Explorer I top stage rotation

When Explorer I was launched, it looks like the top stage and payload
were rotating. Was this for stability? Did any other rockets rotate
like that when launched?

When Explorer I was launched, it looks like the top stage and payload
were rotating. Was this for stability? BRBR


The first Explorers, those launched on Jupiter C boosters (the term Juno never
really caught on) rotated at up to 750 rpm to stabilize the upper stages and
the payload. It also "evened out" the thrust from the ring of solid-fuel
rockets. One of the engineers on the project also told me the spin rate was
varied to avoid setting up destructive harmonics through the booster at
different times of flight, though I must admit I don't understand that topic
very well.

I don't know how many other satellite launchers have used spin-stablization for
the upper stages and payload, although certainly some have. The Navy's
air-launched Project Pilot (or NOTSNIK) satellites of 1958 are an example.


Matt Bille
)
OPINIONS IN ALL POSTS ARE SOLELY THOSE OF THE AUTHOR

In article ,
Jan Philips wrote:
When Explorer I was launched, it looks like the top stage and payload
were rotating. Was this for stability?

Yes. There was no other control or stabilization for the solid-fuel upper
stages, so the whole upper-stage assembly was spun up (to something like
700RPM) before ignition, for gyroscopic stability.

(Actually it was spun up before launch, but the spin rate changed during
flight -- it was actively controlled to keep it away from body-bending
vibration frequencies during first-stage powered flight.)

Since there was no provision to de-spin the satellite after fourth-stage
burnout, it kept that spin.

Did any other rockets rotate like that when launched?

Yes, it's common to spin-stabilize solid-fuel upper stages, although
usually at somewhat lower spin rates. Vanguard's third stage was
spin-stabilized, as was Scout's fourth stage and Delta's third stage.
--
MOST launched 1015 EDT 30 June, separated 1046, | Henry Spencer
first ground-station pass 1651, all nominal! |

On 24 Aug 2003 22:00:20 GMT, (MattWriter) wrote:

When Explorer I was launched, it looks like the top stage and payload
were rotating. Was this for stability? BRBR


I don't know how many other satellite launchers have used spin-stablization for
the upper stages and payload, although certainly some have. The Navy's
air-launched Project Pilot (or NOTSNIK) satellites of 1958 are an example.



The Space Shuttle used PAM (Payload Assist Module) formerly called the
spinning solid upper stage, to launch satellites.



--
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E-mail - | so if you have any boxes...."
Visit my Titan I ICBM website at: | - Steven Wright
http://www.geocities.com/titan_1_missile |

(Henry Spencer) wrote in message ...
Since there was no provision to de-spin the satellite after fourth-stage
burnout, it kept that spin.

A very little known fact is that engineers had neglected the damping
effect of the whip antennae in their computations and the satellite
started spinning around one of the maximum inertia axes instead of the
longitudinal axis (which happens to be the minimum inertia axis). This
spin introduced an unforeseen doppler effect on the satellite
telemetry.
IIRC, one of the physicians who first explained the effect was Owen
Garriot, who later flew on both Skylab and Space Shuttle.
Paolo

Paolo Ulivi wrote:
(Henry Spencer) wrote in message ...

Since there was no provision to de-spin the satellite after fourth-stage
burnout, it kept that spin.


A very little known fact is that engineers had neglected the damping
effect of the whip antennae in their computations and the satellite
started spinning around one of the maximum inertia axes instead of the
longitudinal axis (which happens to be the minimum inertia axis). This
spin introduced an unforeseen doppler effect on the satellite
telemetry.
IIRC, one of the physicians who first explained the effect was Owen
Garriot, who later flew on both Skylab and Space Shuttle.
Paolo

Of course, it would have happened anyway, eventually, since there's
no way it's perfectly rigid. The whip antennas just sped up the event by
providing a quicker way of dissipating energy.

Brett

(MattWriter) wrote


The first Explorers, those launched on Jupiter C boosters (the
term Juno never really caught on) rotated at up to 750 rpm to
stabilize the upper stages and the payload.

BTW, has anything more been discovered about the Waste King Corp./
Jupiter C guidance connection that was the topic of a thread a
couple of months ago? I made some queries, but got nothing.

Brett Buck wrote:
Paolo Ulivi wrote:

(Henry Spencer) wrote in message
...

Since there was no provision to de-spin the satellite after fourth-stage
burnout, it kept that spin.



A very little known fact is that engineers had neglected the damping
effect of the whip antennae in their computations and the satellite
started spinning around one of the maximum inertia axes instead of the
longitudinal axis (which happens to be the minimum inertia axis). This
spin introduced an unforeseen doppler effect on the satellite
telemetry.
IIRC, one of the physicians who first explained the effect was Owen
Garriot, who later flew on both Skylab and Space Shuttle.
Paolo


Of course, it would have happened anyway, eventually, since there's
no way it's perfectly rigid. The whip antennas just sped up the event by
providing a quicker way of dissipating energy.

Brett

Yes, definitely. In fact, I forgot to write that the antennae made the
transition much quicker as Explorer-1 was spinning around the maximum
inertia axis from the first orbit!
Paolo

In article ,
Brett Buck wrote:
Of course, it would have happened anyway, eventually, since there's
no way it's perfectly rigid. The whip antennas just sped up the event by
providing a quicker way of dissipating energy.

Several neglected areas of dynamics suddenly got a lot more attention once
spacecraft started going up, because the frictionless environment gave
small and subtle effects more chance to operate.

Another example is that people originally thought that if you wanted a
satellite spin-stabilized, you could just set it spinning initally and
leave it that way. Fairly soon thereafter :-) it became known that such
a spacecraft needs active control over both its spin rate and its spin
axis, because there are small disturbing forces which will slowly alter
both.
--
MOST launched 1015 EDT 30 June, separated 1046, | Henry Spencer
first ground-station pass 1651, all nominal! |

Henry Spencer wrote:
In article ,
Brett Buck wrote:

Of course, it would have happened anyway, eventually, since there's
no way it's perfectly rigid. The whip antennas just sped up the event by
providing a quicker way of dissipating energy.


Several neglected areas of dynamics suddenly got a lot more attention once
spacecraft started going up, because the frictionless environment gave
small and subtle effects more chance to operate.

Another example is that people originally thought that if you wanted a
satellite spin-stabilized, you could just set it spinning initally and
leave it that way. Fairly soon thereafter :-) it became known that such
a spacecraft needs active control over both its spin rate and its spin
axis, because there are small disturbing forces which will slowly alter
both.

The spin *rate* is usually pretty stable, assuming that it's
oblate. There were some DSCS IIs that were still spinning within +- .05
RPM of their original 60ish RPM after 30 years*. The only time it ever
noticably changed was during eclipses - since it shrank a little bit and
thus sped up. And that's was only in the fourth significant figure.

Of course the spin axis movement depends on the configuration, and
how assymetrical it might be. DSCS II had two pretty big antennas on a
despun platform sticking out of one side, and it needed a bit of a tweak
every month or so. NATO III satellites had only some little Earth
coverage horns, and it lasted a lot longer between delta-phi maneuvers.

Prolate spinners (like the Hughes satellites) were an entirely
different ball game. It's my observation that they were the worst of
both worlds - poor SA efficiency of a spinner, and it went unstable when
something failed like a 3-axis satellite.

Brett

* except for the one they attempted to spin backwards. Seems someone
forgot that to go from positive to negative, one has to pass through 0...