Spaceships: How to take off?

[MaryAnn]

Most systems have horrendous acceleration in G. In addition, decent acceleration systems have an awful delta-V in mps. What system is the best to take off from Earth without dropping nuclear bombs on the task (Orion Drives)?

[Fred Brackin]

Originally Posted by MaryAnn

Most systems have horrendous acceleration in G. In addition, decent acceleration systems have an awful delta-V in mps. What system is the best to take off from Earth without dropping nuclear bombs on the task (Orion Drives)?

HEDM is first, Nuclear Thermal Rocket is second and Antimatter Thermal Rocket is third for reason of fuel cost if nothing else. With unlimited budgets you might get a little bettter fuel enconomy with the Ram-Rocket option.

Oh, there was an lmplied bias against Superscience! drives in your post (also one about takign off from Earth) so I assumed you didn't want those. Reactionless Thrusters (above Rotary) are usable if Superscience! is allowed and Contragravity makes lift-off with almost anything possible.

[MaryAnn]

Originally Posted by Fred Brackin

HEDM is first, Nuclear Thermal Rocket is second and Antimatter Thermal Rocket is third for reason of fuel cost if nothing else. With unlimited budgets you might get a little bettter fuel enconomy with the Ram-Rocket option.

Oh, there was an lmplied bias against Superscience! drives in your post (also one about takign off from Earth) so I assumed you didn't want those. Reactionless Thrusters (above Rotary) are usable if Superscience! is allowed and Contragravity makes lift-off with almost anything possible.

How do they work exactly?

However HEDM is 0.5 mps while the required mps is 5.6 mps for Earth orbit, while Antimatter Thermal Rocket is 0.1G by TL9, 0.2G by TL10, etc. with a delta- V of 1.8 mps, which is lower than the 1G and the 5.6 mps implied to be necessary to take off from Earth...

I guess that I don't get this.

[ham2anv]

You need to use multiple engine systems to get the required acceleration and many fuel tanks to get the total delta-v. Consider building a very large multi-stage design.

[Varyon]

Originally Posted by MaryAnn

How do they work exactly?

However HEDM is 0.5 mps while the required mps is 5.6 mps for Earth orbit, while Antimatter Thermal Rocket is 0.1G by TL9, 0.2G by TL10, etc. with a delta- V of 1.8 mps, which is lower than the 1G and the 5.6 mps implied to be necessary to take off from Earth...

I guess that I don't get this.

You often will have more than one engine (2 HEDM rockets will get you to 1G), and will almost certainly have more than one fuel tank, for liftoff. For HEDM, getting 5.6 mps would call for a little over 12 fuel tank-equivalents - but note that due to the way the rocket equation works, I think somewhere around 4 fuel tanks you functionally get more delta-v per tank than the default, so you'll need markedly less than 12 actual tanks (essentially, so long as fuel isn't a fairly small fraction of vehicle weight, the fact you get lighter as you use it makes it last longer - with 11 fuel tanks, by the time you get to the 11th tank your ship only masses 50% of what it started as). I believe winged designs are also able to reach orbit with less thrust than planetary gravity, by making use of lift (although I think this also tends to burn through a lot more fuel).

[Michael Thayne]

Originally Posted by MaryAnn

How do they work exactly?

However HEDM is 0.5 mps while the required mps is 5.6 mps for Earth orbit, while Antimatter Thermal Rocket is 0.1G by TL9, 0.2G by TL10, etc. with a delta- V of 1.8 mps, which is lower than the 1G and the 5.6 mps implied to be necessary to take off from Earth...

I guess that I don't get this.

Antimatter thermal might make sense for an aerospace fighter but they're not very cost-effective for routine passengers and cargo.

Originally Posted by Varyon

You often will have more than one engine (2 HEDM rockets will get you to 1G), and will almost certainly have more than one fuel tank, for liftoff. For HEDM, getting 5.6 mps would call for a little over 12 fuel tank-equivalents - but note that due to the way the rocket equation works, I think somewhere around 4 fuel tanks you functionally get more delta-v per tank than the default, so you'll need markedly less than 12 actual tanks (essentially, so long as fuel isn't a fairly small fraction of vehicle weight, the fact you get lighter as you use it makes it last longer - with 11 fuel tanks, by the time you get to the 11th tank your ship only masses 50% of what it started as). I believe winged designs are also able to reach orbit with less thrust than planetary gravity, by making use of lift (although I think this also tends to burn through a lot more fuel).

HEDM engines are 2G each, so it only takes one.

[Fred Brackin]

Originally Posted by Michael Thayne

A

HEDM engines are 2G each, so it only takes one.

Indeed 1 engine and then you get 9 Fuel Tank modules whihc would be 4.5 mps of Delta-V except for the table next to the Fuel Tank entry which explains that with 9 tanks you multiply Delta-V by 1.4. That gets you 6.3 and you have not only enough to get to orbit but enough for a vertical landing SpaceX style too.

That leaves 10 spaces and you must have a Control Room. Then you probably want 3 Armor systems to give you a decently durable hull. The remaining 6 spaces you can use for Cargo and you're HEDM shuttle can haul 30% of its' weight into orbit. That's why i rated it best. It's much better than any chemical rocket such as we have now.

For Superscience drives you just take enough engines to add up to over 1 G and then one or more Power Plants to supply the needed energy.

[Agemegos]

Originally Posted by Michael Thayne

Antimatter thermal might make sense for an aerospace fighter but they're not very cost-effective for routine passengers and cargo.

The price of antimatter in Spaceships looks as though it is based on Robert L. Forward's estimate¹ of the cost of producing antimatter at TL8 combined with GURPS' posit that things' prices don't change with TL. I have tried alternatives, such as Georges Dupont-Roc's generalisation that energy technologies' real prices per joule diminish by an order of magnitude or a little bit more from their commercial introduction to their maturity. But it doesn't help very much. You need a superscience or at least limited-superscience way of making antimatter to have affordable AM-powered rocket operations.

I did a study of the minimum cost of orbital launch using GURPS Spaceships, and concluded that far the cheapest means at TL10 is to use ground-orbit lighters propelled by limited-superscience fusion torch engines using water for their reaction mass. For the median human-habitable world (as produced by GURPS Space 4e), which has 0.81 gee surface gravity and an orbital speed of 4.15 mi/sec, one engine with normal thrust and one tank of water minimises the cost. In the case of the the highest-gravity habitable worlds (which have about 1.6 gee and 7.7 mi/sec) cost is minimised by one high-thrust fusion torch and four tanks of water.
____
¹ Which is in Indistinguishable from Magic.

[Ulzgoroth]

The realistic answer is interplanetary drives and launch drives are different drives, and most likely are attached to different vessels. A ship with a high-impulse drive and an interface shuttle with a high-thrust drive.

If you must have a dual-purpose drive the least superscience option that's not economically disastrous like antimatter or environmentally disastrous like external fission drives is probably the fusion torch.

[Emerikol]

Anyway, I know it is super science at this point in our history but solving the unified theory problem is not something completely unthinkable.

As soon as you solve that problem, one type of force can be turned into another type of force. This means those reactors that turn the propellor on an aircraft carrier and push it across the ocean can be used to turn a gravity propeller and push a ship up into space.

For me, if I were going to start a space campaign, this is one of the breakthroughs I'd want to put in my history. Have a FTL drive is far less realistic than a unified theory breaththrough. In fact, I've long posited that just such a breaththrough is what we are waiting for to make our next "big" scientific jump.

What I find less realistic to be honest is small craft jetting all over the solar system on reaction based fuel the way they do in the Expanse. I hope there is a gas station on every single corner in that solar system.