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Sky Engineering Sky Commander XP4 Computer with Flash Cable & Manual - CMP-XP-4000

SKU: SKE-CMP-XP-4000

Sky Commander XP4 Computer with Flash Cable


  • Convert your telescope into an efficient observing performer.
  • Bring thousands of celestial marvels to your fingertips.
  • May be used on its own or in combination with a PC.
  • Identify those "faint fuzzies" you come across as you scan the night sky with your scope.
  • Take full advantage of your valuable observing time.
  • Optimally suited for viewing in light polluted conditions


Initially introduced in 2004, the Sky Commander XP4 is based on the original design, but features the important enhancements and upgrades listed below:

  • Internal memory space has expanded by a factor of 4 from 128kB to 512kB, providing enough room for approximately 30,000 objects to be stored.
  • Flash type memory to allow it to be reprogrammable in the module. Physically replacing an OTP (One Time Programmable) EPROM in order to upgrade is not necessary. To upgrade, connect the XP4 to your PC and run the XP4_Boot-Flash_Utility. Flash memory has essentially infinite reprogramming cycles.
  • Encoder "Fast-Tracking" is the first significant upgrade supported in version 4.2. This enables the use of extremely high resolution encoders, up to 24576 count without having to be concerned with reduced encoder counts if the scope is quickly moved, a nice benefit when used on compact telescopes that can move swiftly. Encoder "Fast-Tracking" only runs with external 12 volt power applied since it consumes more power than an internal 9 volt battery can provide.
  • New custom enclosure made of ABS plastic with battery compartment that is easily accessible externally for quick battery substitution.


XP4 supports the following astronomical catalogs:

  • Abell Planetary Neb: An 82-object list of old and ancient planetary nebulae research by well-known astronomer, George Abell. As these planetaries are ancient, they provide a nice challenge as most are extended and of low surface brightness.
  • Arp Galaxies: A list of 338 galaxies showing different aspects of peculiarity studied by Halton Arp.
  • Bayer Stars: 1,564 stars cataloged by Greek letter and constellation.
  • Double Stars: A collection of 600 fine double stars provided with permission from the Saguaro Astronomy Club.
  • Hickson: A list of small compact galaxy groups, which presents a challenge for the observer. This list, 100 groups, was compiled by a Canadian professional astronomer, Paul Hickson, for research on discordant redshifts.
  • Messier: The famous catalog of Charles Messier. 109 bright deep sky objects.
  • Named Deep Sky: 135 deep sky objects by common name.
  • Named Stars: 142 stars by common name.
  • NGC: Entire NGC catalog of 7,840 deep sky objects.
  • UGC:Entire UGC (Uppsala General Catalog) catalog of 12,921 northern hemisphere galaxies.
  • Herschel 400: The 400 most impressive deep sky objects in William Herschel's catalog of over 2500. Cataloged by NGC number.
  • IC: Index Catalog of 5,250 deep sky objects.
  • Barnard: 343 dark nebulae
  • Berkley: 86 open clusters
  • Collinder: 471 open clusters
  • Trumpler: 34 open clusters
  • Planets: 7 planets plus Pluto
  • Special Objects: 59 user-defined object positions. Enter RA and DEC via keypad.


Sky Commander XP4 Holdover Features


Several of the core operating principals and components of the original Sky Commander have been handed down to the XP4 design. These include:

  • Six Button Control - Unit is controlled through only six buttons: ENTER, MENU, UP, DOWN, LEFT, and RIGHT. This enables operation to be quickly mastered by the user.
  • Large LCD - 32 character (16 x 2 line) Liquid Crystal Display with yellow-green backlight that can be modified in intensity. This soft backlight will not disturb night vision.
  • RS232 - RS232 serial port is available for connecting the XP4 to your PC. Computer screen displays telescope position. Several astronomy programs are compatible with the Sky Commander such as The Sky, Megastar, Guide 7.0, Sky Map Pro, Deep Sky Planner, and more.
  • Search & Identify Mode - As you scan your telescope across the night sky, any database object matching the position of the scope is displayed instantly. Search is "filtered" by an adjustable magnitude limit.
  • Constellation Browsing - Choose a constellation and "browse" the database. Adjustable magnitude limit.
  • User List - Choose items from the internal database and add them to a list of favorite objects for convenient access in the future.
  • Special List - Add any object's coordinates to a "special" list. This can be done spontaneously using the keypad, or via the RS232 interface.
  • Realign to Object - Enhance pointing accuracy, particularly within proximity to the object to which you realign.
  • Ultra Low Power - Single 9 volt battery allows approximately 40 operating hours. Battery current is just 6mA.
  • Standby Mode - With a simple "double-click" of the MENU button, you can extend battery life by suppressing backlight. Pressing any button will return you to regular backlit operation.
  • Battery Monitor - Bar graph indicates relative battery life.
  • External Power - Standard 2.1 mm power jack enables use with 12 volt batter or power supply.
  • Display Heater - In colder climates, the LCD (Liquid Crystal Display) will slow down. An internal heater will activate under thermostat control. To use this feature, an external 12 volt DC power supply is required.
  • Equatorial Table Support - Use the Sky Commander XP4 with an equatorial table. It is not necessary to re-do the two star alignment after resetting the table.


Sky Engineering Sky Commander XP4 FAQs


What is the Sky Commander? - The Sky Commander is a small, self-contained computer designed for the specific purpose of locating and identifying celestial objects with a telescope.

How does it work? - The computer "reads" the position of the telescope using two optical encoder modules. The encoders are attached mechanically to the telescope axes in such a manner that the encoder shaft turns as the telescope is turned. When starting an observing session, the user activates the computer by pointing the telescope at two different stars. The computer is able to establish the orientation of both the telescope and the sky by sensing the change in position between the two stars.

How do I point the telescope to an object? - A six button keypad coupled with an LCD display form a user-friendly interface. First, select a catalog, e.g. Messier, NGC or Planet. Then enter the four digit catalog number using the arrow buttons. Pressing the ENTER button selects the "current" object. The user moves the telescope while watching the LCD. As the scope nears its target objects, the display digits lower to zero in AZ and EL. Arrows are displayed to indicate direction.

What does the display show me? - The Liquid Crystal Display (LCD) indicates the position of the telescope in RA and declination, or its position in relation to the target object ("zero in" display). It also displays the current catalog and object number selected as well as some additional information including object type, magnitude, and constellation.

How do I get it set up on my telescope? - The Sky Commander is compatible with telescopes on both Alt-Azimuth and Equatorial type mounts. For Dobsonians, Sky Engineering offers a general purpose encoder mounting kit. This is available through Sky Engineering. Since this is a general purpose kit, some modifications may be necessary to make it work depending on your existing scope. Dobsonian telescopes are by far the easiest to fit encoders due to the ample amount of room to work with. For other telescope types, the Sky Commander works with most readily available encoder setups. A standard encoder cable connector (modular RJ45 also used for computer network cables) is used.

What's the deal with encoder resolutions? - Angular resolution of the system is determined by the encoders themselves. The Sky Commander can handle a wide range of resolutions. Typical encoders are 4000 step per revolution, but other resolutions are also used, (2160, 4096, 8192, etc). The important thing is that you enter the encoder information into the Sky Commander so it knows how many counts per degree of scope rotation. This information only needs to be entered one time, but can be changed whenever needed.

Do higher resolution encoders mean higher accuracy? - Possibly, but keep in mind that the encoders themselves have an inherent "runout" error which may exceed the step size, especially for higher resolution units.

What is the RS232 connector for? - RS232 is a standard for serial communications between computers. In the Sky Commander it is used to tell a PC the position of the telescope so it can be displayed on the screen. In this way the user can tap into the huge resources provided by many Astronomy programs. On the XP4 RS232 is used as a "Flash Port" when updating the software or internal database.

How is the Sky Commander powered? - The Sky Commander is powered from an internal 9 volt battery which can operate for about 40 hours under normal use. There is also an optional 2.1 mm (5.5 mm OD) power jack for connection to a 12 volt DC power supply.

What do I need to buy? - If your scope already has optical encoders installed with a standard encoder cable, the Sky Commander XP4 by itself will suffice. If you are using a Dobsonian scope, you will have to attach stepper encoders to your telescope ahead of time, and you must have an encoder cable.