On Sunday, May 31, the Cassini spacecraft will perform its last close pass of Hyperion, Saturn’s curiously spongelike moon. At approximately 9:36 a.m. EDT (13:36 UTC) it will zip past Hyperion at a distance of about 21,000 miles (34,000 km) – not its closest approach ever but considerably closer (by 17,500 miles/28,160 km) than it was when the image above was acquired.*
This will be Cassini’s last visit of Hyperion. It will make several flybys of other moons within Saturn’s equatorial plane over the course of 2015 before shifting to a more inclined orbit in preparation of the end phase of its mission and its operating life in 2017.
At 255 x 163 x 137 miles (410 x 262 x 220 km) in diameter, Hyperion is the largest of Saturn’s irregularly-shaped moons. Researchers suspect it’s the remnant of a larger body that was blown apart by an impact. Hyperion’s craters appear to have a “punched-in” look rather than having been excavated, and have no visible ejecta or secondary craters nearby.
Impacts on Hyperion tend to “punch in” the surface material, rather than blasting it out. (NASA/JPL/SSI. Edit by J. Major.)
Hyperion orbits Saturn in an eccentric orbit at a distance of over 920,000 miles (1.48 million km)…that’s almost four times the distance our Moon is from us! This distance – as well as constant gravitational nudges from Titan – prevents Hyperion from becoming tidally locked with Saturn like nearly all of its other moons are. In fact its rotation is more of haphazard tumble than a stately spin, making targeted observations of any particular regions on its surface virtually impossible.
Images from the May 31 flyby are expected to arrive on Earth 24 to 48 hours later.
As small as it is Hyperion is Saturn’s eighth-largest moon, although it appears to be very porous and has a density half that of water. Read more about Hyperion here and see more images of it from Cassini here and here.
*Cassini did come within 310 miles (500 km) of Hyperion on Sept. 26, 2005, but the images to make up the view above were acquired during approach.
UPDATE June 1, 2015: the raw images from Cassini’s flyby have arrived on Earth, check out a few below. (Looks like Cassini ended up with the same side of Hyperion again!)
Hyperion on May 31, 2015. Credit: NASA/JPL-Caltech/SSI. (Minor editing by J. Major.)Hyperion on May 31, 2015. Credit: NASA/JPL-Caltech/SSI.Hyperion on May 31, 2015. Credit: NASA/JPL-Caltech/SSI. (Minor editing by J. Major.)
For more than four years NASA’s MESSENGER spacecraft has been orbiting our solar system’s innermost planet Mercury, mapping its surface and investigating its unique geology and planetary history in unprecedented detail. But the spacecraft has run out of the fuel needed to maintain its extremely elliptical – and now quite low-altitude – orbit, and the Sun will soon set on the mission when MESSENGER makes its fatal final dive into the planet’s surface at the end of the month.
On April 30 MESSENGER will impact Mercury, falling down to its Sun-baked surface and colliding at a velocity of 3.9 kilometers per second, or about 8,700 mph. The 508-kilogram spacecraft will create a new crater on Mercury about 16 meters across.
The impact is estimated to occur at 19:25 UTC, which will be 3:25 p.m. at the John Hopkins University Applied Physics Lab in Laurel, Maryland, where the MESSENGER operations team is located. Because the spacecraft will be on the opposite side of Mercury as seen from Earth the impact site will not be in view.
MESSENGER image of “hollows” around a crater’s central peak – one of the many unique discoveries the mission made about Mercury. Read more here.
But while it’s always sad to lose a dutiful robotic explorer like MESSENGER, its end is bittersweet; the mission has been more than successful, answering many of our long-standing questions about Mercury and revealing features of the planet that nobody even knew existed. The data MESSENGER has returned to Earth – over ten terabytes of it – will be used by planetary scientists for decades in their research on the formation of Mercury as well as the Solar System as a whole.
“For the first time in history we now have real knowledge about the planet Mercury that shows it to be a fascinating world as part of our diverse solar system,” said John Grunsfeld, associate administrator for NASA’s Science Mission Directorate. “While spacecraft operations will end, we are celebrating MESSENGER as more than a successful mission. It’s the beginning of a longer journey to analyze the data that reveals all the scientific mysteries of Mercury.”
