United Launch Alliance (ULA) stands ready to conduct its third mission in as many months on the night of Thursday, 12 March, when it flies an Atlas V booster out of Cape Canaveral Air Force Station, Fla., to deliver the four-spacecraft flotilla of NASA’s Magnetospheric Multiscale Mission (MMS) into a Highly Elliptical Orbit (HEO) to investigate the microphysics of “magnetic reconnection,” a process which converts magnetic field energy into heat and kinetic energy, as well as examining energetic particle acceleration and turbulence, which are known to occur in many astrophysical plasmas. Liftoff of the Atlas V is scheduled to take place from the Cape’s storied Space Launch Complex (SLC)-41, during a 30-minute “window” which extends from 10:44 p.m. until 11:14 p.m. EDT. Current weather predictions anticipate a 70 percent likelihood of acceptable conditions for Thursday, with conditions worsening to just 60 percent favorable in the event of a 24-hour scrub to Friday.
This mission will mark only the fourth flight of the Atlas V’s “421” configuration, equipped with a 13-foot-diameter (4-meter) payload fairing, two strap-on solid-fueled boosters, and a single-engine Centaur upper stage. Capable of delivering up to 31,012 pounds (14,067 kg) into low-Earth orbit and up to 15,190 pounds (6,890 kg) to geostationary transfer orbit, the 421 was previously used to launch the inaugural Wideband Global Satcom (WGS-1) in October 2007, followed by the 14,625-pound (6,634-kg) ICO G-1—which was, at the time, the largest commercial communications satellite ever flown—in April 2008 and, most recently, WGS-2 in April 2009. Although flown relatively sparingly, it remains possible that up to two more 421 missions may take place in 2015, with Mexico’s MexSat-2 satellite expected to ride one of these beasts out of Cape Canaveral Air Force Station in October and, perhaps, the National Reconnaissance Office’s NROL-55 doing likewise out of Vandenberg Air Force Base, Calif., in August.
Thursday night’s launch will get underway at T-2.7 seconds, with the ignition of the Atlas’ Russian-built RD-180 first-stage engine, which burns liquid oxygen and a highly refined form of rocket-grade kerosene, known as “RP-1,” and generates 860,000 pounds (390,000 kg) of thrust. The two Aerojet-built solid-fueled boosters, each measuring 67 feet (20.4 meters) tall, will also ignite and produce a combined thrust of almost 700,000 pounds (316,000 kg) to supplement the boost away from SLC-41. Climb-out of the 195-feet-tall (59.4-meter) Atlas V 421 will commence at T+1.1 seconds, beginning an apparently slow ascent to about 85 feet (25.9 meters), after which the avionics of the Centaur upper stage will command a pitch, roll, and yaw program maneuver to establish the vehicle onto the proper flight azimuth of 99.0 degrees, in order to deliver the MMS quartet into orbit.
Sixty-two seconds into the flight, the Atlas V will pass through a period of maximum aerodynamic turbulence, colloquially known as “Max Q,” and will throttle down its RD-180 engine and begin a nominal zero-pitch and zero-yaw angle of attack to minimize these loads. At T+138.6 seconds, the two strap-on boosters, now exhausted of their fuel, will be jettisoned, and the RD-180 will continue to burn hot and hard for almost another two minutes. When the vehicle reaches a peak load of 4.6 G, the RD-180 will be throttled back to maintain this level.
Booster Engine Cutoff (BECO) is timed to occur at T+249.7 seconds and will be followed, six seconds later, by the separation of the 41.5-feet-long (12.6-meter) Centaur and the attached MMS payload from the spent first stage. To support the delivery of the four satellites into their correct orbital “slot,” the Centaur will execute two lengthy firings of its 22,300-pound-thrust (10,100 kg) RL-10A engine. The initial burn will get underway at T+265.7 seconds and will run for more than nine minutes, terminating at about 13 minutes and 29 seconds into the mission. A few seconds after the burn begins, the two-piece (or “bisector”) Extra Extended Payload Fairing (XEPF)—which, at 45.9 feet (14 meters) long, is the largest of three 13-foot-diameter (4-meter) payload fairing types utilized by the Atlas V—will be discarded. After the conclusion of the first Centaur burn, the stack will drift for almost an hour, before the second burn gets underway about 72 minutes after launch. This firing will run for just under six full minutes, with the RL-10A shutting down and falling silent for the last time at T+78 minutes and 11.3 seconds. The stage will thus be set to deploy the four-strong MMS stack into a Highly Elliptical Orbit (HEO) with an apogee of about 43,600 miles (70,165 km) and a perigee of 364 miles (585 km), inclined 28.77 degrees to the equator, with each spacecraft departing the Centaur at five-minute intervals from about 92 minutes to about 107 minutes after launch. The highly elliptical orbital path will send the MMS flotilla “upstream” toward the Sun, then “downstream,” away from the Sun, in order to better study the processes of the magnetic reconnection phenomenon.
