Tag Archives: space debris

Chandrayaan-1: the Lost and Found Lunar Orbiter

This is pretty cool. ¬†ūüėČ

On October 22, 2008, India joined the elite group of nations which have successfully sent spacecraft to orbit the Moon. ¬†The mission was successful, conducting joint operations with NASA’s Lunar Reconnaissance Orbiter and LCROSS impactor, deploying an impactor of its own to help search for lunar ice (and making India only the fourth country to place its flag upon the Moon), and providing the first definitive proof of water ice in the lunar soil. ¬†The mission was cut short, however, when the spacecraft abruptly stopped responding to ground commands on August 29, 2009. ¬†The cause of the failure was never determined, but it had been experiencing issues in several systems, including the star tracker that keeps its antenna aligned with Earth.

Like other deep space spacecraft, the moment it stopped transmitting it became impossible to track from Earth — the Moon is much too far away to track such small objects (in Chandrayaan-1’s case, about 1.5 meters by 1.5 meters) by radar.

Or is it?

As international governmental and private space programs grow at an astonishing rate, it has become clear that space traffic will increasingly become a problem not just in Low Earth Orbit (LEO) and in the immensely valuable Geostationary Earth Orbit (GEO, the province of most communications satellites) but in deep space as well. ¬†The recent move of the MAVEN spacecraft to dodge Mars’ innermost moon, Phobos, also underscores the hazards. ¬†So JPL conducted a study to see whether lunar spacecraft actually¬†could be tracked from Earth. And guess what — they can!

JPL’s first target was LRO, because it’s an active spacecraft and therefore its real position is known with exquisite precision. ¬†Having located it with ground-based radar, the team moved on to something trickier: the Chandrayaan-1 spacecraft. ¬†Lunar spacecraft are difficult, because the Moon is so lumpy that a) dead spacecraft don’t stay long unless their orbits are fairly high, and b) orbits can be difficult to predict over long timescales. ¬†Nevertheless, they found it. ¬†Chandrayaan-1 is dead, but not gone, and certainly not forgotten.

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HTV space debris experiment is a bust — better luck next time!

The Kuonotori-6, the latest H2 Transfer Vehicle (HTV) to fly from Japan to the ISS, also carried a space debris experiment. ¬†After completing its cargo delivering mission (including delivery of the first set of new batteries for the station’s main power system) and loading up with trash and an old set of batteries, it departed the ISS on January 27. ¬†Not ones to waste a good opportunity, JAXA had equipped it to carry out additional experiments between undocking and its ultimate fiery demise. ¬†For this mission, it carried an electrodynamic tether which, when fully unspooled, would stretch half a mile into space, to test the effectiveness of such a system in passively lowering a satellite’s orbit purely through interaction with the Earth’s ionosphere.

Unfortunately,¬†they ran into problems during deployment. ¬†First, one of the four bolts holding the tether’s counterweight failed to separate on the first try. ¬†On a second attempt, telemetry indicated that the bolt finally separated, but the tether still would not deploy. ¬†Possibly the bolt did not fully separate, or possibly there was some other problem with the mechanism; JAXA engineers will certainly be closely evaluating the telemetry before attempting the experiment again. ¬†One thing is certain: they will not be attempting again with this spacecraft: after abandoning the tether deployment, Kuonotori-6 was deorbited last Sunday, making a self-destructive reentry over the South Pacific.

Still, Japanese engineers do not tend to give up easily, so I expect they will try again. ¬†They’ll have additional opportunities: although HTV does not fly as often as many other ISS cargo ships, it is vital for delivery of the new batteries for the main power system. ¬†New methods for disposal of space hardware is urgently needed; if successful, tethers like this could even be used on things like spent rocket stages, since it is a completely passive system and doesn’t weigh much. ¬†Being able to dispose of spent hardware means it doesn’t stick around to contribute to the growing problem of space debris.

So here’s hoping they can get it working next time!

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The Visible Threat of Space Debris

Small, untrackable space debris is, according to NASA, the number one threat to human spaceflight, and according to the USAF, it’s also a major threat to national security — and these days, it’s not just a threat to nations with space assets. ¬†Every nation uses space in some way; even if they don’t have satellites of their own, every nation relies on commercial and government-operated satellites from other nations. ¬†Weather forecasting, telecommunications, and navigation have benefitted so massively from satellites that we now depend on them.

So how much damage can be done?  Well, the infamous collision between Iridium-33 and the defunct Cosmos-2251 is the most obvious example, as the first known hypervelocity unintentional collision between two artificial satellites.  It destroyed Iridium-33, of course, and littered the shared orbital space with debris.  At least twice, the ISS has had to respond to near passes of some of the shrapnel, much of which remains in orbit today, and continues to threaten spacecraft in low Earth orbit.  The orbits are unstable, and so the debris is continually sinking, and eventually it will no longer be a problem.  But a great deal more debris remains, and many old satellites were not built to safe themselves after a mission; their tanks may still hold propellant, and their batteries may still be able to charge off of the solar panels.  Without heaters to maintain propellant, and without a computer to govern voltage in the batteries, this turns such dead satellites into time bombs.