On April 6 MESSENGER used up the last vestiges of the liquid hydrazine propellant in its tanks, which it needed to make course corrections to maintain its orbit. But the tanks also hold gaseous helium as a pressurizer, and system engineers figured out how to release that gas through the complex hydrazine nozzles and keep MESSENGER in orbit for a few more weeks.
Earth and the Moon imaged by MESSENGER on Oct. 8, 2014. Credit: NASA/JHU APL/Carnegie Institution of Washington.
On April 24, though, even those traces of helium will be exhausted after a sixth and final orbit correction maneuver. From that point on MESSENGER will be coasting – out of fuel, out of fumes, and out of time.
“Following this last maneuver, we will finally declare MESSENGER out of propellant, as this maneuver will deplete nearly all of our remaining helium gas,” said Mission Systems Engineer Daniel O’Shaughnessy. “At that point, the spacecraft will no longer be capable of fighting the downward push of the Sun’s gravity.
“After studying the planet intently for more than four years, MESSENGER’s final act will be to leave an indelible mark on Mercury, as the spacecraft heads down to an inevitable surface impact.”
But MESSENGER scientists and engineers can be proud of the spacecraft that they built, which has proven itself more than capable of operating in the inherently challenging environment so close to our Sun.
“MESSENGER had to survive heating from the Sun, heating from the dayside of Mercury, and the harsh radiation environment in the inner heliosphere, and the clearest demonstration that our innovative engineers were up to the task has been the spacecraft’s longevity in one of the toughest neighborhoods in our Solar System,” said MESSENGER Principal Investigator Sean Solomon. “Moreover, all of the instruments that we selected nearly two decades ago have proven their worth and have yielded an amazing series of discoveries about the innermost planet.”
True-color image of Mercury made from MESSENGER data. Credit: NASA/JHU APL/Carnegie Institution of Washington.
The MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) spacecraft launched on August 3, 2004, and traveled over six and a half years before entering orbit about Mercury on March 18, 2011 – the first spacecraft ever to do so. Learn more about the mission’s many discoveries here.
The video below was released in 2013 to commemorate MESSENGER’s second year in orbit and highlights some of the missions important achievements.
Have you ever heard that spacecraft can speed themselves up by performing gravitational slingshot maneuvers? What’s involved to get yourself going faster across the Solar System.
Let’s say you want to go back in time and prevent Kirk from dying on the Enterprise B.
You could use a slingshot maneuver. You’d want to be careful that you don’t accidentally create an alternate reality future where the Earth has been assimilated by the Borg, because Kirk wasn’t in the Nexus to meet up with Professor Picard and Sir Iandalf Magnetopants, while they having the best time ever gallivanting around New York City.
*sigh* Ah, man. I really love those guys. What was I saying? Oh right. One of the best ways to increase the speed of a spacecraft is with a gravitational slingshot, also known as a gravity assist.
There are times that fantasy has bled out too far into the hive mind, and people confuse a made up thing with an actual thing because of quirky similarities, nomenclature and possibly just a lack of understanding.
So, before we go any further a “gravitational slingshot” is a gravity assist that will speed up an actual spacecraft, “slingshot maneuver” is made up bananas nonsense. For example, when Voyager was sent out into the Solar System, it used gravitational slingshots past Jupiter and Saturn to increase its velocity enough to escape the Sun’s gravity.
So how do gravitational assists work? You probably know this involves flying your spacecraft dangerously close to a massive planet. But how does this help speed you up? Sure, as the spacecraft flies towards the planet, it speeds up. But then, as it flies away, it slows down again. Sort of like a skateboarder in a half pipe.
This process nets out to zero, with no overall increase in velocity as your spacecraft falls into and out of the gravity well. So how do they do it? Here’s the trick. Each planet has an orbital speed travelling around the Sun.