The MMS mission was selected for support by NASA more than a decade ago, tasked with studying the process of “magnetic reconnection” and observing the three-dimensional structure of this Universe-wide ubiquitous phenomenon by flying through areas where the Sun’s and Earth’s magnetic fields connect and disconnect in an explosive transfer of energy. “Magnetic reconnection is a universal that happens when magnetic fields in two adjacent regions of space interconnect across their boundary, converting magnetic energy into heat and high-energy charged particles,” explained ULA in its MMS press kit. “This process lies at the heart of giant explosions on the Sun, such as solar flares and Coronal Mass Ejections, which can fling radiation and particles across the Solar System. Because it’s so difficult to see this process on the Sun, and it’s also a difficult process to recreate and study in the lab, researchers plan to take a closer look at magnetic reconnection in space.”
Two proposals for scientific instruments were submitted in March 2003, in response to NASA’s MMS Announcement of Opportunity, both of which were selected the following September to conduct a six-month implementation-feasibility study, focused on cost, management, and technical planning, as well as educational outreach and small business involvement. The two proposals were led by Dr. James P. McFadden of the University of California at Berkeley and Dr. James L. Burch of Southwest Research Institute (SwRI) in San Antonio, Texas. At length, in May 2005, the SwRI team was selected and assigned responsibility for formulating a $140 million suite of instruments for MMS. A year later, in May 2006, NASA’s Goddard Space Flight Center in Greenbelt, Md., was selected to manage the development of the four spacecraft. By this stage, launch was anticipated in 2013, with the likelihood that MMS would ride aboard a Delta II booster.
The already well-baselined mission would “employ four identically instrumented spacecraft to make co-ordinated high-resolution observations of fundamental plasma physical processes in the Earth’s magnetosphere.” All four would fly in a tetrahedron-like formation. The mission’s highly inclined orbit was optimized to spent long periods within the “magnetopause,” where pressure from the solar wind and our planet’s magnetic fields meet in balance, and the “magnetotail,” which is formed by pressure from the solar wind on the magnetosphere. “MMS results will directly contribute to understanding the Sun and its effects on Earth, the Solar System and the space environment human explorers will experience,” said NASA’s then-Deputy Associate Administrator for the Science Mission Directorate (SMD), Dr. Ghassem R. Asrar. “Because the Earth’s magnetosphere is the only accessible laboratory we have in which to study this fundamental astrophysical process, what we learn from MMS will also have broad application to our studies of the Universe.”
Moving swiftly, the mission passed its Preliminary Design Review (PDR) in mid-2009 and its Critical Design Review (CDR) in March 2010, the latter of which enabled the teams to press ahead with the fabrication of flight hardware. By this point, the launch date had been realigned to no sooner than August 2014 and the choice of booster had shifted to ULA’s Atlas V. Each of the four octagonal MMS spacecraft weighs about 2,750 pounds (1,250 kg) and measures about 4 feet (1.2 meters) tall and about 12 feet (3.6 meters) in diameter. Each carries four 200-feet-long (60-meter) wire booms in the spin plane and two 41-feet-long (12.5-meter) booms in the axial plane for its electric field sensors, as well as a pair of 16-feet-long (5-meter) spin-plane booms for its magnetometers. A monopropellant attitude-control system will utilize 12 thrusters to achieve small-formation maintenance—keeping the spacecraft within plus or minus 0.5 degrees of the desired orientation during science operations—and larger apogee-raising maneuvers, whilst electrical power will be provided by eight body-mounted solar panels on each of the spacecraft’s faces.
In addition to its role in the environmental testing of the spacecraft, as well as supporting integration with the Atlas V and the development of the MMS Mission Operations Center, NASA-Goddard also built the Fast Plasma Investigation (FPI) research instrument. Tasked with operating 100 times faster than any previous similar instrument, the FPI will collect a full-sky map of data at the rate of 30 times per second, measuring plasma concentrations with four dual electron and four dual ion spectrometers to create three-dimensional images of the plasma and capture as much detail as possible during its second-long journey through the magnetic reconnection “site.” In addition to the FPI, each spacecraft carries instrumentation for the analysis of hot plasma composition and fields and energetic particles.
The four spacecraft were assembled and integrated inside a 4,200-square-foot (390-square-meter) clean room at NASA-Goddard, which actually represents the center’s second-largest such facility. “The biggest requirement was space,” explained NASA-Goddard contractor Scott Clough, speaking in early 2012. “The MMS mission needed a single location from which to assemble the four spacecraft. If we hadn’t found a suitable location, the mission would have had to use four different locations, requiring technicians to move equipment around. This would have slowed down spacecraft assembly. With one large space, we were able to save money and time.” By mid-2012, integration of the 25 sensors for the scientific instrument “decks” for the four spacecraft had gotten underway. “This is the first time NASA has ever built four satellites, near-simultaneously, like this,” said NASA-Goddard’s MMS Project Manager, Craig Tooley. “It feels like we’re planning a giant game of musical chairs to produce multiple copies of a spacecraft. One instrument deck might be two-third finished, while another one is one-third finished, and the same people will have to test a nearly complete deck one day and install large components on another one another day.” In late-August 2012, the mission passed its Systems Integration Review (SIR), which paved the way for the scientific instruments to be installed aboard the spacecraft.
