Even space flight should have ADS-B

Space ADSB is called "USSTRATCOM" (formerly NORAD). They track as much space junk as they can, which is a whole lot, but still just a fraction of what's out there. There's a flight control position in NASA's Mission Control in Houston that's in regular communication with those guys to stay aware of potential "conjunctions" between space debris and the International Space Station, or vehicles coming/going to it. There are criteria established for when the ISS will ajust its orbit to avoid a potential collision; such adjustments happen something like 1-5 times a year, but potential collisions are identified almost weekly and monitored to ensure they don't meet the stricter criteria for a maneuver.
 
i bet that is some job when the targets are closing at 52,000mph!
predictive computers, no doubt.
I wonder what a collision warning from "stc" would sound like!
 
Let'sgoflying! said:
i bet that is some job when the targets are closing at 52,000mph!
predictive computers, no doubt.
Click to expand...
Nitpicking, but closure rates that high don't happen. No reason to launch due west, good reason to avoid it. Would have to be satisfied with a paltry 45,000 MPH or so....closer to 36,000 MPH, more likely. Hardly reason to change lanes. :-)

Another factor to consider is that one of the objects is debris, and, depending on its size, the tracking isn't too precise. Having an object the size of a beer can and ~50 km of position resolution means you've either got to jink far, or just let it ride and trust the tracks don't truly cross.

In our case, our satellites were in geosynchronous orbit, so the tracking accuracy was less (longer range) but the relative motion was very low in comparison. In one case, it was slow enough to actually watch the object pass through the field of view of the telescope.

Let'sgoflying! said:
I wonder what a collision warning from "stc" would sound like!
Click to expand...

In our case, it was the sound of a telephone ringing.....

Ron Wanttaja
 
There was a nice news piece the other day when they reported on that Japanese mission that failed, it was a satellite sent up to remove space junk. They said there is millions of objects floating around waiting to cause havoc.

I think we need to send more F-15's up to start shooting down more satellites and crap! They could sell the backseat to those of us who would give our left nut and first born for a ride in an eagle!
 
wanttaja said:
I was operating Air Force early warning satellites nearly 40 years ago. Even then, we had to maneuver occasionally due to debris.

Ron Wanttaja
Click to expand...

COMSATS at Sunnyvale 30 yrs ago. (Learned to fly at Moffett Field Aero Club). We never maneuvered for close approaches.

Let'sgoflying! said:
I wonder what a collision warning from "stc" would sound like!
Click to expand...

We got a TWX once a week with close approach predictions. It told us which one of ours was being approached, what the other body was, time of closest approach, and closest approach distance.

wanttaja said:
.

Another factor to consider is that one of the objects is debris, and, depending on its size, the tracking isn't too precise. Having an object the size of a beer can and ~50 km of position resolution means you've either got to jink far, or just let it ride and trust the tracks don't truly cross.

In our case, our satellites were in geosynchronous orbit, so the tracking accuracy was less (longer range) but the relative motion was very low in comparison. In one case, it was slow enough to actually watch the object pass through the field of view of the telescope.

Ron Wanttaja
Click to expand...

Cool!

Closest prediction I ever saw was 1 km. That got our attention, so we looked at it closely. Since our knowledge of our own position wasn't much better than a kilometer, and NORAD's knowledge of the other body's position was much worse than a km, the decision was to do nothing. RFI of somebody passing by was a much bigger concern than actual collision.
 
how do they map position of things in space? Do they extend lat & long up from the surface then add an altitude?
 
Van Johnston said:
COMSATS at Sunnyvale 30 yrs ago.
Click to expand...
Defense Support Program, 1977-1981.

Let'sgoflying! said:
how do they map position of things in space? Do they extend lat & long up from the surface then add an altitude?
Click to expand...

Lat/Long/Altitude is what I've been using for quite a few years, and I believe that's standard. I convert it to Earth-Centered XYZ coordinates when computing ranges, etc.

Ron Wanttaja
 
Let'sgoflying! said:
how do they map position of things in space? Do they extend lat & long up from the surface then add an altitude?
Click to expand...

