All (Digital) Eyes Are on Discovery
Imaging and sensor technologies will play a key role in making NASA shuttle flights safer.
The Space Shuttle Discovery’s 13-day mission to the International Space Station, where it was scheduled to test new safety features implemented after the Columbia disaster in 2003, was scrubbed on Wednesday due to a faulty sensor. While NASA announced no definitive timeline for a new launch, it’s clear that the U.S. shuttle program will soon take flight again.
And, when it does, the three remaining shuttles will be equipped with state-of-the-art technologies designed to make space flight as safe as possible.
Since the shocking loss of seven astronauts two years ago, the Columbia Accident Investigation Board (CAIB) has recommended 15 necessary improvements, including new digital imaging and sensor technologies. And NASA has made 30 different improvements itself.
Together, these comprise NASA’s “Return to Flight” plan, which outlines the latest technologies used in the revived Shuttle program. Among the overhaul’s most cutting-edge technologies are new imaging and sensor systems, to improve the ability of detecting debris falls and impacts.
“Technologically speaking, the biggest improvements are the impact sensors in the wings and a new shuttle boom equipped with the new laser imagers,” says Bruce Sauser, Manager of the Government Furnished Equipment and Flight Crew Equipment Management Office/MV5 for the Space Shuttle at NASA’s Johnson Space Center. Sauser’s office was instrumental in developing and procuring much of Discovery’s new equipment.
Here’s a brief summary of the key technologies used to upgrade the three active space shuttles:
Orbiter Boom Laser Imager: Perhaps the most crucial of all the Shuttle’s enhancements is a new laser imaging system mounted on a boom attached to a 50-foot-long arm extension to the existing 50-foot manipulator. The combined 100-foot system will extend camera views to all parts of the Shuttle. The boom has an electrical grapple system on one end and a new laser imaging system on the other that consists of a Laser Dynamic Range Imager (LDRI), a Laser Camera System (LCS), and an Intensified Television Camera. Made by Sandia Labs, the LDRI uses an infrared laser illuminator and camera receiver to provide 2D and 3D video imagery. The LCS can make 3D video images or CAD models of impacts.
“The 3D views are important for depth measurements,” says Sauser. “If a gouge or a crack exceeds a certain depth, it becomes critical. The quality of the 3D views in these systems has improved a lot over the last few years.”
On the second day of the flight, the astronauts will use the boom’s automated and manual arm systems to investigate the nose and wing leading-edge areas. The operators will need to maneuver these imagers within seven feet of the orbiter to get the necessary resolution. They must be careful not to hit anything and the lasers are sensitive to sudden movement – which means the task will take over six hours.
On future missions, says Sauser, NASA plans to add higher-resolution digital cameras to the orbiter boom, which should speed up the monitoring of impacts and also avoid collisions.
“If we could back that boom assembly up another ten or twenty feet, with a high-rez camera, we could use a wider viewing area and complete the task much quicker,” says Sauser. “If we see an area that might have damage we can go in closer with the lasers and get a 3D measurement.”
Wing Leading-Edge Sensors: Although it was not required, NASA has added 88 accelerometer sensors behind the wing leading-edge panels, which, added to the existing temperature sensors, make a total of 176 sensors. Acceleration and temperature data will be combined with voltage data to detect debris impacts and their locations. The data is transmitted to both a cockpit laptop and Mission Control.
According to Sauser, accelerometers had been used elsewhere on the Shuttle, but not on the wings. Detecting impacts would be guesswork, Sauser says, without new software that improves data reduction. “We’ve been working hard on using the software to determine what is noise and what is critical data.”
Ground Monitoring: There are now 107 cameras, both ground-based and on the aircraft, in place to monitor lift-off, ascent, and re-entry. Improvements include better film cameras that run at higher frame rates (100 fps), the addition of HDTV cameras, and more widespread locations designed for triangulating different events from multiple angles. Film, video, and stills are integrated with radar, with mirrored servers added for faster communication between ground teams. HDTV results will be available for review within a few hours, and film will be compiled over one to two days. The combined system can detect debris objects as small as one inch in diameter up to 30 seconds from launch, and up to 15 inches at booster separation.
