NASA | Fermi's Close Call with a Soviet Satellite

[catdlr]

Published on Apr 30, 2013
By: NASAExplorer
NASA scientists don't often learn that their spacecraft is at risk of crashing into another satellite. But when Julie McEnery, the project scientist for NASA's Fermi Gamma-ray Space Telescope, checked her email on March 29, 2012, she found herself facing this precise situation.

While Fermi is in fine shape today, continuing its mission to map the highest-energy light in the universe, the story of how it sidestepped a potential disaster offers a glimpse at an under appreciated aspect of managing a space mission: orbital traffic control.

As McEnery worked through her inbox, an automatically generated report arrived from NASA's Robotic Conjunction Assessment Risk Analysis (CARA) team based at NASA's Goddard Space Flight Center in Greenbelt, Md. On scanning the document, she discovered that Fermi was just one week away from an unusually close encounter with Cosmos 1805, a dead Cold-War era spy satellite.
The two objects, speeding around Earth at thousands of miles an hour in nearly perpendicular orbits, were expected to miss each other by a mere 700 feet.

Although the forecast indicated a close call, satellite operators have learned the hard way that they can't be too careful. The uncertainties in predicting spacecraft positions a week into the future can be much larger than the distances forecast for their closest approach.
With a speed relative to Fermi of 27,000 mph, a direct hit by the 3,100-pound Cosmos 1805 would release as much energy as two and a half tons of high explosives, destroying both spacecraft.

The update on Friday, March 30, indicated that the satellites would occupy the same point in space within 30 milliseconds of each other. Fermi would have to move out of the way if the threat failed to recede. Because Fermi's thrusters were designed to de-orbit the satellite at the end of its mission, they had never before been used or tested, adding a new source of anxiety for the team.
By Tuesday, April 3, the close approach was certain, and all plans were in place for firing Fermi's thrusters. Shortly after noon EDT, the spacecraft stopped scanning the sky and oriented itself along its direction of travel. It then parked its solar panels and tucked away its high-gain antenna to protect them from the thruster exhaust.

The maneuver was performed by the spacecraft based on previously developed procedures. Fermi fired all thrusters for one second and was back doing science within the hour.

In 2012, the Goddard CARA team participated in collision-avoidance maneuvers for seven other missions. A month before the Fermi conjunction came to light, Landsat 7 dodged pieces of Fengyun-1C, a Chinese weather satellite deliberately destroyed in 2007 as part of a military test. And in May and October, respectively, NASA's Aura and CALIPSO Earth-observing satellites took steps to avoid fragments from Cosmos 2251, which in 2009 was involved in the first known satellite-to-satellite collision with Iridium 33.

[iamlucky13]

Nice read, although the video was a bit overly-dramatic. Bottom line, the conjunction analysis did it's job and gave them the time they needed eliminate the risk.

Thanks for sharing it.

[Robert Thompson]

"3,100-pound Cosmos 1805"

Ignoring national spy IP, what is the TRL to salvaging this already-lifted mass? Mass costs ~$x/kg to LEO. Is anything here particularly suited to any HSF use?

[kevin-rf]

Thank goodness they had the ability to eliminate the risk. On space craft with no propulsion systems it is brown pants time for everyone involved.

[Nickolai]

"3,100-pound Cosmos 1805"

Ignoring national spy IP, what is the TRL to salvaging this already-lifted mass? Mass costs ~$x/kg to LEO. Is anything here particularly suited to any HSF use?

I think DARPA is working on a project like this. Project Phoenix: http://www.darpa.mil/Our_Work/TTO/Programs/Phoenix.aspx

[Nickolai]

Because Fermi's thrusters were designed to de-orbit the satellite at the end of its mission, they had never before been used or tested, adding a new source of anxiety for the team.

The propulsion system was never tested on the ground? No qualification tests of any sort?

Edit: The satellite appears to be built on a LEOStar-3 Bus from Orbital Sciences, which has been used on a number of satellites before Fermi. Even if they didn't explicitly test these thrusters on the ground before launch, it seems like they already have some flight history, so I can't imagine it caused *that* much anxiety of the team. Seems like they're over-dramatizing it a bit, like iamlucky13 said.

[RichardF]

This article highlights the problem of space debris avoidance, and its good to raise awareness, but it's not exactly news.

Satellites in the most populated areas of low Earth orbit (LEO) make, on average, about one such manoeuvre per year, each (if they can). And 700 feet (213 m) isn't that close -- depending on the uncertainties in the orbit of the debris piece, and on the conjunction geometry, we would tend to go for a manoeuvre if the predicted conjunction was less than about 50 m. But each case has to be judged individually.

The closest I heard was an EnviSat conjunction which was predicted to be very close so a manoeuvre was made: analysis made a postiori gave the miss distance (between centres of mass) at 10 m. EnviSat is 26m x 10m x 5m, so we can assume this would have been a collision. This was in late 2010 when we were simultaneously planning a collision avoidance manoeuvre for CryoSat-2.


cheers,
Richard

[ugordan]

The propulsion system was never tested on the ground? No qualification tests of any sort?

I took that to mean they were never checked out in orbit, on this particular spacecraft. As such, I can imagine some anxiety the team might have had.

[RichardF]

Thanks to ESA's equivalent of the CARA software mentioned in this post (called CRASS), I get notified every morning of the top 10 collision risks for CryoSat-2.

The highest risk today was a conjunction with a bit of Cosmos-2251 debris with ID 93036BPR. It has an estimated mass of 0.6 kg. The conjunction was at 2013-05-03T03:58:31 with an estimated distance of 932 m.

If you have orbit tracking software you can see the conjunction for yourself. CryoSat-2's ID is 10013A. Here is a view of the conjunction using SatTrackerBasic (see http://forum.nasaspaceflight.com/index.php?topic=31501.0)

cheers,
Richard

[kevin-rf]

The propulsion system was never tested on the ground? No qualification tests of any sort?

I took that to mean they were never checked out in orbit, on this particular spacecraft. As such, I can imagine some anxiety the team might have had.

Toxic propellants, a good change the parts where tested, but the completed system on the ground, most likely not.