Density of Stars Compared to Real Galaxy

[JimMarn]

Yep. 300 thousand stars in a flat 100 parsec radius disk means the stars are around 1.2 light years apart. Accelerate at 1G for about a month, coast for about 12 years, decelerate for another month. Not exactly easy, but a lot easier than trying to hit the speeds or travel times needed for the Alpha Centauri sublight run.

I saw a documentary on Discovery Science channel last year on the plasma engine that tosses atoms out the back. It starts out very slow, but can build up speed over long periods of time.

 

[aramis]

I saw a documentary on Discovery Science channel last year on the plasma engine that tosses atoms out the back. It starts out very slow, but can build up speed over long periods of time.

The problem with those is that each 10kg unit is producing fractions of a newton. As in, around 100mN (0.1N). Or, in other words, 0.01G on the drive alone. They don't even generate 1mm/s^2 of acceleration on the spacecraft they're to be used on. But they will do so for months of continuous thrust on 100kg of reaction mass.

 

[JimMarn]

Yes, they are slow to build up speed. Certainly cannot lift off even from smaller planets. But if they accelerate for months, they could reach Pluto in a couple of years. Including deceleration.

 

[aramis]

Yes, they are slow to build up speed. Certainly cannot lift off even from smaller planets. But if they accelerate for months, they could reach Pluto in a couple of years. Including deceleration.

We could put a probe at pluto in about 3-4 years.

 

[JimMarn]

We could put a probe at pluto in about 3-4 years.

I think it was Robert A. Heinlein who, in one of his few fact books, talks about this. I don't remember the time intervals he mentioned though 3-4 years does sound familiar.

 

[whulorigan]

New Horizons Probe

Yes, they are slow to build up speed. Certainly cannot lift off even from smaller planets. But if they accelerate for months, they could reach Pluto in a couple of years. Including deceleration.

We could put a probe at pluto in about 3-4 years.

A slight aside for those who are interested:
The real-world NASA New Horizons Probe is slated for arrival at Pluto in July 2015.
http://www.space.com/18377-new-horizons.html

 

[aramis]

A slight aside for those who are interested:
The real-world NASA New Horizons Probe is slated for arrival at Pluto in July 2015.
http://www.space.com/18377-new-horizons.html

It's not a continuous burn design, and used slignshots. Hence the nearly 10-year flight path. (It was launched early 2006.)

An ion propellant craft won't have the fuel for a true full burn, either - optimal to pluto really looks like about 3 years, with only 2 of those under acceleration. (More fuel mass= lower initial acceleration, and hence longer trip times.) A higher payload fraction pushes it to 2 years coasting.

The current electric thrusters simply don't have the ISP yet to make it better than about 3 years. Still, that's far better than New Horizons' 9.5 year odyssey.

 

[JimMarn]

We can always hope for a scientific breakthrough, and the Bussard ram jets become feasible. But I don't see the kilometers wide magnetic funnels to gather up hydrogen happening anytime soon.