Air Monitoring: An experimental air monitoring system will augment ground views with HDTV and infrared imaging cameras mounted on the ball-turret systems of the last two active WB-57 high-altitude weather reconnaissance aircraft. Two aircraft flying at up to 6,000 feet on either side of launch will track the ascent until eight minutes and thirty seconds after launch.
Radar Monitoring: New Wideband Coherent C-Band Radar and Weibel Continuous Pulse Doppler X-Band radar tracking systems will be used to improve tracking of falling debris. The C-Band system provides high spatial resolution, and the Doppler system tracks debris velocity and differential motion. Data from both systems will be correlated from three different angles, with the C-Band data available in near real time.
Shuttle-Based Cameras and Radar: An Enhanced Launch Vehicle Imaging System (ELVIS) incorporates additional “lipstick” cameras located on the surfaces of the Orbiter, its rockets, and the external tank, to improve views of damage during ascent. Cameras are positioned to focus on potential problem areas and new equipment. Also, crew handheld digital cameras have been improved, and there’s a new high-resolution camera designed for spacewalks.
External Tank: Dwarfing the Shuttle orbiter, the 15-story external tank dispenses 535,000 gallons of liquid hydrogen and oxygen during the first two minutes of ascent. The foam shielding that damaged Columbia’s wing likely broke off from the tank’s “bipod” fitting – an area that also produced debris falling during the October 2002 launch of Atlantis. The existing tanks have been retrofitted, and the bipod shielding replaced with electric heaters to avoid the buildup of ice.
Solid Rocket Booster: NASA strengthened the bolt-catcher – it catches the foot-long bolt that breaks free when the external tank is jettisoned – and swapped out the cylindrical energy-absorbing material with a honeycomb design. The solid rocket boosters that separate from the external tank two minutes after launch are redesigned with better beveling and other enhancements to make sure the tank disengages smoothly.
Reinforced Tiles: To optimize protection against space “junk” and micrometeoroids, NASA inspected all wing leading-edge panels, nose cap, and related parts, repairing or replacing tiles. In addition to traditional ultrasound, X-ray, and sampling inspection techniques used to look for flaws in the panels’ Reinforced Carbon-Carbon (RCC) coating, NASA added new infrared thermography systems. In addition, the lower two inches of the front spar (to which the wing panels are attached) were modified to prevent heat from entering the interior. Debris from the shuttle stack is still probably the most likely danger for impact.
Other Structural Improvements: On the Orbiter itself, the Rudder Speed Brakes were corroded and had other flaws. They’ve been refurbished. To avoid debris chipping off the structures that hold the Shuttle in place during liftoff, the gantries have been stripped and repainted with special epoxy. In addition, fuel vent arms have been improved to avoid contact with the tower structures during liftoff. Further, maintenance procedures have now been strengthened, with a stricter examination of equipment waivers, improved photo closeouts, and tighter standards for Foreign Object Debris (FOD) inspections.
Rescue or Repair: As the Shuttle approaches a rendezvous with the Space Station on day three, the astronauts will roll the craft to expose its underbelly, so Space Station personnel can use digital cameras to photograph the heat shield. Once the Shuttle is docked, the data will be evaluated over several more days to assess whether there’s a critical problem. For this flight, such an event would activate contingency plans for rescuing the stranded Shuttle astronauts. Discovery is delivering a container full of several tons of supplies to the station, to allow for an extended stay, until a rescue mission could arrive.
In the future, though, impacts such as the one that downed Columbia could probably be repaired. Two such repair technologies will be tested in a spacewalk. The first option uses Shuttle Tile Ablator-54 (STA-54), a caulk-like substance that can be used to fill cavities as well as to replace entire tiles. This silicone-based material is applied using an EVA backpack with tanks that separately contain the catalyst and components of the material and feed into a static-mixer applicator gun. The second method, an emittance wash, is primarily used as a heat-rejection layer to protect shallow abrasions, but it will also be tested as a primer for STA-54. The wash mixes fine-grit silicon carbide granules with a vulcanizing material.
The chemical repair techniques could probably handle a crack as large as two to three inches, says Sauser, but further tests will also be required to make sure the application does not affect aerodynamics.
“We did a lot of ground testing, but to really get comfortable that the techniques we have to do them in orbit,” Sauser says. “We’ll be able to try these things in a micrograv environment and bring those samples back home and do testing that simulates coming home in a high-heat landing scenario.”