Solar Powered Space Yacht - revisited.

[aero]

I'm conceptualizing a spacecraft similar in shape to two 100 meter racing yachts, attach one upside down on the other. Remove the keels and replace them with masts. I use light weight solar panels in place of triangular sail cloth. The boom can pivot and the spacecraft can roll to catch the sunlight. How long or tall can I make the boom and mast, feasibly? (428.6 meters?) How much power can my spacecraft generate? What would be the best choices of electric engines/reaction mass and could I conceviably win the as yet to be thought of X-prize for the shortest time from LEO to LMO and back to LEO? Note that it is a requirement that the masts fold down against the hull and telescope down to no more than the length of the spacecraft hull for stowage.

[IRobot]

There is no Venturi effect or airfoil with solar sails, so you can only go "downwind".

[aero]

There is no Venturi effect or airfoil with solar sails, so you can only go "downwind".

Sorry, I thought it was clear that I am using solar cells, (panels) to generate electricity for my solar electric engine. I'm just mounting them like sails.

[savuporo]

Yeah, you might want to change the thread title.
Related, i think there needs to be a subcategory for "harebrained plans", in addition to "advanced concepts"

[aero]

Changed the title from sail boat to yacht.

Harebrained? Well maybe.

My purpose of this thread is to illustrate how massive solar power is, and to hopefully identify a lowest mass solar power panel solution. My friend Google gives current state of the art as 28% efficiency at 84 mg/cm^2 but I think that is only the wafer. Even assuming no additional structure that gives only 0.45 kW/kg. Hopefully this thread will answer the question, "How feasible is solar electric propulsion, DAWN not withstanding?"

[A_M_Swallow]

{snip}Note that it is a requirement that the masts fold down against the hull and telescope down to no more than the length of the spacecraft hull for stowage.

Is the fold down only during launch from the Earth's surface?
Re-folding is a much harder problem and may not be needed.

[aero]

{snip}Note that it is a requirement that the masts fold down against the hull and telescope down to no more than the length of the spacecraft hull for stowage.

Is the fold down only during launch from the Earth's surface?
Re-folding is a much harder problem and may not be needed.

I was thinking that the solar panels would be extremely large, large enough that photon pressure might induce orbital drift. Folding the panels would allow the spacecraft to rest at "anchor" so to speak, without undue forces imposed. Plus, with potentially dozens of spacecraft in the "Yacht Basin," distance between spacecraft might at a premium.

[A_M_Swallow]

{snip}Note that it is a requirement that the masts fold down against the hull and telescope down to no more than the length of the spacecraft hull for stowage.

Is the fold down only during launch from the Earth's surface?
Re-folding is a much harder problem and may not be needed.

I was thinking that the solar panels would be extremely large, large enough that photon pressure might induce orbital drift. Folding the panels would allow the spacecraft to rest at "anchor" so to speak, without undue forces imposed. Plus, with potentially dozens of spacecraft in the "Yacht Basin," distance between spacecraft might at a premium.

To follow the sun the solar arrays need to turn.  When parked just turn then side on to the sun.

[aero]

Ok, I've worked out one proposal, sort of.  Using the 4% efficient ultra thin film solar posted earlier on this thread, mounted on two 428 meter masts supporting 4 triangular sails (it masses only 4 g/m^2) gives 40 MW power  for only 3 tonnes mass. That is very good as solar power goes.  I assumed that my yacht masses 100 tonnes total, most of that is engine mass equal to 200 VASIMR engines  totaling 60 tonnes.  The yacht accelerates at a blazing 12 mm/s, so it only takes a little over a week to reach 8km/s, the delta V needed from LEO to LMO.

Unfortunately, after buying my solar thin film at $0.50 per Watt, (That is, ~ $7000/kg) I couldn't afford enough fuel so I had to leave my yacht in orbit and return on NASA's 100 tonne hydroLOX OTV. Luck for me that the OTV has payload capicity so I was able to return my solar thin film. Had to leave the VASIMRs so now I need low mass electric  engines. I'd prefer something that used lunar hydrogen or oxygen as reaction mass. Any ideas?

