OpenVMS, numerical control and electric power in space

The causal relationship between these matters is probably not self-evident at first - or even second - glance, and a connection might appear a tad abstruse. Nevertheless a quite tight connection does exist:

The power supply of about 100 (as of 2010) satellites in Earth's orbit is based upon solar generators whose monocrystalline cells were welded to each other by a machine whose NC production data was processed on a VAX running the OpenVMS operating system and a NC programming system.

The most beautiful aspect about this is the

Legacy Hardware

The solar cell welding-machine is now more than 25 years old, but its continued right to exist is justified by its robustness and most notably by its production accuracy. Attempts to replace this machine made for a very special purpose with more modern types failed miserably due to insufficient manufacturing quality for orbital purposes.

The IT devices used for producing NC data are a MicroVAX 3100-85 and Facit punch tape reader/printer which both are nearly as old as the welding machine, perhaps just up to five years younger.
NC data is brought from the VAX to the welding machine via paper tape using a punch tape printer - since the welding machine does not feature an interface other than a punch tape reader.

The MicroVAX 3100-85 used to process the data

The Facit punch tape reader/printer

Integrating the punch tape device with a serial interface of the VAX was an interesting challenge since both printing and reading of these paper tapes was required. Printing is done using the PRINT command to a related queue - which monopolises the serial interface so that it is not then available for read access.
Since punch tapes need to be verified because of their mechanical production by reading them in again (the print head assembly can lose adjustment), read access is mandatory. Hence a command procedure was implemented for this to stop the queue, to set some required interface parameters and to start a program for reading in the paper tape. As soon as reading the tape is finished, the procedure reverses the aforementioned changes to enable print mode again.

Display larger video

Space flight in the hobby room

The reason why production data for orbital technology emerged from my hobby room since the mid 1990s is a story too long and probably hardly traceable for outsiders. In short, it's the result of hasty decisions made at corporate-level during the Mehdorn era at Deutsche Aerospace (now EADS). The result was a relocation of the solar generator production plant all across Germany causing a loss of the required IT infrastructure onsite.


The purpose of NC programming is providing a machine tool with data based upon a geometrical description and which it's able to read and execute. The geometrical descriptions shown below emerged from rudimentary sketches from former Daimler-Chrysler Aerospace, now EADS. Orbital projects, especially in the satellite technology area are managed by another group company called Astrium (now EADS space) since quite a few years now.

Description of geometrical conditions

Description of obstacles in platform's travel distance

The geometrical descriptions contain data related to shape and dimensions as well as to obstacles on the platform for the required number of cells, which in the end need to make a generator providing the required power. In short: Nesting, optimization of the traveling distances and piloting the resulting welding points. The computer was of some help here:

Excerpt from the geometrical description - loops for a minimization of efforts.

Visualization of the traverse path with welding points

Spot check: Checkup of particular welding points

Running the NC processor results in a NC program which is printed to a paper punch tape. This is read by the solar cell welding-machine which welds the cells to each other forming the generator's panels.

The projects in particular

comprise satellites for various purposes such as research, communication and environmental monitoring as well as weather forecasts and last but not least matters being subject to secrecy. The following list is just an incomplete selection of satellites whose power supply is based on welding data processed under OpenVMS:

Name Year International Identifier
Telstar 11 1994 079A
SAX 1996 027A
Italsat-2 1996 044A
Insat 2D 1997 027B
SOHO 1998 -
Landsat 7 1999 -
Globalstar 1998-2000 -
SPOT 2000 -
Cluster II 2000 041A,041B,045A,045B
Globalsat 2002 -
Eutelsat W5 2002 051A
Radarsat-2 2007 061A
Metop 1 2005 044A

Some of these names are related to voluminous spates of devices. The GLOBALSTAR devices f.i. comprise 52 units, hence their identifiers are not mentioned here.

Realtime pictures of LandSat can be found at NASA.
Pictures of both SPOT4 and SPOT5 satellites can be found on Google Earth. In the sidebar open "Layers", then "More" and select "Spot Image" (see picture on the right).