[Space/Spaceships] Getting the velocity/Delta V I want with the tech I want

[scc]

Originally Posted by adimar

The simplest solution for getting the required delta-V is to just use staging.
A basic TL9 fusion rocket design (i.e. single fusion rocket engine with 13 hydrogen fuel tanks)
provides approx 250mps. Each stage burns through it's fuel in approx 2 month of continuous operation. Just stack these one over the other for whatever performance is needed.
Personally I would design this ship as a-SM11 automated cargo vessel.
It don't require exotic fuel which may be difficult to produce in a still developing colony. The craft is relatively cheap (43 mil SM9 stage, 140 SM10 stage, 430mil sm11 stage) So approx 610mil (not including hydrogen cost) for 750mps
Final stage would SM8 (4mil cost) and include a control room.
if this is a shipment from earth to another planet it would have two soft-landing systems (since destination doesn't necessarily have infra to go get the shipment from orbit) and contains 850 tons of cargo.
That's a shipment cost of less than 1mil per ton of cargo. (we pay more than that to launch to low earth orbit).

Hope this helps
Adi

I specifically stated in the OP that staging was not really a viable option

[malloyd]

Originally Posted by Anthony

Absent TL^ stuff, colonization at these distances is always going to be a vanity project; the return on investment is the prestige you get out of its success.

Vanity may be the wrong word. It doesn't pay off in movable goods, but prestige isn't the only non-physical thing of value, even for humans.

[Anthony]

Originally Posted by malloyd

Vanity may be the wrong word. It doesn't pay off in movable goods, but prestige isn't the only non-physical thing of value, even for humans.

True. Perhaps it's more accurate to say that it has value mostly as an end in itself, rather than its investment value.

[adimar]

Originally Posted by scc

Boosters/upper-stage's are just sort of wrong for the setting, there's supposed to be a lot of traffic so it doesn't work out

Originally Posted by scc

I specifically stated in the OP that staging was not really a viable option

The reason I mentioned staging was the reason you wrote for rejecting it.
You stated that staging wouldn't work because there was a lot of traffic. (presumably a cost issue and not the cluttering of outer space).
I suggested a design where the cost of a single use craft would lower shipment costs to less than a million $ per ton.
The notion of reusable being cheaper than single use is not necessarily true.
If the reason for the rejection of staging is not a cost issue, but an aesthetic setting consideration than no probs. But on a purely functional basis...

This holds especially true if shipments are unbalanced (weight wise, i.e. one side sends the other a lot more tonnage than he gets.)
For example earth ships the colonies oxygen and other consumables (a lot of stuff) but gets back an equally valuable cargo that weights only a fraction. (helium-3) .
This means that any spacecraft would make one way full and the other way practically empty. The spacecraft itself isn't worth the cost of refueling it and sending it home for another round trip.

Adi

[Belial666]

The solution is both low-tech and simple; don't build a ship with engines, powerplant or onboard fuel.


1) Build ships equipped with solar sails.

2) Build space mirror(s). A big one 100 times wider than each ship's sail should do. More smaller ones might also do if you can deal with the destructive interference.

3) Aim sunlight from the mirror to the ship, propelling it with solar radiation pressure. Except you use concentrated sunlight at 10.000/1 concentration, not the pansy acceleration given by normal starlight.

4) Ship accelerates all the way to the halfway point. Assuming mirror array around Earth or similar light intensity, 10.000/1 concentrated sunlight and average mass of ship ~1 kilo per square meter of sail (total mass 1000 tons), you're going to get 0,01 gs or 0,1 meters per second per second. That is 8,6 Km/second per day. After 5 months you'll be halfway there.

5) Spend another 5 months with the array on the other star decelerating you. Because you don't want to smack on the planet at 2000 km/sec which is what you'd do if you accelerated constantly. Of course, if you could survive such impacts you'd make the trip in 7 months total, not 10. You'd also make a big hole on the surface of the planet though. Like, New-York-sized.

[Ulzgoroth]

Originally Posted by Anthony

True, but in that case it's likely that you're okay with a 40 year transit time instead of a 4 year transit time, and that reduces the energy budgets by a factor of 100.

Quite true.

[scc]

Originally Posted by adimar

The reason I mentioned staging was the reason you wrote for rejecting it.
You stated that staging wouldn't work because there was a lot of traffic. (presumably a cost issue and not the cluttering of outer space).
I suggested a design where the cost of a single use craft would lower shipment costs to less than a million $ per ton.
The notion of reusable being cheaper than single use is not necessarily true.
If the reason for the rejection of staging is not a cost issue, but an aesthetic setting consideration than no probs. But on a purely functional basis...

This holds especially true if shipments are unbalanced (weight wise, i.e. one side sends the other a lot more tonnage than he gets.)
For example earth ships the colonies oxygen and other consumables (a lot of stuff) but gets back an equally valuable cargo that weights only a fraction. (helium-3) .
This means that any spacecraft would make one way full and the other way practically empty. The spacecraft itself isn't worth the cost of refueling it and sending it home for another round trip.

Adi

UM, possibly. But using external tanks might be a better solution, use the Equipment Packs from Pyramid 3/40

[Belial666]

Also, you could use combination of solar panels and magnetrohydrodynamic propulsion. Basically same array of mirrors as before, except the ship has solar panels instead of mirrors and is built around a really powerful accelerator and lots of water supply.

1) Mirrors feed ship with solar power at long distances. Current efficiency of triple-layer solar panels has reached 47% or so thus if you're hitting the ship with a beam 100 KW/square meter in energy density, you'll get about 50 KW per square meter of panel, which is not bad. Assuming your panels can take it, that is.

2) You use a tiny portion of the energy to ionize water and throw the plasma into the accelerator.

3) Accelerator pushes out the plasma at 1/10 the speed of light or so. That should give a LOT of Delta-V for a ship that's 80% water.

[Ulzgoroth]

Originally Posted by scc

UM, possibly. But using external tanks might be a better solution, use the Equipment Packs from Pyramid 3/40

Fuel tanks, under GURPS Spaceshiips rules, have no dead weight. The way to get the delta-V benefits of staging without actually staging is simply to push the fuel fraction up past the normal resolution limits. The payload and control will be only a small fraction of one system, and you might use a sub-size engine as well. You'll have to use the rocket equation to figure the benefit of the high fuel fraction since the chart in the book doesn't go that far.

Not using staging makes it inconvenient to get high thrust early in the process, but that's not as much a problem here as it is in surface-to-orbit work.

[Anthony]

Originally Posted by Ulzgoroth

Not using staging makes it inconvenient to get high thrust early in the process, but that's not as much a problem here as it is in surface-to-orbit work.

It can be, but it usually takes rather large fractions of a G to get much out of the Oberth effect and it's not that relevant when you're shooting for 300 miles/sec (though a near-solar approach with a burn at the bottom is a not-terrible way of getting a few hundred km/sec).