features

Cluttering Up Space

November 8, 2013

 

A US Air Force Minotaur 1 rocket carrying the Department of Defense Operationally Responsive Space office’s ORS-1 satellite lifts off from pad 0B at the NASA’s Launch Range at the Wallops Flight Facility and the Mid-Atlantic Regional Spaceport in Virginia. credit: NASA/Wallops Flight Facility

This piece originally ran in the September/October 2012 edition of Digital Battlespace, and is reproduced here with the editor's kind permission. 

 

Military dependence on space-based assets, including commercially owned ones, is growing, but they are at an increasing risk of damage from orbital debris. As a result, space situational awareness has become a high priority, discovers Angus Batey.

While the challenges of operating in the domains of land, sea and air are clear to most defence outsiders, when it comes to military use of space the complications and paradoxes begin to mount.

Response times in the terrestrial domains are a function of extant military capabilities and political or operational considerations, but in space, decisions often have to be taken months or years in advance. If something goes wrong on a surface-based or air-breathing platform it can be brought back in for upgrade or maintenance, but if a satellite breaks down it may never be possible to repair. It is usually only military-owned and -operated vehicles that perform military tasks on or near the Earth's surface - yet in space, military reliance on civilian-owned and -operated spacecraft is extensive, to the point that distinctions between military and non-military platforms may be entirely meaningless.

UNIVERSAL USE

'Space is truly a joint environment,' said Group Captain Neale Dewar, whose job title - HQ1Group Group Captain Space Control and Battlespace Management - reflects the complicated role he has within the Royal Air Force's space command. 'It's probably the truest joint environment, because everybody uses it now, and everybody is affected by it,' he continued. 'It is a true joint enabler, in the same way as terrestrial communications or computer information systems are. So it doesn't fall neatly into any one environment, and neither should it.'

Key among Dewar's portfolio of responsibilities is the RAF's Space Operations Coordination Centre (SpOCC). Housed in a bunker at Air Command, near High Wycombe, the SpOCC's role includes compiling and maintaining the UK's recognised space picture - a constantly updated 3-D mapping of objects in orbit. Unlike the maintenance of the recognised air picture, which the RAF does as part of its job of defending British airspace, the recognised space picture spans the globe and relies to varying degrees on international collaboration.

'The UK's ability in space, be it government-owned or commercial-industrial owned, is all part of enhancing or protecting national power or national capability,' Dewar explains. '[Space] is something that we are all involved in, whether it's the SatNav on your car or the GPS for a precision weapon - the loss of that service has an effect right across.'

Damage to the Space Shuttle windscreen sustained following collision with a tiny fleck of paint. The black line in the lower portion of the photograph is one milimetre long. credit: NASA Orbital Debris Program Office

Unlike the recognised air picture, which is made up of aircraft that are each flying for a specific purpose, the recognised space picture contains many objects that were put in orbit accidentally. And unlike aircraft, which will come back down to Earth in relatively short order, it can take years before a space object's orbit decays and it re-enters Earth's atmosphere. Despite their sometimes very small size, the high velocities mean that every one of those objects poses a risk to both manned and unmanned spacecraft: in 1983 NASA released imagery of a crater formed in the Space Shuttle's orbiter vehicle's windshield following a collision ("conjunction" is the preferred space terminology) with a 0.2mm fleck of paint.

It is little wonder that the US Air Force has designated space situational awareness (SSA) as one of its prioritised space capabilities.

FINAL CHOICE

As Digital Battlespace went to press, the Pentagon was about to announce its final selection for the provider of its Space Fence programme - a ground-based SSA solution to replace a VHF system that has been operating since the 1960s, which will offer an order of magnitude of improvement over current capabilities in terms of the number of smaller objects it can detect and track. (See footnote)

'In equipping Air Force forces to perform the SSA mission we are focusing on three capability areas,' said a spokesperson for USAF's Space Command, in an email to DB. 'One, to provide the ability to integrate, fuse, process and share SSA data; two, the ability to detect, track, and identify objects and events in space; and three, to become much more proactive in our ability to meet the growing challenges in the space domain.' 

Increased reliance on the low-Earth orbit (LEO) regions (between about 100 and 1200 km from the Earth's surface) for both civilian and military space applications is only part of the reason for the current demand for enhanced SSA. There has also been an exponential rise in the amount of debris objects in LEO space following two events in the late 2000s - the collision between an obsolete Russian Cosmos satellite and an active member of the Iridium constellation, and the deliberate destruction of a non-functioning satellite in a test-firing of a Chinese ASAT (anti-satellite) system.

