Last week I attended the ceremony at Tidbinbilla to celebrate the inscription of the three ACT tracking stations, Tidbinbilla, Orroral Valley and Honeysuckle Creek, on the AIAA Historic Aerospace Sites register. Caught up with the darling Gordon Pike (SingTel Optus), with whom I discussed the relative advantages of spin stabilisation and three-axis stabilisation. He also told me about Optus' tracking station at Frenchs Forest in Sydney (aha!). I had some fascinating chats with former tracking station staff - of that more soon. Orbital debris guru Duncan Steel (QinetiQ) was there, as well as Ian Tuohy of BAE Systems, taking a brief respite from gearing up for Hayabusa's return. Michael West, chair of the AIAA Sydney Section, gave me a lift there and back (Tidbinbilla is about half an hour out of Canberra). A truly wonderful occasion.
Sunday, May 30, 2010
Monday, May 10, 2010
Zombiesat! What's Next for the Out-of-Control Galaxy 15 Satellite
By Clara Moskowitz
SPACE.com Senior Writer
posted: 04 May 2010
By Clara Moskowitz
SPACE.com Senior Writer
posted: 04 May 2010
The Galaxy 15 commercial satellite that recently lost contact with the ground has joined the ranks of a boatload of other debris adrift in space. It's now termed a "zombiesat" by engineers who have a better sense of humor than you might have imagined. So what's next for this 4,171-pound (1,892-kg) zombiesat?
This defunct satellite will probably drift to one of two "gravity wells" that catch most out-of-control spacecraft, experts say. Galaxy 15 could threaten nearby satellites because its communications package is stuck on and it may start interfering with its neighbors by siphoning off their signals. It's the first time such an event has ever occurred, and it sent Orbital Sciences, the satellite's builder, on a dash to figure out how to stop the satellite-run-amok.
Galaxy 15, like many communications satellites, was circling Earth about 22,369 miles (36,000 km) high in what's called geosynchronous orbit, meaning that it orbited at the same speed the Earth rotates, so that it sat perched above the same part of Earth all the time. "There are two points in geosynchronous orbit called geopotential wells," explained Nicholas Johnson, chief scientist for Orbital Debris at NASA's Johnson Space Center in Houston. "These are perturbations in Earth's gravity field. Typically when satellites lose control they will drift toward the nearest geopotential well and just oscillate around it." The two spots, also called libration points, are located at longitudes of 105 degrees west and 75 degrees east. There are already between 150 and 200 objects oscillating around these points, Johnson said.
Still a large place
In that sense, the new zombiesat doesn't significantly increase the space debris problem or pose a serious risk of colliding with an operational satellite.
"Space is still a very large place," Johnson told SPACE.com. "There are a lot of objects that are drifting back and forth. Galaxy 15 really just kind of joins a relatively large number of objects – it's not a significant new hazard from a global standpoint. But if your satellite happens to be near where Galaxy 15 is drifting then it's of more concern." Eventually, everything in low-Earth orbit will eventually fall back down toward Earth because of atmospheric drag. The small amount of atmospheric particles in space create friction with spacecraft, causing their orbits to decay. The time it takes for an object's orbit to decay depends on its altitude.
For example, the International Space Station orbits at about 250 miles (400 kilometers) above Earth, while the Hubble Space Telescope circles much higher, at 353 miles (569 km). "When things fall off the International Space Station, they typically fall back within a couple months, but where Hubble is, it typically takes several years to fall back to Earth," Johnson said. "At 800 km you're talking many decades or even hundreds of years."
To prevent the buildup of dead spacecraft in heavily trafficked areas of geosynchronous orbit, guidelines recommend that when a satellite reaches the end of its life it is boosted to a higher orbit out of the way. This "graveyard orbit" is about 186 miles (300 km) above where most satellites orbit. "The whole idea is to get to an altitude so they don't drift back into the operational region for a very, very long time – over 100 years," Johnson said.
It's actually easier to boost a spacecraft up just this much higher than to maneuver a craft down to where it would immediately fall back to Earth and burn up in the atmosphere, he said.
