DPF for the Icarus Interstellar Spaceship project

[QuantumDot]

http://www.icarusinterstellar.org/icarus_project.php

The goal of the Icarus project is to design a space ship using current or near term technology to go to another star, and it must get there in the life time of a human.

So i would like to know from the team working on the FoFu if you can imagine a DPF or a group of DPF fitting the bill for the propulsion and power or for just one of them?

What other technologies do you see needing for it to work? (like capacitor energy density, how many discharge life cycle, energy primer traveling wave reactor)

What would it operating requirement be?( ion temp, electron temp, density, confinement time, pulse rate, would it need something to ablate or would it work directly, the about of fuel necessary)

How long in the future do you see it being before it could fly?

[zapkitty]

Hmmm… how about something less ambitious?

Let’s try powering a small commercial space station in LEO first.

There you can learn about whatever quirks lie within the system in a working environment of vacuum and microgravity… but you have auxiliary systems on hand in case of teething pains… and Earth is only an hour away by capsule if things go really south on you.

Attached is a rorschach test… see what you can make of it… I don’t see so well myself but everything should be in place…

Attached files

[QuantumDot]

Well since fusion propulsion is one of the only options for interstellar flight and the DPF is about the only near term option, its worth a serious look.

the other options are light sails, antimatter catalyzed fusion, a field reversed configuration( think VASMIR only blown up to cause fusion), and pulsed detonation either with small pellets ignited with lasers or small bombs, the last option is one based on Bussards work either the polywell or the ram-scoop. And from what i have heard only the light sails can be said to be near term.

And of course you would want to test it in the solar system first with a direct flight to mars which should only be 30 days and a gravity spin around the sun but after a few years of tests you would want to try to use it for the real deal and send it to another star.

[Breakable]

Unless someone will get this to work:
http://en.wikipedia.org/wiki/Reactionless_drive

[QuantumDot]

Recently some physicist have observed electrons having a negative mass before undergoing acceleration which is more or less what woodward expected which means that his theoretical mach reaction-less propulsion device might just be possible, but you would still have to power the thing and scale up it performance to meaningful levels.

various people are studying the mach drive and some have reported limited success, work is still ongoing.

electron negative inertial mass
http://www.sciencedaily.com/releases/2010/04/100412084525.htm
http://www.technobahn.com/news/Negative_Mass_and_High_Speed:_How_Electrons_Go_Their_Own_Ways_2010041200003007.html

woodward mach drive
http://www.centauri-dreams.org/?p=1324
http://en.wikipedia.org/wiki/Woodward_effect

[vansig]

Let’s throw some numbers in…

Distance to a star 4.2 light years away,
= 365.25 days/year x 86400 s/day x c = 9.467e15 m;

.5 of the journey is acceleration, and .5 is deceleration, each taking at most 50 years, to meet the project’s goal,
= 1.57788e9 s each;

Continuous acceleration required to travel .5 of the total distance in that time,
.5 d = .5 a t²;
9.467e15 m = a (1.57788e9 s)²;
a = 3.8e-3 m/s² (=.00039 g);
not too bad, so far.
So long as average acceleration is at least this through the whole journey, you can get there.

Top speed will need to be, at least
a t = 3.8e-3 m/s² x 1.57788e9 s
= 6000 km/s
= .02 c;

So, you’ll want calculate drag on a craft travelling through interstellar space at .02 c, which will yield important info about the maximum speed of the ship.

But also, unless/until reactionless drive is invented (a.k.a. star trek impulse drive), or unless this is a Bussard ramjet, you’ll have to carry sufficient reaction mass for the journey, and apply the rocket equation. — http://en.wikipedia.org/wiki/Rocket_equation

delta-V = Ve ln ( m0 / m1 );

Ve is the effective exhaust velocity, which could be as great as .028 c for Focus Fusion. delta-V = .02 c; so,
neglecting drag, m0/m1 ~= 2.0, for each leg of the journey.

