...interfaces...more confusing and complex
than I thought they would be"160. One statistic that supports his perception is that
the 13,000 keystrokes used in a week-long lunar mission are
matched by a Shuttle crew in a 58-hour flight161.
Another aspect of the "working for the
computer" problem is that steps normally done by computers using
preprogrammed functions are done manually on the Shuttle. The
reconfiguration of PASS from the ascent redundant set to the
on-orbit groupings has to be done by the crew, a process taking
several minutes and needing to be reversed before descent. Aaron
acknowledges that the computer interfaces are too close to machine
level, but points out that management "would not buy" simple
automatic reconfiguration schemes. Even if they had, there is no
computer memory to store such utilities.
Tied to the computer memory problem is the
fact that many functions [124] have to be
displayed together on a screen because of the fact that such
displays are "memory hungry." As a result, many screens are so
crowded that reading them quickly is difficult, the process being
further affected by the blandness and primitive nature of any
graphics available. Astronaut Vance Brand claimed that after
initial confusion, several hours with simulators makes things
easier to find; he makes a point of checking his entries on the
input line before pressing the execute key162. Young does that as well, but for additional
reasons: The keyboard buffer is so small that entering data too
quickly causes some to be lost, and he wants to check whether he
is accessing the right screen display with the proper keyboard.
This latter concern arises because there are only two keyboards
for the three forward CRTs. Since both keyboards can be assigned
to the same screen, two CRTs may not be currently set up for
input. Even if the two keyboards are assigned to different
screens, one CRT is left without capability for immediate crew
input. Astronaut Henry Hartsfield termed this situation "prone to
error"163.
Since flying the Shuttle is in many ways
flying the Shuttle computers (they provide the active flight
control, guidance and navigation, systems management, and payload
functions), the astronauts are interested in making suggestions
for improving the computer system. Most revolve around more
automation, more user friendliness, more color, better graphics,
and more functions, such as adding a return-to-launch-site (RTLS)
abort with two engines out in addition to the present version with
only one engine out164. Each of these enhancements is tied to increasing
memory. IBM proposed a new version of the Shuttle computers with
256K of memory and software compatibility with the existing
system. Johnson Space Center began testing these AP-101F computers
in 1985, with the first operational use projected for the
resumption of Shuttle missions in 1988.
In the meantime, the astronauts themselves
pioneered efforts to use small computers to add functions and back
up the primary systems. Early flights used a Hewlett-Packard
HP-41C programmable calculator to determine ground-station
availability, as well as carry a limited version of the
calculations for time-to-retrofire. Beginning with STS-9 in
December, 1983, a Grid Systems Compass portable microcomputer with
graphics capabilities was carried to display ground stations and
to provide functions impractical on the primary computers. Mission
Specialist Terry Hart, responsible for programming the HP-41Cs,
said that placing the mission documentation on the computer was
also being considered165.