As Mars Month gets underway, preparations for two upcoming missions by United Launch Alliance (ULA) have ramped up significantly in recent days. NASA’s Perseverance rover, encapsulated within its bulbous payload fairing, was transferred to the Vertical Integration Facility (VIF) at Space Launch Complex (SLC)-41 at Cape Canaveral Air Force Station, Fla., on 7 July. It was later installed atop the giant Atlas V booster for two weeks of checkouts, ahead of launch to Mars no sooner than 30 July. Elsewhere on the Space Coast, rocket hardware for a classified National Reconnaissance Office (NRO) mission later this summer also arrived last week aboard ULA’s RocketShip.
The voyage of Perseverance—characterized by a surface rover not dissimilar to Curiosity, which has been on Mars since August 2012—will see a significantly expanded science toolkit and, for the first time on another planetary body, a helicopter, brought to bear on the geologically-rich Jezero Crater. This location, just north of the Martian equator, is expected to be the setting for the next phase of Red Planet exploration after Perseverance conducts its Entry, Descent and Landing (EDL) on 18 February of next year.
As previously described by AmericaSpace’s Paul Scott Anderson, Jezero Crater offers the potential to explore landforms dating back around 3.6 billion years, thus helping to answer significant questions about planetary evolution and astrobiology. The 28-mile-wide (45 km) crater sits on the westernmost edge of Isidis Planitia and contains the remnants of an ancient river delta and possibly a long-since-vanished lake. Indeed, the very word “jezero”, in Slovenian, denotes “lake”.
The campaign to ready the Atlas V hardware for this important mission began in earnest back in April, when the 41-foot-long (12.6-meter) Centaur upper stage was delivered overland by truck to the Cape. A few weeks later, the 107-foot-long (32-meter) Common Core Booster (CCB)—the Atlas V’s main segment—also arrived in Florida aboard an Antonov An-124-100 aircraft.
Both components were hoisted into the VIF in late May to wrap up the significant Launch Vehicle On Stand (LVOS) milestone. With its 17-foot-diameter (5-meter) payload fairing, four strap-on boosters and single-engine Centaur upper stage, this particular configuration of the Atlas V is known as the “541” and has only been used six times previously, including Curiosity itself.
One key difference about the Perseverance launch campaign was the need to conduct a Wet Dress Rehearsal (WDR) at the pad, which was satisfactorily completed late last month. In the case of missions with very tight “launch windows”, WDRs allow ground personnel to rehearse the entire countdown, including fueling the Atlas V with 25,000 gallons (113,650 liters) of rocket-grade kerosene (known as “RP-1”) and 66,000 gallons (300,000 liters) of liquid oxygen and hydrogen. But whilst the cryogenic propellants were drained at the end of the WDR, the RP-1 will remain aboard the Atlas V tanks through launch day.
And Perseverance’s launch window—dictated by the need to reach Mars under the most optimum conditions of time and energy—is nothing if not “tight”. It originally extended from 17 July through 11 August, with a possibility that trajectory specialists might eke out a few more days at the window’s end. Launch initially slipped until 20 July, due to a crane controller fault, then to the 22nd in response to a contamination concern found during the encapsulation of Perseverance in its payload fairing, and finally to the 30th.
This latter move occurred after a liquid oxygen sensor line presented off-nominal readings during the WDR. In an update at the end of June, NASA noted that “flight analysis teams have expanded the mission launch opportunities to 15 August” and that examinations were underway to determine if the window could extend further into August if needed.
Following the completion of the WDR, the Atlas V was returned to the VIF and on Tuesday, 7 July, ULA CEO Tory Bruno tweeted that the Perseverance rover—snugly encapsulated within her bulbous payload fairing—had arrived for installation atop the stack. “Proud to report that she has just arrived at the VIF for mate to the Mighty Atlas,” Mr. Bruno wrote. Perseverance was enclosed in its fairing in the Payload Hazardous Servicing Facility (PHSF) at the Kennedy Space Center (KSC), prior to being transferred to the VIF atop ULA’s KAMAG payload transporter.