But the worst fear for agencies like NASA is that much of the debris is too small to be tracked.  Pieces a few inches or larger can be tracked, which allows the ISS crew to either relocate the station or seek shelter in their Soyuz lifeboats until the danger has passed.  Smaller pieces are still deadly, but can strike with no warning because their positions are unknown.

Europe’s Sentinel 1A radar imaging satellite recently drove that point home, when ground controls noticed the power output of one of its solar arrays abruptly drop. ¬†It didn’t drop much, not enough to affect operations in any way, but it was concerning. ¬†Soon, they noticed something else: the spacecraft’s orbit had changed ever so slightly. Something had imparted kinetic energy to it. ¬†Unusually for satellites, Sentinel 1B is equipped with cameras that can see its solar arrays; they were installed for engineering purposes, to monitor deployment of the solar arrays. ¬†After the unexplained drop in power output, engineers turned the cameras back on and saw a divot about¬†40 cm across. ¬†Something struck the spacecraft. ¬†By the nature of the damage, controllers estimate the impactor was less than 5 mm in size. ¬†Perhaps a paint fleck; there are a lot of those up there. ¬†It could also have been a natural object; many meteors are that size or smaller. ¬†But it drives home the seriousness of the threat:

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This obviously isn’t the first time an impact crater has been found on a spacecraft. ¬†Most spacecraft are never seen again after launch, with one notable exception: crewed spacecraft. ¬† The Space Shuttles bear many scars from micrometeoroids. ¬†This one was found on a window of the Space Shuttle Challenger¬†after STS-7:

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This much larger hole was found on Endeavour after STS-118; this¬†hole is much bigger, having punched straight through Endeavour’s radiator panel, and one wonders how much more harm it would have done had it struck a window:

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Atlantis also suffered an impact like this; luckily, in both cases the impactor missed the critical Freon loops inside the panel; such an impact would trigger an immediate mission abort as the Shuttle would be forced to switch to its flash evaporation system to keep the computers cool and alive, and that has only a limited supply of coolant as it’s only meant to keep things going during launch and entry, when the payload bay doors are closed and the radiators stowed.

ISS has had MMOD strikes on itself too, of course. ¬†Here’s one in the Cupola, with a pen for size comparison:

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And here’s one on the Hubble Space Telescope, on its main antenna dish:

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This problem is very, very real, and right now, we don’t have many solutions. ¬†Shuttle mitigated the danger a little by, whenever possible, orienting the Orbiter so that its massive main engines were facing into the direction of travel. ¬†While those engines are absolutely critical, at that point in the mission they have done their job and are just dead weight; if they have to get hit, it would be better to be hit there. ¬†But when docked to ISS, Shuttle did not have this option; as they were mainly using the forward PMA port, when docked Shuttle was forced to be traveling with the delicate and critical heat shield facing forwards. ¬†This is why, after Columbia, NASA mandated a heat shield inspection — immediately after launch, to find damage due to the foam shedding from the ET, and again right before undocking in order to find MMOD damage. ¬†But few spacecraft have this luxury. ¬†They must point wherever they must point in order to carry out their missions. ¬†And so, the threat will persist.

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WT1190F has returned home

The mysterious object that is presumed space debris and designated WT1190F has returned to Earth.  As predicted, it reentered off the coast of India and Sri Lanka early today.  There is no word of debris reaching the surface.  A team of observers from NASA, ESA, and the UAE Space Agency flew out over the Indian Ocean to observe the reentry and were able to capture footage:

This footage and other data collected during the flight will be used to validate and adjust reentry prediction models.¬† It’s rare to observe a reentry of something with such a high orbit, so this was a very valuable opportunity.

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The Earth’s *other* satellites

We all know the Earth has one moon, right?

Right?

Well, it sure seems like an obvious answer.  Sure, there are a bazillion artificial satellites, and probably some dust and stuff, but the Moon is our only moon.  A freakishly large moon for our size of planet, orbiting quite distant, but still, just one moon.  Right?

Well, sort of. ¬†It turns out the Earth has relationships with other bodies that are . . . moon-like. ¬†And sometimes it captures new moons, which generally don’t stay long, because our huge Moon ejects them. ¬†There’s no way of knowing how many temporary moons the Earth has captured through the past few billion years, nor whether any of them stuck around for any significant length of time or were ever visible from the ground. ¬†But in 2002, an astronomer spotted what appeared to be one — the first ever formally identified. ¬†It was duly given the provisional designation J002E3, signifying the time and sequence of its discovery, and soon was confirmed to be orbiting the Earth.

This of course sparked a frenzy of astronomical observations. ¬†It was soon found to be very bright, suggesting it was¬†perhaps 30 meters across, a size which caused some alarm, as orbital predictions suggested it would leave the Earth-Moon system and return around 2040. ¬†A 30 meter asteroid could cause severe damage, depending on where it hit. ¬†But then astronomers realized two other strange things. ¬†First, backtracing its orbit to try to find “precovery” images, they realized that it had likely last been in the Earth-Moon system in 1971 – during the Apollo program, when an object in such an orbit would surely be more conspicuous. ¬†And secondly, spectrographic analysis showed its surface was covered by a material never before seen in an asteroid: titanium dioxide. ¬†That’s never been seen on an asteroid, but we see it all the time on Earth; it’s very popular in white paint. ¬†Because that’s what the asteroid was covered with.

