(Article accepted by major spaceflight publication)
The Space Shuttle era is coming to an end. For decades the winged Orbiters have symbolized humanity’s reach into Space. For American astronauts, the Shuttle held monopoly on their ability to reach orbit. The Columbia accident of 2003 led to a new Vision for the Moon, Mars and Beyond. With the coming of Orion and other spacecraft, the Shuttles are scheduled to retire in 2010.
Cosmic rays represent some of the biggest mysteries in science. The most energetic particles ever found, they may hold the key to mysteries like antimatter and “dark” matter. A new international experiment, the Alpha Magnetic Spectrometer has been built to study cosmic rays. Carried aloft by Shuttle and mounted on the Space Station, AMS would be one of the Station’s key experiments.
As the year 2010 nears, a conflict has developed between science and program. Congress and the science community want an additional flight for AMS. Eager to retire Shuttle, some in NASA would prefer that the experiment be grounded. One possible solution is simple, safe and already being planned for.
Cosmic Rays and AMS
Though they bombard Earth constantly, relatively little is known about cosmic rays. First discovered by balloon experiments in 1912, these particles present some of the biggest mysteries in science. For decades the very origins of cosmic rays were a mystery. They can have enormous energies, far higher than those produced in human accelerators. The highest energy cosmic rays, nicknamed "Oh My God particles,” defy today’s physics to explain. Ultra-high energy cosmic rays may have originated at a time near the Big Bang, when even the speed of light may have been different.
As one example, nearly everyone has experienced the power of a thunderstorm. We are taught in school that lightning originates from static buildup within storm clouds. What triggers the discharges is unknown. Since cosmic rays fall nearly steadily across Earth's surface, some researchers have suggested that cosmic rays are the cause of lightning! That may be one more example of how Space science affects life on Earth.
The Alpha Magnetic Spectrometer is the most ambitious physics experiment designed for ISS. From its perch on the S3 Upper Inboard Payload Attach Site, AMS will intercept cosmic rays from Space. The project was first proposed in 1995, shortly after cancellation of the Superconducting Supercollider. As conceived by Nobel laureate Samuel Ting, AMS would explore energies far greater than Earthly accelerators. While the Large Hadron Collider can produce particles of 10^12 electron–volts, cosmic rays have energies in excess of 10^20 electron-volts.
The heart of AMS is a two-ton superconducting magnet, cooled to a temperature of only 1.8 degrees Kelvin. The paths of charged particles are bent by magnetic fields. As in a bubble chamber, scientists can identify different particles by their tracks. For instance, the tracks of matter and antimatter would be bent in opposite directions. Study of antimatter particles would offer clues as to why our Universe is made mostly of matter.
One of the most ambitious physics experiments ever built, the Alpha Magnetic Spectrometer is international in scope. Building AMS has employed 500 researchers from 16 nations. After a cost of 1.5 billion, the device is nearly completed. A prototype AMS-01 visited Space with STS-91 in 1998, returning data that validated the concept. During 2008 AMS will be moved from CERN to Kennedy Space Center for launch. Unfortunately, plans and lives were cut short by Columbia.
If NASA had known about the damage to Columbia’s Thermal Protection System, there would have been a small but fighting chance of rescue. While STS-107 was in orbit, Atlantis was being readied for STS-114. If certain safety protocols had been waived, she could have been launched early on a rendezvous attempt. Space would then have seen its greatest drama since Apollo 13. As the world below watched breathlessly, for the first time in history one spaceship would try to rescue another.
If her crew were evacuated, Columbia would have been left to her fate. She would have been boosted into a higher orbit to await another rendezvous. Possibly a way would have been found to repair the damage and return Columbia to service. More likely her orbit would have decayed until she met her end in the atmosphere.
Since return to flight in 2005, the biggest concern is another Columbia accident. Batteries of cameras on the ground and spacecraft now monitor every launch for foam strikes. Before and after docking each Shuttle is minutely inspected for damage using the Orbiter Boom Sensor System. Each mission carries some risk of TPS tiles being lost.
If damage were found that prevented safe reentry, a Shuttle crew would evacuate to the Station. A Contingency Shuttle Crew Support (CSCS) mission would Launch On Need to bring the crew home. Since the Station has never hosted two Shuttles simultaneously, the damaged Orbiter would be jettisoned before the rescue mission docked.
In the aftermath of Columbia, every remaining Shuttle flight was directed toward completing ISS. To make way for Constellation, the Shuttles were scheduled for retirement in 2010. Despite its expense, importance to science and international partners, the Alpha Magnetic Spectrometer was taken off the launch manifest. Studies have since shown that Shuttle is the only feasible vehicle for carrying AMS into Space.
Hubble Servicing Mission STS-125 poses its own challenges. HSM-4 was removed from the manifest following Columbia, but restored after pressure from the public and Congress. Evacuating to ISS from Hubble’s orbit will not be possible. As Atlantis ascends from Pad 39-A, Endeavour will be poised on Pad 39-B for Launch On Need. At the conclusion of HSM-4 Endeavour will be moved from 39-B, which will then be modified for the Ares 1-X test.
At this writing, Contingency Logistics Flights STS-132 (Discovery) and STS-133 (Endeavour) are scheduled for launch April 8 and May 31, 2010. After flight Discovery will re-enter the Orbiter Processing Facility and begin preparations for Launch On Need. A new External Tank ET-138 and two Solid Rocket Boosters must also be prepared. If STS-133 needs no rescue, those expensive pieces of hardware will go unused. Launching 7 months before the end of 2010, STS-133 may be the last Shuttle mission.