When Neil Armstrong set foot on the moon in 1969, the SatCat - the catalogue of objects in orbit - stood at around 4000 items. Today, the UK SpOCC is tracking some 16,770 objects (and there are countless objects too small for current SSA systems to detect). Any one of these could not only damage or destroy an active spacecraft, but in doing so, contribute further to the growing clutter in the LEO regions and further erode access to space.

'A piece of debris taking out anybody's satellite is going to have a huge detrimental effect on the overall environment,' said Dewar. 'And while the payload that's lost immediately may have no military value or no military purpose - it may not even belong to our nation or our alliance - the debris created by that conjunction is going to have second- or third-order effects further on.'

SPREADING OUT

The US Air Force's present Space Surveillance System (AFSSS) comprises a network of separate radar transmitters and receivers, spread across the continental US along the 33rd parallel of latitude.

'It's pretty capable of detecting larger objects,' said Steve Bruce, vice-president of space surveillance systems at Lockheed Martin. 'But as targets get smaller its ability to see them is limited somewhat. The other thing that it does not do is precision tracking. When you have a thousand objects that are up there that are pretty much all man-made it works OK; but when you get debris and a lot of other things up there, it's really not capable of either detecting it all or sorting it all out.'

A concept illustration of a possible computer monitor display for Lockheed's Space Fence, showing objects in low-earth orbit (credit: Lockheed Martin)

Hence the Space Fence programme, which Lockheed and rivals Raytheon have built competing concepts for. The capability will not only dramatically increase the space catalogue by permitting detection of smaller orbital objects, but will enable real-time tracking of this vastly increased amount of material in LEO space.

'Space Fence is a much higher frequency - up around 3000MHz versus AFSSS which is somewhere in the order of 150 MHz,' said Bruce. 'So it's 20 times the frequency, and it not only can detect that the object is there, but also precision track it, so that you can very quickly figure out where the object is in 3D space.

'When Space Fence goes online, the catalogue of objects the United States has to monitor will grow [to] anywhere between 100,000 and 200,000,' said Bruce. 'There's a lot of stuff up there that is small: currently we have some idea where some of it is, because it was, say, created during the Iridium and the Cosmos collision, so the physics dictate where it goes. But we don't know precisely where - so Space Fence will go figure out where it is precisely, so we can do a better job of assessing if any of these smaller objects that we don't currently know much about could possibly hit something of value.'

The AFSSS and its planned successor are just one small part of the much larger, layered space surveillance network (SSN) operated by the USAF. The multiple sensors - including assets dedicated to the SSA mission, such as the Ground-Based Optical Deep Space Surveillance System (known as GEODSS) and the new Space-Based Surveillance System (SBSS), as well as sensors that supply SSA when their primary missile defence/early warning role permits - feed data into the SPADOC (Space Defense Operations Centre).

NEW TOOLS

However, the new generation of sensing technologies, with their dramatic increase in ability to track smaller objects, require new tools to permit operators to keep on top of the much larger output. So in tandem with Space Fence, SPADOC is due to be replaced by a new data management infrastructure called JMS (JSpOC [Joint Space Operating Center] Mission System).

'SPADOC tasks sensors, receives sensor track data, does orbit determination, produces and maintains the space object catalogue, and performs processing for events like launches, manoeuvres, etc.,' said the USAF Space Command spokesperson. 'SPADOC was delivered in the early 1990s, and needs to be replaced by a higher performance, more maintainable system, which is why JMS is so important. [JMS will] leverage advances in information technology to replace and increase these capabilities with the framework and foundation of data and services on a scaleable/extensible architecture.'

Of course, even with enhanced awareness of an increasing amount of potentially hazardous LEO objects, the options available to military or civilian satellite operators are limited.

The International Space Station has carried out 13 debris-avoidance manoeuvres since it became operational, the most recent in January of this year when a piece of the destroyed Cosmos satellite was projected to fly within 120m of it. But the ISS is manned and receives regular resupplies: for a satellite with finite fuel reserves, any decision to manoeuvre to avoid a potential conjunction effectively reduces its operational life.

As human spaceflight becomes more common, more debris enters LEO space: a theory known as the Kessler Syndrome (named after American astrophysicist Donald J Kessler, who first promulgated it) shows that the rate of collisions in orbit increases exponentially in relation to the number of objects in LEO space.

