Author Topic: Roll Out Solar Array (ROSA) headed to the ISS  (Read 17281 times)

Offline Orbiter

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Re: Roll Out Solar Array (ROSA) headed to the ISS
« Reply #60 on: 06/26/2017 11:39 PM »
Wonder how noticeable it'll be from the ground; solar panels can be quite reflective.
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Offline speedevil

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Re: Roll Out Solar Array (ROSA) headed to the ISS
« Reply #61 on: 06/26/2017 11:53 PM »
Tracking should be fun - I wonder how fast it's spinning and if that'll change.
Pity it didn't lock, from a mission success POV, but certainly more interesting from a sighting POV.

Offline Hobbes-22

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Re: Roll Out Solar Array (ROSA) headed to the ISS
« Reply #62 on: 06/27/2017 08:08 AM »
That seems an awfully large object to jettison. What's keeping ROSA from crashing into the station on the next orbit?

Offline Star One

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Re: Roll Out Solar Array (ROSA) headed to the ISS
« Reply #63 on: 06/27/2017 09:27 AM »
How long until it deorbits as that seems to be an awfully large piece of space junk to be floating around up there near ISS?

Offline speedevil

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Re: Roll Out Solar Array (ROSA) headed to the ISS
« Reply #64 on: 06/27/2017 10:42 AM »
Looking at the size, the width of the solar part of the array seems to be pretty close to 1m. This would, together with the images, put the length at around 10m, for about 10m^2, or 12kW of solar incident power.
Or perhaps 3000W.
This would conservatively place the weight in the 30kg range.
The area, assuming that it is randomly spinning and 10m^2 would be about 5m^2, so the effective sectional density is 6kg/m^2.

https://spaceflight.nasa.gov/realdata/sightings/SSapplications/Post/JavaSSOP/orbit/ISS/SVPOST.html gives the area of ISS as 17659ft^2, or ~2000m^2, and mass of 420000kg. Or 210kg/m^2.

ROSA decelerates at about 210/6 = 35 times the rate of ISS.
ISS started June at ~405.2km, and will end at 404.7 or so. A drop of 500/30 =16 meters a day, ~1m/orbit.

ROSA should lower in altitude by ~35m per orbit, 560m/day.
This would alter its period by one part in 10000 or so.

Handwaving stuff that I don't understand, this would lead to a miss by of the order of ~5s*8000m/s,  or 40km, after one day.

However, it's going to come uncomfortably close for a significant period. An old source says the collision avoidance box is 1km 'deep' from ISS towards earth, so to drop out of that box would take ROSA a couple of days.

It's at least possible that proper understanding of the drag model, and release time could mean that there is no risk to ISS.


500m a day, it could easily be a large fraction of a year before it reenters.

(Above orbital calculations according to Wil.E. Coyote's book of orbital mechanics, where all orbits are linear or square as convenient. I'd love someone to do it properly).
« Last Edit: 06/27/2017 11:03 AM by speedevil »

Offline Ictogan

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Re: Roll Out Solar Array (ROSA) headed to the ISS
« Reply #65 on: 06/27/2017 12:52 PM »
Besides ROSA decaying much faster than ISS, it also seperated retrograde from ISS, meaning that it'll already start out in a slightly lower orbit. In the video it looks like ROSA seperated at ~1m/s. This would lower the semi-major axis of the array by about 1750m and reduce the orbital period by about 2 seconds. This means that on the next orbit it would arrive at the same spot as ISS about 2s later and given the ~7.7km/s speed of those orbits they'd be seperated by ~15km after just one orbit.

Offline speedevil

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Re: Roll Out Solar Array (ROSA) headed to the ISS
« Reply #66 on: 06/27/2017 03:21 PM »
I had missed this most excellent video.


This goes into the deployment of the as-orbited config, as well as detailed design.
The truss expansion at high speed is neat.

Offline SWGlassPit

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Re: Roll Out Solar Array (ROSA) headed to the ISS
« Reply #67 on: 06/27/2017 08:55 PM »
That seems an awfully large object to jettison. What's keeping ROSA from crashing into the station on the next orbit?

They jettison down and retrograde, which places it in a different orbit that won't intersect ISS's orbit as it decays.  It's the same approach they use for deploying cubesats.

Offline Lars-J

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Roll Out Solar Array (ROSA) headed to the ISS
« Reply #68 on: 06/28/2017 09:41 PM »
That seems an awfully large object to jettison. What's keeping ROSA from crashing into the station on the next orbit?

They jettison down and retrograde, which places it in a different orbit that won't intersect ISS's orbit as it decays.  It's the same approach they use for deploying cubesats.

And the reason Dragon and Cygnus approach from below - should they have a problem, they will naturally drift away from ISS with a minimal risk for recontact.
« Last Edit: 06/28/2017 10:45 PM by Lars-J »

Offline Lewis007

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Re: Roll Out Solar Array (ROSA) headed to the ISS
« Reply #69 on: 06/29/2017 06:56 AM »
Some pics released by NASA

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