Sahreiberj Bentkowsky and Kerr 



half the distance to the hatch, then attempts to maintain altitude 

 while adjusting his x and y coordinates. In the process the yaw 

 angle has been increased to about 35 degrees. The final descent is 

 made, the DSRV touching the deck somewhat in excess of 3. 5 minutes 

 after the start of the problem. At touchdown the DSRV was almost 

 perfectly aligned in the x direction but was nearly 2.5 feet off 

 center in the y direction. On the deck, vertical thrust was applied 

 (trace not shown) in an attempt to keep from being lifted off by the 

 current. Roll and pitch angles were adjusted to try to position all 

 four legs in contact with the deck. Note that during this time the 

 DSRV continues to roll and pitch. The transients at impact caused 

 the DSRV to slip aft about 2,5 feet. This was corrected, as was 

 the misalignment in the y axis. After nearly 5 minutes the pilot had 

 the DSRV under control and could commence the final retraction of 

 the shock mitigation ring and start up the de^yatering pump. At this 

 time the computer was placed into HOLD. The final misalignments 

 were 0,10 feet in the x direction and 0,16 feet in the y direction, 

 within the required tolerances. The final yaw pitch and roll angles 

 were 36, 6 and 16 degrees, respectively. 



Unfortunately, this would not have been a completely success- 

 ful landing. At the time the pilot terminated the run, the DSRV seal 

 plane and the deck hatch plane were misaligned about 7 degrees in 

 roll and 2 degrees In pitch so that all four shock mitigation legs 

 were not In contact with the deck and a satisfactory seal could not be 

 made. No Instrumentation exists on the DSRV to provide this relative 

 attitude data which could result In a serious operational limitation. 

 The problem can be alleviated In part by use of the hauldown system 

 which provides a larger stabilizing moment, reducing the offset 

 angles, 



A major assistance was obtained by Installing, In the simu- 

 lation, a set of 4 Indicators which measured the stroke of the shock 

 mitigation hydraulic cylinders. Roll and pitch alignment could be 

 achieved with this system, while maintaining the horizontal plane 

 edignment. 



A review of the thruster activity leads to two Interesting 

 observations. First, the thrusters are operated In a bang-bang 

 fashion, that Is, either maximum thrust or zero thurst Is comnnanded. 

 This, despite the fact that an accurate proportional control system Is 

 available. Second, the activity of the horizontal thrusters Is much 

 greater than either the vertical thruster or the main propeller. This 

 was somewhat predictable from the environmental curves of Fig, 9. 

 The frequency of the horizontal thruster activity has Implications 

 In the thermal design of the thruster motors. 



1178 



