Questions about Spaceships

[Nyarli]

First of all let's assume, that I ask about hard-sf(at least in regard to spaceships) setting, like Transhuman Space.

1) High- and low-thrust engines:
If I want one engine to work as both high-thrust and low-thrust, then realistically it should be available
a) only at TL 11 as reconfigurable system
b)at TL of introduction at no extra cost(this is just settings of engine, not design)
c) Something in between?

2) Same question about different reaction mass( hydrogen, water or whatever).

3)Ramscoop:
a) Is it reasonable to allow multiple ramscoop systems(to represent one big, like space sails)?
b) Can it be used with high-thrust engines?
c) Can it be used (again - realistically) to refuel( while moving on sufficent speed with engines shut off)?

4) Frontal DR
Even assuming zero micrometeorites, there should be some amount of required protection to move on large fractions of speed of light (and such speeds are achievable with ramescoops) through interstellar medium.
a) Does anyone know some approximations of such requirements?
b) If spaceship use ramscoop should such requirements be lowered, waived, raised or unchanged?

Thanks in advance.

[Fred Brackin]

Originally Posted by Nyarli

First of all let's assume, that I ask about hard-sf(at least in regard to spaceships) setting, like Transhuman Space.

1) High- and low-thrust engines:
If I want one engine to work as both high-thrust and low-thrust, then realistically it should be available

c) Something in between?

2) Same question about different reaction mass( hydrogen, water or whatever).

3)Ramscoop:

4) Frontal DR
Even assuming zero micrometeorites, there should be some amount of required protection to move on large fractions of speed of light (and such speeds are achievable with ramescoops) through interstellar medium.
a) Does anyone know, some approximations of such requirements?
b) If spaceship use ramscoop should such requirements be lowered, waived, raised or unchanged?

Thanks in advance.

1. Search on "VASIMR". That's a real world concept/prototype that is supposed to be switchable between what I'd call very low thrust and extremely low thrust. Some concepts for other engines would allow some variation in thrust.

2. Sort of the same answer. All TL9+ engines are highly speculative and some bt defniteiy not all could work with multiple sorts of reaction mass.

3. The numbers on ramscoops don't actually work out right in terms of hard science at least in terms of interstellar denstiy anywhere within a 100LY of Earth. They don't work out at all at very high speeds. Ramscoops would make much better brakes than fuel gatherers.

4. One figure I read once was that at 40% of lightspeed collisions with interstellar hydrogen start ionizing your frontal hull material. Local density would only affect how much got ionized per unti of time. Around that speed you're looking at an area where solid matter won't stay solid so armor would only exist in an ablative form.

Spacecraft that can accelerate to high percentages of the speed of light are something else that doesn't ho;ld up very well in terms of hard science. I asked once if a rubber scicne ramscoop based on some sort of pseudogravitic affect would work better and the answer was "reply hazy, ask again alter".

Sorry if I seem alternately vague and negative but that's the way these things work out. You can take the Rules As Written and use them as they are whether they are fully accurate or not but when you start trying to modify for greater accuracy.....well, an advanced degree in physics wouldn't hurt but it probably won't supply all your answers either. This stuff si all made up to some degree.

The good news is that you could make your answers whatever you like as long as you don't insist that the science be really hard. :)

[Nyarli]

Originally Posted by Fred Brackin

The good news is that you could make your answers whatever you like as long as you don't insist that the science be really hard. :)

I don't. Medium well would suffice, thank you.

Well, the first three question may be re-formulated as "Per RAW, in non-superscience setting what <insert question here>". At least such accuracy would be better than (maybe) misunderstood RAW.

[munin]

4) Spaceships 5 has stats on required frontal DR for relativistic travel (pp. 39-40), with ablation rates. A ramscoop removes the need for impact shielding armor.

[David Johnston2]

Originally Posted by Nyarli

3)Ramscoop:
a) Is it reasonable to allow multiple ramscoop systems(to represent one big, like space sails)?

Yes, of course. The sections are abstractions, and a single section could be dozens of different thrusters or 1/3 of a really big engine.

b) Can it be used with high-thrust engines?

