With just two weeks remaining before its second Antares rocket is due to roar away from Pad 0A at the Mid-Atlantic Regional Spaceport (MARS) on Wallops Island, Va., Orbital Sciences Corp. plans to launch the first Minotaur V booster from neighboring Pad 0B at 11:27 p.m. EDT Friday, 6 September. The mission will send NASA’s Lunar Atmosphere and Dust Environment Explorer (LADEE) on an expedition to observe the Moon’s thin atmosphere and dust environment in unprecedented depth. LADEE marks Orbital’s first launch of a deep-space mission from the MARS site and the 24th flight by a Minotaur since the rocket family’s maiden voyage back in January 2000.
Led by NASA’s Ames Research Center of Moffett Field, Calif., together with the Goddard Space Flight Center of Greenbelt, Md., the $280 million LADEE mission will be placed into a near-circular equatorial orbit with a final “Science Phase” altitude of 31-93 miles above the Moon. The spacecraft will utilize a Lunar Dust EXperiment (LDEX), a Neutral Mass Spectrometer (NMS), and an Ultraviolet-Visible Spectrometer (UVS) to determine the density and composition of the Moon’s atmosphere, as well as helping to determine if observations by Apollo astronauts of diffuse, high-altitude emissions were due to “sodium glow” or dust and documenting the dust-impactor environment to guide plans for future missions.
“The Moon’s tenuous atmosphere may be more common in the Solar System than we thought,” said former astronaut John Grunsfeld, now NASA’s associate administrator for science in Washington, D.C. “Further understanding of the Moon’s atmosphere may also help us better understand our diverse Solar System and its evolution.”
NASA-Ames has overall responsibility for the operation of the LADEE spacecraft, whilst NASA-Goddard carries oversight of the scientific sensors and technology payloads. The latter includes an experimental laser communications (or “lasercom”) terminal, known as the Lunar Laser Com Demo (LLCD), which will transmit and receive data as pulses of light from three ground stations. The 844-pound spacecraft measures 7.7 feet tall by 4.7 feet wide by 4.7 feet deep and will be powered by 30 panels of silicon cells on its exterior faces, together with a lithium-ion battery pack.
LADEE completed the bulk of its pre-launch checkout earlier this year, with final thermal vacuum chamber tests conducted at NASA-Ames in April. The spacecraft was delivered to Wallops for final processing in early June. Encapsulated within its 7.7-foot-wide payload fairing, the spacecraft was stacked atop the Minotaur V on 27 August.
Although this will be the 24th mission by a member of the Minotaur rocket family—which first flew in its Minotaur I configuration from Vandenberg Air Force Base, Calif., back in January 2000, lofting the Joint Air Force-Weber State University Satellite (JAWSAT) into low-Earth orbit—Friday’s flight will be the first by the uprated Minotaur V. The new vehicle is described by Orbital Sciences as “a five-stage evolutionary version of the Minotaur IV.” The Minotaur IV has itself completed five flights between April 2010 and September 2011, staged from Vandenberg and from Kodiak Island, Alaska.
The Minotaur V stands 80.5 feet tall and its five stages are all solid-fueled. Its lower three stages are all former motors from the Peacekeeper missile family, with a launch record of over 50 missions apiece, whilst the upper two stages are commercial Star motors. “The Minotaur V concept leverages Orbital’s flight-proven heritage of the Minotaur family of launch vehicles to create a low-risk, readily-developed system,” noted Orbital’s Minotaur V fact sheet. “The Minotaur V avionics, structures, and fairing are common with the Minotaur IV, with relatively minor changes to create the five-stage configuration. Moreover, the avionics and flight software are highly common across all Minotaur launch vehicles.”
