Re: Tracking satellites with Meade ETX-90 EC

Dave Mullenix (
Mon, 29 Mar 1999 01:05:52 -0600

Bjvrn Gimle wrote:

> Correction:
> "Optional #497 Autostar Computer Controller" does mention "9-speed
> dual-axis" but "any speed from 2x sidereal to 50 per second", and
> "12,000 database objects" and "50 satellites". It is not obvious
> if the computer-control port is on this unit, or the telescope.

Hi Bjorn, I'll try to answer a few of your questions:

When using the Autostar, pressing a digit from 0 to 9 changes the slew
speed for the up/down/left/right buttons.  I normally use 5 when slewing
around looking for something, then 3 or 4 for fine centering.  0-3 are
VERY slow, but should be excellent for guiding a time exposure.  5
through 9 are strictly for moving from one side of the sky to another. 
Objects whiz through the field of view too fast to register as anything
but a blur or a flash.

The computer port is on the Autostar computer unit.  

Let me give more detail: the telescope comes with a hand controller
which has up/down/left/right buttons, 4 LEDS to show which of the four
available slew/tracking speeds are in use, a button to select one of the
four speeds and a mode button which lets you select az/el or ra/dec
tracking.  The hand controller won't track stars in az/el mode, but it
will if you mount the telescope equatorially and select ra/dec mode.  It
draws its power from the telescope.  The hand controller is about the
size of a pocket calculator and fits easily in your hand.  The buttons
can be used with gloved hands, if you're careful.

The Autostar computer is the same general shape as the hand controller
and a little bigger.  It replaces the hand controller, which you don't
really need once you have the Autostar.  The Autostar has
up/down/left/right buttons plus a numeric keypad, two cursor keys, a
help button and three keys for navigating the unit's menus.  It also has
a 2 line / 16 char per line LCD display which is back lit with
adjustable brightness red LEDS.  (Another LED lights up when you're
being asked to enter date and time, so you can read your wrist watch. 
Time is lost and the date freezes when you turn the telescope off.) 
Both units have long coiled cords that plug into a telephone-style 8 pin
jack on the telescope.  The Autostar computer also has a 4 pin telephone
style jack on it's base.  This is the connection to your home computer. 
If you're using the ETX-90/EC with a PC, you'll have two cords coming
out the bottom of the Autostar - one going to the telescope and one
going to the PC. However, nobody has the interface cable yet or
information on how they're wired or what voltages and protocols are
used.  I don't know if it uses RS-232 voltages, TTL voltages or
something else entirely.  No idea on how the hand controller and
Autostar control the telescope, either.  I have a hunch that it's a
simple enough interface so that a properly programmed PC could control
the telescope directly without the Autostar, but of course this software
doesn't exist at this time and probably wouldn't be produced by Meade

The Autostar is a very well designed unit, judging by my limited usage. 
Somebody put a lot of thought into it's overall design.  It's not
totally finished, though.  Mine has version 1.0 software in it and at
least once I've run into a message that says, "Under construction".  All
software and data is kept in a 1 megabyte flash memory, so it can be
upgraded.  The satellite elements also are stored in this Flash memory. 
The Autostar uses an 8 MHz Motorola 68HC11 microprocessor, which is
basically an 8 bit chip.  I wouldn't be surprised if all future Meade
telescopes ar designed to use the Autostar.

Some people seem to fault Meade for releasing a unit that doesn't have
all the bells and whistles available yet.  I think they did the right
thing.  What they have released, the telescope and Autostar, work fine. 
The units that aren't available yet, namely the computer cable and PC
downloading software, are refinements that are probably not very
important to 99% of the users.  I'm sure they'll be released soon.  (Of
course, if they're not out in a couple of months, my opinion will

Three more items: 

First, a non-astronomically literate friend says that a local store
(American TV) has the ETX-90 for about 30 dollars below the $595 list
price, so shop around a little.  American TV has a mail order division,
and they might be on the web.  Personally, I don't mind paying the extra
bucks to purchase from a telescope store (Eagle Optics - they also mail
order) which is staffed by people who know a galaxy from a black hole. 
(Also, I dislike American TV enough to pay 30 dollars to stay away from

Second, my ETX-90/EC's azimuth motor stopped functioning the third night
I used it.  I was trying to center a star while doing the initial
alignment when the up/down buttons just stopped working.  They worked
intermittently for two more days and then gracefully failed totally when
I took the scope back to the store.  They swapped my broken telescope
for a new one without any hassle.

Third: Count on purchasing a replacement finder scope.  You HAVE to have
one with a right angle eyepiece.  The ETX-90/EC is just too small and
crowded for you to get your eye to the stock finderscope's straight
through eyepiece when you're pointing much more than 30-40 degrees above
the horizon.  The Meade deluxe right angle finder isn't available yet,
but I've seen ads from at least one third party supplier in Sky and
Telescope.  I'll be ordering soon.  They really should make a right
angle finder standard on this scope.

Dave Mullenix