NASA Investigation Board Report On The INITIAL FLIGHT ANOMALIES OF SKYLAB 1

Launch and Environment

Skylab 1 was launched at 1730:00 (Range time, R=0) on May 14, 1973, from Complex 39 A, Kennedy Space Center. At this time. the Cape Kennedy launch area was experiencing cloudy conditions .with warm temperatures and gentle surface winds. Total sky cover consisted of scattered cumulus at 2,400 feet. scattered stratocumulus at 5,000 feet, broken altocumulus at 12,000 feet, and cirrus at 23,000 feet. During ascent, the vehicle passed through the cloud layers but no lightning was observed in the area. As shown in tables II-1 and II-2, upper area wind conditions were benign compared to most other Saturn-V flights. Figure 2-1 shows a comparison between wind speed. altitude, and time during the launch. Figure 2-2 shows altitude vs. range time. Figure 2-3 is a plot showing SL-1 history in the region of maximum bending moment. As can be seen. the flight environment was quite favorable.

Major Events

The automatic countdown proceeded normally with Guidance Reference Release occurring at R-17.0 seconds and orbit insertion, occurring at R+599.0 seconds. Table II-3 lists the pertinent orbit parameters and table II-4 is a summary of the normal major events through orbit insertion. All times are referenced from Range time, R-0, which is defined as the last integral second prior to liftoff. As can be seen from table II-4, the OWS solar array deployment was commanded on time; however, real time data indicated that the system did not deploy fully.

Description of Solar Array System and Meteoroid Shield

The Solar Array System (SAS) on the OWS consists of two large beams enclosing three major sections of solar cell assemblies within each. During ascent, the sections are folded like an accordion inside the beams which in turn are stowed against the workshop as shown in figure 2-4. The MS is a lightweight structure wrapped around the converted S-IVB stage orbital workshop and is exposed to the flight environment. The MS, and its attachment to the OWS, is described in detail in Chapter IV of this report. The two hinged SAS wings are secured to the OWS by tie downs above and below the MS. Seals attached to the SAS perimeter actually press against the shield to form an airtight cavity prior to launch. Once in orbit, the SAS beams are first deployed out 90 degrees. The MS is deployed later to a distance of about five inches from the OWS wall (see fig. 2-4). After the ordnance release is fired, MS deployment is effected by torsion rods and swing links spaced around the structure fore and aft. The rods are torqued prior to launch and simply "unwind" in orbit to move the MS away from the tank. Detection of pertinent conditions associated with the MS and SAS is afforded by measuring various parameters by telemetered instrumentation. Figure 2-5 shows a plan view of the MS and SAS configuration and identifies the location of instrumentation sensors.

Early Indication of Anomalies

When the OWS Solar Array System was commanded to deploy, telemetered data indicated that events did not occur as planned. The flight data was analyzed by flight operations personnel to reveal the possible source of the problem. At about R+60 seconds, the S-II telemetry reflected power increased slightly. At about 63 seconds, numerous measurements indicated the apparent early deployment and loss of the MS. At this time, the vehicle was at about 28,600 feet altitude and at a velocity of about Mach 1.

At this time, vehicle dynamic measurements such as vibration, acceleration, attitude error and acoustics indicated strong disturbances. Measurements which are normally relatively static at this time, such as torsion rod strain gages, tension strap breakwires, temperatures, and SAS position indicators, indicated a loss of the MS and unlatch of the SAS-2 wing. Further preliminary evaluation revealed abnormal vehicle accelerations, vibrations, and SAS temperature and voltage anomalies at about R+593 seconds. Temperature data loss and sudden voltage drops indicated that the SAS-2 wing was separated from the OWS at this time. Other data later in the flight indicated the SAS-1 wing did not fully deploy when commanded to do so. Although not apparently associated with the 63-second and 593-second anomalies, the S-II stage Range Safety Receiver signal strengths showed several drops throughout the flight beginning at about R+260 seconds.

    Figure 2-1. - Scalar wind speed at launch time of SL-1.   

    Figure 2-2. - Altitude comparisons for early portion of S-V launch vehicle boost trajectory.   

    Figure 2-3. - SL-1 alpha-beta limit at maximum bending moment.   

   Figure 2-4. - Meteoroid shield and solar array system.  (a) STOWED.   

   Figure 2-4. - Meteoroid shield and solar array system.  (b) DEPLOYED.   

    Figure 2-5. - Meteoroid shield and instrumentation layout.   

TABLE II-1. - MAXIMUM WIND SPEED IN HIGH DYNAMIC PRESSURE REGION FOR APOLLO / SATURN 501 THROUGH SATURN 513 VEHICLES

TABLE II-2. - EXTREME WIND SHEAR VALUES IN THE HIGH DYNAMIC PRESSURE REGION FOR APOLLO / SATURN 501 THROUGH SATURN 513 VEHICLES

Table II-3 -- Orbit Parameters *

* Data source is from radar data processed by the Mission Operations Computer at JSC.

Table II-4 -- Normal Major Events