By Michael Gerzanics
Growing up in the USA in the 1960s I was captivated by the space programme as we raced the Soviet Union to the Moon. Most of my generation can tell you where they were when Neil Armstrong and Buzz Aldrin landed at Tranquility Base on 20 July 1969.
After that, "one giant leap for mankind" and the conclusion of the Moon programme, the Space Shuttle promised to make space missions routine.
The Space Shuttle was the first reusable space vehicle - one that could return to Earth and land like an aircraft. Each orbiter was designed to have a life span of 100 launches. While the planned launch rate was 12 a year, NASA estimated at one point that the vehicles could launch a maximum of 25 missions a year.
The Space Shuttle promised to bring down the cost of space access with unprecedented economies of scale. While it never lofted payloads at its planned rate, the Shuttle has been a great success. Despite the tragic loss of two orbiters and their crews, the Shuttle has put numerous civil and military satellites into orbit. The International Space Station and Hubble Space telescope are two of the Shuttle's brightest success stories.
As the Shuttle programme winds down, Flight International was able to sample the atmospheric flight experience of the delta-winged spacecraft in Houston during multi-hour training sessions in two types of simulators on 12 October - a full-motion launch and landing simulator and a fixed-based avionics integration laboratory simulator.
For the recovery/landing phase of Shuttle flight, two programmes stand out as essential to its successful development: the several lifting-body flight programmes and the X-15 hypersonic research programme. The experience gained by flying the numerous lifting bodies in the 1960s and 1970s showed that "wingless" aircraft can be controlled in flight and glided to a safe landing on a runway. The thermal stress environment of hypersonic atmospheric flight, vehicle control schemes as well as descent and landing profiles were all explored by the X-15.
While the Shuttle has a delta wing planform, its design was significantly influenced by the lessons learned from flying lifting-body vehicles.
Landing an unpowered aircraft is routine for a glider pilot. Pilots of single-engined fighters often practise engine-out landing patterns, often called an SFO (simulated flame-out landing). Real dead-stick landings are a rare event, a direct consequence of reliable jet engines and ejection seats.
While Capt Chesley Sullenberger ditched an unpowered US Airlines Airbus A320 in the Hudson river, a dead-stick landing in a transport-class jet aircraft is not even a practised event. Dead-stick landing a Space Shuttle-sized aircraft was uncharted territory. While achievable in theory, NASA set out to quantify the magnitude of the task. Using a Convair CV-990, a Boeing 707-class four-engined jet transport, NASA accomplished Shuttle-like approach and landing trials in a real aircraft. The pattern airspeed for the trials was 210-220kt (390-410km/h), well below the Shuttle's airspeed of around 295kt.
In an unpowered approach the only energy available to the aircraft is its speed and altitude. The aircraft must have enough energy to reach the desired runway, with an excess of energy desirable. NASA determined there were two possible ways to modulate the aircraft's total energy in relation to the touchdown point: path length variation and lift-to-drag ratio (L/D) modulation.
An accomplished glider pilot uses both methods on a typical approach, judging the turn to the field upon the total energy state. Once on final an aim-point is selected and L/D changed by using the speed brakes to control aircraft speed.