It wasn’t a 30 meter wide rock at all. ¬†Recalculating with the knowledge that it was covered in titanium dioxide and therefore bright white, they realized it was much smaller, less than half that size. ¬†In fact, once they put that fact together with the orbital data, they realized it wasn’t a rock at all. ¬†It was a rocket — the spent S-IVB upper stage from the Apollo 12 mission, which is painted white, and 17.8 meters long. ¬†The Apollo 12 mission¬†was the last time a Saturn V was sent to the Moon without the upper stage being aimed at the Moon itself; all subsequent ones were deliberately crashed to generate moonquakes for the seismographs left by previous Apollo missions. ¬†Its predecessors expended the last of their propellants to boost themselves into heliocentric orbit, preventing them becoming navigational hazards, but this one had to burn its ullage motors a bit longer earlier in the flight, which left it with insufficient delta-vee to escape Earth. ¬†It wound up in a high and rather unstable orbit, and was soon lost to tracking, as attention was wrenched back to Earth with the sudden cancellation of Apollo.

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Apollo 12’s S-IVB, at the top of the SA-507 Saturn V stack, awaiting its payload in the Vehicle Assembly Building. The S-IVB is the third stage of the Saturn V rocket; above it goes the LM, the SLA panels that shroud it from the atmosphere during ascent, the CSM, and the escape tower and CM shroud. In addition to briefly alarming astronomers in 2002, this rocket also experienced a bit of a scare on ascent, as it was struck by lightning. But the vehicle recovered and the mission went off flawlessly.

 

Sometime in 1971, it wandered through a Lagrange point and slipped into heliocentric orbit; sometime near 2002, it slipped back in. ¬†It has left Earth orbit again, and has not been seen since 2003; it is too small to easily track away from Earth, but calculations indicate we’ll see it again in 2040, when Earth is likely to recapture it once again. ¬†It does present some hazard of impact with either Earth or Moon, but because we now know it to be a hollow rocket body rather than a chunk of nickel and iron, we know it will¬†not be a major hazard after all. ¬†Rocket bodies fall to Earth all the time, usually landing fairly intact since they’re not going very fast, but this would be going very fast and would mostly burn up. ¬†Therefore, it is actually not listed as a Potentially Hazardous Asteroid.

And this isn’t the only time that’s happened. ¬†On August 28, 2006, astronomers working with the Catalina Sky Survey discovered an object provisionally designated¬†6Q0B44E. ¬†This object is in a very high orbit, higher than the Moon, and is much fainter than J002E3. ¬†It’s estimated to be just a few meters across, and it’s orbit is rather similar to J002E3. ¬†There’s also another, discovered in 2008 , which received the minor planet designation 2006 RH120. ¬†This object, like J002E3, appears to have a spectrum consistent with titanium dioxide, but it has been observed after escaping Earth, and observations of perturbations due to solar wind are not consistent with an artificial object, but rather with a more solid object such as a rocky asteroid or perhaps a fragment of the Moon. ¬†The jury, realistically speaking, remains out for both of these sometimes-moon objects; one is believed artificial, one is believed natural, but both have orbits reminiscent of J002E3 and the Apollo program. ¬†Are they space debris, or itinerant companions of the Earth?

And, of course, there is one more misidentification worth mentioning. ¬†Although it didn’t enter Earth orbit, an object was observed on an imminent near-collision course with the Earth. ¬†Its orbit was quickly confirmed by alert astronomers, allowing it to receive the minor planet designation 2007 VN84. ¬†But backtracing its orbit revealed it had made another startlingly close encounter with the Earth before — and then someone worked it out. ¬†It was the Rosetta spacecraft, performing a gravity assist maneuver.

The_Rosetta_Spacecraft

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What goes up, must come down: Falcon 9 and TRMM

The old truism, “what goes up must come down”, is still true today, unless you launch high enough, but almost everything launches low enough that it is ultimately doomed. ¬†Sometimes things come back neatly, like the Falcon 9 first stage, incrementally working towards a controlled landing of the booster. ¬†SpaceX has released a new video from a chase plane:

And sometimes things come back down completely out of control. ¬†The¬†Tropical Rainfall Measuring Mission, a joint project between NASA and JAXA, is out of propellant. ¬†It is beginning its slow descent under the combined forces of gravity and atmospheric drag. ¬†Since it has no propellant, the venerable spacecraft could come down pretty much anywhere under its flight path (from 35 north to 35 south), and NASA expects it to come down sometime between spring of 2016 and autumn of 2017, depending on solar activity and such. ¬†I don’t have any video of that, obviously, but I did find this lovely animation showing NASA’s entire fleet of weather satellites, as of January 2014.

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