

The spy satellite Lacrosse 5 and its “disappearace trick” - gokhan
http://www.astrophoto.fr/spy_satellites.html#Lacrosse-5

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antimagic
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](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.

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

[https://www.youtube.com/watch?v=JwjvduR3_Ho](https://www.youtube.com/watch?v=JwjvduR3_Ho)

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

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deanclatworthy
There is a link buried on this page that goes into more detail:
[http://sattrackcam.blogspot.dk/2011/11/lacrosse-5-disappeara...](http://sattrackcam.blogspot.dk/2011/11/lacrosse-5-disappearance-
trick-captured.html)

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?

~~~
darkmighty
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).

~~~
ckozlowski
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

~~~
andor
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.

~~~
mikeash
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](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.

~~~
darkmighty
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.

~~~
mikeash
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.

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jgrahamc
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...](https://en.wikipedia.org/wiki/Naval_Ocean_Surveillance_System#/media/File:NOSS-
Trio.jpg) and article
[https://en.wikipedia.org/wiki/Naval_Ocean_Surveillance_Syste...](https://en.wikipedia.org/wiki/Naval_Ocean_Surveillance_System)

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

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sandworm
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.)

