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This document does a pretty decent job of detailing the ISS solar array. There's one part, however, that is sort of ambiguous and critical to an analysis I'm performing, and so I thought I might ask about it here.

On page 11, paragraph 1, the Integrated Equipment Assembly (IEA) for the photovoltaic modules is described. The first part of the paragraph says that there are four of these IEAs, located at P6, P4, S4, and S6 on the main truss. It then goes on to describe all of the subassemblies which compose the IEA. However, the ambiguity appears when describing the dimensions of the IEAs:

The IEA measures 16 feet (4.9 meters) by 16 feet (4.9 meters) by 16 feet ((4.9 meters), weighs nearly 17,000 pounds a (7,711.1 kilograms) and is designed to condition and store the electrical power collected by the photovoltaic arrays for use on board the Station.

So is EACH IEA a cube 5 meters on a side weighing 7.7 metric tons, or are ALL FOUR of these IEAs, in total, these dimensions?

The total mass of the ISS is ~390 metric tons, and the radiators are huge, so the total mass of these four IEAs COULD weigh ~30 metric tons in total.

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  • $\begingroup$ I would read it that the dimensions and mass apply to each IEA separately. $\endgroup$
    – Ross Millikan
    Jun 20, 2015 at 19:38
  • $\begingroup$ I find your question a bit confusing. It could help if you mentioned what analysis would you like to perform, because it's not clear to me at which point we should stop calculating total mass that you're interested in, if you include some assembly parts (IEA) to solar array wings (SAW), but not all of them (like complete truss segments, batteries, PV radiators,... see here nasa.gov/externalflash/ISSRG/pdfs/electrical.pdf). See e.g. the table here en.wikipedia.org/wiki/… (4 x 15,824 kg were delivered by STS). $\endgroup$
    – TildalWave
    Jun 21, 2015 at 14:35
  • $\begingroup$ BTW the ISS total mass is closer to 390 metric tons (see here isslive.com/displays/adcoDisplay1.html when it'll want to connect) but that doesn't include visiting spacecraft. Your number seems to include one docked Space Shuttle orbiter (dry mass somewhere in the range of 75 - 80 metric tons if memory serves correctly, depends on which one). For SAW (there's 8 of them), see here nasa.gov/mission_pages/station/structure/elements/… $\endgroup$
    – TildalWave
    Jun 21, 2015 at 14:43
  • $\begingroup$ @tildalwave corrected :) There are 8 wings, but four PV modules (modules have 2 wings apiece) Also, I totally agree that total per-truss mass is what I ended up going with. Wikipedia is not perfectly accurate here, as this document shows, but I agree that the BGAs and the SARJs are also contributing, as is the structure. $\endgroup$
    – Mephistopheles
    Jun 21, 2015 at 21:47
  • $\begingroup$ STS-97, which carried up the P6 truss assembly (2 solar array wings, the IEA, the cooling radiator, etc) had a payload mass of ~36,000 lbs. If you want to know the mass of each element at launch you can comb through the Shuttle Missions Summary at jsc.nasa.gov/history/reference/TM-2011-216142.pdf $\endgroup$
    – Organic Marble
    Jun 30, 2015 at 13:15

1 Answer 1

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I am going to answer your specific question, to wit:

So is EACH IEA a cube 5 meters on a side weighing 7.7 metric tons, or are ALL FOUR of these IEAs, in total, these dimensions?

This question was ridiculously difficult to answer, because NASA seems to go out of their way to obfuscate simple info like this. But here goes.

First of all, the dimensions given in that document are clearly wrong. Why is that? Well, it says the IEA is a 16 foot cube. All you have to do is recollect that the shuttle payload bay was a 60 x 15 foot cylindrical volume and you will immediately realize that it would not fit. You can not fit a 16 foot wide IEA in a 15 foot wide payload bay, especially since you have to have clearance to deploy it, room for the trunnions and payload attach system mechanisms, etc.

Also, even in that document you linked, it clearly isn't a cube. It's more like a cube sawn in half. It was also ridiculously difficult to find a decent picture of the IEA in space, in fact I gave up, but on this one you can at least tell that it isn't a cube. (The letters 2B are right on the IEA in this picture) enter image description here

So if we know the dimensions of the payload bay, and we can find a picture of the element in the payload bay, we can do some high tech photogrammetry. In other words, count some pixels. I used this one: enter image description here.
The IEA is at the aft end of the truss segment. You can see the battery boxes under the folded up solar array. From this we can figure out that the IEA is about 16 feet long by 14 feet wide (so at least the 16 foot number was valid for something). You can figure that the IEA is about 7.5 feet thick max because it does not stick up much above the sill of the payload bay so it's about half the payload bay dimension.

So if you accept my highly technical analysis, the IEA is roughly 16 x 14 x 7.5 feet and the document linked is pretty incorrect about the size. Now how about the mass?

Again NASA makes it ridiculously difficult to find this information. But we can reason it out to a first approximation. That document says the IEA weighs 17,000 lb. The Shuttle Missions Summary document, which I do trust, says the P6 had a payload weight of ~36,000 lbs. Since the IEA is about half of the truss segment, I'm willing to buy that 17K number. Also, if 17K lbs was for all 4 IEAs, each one would only weigh 4250 lbs, and that does not make sense in light of the credible 36klb weight of the P6.

So, the tl;dr version of the answer:

  • The document is incorrect on the dimensions of a single IEA. It's more like 16 x 14 x 8 than a 16 ft cube.
  • The document's figure for the mass of a single IEA of 17klb is reasonable.
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  • $\begingroup$ In my discussion with TildalWave, we came to the conclusion that the most accurate measure of the total mass of the whole system is the mass of the truss segments P6, S6, P4, and S4. In that respect, their mass can be given quite clearly in this document (which I also linked): nasa.gov/externalflash/ISSRG/pdfs/on_orbit.pdf Using that document, I came to the conclusion that the total mass of the solar array, panels, IEAs, structure, and positioning, was 15873+15750+16165+14026 = 61814 kg $\endgroup$
    – Mephistopheles
    Jul 3, 2015 at 21:46
  • $\begingroup$ can you share this documents i can not open it is deleted nasa.gov/externalflash/ISSRG/pdfs/on_orbit.pdf $\endgroup$
    – Aditya Baraskar
    Apr 5, 2021 at 7:57
  • $\begingroup$ @AdityaBaraskar Here you go: web.archive.org/web/20170225143620/nasa.gov/externalflash/ISSRG/… $\endgroup$
    – called2voyage ♦
    Apr 5, 2021 at 13:34

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