The Space Power Facility at NASA Glenn Research Center’s Plum Brook Station in Sandusky, Ohio, houses the world’s largest vacuum chamber. Image Credit: NASA/Michelle Murphy (WYLE)
Albert Einstein, who won the Nobel Prize in Physics in 1921, contributed an alternate theory of gravity in the early 1900s. It was part of his famous General Theory of Relativity, and it offered a very different explanation from Newton’s Law of Universal Gravitation. Einstein didn’t believe gravity was a force at all; he said it was a distortion in the shape of space-time, otherwise known as “the fourth dimension”.
Einstein, in his theory of special relativity, determined that the laws of physics are the same for all non-accelerating observers, and he showed that the speed of light within a vacuum is the same no matter the speed at which an observer travels. As a result, he found that space and time were interwoven into a single continuum known as space-time. Events that occur at the same time for one observer could occur at different times for another.
Brian Cox visits NASA’s Space Power Facility in Ohio to see what happens when a bowling ball and a feather are dropped together under the conditions of outer space.
Basic physics states that if there are no external forces at work, an object will always travel in the straightest possible line. Accordingly, without an external force, two objects travelling along parallel paths will always remain parallel. They will never meet.
But the fact is, they do meet. Particles that start off on parallel paths sometimes end up colliding. Newton’s theory says this can occur because of gravity, a force attracting those objects to one another or to a single, third object. Einstein also says this occurs due to gravity — but in his theory, gravity is not a force. It’s a curve in space-time.
According to Einstein, those objects are still travelling along the straightest possible line, but due to a distortion in space-time, the straightest possible line is now along a spherical path. So two objects that were moving along a flat plane are now moving along a spherical plane. And two straight paths along that sphere end in a single point.
In 1905, Albert Einstein determined that the laws of physics are the same for all non-accelerating observers, and that the speed of light in a vacuum was independent of the motion of all observers. This was the theory of special relativity. It introduced a new framework for all of physics and proposed new concepts of space and time.
Einstein’s theory of general relativity predicted that the space-time around Earth would be not only warped but also twisted by the planet’s rotation.
Still more-recent theories of gravity express the phenomenon in terms of particles and waves. One view states that particles called gravitons cause objects to be attracted to one another. Gravitons have never actually been observed, though. And neither have gravitational waves, sometimes called gravitational radiation, which supposedly are generated when an object is accelerated by an external force .
Gravitons or no gravitons, we know that what goes up must come down. Perhaps someday, we’ll know exactly why. But until then, we can be satisfied just knowing that planet Earth won’t go hurdling into the sun anytime soon. Gravity is keeping it safely in orbit.
The Space Power Facility (SPF) is a vacuum chamber built by NASA in 1969. It stands 122 feet (37 m) high and 100 feet (30 m) in diameter, enclosing a bullet-shaped space. It is the world’s largest thermal vacuum chamber. It was originally commissioned for nuclear-electric power studies under vacuum conditions, but was later decommissioned. Recently, it was recommissioned for use in testing spacecraft propulsion systems. Recent uses include testing the airbag landing systems for the Mars Pathfinder and the Mars Exploration Rovers, Spirit and Opportunity, under simulated Mars atmospheric conditions.
The facility was designed and constructed to test both nuclear and non-nuclear space hardware in a simulated Low-Earth-Orbiting environment. Although the facility was designed for testing nuclear hardware, only non-nuclear tests have been performed throughout its history.
Some of the test programs that have been performed at the facility include high-energy experiments, rocket-fairing separation tests, Mars Lander system tests, deployable Solar Sail tests and International Space Station hardware tests. The SPF is located at the NASA Glenn Research Center at the Plum Brook site.
The facility can sustain a high vacuum (10−6 torr); simulate solar radiation via a 4 MW quartz heat lamp array, solar spectrum by a 400 kW arc lamp, and cold environments (−320 °F (−195.6 °C)) with a variable geometry cryogenic cold shroud.
The facility is available on a full-cost reimbursable basis to government, universities, and the private sector. In Spring 2013 SpaceX conducted a fairing separation test in the vacuum chamber.
Aluminum Test Chamber
The Aluminum Test Chamber is a vacuum-tight aluminum plate vessel that is 100 feet (30 m) in diameter and 122 feet (37 m) high. Designed for an external pressure of 2.5 psi (17 kPa) and internal pressure of 5 psi (34 kPa), the chamber is constructed of Type 5083 aluminum which is a clad on the interior surface with a 1⁄8 in (3.2 mm) thick type 3003 aluminum for corrosion resistance. This material was selected because of its low neutron absorption cross-section. The floor plate and vertical shell are 1 inch (25 mm) (total) thick, while the dome shell is 1 3⁄8 in (35 mm). Welded circumferentially to the exterior surface is aluminum structural T-section members that are 3 feet (0.9 m) deep and 2 feet (0.6 m) wide. The doors of the test chamber are 50 by 50 feet (15 by 15 m) in size and have double door seals to prevent leakage. The chamber floor was designed for a load of 300 tons.
Concrete Chamber Enclosure
The concrete chamber enclosure serves not only as a radiological shield but also as a primary vacuum barrier from atmospheric pressure. 130 feet (40 m) in diameter and 150 feet (46 m) in height, the chamber was designed to withstand atmospheric pressure outside of the chamber at the same time vacuum conditions are occurring within. The concrete thickness varies from 6 to 8 feet (1.8 to 2.4 m) and contains a leak-tight steel containment barrier embedded within. The chamber’s doors are 50 by 50 feet (15 by 15 m) and have inflatable seals. The space between the concrete enclosure and the aluminum test chamber is pumped down to a pressure of 20 torrs (2.7 kPa) during a test.