High thrust ramscoops are pretty fantastic. (In truth the very idea of ramscoops has issues but I assume you don't want to get so hard sci fi that it's as impossible as real life.)

c) Can it be used (again - realistically) to refuel( while moving on sufficent speed with engines shut off)?

Yes. A ramscoop should begin it's deceleration phase with full tanks.

4) Frontal DR
Even assuming zero micrometeorites, there should be some amount of required protection to move on large fractions of speed of light (and such speeds are achievable with ramescoops) through interstellar medium.

The assumption I go with is that the ramscoop itself protects the rest of the ship.

[Fred Brackin]

Originally Posted by Nyarli

I don't. Medium well would suffice, thank you.

Well, the first three question may be re-formulated as "Per RAW, in non-superscience setting what <insert question here>". At least such accuracy would be better than (maybe) misunderstood RAW.

Both 1 and 2 would be "no". These are all build options, fixed at construction to my understanding.

I would think that for 3 you could have multiple ramscoop modules.

$. ? Well the ramscoop ships in Larry Niven's books and Anderson's Tau Zero seemed to ignore the questions of armor possibly because the ramscoop was supposed to e scooping up everything in tis' path. If that's what you emulating they can work that way if you want them too.

[vierasmarius]

You might be interested in a spreadsheet I wrote up comparing the Reaction Engines from Spaceships, including their Delta V with various numbers of fuel tanks. I've marked which engines are capable of achieving the 1800 mps required to use a Ramscoop, and how many fuel tanks it takes. My interpretation is that you only need enough fuel to accelerate, and can refuel in flight with the Ramscoop, but I don't know how long that would take. This makes it possible at TL10 using a Fusion Rocket with 80% of the ship's mass in fuel.

Originally Posted by Fred Brackin

Both 1 and 2 would be "no". These are all build options, fixed at construction to my understanding.

I think multiple fuel types can be used by the same engine by RAW.

[Peter Knutsen]

Originally Posted by vierasmarius

I think multiple fuel types can be used by the same engine by RAW.

Yes, of the same anti-matter "grade". IIRC Spaceships has 4 AM-grades:

1. Uses no AM.
2. Uses a tiny amount of AM.
3. Uses a large amount of AM.
4. Uses 50% AM (Anti-Matter Pion Drive, or something).

I've forgotten exactly what type 2 and 3 are called, but you can't switch between fuel types fom one grade and another. Within grades, it ought to work fine, at least once you're past TL8.

Also, switching between high-thrust and ow-thrust... It doesn't sound reasonable to have to wait until TL11 to do that, nor to pay the full - very high - cost for Reconfigurable System. So somewhere in between. A somewhat higher cost, a cost multiplier on the drive system, and maybe +1 TL, sounds much more reasonable to me.

[vierasmarius]

Originally Posted by Peter Knutsen

Yes, of the same anti-matter "grade". IIRC Spaceships has 4 AM-grades:

1. Uses no AM.
2. Uses a tiny amount of AM.
3. Uses a large amount of AM.
4. Uses 50% AM (Anti-Matter Pion Drive, or something).

I've forgotten exactly what type 2 and 3 are called, but you can't switch between fuel types fom one grade and another. Within grades, it ought to work fine, at least once you're past TL8.

I don't think it states it in quite that way, but I see your point. There are engines like the Fusion Rocket (Hydrogen), AM Thermal Rocket (AM Catalyzed Hydrogen), AM Plasma Rocket (AM Boosted Hydrogen) and AM Pion (Matter/Antimatter). Any of those could replace the Hydrogen with Water, without requiring any new equipment.

Also, switching between high-thrust and ow-thrust... It doesn't sound reasonable to have to wait until TL11 to do that, nor to pay the full - very high - cost for Reconfigurable System. So somewhere in between. A somewhat higher cost, a cost multiplier on the drive system, and maybe +1 TL, sounds much more reasonable to me.

Sounds good.

[Peter Knutsen]

Oh, and pedantiaclly, we're talking reaction mass types, not fuel types...