Unguided orbital insertion (cheap upper stages)

(MattWriter) wrote in message ...
Vincent Cate wrote:
One trick (from Henry Cate) is that you could have your apogee
kick motor in front of the payload aimed the opposite way so
that when your spin stabilized vehicle got to the other side of
the Earth it would be aimed the right way.

This is exactly what the Navy guys from China Lake tried in the NOTSNIK
launches of 1958.

This is very interesting. A good URL (search for NOTSNIK) is:

http://ftp.seds.org/pub/info/newslet...views.9807.txt

It seems they had 4 months and $300,000 to get something to orbit.
This has got to be one of the shortest times and the lowest budget
for any orbital launch vehicle development.

It was also the first air launch to orbit (or at least attempted).

From URL:
This rocket had a total length of 4.38 meters (14.4 feet), a
fin span of 1.65 meters (5.42 feet) and weighed only 950 kilograms
(2,100 pounds). Even with the mass of the Skyray included,
NOTSNIK is the smallest known system ever built to launch satellites.

Some more info and pictures at:
http://www.ninfinger.org/~sven/models/vault/NOTSNik/

This seems like a general method that a few guys with an X-prize vehicle
would want to think about trying. :-)

-- Vince

(Henry Spencer) wrote in message ...
Likewise the rocket motors. At 700RPM, the centrifugal force on the
Juno I second-stage motors was 180G!

Ouch, this hurts. High G thrust may not take any extra motor
strength if the internal pressure is high enough, which for a
solid I think it is. But high RPM is just additional stress
on your case, and so you will need additional strength and mass.
So your mass ratios will be worse with high RPM spin stabilized
motors. So you won't get as good a delta-V per stage. This is
probably the big drawback to spin stabilization.

I don't find anything in my books explaining how you would decide
what RPM you needed to spin your rocket at. Do you know of anything
on this?

-- Vince

(Henry Spencer) wrote in message ...
Spin stabilization can last much more than 40 minutes, if the thing is
balanced properly and is spinning around the right axis. Trying to spin a
long skinny stack of hardware around its long axis, in particular, is a
disaster. This may be a problem with two solids underneath the payload
and an apogee motor on top.

In NOTSNIK [1] the payload was a 2.3 lb doughnut (8 inch diameter) with
a 1.25 lb apogee kick motor in the middle. So this is the type of
thing you would want to do to for your spin to last half an orbit.
This is an extra payload design requirement, that might bother
customers, but could be ok for some X-prize guys who just want to
get something into orbit.

-- Vince

[1] For info on NOTSNIK see:
http://ftp.seds.org/pub/info/newslet...views.9807.txt

Michael Smith wrote in message .au...
The only thing is that these days a guidance system doesn't have
to be that expensive. Computers and GPS chipsets are pretty cheap
now.

I can see that the electronics are easier (cheaper and less mass)
these days. But what mechanisms do you want to use to control
the aim/spin of a very small guided rocket? Like do you want to
use fins while there is air and then paddles in the exhaust
when you are too high? What sort of servos/actuators? How
much will servos, wires, fins add to your mass? Imagine you
have a small 3 stage solid rocket (like 150 Kg, 30 Kg, 0.5 Kg,
with a 4 Kg payload) and are starting at 90 to 100 km high. What
approaches would be reasonable to control a rocket like this?

-- Vince

On 16 Nov 2003 10:55:13 -0800
(Vincent Cate) wrote:

Michael Smith wrote in message .au...
The only thing is that these days a guidance system doesn't have
to be that expensive. Computers and GPS chipsets are pretty cheap
now.

I can see that the electronics are easier (cheaper and less mass)
these days. But what mechanisms do you want to use to control
the aim/spin of a very small guided rocket? Like do you want to
use fins while there is air and then paddles in the exhaust
when you are too high? What sort of servos/actuators? How
much will servos, wires, fins add to your mass? Imagine you
have a small 3 stage solid rocket (like 150 Kg, 30 Kg, 0.5 Kg,
with a 4 Kg payload) and are starting at 90 to 100 km high. What
approaches would be reasonable to control a rocket like this?

I think your idea of having paddles in the exhaust would work pretty well. Or possibly venting gas from the side of the engine bell.

Perhaps the guidance system should be in the second stage. Right before staging an electric motor between the second and third stages would spin them against each other and stabilise the third stage for a short burn.

Electronics, servos, cables, etc are made very lightweight for aeromodeling applications. I am sure it could be done for a rocket as well.
----
Michael Smith
Mail address and GPG key available from www.netapps.com.au

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In article ,
Vincent Cate wrote:
I don't find anything in my books explaining how you would decide
what RPM you needed to spin your rocket at. Do you know of anything
on this?

It's somewhat of a black art. You need to model possible disturbing
torques, and decide how much gyroscopic stability you need to handle them.
Spin rates for comsats with solid-fuel apogee motors are not high, tens of
RPM at most. My guess is that the very fast spin of the Juno upper stages
was to even out possible performance differences between the solids in
each stage.
--
MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer
pointing, 10 Sept; first science, early Oct; all well. |

In article ,
Ian Stirling wrote:
Spin stabilization can last much more than 40 minutes, if the thing is
balanced properly and is spinning around the right axis...

Liquids are of course a real problem, as liquid filled objects tend
to do odd things when spun.

While there are problems, they can be tamed with careful design. It's
not a common choice for liquid-fuel systems, but it has been done.

Diddn't the black arrow series of launches from the UK do essentially
this?

No, Black Arrow's liquid first and second stages were three-axis
stabilized. Only the solid third stage was spun.
--
MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer
pointing, 10 Sept; first science, early Oct; all well. |

In article ,
Vincent Cate wrote:
...But what mechanisms do you want to use to control
the aim/spin of a very small guided rocket? Like do you want to
use fins while there is air and then paddles in the exhaust
when you are too high?

It's hard to make exhaust paddles stand up to the exhaust of a modern
rocket motor for very long. Spin, gimbals, fluid injection into the
nozzle, or control thrusters are preferred, especially for a vacuum upper
stage where there are few disturbing torques.

have a small 3 stage solid rocket (like 150 Kg, 30 Kg, 0.5 Kg,
with a 4 Kg payload) and are starting at 90 to 100 km high. What
approaches would be reasonable to control a rocket like this?

Small solids are almost always spun, although a few spacecraft have used
control thrusters to stabilize themselves during burn of a final solid
stage. The mass overhead of active control systems tends to loom large
when the overall size of the vehicle is small.
--
MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer
pointing, 10 Sept; first science, early Oct; all well. |

A while back, I wrote:
...My guess is that the very fast spin of the Juno upper stages
was to even out possible performance differences between the solids in
each stage.

Confirmed. In fact, they would have liked a still higher spin rate --
they grumbled about how they couldn't really do precision orbit insertion
because of dispersion due to motor non-uniformities -- but the motors
just couldn't take it.
--
MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer
pointing, 10 Sept; first science, early Oct; all well. |

A while back, I wrote:
...My guess is that the very fast spin of the Juno upper stages
was to even out possible performance differences between the solids in
each stage.

Confirmed. In fact, they would have liked a still higher spin rate --
they grumbled about how they couldn't really do precision orbit insertion
because of dispersion due to motor non-uniformities -- but the motors
just couldn't take it.
--
MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer
pointing, 10 Sept; first science, early Oct; all well. |