NASA saves significant development costs by using commercially available field computer

Citation

Huber, H. (1999), "NASA saves significant development costs by using commercially available field computer", Aircraft Engineering and Aerospace Technology, Vol. 71 No. 2. https://doi.org/10.1108/aeat.1999.12771baf.003

NASA saves significant development costs by using commercially available field computer

NASA saves significant development costs by using commercially available field computer

Harold HuberKendall JunenDavid Pinkleton

Keywords Aerospace, Computers, Data collection, NASA

The NASA's Marshall Space Flight Center (MSFC) saved significant Program development costs by using a $12,000 commercial field computer as the basis for a Space Shuttle's Solid Rocket Booster (SRB) data acquisition system. By finding an off-the-shelf product that could withstand the extreme shuttle environment, NASA eliminated the need to develop the data acquisition system from scratch. The Enhanced Data Acquisition System (EDAS), NASA's name for the commercial data acquisition system as modified by NASA, flies on SRBs to collect data during Booster ascend, descend, and water splashdown; NASA is using the EDAS to characterize flight environments in support of planned upgrades to the SRB. Additionally, some SRBs have experienced damage at water impact, NASA will use the data to determine whether a redesign is necessary to prevent future damage. The use of the commercial SoMat Model 2100 Field Computer System from SoMat Systems UK Limited, Luton, Bedfordshire, enabled NASA/Marshall Space Flight Center (MSFC) and Boeing North American to design the EDAS in one year versus the three years required to develop a flight data acquisition system from scratch.

The SRB is made up of four solid rocket motor segments plus forward and aft assemblies. These components are combined to form the solid rocket booster flight configuration. During the first two minutes of ascent, the SRBs provide 80 percent of the Shuttle's total thrust. They separate from the vehicle at an altitude of about 28 miles, while the Shuttle is traveling at about 3,100 mph. The SRBs parachute into the Atlantic Ocean where they are recovered for re-use. Typically, the SRBs impact the ocean at first at 60 mph and submerge to a depth of 90 feet then shoot back up and slap over flat onto the surface. On past missions, portions of the boosters have been damaged during water impact. In one of the worst cases, the 12-foot long forward skirt of the SRB was torn so badly on impact that it broke off and sank. Replacing the forward skirt of the SRB is estimated at more than $6 million. Even slight damage to the skin can cost a million in repairs. Data collected on shuttle flights during the 1980s are of low fidelity and do not correlate well with cases of observed structural damage. The improved data acquisition capability provided by EDAS will help NASA understand the water impact forces on the SRB so that steps can be taken to minimize damage.

NASA plans to continue flying the shuttle until 2030. To keep the shuttle flight-worthy, the agency has undertaken a program to upgrade various shuttle components. NASA is using EDAS to verify thermal, vibration and acoustic models that justify SRB upgrades. The MSFC shuttle integration contractor, Boeing Reusable Space Systems, had to meet stringent shuttle program criteria in order to qualify EDAS for flight. The SoMat computer, installed in an enclosure designed and built at MSFC, underwent rigorous testing to prove that EDAS would not endanger the shuttle in any way. A second consideration was the extreme environment of the SRB. Any equipment onboard must operate perfectly after experiencing liftoff forces. Flight safety was the number one concern, but time and cost were also important considerations. Typically a data acquisition system designed from scratch takes years and millions of dollars. NASA wanted something ready quickly and at a lower cost.

NASA and Boeing decided to use off-the-shelf components to keep costs and development time down. For the data acquisition computer, they chose the SoMat Model 2100 Field Computer System because its durability had been well established, both by NASA and by other companies. The SoMat 2100 had flown on previous shuttle flights, controlling a camera in the SRB nose cone. The excellent performance of the SoMat 2100 in that setting gave NASA and Boeing confidence in the product. Other companies have used the SoMat 2100 in demanding applications as well, attaching it to off-road vehicles, a helicopter rotor, and heavy equipment working in mines. This field computer is compact and rugged enough for these sorts of applications. The SoMat 2100 is powered by three nine-volt batteries, which provide enough power to sample and record for three hours.

