# InternetGravity, space movie directed by Alfonso Cuaron. Trailer up!

#### Ark

##### New member
Saw the film. Let's jut say it's mandatory viewing for any regular Orbitnaut!

The destruction is all sequenced on 90 minute orbits (= 5400 seconds) repeating on clockwork. Sounds reasonable, right, as we would recognize this is a typical T time for orbiting at ISS's altitude.

Except why the repeat?! If the debris was going the opposite way to us, it would meet us in 45 mins, not 90 mins. If it was going in our direction, it would not meet every 90 mins. Any other angle, we'd also meet it every 45 mins. The only way we would meet it every 90 mins would be if it were stationary, but then it would fall to the Earth.

Ho hum ...

But it was a gorgeously shot movie nonetheless.

Yeah, I was wondering about that. Would it work if the debris was in an elliptical orbit coming down from a higher altitude with a roughly 90 minute orbital period? Very unlikely, but wouldn't that give you an intercept every 90 minutes, assuming a debris cloud a few hundred KM across with the Hubble, ISS, and Tiangong all within a couple hundred KM of each other?

##### Scientist
Yeah, I was wondering about that. Would it work if the debris was in an elliptical orbit coming down from a higher altitude with a roughly 90 minute orbital period? Very unlikely, but wouldn't that give you an intercept every 90 minutes, assuming a debris cloud a few hundred KM across with the Hubble, ISS, and Tiangong all within a couple hundred KM of each other?

I can't see how you could make an elliptical orbit with a period of exactly 5400 seconds, with either a peri or an apo on our altitude. If the orbit were circular, then we know that the period varies by altitude (e.g. up to a ~24 hour period at geostationary altitude). If you start at a 5400 sec circular orbit, and boost it or retro it into an eccentric orbit, you are bound to create a different period.

Or am I missing something?!

Anyway - it was a good movie, and I would have totally bought a 45 min repeating period for the debris!

#### Izack

##### Non sequitur
I can't see how you could make an elliptical orbit with a period of exactly 5400 seconds, with either a peri or an apo on our altitude. If the orbit were circular, then we know that the period varies by altitude (e.g. up to a ~24 hour period at geostationary altitude). If you start at a 5400 sec circular orbit, and boost it or retro it into an eccentric orbit, you are bound to create a different period.

That's what I was thinking. Though I suppose the intersects don't need to be at the apses.

In any case, looking at the average level of realism of the orbital mechanics presented in this movie, the point is moot. The physics there are highly cinematic.

#### Kyle

##### Armchair Astronaut
Could it be possible the debris is in polar orbit? Couldn't that yield an impact about every 90 minutes?

#### dgatsoulis

##### ele2png user
That's what I was thinking. Though I suppose the intersects don't need to be at the apses.

Exactly. In order to have regular 90 min encounters you need to have the same SMa and different SMi, thus different eccentricity.
If we assume a SMa of 6771km (400km circular orbit for the ISS) and that the SMi cannot be less 6764 km (100km Periapsis altitude) we get a maximum eccentricity of ~0.044. (100x700 km orbit).
At the same altitude they will have exactly the same orbital velocity but the one with the eccentric orbit will be either speeding up or slowing down depending on whether it's headed for the periapsis or the apoapsis.

You get only one encounter per orbit with an encounter velocity of 0 m/s at 0° relative inclination and a maximum 10.85 km/s at 90° relative inclination.

#### Kyle

##### Armchair Astronaut
The 10.85km/s speed is supported by the dialogue in the movie, were Kowalski claims the satellite debris is moving at over 20,000mph.

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#### dgatsoulis

##### ele2png user
The 10.85km/s speed is supported by the dialogue in the movie, were Kowalski claims the satellite debris is moving at over 20,000mph.

"Over 20000mph" is roughly 9 km/s (depending on how much "over" really is).

That gives a R.Inc of about 72°.

#### Yoda

##### Donator
Donator
Its a movie guys.......dont over analyse it

#### Kyle

##### Armchair Astronaut
We're nerds, we over analyze what we want.

##### Scientist
Exactly. In order to have regular 90 min encounters you need to have the same SMa and different SMi, thus different eccentricity.
If we assume a SMa of 6771km (400km circular orbit for the ISS) and that the SMi cannot be less 6764 km (100km Periapsis altitude) we get a maximum eccentricity of ~0.044. (100x700 km orbit).
At the same altitude they will have exactly the same orbital velocity but the one with the eccentric orbit will be either speeding up or slowing down depending on whether it's headed for the periapsis or the apoapsis.

You get only one encounter per orbit with an encounter velocity of 0 m/s at 0° relative inclination and a maximum 10.85 km/s at 90° relative inclination.

Hmm interesting. I didn't realize that the orbital period just depends on the SMa, so it's possible as you say to have a lower x higher orbit that has an SMa the same, and we get an encounter each 90 mins. Wow! And of course, with the elliptical orbit, it's going to duck around the low part of the orbit faster than our circular orbit, so we won't hit it on the far side.

This would look great as a .SCN file with 2 x DG's, plotted with Videnie. (Hint for anyone?)