[vansig]

er, my bad.
i gave total distance of 1 lt yr, in error. correcting this, acceleration has to be 0.016 m/s². top speed will need to be .084 c,
and m0 / m1 = 20, for each leg.

so mass of fuel will end up having to be 400 x the mass of the ship.

[Lerner]

You are not accounting for slowing down at the other end. However, it seems quite possible that magnetic breaking could be possible–deploying a current loop to interact with interstellar magnetic fields to slow the ship down without much expenditure of fuel.

[vansig]

actually i think the 400:1 ratio does account for slowing down. but, there are still problems.
i calculate the thrust needed to meet this as:

Thrust = ( delta-m/delta-t ) x Ve
— http://en.wikipedia.org/wiki/Specific_impulse

if m1 = mass of the ship, without fuel, then delta-m on the last leg (slowing down) is 19 m1. and
delta-m on the first leg is 380 m1.

mass flow rate = 380 m1 / 1.57788e9 s = 2.4e-7 m1 ( kg/s );
for a 1t stage, = 1e3 kg, then this yields 2.4e-4 kg/s, = 0.24 g/s flow rate.

then thrust needed = 2.4e-4 kg/s x 8.4e6 m/s = 2016 N.

but that seems unrealistic.. too high for FF, which consumes ~ 1 kg/year,
= 3.17e-8 kg/s, yielding 0.27 N

ability to use magnetic breaking would improve the situation; as would ability to run a million pinches per second

[Lerner]

A 5MW FF device would power a nearly microscopic payload. Even for getting around the solar system you are looking at more like multi-GW systems with thousands of electrodes. Cooling is the big problem since excess heat has to be radiated.

[vansig]

right, so that may lead to a fundamental limit.
what’s the lower bound on mass, of a ship with a 37 GW focus fusion power source,
including radiators and fuel tank, but empty of fuel?

[vansig]

i’m calculating that a large radiator, 1 km² area, could keep a 37 GWt heat source below about 900 kelvin.

in terms of 5 MW generators, that’s about 135 m² area each.
still quite onerous to keep the total mass really low.

[zapkitty]

Either you or I have misplaced a decimal point somewhere…

gigawatts (electrical)
37.95
(gives you .95 gw to actually operate the ship)

gigawatts (thermal)
18.97
(assumes 50% efficiency)

stefan’s
5.67E-008

emissivity
0.85

temp (c)
627
(That’s 900k)

area (m2)
600000
(over 774 meters on a side)

Specific Mass (kg/m2)
10
(assuming a lead/bismuth eutectic for coolant the usual 10kg per square meter seems plausible given advanced construction and economies of scale)

Total Mass (kg)
6000000
(So I make that as 6000 tons worth of radiator… hows your mass margins? 🙂 )

But… the Aero-person said over on talk-polyglennbeck that FF DPFs should run at temperatures of approx 444c so molten lead wouldn’t exactly be a coolant…

Use NaK (Sodium Potassium mix) and run it at 410c… and the radiator size goes up proportionately… the 4th power kills you… (… you were warned about the dangers of reading Perry Rhodan when you were young…)

temp (c)
410

area (m2)
1809000
(over 1344 meters on a side)

Specific Mass (kg/m2)
10

Total Mass (kg)
18090000
(Over 18000 tons of radiator…)

… now if I could only figure out why either of you think 37 gigs electric is needed for interplanetary travel i could die happy…

[vansig]

we’re close, but oh! so far..

the figure of 37GW was to provide 2016 N thrust at effective velocity of 0.028 c,
(which was the thrust needed per tonne of mass of the ship!)

at 50% efficiency, that’s 37GW useful work, and an additional 37 GWt to reject.

the radiator is way too massive, so the only way to reject heat is to send it off as additional propellant,
which increases thrust per engine, but reduces the specific impulse.

[Breakable]

Better radiators can do better job at expelling heat. Just because these technologies are not available today, it does not mean it wont be tomorrow.
The alveolar surface area of lungs (one person) is 30-100 m2 — often described as the size of a tennis court. Think about how much heat can this surface radiate.

[Author]

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