Despite the technical challenges of assembling four spacecraft at the same time, by January 2013 the NASA-Goddard team seemed to have hit their stride. To streamline the process, an architecture was developed, whereby all MMS spacecraft components were mounted onto a single deck and the scientific instruments were attached to a separate deck. The two decks were affixed to a common center structure, known as the “thrust tube,” which allowed the spacecraft and instruments to be separately integrated and tested in parallel, prior to final assembly. Lessons learned in the integration of the first MMS spacecraft significantly reduced the amount of time needed for its three siblings. By the end of May 2013, the fourth and final spacecraft had been fully integrated, with launch scheduled for the fall of the following year.
Environmental evaluations followed throughout the summer months, including evaluations to ascertain their ability to withstand the shock of liftoff, as well as acoustic, thermal, electrical, and vibration tests. By April 2014, the four spacecraft had been lifted by a large overhead crane and stacked, one atop the other, and transported for vibration tests as an integrated payload, and in late-October and mid-November they were transported in separate pairs to Florida and ensconced in Astrotech Space Operations’ facility for final pre-launch preparations. Over the course of the next several weeks, Astrotech engineers undertook final testing, fueling, stacking, and removal of protective covers from the spacecraft sensors, prior to integration with the XEPF fairing of the Atlas V. As described in a recent article by AmericaSpace’s Mike Killian, the four MMS spacecraft were encapsulated within the XEPF on 23 February, ahead of rollout to SLC-41 a few days later and stacking atop the Atlas V last week.
Weather conditions for Thursday night’s opening launch attempt are currently expected to be around 70 percent favorable, according to the 45th Space Wing at Patrick Air Force Base. Rollout of the Atlas V 421 stack atop its Mobile Launch Platform (MLP) from the Vertical Integration Facility (VIF) to the pad is scheduled for tomorrow (Wednesday), with a “warm, moist southerly flow” expected to “increase moisture, resulting in an isolated shower threat,” coupled with a “small threat” of a thunderstorm in the late morning and early afternoon. On Thursday, a stationary front “is expected to remain in North Florida/South Georgia with a developing low-pressure system in the Central Gulf of Mexico,” it was noted. “Upper-level moisture over Central Florida from this system increases through the evening hours. Likewise, south-easterly winds deepen and strengthen by the evening, increasing the coastal shower threat.” That said, the core concerns for a successful launch on Thursday are Cumulus Clouds and Thick Clouds, with the same conditions expected to worsen to just 60 percent favorable in the event of a 24-hour scrub to Friday evening.
After insertion into their highly elliptical orbit, the MMS quartet will assume an adjustable pyramid-like configuration, with each spacecraft spinning once every 20 seconds, as they pass directly through nearby magnetic reconnection regions to observe the minute details of this ubiquitous phenomenon, which is known to be a catalyst for space weather events, such as Coronal Mass Ejections (CMEs). In order to gather their required data during a project 2.5-year mission, the MMS satellites will employ a next-generation Global Positioning System (GPS) receiver, known as “Navigator,” to provide orbit knowledge and frequent formation-maintenance maneuvers.
Thursday’s planned launch of MMS comes on the heels of the U.S. Navy’s Mobile User Objective System (MUOS)-3 spacecraft, lofted from the Cape atop an Atlas V 551 heavylifter on 20 January, and NASA’s Soil Moisture Active Passive (SMAP) satellite, delivered to orbit by a Delta II from Vandenberg less than two weeks later, on 31 January, and forms part of ULA’s wider plan to fly as many as 13 missions during 2015. Following MMS, the Centennial, Colo.-based launch provider—which has to date scored 93 successful missions since its formation as part of a merger between Lockheed Martin and Boeing, back in December 2006—will launch a fourth MUOS, three members of the Global Positioning System (GPS) Block IIF constellation, the fourth voyage of the U.S. Air Force’s secretive X-37B Orbital Test Vehicle (OTV), a pair of classified National Reconnaissance Office (NRO) payloads, the latest member of the Wideband Global Satcom (WGS) network, the MexSat-2 communications satellite, and ULA’s first Orbital Sciences Cygnus cargo mission (ORB-4) to the International Space Station (ISS). If all goes according to plan, 2015 should see the 60th flight by an Atlas V, which embarked on its maiden voyage back in August 2002, as well as seeing ULA break through a cumulative 100 missions by its highly reliable fleet of Atlas V, Delta II, and Delta IV boosters.
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