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#### Kyle

##### Armchair Astronaut
Speaking of addons, I actually might make an addon based off this movie for a challenging UMMU mission.

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#### dgatsoulis

##### ele2png user
This would look great as a .SCN file with 2 x DG's, plotted with Videnie. (Hint for anyone?)

60 seconds to impact. R.Inc chosen for a 20000 mph-ish encounter velocity.

Code:
BEGIN_DESC
Contains the latest simulation state.
END_DESC

BEGIN_ENVIRONMENT
System Sol
Date MJD 56572.0750777030
END_ENVIRONMENT

BEGIN_FOCUS
Ship GL1
END_FOCUS

BEGIN_CAMERA
TARGET Earth
MODE Extern
POS 3.18 143.99 -40.71
TRACKMODE TargetRelative
FOV 45.00
BEGIN_PRESET
Track:Earth:45.00:RELATIVE 2.535 2.506 -0.598
END_PRESET
END_CAMERA

BEGIN_HUD
TYPE Docking
REF 2 0
END_HUD

BEGIN_SHIPS
GL1:DeltaGlider
STATUS Orbiting Earth
RPOS 11008.81 1123464.16 6677135.86
RVEL -7672.376 58.422 2.820
AROT -72.49 6.17 18.47
RCSMODE 2
AFCMODE 7
PRPLEVEL 0:0.500000 1:0.298916
NAVFREQ 0 0 0 0
XPDR 0
GEAR 1 1.0000
SKIN RUSTY
AAP 0:0 0:0 0:0
END
2:Deltaglider
STATUS Orbiting Earth
RPOS -292266.04 693604.24 6708633.24
RVEL -2623.342 7215.931 -520.399
AROT 107.80 -5.14 161.41
AFCMODE 7
PRPLEVEL 0:1.000000 1:1.000000
NAVFREQ 0 0 0 0
XPDR 0
AAP 0:0 0:0 0:0
END
END_SHIPS

BEGIN_ExtMFD
END

BEGIN_Attachment Manager
END

#### Wolf

##### Donator
Donator
Speaking of addons, I actually might make an addon based off this movie for a challenging UMMU mission.

That would be nice!:thumbup:

#### Kyle

##### Armchair Astronaut
Thanks! I've already created a shuttle Explorer texture, it'll use ShuttleFleet's OV-007 "Moonraker," and simulate all four vehicles to be within a few kilometers of each other. Going off dgatsoulis's calculations, I'll also probably attempt to put a debris field using those same orbital elements. Any idea what I should use that would work for a debris field? Also will probably recommend collision detector for this scenario, isn't fun if you can't ram into the ISS and instead pass right through it

#### francisdrake

Saw the film today. I agree, it is a must for anyone who ever flew around the ISS in Orbiter :thumbup: The CGI is visually impressive on the exterior and the interior of station and spacecraft are setup with a lot of love to details.

Regarding the encounter with the debris every 90 min: It may work if there is a stream of debris, created by multiple collisions, in an elliptical orbit with apo- or periapsis coinciding with the ISS orbit.

Anyhow, it is a plot device to create danger. While space is vast even in LEO, the story has the Hubble telescope, the ISS and the Tiangong space station co-orbiting within a few hundred kilometers. I would not spend too many thoughts on the details of the graivtational mechanics here

#### dgatsoulis

##### ele2png user
Going off dgatsoulis's calculations, I'll also probably attempt to put a debris field using those same orbital elements.

I can refine the orbits for better visuals. The scenario I posted above has the encounter on the night-side, just before the terminator. Moving it on the day-side would be much better.

Start with the Hubble and the "Explorer" on a 600(?) km circular orbit (the trailer says 372 miles above Earth) with the real inclination (28.5°) and then adjust the ISS and Tiangong to be within 100 km from that.
Then bring in the debris field for an encounter on the day side. The orbit doesn't have to be so elliptical. 700x500 km would be enough to get one encounter per orbit and clear the field on the far side.

A R.Inc of ~70° would be enough to get a ~20000 mph (~9 km/s) encounter velocity, but it's a "blink and you missed it" situation. To have fragments hitting the Hubble/Explorer for at least 20 seconds (as shown in the trailer) you need a debris field 180 km long.

To me the velocity of the debris seems much slower. In order to actually see it the way it's depicted in the movie the encounter velocity can't be higher than a couple of km/s. (R.Inc ~15°). Anyway, I can setup a few scenarios with varying encounter velocities to see which looks closer to the movie.

Any idea what I should use that would work for a debris field?

The taikocrash mesh from the World of 2001 could be a good place to start. It's a bit flat (the debris is scattered on the surface of the Moon) but it wouldn't take a lot of work to turn it into something that looks good. Perhaps also add a few single big pieces with a fast rotation on all three axes.

Also will probably recommend collision detector for this scenario, isn't fun if you can't ram into the ISS and instead pass right through it

Don't forget the grappable fire-extinguisher/thruster.

#### Kyle

##### Armchair Astronaut
What if you wanted HST to be in a 51.6 degree orbit with the ISS? And if I want to get the debris cloud that big, I will probably have to use something that has a low polygon count to avoid massive lags.

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