The theory predicts that at some point there will be so much debris in LEO space that one conjunction will set off a chain of further random in-orbit collisions, potentially sparking catastrophic damage to operational satellites and hugely increasing the dangers of spaceflight. Cleaning up LEO space is becoming an increasingly urgent concern.

Parts of the Hubble Space Telescope were removed and returned to earth during maintenance; this photo highlights numerous examples of damage to the device caused by collisions with small objects in orbit (each notation in yellow is a number and an arrow pointing to an impact) credit: NASA Orbital Debris Program Office

CLEANING UP

Earlier this year, the Swiss Space Centre (SSC) announced its CleanSpace One project, which proposes to take one of two small Swiss satellites out of orbit once they cease being operational.The initial CleanSpace One launch will either target Switzerland's first orbiting project, the Swisscube picosatellite, which was put in orbit in 2009, or its cousin Tlsat, Launched in July 2010.

CleanSpace One is a small (30cm x 10cm x 10cm) spacecraft containing a grappling device: it will rendezvous with the spent satellite, take hold of it, and the mated pair will then descend, burning up during re-entry. The estimated cost is 10m Swiss Francs and the SSC claims it could be operational within three years.

Meanwhile, the US Naval Center for Space Technology, part of the Naval Research Laboratory (NRL), has proposed a concept for using tungsten dust to clean LEO space: dispersed into orbit, the dust would act like a dragnet.

'Debris is mostly localized at high inclination sun synchronous orbits because of their extensive use over the last 50 years of space operations,' said the NRL's Dr Gurudas Ganguli in an email to DB. 'Also, the long-lived small debris is localized in an altitude band between 900 and 1100 km. So we know the most affected region and can target it for cleaning.   

'Unfortunately, over time the debris orbits have spread over a very large volume around the earth in a shell,' he continued. 'Filling this large volume with dust is impractical. Our idea is to introduce a narrow altitude layer of high mass density, tens-of-micron-sized dust in polar orbit at the upper end of the debris altitude band.

'While the background natural atmosphere at these altitudes is too rare to produce sufficient drag on the larger debris pieces to affect their orbits significantly,' he continued, 'it is enough to produce significant drag on the finer dust orbits and cause them to decay. By synchronizing the rate of dust and debris decay we can use the narrow dust layer to “snow-plough” the entire region below 1100 km of all debris. As the debris and the dust orbits decay to lower altitudes where the atmosphere is dense enough they are incinerated.'

EXTANT CAPABILITIES

Unlike the Swiss proposal, which requires the development of entirely new technologies to overcome key aspects of the mission, the NRL's concept could be made operational using extant capabilities. And while a new member of the proposed CleanSpace One satellite family would have to be launched every time an operator wanted to de-orbit a spent satellite, the dust debris sweep could potentially be achieved with a single launch.

'The major work in realising this concept is quite low tech,' Dr Ganguli wrote. 'It requires packaging and transport of 20–40 tons of dust as "dumb" mass to orbit. This may be achieved by one large rocket or in instalments by utilising excess launch capacities which would otherwise be unused. Optimistically, this may be a one-time operation rather than an ongoing endeavour.'

The US remains the dominant entity in space, but the growth of the commercial launch sector may help ensure other spacefaring nations are able to do more to protect their own interests, and shore up global defences against LEO conjunctions. There are security concerns around deploying sensitive military capabilities on board commercially operated launch vehicles, but the issues are well understood.

'I can say pretty categorically that there's never going to be a UK military space launch capability,' said Dewar, 'so we will have to rely on other governments. And as other governments move more and more to the commercial sector themselves, it's going to mean more use of the commercial sector on our part.

'From the military side, [we need] to ensure whoever it was that we were contracting with can provide us the assurance that we need, of the protection of both the payload itself and any data associated with it, from the time it leaves the factory to the time it gets into space and then is providing us with information. There's also the [political] sides as well - who we conduct commercial activity with will be decided by the government policy of the day.'

He concluded: 'If value for money comes at the cost of compromising security, then there's a balance to be struck; but provided it meets the assurance and [other] criteria there's no reason to exclude anybody in order to get best value for money.'

 

* Since this piece was published, sequestration has delayed a final decision on the next-generation Space Fence, and caused the existing US capability to be closed. For further details, please see this USAF press release and this report from SpaceNews

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