As the spacecraft approaches the planet, its gravity pulls the much lighter spacecraft so that it catches up with the planet in orbit. It’s the orbital momentum from the planet which gives the spacecraft a tremendous speed boost. The closer it can fly, the more momentum it receives, and the faster it flies away from the encounter.
To kick the velocity even higher, the spacecraft can fire its rockets during the closest approach, and the high speed encounter will multiply the effect of the rockets. This speed boost comes with a cost. It’s still a transfer of momentum. The planet loses a tiny bit of orbital velocity.
If you did enough gravitational slingshots, such as several zillion zillion slingshots, you’d eventually cause the planet to crash into the Sun. You can use gravitational slingshots to decelerate by doing the whole thing backwards. You approach the planet in the opposite direction that it’s orbiting the Sun. The transfer of momentum will slow down the spacecraft a significant amount, and speed up the planet an infinitesimal amount.
Messenger’s complicated flyby trajectory. Credit: NASA
NASA’s MESSENGER spacecraft made 2 Earth flybys, 2 Venus flybys and 3 Mercury flybys before it was going slowly enough to make an orbital insertion around Mercury. Ulysses, the solar probe launched in 1990, used gravity assists to totally change its trajectory into a polar orbit above and below the Sun. And Cassini used flybys of Venus, Earth and Jupiter to reach Saturn with an efficient flight path.
Nature sure is trying to make it easy for us. Gravitational slingshots are an elegant way to slow down spacecraft, tweak their orbits into directions you could never reach any other way, or accelerate to incredible speeds.
It’s a brilliant dance using orbital mechanics to aid in our exploration of the cosmos. It’s a shining example of the genius and the ingenuity of the minds who are helping to push humanity further out into the stars.
What do you think? What other places is the general comprehension between actual facts and fictional knowledge blurring, just like the “slingshot maneuver” and “gravitational slingshot”?
And if you like what you see, come check out our Patreon page and find out how you can get these videos early while helping us bring you more great content!
Eureka – it’s Europa! And a brand-new image of it, too! (Well, kinda sorta.)
The picture above, showing the icy moon’s creased and cracked surface, was made from images acquired by NASA’s Galileo spacecraft during its exploration of Jupiter and its family of moons in 1997 and 1998. While the data itself isn’t new per se the view seen here has never been released by JPL, and so it’s new to you! (And to me too.)
Europa’s bizarre surface features suggest an actively churning ice shell above a salty liquid water ocean. Credit: JPL
The original high-resolution images were acquired on Nov. 6, 1997, in greyscale and colorized with data acquired during a later pass by Galileo in 1998. The whiter areas are regions of relatively pure water ice, while the rusty red bands are where ice has mixed with salts and organic compounds that have oozed up from deeper within Europa.
The entire image area measures about 101 by 103 miles across (163 km x 167 km).
Europa has long been one of the few places we know of outside our own planet where life could very well have evolved and potentially still exist. Getting a peek below the icy moon’s frozen crust — or even a taste of the recently-discovered water vapor spraying from its south pole — is all we’d need to further narrow down the chances that somewhere, something could be thriving in Europa’s subsurface seas. Get a planetary scientist’s perspective in a video interview with Dr. Mike Brown here.
Launched in October 1989, the Galileo spacecraft arrived at Jupiter in December 1995. Through primary and extended missions Galileo explored the giant planet and its family of moons until plunging into Jupiter’s atmosphere on September 21, 2003. Learn more about Galileo here, and check out some of the amazing images it acquired on the CICLOPS imaging diary page here.
SpaceShipOne is the spacecraft created by Scaled Composites to win the $10 million Ansari X-Prize in 2003. It was the first privately built spacecraft to reach 100 km in altitude, twice in two weeks, carrying the equivalent of 3 people. It’s the prototype of the upcoming SpaceShipTwo, created for Virgin Galactic to carry paying passengers into space. Continue reading “Astronomy Cast 350: SpaceShipOne”
While many kids in the U.S. are starting their school summer vacations, New Horizons is about to get back to work! Speeding along on its way to Pluto the spacecraft has just woken up from hibernation, a nap it began five months (and 100 million miles) ago.
