definition of velocity, and here’s an article about the X-Prize Entrant completing the Drop Test

If you’d like more info on the Terminal Velocity, check out a Lecture on Terminal Velocity, and here’s a link to a NASA article entitled, The Way Things Fall.

We’ve also recorded an entire episode of Astronomy Cast all about Gravity. Listen here, Episode 102: Gravity.

Sources:
NASA
Wikipedia
GSU Hyperphysics

September 14, 2010December 24, 2015 by Nancy Atkinson

NASA Names Crew for Rescue Mission or Potential Added Shuttle Flight

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NASA announced the names of the four astronauts who will make up the crew of STS-335, the rescue mission that would fly only if there is a problem with the current final scheduled shuttle flight, Endeavour’s STS-134 mission. Additionally, the four crew members will prepare for the “final final” shuttle flight which may be added to the launch manifest, depending on what Congress decides on adding one more mission since Atlantis will be ready to fly.

“These astronauts will begin training immediately as a rescue crew as well as in the baseline requirements that would be needed to fly an additional shuttle flight,” said Bill Gerstenmaier, associate administrator for NASA’s Space Operations. “The normal training template for a shuttle crew is about one year prior to launch, so we need to begin training now in order to maintain the flexibility of flying a rescue mission if needed, or alter course and fly an additional shuttle mission if that decision is made.”

Having a “Launch On Need” crew ready for a rescue flight is based on recommendations made after the loss of space shuttle Columbia in February 2003. NASA has trained a launch on need crew to be ready to fly in the event of irreparable damage to a shuttle while in orbit. Typically, the next crew to fly serves as the rescue crew for the current mission.

The four astronauts are:

Chris Ferguson, a retired U.S. Navy captain and veteran of two previous shuttle missions, would command the flight. Astronaut and U.S. Marine Col. Doug Hurley would serve as pilot, and astronauts Sandy Magnus and retired U.S. Air Force Col. Rex Walheim would be the mission specialists.

If required, the STS-335 rescue mission would launch on shuttle Atlantis in June 2011 to bring home the STS-134 crew from the International Space Station. STS-134 currently is scheduled to lift off on Feb. 26, 2011, from NASA’s Kennedy Space Center in Florida. If converted to an additional shuttle flight, STS-335 would be redesignated STS-135 and targeted to launch in June 2011.

Source: NASA

September 14, 2010December 24, 2015 by Nancy Atkinson

NASA Considering Rail Gun Launch System to the Stars

Different technologies to push a spacecraft down a long rail have been tested in several settings, including this Magnetic Levitation (MagLev) System evaluated at NASA's Marshall Space Flight Center. Engineers have a number of options to choose from as their designs progress. Photo credit: NASA

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The idea for using rail guns to launch objects to space has been around for years – even Isaac Newton considered the concept. But now a group of NASA engineers is seriously studying the possibility of using a rail gun as a potential launch system to the stars, and they are looking for a system that turns a host of existing cutting-edge technologies into the next giant leap spaceward. Stan Starr, branch chief of the Applied Physics Laboratory at Kennedy Space Center said that nothing in the design calls for brand-new technology to be developed, but counts on a number of existing technologies to be pushed forward. He said developing such a system would be a “major technology revolution.”

“All of these are technology components that have already been developed or studied,” he said. “We’re just proposing to mature these technologies to a useful level, well past the level they’ve already been taken.”

A rail gun utilizes a magnetic field powered by electricity to accelerate a projectile along a set of rails, similar to train rails. One early proposal from the NASA group calls for a wedge-shaped aircraft with scramjets to be launched horizontally on an electrified track or gas-powered sled. The aircraft would fly up to Mach 10, using the scramjets and wings to lift it to the upper reaches of the atmosphere where a small payload canister or capsule similar to a rocket’s second stage would fire off the back of the aircraft and into orbit. The aircraft would come back and land on a runway by the launch site.

The engineers, from KSC and other NASA centers, contend the system, with its advanced technologies, will benefit the nation’s high-tech industry by perfecting technologies that would make more efficient commuter rail systems, better batteries for cars and trucks, and numerous other spinoffs.

For example, electric tracks catapult rollercoaster riders daily at theme parks. But those tracks call for speeds of a relatively modest 100 km/h (60 mph) — enough to make the ride exciting, but not nearly fast enough to launch something into space. The launcher would need to reach at least 10 times that speed over the course of two miles in Starr’s proposal.

The good news is that NASA and universities already have done significant research in the field, including small-scale tracks at NASA’s Marshall Space Flight Center in Huntsville, Ala., and at Kennedy. The Navy also has designed a similar catapult system for its aircraft carriers.

As far as the aircraft that would launch on the rail, there already are real-world tests for designers to draw on. The X-43A, or Hyper-X program, and X-51 have shown that scramjets will work and can achieve remarkable speeds.