[Moe Grills]

There is no Venturi effect or airfoil with solar sails, so you can only go "downwind".

Sorry, I thought it was clear that I am using solar cells, (panels) to generate electricity for my solar electric engine. I'm just mounting them like sails.

Solar electric engine (plasma or ion?). A plasma engine is a better bet than ion engines for manrated craft.
I remember reading somewhere that the ratio between power and thrust
for any plasma rocket motor is? 20KW per pound of thrust.

OK! Assuming your space yacht's solar power collection is rated at 40,000 KW.
Then? Solar power-to-thrust conversion efficiency at 20 percent = 8,000 KW. Twenty percent sounds reasonable.

So your thrust would equal only 400 Ibs of force.
Your 100 metric ton (220,000 Ib)  'space yacht' in parking orbit at LEO would need anywhere from 150,000-170,000 seconds of aggregate thrust time to obtain a Delta-vee of between 9,000 - 11,000 feet/second to spiral you out towards the Moon from LEO.
170,000 seconds is almost equivalent to two days.
Obviously that can't be continuous thrust time, since there is Earth's shadow to contend with.
And then there is the matter of the slow passage through the Van Allen radiation belt. Not a good thing to do slowly.
I suppose you could use (potable & waste) water tanks for shielding;
living inside the yacht's cramped protective sheltering space while you pass through the belts.

If you want to enjoy a trip onboard such a craft in the future, I hope you're very young, very brave, very patient, very hardy, perhaps very rich. 

[aero]

I have conceived a new space yacht using laboratory level thin film solar panels, the ELF-375 engine design, and allowing 100 tonnes for the balance of the spacecraft. I parameterized mast height and settled on 1500 meters. This configuration masses almost 500 tonnes fully fueled, giving a time to accelerate to the moon (8 km/s delta V) of 35.3 hours at high thrust.
 
Thin film solar http://www.nature.com/ncomms/journal/v3/n4/full/ncomms1772.html
 
Note that using 4.2 % efficiency and 4 grams per square meter for this thin film actually gives the power to mass ratio of 14.29 kW/kg instead of 10 kW/kg as given in the reference. With two 1500 meter masts and the resulting four 1500 meter booms, this thin film solar masses 18 tonnes and produces 257.3 megawatts.
 
ELF-375 engine http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA513936
 
The ELF-375 engine gives the highest electric engine thrust to weight ratio that I could find. The design point is 200kW giving high thrust of 95 mN/kW,  (Isp ~ 1500 seconds), and high Isp of 5000 seconds at 35 mN/kW thrust. The engines are still quite massive at 64 tonnes for thrusters and 115 tonnes for the PPUs. The run to the moon, 35.3 hours at high thrust, used 196 tonnes of Xenon propellant and ended with tanks empty. The same run at high Isp took 80 hours, a propellant load of 51.7 tonnes and again ended with tanks empty.
 
Mast height http://yachtpals.com/largest-sailboat-4155
 
Note that the Mirabella V is 765 tonnes, 75.22 m long, with a 14.8 m beam and an 88.5 m mast.  Look at the photos to see a really impressive luxury sailing yacht. The solar panels on my space yacht are configured somewhat like the sails on the Mirabella V, except that my space yacht has the second mast where the keel is on the Mirabella V and of course the deck is domed over air tight. Like the Mirabella V, my space yacht is for party cruises, but around the moon instead of the Caribbean.
 
Comments:
 
Point 1 - The engines are far too massive. What can be expected by way of mass reduction, (thruster, PPU), if the engine design point was 20 or 50 megawatts instead of 200 kW?
 
Point 2 - Xenon propellant from Earth is a show stopper. Lifting 200 tonnes from Earth to LEO for each cruise is not going to happen.

