This spring marks 40 years because the House Shuttle Program lastly broke the shackles of Earth with the inaugural test flight of the orbiter Columbia on STS-1. Over a interval of somewhat greater than two days in April 1981, veteran Gemini and Apollo astronaut John Young and “rookie” spacefarer Bob Crippen launched from historic Pad 39A at the Kennedy Space Center (KSC) in Florida, piloted America’s first shuttle into low-Earth orbit, accomplished 36 circuits of the Dwelling Planet and returned to an unpowered “deadstick” touchdown at Edwards Air Force Base, Calif. It was the beginning of a brand new period of human exploration in a reusable spacecraft which might display its outstanding capabilities over 135 missions earlier than its remaining swansong in July 2011.
However earlier than STS-1 might start, precisely 40 years in the past at present, on 20 February 1981, Columbia’s three Space Shuttle Main Engines (SSMEs) have been fired for 20 seconds on the launch pad. It was a part of a remaining collection of important checks to make sure that America’s latest and most complicated flying machine was able to go.
Often known as the Flight Readiness Firing (FRF), these workout routines have been carried out earlier than the maiden voyages of all 5 shuttles: Columbia, Challenger, Discovery, Atlantis and Endeavour. And with Challenger put through two FRFs ahead of her first mission, and Discovery additionally performing the second FRF of her profession in August 1988 earlier than her STS-26 Return to Flight (RTF), no fewer than seven of those dramatic checks have been carried out between February 1981 and April 1992.
The aim of the FRF was to impose launch situations on the cluster of engines, in addition to testing the suite of Auxiliary Energy Items (APUs) in high-speed mode. Visually and acoustically, it was maybe the closest analog to a launch, with out truly launching the automobile.
The STS-1 “stack”—which comprised Columbia herself, bolted to her twin Stable Rocket Boosters (SRBs) and bulbous Exterior Tank (ET)—had been rolled out from the Car Meeting Constructing (VAB) to Pad 39A at dawn on 29 December 1980.
Formally referred to as the Moist Countdown Demonstration Take a look at (WCDT)/Flight Readiness Firing (FRF), the ultimate steps on the launch pad to prepared STS-1 for flight have been meant to imitate the countdown operations as intently as doable. A basic aim was to “confirm the potential of the launch facility to supply propellants to the shuttle underneath launch situations”, with the ET/SRB combo “uncovered to the identical thermal atmosphere they may expertise throughout STS-1 launch preparations”.
Elsewhere, all Essential Propulsion System (MPS) management components have been “required to keep up stress within the Exterior Tank and in the primary engines in the course of the check firing, as they’d throughout an precise launch”, while the power of the APUs, hydraulics and flight controls needed to confirm their means to throttle the SSMEs at between 94-100 % of rated thrust and “gimbal” them to impact steering.
By daybreak on 20 February 1981, the six-day-long WCDT was approaching its conclusion and would culminate with the FRF. In readiness for the check firing, launch controllers began the countdown clock at T-53 hours, once they powered up the SRBs, the Floor Help Gear (GSE) and the shuttle’s on-board programs. Within the remaining seconds, NASA commentator George Diller’s calm tones described the occasion for his viewers. “The Stable Rocket Booster hydraulic models are activated,” he reported. “The countdown now being carried out by the on-board computer systems, with the bottom pc performing as backup.”
4 seconds previous to the simulated liftoff, Columbia’s SSMEs roared to life at 120-millisecond intervals—“We’ve Essential Engine Begin,” exclaimed Diller, “all three engines are up and working”—then reached 90 % of rated efficiency inside three seconds and hit 100 % exactly at T-0.
As a thick pall of grey cloud obscured the shuttle, leaving solely the information of her wings and the Roman candles of the boosters clearly seen, the FRF proceeded to perfection. Three seconds into the burn, engineers simulated the retraction of the ET umbilical and the SRB hold-down posts, till finally after a interval of steady thrust from the SSMEs, shutdown instructions have been issued to the engines.
“And we now have had shutdown, we now have had shutdown of all three engines,” Diller famous. “A full 20-second burn, as anticipated.”
The check had gone effectively, with a few unanticipated points. Considered one of its goals was to guage and measure the impact of the “twang”—the quantity of motion in Columbia, in opposition to the remainder of the stack in the course of the SSME start-up sequence—and in STS-1’s case this triggered a ahead shift by about 25.5 inches (64.7 cm).
That was inside anticipated structural limits, however was nonetheless considerably larger than the 19 inches (48.2 cm) predicted by the engineers. Moreover, the STS-1 FRF was notable in that the sparker-like hydrogen burn-off igniters have been fired similtaneously the SSMEs, however post-test evaluation led to a choice to provoke this course of at T-4.Four seconds—forward of Essential Engine Begin—on STS-1 and all future missions.
As outlined previously by AmericaSpace, not all FRFs went totally based on plan, however each basically demonstrated the capabilities of the entire system earlier than committing to flight.