The group sees NASA’s field centers taking on their traditional roles to develop the Advanced Space Launch System. For instance, Langley Research Center in Virginia, Glenn Research Center in Ohio and Ames Research Center in California would work on different elements of the hypersonic aircraft. Dryden Research Center in California, Goddard Space Flight Center in Maryland and Marshall would join Kennedy in developing the launch rail network. Kennedy also would build a launch test bed, potentially in a two-mile long area parallel to the crawlerway leading to Launch Pad 39A.

Because the system calls for a large role in aeronautic advancement along with rocketry, Starr said, “essentially you bring together parts of NASA that aren’t usually brought together. I still see Kennedy’s core role as a launch and landing facility.”

The Advanced Space Launch System is not meant to replace the space shuttle or other program in the near future, but could be adapted to carry astronauts after unmanned missions rack up successes, Starr said.

The studies and development program could also be used as a basis for a commercial launch program if a company decides to take advantage of the basic research NASA performs along the way. Starr said NASA’s fundamental research has long spurred aerospace industry advancement, a trend that the advanced space launch system could continue.

For now, the team proposed a 10-year plan that would start with launching a drone like those the Air Force uses. More advanced models would follow until they are ready to build one that can launch a small satellite into orbit.

A rail launcher study using gas propulsion already is under way, but the team is applying for funding under several areas, including NASA’s push for technology innovation, but the engineers know it may not come to pass. The effort is worth it, however, since there is a chance at revolutionizing launches.

Source: NASA

September 14, 2010December 24, 2015 by Jerry Coffey

What Is Mechanical Energy

Millennium Force roller coaster Credit: Cedar Point

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The straight forward answer to ‘what is mechanical energy’ is that it is the sum of energy in a mechanical system. This energy includes both kinetic energy(energy of motion) and potential energy(stored energy).

Objects have mechanical energy if they are in motion and/or if they are at some position relative to a zero potential energy position. A few examples are: a moving car possesses mechanical energy due to its motion(kinetic energy) and a barbell lifted high above a weightlifter’s head possesses mechanical energy due to its vertical position above the ground(potential energy).

Kinetic energy is the energy of motion. An object that has motion, vertical or horizontal motion, has kinetic energy. There are many forms of kinetic energy: vibrational (the energy due to vibrational motion), rotational (the energy due to rotational motion), and translational (the energy due to motion from one location to another).

Potential energy is the energy stored in a body or in a system due to its position in a force field or its configuration. The standard unit of measure for energy and work is the joule. The term “potential energy” has been used since the 19th century.

Because of the different components of mechanical energy, it exists in every system in the universe. From a baseball being thrown to a brick falling off of a ledge, mechanical energy surrounds us. Defining what is mechanical energy is easy, but finding examples of it are even easier.

We have written many articles about mechanical energy for Universe Today. Here’s an article about how generators work, and here’s an article about what is energy.

If you’d like more info on Mechanical Energy, check out a Discussion on Energy, and here’s a link to an article about Momentum.

We’ve also recorded an entire episode of Astronomy Cast all about Gravity. Listen here, Episode 102: Gravity.

September 14, 2010December 24, 2015 by Jerry Coffey

What Is Lithosphere

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Every rocky planet has a lithosphere, but what is lithosphere? It is the rigid outermost shell of a rocky planet. Here on Earth the lithosphere contains the crust and upper mantle. The Earth has two types of lithosphere: oceanic and continental. The lithosphere is broken up into tectonic plates.

Oceanic lithosphere consists mainly of mafic(rich in magnesium and iron) crust and ultramafic(over 90% mafic) mantle and is denser than continental lithosphere. It thickens as it ages and moves away from the mid-ocean ridge. This thickening occurs by conductive cooling, which converts hot asthenosphere into lithospheric mantle. It was less dense than the asthenosphere for tens of millions of years, but after this becomes increasingly denser. The gravitational instability of mature oceanic lithosphere has the effect that when tectonic plates come together, oceanic lithosphere invariably sinks underneath the overriding lithosphere. New oceanic lithosphere is constantly being produced at mid-ocean ridges and is recycled back to the mantle at subduction zones, so oceanic lithosphere is much younger than its continental counterpart. The oldest oceanic lithosphere is about 170 million years old compared to parts of the continental lithosphere which are billions of years old.

The continental lithosphere is also called the continental crust. It is the layer of igneous, sedimentary rock that forms the continents and the continental shelves. This layer consists mostly of granitic rock. Continental crust is also less dense than oceanic crust although it is considerably thicker(25 to 70 km versus 7-10 km). About 40% of the Earth’s surface is now covered by continental crust, but continental crust makes up about 70% of the volume of Earth’s crust. Most scientists believe that there was no continental crust originally on the Earth, but the continental crust ultimately derived from the fractional differentiation of oceanic crust over the eons. This process was primarily a result of volcanism and subduction.

