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Archive for January, 2008

28-Jan-08 | Reentering spy satellite may have been Delta payload

Numerous news sources (AP via the Washington Post, The New York Times, Observer, Globe and Mail) have reported a U.S. spy satellite that is out of control and is expected to fall back to Earth some time in late-February or early-March. Although the government is not providing specifics on the spacecraft, speculation is pointing toward the National Reconnaissance Office’s L-21, also known as USA 193, which launched aboard Delta 322 in December 2006. L-21 “carried sophisticated cameras to take high-resolution pictures and test equipment intended for use on the broader Future Imagery Architecture (FIA) program”[Reuters] and was delivered into the correct (low altitude, high inclination) orbit by its two-stage 7920 vehicle, but was soon declared a loss due to its failure to communicate with ground control.

Early estimates of its size—“about 20,000 pounds and the size of a bus”—presumed that the satellite is one of the massive Keyhole-class spy birds that were once launched aboard giant Titan-IV rockets. If it is L-21 instead, these figures would be grossly overstated. L-21’s weight was classified “for official use only,” but given the payload capacity of the Delta II it would have been on the order of 4,000 pounds and about the size of a four-door sedan.

Since it cannot be controlled, there is no way of knowing exactly when and where the satellite will reenter the atmosphere. Most news outlets are focusing on the potential of the debris to damage something, or injure someone, both of which carry relatively insignificant odds. Given the highly-classified nature of the satellite—independent observers have been unable to determine even the most basic parameters of it, such as whether it was designed to use solar panels—it may be more pertinent to consider the potential for sensitive technology to fall into the wrong hands.

Another issue that has been raised is the possibility that L-21 might carry a radioisotope thermoelectric generator, or RTG, as its power source. Whether this is the case is unclear: the NRO refuses to confirm or deny; a professional analyst deems it “unlikely,” yet is the same person who overestimated the size of the craft; meanwhile amateur skywatchers have published grainy photographs of L-21 that purport to show a lack of solar panels, implying an alternative power source. Regardless, current RTG design makes the chance of a containment rupture fairly remote, even in the case of a hard landing, and the fuel pellet is in a ceramic form that resists heating and vaporization; the odds of environmental impact are extremely low. (In the case of close contact, the highly corrosive hydrazine thruster fuel poses a greater health risk, and the U.S. military is developing contingency plans to quickly retrieve any debris should L-21 end up on land.)

23-Jan-08 | MESSENGER on course, data dump complete

On 18 January the MESSENGER team announced that the spacecraft missed its targeted aim point by a mere 5.12 miles—not too shabby considering the billions of miles it has already travelled, and well within nominal. The gravity assist it received from Mercury put it on course for the next fly-by in October. A trajectory correction known as DSM-3 is expected some time during that cruise. Meanwhile, data from the fly-by have been received on Earth, and the handful of images released so far have been spectacular.

15-Jan-08 | MESSENGER survives Mercury Flyby 1

Yesterday MESSENGER survived its first encounter with Mercury, collecting extensive data as it passed a mere 124 miles above the surface. Today, following further departure observations, it will turn its antenna back toward Earth to begin the downlink process. The initial results will not be announced until a press conference scheduled for 30 January, although some excellent early photos have started to trickle out. The spacecraft is reported to be “still operating nominally,” but there has been no word yet on whether the trajectory change caused by the gravitational assist was on target.

10-Jan-08 | MESSENGER on course for first Mercury fly-by

NASA’s Mercury probe MESSENGER will pass within 124 miles of the First Rock from the Sun on Monday, 14 January 2008. It will make its closest approach at 19:04 UTC. This will be the first mission to provide a close-up view of the mysterious little planet since Mariner 10 made its third and final fly-by in 1975, nearly thirty-three years ago.

The mission team has been receiving and analyzing batches of optical navigation images for the past few days, in order to determine the spacecraft’s exact position relative to Mercury and to ascertain whether any trajectory corrections are needed to remain on course. As yet no adjustments have occurred since the regularly-scheduled TCM-19 on 19 December, and a 10 January follow-up burn was cancelled. The team will continue to monitor these navigational images until shortly before the fly-by, when course corrections will no longer be possible and the spacecraft’s instruments will be turned toward the planet.

MESSENGER (short for “MErcury Surface, Space ENvironment, GEochemistry, and Ranging”) was launched by Delta 307 in August 2004. Along with providing some early science returns, the fly-by is a gravity assist manoeuvre to alter MESSENGER’s trajectory. The spacecraft will pass Mercury twice more before settling into orbit in March 2011.

     

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