The
launch escape apparatus pulls an Apollo Command Module (CM) to safety
during the Pad Abort Test-2 in June 1965. Photo Credit: NASA
If all goes according to plan on Wednesday morning—and SpaceX has already explained that “Winds above 25 knots and Phase II Lightning are the primary Range weather constraints”—the Pad Abort Test will get underway at 7 a.m., about 22 minutes after local sunrise. “Winds have become gusty out of the east and will remain so for the next couple of days as a low-pressure area develops south-east of Central Florida,” it was highlighted by the 45th Weather Squadron in an update on Monday. “The increase in winds also increases the threat of showers along the Space Coast. Showers will be most prevalent in the morning hours and typically diminish after noon. On Wednesday, the low-pressure area will drift north and east, relaxing the pressure gradient, which will result in lower wind speeds over the Spaceport.” Maximum winds to 5,000 feet (1,500 meters) are expected to be easterly at 20 knots, producing a 70-percent likelihood of acceptable conditions on Wednesday. That probability is expected to improve to 80-percent favourable on the backup day on Thursday, as the low-pressure region continues to move north-west and winds continue to weaken. In the event of a 24-hour scrub, the maximum winds to 5,000 feet (1,500 meters) on Thursday will be north-easterly at 17 knots.
Abort trajectory profile for tomorrow’s Dragon Pad Abort Test. Image Credit: SpaceX
At T-0, the eight hypergolic SuperDraco thrusters, built into the sides of the Dragon, will roar to life and ramp up to their maximum 120,000 pounds (54,430 kg) of thrust. This impetus will propel the vehicle away from SLC-40. “After half a second of vertical flight, Crew Dragon pitches toward the ocean and continues its controlled burn,” SpaceX reported Monday, 4 May. “The SuperDraco engines throttle to control the trajectory, based on real-time measurements from the vehicle’s sensors.” Two seconds into the ascent, the spacecraft will have already attained an altitude of 328 feet (100 meters) and will hit 1,640 feet (500 meters) at five seconds. “The abort burn is terminated once all propellant is consumed,” it was continued, “and Dragon coasts for just over 15 seconds to its highest point about 0.93 miles (1,500 meters) above the launch pad.”
The unpressurized “trunk” will be jettisoned at T+21 seconds and the Dragon capsule will commence a slow rotation, with its base heat shield positioned towards the ground. Four seconds later, the drogue parachutes will be deployed, within a 4-6 second window, stabilizing the vehicle in advance of the unfurling of the three main canopies at T+35 seconds. Current expectations are that the Dragon capsule will hit the waters of the Atlantic Ocean at T+107 seconds, with the impact point predicted about 1.4 miles (2,200 meters) downrange of SLC-40.
During Wednesday’s test, SpaceX hopes to acquire significant data in the areas of Sequencing, Closed-Loop Control, Trajectory and External and Internal Environments. It will demonstrate the proper sequencing of the pad-abort timeline, serving to validate the execution of multiple critical commands in a very short period, as well as testing as many as eight SuperDracos in unison for the first time. It will obtain trajectory data for both maximum altitude and downrange distance from the pad and will gather data on “various internal and external factors to Crew Dragon to help ensure safe conditions for crew transport.” Interestingly, SpaceX also noted that the crash test dummy is actually not nicknamed “Buster”, despite media reports to the contrary and SpaceX Vice President of Mission Assurance Hans Koenigsmann referring to the dummy as such during last Friday’s press briefing. “Buster the Dummy already works for a great show you may have heard of, called MythBusters,” SpaceX said in a press statement Monday. “Our dummy prefers to remain anonymous for the time being.”
However, Wednesday’s Pad Abort Test is the latest in a long series of such exercises to validate pad systems, booster systems and spacecraft systems, ahead of piloted flights. As described in yesterday’s AmericaSpace article, the Little Joe booster advanced U.S. knowledge of the intricacies of high-altitude abort events in readiness for Project Mercury, and its immediate descendent (the “Little Joe II”) was employed between August 1963 and January 1966 for five unmanned tests of the escape system for the Apollo Command and Service Module (CSM), as America strove to plant human bootprints on the Moon before the decade’s end. Early studies for Little Joe II (initially dubbed “Little Joe Senior”) got underway in mid-1961, not long after the completion of Little Joe’s involvement with Project Mercury. It would be required to support two launches in 1963 for tests in the Max Q region—an area of maximum aerodynamic turbulence upon a launch vehicle’s flight surfaces, typically encountered about a minute into ascent—followed by two very-high-altitude atmospheric aborts and finally a “Confirming Max Q Abort.” In May 1962, General Dynamics/Convair won the contract to develop the Little Joe II vehicle, with White Sands Missile Range, near Alamagordo, N.M., chosen as the launch site.
