Re: [Propulsion] Minimum Isp

```All really good points.

[EMAIL PROTECTED] wrote:
> Glad to see new activity here.
>
> I did a lot of independent research and calculations on this stuff a
> few years back, and my conclusion was basically that the propulsion
> team should think about designing one stage of a hypothetical three
> stage rocket - that is, a stage with a delta-v of ~3.2km/s when the
> payload mass is based on the non-propulsion components of previous
> launch vehicles. Achieving such a thing would go a long way toward
> gaining credibility, and it'd make one hell of a sounding rocket on
> its own. A really conservative rough estimate, assuming 50% kinetic
> energy lost due to drag effects, still puts the rocket at more than
> 200km altitude.```
```
It would be great to get this kind of calculation up on the Wiki. I'm
not claiming i currently have time to do it, or that Richard does
either, but it would be a great reference to give people interested
in the orbital aspects of the project.

> An actual three stage orbital LV would benefit from not having each
> stage contribute an identical amount of delta-v. Specifically, it
> makes sense for the first stage to be very high acceleration for a
> short amount of time, and the last stage to be a longer, slower, high-
> efficiency burn. The reason for this is that high acceleration is
> desirable when lifting off vertically because you're losing 1 g just
> to overcome gravity. However, if your mass ratio for that stage mo/mf
> is, say, 0.5, this means your total accelerating mass is going to
> drop in half over the burn, and in the absence of throttling (a
> recommended absence) your acceleration is going to be twice as high.
> Therefore the limiting factor on the delta-v contributed by any stage
> is that the initial acceleration must be great enough that the 1g
> loss is not significant, but the final acceleration must not tear the
> vehicle apart.

If we do design an LV3, we'll need at least 1/2-good detailed models
of the ascent environment to make decent trade offs. I've always
claimed that we're a little fast on LV2. (Too high thrust and too
short a burn time given our total impulse.) The idea being that by
slowing down in the lower atmosphere we'd cut our wave drag enough to
make up for the increased gravity loss, but i think this was based on
less than a back of the envelope calculation that i've since
forgotten, so i can't justify the conclusion now.

> This leads to a more realistic estimate of perhaps 2 to 2.5km/s delta-
> v from the first stage, as a design goal. This is doable with an
> exhaust velocity of 2500m/s and a fuel/total mass ratio of 63%. Still
> pretty technically challenging, but within reason. Keep the design as
> simple as possible, consider doing some test launches without the
> full avionics and recovery package - just having the nose cone pop
> off and deploy a streamer to spoil the aerodynamics is a lot more
> reliable than a parachute recovery system deployed by a computer
> running Java. By now it should be obvious that the Shuttle is the
> opposite of good design practices in terms of reliability,
> infrastructure required to launch, frequency of launch, &c.

Sounds credible.

Any next generation design will seek the path to elegant simplicity.

---

This is off topic, but i don't understand the recovery details you
mentioned.

What do you envision popping the nosecone?

AFAIK a streamer will stabilize the vehicle, but the descent will be
too rapid for undamaged recovery.

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