Notes on fabrication of spacecraft, Part III

Speculation alert still applies: Series continued from last post.

Now we consider the internal layout of the X-33.  Since the X-37C will be mounted outside, that should leave even more room.  Will all of the fuel fit inside, or do we need a bigger bird?  Let's do some calculations to answer that question.

An earlier calculation gave 1000 cubic meters as the internal volume of the bird.  The NTR rocket casing should take up about 300 cubic meters of it.  From the spreadsheet in an earlier post, it can be deduced that the LH2 tank will have to contain 22k kg of hydrogen.  How much volume for such a tank?  Eyeballing the NTR's tank, we can see that this is roughly equivalent to that.  In other words, about 300 cubic meters.  Set aside 1/2 of that for each side and you've got 150 cubic meter tanks that would be roughly about half the size of the NTR's tank.

What about the oxygen tanks?  Once again from the spreadsheet, it looks like 32k kg for that.  From the Wikepedia page on oxygen, we see that the ratio in density equals the ratio between atomic weights.  What a surprise!  Well, the ratio of volume should be the same as well.  If it isn't, I don't have time to look it up.  Assuming that to be correct, then an quick estimate yields the following:  150 cubic meters for hydrogen calculated above gives 11k mass if it were hydrogen.  Multiply it by 3 to give 33k mass which is close to the mass of the oxygen.  Now, if it were hydrogen that would be 450 cubic meters, but since it is oxygen, divide that by 16 in order to yield the size of the oxygen tank in cubic meters--- 28 cubic meters.

These calculation yield a total for the tanks and the NTR casing of 628 cubic meters.  That leaves plenty of space for equipment and other things.

A consideration for where we would be mounting the engines comes into play.  Since there is so much volume available inside the X-33 aeroshell, we can mount the engines inside it.  This means that the final appearance of the X-33 will be essentially the same as in the pics.  We won't need a bigger bird.





There may be some refinements in later posts, but that's all for now.  I just got an idea that may make the thing ride better in the atmosphere--- you would have it on a ladder device that allows the X-37C to crawl forward along the rocket's casing until it is better position in space.  More on that in a later post.

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