The
A-002 Little Joe II mission delivers a boilerplate Apollo Command and
Service Module (CSM) to altitude on 8 December 1964. Photo Credit: NASA
It was agreed that the maiden voyage of the Little Joe II would be for qualification purposes, and in the meantime, by March 1963, the first booster had emerged from production and was delivered to White Sands at the end of April. The Qualification Test Vehicle (QTV) followed in mid-July and was successfully fired from Army Launch Area (ALA)-3 on 28 August, carrying a dummy aluminum shell in the basic shape of the Apollo CSM and an inert launch escape system. In spite of failing to destruct when commanded, due to an improperly installed primacord, the Little Joe II reached a maximum altitude of 4.5 miles (7.3 km), covered a distance of 8.7 miles (14 km) and accomplished its test objectives to determine base pressures and heating on the vehicle.
Six months later, in February 1964, the second Little Joe II arrived at White Sands, and a boilerplate Apollo CSM was installed at the end of March, prior to the “A-001” flight on 13 May. With the six Recruit motors firing for 1.5 seconds and the Algol-1D sustainer operating for 42 seconds, the flight attained an altitude of 3.1 miles (5 km) and at 44 seconds accomplished the first successful abort with a “live” launch escape system. The landing sequence of the spacecraft also ran normally, with the exception of a failure of one of the mortar-deployed main parachutes, which produced a faster than intended landing. A third (“A-002”) mission took place on 8 December and evaluated the effectiveness of the launch escape system at equivalent pressures and stresses to those expected during a Saturn IB or Saturn V ascent.
On 19 May 1965, the fourth (“A-003”) mission failed in spectacular fashion when one of the Little Joe II’s four stabilizing fins failed, inducing an uncontrollable roll and precipitating the disintegration of the vehicle. A subsequent NASA-General Dynamics/Convair investigation revealed that the No. IV fin inadvertently moved into a “hard-over” position, about a second after liftoff, due to an internal mechanical failure. By 2.5 seconds into the flight, the fin had reached a fully deflected position, where it remained until the vehicle disintegrated. Consequently—and a little ironically—what should have been an abort test turned into a real abort situation, although it was executed at low altitude, rather than the intended higher altitude.
“The faster the rocket went up, the faster it spun around,” remembered instrumentation and electronics engineer Gary Johnson in a 2010 NASA oral history, who observed the A-003 failure. “It had six solid-rocket motors … and those six motors all just came apart. We were only a half-mile away from the launch pad and, all of a sudden, these rockets were coming flying in every direction, almost like they were coming back at us, but they weren’t, of course.” However, the launch escape system fired on time and successfully pulled the Apollo CSM away from the blazing booster and it parachuted to safety.
Also watching the ill-fated A-003 ascent was NASA’s Little Joe II Program Manager Milt Silveira and his wife. “The vehicle started to roll, and when it rolled to the point, structurally, [that] it wouldn’t take it, and it blew apart, and then the payload aborted off the launch vehicle,” Silveira told the NASA oral historian in 2005. “So it was a little more realistic than what we thought! It was supposed to go to a hundred miles down, around, and downrange, and it only went about twenty. But it scattered aluminum all over the sky and things like that. It was a very realistic test from that point, even though it wasn’t the planned one.”
The SpaceX Crew Dragon Pad Abort Test vehicle atop SLC-40 / Cape Canaveral AFS, Fla. Photo Credit: SpaceX
The final, seven-minute-long Little Joe II test (“A-004”) occurred on 20 January 1966, delivering a production Apollo Block I spacecraft (CSM-002) to a peak altitude of 14 miles (23 km) and demonstrating its twin objectives of proper LES orientation/stabilization and full structural integrity of the escape vehicle.