[A_M_Swallow]

{snip}
The ELF-375 engine gives the highest electric engine thrust to weight ratio that I could find. The design point is 200kW giving high thrust of 95 mN/kW,  (Isp ~ 1500 seconds), and high Isp of 5000 seconds at 35 mN/kW thrust. The engines are still quite massive at 64 tonnes for thrusters and 115 tonnes for the PPUs. The run to the moon, 35.3 hours at high thrust, used 196 tonnes of Xenon propellant and ended with tanks empty. The same run at high Isp took 80 hours, a propellant load of 51.7 tonnes and again ended with tanks empty.

80 hours is 3 1/3 days.  IMHO a SEP Yacht that fast will be brought back to the Earth.

A Falcon Heavy may be able to lift 53 tonnes, so the fuel load could go up in a single launch.
http://www.spacex.com/falcon_heavy.php

Hall Effect thrusters can use Argon as a propellant.  Argon is a lot cheaper than Xenon.
http://www.busek.com/technologies__hall.htm

[nacnud]

There is no Venturi effect or airfoil with solar sails, so you can only go "downwind".

To sail you use the different velocities of two fluids (the air and the water) to be able to move to any point you wish. You can use similar ideas to use a solar sail to move to any orbit.

Think of the gravitational force as the water and the light at the wind. Angle the the sail so there is a thrust component against the orbital velocity and you drop into a lower orbit, thrust in the same direction as the orbital velocity and you can raise the orbit.

OT though as the discussion has move to SEP

[aero]

{snip}
The ELF-375 engine gives the highest electric engine thrust to weight ratio that I could find. The design point is 200kW giving high thrust of 95 mN/kW,  (Isp ~ 1500 seconds), and high Isp of 5000 seconds at 35 mN/kW thrust. The engines are still quite massive at 64 tonnes for thrusters and 115 tonnes for the PPUs. The run to the moon, 35.3 hours at high thrust, used 196 tonnes of Xenon propellant and ended with tanks empty. The same run at high Isp took 80 hours, a propellant load of 51.7 tonnes and again ended with tanks empty.

80 hours is 3 1/3 days.  IMHO a SEP Yacht that fast will be brought back to the Earth.

A Falcon Heavy may be able to lift 53 tonnes, so the fuel load could go up in a single launch.
http://www.spacex.com/falcon_heavy.php

Hall Effect thrusters can use Argon as a propellant.  Argon is a lot cheaper than Xenon.
http://www.busek.com/technologies__hall.htm

I'd be happy to calculate the time/propellant load needed for a round trip but I need a little information first. I've used the delta V from a Wikipedia table for electric propulsion.
 
http://en.wikipedia.org/wiki/Delta-v_budget

Obviously, I can't use the Oberth effect in my yacht, but with this power level, is 8 km/s delta V the right number? Is there a free trajectory calculator available somewhere that I could use?

Table 1 of ELF-375 reference above compares a 200 kW concentric channel HET (3 channels). It is somewhat less efficient than the ELF-375 but mostly it is just too massive. That is, the HET is 1.4 kg/kW (thruster, PPU) compared to 0.7 kg/kW for the ELF-375 (thruster, PPU). The ELF-375 thrusters plus PPUs mass 179 tonnes which would double if using the HETs. The time to the moon (to 8km/s delta V) is very sensitive even the ullage fuel in the tanks so significantly more massive engines without a big increase in efficiency would add a long time to the voyage. I could calculate that, too, if you are interested in seeing the numbers.

I don't know for a fact, but I'm thinking that the cost of lifting the propellant from the Earth's surface to LEO will wash out any difference between the cost of Xenon and Argon.

[aero]

There is no Venturi effect or airfoil with solar sails, so you can only go "downwind".

 .......

OT though as the discussion has move to SEP

Yes, I owned a CAL 30, a nice sailboat. I know how to sail though there is always more to learn.

This thread is about solar electric propulsion except where my analogies between sailboat rigging (sloop rigging) and the solar electric panel rigging on my space yacht have lead people astray.