I hadn't said anything about this long but useful post by Jon Goff, primarily because I hadn't had the time to read it. I just glanced through it, and it's definitely worth a read for those interested in rocket theology.

One point that I didn't really see addressed is (to me) one of the biggest disadvantages of single stage--off-design performance. Because a single-stage vehicle will have a much larger dry mass/payload ratio on orbit, if one wants to take it to higher altitudes or inclinations, the payload penalty will be much more severe than that for an upper stage of a multiple-stage system. Altitudes can be dealt with by staging in space (i.e., a tug that meets the vehicle at low altitude and transfers the payload to a higher-altitude facility), but inclination hits can't be accommodated in this way.

But I remain a launch-vehicle agnostic. I'd like to see a lot of different concepts developed, and let the market sort out which is the best, rather than engineers arguing over napkin sketches, or with Powerpoint charts.

[Update a few minutes later]

I should note that the comments are worth reading too, including contributions from Antonio Elias, Gary Hudson, and Dan DeLong.

Rand,
Yeah, this is only the first in a series of posts. I wanted to talk about several of the most promising approaches for doing RLVs. I decided to start with the air-launched SSTO mostly because:

1-It wasn't one that had been commonly discussed.
2-There were new pieces of technology that made it a lot more feasible than when the approach was first discovered.
3-It is interesting and potentially useful
4-I had a lot of useful data from Dan DeLong and other sources on the pluses and minuses
5-One is less than two, so I figured starting out with SSTO made some organizational sense.

I do note though that particularly with a particular commenter on Clark's site as well as a few on mine, that my comments about just buying into the new conventional wisdom (re: SSTO vs TSTO) without actually understanding the trades seems vindicated.

~Jon

The relevant calculations of an SSTO to me are: (I've put in some dummy values - if you want to be more exact, change numbers to match your desired tech level)

GLOW = M_engines + M_tanks + M_control + M_payload + M_fuel

(for all rockets, all types. Structure can be stuffed into tanks and engines, as appropriate. TPS is part of your payload - you don't need it to go up. Wings, etc, are either tank or payload depending on implementation)

Further:

M_engine ~= 1% GLOW
M_tank ~= 1% GLOW
M_control ~= 10kg * number of stages

So if you know payload and number of stages, you can calculate the amount of propellant you need. So how many stages do you want?

The more stages you have, the more complex the vehicle is, and the more "M_control" stuff you have. Also, you can look at each stage as decreasing the Isp of your engine - your propellant is not just your fuel and oxidizer, but also includes the "dead mass" of the stage's engines, tank, and control. Since stage mass fractions are typically 90% or so, knock 10% off the Isp for staging.

On the other side, staging decreases your in orbit mass by decreasing your M_Engine and your M_tank.

The reason this line of thought is useful (maybe): SSTO makes sense when tanks weigh very little and engines have a high T/W. If some technology comes along that decreases tank mass dramatically, or increases T/W, SSTO is a better design choice. If you want to use lower T/W engines or heavier tanks, use more stages.

Probably useless to most, but there are my thoughts on it.

just read these:

http://www.hobbyspace.com/nucleus/index.php?itemid=5165#c

and these:

http://www.hobbyspace.com/nucleus/index.php?itemid=5179#c

just read these:

http://www.hobbyspace.com/nucleus/index.php?itemid=5165#c

and these:

http://www.hobbyspace.com/nucleus/index.php?itemid=5179#c

sorry for the doubled post

Hey GM, just read Jon's original post.