How big?

Junghalli · Post by **Junghalli** » 2005-03-09 01:47pm

In your opinion how big do you think a spacecraft can realistically get and still be able to take off and land on a planet. Assume fairly high tech propulsion system (much better than present day chemical rockets), but no antigravity or other such magic tech.

dworkin · Post by **dworkin** » 2005-03-09 02:58pm

So big that the launcher can still provide 60 MJ/kg to everything going up.

SirNitram · Post by **SirNitram** » 2005-03-09 02:59pm

The largest one I've ever seen with the numbers to work is the Orion, a ten thousand ton beastie riding nuclear detonations.

dworkin · Post by **dworkin** » 2005-03-09 03:02pm

There's always space elevators. Everything must go!

Junghalli · Post by **Junghalli** » 2005-03-09 04:57pm

SirNitram wrote:The largest one I've ever seen with the numbers to work is the Orion, a ten thousand ton beastie riding nuclear detonations.

OK, I did a Google search and the super-Orion design is 400 meters. I guess that would be a reasonable upper limit.

Post by **Darth Wong** » 2005-03-09 05:00pm

dworkin wrote:So big that the launcher can still provide 60 MJ/kg to everything going up.

Assuming some goof-tech propulsion system as per the OP, the primary limitation would be the ability of the structure to withstand boost acceleration. As ships get bigger, the scaling laws affecting all structures will come into effect and limit the size.

kheegster · Post by **kheegster** » 2005-03-09 05:43pm

SirNitram wrote:The largest one I've ever seen with the numbers to work is the Orion, a ten thousand ton beastie riding nuclear detonations.

Although that would kinda lay waste to the planet it's taking off from...

Junghalli · Post by **Junghalli** » 2005-03-09 09:05pm

kheegan wrote:Although that would kinda lay waste to the planet it's taking off from...

No, just the immediate region of the launch site.

400 meters seems like a good upper limit to me, assuming no goofball tech like antigravity.

Admiral Valdemar · Post by **Admiral Valdemar** » 2005-03-09 09:09pm

Depending on the mode of travel such as an Orion type drive or VASIMR etc. and the structural design along with the materials used, it depends greatly.

If you want a really big ship, it'd be best to build in orbit via space-elevator or skyhook. And having the whole ship land on planet would be wasteful, it'd be better having shuttles or cargo craft separate.

tharkûn · Post by **tharkûn** » 2005-03-10 12:59am

Assuming some goof-tech propulsion system as per the OP, the primary limitation would be the ability of the structure to withstand boost acceleration. As ships get bigger, the scaling laws affecting all structures will come into effect and limit the size.

I'm sure I'm missing something, but if you keep expanding the base area you should be able to increase the mass of the craft without increasing the pressure. Basically I'm thinking of conical spaceship, but rather than simply scaling up, you adjust the height to diameter ratio to keep mass proportional to load bearing area.

Singular Quartet · Post by **Singular Quartet** » 2005-03-10 03:22am

tharkûn wrote:
Assuming some goof-tech propulsion system as per the OP, the primary limitation would be the ability of the structure to withstand boost acceleration. As ships get bigger, the scaling laws affecting all structures will come into effect and limit the size.
I'm sure I'm missing something, but if you keep expanding the base area you should be able to increase the mass of the craft without increasing the pressure. Basically I'm thinking of conical spaceship, but rather than simply scaling up, you adjust the height to diameter ratio to keep mass proportional to load bearing area.

Meaning it'd get a lot fatter than it gets wider.

Post by **Sea Skimmer** » 2005-03-10 04:50pm

SirNitram wrote:The largest one I've ever seen with the numbers to work is the Orion, a ten thousand ton beastie riding nuclear detonations.

An Orion spacecraft could potentially be much larger then 10,000 tons. But the design had no provisions for landing again, and the nature of the engine really wouldn't support doing so.

kheegster · Post by **kheegster** » 2005-03-10 05:28pm

Junghalli wrote:
kheegan wrote:Although that would kinda lay waste to the planet it's taking off from...
No, just the immediate region of the launch site. 400 meters seems like a good upper limit to me, assuming no goofball tech like antigravity.

I was exaggerating a bit, but watch a video of a real-life rocket launch some time....after lift-off, the trajectory is approximately parabolic, so it does fly over a lot more area than just the launch site, and air-burst thermonuclear detonations aren't particularly pleasant.

Post by **Darth Wong** » 2005-03-11 04:34pm

tharkûn wrote:
Assuming some goof-tech propulsion system as per the OP, the primary limitation would be the ability of the structure to withstand boost acceleration. As ships get bigger, the scaling laws affecting all structures will come into effect and limit the size.
I'm sure I'm missing something, but if you keep expanding the base area you should be able to increase the mass of the craft without increasing the pressure. Basically I'm thinking of conical spaceship, but rather than simply scaling up, you adjust the height to diameter ratio to keep mass proportional to load bearing area.

What happens when you end up with a giant pancake? Massive cantilever forces unless you have thousands of engines distributed evenly across the bottom of the pancake? Sooner or later, any such design becomes wildly impractical and it is far more efficient to have several small ships.