Daedalus Pulse Drive question

[Tellon]

a quick lil something I forgot to ask from the thread before..

the weight of the fuel ...

so an example: (using FFS, pg 74)

vol - 1000 kl
wt - 1000 tons
pr - 500 Mcr
pwr - n/a
TT - 1500
SufA - 75 sq met

fuel vol = 43,800 kl for 10 years (@.5kl/hr)
fuel cost = 153.3 Mcr (@H2 x100 -- making it a VERY expensive fuel)

now -- *the* question --

the weight

if the weight is a part of the above -- then great -- one can make a 1G ship actually; if the weight is needed -- what do we use? -- I have looked at Liq Hyd (which would give me 3066 tons [for 43,800 kl of fuel @ .07 tons/kl]

 

[aramis]

The Daedelus fuel is fissionables.

You ARE looking at massive fuel loads.

 

[Lycanorukke]

The Daedelus fuel is fissionables.

I have to disagree - the propellant for the D-drive is a specially tailored He3/Deuterium mix (both in RL and the FFS version) in a shell which is then fused by lasers/particle beams. Hence the thermonuclear pulse drive. It's the inertial confiement fusion version of the (fission) Orion pulse drive. Of course, the power source could be fissionables but could also be fuel cells, etc.

I can't see where the volume came from though - the exact sentence is...

Each cubic meter of engine masses 1 tonne, generates 1.5 tonnes of thrust and consumes 0.0005 tonnes of fuel per hour

Looking at the consumption rates in the book though it consumes 0.0005 metric tonnes (1/2 kilo or 500 grams) of fuel _mass_ per hour not displacement tonnes (volume).

 

[Peter Schutze]

>I have to disagree - the propellant for the D-drive is a specially tailored He3/Deuterium mix (both in RL

that was my understanding as well .... a fission reactor for (general power and) the lasers to trigger fusion pulses in the drive

 

[G. Fieendish]

The recent Project Icarus symposium held by the British Interplanetry Society, a couple of months ago, which basically updated the Daedalus proposal, argued that a Daedalus-type pulse drive system could use a Deuterium/Tritum mix for intra system use, rather than the He3/Deuterium mix proposed for Daedalus...
Incedentally, the symposium argued that Lunar He3 mining may never be viable, due to possible He3 yield, being as possibly as low as 1 nanogram per gram of regolith mined...
Other conclusions drawn from the symposium, was that a Daedalus-type probe would have to de-accelerate inside the target system, (either Alpha Centauri or Epilson Eridrani, as opposed to the original target of Barnard's Star) rather than just fly by.
The reason given for the above, was a interferometer 1 lunar diameter across, would have a higher resolution, than the sensors carried aboard a Daedalus-type probe, until said probe, was 1AU from it's Target...

 

[Lycanorukke]

...argued that a Daedalus-type pulse drive system could use a Deuterium/Tritum mix for intra system use, rather than the He3/Deuterium mix proposed for Daedalus...

Hmm, I thought they would have avoided tritium like the plague as it only has a half life of about 10 years, whereas He3 is stable. Also He3-D fusion has no neutron release which reduces the wear/embrittlement on the engine frame (the proton from He3-D is easily shoved away by a magnetic field).

Even though tritium eventually decays into He3, it would probaly throw the 'tuning' of the engine right out if the exact ratios of fuel are important, and He3-D fusion requires a lot more energy to fuse than D-T.

I'll have to read up on the BPS Icarus project you mentioned...

 

[Tellon]

so D-T -- heavy water eh?

Hmm, but fusion reactions -- pg 64 FFS -- speaks of Helium-3 reactions for fusion rockets -- and the fusion rockets technically burn liq Hy (.07 tons/kl) instead of fissionables which are U-235/238 and thus the atoms are very hvy compared to H-3.

Bussard Ram + Fusion Rocket -- pg 73 FFS ---

I also looked at Rocket fuel (HRF @ pg 70 FFS) which is Hy + LOx -- so the combination is atomic wt 2 + 16 = 18/2 = 9... thus heavier than an H-3 reaction

So I just can't see the fuel as per FFS being a Fissionable (which weighs 19 tons/kl -- as that implies a Fission (U-235/238) reactor.

 

[Tellon]

Interesting blurb -- "The Daedalus craft at launch has a mass of 54,000 tons; most of that is fuel."

http://www.peregrinus-interstellar.net/index.php?option=com_content&task=view&id=155&Itemid=28

So they key here then is to ask -- how big is that engine -- and how much fuel is there is the craft.

"To keep the total mission time down to an acceptable duration, the Daedalus probe does not brake. Once it is accelerated up to its cruising speed of approximately 12% of the speed of light, it maintains this even through the encounter phase at the destination. This means that after a flight of about fifty years"

So, this thing will carry 50 years of fuel -- and so that is roughly say 5200 tones per decade -- (taking into account 200 tons for engine + ship per decade of flight)

So 50 years of fuel -- and my ship example carries 10 years ... so I am thinking that there is no way the fuel are fissionables (19 tons/kl)

----

to anser the other post regarding the H-3 from the moon idea ...

