'Terminator Tape' did its job in space-junk test-and it will be back

[WKTaylor]

Finally... a reliable way to deorbit small-sats… assuming it's own robust communications system??

https://www.space.com/space-junk-removal-terminator-tape-satellite-test.html

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[IRstuff]

I think that the devil is in the details.
> the deployment implies working chain of hardware, from comms to processor to deployment mechanism -- any stoppages along the way results in a dead satellite trapped in its natural orbit
> once deployed, the descent is essentially uncontrolled, if the mechanism is purely drag, since the drag isn't necessarily a consistent thing -- if the satellite is sufficiently crippled, it might not be able to avoid any satellite in its path in lower orbits

It seems to me that the mechanism needs to be fail-safe, i.e., automatically activated in the event of catastrophic failure of the satellite comms, electronics, power, etc. But, at the same time, it needs to be able to keep its deorbit trajectory from intercepting satellites in lower orbits. It has to have sufficient power to initiate the deployment, so there are some issues there that have to be worked out. It might need to have its own comms, but dormant reliability means that something can still die and possibly kill the process.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[btrueblood]

Not necessarily uncontrolled. The tape is electrically conductive, which though not explicitly stated, at least implies it's an electrodynamic tether, intended to interact with the earth's magnetic field to induce a electromagnetic drag force, dumping the waste current to a resistor. If you power a conductive tether, you can also create a net thrust, but I don't think they have that capability in the demo. They should, however, be able to switch the circuit on/off, or even modulate the current, which would vary the drag, and give a modicum of control to the de-orbiting.

But globally, yes, they need this thing to work on its own accord, regardless of comms and power from the parent spacecraft, etc. Still, better than a dead satellite with no control whatsoever...

 

[Sparweb]

This predicted event is timely:

https://www.forbes.com/sites/ericma...te-over-pittsburgh-didnt-happen/#2af73bef5724

Both of those sat's are very old (1967 & 1983) with no way to de-orbit themselves.
No collision this time, but we are powerless if/when the next collision is possible.

http://www.sparweb.ca

 

[IRstuff]

True, but you can't necessarily force everyone to put in a de-orbit mechanism that's 100% reliable over 30 yrs, since that might wind up costing more than the actual payload itself, or convince Iran to install a de-orbit system for their putative satellite when they're under export restrictions.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[Sparweb]

to install a de-orbit system for their putative satellite when they're under export restrictions

I don't think any de-orbit system has proven to be accurate enough to do what you are implying. But I get what you mean...

http://www.sparweb.ca

 

[Comcokid]

Actually the tape is electrically conductive possibly so that it's deployment in this test case could be detected by radar tracking.

If designed right, the mechanism that deploys the module could be made such that unless the main satellite controller sends signals, it does not deploy. Then, if the satellite goes dead then the mechanism would deploy after a few weeks. If they could come up with a clever mechanical/chemical design that in no way depends upon electronics, then the mechanism would be able to function after decades.

Would only work in relative low Earth orbits.

 

[WKTaylor]

Another de-orbit technology ready for demonstration[?]…

Aurora to test deorbit tether on Momentus mission [similar concept to the Terminator Tape system?] on a 1.5X cube-sat.

https://spacenews.com/aurora-momentus-plasma-brake/

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[Sparweb]

Another strategy to spacecraft maintenance:

In a historic first, one private satellite docks to another in orbit

The target satellite, Intelsat-901, is in geostationary orbit and needs to be moved to the "graveyard" a little farther beyond it. This is a case where de-orbiting is not practical because of the energy already expended to boost the original satellite to GEO would need to be expended again to knock it out. Far more efficient to move it farther away.
The MEV can assist the disposal of GEO sat's that can't propel themselves to the graveyard.

http://www.sparweb.ca

 

[Comcokid]

I though this technology was still a few years away. Hurrah! for them. The last picture in the link indicates they're using a probe into the transfer-orbit engine nozzle to latch on.

Hopefully in a in a few years all geostationary satellites being launched will be designed for in-orbit robot service by more capable MEV-like vehicles. For now Intelsat-901, after some check-out will be moved and attitude-controlled by the MEV in a new geostationary slot for additional use.

Unfortunately, the delta-V energy required for a complete de-orbit is prohibitive from geostationary. But it will ensure that the lifetime of otherwise working geostationary satellites that are low on fuel can have an extension and afterwards be moved to a safe graveyard orbit.