The SoMat system is a series of stackable modules, one module per data channel. As many as ten channels can be stacked to handle user-defined data collection needs. Multiple types can be collected on a single channel. The data acquisition configurement that NASA and Boeing engineers created consists of six modules that monitor strain gauges, accelerometers, and calorimeters. The sensors are attached to the forward skirt of the SRB and connected to the SoMat 2100 via cables. The accelerometers measure the g forces experienced by the forward skirt. The strain gauges measure any deflection of the skirt's aluminum skin, and the calorimeters measure heat flux. The total height of the six modules is about six inches.

Programming the field computer was done using SoMat Test Control Software for Windows (WinTCS). This software is easy to use and features Window 95-style dialogs. WinTCS made it simple to set up the data acquisition channels with different sampling rates, gain, excitation and other parameters as required by the various sensors. The field computer was set up to begin recording at liftoff by means of a g switch. This switch is simply a ball that compresses a spring in response to g forces until contact is made. The tension in the spring determines the g level at which contact is made. The contact signals the SoMat to begin recording.

MSFC engineers designed an enclosure to house the EDAS. This box was built to survive even when positioned in the booster aft skirt, the region that experiences the most stress. The enclosure was made sturdy enough to remain bolted to its mounting on the SRB structure. The upper and lower halves of the enclosure are securely sealed to prevent outgassing or fire that might result from faulty or damaged batteries.

The SoMat computer, installed in the EDAS enclosure, was subjected to extensive vibration testing at MSFC. During testing, the EDAS experienced a worst case SRB water impact scenario ­ a force of 250 Gs. A few minor problems were encountered. For example, some of the screws, that hold the SoMat modules in place, came loose. The problem was corrected by applying Locktite to the screw threads. The authors believe that these vibration levels are the highest the SoMat 2100 has ever seen, but it passed all required testing and was qualified to fly in less than one year.

Four EDAS units were installed in the forward skid on the right hand booster for shuttle mission STS-91 (Figure 1). The launch occurred on June 2, 1998. The mission ended with the orbiter landing at Kennedy Space Center on June 12. In its first flight, the EDAS started recording at about six seconds after liftoff. In future flights, engineers will update software so that data recording starts sooner. As programmed, the system recorded data from the sensors for ten minutes and then shut down. After the SoMat was recovered, the data were evaluated by using a SoMat program entitled EASE. EASE is a SoMat program created to handle large data sets. The program integrates functions such as digital filtering, frequency analysis, and fatigue estimation capabilities. After Boeing had determined that the data looked good, they converted them to ASCII and provided the readouts to NASA. The first flight of the EDAS took place in the summer, and because of lighter winds and calmer seas the boosters experienced no damage. NASA plans to fly the EDAS for several flights to achieve a better understanding of the effect of rougher water on the SRBs.

Figure 1 Four EDAS units were installed in the forward skirt on the right hand booster for shuttle mission STS-91

When NASA has accumulated a representative data sample, engineers will use the information to determine whether the SRB structure requires strengthening with additional framing or gussets. NASA will also look at the heat flux data to see if it will be possible to eliminate the thermal protection system (TPS) applied to the outside of the booster to regulate SRB skin and internal temperatures. Removal of the TPS would save the time now spent in applying and removing it.

The availability of a $12,000 commercial field computer rugged enough to survive space shuttle SRB flight environments saved time and taxpayers' money. EDAS provides NASA a compact system that at short notice can be put in almost any location on the booster. And it will continue to save money because, whenever NASA needs additional information related to SRB operation, there is a data acquisition system ready to fly. The flight of EDAS in October 1998 on mission STS-95, whose crew included payload specialist John Glenn, the first American to orbit the earth during his Mercury capsule flight in 1962, was fully successful.

For more information contact SoMat Systems UK Limited, Maxet House, Liverpool Rd, Luton, Bedfordshire, UK LU11RS. Tel: +44 (0) 1582 730582; Fax: +44 (0) 1582 730382; Internet: www.somat.com