ESA Rosetta Spacecraft Set to Harpoon Comet 67/P

A jagged horizon of the nucleus of comet 67P/Churyumov-Gerasimenko appears in this image taken by the navigation camera on the European Space Agency's Rosetta spacecraft during the second half of October 2014. 

The image was taken from a distance of less than 6 miles (10 kilometers) from the surface.

Image Credit: ESA/Rosetta/NAVCAM




A patch of relatively smooth ground on the nucleus surface of comet 67P/Churyumov-Gerasimenko appears in this image taken by the navigation camera on the European Space Agency's Rosetta spacecraft in October 2014. 

The image was taken from a distance of less than 6 miles (10 kilometers).

Image Credit: ESA/Rosetta/NAVCAM

Some relatively rough terrain on the nucleus of comet 67P/Churyumov-Gerasimenko appears in this image taken by the navigation camera on the European Space Agency's Rosetta spacecraft in the second half of October 2014. 

The image was taken from a distance of less than 6 miles (10 kilometers).

Image Credit: ESA/Rosetta/NAVCAM

Early tomorrow morning, the European Space Agency's Rosetta spacecraft will deploy its comet lander, "Philae."

A little over seven hours later (8 a.m. PST/11 a.m. EST), the experiment-laden, harpoon-firing Philae is scheduled to touch down on the surface of comet 67P/Churyumov-Gerasimenko.

It will be the first time in history that a spacecraft has attempted a soft landing on a comet. Rosetta is an international mission led by the European Space Agency (ESA), with instruments provided by its member states, and additional support and instruments provided by NASA.

"I know it sounds like something out of Moby Dick, but when you think about the gravity field of a comet, it makes a lot of sense to harpoon one," said Art Chmielewski, project manager for the U.S. participation in Rosetta, from NASA's Jet Propulsion Laboratory in Pasadena, California.

"Comet 67P has approximately 100,000 times less gravity than Earth does. So, if you don't want to float away, you have to go to extraordinary measures to attach yourself to its dusty surface."

"The Philae lander has two harpoons, shock-absorbing landing gear, and a drill located on each of the lander's three feet. It even has a small, upward-firing rocket engine. All this to help keep it on the surface."

The descent of Philae begins at 1:03 a.m. PST (4:03 a.m. EST) when Rosetta releases the 220-pound (100-kilogram) Philae from an altitude of about 14 miles (23 kilometers) from the center of the comet's nucleus.

As Philae descends, it will fall slowly without propulsion or guidance, gradually gathering speed in the comet's weak gravitational field.

During the seven-hour descent, the lander will take images and conduct science experiments, sampling the environment close to the comet.

It will take a "farewell" image of the Rosetta orbiter shortly after separation, along with a number of images as it approaches the comet surface.

The targeted landing site is called Agilkia after an island in the Nile River in southern of Egypt where ancient buildings from the Nile's flooded Philae island were relocated.

Once the lander has touched down and safely anchored, it will begin a primary science mission, which extends to about two-and-a-half days.

Philae will take a panorama of its surroundings and perform on-the-spot analysis of the composition of the comet's surface.

It can drill samples from a depth of nine inches (23 centimeters) and feed them to the onboard laboratory for analysis.

The lander will also measure electrical and mechanical characteristics of the surface of the nucleus.
After the Philae landing is completed, Rosetta will begin the next major part of its mission, the escort phase.

Space Debris: French Corporation use UK design to 'harpoon' old satellites

UK engineers are developing a system to harpoon rogue or redundant satellites and pull them out of the sky.

It is a response to the ever growing problem of orbital junk - old pieces of hardware that continue to circle the Earth and which now pose a collision threat to operational spacecraft.

The harpoon would be fired at the hapless satellite from close range.

A propulsion pack tethered to the projectile would then pull the junk downwards, to burn up in the atmosphere.

"Space has become a critical part of our infrastructure - from weather forecasting and Earth observation, to GPS and telecommunications," said the harpoon's designer, Dr Jaime Reed, from French corporation EADS Astrium (UK).

"Space junk poses a real threat to these vital services if we do nothing about it, and so it's very important we develop capture technologies to remove some of this material. Studies have shown that taking out just a few large items each year can help us get on top of the problem."

Dr Reed's proposal is for a barbed spear about 30cm in length. It would be mounted on a "chaser satellite" that would edge to within 100m of a junk object.

Pictures sent to the ground would then be used to assess the target, before the chaser was moved to within perhaps 20m to take a shot.

Once the harpoon is hooked through the skin of the rogue satellite or rocket stage, the chaser could either pull on a trailing polymer cord itself or deploy a separate thruster unit to do the job of dragging the aimless drifter towards Earth.

Explosive concern
This is research in its very early stages. The BBC has filmed firing tests of a prototype harpoon at Astrium UK's Stevenage base.

EADS, the largest space manufacturer of aerospace and weapons in Europe, is also pursuing other ideas at its centres in France and Germany.

These concepts involve nets and robotic grappling devices. All systems have their pros and cons.

Harpoons could deal well with a satellite that is tumbling, for example, but the approach has its critics because of the fear it could actually add to our problems in space.

"Historically, one of the great sources of debris has been the explosion of fuel tanks in spent rocket stages," explained Dr Reed.

"We obviously don't want to be the cause of that, so our harpoon has a crushable cylinder. It's like a piston, and as soon as the harpoon hits the satellite wall, it rapidly decelerates, ensuring we don't travel right through the spacecraft, puncturing the tanks."

More than 50 years of space activity have left a huge quantity of redundant hardware in orbit.

This includes not just whole satellites and the upper-stages of the rockets used to put them there, but also debris from fuel tank explosions and nuclear powered devices.