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Re: starship-design: Deceleration scheme

>The efficiency problem shows up in other areas.  Another blast from the
>past I'll have to dig up is the derivation of fuel-to-payload ratios for
>various possible fuel sources.  In summary, for a self-powered starship
>to get to high relativistic speeds (I defined that as 0.8 c or greater)
>you need 4-5 times as much matter+antimatter as payload just to boost up
>to about 0.8 c

Using just as much antimatter as matter is a waste of energy for most

It would be more likely that you'd use only 2 times as much anti-matter as
payload. While also using about 4 times as much matter as payload.

Even though you carry more mass, your energy bill will decrease. (Assuming
you don't have a source of free anti-matter.)

>Has anyone else thought of using a lightsail and beamed power to
>accelerate, and a ramscoop to decelerate?

If indeed you can use the interstellar hydrogen as a wall to slam onto, then
that always is a better option. (Unless you've to do a lot of trouble to
build that wall, by gathering the hydrogen.)

In theory if collecting the hydrogen is not to difficult, you could indeed
gain energy instead of needing it.

I do know nothing about collecting interstellar atoms with as scoop. There
are calculations on the shelf (somewhere), but I always doubt about scaling
up such usually small scoops to the sizes we need.