|Getting Together, Space Style||
From the early days of U.S. space flight, one of the challenges has been devising ways to safely bring spacecraft together while they speed through the vast weightlessness of space. |
Until now, the methods used by NASA required hands-on control by astronauts. But the upcoming launch of the Demonstration of Autonomous Rendezvous Technology (DART) spacecraft will usher in a new era by using only computers and sensors to locate and rendezvous with its target.
To understand the significance of DART to the U.S. Space Program and the Vision for Space Exploration, it helps to see just how far the technology has come. The use of this technology and others to be developed in the future will help us return astronauts and supplies to the lunar surface and go beyond.
The earliest attempts brought manned spacecraft together with unmanned targets during the Gemini Program in the 1960s. During the first try at docking the Gemini 8 capsule with the unmanned Agena Target Vehicle, the resulting uncontrolled spinning led to the first emergency landing of a manned U.S. space mission.
Image at Right: The Agena Target Vehicle as seen from the Gemini 8 spacecraft during rendezvous. Image credit: NASA
Ultimately, the astronauts of Gemini 11 and 12 each successfully rendezvoused and docked with an Agena, setting the stage for the Apollo Program.
The success of the Apollo missions to the Moon hinged on the astronauts' skill in undocking and docking the Command-Service Module (CSM) and the Lunar Module (LM). These maneuvers enabled them to descend to the Moon's surface in the LM and return safely to the CSM for their journey back to Earth. During Apollo 9, successful rendezvous and docking with the LM was achieved while in Earth orbit.
Image at Left: Apollo 9 Command/Service Modules (CSM) nicknamed "Gumdrop" and Lunar Module (LM), nicknamed "Spider" are shown docked together as Command Module pilot David R. Scott stands in the open hatch.. Image credit: NASA
Apollo 10 accomplished the first LM undocking and the first manned LM/CSM docking in lunar orbit. The testing of the docking technology and the astronauts' ability to use it paved the way for the successful Moon landings that followed.
While the use of the technology and human skills had been proven within the U.S. Space Program, other challenges existed as the international community began to pursue joint space projects.
Apollo Soyuz, the first international manned space flight, tested the compatibility of rendezvous and docking systems for American and Soviet spacecraft. The mission was a resounding success after a number of obstacles were overcome. Technical challenges included differences in measuring systems, spacecraft designs, and air pressures and mixtures. Language was also an issue, since each crew had to be trained in the other's language.
As the Space Shuttle Program advanced and cooperation with the Russian space program grew, so did the challenges in finding compatibility between U.S. and Russian hardware and technology. The Space Shuttle and Russia's Mir space station were incompatible vehicles developed independently for different purposes. During the Shuttle-Mir Program, many operational solutions were employed to allow joint operation of the docked vehicles. As a result, the U. S. Space Shuttle orbiter and Mir space station were able to dock, creating the largest structure ever placed into orbit at that time.
The International Space Station's (ISS) rendezvous and docking capabilities were first demonstrated in 1998 when the first two modules were launched and joined together in orbit. Other modules soon followed, and the first crew arrived in 2000. Since that time, all transfers of crews and supplies have depended on human-guided technology.
The upcoming test of the DART flight demonstrator will provide a key step in establishing rendezvous capabilities that require no hands-on control by astronauts.
Image at Right: This illustration shows the DART spacecraft approaching its rendezvous with the MUBLCOM satellite. Image credit: NASA
The DART spacecraft depends completely on computers and sensors to perform all of its rendezvous functions as it targets the MUltiple paths, Beyond-Line-of-sight COMmunications (MUBLCOM) satellite. After launch, the entire 24-hour mission will be conducted without any human intervention. Applications of technologies used in the DART project will assist in the development of future space systems that require in-space assembly and servicing, including the ISS.
The DART mission will be launched from Vandenberg Air Force Base in California aboard a Pegasus launch vehicle mated to a Stargazer L-1011 aircraft.
Cheryl L. Mansfield
NASA's John F. Kennedy Space Center and Marshall Space Flight Center