Liftoff on Friday will occur from Pad 0B, which will be hosting the fifth launch in its history. Since it was declared operational in 1999 and received a mobile service tower following a lengthy period of modification in 2004, it supported a Minotaur I mission in December 2006 to insert the U.S. Air Force’s TacSat-2 experimental payload and the NASA/academia-developed GeneSat-1 microsatellite into orbit. The pad was subsequently utilized for three further Minotaur I launches in April 2007, May 2009, and June 2011. These missions lofted the Missile Defense Agency’s Near Infrared Field Experiment (NFIRE), the Air Force’s TacSat-3 technology reconnaissance satellite, and the Operationally Responsive Space (ORS)-1 satellite—subsequently renamed USA-231—for the Department of Defense’s Operationally Responsive Space Office.
At the instant of liftoff, the Minotaur V’s SR-18 first-stage engine will ignite, generating a propulsive yield of 361,000 pounds and pushing the vehicle uphill for the first 85 seconds of the mission. Upon its exhaustion and separation, the second stage’s SR-19 engine, with 307,000 pounds of thrust, will pick up the baton for the next phase of ascent. After its 54-second burn is complete, the turn will come of the third stage, whose SR-20 engine will produce 74,000 pounds and fire for 62 seconds. Shortly after the ignition of the third stage—and by now having reached an altitude of about 77 miles—the payload fairing which encapsulates LADEE will be jettisoned, directly exposing the spacecraft to the harsh space environment for the first time.
Three and a half minutes after launch, the third stage will shut down and separate from the vehicle, leaving the Star-48V engine of the fourth stage to continue the mission. This motor will burn with 14,000 pounds of thrust for 84.8 seconds, delivering LADEE into low-Earth orbit, after which the spin-stabilized Star-37FM engine of the final stage will fire with 10,620 pounds for an additional 63.5 seconds. At length, some 23 minutes and 45 seconds after leaving Wallops Island, the LADEE spacecraft will separate from the vehicle.
“All of LADEE’s mission events, except the lunar gravitational capture, are made using the propulsion system to maneuver the spacecraft,” explained NASA’s LADEE mission press kit. “The Minotaur V launch vehicle will execute a Phasing Orbit Insertion burn to place LADEE on the first phasing loop; however, all maneuvers after that will be done using LADEE’s on-board bi-propellant propulsion system. The first phasing orbit maneuver is scheduled to occur approximately six days after launch. The LADEE spacecraft will orbit Earth three times in a highly elliptical orbit, making trajectory corrections on each pass, if necessary. On the final phasing loop orbit, LADEE’s on-board propulsion subsystem will add enough energy to the orbit until the Moon’s gravity can take over and LADEE begins its approach trajectory to the Moon.”
The spacecraft will coast to our closest celestial neighbor, rotating slowly about its longitudinal axis, which will be oriented toward ecliptic-North, almost perpendicular to both the Sun and the Earth. Upon arrival at the Moon in early October, LADEE will execute a three-minute Lunar Orbit Insertion (LOI) maneuver, which will inject it into an elliptical retrograde equatorial orbit, with a period of about 24 hours. This will be steadily reduced to an almost-circular path at an altitude of 156 miles, selected due to its suitability for communications visibility to Earth during the “maneuvering phase” and to minimize the need for further maneuvers during LADEE’s Commissioning Phase.
About 30 days into the mission—on or around 6 October, assuming an on-time launch—the spacecraft will begin the 40-day Commissioning Phase, during which LADEE’s scientific instruments and the LLCD technology demonstrator will be checked out. In the final few days of this phase, the spacecraft will steadily lower its orbit, initially to about 46.6 miles, and eventually into the Science Phase orbit of between 31-93 miles.
“Due to the unevenness of the Moon’s gravitational field,” noted NASA’s press kit, “the orbit requires significant orbit maintenance activity with maneuvers taking place as often as every 3-5 days or as infrequently as once every two weeks. Orbit Maintenance Maneuvers will be used to keep LADEE’s lowest altitude above 31 miles and highest altitude below 93 miles to the extent possible.” During the 100-day Science Phase, the Moon will rotate more than three times under the spacecraft’s orbit.
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