Getting rid of space junk
To actually go and collect defunct spacecraft to remove the collision risk altogether is currently beyond our ability. "Unfortunately we haven't found a concept which appears to be both technically feasible and affordable," Johnson said. The best way to remove spent rocket stages and other large objects from orbit is to simply send up another spacecraft to rendezvous and dock with it and drag it back down to earth. This method would be extremely expensive and time-consuming, and isn't viable for the vast number of objects already in space. Some more exotic measures involving tethers and other props have been proposed, Johnson said, but aren't yet feasible.
For getting rid of very small pieces of space junk, there are two favorite ideas, he said. One involves shooting lasers at the objects to push them into lower-altitude orbits so they fall back down to Earth more quickly. "That has technical, economic, as well as policy issues," Johnson said. Another concept is to fly up a structure with a large area but low mass so that when particles strike the surface they will penetrate and lose some of their orbital energy, causing them to fall back to Earth more quickly. This option would also need many technical issues ironed out. "If it was easy we'd already be doing it," Johnson said of tackling the debris problem. "But it's prudent to be working the issue now before it becomes a serious impediment to space operations."
Friday, May 07, 2010
The Sydney Section of the American Institute of Aeronautics and Astronautics (AIAA) is proud to announce that the Tidbinbilla, Honeysuckle Creek and Orroral Valley Space Tracking Stations have been designated as global AIAA Historic Aerospace Sites. This is a prestigious award which recognises the significant role these three Australian tracking stations have played throughout the space-faring era, particularly in support of NASA's manned space missions. It is a fitting tribute that these sites should be recognised in this way in 2010, the 50th anniversary of treaty-level cooperation between the Australian Government and NASA.
The AIAA established the Historic Aerospace Sites Program in 2000 to promote the preservation of, and the dissemination of information about, significant accomplishments made in the aerospace profession. Other sites recognised by the AIAA History Technical Committee include NASA Ames Research Center, Moffett Field, CA; the Boeing Red Barn, Seattle, Wash.; Kitty Hawk, N.C.; the site of the first balloon launch in Annonay, France; the Royal Aircraft Research Establishment at Farnborough, England; and Tranquility Base on the moon. Currently Woomera is the only other AIAA Historic Aerospace Site in Australia.
Monday, May 03, 2010
29 April 2010 by Paul Marks
29 April 2010 by Paul Marks
WITH Earth's orbit cluttered with dead satellites, discarded rocket boosters and other space junk, ways to prevent the accumulation of such debris are desperately needed.
How about using a tractor beam to simply steer future junk aside, says space-flight engineer John Sinko of Nagoya University, Japan. Sinko's idea is based on an experimental type of spacecraft engine called a laser thruster. Inside these motors, laser pulses fired into a mass of solid propellant cause a jet of material to be released, pushing the craft in the opposite direction. Sinko realised that the laser did not necessarily have to be on the same craft. "These on-board motors could also be targeted remotely by lasers for tractor beaming," he says. A spacecraft could fire a low-power laser beam at another craft to steer it from a distance
He has designed a series of laser thrusters that can be activated in this way. A spacecraft fitted with a laser would fire a low-power beam at a thruster fitted on another craft to attract, repel or steer it in another direction. Pushing a spacecraft away is a relatively simple matter, but more complex designs using mirrors are needed to use a beam to tug one towards the laser (see diagram).
Combining those designs could allow full control in any direction, says Sinko. He imagines spacecraft being fitted with remotely operated thrusters before launch, so that once they reach the end of their lives it is simple to alter their orbit or even shove them into the atmosphere to burn up - even if they have lost all power (Journal of Propulsion and Power, DOI: 10.2514/1.46037).
Tractor beams could be fired from up to 100 kilometres away, says Sinko, either from a spacecraft in orbit or a mirror in space redirecting a beam from Earth. "It's an interesting idea that could work in principle," says Richard Holdaway, director of space science technology at the Rutherford Appleton Laboratory in Didcot, UK. Keeping a laser beam accurately trained on a distant motor would be a challenge, he adds, "but perhaps not an insurmountable one".
Sinko hopes to test one of his tractor beams on a 10-kilogram satellite within a few years. He is not alone in trying to develop such technology: a team at the Research Institute for Complex Testing of Optoelectronic Devices and Systems in Sosnovy Bor, Russia, is working on similar ideas.