The next time New Horizons awakens from hibernation in December, it will be beginning its actual and long-awaited encounter with Pluto! But first the spacecraft and its team have a busy and exciting summer ahead.
New Horizons tweeted about its Father’s Day wakeup call
After an in-depth checkout of its onboard systems and instruments, the New Horizons team will “track the spacecraft to refine its orbit, do a host of instrument calibrations needed before encounter, carry out a small but important course correction, and gather some cruise science,” according to principal investigator Alan Stern in his June 11 update, aptly titled “Childhood’s End.”
What’ll be particularly exciting for us space fans is an animation of Pluto and Charon in motion around each other, to be made from new observations to be acquired in July. Because of New Horizons’ position, the view will be from a perspective not possible from Earth.
New Horizons LOng Range Reconnaissance Imager (LORRI) image of Pluto and Charon from July 2013 (Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute)
The next major milestone for New Horizons will be its crossing of Neptune’s orbit on August 25. (This just happens to fall on the 25th anniversary of Voyager 2’s closest approach in 1989.) “After that,” Stern says, “we’ll be in ‘Pluto space!'”
Launched on Jan. 19, 2006, New Horizons will make its closest approach to Pluto on July 14, 2015 at 11:49 UTC. Traveling nearly 35,000 mph (55,500 km/h) it’s one of the fastest vehicles ever built, moving almost 20 times faster than a bullet.
Read more from Alan Stern in his latest “PI Perspective” article on the New Horizons web site here, and check out NASA’s mission page here for the latest news as well.
“There is a lot to tell you about over the next 12 weeks, and this is just the warm-up act. Showtime — the start of the encounter — begins in just six months. This is what New Horizons was built for, and what we came to do. In a very real sense, the mission is emerging into its prime.”
– Alan Stern, New Horizons principal investigator
Also, check out a video on Pluto and the New Horizons mission here.
Who knows what mysteries lurk at the military’s Area 51 complex in Nevada? Conspiracy theorists and UFO chasers think it’s a big alien coverup. But it’s probably something more boring, like advanced military aircraft. Let’s talk about what we know, and what we think we know about this infamous military base. Continue reading “Astronomy Cast Ep. 346: Area 51”
Everything dies, including our technology. But when we’ve hurtled a few thousands pounds of robotic instrumentation to another planet, it gets a little difficult to shut it down and clean up. What do we do when a mission has reached the end of its useful life?
After the tragic failure of the first Phobos-Grunt mission to even make it out of low-Earth orbit, the Russian space agency (Roscosmos) is hoping to give it another go at Mars’ largest moon with the Phobos-Grunt 2 mission in 2020. This new-and-improved version of the spacecraft will also feature a lander and return stage, and, if successful, may not only end up sending back pieces of Phobos but of Mars as well.
The origins of Phobos have long been a topic of planetary science debate. Did it form with Mars as a planet? Is it a wayward asteroid that ventured too closely to Mars? Or is it a chunk of the Red Planet blasted up into orbit from an ancient impact event? Only in-depth examination of its surface material will allow scientists to determine which scenario is most likely (or if the correct answer is really “none of the above”) and Russia’s ambitious Phobos-Grunt mission attempted to become the first ever to not only land on the 16-mile-wide moon but also send samples back to Earth.
Unfortunately it wasn’t in the cards. After launching on Nov. 9, 2011, Phobos-Grunt’s upper stage failed to ignite, stranding it in low-Earth orbit. After all attempts to re-establish communication and control of the ill-fated spacecraft failed, Phobos-Grunt crashed back to Earth on Jan. 15, impacting in the southern Pacific off the coast of Chile.
But with a decade of development already invested in the mission, Roscosmos is willing to try again. “Ad astra per aspera,” as it’s said, and Phobos-Grunt 2 will attempt to overcome all hardships in 2020 to do what its predecessor couldn’t.
And, according to participating researchers James Head and Kenneth Ramsley from Brown University in Providence, Rhode Island, the sample mission could end up being a “twofer.”