We may not walk directly the lithosphere, but it shapes every topographical feature the we see. The movement of the tectonic plates has presented many different shapes for our planet over the eons and will continue to change our geography until our planet ceases to exist.

We have written many articles about the lithosphere for Universe Today. Here’s an article about the lithosphere, and here’s an article about the tectonic plates.

If you’d like more info on the Earth’s lithosphere, check out NASA’s Solar System Exploration Guide on Earth. And here’s a link to NASA’s Earth Observatory.

We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth.

September 14, 2010December 24, 2015 by Jerry Coffey

What Is Light Energy

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Just asking ‘what is light energy’ opens you up to a flood of other questions trying to narrow down the context that you are asking the question in. In photometry, luminous energy is the perceived energy of light. It can also be defined as the electromagnetic radiation of visible light. Since light itself is energy, then another definition is relevant: light is nature’s way of transferring energy through space.

The speed of light is about 300,000 km/s. To put that in perspective, when you watch the sun set, it has actually been 10 minutes since that light left the Sun. Light energy is measured with two main sets of units: radiometry measures light power at all wavelengths and photometry measures light with wavelength weighted with respect to a standardized model of human brightness perception. Photometry is useful when measuring light intended for human use. The photometry units are different from most units because they take into account how the human eye responds to light. Based on this, two light sources which produce the same intensity of visible light do not necessarily appear equally bright.

Light exerts a physical pressure on objects in its path. This is explained by the particle nature of light in which photons strike and transfer their momentum. Light pressure is equal to the power of the light beam divided by the speed of light. The effect of light pressure is negligible for everyday objects. For example, you can lift a coin with laser pointers, but it would take 1 billion of them to do it. Light pressure can cause asteroids to spin faster by working on them like wind pushing a windmill. That is why some scientist are researching solar sails to propel intersteller flight.

Light is all around us. It has the ability to tan or burn our skins, it can be harnessed to melt metals, or heat our food. Light energy posed a huge challenge for scientist up to the 1950’s. Hopefully, in the future, we will be able to use light energy and solar wind to travel among the stars.

We have written many articles about light energy for Universe Today. Here’s an article about the prescription for light pollution, and here’s an article about where visible light come from.

If you’d like more info on Light Energy, check out NASA’s Page on Atoms and Light Energy. And here’s a link to an article about How Photovoltaics Work.

We’ve also recorded an episode of Astronomy Cast all about Energy Levels and Spectra. Listen here, Episode 139: Energy Levels and Spectra.

Sources:
Johns Hopkins University
Wikipedia

September 14, 2010December 24, 2015 by Fraser Cain

Spacecraft

Space Travel — Atlantis Breaks Through the Clouds

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When a vehicle or robot is designed to leave the Earth’s atmosphere and travel through space, we call that a spacecraft. There are many different kinds of spacecraft, such as satellites orbiting the Earth, robots sent to other planets, orbiting space stations, and vehicles sent to the Moon carrying human astronauts.

The harsh environment of space is hard on spacecraft, so they have to be built to tolerate temperature extremes that dip down hundreds of degrees below zero, and then hot enough to boil water. There’s no atmospheric pressure in space, so any spacecraft carrying humans needs a rigid shell that keeps its atmosphere inside. There is a constant stream of radiation from the Sun and outside the Solar System constantly raining down on a spacecraft, damaging components and raising the cancer risk for any human astronauts.

Spacecraft also need components to be able to travel in space. They require a form of propulsion that allows them to change their trajectory. These can range from traditional chemical rockets to the newer ion drives and even nuclear engines. Spacecraft need some kind of power system, solar panel arrays or nuclear generators. They need a communications system to send and receive signals from Earth. They require an attitude control system, to keep their instruments pointed in the right directions. And finally, they need the specific components to carry out their mission. In the case of the Apollo capsules, these spacecrafts’ mission was to carry NASA astronauts to and from the Moon safely. These means they needed life support systems, navigation computers, and landing equipment. A spacecraft designed to orbit Jupiter will require different components to a spacecraft designed to land on the surface of Venus.

The first spacecraft – the first object to ever leave the Earth’s atmosphere and orbit the planet – was the Soviet satellite Sputnik 1. It launched on October 4th, 1957. The space age began, and many other spacecraft launches followed. The first human to orbit the Earth was Yuri Gagarin, who was carried to space aboard a Soviet rocket on April 12, 1961. The first spacecraft to travel to the Moon was Luna-2, which crashed into the Moon on September 12, 1959. The first spacecraft to safely carry humans to the surface of the Moon was the Apollo 11 mission, which landed on July 20, 1969.

