How Long Would Scifi Space Travel Really Take?

[Bab5space]

The interesting thing about scifi space travel is that it remains hard even with scifi tech, so long you allow propellant and gravity limits to still exist.
In a way it is kind of a good thing, only in that it prevents widespread easy RKV starship use.
My question is how long would travel take if I give the specification and dimensions of the Venturestar but upgraded it with a literal ton of antimatter safely stored with scifi inert material (so long they do not crash)?
Serious Upgrade: A jump drive. Get to anywhere in vacuum within 7 LY in a blink. Takes an hour to spool up the drive each time, so don't expect to jump instantly.
With my modifications both thrust and delta V increase dramatically.

Mission Profile: Visit an Earth-like world 65 LY away.

Timeframe: 65 hours of spooling up the jump drive is a given, but the real issue is orbital speed differences.

The destination planet has a 100 kilometer speed difference with our Earth and also is orbiting counterclockwise, while our Earth orbits clockwise but rotates counterclockwise.

The Challenge: How long will it take our heavily upgraded Venturestar to reach this new world once they are in the star system? Let's assume we jump 65 LY into the system and attempt to use our propellant abd antimatter to match speed with the 100 kilometer speed difference, then do one more jump into low planetary orbit. So that is a total of 67 houts spooling up, plus however long it takes to match the speed difference via thrust.
How long would 1g take to match a 100 kilometer speed difference in orbital direction going opposite our starship's original orbit?

Why it matters: Plot events. Mission profiles are necessary, since even with antimatter one cannot go anywhere with impunity due to lack of propellant, plus TWR matters for landing anywhere. So some planets will simply be off limits forever if the orbital speed difference is too high... like for example 1000 kilometers per sec orbital speed difference. That may sound implausible but it is an example of a an Earth-like we would probably be unable to visit quickly even if we jumped into their system with antimatter powered rockets.

Discuss.

Propellant
First stage - VentureStar
Launch history
Capacity
Payload to LEO	20,000 kg[1] (45,000 lb)
Status	Cancelled
Launch sites	Kennedy, LC-39A
Total launches	0
Engines	7 RS2200 Linear Aerospikes[1]
Thrust	3,010,000 lb[1] (13.39 MN)

 

[snorkack]

So you have a FTL system that enables you to change location, but the velocity on return to ordinary space is unchanged. If your destination is moving relative to origin, you have to use ordinary space propulsion to match the velocity.
My suggestion would be to do as much as possible of the speed matching by gravitational flyby maneuvers, like Jupiter and Sun.

 

[stefan r]

Like snorkack said jump to someplace that has a lot of gravity. Let the gravity change your velocity then jump again.

If you want to just make it challenging require the ship to match the cosmic microwave background. That is about 370 km/s relative to the Sun. The Parker Solar Probe will periodically be traveling faster. This might just confuse readers and distract from plot. It might be a fun twist for gaming.

...How long would 1g take to match a 100 kilometer speed difference in orbital direction going opposite our starship's original orbit?...

I think the nomogram (basically a slide rule) located here is what you are looking for. I would suggest figuring out how long you want it to take and how much fuel you want the characters to need first. Then put a straight edge on 100 km/s and then you can read off the acceleration or ship mass. The chart even has suggestions for various types of engines do not exist but maybe could. Project Rho has lots of information useful for science fiction.

9.8 meters per second per second is about 1 g. To get to 100,000 m/s would take 9,800 seconds. 2 hours, 43 minutes and, 20 seconds. If you round off to 10 m/s² it takes 2 hours 46 minutes and 40 seconds or about 3 hours since we are rounding.

Units of days stop making much sense if you have an interstellar empire. IMO you should use 10 kiloseconds of acceleration instead of 3 hours. Vernor Vinge uses these units for time in his book A Deepness in the Sky but it should be standard for science fiction. 100 kiloseconds makes a good work/sleep rotation. A work shift could be a quarter centi-kilosecond or a third centi-kilosecond depending on how good your union is. You could fit a round trip into one work shift if you can get acceleration time under 10 ksec and do a quick loading/unloading and one jump. Should get overtime pay if they make you do more than 4 shifts in a half megasecond. So takes one deca-kilosecond to reach 100 km/s at standard acceleration.

 

[DaveC426913]

The destination planet has a 100 kilometer speed difference with our Earth and also is orbiting counterclockwise, while our Earth orbits clockwise but rotates counterclockwise.

What difference does it make which direction the planet rotates on its axis? Are you concerned about matching that 1000mph?

1. You can choose which side of the planet you appear on. There's a 2000mph difference between left and right side velocities. If it's spinning the wrong way, just aim 10,000 miles to the "left" when approaching the system, and now you're matching ground speed.
2. And you can also make planetfall somewhere other than the equator. At 60 degree lat. Earth is only rotating at 500mph.

But in terms of the relative difference in velocity between star systems, is it necessary that jumpspace and sublight direction-of-travel be the same?

What if you re-entered the system in jumpspace from the opposite side of the system? Now your sublight speed is mostly matched with the planet's orbital speed.Aside:
Niven had a cool trick he used to avoid danger when traveling to unknown systems. Niven's FTL travel does not interfere with Newton's Laws - you drop out of hypersapce with the same velocity (mag and direction) as you went in. So his pilots would start out by building up a huge velocity away from the target in normal space, then jump forward into the uncharted solar system. Upon exiting from hyperspace, they'd retain that huge normal space velocity, hauling serious butt backward out of the solar system, just in case there were some Bad Things awaiting.

 

[jedishrfu]

There’s this great warp speed video on YouTube comparing warp 1 thru warp 9.9



and this more talkative one with parallel runs