Solid boosters

Because they are:
a) simple
b) cheap
c) you can manufacture them and then have them lying around for a long time before using them

None of those points means, that solid rockets are desirable for every situation, but they can be a good choice in some situations.

Actually, ESA is currently building a brand new, solid only (apart from the orbital stage) 3 stage rocket, VEGA:
http://www.esa.int/SPECIALS/Launchers_A ... CNC_0.html

It might be interesting to see how well this is going to work.

Those are four very different programs, and all have different reasons.

Shuttle: The shuttle is a study in design compromises and political decisions overruling technical ones. It is full of bad ideas, implemented as best they could.

Sounding rockets: Losing a sounding rocket payload is unimportant, people don't fly on them. But a number of companies are working on liquid fueled sounding rockets. Sounding rockets also have seen way more iterative and incremental design work than the shuttle SRB, as you can fly thousands of them.

ICBMs: solids are the ultimate in storable propellants. It also allows them to have shorter burn times, to minimize thermal signature of launch seen from space.

Atlas and other strap-on uses: it's easier to strap solids on to an existing vehicle than it is to design an entirely new, bigger vehicle.

Ben
Ever see a solid rocket hover?

Monroe

Crazy enough, yes. There were a couple guys who put servo actuated gimbals on an Estes motor and for the few moments when weight was equal to thrust, the thing hovered.

You can also do it by having, say, four solids on hinges, so they can each point any angle between straight down and straight out (such that they'd make an X if they were straight out, canceling out each others' thrust). Then you hinge them up and down with actuators, so the downward component of the thrust is equal to the weight of the vehicle.

It's super lossy, compared to a throttlable liquid, but possible. They've even made throttlable solids.

It's just that all of those schemes are incredibly ungainly and failure prone, and can't ever be much more than a stunt or very specific solution to an improbable problem or poor set of design requirements.

Ben
It is a novelty I admit. We have one called the "Quad Pod" If you like have a peek at: http://www.teamprometheus.org/QuadPod.html

There is a video there of a stable hover. We plan to use solids for now to work up the guidance systems. For now it's cheaper and we have access to motors. That was a F-10 the H-25 should alow for more guidance experience for us starving rocketeers

Monroe

Oh as soon as I can I'll fix the video by zooming in on the flight you have to watch it full screen to see much as it is.

Your quad pod does exactly the same thing as Ben has said:


However it is a really nice achievement for you guys at team prometheus!

A little off topic: as you have a link to Dave Hein's "quad pod II" on your site it is imho interesting to note, that his original "quad pod" seems to be an example of the pendulum rocket fallacy.

But to be honest, there isn't that much information on the quad pod to be entirely sure how his "passive guidance" was supposed to work exactly. But he did draw the correct conclusion "that the rocket motor must be maintained in a vertical postion" and his quad pod II design is really a nice piece of (amateur?) engineering!

Yes, I thought the original Quad Pod would be stable. I would suspend it from the bottom of the motor mount, and it balanced fine. Of course, a force vector analysis shows that a vertical force will automatically correct for an off-axis center of mass. However, the rocket motor thrust is always inline with the center of mass, so there is no correcting force. I didn't bother doing the vector analysis unitl after I launched the Quad Pod I a couple of times.

It is very difficult to hover with a rocket motor. The rocket thrust must exactly cancel out the gravitational force. Hobby motors have a manufacturing tolerance around +/- 10 percent, which makes a big difference in the maximum altitude. If the thrust is 10% lower the altitude of Quad Pod II is something like 4 feet. If the thrust is 10% higher it's around 100 feet. A nominal thrust should achieve a height of around 35 feet. The launch on Saturday seem to be close to the predicted nominal altitude.

Dave

As far as I am aware, Hybrids have the dubious position of being the only New Space or alt.Space systems to actually kill anyone yet.

One accident can hardly be considered statistically significant though. And that flow test could just as easily have been for a liquid monopropellant...

No sensical person would use a monopropellant for a space launch vehicle.

Monroe, Dave, the quad pod is very cool. At the scale necessary for the N-Prize, solids may be the right way to go. That you're already thinking of guidance is a good sign.

Ben
Thanks for the encouraging words! We need all of that we can get. I know I don't have to tell you about the scope of a project like this we have so far to go and our guy's need a little recognition for putting in any effort at all. We are getting off the ground! We are leaving tera firma. We are going to space, today!

Monroe
Team Prometheus