Not really. For geo satellites that -- in theory -- stay in place over the equator that generally works. But for everything else you need an inertial reference frame. Either a Cartesian reference frame centered on a non- rotating earth, or there are other systems to define orbits. Most commonly known and what everyone learns first is the Keplerian elements.

One of the cool/morbid things I learned in grad school was the math to target ICBMs that took time of launch out of the equations.
 
Acrodustertoo said:
There was a nice news piece the other day when they reported on that Japanese mission that failed, it was a satellite sent up to remove space junk. They said there is millions of objects floating around waiting to cause havoc.
Click to expand...
Point of clarification: The primary mission of the satellite in question (HTV) was a cargo delivery to the ISS, which was a complete success. There was a secondary payload attached to the cargo vehicle (that was supposed to be released on a tether between the time the cargo vehicle departed ISS and re-entereed the atmosphere), and that secondary payload (called KITE) is what failed. The bit about potentially using data attained from the payload in future space debris missions was only one potential application of the tech.

BTW, tethered satellite experiments do not have a good track record (Shuttle TSS missions).

I think we need to send more F-15's up to start shooting down more satellites and crap! They could sell the backseat to those of us who would give our left nut and first born for a ride in an eagle!
Click to expand...
Shooting down satellites is not the way to get rid of orbital debris. The two primary sources of debris are spent booster components, which are more likely to fall out of orbit "quickly", and derelict satellites, of which there are now so many that there are occasional collisions, or somewhat more commonly simply spontaneously explode (due to propellant system malfunctions). Both events cause "clouds" of debris that expand over time, and that's also what would happen if you tried to "shoot down" a satellite. (When we did it, orbital debris was not as big a concern, but when the Chinese did just this more recently, they were highly criticized for it.)

There are some concerns that debris density will reach (or has already reached) a "tipping point" where you get a chain reaction-type situation, and satellite-disabling debris hits will self-perpetuate and rapidly increase in frequency to the point that entire altitude ranges above earth will be "saturated" with debris and essentially unusable. There are a lot of folks thinking about ways to clean up orbital debris, but there's a lot of volume to cover, and it takes a lot of energy to change orbits, so it's a hard problem to solve.
 
Last edited:
Jim_R said:
Point of clarification: The primary mission of the satellite in question (HTV) was a cargo delivery to the ISS, which was a complete success. There was a secondary payload attached to the cargo vehicle (that was supposed to be released on a tether between the time the cargo vehicle departed ISS and re-entereed the atmosphere), and that secondary payload (called KITE) is what failed. The bit about potentially using data attained from the payload in future space debris missions was only one potential application of the tech.

BTW, tethered satellite experiments do not have a good track record (Shuttle TSS missions).


Shooting down satellites is not the way to get rid of orbital debris. The two primary sources of debris are spent booster components, which are more likely to fall out of orbit "quickly", and derelict satellites, of which there are now so many that there are occasional collisions, or somewhat more commonly simply spontaneously explode (due to propellant system malfunctions). Both events cause "clouds" of debris that expand over time, and that's also what would happen if you tried to "shoot down" a satellite. (When we did it, orbital debris was not as big a concern, but when the Chinese did just this more recently, they were highly criticized for it.)

There are some concerns that debris density will reach (or has already reached) a "tipping point" where you get a chain reaction-type situation, and satellite-disabling debris hits will self-perpetuate and rapidly increase in frequency to the point that entire altitude ranges above earth will be "saturated" with debris and essentially unusable. There are a lot of folks thinking about ways to clean up orbital debris, but there's a lot of volume to cover, and it takes a lot of energy to change orbits, so it's a hard problem to solve.
Click to expand...
Thank you Jim. Maybe you could answer this question since I'm too lazy to sort through all the chaff. How many million pieces of debris are floating around up there?
 
Acrodustertoo said:
Thank you Jim. Maybe you could answer this question since I'm too lazy to sort through all the chaff. How many million pieces of debris are floating around up there?
Click to expand...
It's not possible to know the answer to that question. Radar tracking of debris can only resolve pieces that are of a size, shape, and material composition to provide an adequate reflection. i don't know how many pieces USSTRATCOM has in their tracking database, but certainly orbital debris is like roaches: For every one you see, there are lots more out there that you don't see.
 