We have written many articles about the spacecraft for Universe Today. Here’s an article about spacecraft propulsion, and here’s an article about the manned spacecraft of China.

If you’d like more information on spacecrafts, here’s a link to NASA’s Official space shuttle page, and here’s the homepage for NASA’s Human Spaceflight.

We’ve recorded an episode of Astronomy Cast all about the space shuttle. Listen here, Episode 127: The US Space Shuttle.

Source: Wikipedia

September 14, 2010December 24, 2015 by Fraser Cain

Voyager 2

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Voyager 2 is easily the most famous spacecraft sent from Earth to explore other planets. Launched on August 20, 1977, Voyager visited Jupiter and Saturn, and is the only spacecraft to have ever made a flyby of the outer planets Uranus and Neptune. It flew past Neptune in 1989, but it’s still functioning and communicating with Earth.

Voyager 2 and its twin spacecraft Voyager 1 were built at NASA’s Jet Propulsion Lab in Pasadena, California. The two spacecraft were built with identical components, but launched on slightly different trajectories. Voyager 2 took advantage of a rare alignment of the planets so that it could use a gravity assisting boost as it flew past each one. The increased velocity from Jupiter would help it reach Saturn, Saturn helped it get to Uranus and then to Neptune.

It made its closest approach to Jupiter on July 9, 1979, passing within 570,000 km of the planet’s cloud tops. It captured some of the first, highest resolution images of Jupiter’s moons, showing volcanism on Io, and cracks in the icy surface of Europa. Astronomers now suspect that Europa’s surface hides a vast ocean of water ice.

Voyager 2 then went on to visit Saturn on August 26, 1981, and then onto Uranus on January 24, 1986. This was the first time a spacecraft had ever encountered Uranus, and captured images of the planet close up. Voyager studied Uranus’ rings, and discovered several new moons orbiting the planet. Voyager 2 made its final planetary visit with Neptune on August 25, 1989. Here the spacecraft discovered the planet’s “Great Dark Spot”, and discovered more new moons.

Voyager 2 is now considered an interstellar mission. This means that it has enough velocity to escape the Solar System and travel to another star. Of course, at its current speed, it would take hundreds of thousands of years to reach even the closest star. Scientists think that the spacecraft will continue transmitting radio signals until at least 2025, almost 50 years after it was launched.

We have written many articles about Voyager 2 for Universe Today. Here’s an article about NASA’s diagnosed problems with Voyager 2, and here are some Voyager 2 pictures.

If you’d like more information on the Voyager 2 mission, here’s a link to Voyager’s Interstellar Mission Homepage, and here’s the homepage for NASA’s Voyager Mission Website.

We’ve recorded an episode of Astronomy Cast all about Interstellar Travel. Listen here, Episode 145: Interstellar Travel.

Source: NASA

September 13, 2010January 20, 2016 by Nancy Atkinson

Watch SETI Webcast This Week

The National Radio Astronomy Observatory (NRAO) is sponsoring a workshop this week on the past and next 50 years of SETI (Search for Extraterrestrial Intelligence) an (SETI), and they are webcasting many of the sessions on Monday, Tuesday and Wednesday of this week, September 13-15. The workshop featuring leading scientific researchers as well as authors, historians, religious leaders, and biologists. Viewers will be able to send questions to the presenters. The webcasts begin at 8:30 a.m., EDT, on September 13, 14, and 15, and can be watched above, or at this link.

You can see the workshop schedule at this link.

Drake will webcast his views on “SETI in 2061 and Beyond”, at 8:30 a.m., EDT, on September 15.

“This workshop focuses on a topic that has a profound influence on the way we view ourselves and our place in the Universe,” said Dr. Glen Langston, NRAO astronomer and workshop organizer. “We are pleased to present this to the public through the webcast.”

September 13, 2010December 24, 2015 by Nancy Atkinson

Daylight Occultation of Venus by the Moon

Composite images of Venus occultation on Sept. 11, 2010. Credit: Kerneels Mulder

On September 11, 2010 South Africa had an amazing view of a full daylight occultation of Venus by the Moon, and Kerneels Mulder captured it, and shared it with Universe Today. He sent us this video created from the images he took of the event, and below is a composite look at all the images, showing Venus as it reappears from behind the Moon.

“The occultation happened in full daylight, with the Moon only 40° from the Sun, making it difficult to capture detailed images,” Mulder wrote us. “Venus disappeared behind the dark side of the Moon at around 14:20 (GMT+2) and reappeared on the bright side of the Moon at 15:54 (GMT+2).”

Mulder said the sight was amazing. “With the naked eye Venus was easily visible as a bright dot close to the crescent Moon. The 3.5” refractor used during imaging showed an even more awe-inspiring view with both the crescents of the Venus and the Moon visible in the same field of view.”

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