"The Daedalus plan requires a system for obtaining the He3 from the atmosphere of Jupiter."

-- Atmospheric fueling maybe? --

 

[Tellon]

-- small update I found this info on wikipedia
http://en.wikipedia.org/wiki/Project_Daedalus

"initial mass of 54,000 metric tons, including 50,000 tons of fuel and 500 tons of scientific payload. "

ok -- so we know 50,000 tons of fuel

"The first stage would operate for two years, taking the spacecraft to 7.1% of light speed (0.071 c), and then after it was jettisoned the second stage would fire for 1.8 years, bringing the spacecraft up to about 12% of light speed (0.12 c) before being shut down for a 46-year cruise period."

ok -- so a 3.8 year burn period then.

ok -- so 50,000 tons of fuel over 3.8 years = 13158 tons/year of burn --

Here are the specifics

Overall length: 190 meters
Propellant mass first stage: 46,000 metric tons
Propellant mass second stage: 4,000 metric tons
First stage empty mass: 1,690 metric tons
Second stage empty mass: 980 metric tons
Engine burn time first stage: 2.05 years
Engine burn time second stage: 1.76 years
Thrust first stage: 7,540,000 newtons
Thrust second stage: 663,000 newtons
Engine exhaust velocity: 10,000,000 m/s
Payload mass: 450 metric tons


-- so then we know the TT --Thus we can reverse engineer the size of the engine and the volume of fuel -- as we know the weight of it.

So back to the original assertion -- there is no way the fuel can be a fissionable (19 tons/kl)

 

[aramis]

My mistake; I confounded it with the other nuclear pulse drive, the Orion Drive, using fission bombs, rather than fusion...

 

[Tellon]

My mistake; I confounded it with the other nuclear pulse drive, the Orion Drive, using fission bombs, rather than fusion...

Hey no sweat Aramis ..

http://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsion)

It does look trippy though -- and earlier (maybe TL 6/7) version of Daedalus

One could make an Orion Drive -- w/ a Nuc reactor for planetary trips -- if one didn't want to use the Nuclear Thermal Rocket (pg 84 Hard Times)

so then -- a possible time line of planetary/interplanetary drives for game use.:

Orion
Nuclear Thermal Rocket
Ion
Daedalus

 

[Mithras]

Ion? Are you sure about that? Where's the specific impulse in an ion drive. Good for small probes yes, but not for multi-ton warships and cargo craft...

EDIT: BTW is FFS actually any good at building low tech spacecraft, you know, reaction drive ships of the 2010, 2001, Red Planet, timeframe? Is it worth my money if I want a 2050 campaign??????

 

[aramis]

Ion? Are you sure about that? Where's the specific impulse in an ion drive. Good for small probes yes, but not for multi-ton warships and cargo craft...

EDIT: BTW is FFS actually any good at building low tech spacecraft, you know, reaction drive ships of the 2010, 2001, Red Planet, timeframe? Is it worth my money if I want a 2050 campaign??????

If you ignore HEPlaR, yes. Not great, but decent.
MT's One Small Step (reprinted in HT) is better, but has the usual MT issues.

 

[Tellon]

yeah ... how low tech do you wanna go

The TL 5 & 6 Solid/Liquid Fuel Rockets (Gemini/Mercury/Apollo missions -- so obviously, rockets can work for several days to settle nearby moons -- but will be near-impossible for planetary travel)

[Both HT and FFS go over SF/LF rockets and advancements]

I can make a TL8 Experimental Fusion rocket or a TL 9 Fusion rocket for say 10/20 days duration and crank out some good G's for a close planetary trip. TL 7 Ion is heavy but uses very little fuel -- while TL 7 Nuclear rocket uses Liq Hyd and so is "light" but takes up volume due to it's voracious appetite for fuel.

note: Fusion rockets give you energy to use -- while the other early TL ones need energy to work -- so a big advantage when ya "discover" fusion rockets.

That is using Hard Times

One can do TL 8 Solar Sails for small craft -- say yachts or specialty traders -- say a gem smuggler or booze runner .. and doesn't want to attract much attension. Of course -- it is best to stay in the Inner system. And they get better as TL's come along. Also oine has the FFS version of Fusion Rockets which are good, the one is HT is (in my opinion) a bit better (which is why I use the HT version)

so for say a 1950 - 2050 -- You have several easily seen options. [Lox/Chem Rockets thru TL 9 Fusion rockets]

so for me I use Hard Times with FFS -- being a gearhead -- I like FFS --

so ultimately it's a good solid book, and I'm glad I have it.

 

[G. Fieendish]

Project Icarus now has it's own website at http://www.icarusinterstellar.org if anyone wants a look...