Phobos floats in front of Mars’ horizon in a Mars Express image from January 2007 (ESA)
Orbiting at an altitude of only 5,840 miles (9,400 km) Phobos has been passing through plumes material periodically blown off of Mars by impact events. Its surface soil very likely contains a good amount of Mars itself, scooped up over the millennia.
“When an impactor hits Mars, only a certain of proportion of ejecta will have enough velocity to reach the altitude of Phobos, and Phobos’ orbital path intersects only a certain proportion of that,” said Ramsley, a visiting researcher in Brown’s planetary geosciences group. “So we can crunch those numbers and find out what proportion of material on the surface of Phobos comes from Mars.”
Determining that ratio would then help figure out where Phobos was in Mars orbit millions of years ago, which in turn could point at its origins.
“Only recently — in the last several 100 million years or so — has Phobos orbited so close to Mars,” Ramsley said. “In the distant past it orbited much higher up. So that’s why you’re going to see probably 10 to 100 times higher concentration in the upper regolith as opposed to deeper down.”
In addition, having an actual sample of Phobos (along with stowaway bits of Mars) in hand on Earth, as well as all the data acquired during the mission itself, would give scientists invaluable insight to the moon’s as-yet-unknown internal composition.
“Phobos has really low density,” said Head, professor of geological sciences at Brown and an author on the study. “Is that low density due to ice in its interior or is it due to Phobos being completely fragmented, like a loose rubble pile? We don’t know.”
The study was published in Volume 87 of Space and Planetary Science (Mars impact ejecta in the regolith of Phobos: Bulk concentration and distribution.)
The sleek and sexy-looking GOCE spacecraft has been mapping Earth’s gravity for over four years, but soon its xenon fuel will run out and the satellite will end up re-entering our atmosphere. But no one can say for sure when or where the 1-ton satellite will fall.
The Gravity field and steady-state Ocean Circulation Explorer has been orbiting Earth at super-low orbits, mapping out variations in Earth’s gravity with extreme detail. Launched in March 2009, the GOCE spacecraft was designed to fly low and has spent most of its mission roughly 500 km below most other Earth-observing missions, at an altitude of 255 km (158 miles), but has recently been at the lowest altitude of any research satellite at 224 km (139 miles).
With its sleek, aerodynamic design, some have called it the ‘Ferrari of space,’ but we’ve just called it sexy, like a satellite straight out of a James Bond movie.
And the satellite has delivered with unique results of Earth’s ‘geoid’ — precise measurements of ocean circulation, sea-level change and ice dynamics, greatly improving our knowledge and understanding of the Earth’s internal structure. The mission has also been studying air density and wind in space. Its data also produced the first global high-resolution map of the boundary between Earth’s crust and mantle, called the Mohorovicic, or “Moho” discontinuity.
Mission managers predict that in mid-October 2013 the spacecraft will run out of fuel and the satellite will begin its descent towards Earth. There will be no remaining fuel to guide its re-entry, and while most of GOCE is predicted to disintegrate in the atmosphere, several parts might reach Earth’s surface. Experts predict as much as 25% of the spacecraft will survive reentry, as many parts are made of advanced materials, such as carbon-carbon composites.
But when and where these parts might land cannot yet be predicted, ESA says.
As the re-entry time nears, better predictions will be made. Re-entry is expected to happen about three weeks after the fuel is depleted.
ESA says that taking into account that two thirds of Earth are covered by oceans and vast areas are thinly populated, the danger to life or property is very low.
Recently, other larger satellites have made uncontrolled re-entries, such as NASA’s 6-ton UARS spacecraft and Germany’s 2.4-ton ROSAT in 2011 and the 13-ton failed Russian Mars probe, Phobos-Grunt in 2012.
About 40 tons of human-made space debris reach the ground per year, but the spread and size mean the risk of an individual being struck is lower than being hit by a meteorite.
An international campaign will be monitoring the descent, involving the Inter-Agency Space Debris Coordination Committee. The situation is being continuously watched by ESA’s Space Debris Office, which will issue re-entry predictions and risk assessments.
ESA says they will keep the relevant safety authorities permanently updated.
