with determination and imagination,
anything is possible!
I'm pretty sure someone mentioned a takeoff like this is great for places like the moon.
I think on the earth air drag is too big of a factor to not take it into account and one of the main benefits of sticking around in the atmosphere is so the engines can breath it, otherwise its just slogging. The real question is does it take more or less fuel to slog through the atmosphere for greater lengths of time or is the idea behind it overshadowing it's usefulness? How about developing propulsion so that we don't have to count pennies to get to where we're going?
Can't calculate the drag unless there is a model or a shape to work with otherwise it's just speculation and guesswork. I suppose a coefficient could be "borrowed" from a similar device, however it sounds like you would like it to assume different attitudes in which case the amount of drag would be changing as the device flew in different configurations.
It is my opinion that we live below the surface of our planet and though we move through it easily (as if nothing was there) the atmosphere is still there but we have special eyes that make it invisible and less tangible seeming. Something colliding with earth doesn't collide with the dirt it collides first with the atmosphere and this is a formidable collision.
I like that phrasing that we live beneath the "surface" of our planet, which just happens to be transparent to our eyes.
About the prior post where I was able to get low 8,100 m/s to 8,200 m/s drag-free delta-V's using a partial straight-line trajectory, I realized afterwards that it was requiring quite large lift-off thrust/weight ratios, in the range of 3 and above. This might be unrealistic for a SSTO where you have to greatly minimize your dry weight, and an engine mass two to three times larger than usual might eliminate the mass ratio needed to be SSTO.
However, this might be doable for a multi-stage rocket because of the curious fact that for a lower stage having a heavy dry weight only reduces your final payload to orbit to a small degree. This interesting point is made by Robert Zubrin in his book
Entering Space: Creating a Spacefaring Civilization when discussing the space shuttle:
"The shuttle is a fiscal disaster not because it is reusable, but because both its technical and programmatic bases are incorrect. The shuttle is a partially reusable launch vehicle: Its lower stages are expendable or semi-salvageable while the upper stage (the orbiter ) is reusable. As aesthetically pleasing as this configuration may appear to some, from an engineering point of view this is precisely the opposite of the correct way to design a partially reusable launch system. Instead, the lower stages should be reusable and the upper stage expendable. Why? Becasue the lower stages of a multi-staged booster are far more massive than the upper stage: so if only one or the other is to be reusable, you save much more money by reusing the lower stage. Furthermore, it is much easier to make the lower stage reusable, since it does not fly as high or as fast, and thus takes much less of a beating during reentry. Finally the negative payload impact of adding those systems required for reusability is much less if they are put on the lower stage than the upper.
In a typical two-stage to orbit system for example every kilogram of extra dry mass added to the lower stage reduces the payload delivered to orbit by about 0.1 kilograms, whereas a kilogram of extra dry mass on the upper stage causes a full kilogram of payload loss. {emphasis added - R.G.C.}The Shuttle is actually a 100-tonne to orbit booster, but because the upper stage is reusable orbiter vehicle with a dry mass of 80 tonnes, only 20 tonnes of payload is actually delivered to orbit. From the amount of smoke, fire, and thrust the Shuttle produces on the launch pad, it should deliver five times the payload to orbit of a Titan IV, but because it must launch the orbiter to space as well as the payload, its net delivery capability only equals that of the Titan. There is no need for 60-odd tonnes of wings, landing gear and thermal protection systems in Earth orbit, but the shuttle drags them up there (at a cost of $10 million per tonne) anyway each time it flies. In short the Space Shuttle is so inefficient because
it is built upside down. {the emphasis here is in the original - R.G.C.}
Entering Space, p. 29.
I strongly recommend this book by the way for anyone interested in space travel, which I suppose includes everyone reading this forum.
I observed this effect recently in my calculations. I was trying to see what payloads I could get to orbit given the dry mass and propellant mass of the stages of my proposed multi-stage system by varying the payload mass while requiring the total delta-V to exceed some minimum value.
I found that if I added some amount to the payload the delta-V provided by last stage of the vehicle changed greatly while the first stage delta-V changed minimally. And the change in the delta-V in the first stage was even smaller for 3-staged systems compared to 2-staged systems. I realized that this is in accordance to what Zubrin was saying.
So if we added more engines on the first stage of a multi-stage system to allow a large say 3 to 1 lift-off thrust/weight ratio, then the extra weight in the dry mass of the first stage would only subtract minimally from the payload to orbit. But IF this higher lift-off T/W allowed you to reduce the required delta-V to 8,500 m/s or even to 8,100 m/s then this results in a *major* increase in the payload you can deliver to orbit.
Try this yourself for some multi-stage systems you are considering. Add more engines to the first stage to raise the lift-off T/W to 3 to 1. You'll find the payload you can lift to orbit assuming the same delta-V as you were using before, say, 9,200 m/s or so, will be only minimally reduced by the extra weight of the engines in the first stage.
But then assume that this new configuration only requires a 8,100 m/s delta-V to orbit, you'll see the payload will be increased to a large degree. I was getting increases in the range of 70%.
BTW, because my partial straight-line trajectory only was able to get these low delta-V's to orbit by using high lift-off T/W ratios in the range of 3 or 4 to 1, it occurs to me it is just an artifact of the high lift-off T/W. This could indeed be the case since a high lift-off T/W will reduce your gravity loss.
So perhaps you can do a simulation with your standard trajectory to orbit only assuming a high lift-off T/W of for instance 3 to 1. Does this reduce your delta-V to orbit to the low values I was getting for my partial straight-line trajectory?
Bob Clark