 

[Compositepro]

Maybe I am being too picky but it appears in some of the animations that the satellites in GEO are moving east to west, while they should be moving west to east.

I was wondering why the launch was from Kazakhstan. Turns out that is where the Baykonur Cosmodrome is located, which is leased to the Russians until 2050.

https://en.wikipedia.org/wiki/Baikonur_Cosmodrome.

Nice accomplishment though.

 

[Sparweb]

Compositepro,
Are you referring to the transfer from GEO to Graveyard at 1:26 in the video?

The reason is the graveyard is farther from Earth, therefore a higher orbit, therefore a longer orbital period, therefore a slower velocity.
So the process of rising to a higher orbit involves both increasing energy, and less velocity at the end.
It's a counter-intuitive part of orbital dynamics, and easily forgotten even by spacebuffs like me. I've been mixed up by that before myself.

http://www.sparweb.ca

 

[Sparweb]

Oh, the coin just dropped:
The MEV also extends the useful mission life of the Intelsat-901, by keeping it on station after its own internal propellant has been exhausted. Another reason for the Intelsat's thruster to be a convenient docking point.

http://www.sparweb.ca

 

[Compositepro]

Sparweb, I believe that higher orbits always require higher velocity, although the orbital period is longer.

 

[Sparweb]

The counter-intuition is still getting you.
To change orbit to a higher orbit, you first need to increase your velocity. But once you get to the higher orbit, you will be slower.
See if this helps:

https://en.wikipedia.org/wiki/Geost...le:Comparison_satellite_navigation_orbits.svg

http://www.sparweb.ca

 

[btrueblood]

"I believe that higher orbits always require higher velocity, although the orbital period is longer."
Great post!

"To change orbit to a higher orbit, you first need to increase your velocity. But once you get to the higher orbit, you will be slower."

You're both right, but not explaining it properly . Higher velocity in higher orbits, but in higher orbits the orbital period is longer. Thus, for a ground observer, the higher orbiting satellites will appear to move westward, i.e. appear to be slower in angular velocity, than the GEO sats.

 

[Compositepro]

Thanks guys. I see the error in my thinking now. Although a forward thrust is required to get to a higher orbit, and another forward thrust is required at apogee to stay at the higher orbit, all of the added energy goes into increasing potential energy. In this case, the satellite has an ion thruster so the engine operates continuously, rather than in short burns. The kinetic energy of the satellite does actually decrease, even though the thruster is adding energy in the forward direction.
That is kind-of mind-blowing.

 

[IRstuff]

The most efficient orbit change maneuver is the Hohman transfer:

https://en.wikipedia.org/wiki/Hohmann_transfer_orbit.

The simplest approach to estimating the velocity is to equate v^2 / (r_earth+alt) = g_earth * r_earth^2 / (r_earth+alt)^2, since the centripetal acceleration must equal the radial gravity in a stable orbit. This results in v^2 = g_earth * r_earth^2 / (r_earth+alt) As altitude increases, velocity decreases, which means that angular velocity likewise decreases; at the geostationary orbit altitude, the angular velocity difference between earth rotation and the satellite goes to zero, since that's essentially the definition of geostationary orbit. Therefore, beyond geostationary orbit altitude, the apparent angular velocity difference, i.e., how the satellite moves across the sky, must appear to be in the opposite direction relative to a low orbit satellite's motion. The bottom graphic shows the LLA displays for 3 satellites, one at 300-km altitude (LEO), one at geostationary, and one above that orbit. The lon(gitude) rate displays show a positive value for LEO, indicating that it's moving west to east, relative to the Earth, the geosync shows zero lon rate, as expected, and the higher orbit shows a negative lon rate, indicating that it will appear to be moving east to west from the Earth.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[Sparweb]

Higher velocity in higher orbits

Sorry for being a stick in the mud, but that doesn't work. Your velocity increase can be traded for higher potential energy, but not BOTH more potential energy AND kinetic energy at the same time. When stabilized at a higher orbit, your velocity is lower, not higher. Newton's law:

G*M = r * V^2

"G" and the mass of the Earth are constant, so every orbital radius is inversely proportional to velocity.

LEO is about 7,000 meters per second
GEO is about 3,075 meters per second

The confusion comes (in IRStuff's example) because to transfer (eg. Hohmann) you have to speed up first, to get to a higher orbit. But during the transfer you slow down.

http://www.sparweb.ca

 

[btrueblood]

Fair enough, I was thinking delta-V required, not orbital velocity.