Many in the Space community are concerned about the “gap” after Shuttle retirement. Scientists are eager to see AMS fly on Shuttle. Without AMS, the Station is open to charges that it lacks scientific purpose. The 15 nations that have funded AMS wish to see the US fulfill its commitment. On June 18, 2008 a new NASA authorization bill passed the House of Representatives by an overwhelming 409-15 margin. In addition to increasing NASA funding, H.R. 6063 directs an additional Shuttle flight for AMS. As they supported Hubble Space Telescope, the people have spoken in support of science.
A scenario for an AMS mission is described here. It is similar to most Shuttle flights with one notable exception. The rescue contingencies previously described all include retiring the damaged Orbiter in Space. Prior to the Shuttle era, NASA threw away nearly all its spacecraft. This may represent a simple, safe way to launch AMS while ending the Shuttle program.
The AMS mission would bring new duties for ISS crew. During 2009 the Station will establish a permanent six-person capability. Three-person expeditions or “increments” will arrive and depart via Soyuz. To prepare for AMS, one increment would temporarily be reduced to two persons. A Mission Specialist would arrive in a Soyuz, along with a Russian pilot who would join the ISS increment. Four persons would then be aboard to welcome the Shuttle, supported by two Soyuz spacecraft.
AMS would fly aboard an Orbiter already prepared for STS-133 rescue, using the External Tank and the Solid Rocket Boosters already purchased. A Commander and Pilot in the flight deck would be responsible for docking with the Station. For EVA the Orbiter would bring the normal complement of three Extravehicular Mobility Units (spacesuits.) The Mission Specialist would be responsible for installing AMS assisted by the Pilot, with the ISS crew available for EVA support.
The Commander, Pilot and Mission Specialist would return to Earth by Soyuz. This removes the risk of a Columbia accident, and the requirement to prepare another Shuttle for Launch On Need. (Hopefully the Soyuz problem of ballistic entry will be solved by 2010.) After its last mission is complete, the Orbiter will no longer be needed.
Concerning spacesuits, three Extravehicular Mobility Units would add to the ISS collection. The EMU was designed for Shuttle and is not cleared for Soyuz or Orion. Once the Shuttles stop flying the ISS is currently due to have just four EMU's onboard. Since there is no precedent for EMU’s lasting over a 5-year gap, the additional suits would be invaluable. Any Shuttle visit to ISS is valuable for extra small payloads. STS-124 was especially welcome for bringing parts to repair the toilet.
At the mission’s conclusion the crew would arm the Orbital Maneuvering System, exit to ISS and ceremoniously close the hatch. Mission Control in Houston can command the Orbiter to separate, maneuver and fire the OMS engines. A tail-first reentry over the Pacific would likely be chosen. In 50 years dozens of unmanned spacecraft and boosters have broken up over oceans without a single injury. The AMS mission would be a memorable end to the Shuttle era.
The Logical Thing To Do?
Safety is a primary concern of Shuttle operations. Unlike most other Space flights, the AMS mission has redundant rescue capability. At no point does the total number of people aboard ISS exceed the six-person capacity of the two Soyuz. In an emergency, the Shuttle will still be able to evacuate all six crew.
Because an Orbiter, External Tank, SRB’s and launch facilities must be prepared for STS-133 rescue, adding the AMS mission would be relatively inexpensive. The Mission Specialist and her crewmates would ascend and return in Soyuz flights already purchased. Returning by Soyuz avoids the expense and risk of landing an Orbiter on Earth. Along with Enterprise, which today sits in the National Air and Space Museum’s Udvar-Hazy facility, two Orbiters would be available for display. For the final mission, retiring an Orbiter in Space is an unusual but logical step.
Aside from safety issues, the cost of recovering an Orbiter is many millions of dollars. The Shuttle Landing Facility at Kennedy Space Center and the alternate runway at Edwards Air Force Base must be prepared and the airspace cleared. Helicopters and chase planes must be deployed for rescue and security. At each location, a land armada of 20-30 specialized vehicles and 150 trained personnel also stand ready. Their jobs include disembarking the astronauts, “safing” the Orbiter and removing its explosive propellants. The Edwards Space Shuttle Recovery Team alone has several hundred members. After an Edwards landing, the Shuttle must be mounted atop its 747 carrier and flown to an Orbiter Processing Facility at KSC. There an additional Orbiter, External Tank and Solid Rocket Boosters must be prepared for Launch On Need in case the reentry is aborted. For the Shuttle program, the price of reusability is high.
While two Orbiters have been lost in flight, no precedent exists for retiring a Space Shuttle on Earth. The costs of safing an Orbiter and putting it on display are unknown but probably beyond the means of most museums. Only a few sites have a history of operating Shuttles. Kennedy Space Center could convert an Orbiter Processing Facility for Shuttle display. The Manned Spaceflight Center in Houston and the Air Force Flight Test Center Museum at Edwards would also be competing locations. Kennedy and Edwards both have the advantage of a Mate/Demate facility for an Orbiter and 747. Along with the two carrier aircraft, many Shuttle mockups and parts remain for museums.
Future generations will look upon the Orbiters with wonder. Starting with dreams of a reusable Spaceplane, the Shuttle has maintained humans in Low Earth Orbit for 3 decades. This period has provided both hope and tragedy. Hundreds of trained astronauts have reached LEO via the Shuttle Orbiters. As the year 2010 approaches, private industry is prepared to ferry humans into orbit and NASA is ready to again move beyond. The Space Shuttles will long remain as symbols of an era.
Labels: Cosmic rays, space shuttle