Coaster, No. 13

Getting an idea of how big the hydrogen tank should be.  Let's go small ball and make this thing lightweight.  If the dry mass of the is held to about the mass of a Bigelow space hab, plus the coaster as propulsion, the entire assembly could be held under 50k pounds.  Realistic?  Perhaps not.

I've got a png file from Ubuntu that shows the calcs from the rocket equation.  Drat it.  I forgot how to get it into jpg format show I could put it up here.

What it shows is that by firing the engine for about 3 days gets you up to escape velocity.  A trip to the moon could do nicely.

The mass flow rate of a car at all acceleration was used as a benchmark of sorts to get an idea of what we're dealing on this score.  Then working backward from the rocket equation, a comparison of sorts could be made that seemed to this amateur to be "in the ballpark".    It is a surprisingly small amount of mass.

Now going back to the pic below, it is about 4 or 5 pounds per cubic foot for the Shuttle tank.  Using that as a guide, then at 11k pounds hydrogen gives about 2200 cubic feet.  Not that big of a tank needed.

All of this is very imprecise, but I am an amateur.  If these numbers are anywhere at all in the ballpark, the system doesn't need to be big.  That's the point.  A small system may do the trick.

It can be made small because a firing of even a small amount of thrust can build up an impressive amount of velocity.  This has been demonstrated with electric thrusters--- Hall effect thrusters.  This will have more thrust than that, with an ISP that is smaller too, but much larger than conventional chemical rockets.  All assuming, of course, that you can pull this off technically.

About .6 lb per gallon, about 7.5 gallons per cu. ft.

Update:

Finally got that png file converted to jpg.  Incidentally, the numbers are too low.  I thought the Bigelow space habs didn't weigh quite so much.  The mass of the BA 330 is 20k kg.  Dry mass in the spreadsheet is only 12k, which would have to include a lot more hardware than the 20k kg for the BA 330.

will have to redo this since the updated info varies greatly

Update: It may be possible to substitute the Dragon Capsule in place of the Bigelow space hab. The Dragon capsule fully loaded has a mass of 7500 kg. Combined with the additional hardware, it may be possible to arrive at a final mass of 12k kg as the spreadsheet above indicates.

The only question remaining, in terms of mass remaining, is the mass of the mirrors, heat exchanger, and rocket nozzle assembly.   This need not be massive, so the final mass shouldn't be over the limit.