Solar Thermal Rocket Series Part VI

A short series here.  It isn't even a challenge.  The Solar Thermal Rocket concept could work.  It may even be installed fairly easily.  The Canadarm was on the Shuttle and will be on the Nautilus--- if it ever gets built.

This arm can deploy the mirrors on booms, or deploy booms with pre-installed mirrors on booms.  The booms can be assembled like a Lego kit, I imagine.  The entire boom assembly fully completed shouldn't weigh all that much.  Comparable in size and mass to the existing PV panels on the ISS.  It should be more capable, though.

Speculation alert---- I'm not well versed in physics, so there could be an error in here.

The calculations for thrust seem impressive as well.  Hopefully, this is correct, so here goes:

1 Joule equals 2.78×10−7 kW·h, or 1 Kwh equals 2.78  ×10 ^7 Joules.

A Newton Meter is 1 Joule.  So that should figure.  Dividing by 3600 seconds in an hour gives the thrust number that gets quoted so often.  This gives result of 0.77  ×10 ^4, or 7700 Newton Meter per Kilowatt second capacity.  At 250 kw installed on the ISS, that gives 

          1, 925,000  Newton meters of thrust available.  If that's correct.  It seems a bit high.  If correct, that would give 19.25 Meters per second of acceleration for a mass of 100k kg in wet mass.  That's nearly 60 feet of delta V per second.  You would not have to fire the rockets for long in order to get a respectable amount of velocity going.  After 8 minutes of firing, you would get 9240 meters per second delta V.  That's firing as long as the shuttle main engines fired in order to get to near orbital velocity.  Nearly 20k mph.  That's added to the 17k for orbital velocity giving nearly 35k mph of total velocity.  After escaping Earth, we'd be heading to Mars at about 10k velocity, if I am not mistaken.

If the ISP is near the ISP of a nuclear thermal rocket (850) the amount of reaction mass needed to achieve this velocity is calculated.  The rocket equation shows 32k kg of dry mass, with 68k kg of fuel.  That surprises me.  I wouldn't have thought it to be that high.  The 32k dry mass includes everything, including the now empty propellant tank.  Also living quarters and supplies for a long journey.

Even with this, assuming it is correct, you will need a bigger ship and more propellant.  But this isn't out of the question.  You will need a lot of fuel, and a lot of launches to build the ship and supply it.

Just for kicks, it looks like about 3/4 million kg  in wet mass, assuming 120 kg for dry mass, will get you there in 150 days.  That's assuming a 100 million mile trip.  If you can make it shorter than that, it would help.

Note: the lunar and command modules together weighed only about 45k kg.  It went to the moon and back.