Wandering U.S. Spy Satellite Prompts Continuing Concerns
This image is a still from a short video produced by Greg Roberts of the U.S. secret satellite DSP-F23 (bright dot at bottom) as it approached the ASTRA 1 constellation group.
Credit: Greg Roberts

This story was updated at 5:17 p.m. EST.

While the unprecedented smashup between a U.S. and Russian satellite earlier this month sparked a lot of attention, another wayward spacecraft — out-of-whack U.S. secret satellite DSP-23 — remains a serious concern.

Lofted into orbit in November 2007, this Defense Support Program (DSP) spacecraft apparently went belly-up the following year. Making matters worse, DSP-23 died before it could be nudged into a graveyard orbit, where it would no longer be a collision threat for other satellites.

The satellite is one of a constellation of Earth-staring spacecraft designed to spot orbits rocket launches, nuclear blasts, as well as gather other types of technical intelligence from their 22,300-mile (35,888-km) geosynchronous (GEO).

Last month, space reporter Craig Covault at Spaceflight Now broke the story that two Micro-Satellite Technology Experiment (MiTEx) satellites were dispatched to peek in on the errant satellite. Of course, mum?s the word from the U.S. military on the DSP-23?s off-kilter status.

But, fingers are crossed at SES ASTRA — operator of the ASTRA Satellite System that provides satellite services in Europe — regarding the meanderings of DSP-23.

The misbehaving DSP-23 spacecraft has ?visited? ASTRA satellites for the last two months. That SES ASTRA system is used by a wide range of broadcast and multimedia companies to deliver revenue generating broadcast and broadband services to 117 million households.

?It will be of concern for many other positions?for a very long time,? said Hugues Laroche of SES Engineering. ?As operators of GEO satellites I guess we are still exposed to lower risks of collision probabilities than low Earth orbits, but still this is a concern,? he told SPACE.com.

That?s especially the case, Laroche added, since the GEO ring is such a tiny resource. When a satellite dies prematurely there, it remains in the vicinity for a long time?with a longitude swing on one hand and an inclination drift on the other, he said.

Laroche said it?s time for the actors in the satellite field ?to stop acting each one on their side.? Rather, there?s need to increase coordination, he concluded.

Spacecraft drift

Meanwhile, a loosely knit — but high-tech — group of amateur satellite detectives has been keeping tabs on the orbital wandering of DSP-23.

For example, skywatcher Ted Molczan of Toronto, Canada, has used a computer program developed by fellow hobbyist Mike McCants to predict DSP-23's orbit through 2051, to chart the spacecraft's drift — a plot that tracks the satellite's oscillation between longitude extremes over a long period of time.

?Currently, DSP-23?s orbit is inclined about 2.8 degrees, which is slowly decreasing, such that by 2012, it will be inclined just 0.3 deg, whereupon it will begin to increase,? Molczan told SPACE.com. ?By 2015, it will have returned to its present inclination.?

Since many, if not most, operational GEO satellites have similarly small inclinations, this means that DSP-23 will remain in their immediate vicinity for at least the next six years, Molczan said. By about 2036, the spysat?s inclination will rise to about 15 degrees, which will reduce the time it spends in close proximity to operational GEO satellites, he added.

?But decades later, its inclination will return to its present small value, increasing the hazard it poses to operational satellites of that time. This long-term oscillation in inclination will continue for a very long time,? Molczan said.

Close encounters

Molczan spotlights the efforts of his satellite watching colleagues, Greg Roberts of South Africa and Peter Wakelin of the U.K., since they performed a load of hard work to track DSP-23 during its time in the eastern hemisphere.

Roberts used a collection of sophisticated gear to observe DSP-23, though his sightings suggest that nothing too dramatic is happening to the satellite.

?It has speeded up its eastward drift... but that?s because of natural causes as I don?t think the satellite is under any form of human control,? Roberts told SPACE.com.

The two MiTEx micro-satellites inspectors, Roberts added, are both drifting eastward and are now too low in his eastern sky to track optically.

?I haven?t heard anything about the results of their inspections in late December 2008 and early January 2009,? Roberts said. ?Since then, the two MiTEx satellites have not changed their orbits so either the operators are happy to leave them in their current drifting orbits or the satellites are no longer operable — probably the former.

?Of course DSP-23 continues on its course and passing close to operational craft quite frequently?from what I have heard, the closest approach so far has been just under 12 kilometers (7.5 miles),? Roberts said. 

Other than tracking DSP-23 as a matter of course, Roberts pointed out that the amateur network is not keeping a look-out for ?close encounters? with other spacecraft.

Half of these occur in the daylight hours in this part of the world so could not be seen even if there was a possible chance of collision, he said.

?I don?t know if the U.S. Department of Defense is alerting commercial operators of the possible need to move craft,? Roberts said.

But he would imagine such groups as the International Scientific Optical Network (ISON), a far flung group of scientific optical facilities for observation of high altitude geocentric orbit, is busy keeping an eye on all the celestial action. Network data collecting and crunching is done at the Keldysh Institute of Applied Mathematics of the Russian Academy of Sciences.

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Leonard David has been reporting on the space industry for more than four decades. He is past editor-in-chief of the National Space Society's Ad Astra and Space World magazines and has written for SPACE.com since 1999.