Reactionless drive ships orbital flight in 3rd ed physics?

[Fred Brackin]

Originally Posted by weby

In 3rd edition space there was a thing where low thrust ships with wings could fly to orbit on planets with atmosphere if they had a certain % of their mass as thrust.

?

I never saw any mathemtical support for this idea. It first showed up in Space 1e I think but i don't know how the idea got there. It never made any sense to me.

I'm not sure anything with a thrust-to-weight ratio that low could even make a runway take off. The earliest jetliners (i.e. 707) had a thrust-to-weight of 0.15 to 1. A 747 at full throttle was more like 0.25 to 1. At 0.05 to 1 you'd need at least 3x as much runway and you might not be able to get to take-off speed due to rolling resistance or drag.

Further problems would come up with airframe shape and re-entry. You'd need a shape like the Space Shuttle for re-entry but that would give you poor performance at low speed in thick air. That's why the Shuttle's landing speed was so high. Getting up to that speed for take-off with a super low thrust-to weight ratio would take a long, long runway. Even longer than the special landing strip at KSC.

Now, if you had enough _contragravity_ lift you could get by with low thrust-to-weight but it'd still take a long, long time to reach orbital speed.

[weby]

Originally Posted by Fred Brackin

I never saw any mathemtical support for this idea. It first showed up in Space 1e I think but i don't know how the idea got there. It never made any sense to me.

Me neither, thus the question to ask if there was something I had missed.

I'm not sure anything with a thrust-to-weight ratio that low could even make a runway take off. The earliest jetliners (i.e. 707) had a thrust-to-weight of 0.15 to 1. A 747 at full throttle was more like 0.25 to 1. At 0.05 to 1 you'd need at least 3x as much runway and you might not be able to get to take-off speed due to rolling resistance or drag.

Further problems would come up with airframe shape and re-entry. You'd need a shape like the Space Shuttle for re-entry but that would give you poor performance at low speed in thick air. That's why the Shuttle's landing speed was so high. Getting up to that speed for take-off with a super low thrust-to weight ratio would take a long, long runway. Even longer than the special landing strip at KSC.

And the "maximum lift from air" that you need to take off and to raise hight enough to keep the air resistance low so you can go fast.. contradicts also "minimum drag" you need as well for the fast thing..

Now, if you had enough _contragravity_ lift you could get by with low thrust-to-weight but it'd still take a long, long time to reach orbital speed.

Not really that long overall, few hours in those single digit % of G for earth sized planets.