The spy satellite Lacrosse 5 and its “disappearace trick” | Hacker News Reader

The spy satellite Lacrosse 5 and its “disappearace trick”

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81 pointsgokhan18 comments

Background information for anyone not aware, Thierry Legault is a guy that has built a reputation around getting amazing images of various spacecraft in orbit around the Earth. Here's one that he took during last Friday's eclipse: http://apod.nasa.gov/apod/ap150322.html

All of which is to say he's one of the foremost civilian experts at imaging satellites from the ground.

It's worth watching the video of that (link from APOD):

https://www.youtube.com/watch?v=JwjvduR3_Ho

The video is 15 seconds long, the actual transit is less than 1 second.

There is a link buried on this page that goes into more detail: http://sattrackcam.blogspot.dk/2011/11/lacrosse-5-disappeara...

The key questions:

> Is it a matter of strongly differing reflectance properties of the satellite body with illumination angle? Is it some brightly reflecting appendage on the satellite disappearing from view? Is it a dark appendage on the satellite starting to block view of the illuminated satellite body, or casting a shadow on it? Is it due to some moving part of the satellite, e.g. a moving dish antenna?

It's all rather fascinating. Presumably having a stealth satellite is somewhat redundant as the objects will eventually be seen or tracked by other spacecraft or satellites?

Well the Misty project did try

http://en.wikipedia.org/wiki/Misty_%28satellite%29

I'm not sure either, but I believe the orbit of pretty much all satellites is known. You can't conceal a rocket launch, so people know when objects go up and look for them, and comparing to deep space objects you don't need a very powerful telescope to resolve one (but presumably you need good tracking). What's going to be hard is to know the exact purpose of the satellite (so the enemy can't assess you capabilities).

You're right. However, they can still maneuver in orbit. Having a stealth, or low-observable capability allows the operator to "turn the cloaking device on", maneuver the satellite, and potentially get an image of something that would have otherwise been hidden were the orbit known.

It has its limitations, of course. But it's a step above a visible satellite with fixed orbit.

EDIT: I missed the part where he says it is definitely NOT a stealth capability being demonstrated. So that's not applicable here. Still, a low-observability capability makes sense

Satellites are pretty much bound to their orbit once they are launched. They fire their engines only to restore speed (and thus height), and to control rotation. Their speed is such that centrifugal force is in equilibrium with gravity, and most of the kinetic energy is from launching the satellite (with a large rocket). They don't carry enough fuel for arbitrary maneuvers a la Star Trek.

I disagree. Certainly, there's no "arbitrary" maneuvers, "set course", etc. But surveillance satellites will carry maneuvering propellant for a number of reasons: - Station keeping (as you listed) to maintain altitude. LEO satellites will be affected by atmospheric drag. - Assignments - Radar and imagery satellites cannot view everything via a change in rotation alone, and orbital adjustments can be made to the inclination and eccentricity in order to produce an ground track over a target that it didn't follow before. the importance of the target must justify the expenditure in fuel. - Defense - ASATs are a real concern, consisting either of missiles or another satellite steered onto an intercept. Placing one object deliberately onto the path of another is hard enough, surveillance and military satellites will carry propulsion to perform evasion (again, eccentricity, inclination, or altitude adjustments) and mess up a solution.

There are no satellites (to my knowladge) that are carrying anything approaching the delta-v required to break orbit, but radical changes in orbit are feasible, and especially for surveillance and reconnaissance satellites, essential.

That's not really true. Most satellites will only carry out those maneuvers because anything else is expensive and unnecessary. Plane changes are generally pointless for a civilian satellite because they're launched into the appropriate plane to begin with.

Spy satellites are different because the nature of the mission means you can't really guarantee you'll pick the appropriate plane in advance. If something interesting starts happening somewhere in the world, you may want satellites over it sooner than would occur in their current orbits. Spy satellites can and do maneuver to accomplish this. The amount of maneuvering is pretty limited by basic physics and the size of the satellites, but it is done. Here's a page that discusses one:

http://fas.org/spp/military/program/imint/kh-12.htm

"The primary difference between the 28,000 pound KH-11 and the heavier KH-12 is that the additional amount of maneuvering propellant carried on the IMPROVED CRYSTAL. This additional propellant can be used to prolong the operating life of the IMPROVED CRYSTAL, to maneuver to improve coverage of areas on the Earth of particular interest, and to maneuver to evade Soviet anti-satellite interceptors."

A quick calculation: taking the numbers in the article to mean there's 7 tons of fuel on board and 11 tons of non-fuel stuff, assuming the fuel is hydrazine giving a specific impulse of about 220, that gives the satellite a delta-v of about 1km/s, which is fairly substantial.

A quick back of the envolope calculation tells me a plane change of D degrees requires a delta-v of D/60*v for small D, where v is orbital velocity. Not that much.

So 1000m/s would get you about 7-8 degrees of plane change in low orbit? Sounds about right. That's not a whole lot, but it should be plenty to dodge sky watchers for a while if you have the ability to hide for a bit and change course while doing it.

Surely the active radar signals are detectable on the ground even if the exact orbit is unknown?

Maybe it is one of these systems http://en.m.wikipedia.org/wiki/Kinetic_bombardment

Thanks for that link. Very neat how towards the end of the video a Russian rocket booster travels across the frame from right to left. An unintended sighting of some well know space-junk!

With recent discussions of space debris problems, it's like seeing a rusted out Camaro parked in the middle of Yosemite.

One night literally lying on the grass in my back garden in Palo Alto I saw a fleet of satellites cross the sky. These were most likely a triplet of NOSS satellites that 'fly' in formation.

Wikipedia has a nice picture of these https://en.wikipedia.org/wiki/Naval_Ocean_Surveillance_Syste... and article https://en.wikipedia.org/wiki/Naval_Ocean_Surveillance_Syste...

wow, I seen that formation as child and freaked out, thought i was looking at a gigantic triangular alien spacecraft.

Imho this might be an orbital adjustment tool.

The thing has solar panels and is in a low orbit. So those panels are a significant source of drag. Normally this is a problem, but perhaps they are using this drag to adjust the orbit. I'm not talking plane change. I mean controlling the amount of drag to adjust orbital speed/altitude/period.

Even with all their extra fuel, spy sats do not make plane changes. A significant change would require hundreds of m/s and they have, at best, 1000m/s for their lifetime. (Xenon is power-hungry/tricky/slow and therefore not suitable for quick plane changes). These are multi-billion dollar assets with lifetimes measured in decades. You aren't going to spend 100m/s and shorten the lifetime of the asset by years, effectively spending a billion or more, on a plane change.

What they might do is adjust the timing of flyovers by controlled changes to orbital periods. Rotating solar panels, a significant source of drag and reflection, could give some control. Such a maneuver would probably be done at the lowest point in the orbit (highest drag) and could explain the quick and apparently random change in reflectivity.

The test for my theory: Does this disappearing trick happen more often at the low point of the orbit? (If you call that the periapsis we know you spend weekends on Duna.)

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