Jim_R said:
There are a lot of folks thinking about ways to clean up orbital debris, but there's a lot of volume to cover, and it takes a lot of energy to change orbits, so it's a hard problem to solve.
Click to expand...

Selecting higher orbits to avoid the low flying stuff is....expensive?....deteriorates the capability of the satellite due to distance from earth?
 
We should have a space program. We could send people up in orange space suits to pick up that space debris.

The program would be popular among folks who need to do community service.
 
Let'sgoflying! said:
Selecting higher orbits to avoid the low flying stuff is....expensive?....deteriorates the capability of the satellite due to distance from earth?
Click to expand...
Several factors.

The longer the distance to your target, the fancier your equipment needs to be. Take a picture from the upper levels of a football stadium, you need a camera with a big, long, expensive lens. Join the huddle with the players, and an old Instamatic will do.

So going higher means you need better cameras, bigger antennas, and, of course, more-expensive, more powerful launch vehicles.

The second factor is radiation. The Van Allen belts start getting particularly nasty about 1,000 km altitude or so. Modern electronics is very sensitive to radiation, so you need special rad-hardened parts (more expensive) and increased shielding (way heavy, and not that effective). In addition, you'll suffer an increasing occurrence of Single Event Upsets that usually need a reset triggered.

Ron Wanttaja
 
Of course; Van Allen belts. Totally missed that! :D
I guess that leaves Laser Blasters installed in the nose of each satellite!
 
Acrodustertoo said:
Thank you Jim. Maybe you could answer this question since I'm too lazy to sort through all the chaff. How many million pieces of debris are floating around up there?
Click to expand...
I've heard they're tracking half a million, but as Jim said, there's a lot of teeny tiny stuff that we can't see from Earth. One of the Shuttles came back with a chipped windshield that they believe was caused by a paint chip.

There are international agreements that try to limit the amount of debris (captured components from explosive actuators, etc.) and most of the programs I've worked have been required to retain some sort of end-of-life action to minimize the risk. This might be a propellant reserve for a deorbit for Low Earth Orbit satellites, or to put a Geosynchronous satellite into a disposal orbit that is separated from the main GEO ring.

I was a judge for a high-school science fair a couple of years back, cleaning up orbital debris was a popular topic.

Ron Wanttaja
 
Large nets, I tell you. Connected to 4 space ships - couple of passes and they will clean that up like a Zamboni after free-skate cleans up bubble gum and cigarette butts.

More seriously; perhaps little will really be done until a chunk of metal passes through something carrying a human.
 
Let'sgoflying! said:
Selecting higher orbits to avoid the low flying stuff is....expensive?....deteriorates the capability of the satellite due to distance from earth?
Click to expand...
Orbit selection is determined by lots of factors. In addition to the physical considerations on the satellite mentioned by Ron, there are other mission objective-related drivers. Orbits do not have to be circular; physics dictates that orbits must be elliptical, and a ciricle is just an ellipse whose foci overlap. So you can have orbits where the highest point is much much higher than the lowest point. Russia has used highly-elliptical orbits for communications and for spy satellites.

Physics also dictates the speed of your satellite. For two circular orbits at different altitudes, the satellite in the lower orbit will have to go faster to stay in orbit. Low-orbiting satellites therefore circle the globe much more quickly than high-orbiting satellites. That might not be good if you're trying to stay in view of a fixed point on the surface, but it might be great if you're trying to take imagery of as much surface area as possible in a given time. A circular orbit with a height of ~22,000 miles makes one revolution every 24 hrs, so that's where geostationary satellites are. ("Geostationary" only works over the equator, btw. Incline the orbit, and your satellite will still be "geosynchronous" and stay at the same longitude, but it will oscillate between + / - some latitude every 12 hrs.)

When you vary the altitude, move away from circular orbits and into elliptical ones, and vary the inclination of the orbit, you can get your satellite to spend more or less time over certain parts of the world, or affect the frequency at which different parts of the world come into view, etc.
 
You must log in or register to reply here.
Back
Top