ASCA data tapes are in FITS tape format. This means that every file is a FITS file with a record size of 2880 and a block size of 28800. The text, PostScript, and GIF files included on the tape have been converted to FITS format (i.e., FITS wrapped). The first file on each tape is a FITS ASCII table catalog of the files on the tape.
The ASCA/GSFC tapes were created using the Unix command dd with the parameter obs set to 28800 (see Unix man pages for more information). They should be readable on any system supporting simple blocked data with no labels.
Your tape is best read with the ascatape FTOOL. The IRAF t2d program, the Unix dd, and VMS copy utilities will also work, but assigning file names and unwrapping non-FITS files will be up to you. The ASCA processing team and GOF do not support these methods.
The ascatape tool allows you to read some or all of the files on your tape and can set up the recommended directory structure. Since ASCA data sets can occupy hundreds of megabytes, ascatape can also report the size of a data subset before reading the tape to disk. This will help you keep from exceeding your available disk space.
ascatape assigns file names according to a file catalog on the tape. You can consult the FNAME keyword in the primary header of most FITS files to confirm that the files have been named properly.
For more information consult the ascatape help page by typing `fhelp ascatape'.
The Processing Team verifies that all tapes are readable before they are sent. However, tape drives are intrinsically troublesome, and problems can still occur. Below we discuss the most common problems and how to correct them.
Dirty tape drive: Tape drives commonly misread tapes or report I/O errors because their heads are dirty. This is the cause of nearly all tape reading problems. To fix, simply clean the drive heads with a tape cleaning cartridge.
ncorrect read/write permissions: Files from the tape cannot be loaded onto disk unless you have permission to read from the tape drive and write to the file system. Make sure you have permission to do both, and if not, consult your system administrator.
Not enough disk space: If the tape read fails part way through, you have probably run out of disk space. If so, you can use ascatape to report the amount of disk space required and either clear some space or select a smaller file set. Also, on Unix systems ascatape allows you to spread the files over several partitions by creating the subdirectories as links before the tape is read.
Quirky drive: Some drives don't work right or don't "like" certain tapes. If you can, try reading your tape in a different drive.
Software trouble: ascatape has been widely tested and has been stable for several years. Even so, some problems may occur. Make sure that the correct operating system flags were set when compiling ascatape. This can be a problem when upgrading from SunOS to Solaris.
Incompatible format: Tape drives can write in different density and compression modes, and larger capacity formats may not be compatible with all drives. Before Summer 1996, sequences which were too large to fit on a low density tape were written in high density. Currently we split such sequences onto more than one low density tape. We never use compression. If you are reading an old tape, tape density may a problem, and you can contact the processing team for a new tape.
Corrupt data tape: All tapes are verified before being sent. However, tapes may still be corrupted in shipping. If none of the above seem to be the problem, contact the processing team and we will send you a new tape.