In the meantime, separate tests were also underway to demonstrate the capacity of the launch escape system to pull the spacecraft away from an exploding booster on the pad. Unlike Little Joe II altitude flights, which sought to demonstrate the system’s capability to boost a spacecraft away from a failing booster in high-dynamic-pressure conditions, a pair of Pad Abort Tests, also at LC-36 at White Sands, saw the launch escape mechanism fired at ground level. On 7 November 1963, Pad Abort Test-1 successfully lifted a boilerplate Apollo CSM and attached Launch Escape System (LES) from LC-36. Fifteen seconds into the abort, the LES separated and the CM successfully parachuted to a safe landing. With the exception of soot deposited on the spacecraft’s exterior surfaces and a less-than-predicted stability, the 165-second test was considered a great success, reaching a peak altitude of 1.7 miles (2.8 km). This was followed by a highly successful Pad Abort Test-2 on 29 June 1965, closing out Little Joe’s final involvement with a soon-to-be-piloted spacecraft.
A mockup of NASA’s Orion spacecraft is boosted to altitude on 6 May 2010. Photo Credit: NASA
Groundbreaking operations for the construction of the abort test pads got underway at the Army’s White Sands Missile Range, near Las Cruces, N.M., in November 2007, and the solid-fueled motor to jettison the LAS was static-fired by prime contractor Aerojet in April 2008. The Pad Abort Test-1 took place at White Sands—the very same location from where the Little Joe II launches originated, so many years earlier—on 6 May 2010. An abort motor, with a momentary 500,000 pounds (226,800 kg) of thrust, burned for six seconds to boost Orion away from the pad. It reached a peak velocity of 540 mph (870 km/h).
Simultaneously, a 7,000-pound-thrust (3,170 kg) attitude control motor was also ignited to provide steering, whilst a jettison motor pulled the LAS away from the capsule to permit parachute deployment and a safe landing. Overall, Pad Abort-1 lasted 135 seconds and Orion was brought to a touchdown about a mile (1.6 km) north of the pad. At the time of writing, an Orion Ascent Abort Test (AA-2) is planned from Space Launch Complex (SLC)-46 at Cape Canaveral Air Force Station, Fla., in 2018.
With SpaceX’s fellow CCtCap winner, Boeing, expected to conduct its own Pad Abort Test in support of its CST-100 spacecraft, sometime next year, ahead of inaugural unpiloted and manned missions in 2017, the roar of abort engines on Wednesday morning promises to be a significant milestone as these new crew-carrying vehicles draw closer to maturity. As cautioned by NASA’s Jon Cowart and SpaceX’s Hans Koenigsmann in Friday’s press briefing, the Dragon Pad Abort Test is a development test, “not a shiny, well-polished Space Shuttle launch.” Its ascent will be neither slow or sedate; rather, it will blaze to 5,000 feet (1,500 feet) in about six seconds, before the capsule plummets back to an oceanic splashdown. “I can hold my breath the entire time,” quipped Koenigsmann.
However, what we should see on Wednesday morning will draw more than a few uncanny parallels with the Little Joe missions of yesteryear. It will also closely mirror the Beach Abort Test from 9 May 1960, which was described as “a sterling qualification test, but … hardly spectacular to the public.” Speaking back in 1999, Rodney Rose recalled inviting the media to one of the early Little Joe tests. On one occasion, Rose briefed a group of photojournalists about what they were about to behold.
“Well, this is not quite like what you’re used to, guys,” he explained. “This thing goes off pretty fast.”
“No sweat,” came the reply from one of the photojournalists. “We’ll follow that.”
On the morning of the test, however, he zoomed his camera in on the pad … and missed the Little Joe completely, so rapid was its departure and ascent. “Where did it go? Where did it go?” the hapless photojournalist asked Rose. He had failed to appreciate the sheer impetus with which the launch escape system propelled its precious payload away from the booster. “Six G makes a difference,” Rose explained, “because, you know, 1.1 or less G, they take off pretty sedately from the Cape.”
And therein lies the singular lesson of a Pad Abort Test: Whatever happens on Wednesday morning—whether spectacular to the public or not—the lesson is to Watch Carefully.
For one thing is certain: It’ll be fast.