Space Forum / Shuttle / November 2003

Yeah!...so what's your point?

Pat

And a padded room to practice it in. How long do you think it will be
before his wife is found in a coffin made of matchsticks in the crawl
space under the house?

Pat

[snip]

Yeah...in some of those pics I think I detect the SRBs crossing over... :)

Ha! Wow, what a sight.  It looked like it maybe didn't do what you would
have liked it to after SRB sep.  And the orbiter was powered after sep?
<<<<<

No, it did what it was supposed to. Just that there’s not much time to do it
all.

The F25 motor burns for 3 seconds. But it has a regressive, almost linearly
diagonal, thrust curve that is at max thrust at liftoff and drops to zero at
about 3 seconds. Max velocity is at about 1.5 seconds into the burn, the last
half there is still thrust but the drag is enormous, plus the mass is about 2.2
pounds. So by burnout it’s been slowing down already but not as slow as though
the motor had stopped burning completely at 1.5 seconds (there are various
sorts of model rocket flight simulation software out there. It’s interesting to
look for things like that. Someone might have thought that a mercury switch
would be a good way to detect burnout in this shuttle model but it would have
triggered at 1.5 seconds, about 1.5 seconds early if the motor burned normally
for about 3 seconds).

A flight computer in the ET nose, made by a friend (using two Basic Stamps) is
programmed with various steps and looks at three small SPDT lever switches to
determine what to do. The compute goes from preflight mode to flight mode when
a thrust detect switch (motor pressed onto the switch) is on and a liftoff
switch that was held down by a rod in the launcher goes to the off position.
When the motor thrust is almost down to zero, a spring helps to push the motor
backwards, and the thrust switch is no longer pressed. The computer sees that
as motor burnout, waits 1/2 second, then commands a servo in the intertank to
sep the SRB’s. That flights computer and the mechanism for making the SRB’s sep
cleanly and much like the real things appear to sep were among the last key
parts to the puzzle to make the project work.

So, that’s automatic. The orbiter has an R/C system in it, including a servo to
trigger a separation latch so it will come off of the ET. When I decide to, I
flip a toggle switch on the R/C transmitter that simultaneously causes that
orbiter/ET sep servo to trip the latch, and for the transmitter to do other
things to go from rocket boost set-up to glide set-up.

On that flight, I sepped the orbiter about 1 second after the SRB’s sepped. I
usually do not wait more than 2 seconds. It’s because it is so draggy that it
just does not coast long, so by one second it is usually at the peak altitude.
Sometimes it is at peak altitude when the SRB’s sep, and I am ready to sep the
orbiter but waiting for the SRB’s to sep first (now if I want to, I can sep the
orbiter at any time. And in two boilerplate boosts going very badly due to an
SRB attachment flaw, I sepped the orbiter first, as an abort. The flight
computer recognized that as an abort (orbiter sep detected before burnout
detected) and did an immediate SRB sep followed by ET ejection firing so
everything could hopefully land safely, which they did both times).

Now, when the orbiter seps from the ET, I’m flying the orbiter by R/C from then
on, but automation continues with the ET (and SRB’s). The ET has an orbiter sep
detect switch on it, to let the flight computer know the orbiter is gone. So
the computer waits 1 second, then fires an ejection charge in the ET nose to
pop off the nose and to deploy the chutes for the ET nose and for the main ET
also. So what you saw a little bit of in thevideo  was the ET ejection go off,
then the ET and nose go out of frame, with only the orbiter visible.

Meanwhile, the SRB’s each have their own timer. To save weight, they use a very
tiny wind-up toy motor as the core for a timer that causes the SRB noses and
chutes to be deployed about 2 seconds after the SRB’s sep. They are
all-mechanical, and a rubber band drives a rod upward to push the noses off,
when the wind-up timer rotates a disc with a slot in it to the correct position
to release the rod upwards.

Now, back to the orbiter. In that flight, it did ignite a small “A” sized motor
right after sep from the ET (an attempt to simulate and OMS burn, as
“staging”). That was automatic, a SPDT switch in the orbiter’s aft strut
interface area pressed “off” when the orbiter was attached to the ET. So on sep
from the ET, the switch moved to the on position to ignite the motor. I had
some problems with that arrangement, so for the contest model I chose not to
risk doing it. Also the contest model is just on the limit of the FAI’s 1000
gram weight limit, so had I built in that capability I could not have afforded
the weight of the engine, and the weight invested in beefing up the structure
to carry the thrust, and the weight of other things like the switch and wiring
would have made the model overweight and required deleting some mass from
places I would not have wanted to (Already have done that, using smaller
parachutes than I would prefer, and those chutes also add noseweight which is
important in this model).

There’s more info about that on the website, if you are curious and didn’t
check around a lot.

http://members.aol.com/narshuttle/shuttlehome.htm

The Model Details portion gives some nuts and bolts information/drawings on how
the modle works.

The pictures show a lot of how those work out.

And the modle information gives a rundown of the final boilerplate (1998) and
what preceded it.

And the link for the NARAM-41 shuttle.

Is it still intact? Do you still fly it?
<<<<

The contest model, built for NARAM-41 in 1999, is still around. But since there
is the risk of even minor landing damage, plus a bigger risk overall, I have
only entered it in three contests. In 2000 and in 2002, with an improved ET
(better details) I flew it in the scale (S7) event at the World SpaceModeling
Championships (WSMC). That’s a fancy name for FAI’s world championships for
model rocketry.  It did not fare too well in judging, though the judges did
enjoy seeing a shuttle model entered, and the spectators even more so. But at
the world level my workmanship is not up to the level (and patience) of the
best, it was middle of the pack during judging in 2000 and a bit further back
in 2002. In 2000, the ET ejection charge did not go off, so the ET crashed. In
2002, I rebuilt the 2000 ET, and the model flew very well. It ended up in about
11th place out of 19 entries when the flying was over.  

At the WSMC some of the top models are models such as Ariane 2’s or 4’s,
Soyuzes, and Saturn-IB’s which are actually more difficult to build than
Saturn-V’s. Many of the models go for as many possible flying points as
possible, so they often are at least 2-staged, if not 3-staged, and clustered.
And they do other flight tricks such as separating boosters, clamshell shrouds
opening apart to deploy a satellite or spacecraft, and so forth. Hey, even a
Saturn-IB can be 3-staged, the CM/SM being fired as a 3rd stage.

Here’s a page showing some of the FAI scale models from the 1990’s:

http://members.aol.com/gcgassaway/FAIscale.htm

Here’s a page of some photos I took in 2002, showing various scale models plus
the team and non-scale models (scale are only 2 of the 8 events held)

http://www.spacemodeling.org/gcg/wsmc2002_gcg/index.html

And here’s a page with some of the other scale model stuff I’ve done.

http://members.aol.com/gcgassaway/scale.htm

There’s other rockets on that site that are not scale related, and scale models
are not my main interest. Actually my AOL pages are in need of a lot of
updating, someday. I didn’t even have a digital camera when I put them
together.

- George Gassaway

That's fantastic!
<<<<<

Thanks.

Major criticism though - the music!!!! Aaaugh!!!!!!!!
<<<<

I forgot to warn to turn down the volume first.

The video was shot by a professional, Greg Warren, who also flies rockets and
knows how to track them. Also a high-level zoom with a pro camera helps (when
the camera person has experience following rockets). I've seen video shot by
other people of that shuttle model and nothing comes close. Greg added the
generic music.

Oh well, for successfully following the model in flight while at a relatively
close zoom in, and the rest, the music doesn't matter much.

- George Gassaway