With the fairing in place, the complete Atlas V 541 now stands 197 feet (60 meters) tall. “An integrated electrical test with both the rocket and the payload will be performed to verify all systems are functioning correctly,” ULA explained in a Wednesday update. “Then, two weeks of mission-unique activities for the payload are scheduled.”
In tandem with preparations for its next Mars-bound voyage, ULA teams are also hard at work readying boosters for upcoming Atlas V missions in support of national security and defense. Perseverance will mark the fourth Atlas V launch of 2020—snapping at the heels of Solar Orbiter in February, the sixth and final Advanced Extremely High Frequency (AEHF) military communications satellite in March and the latest flight of the X-37B Orbital Test Vehicle (OTV) in mid-May—with up to four others planned for the Department of Defense, the National Reconnaissance Office and the U.S. Space Force, as well as a second uncrewed test flight of the CST-100 Starliner for NASA and Boeing.
And it is in support of one of these classified military missions that the CCB and Centaur components arrived at the Cape last week via RocketShip from ULA’s facility in Decatur, Ala., targeting a September launch from SLC-41 to deliver the classified NROL-101 payload for the National Reconnaissance Office. The Atlas V for this mission is the “531”, equipped with a 17-foot-diameter (5-meter) payload fairing, three strap-on solid-fueled boosters and a single-engine Centaur. Although the nature of NROL-101 remains classified, the 531’s payload-lifting capability amounts to around 34,330 pounds (15,575 kg) to low-Earth orbit and 16,480 pounds (7,475 kg) to geostationary altitude, indicative of the energy needed to lift this highly secretive mission.
The 531 has previously seen service only three times, lofting the first three members of the AEHF satellite constellation between August 2010 and September 2013. “It’s just a less frequent mass and orbit combination,” Mr. Bruno explained in response to a tweeted question from AmericaSpace. “For perspective, Atlas and Delta together come in over 41 configurations, with most of those being Atlas variants. So small numbers (even zero) for some configurations is to be expected.”
Yet the 531 for the NROL-101 marks a significant difference in that, for the first time, this mission will utilize upgraded Graphity Epoxy Motor (GEM)-63 solid-fueled boosters. Derived from the heritage of their predecessor, the GEM-60—which provided much of the liftoff muscle for Delta IV Medium launches—the 63-inch-diameter (1.6-meter) GEM-63 stands 65 feet (20 meters) tall and is the longest single-case solid-fueled rocket motor ever developed by Northrop Grumman. It will replace the GEM-60s used by the now-retired Delta IV Medium fleet and the Aerojet Rocketdyne-built AJ-60A boosters previously employed by the Atlas V. In parallel developments, the slightly taller GEM-63XL will be used alongside ULA’s Vulcan heavylifter, which is due to make its maiden flight next year.
The origins of the GEM-63 date back to contracts awarded to Orbital ATK back in September 2015, with a key aim to “significantly lower the price to ULA and to the U.S. government”. In tandem with the barebones booster for Atlas V operations, an “extended length” (GEM-63XL) variant was developed for Vulcan, whose 72-foot (22-meter) height makes it the longest single-case solid-fueled rocket motor ever built. Within just three years, in September 2018 the GEM-63 completed its first 110-second static fire test at Northrop Grumman’s test area in Promontory, Utah, which qualified it for use on the Atlas V, followed by a second test in April 2019 which qualified it for Air Force missions. A third was completed last October to “satisfy additional requirements by the Air Force”.
Up to five of these GEM-63s can support a single Atlas V, with three assigned to power the NROL-101 mission away from the pad in September. Each booster generates 373,000 pounds (169,000 kg), which—when combined with the 860,000 pounds (390,000 kg) of liftoff thrust afforded by the Atlas V’s own RD-180 engine—will produce a total thrust at liftoff of close to 2 million pounds (900,000 kg).