Orbital Sciences Corp. has successfully launched its first Minotaur V rocket from Pad 0B at the Mid-Atlantic Regional Spaceport (MARS) on Wallops Island, Va., carrying NASA’s Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft on a multi-month journey to explore the mysteries of the Moon. Liftoff of the five-stage Minotaur—which represents a marriage of the lower three stages of the Peacekeeper missile, topped by the Star-48V motor of the fourth stage and a spin-stabilized Star-37FM of the fifth—occurred precisely on time at 11:27 p.m. EDT Friday, 6 September. Separation of LADEE in orbit was confirmed by NASA at 11:50 p.m., and the spacecraft will now execute a series of “phasing loops” to reach the vicinity of the Moon in early October.
The final days leading up to this mission have proceeded without incident, and on Wednesday the gantry at Pad 0B was rolled back to expose the giant Minotaur V. Last night offered virtually perfect conditions for liftoff on the Wallops stretch of the Virginia coast, with weather classified as “Green” throughout the final minutes and no technical issues being tracked by either the Launch Vehicle (LV) or Spacecraft (SC) teams. At 11:15 p.m., the Minotaur’s flight computer was loaded with the T-0 liftoff time and the Flight Termination System (FTS)—which would destroy the vehicle in the event of a dire, off-nominal situation—was armed and transferred to internal power. Shortly afterwards, final weather checks were made, and at T-2 minutes the Launch Computer assumed primary control of the countdown, producing a picture-perfect, on-time liftoff.
The Minotaur V’s SR-118 first-stage engine was responsible for the start of a fast climb away from Pad 0B at the MARS site, which supported its fifth total launch by a member of the Minotaur rocket family. Since Pad 0B was declared operational in 1999, and received a mobile service tower following lengthy modifications 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 later used for three further Minotaur I launches in April 2007, May 2009, and June 2011. These lofted the Missile Defense Agency’s Near Infrared Field Experiment (NFIRE), the Air Force’s TacSat-3 technology reconnaissance payload, and the Operationally Responsive Space (ORS)-1 satellite—subsequently named USA-231—for the Department of Defense’s Operationally Responsive Space Office.
As noted by Spaceflight101, the SR-118 burned for almost a minute and achieved an altitude of about 14 miles, after which the SR-119 second stage engine ignited to continue the climb uphill. This engine also fired for around a minute and, upon exhaustion, was separated and replaced by the burn of the SR-120 third stage. Whilst it was burning, the payload fairing was jettisoned to expose the LADEE spacecraft to the harsh space environment, and the separation of the third stage—the final component of the vehicle to originate from Peacekeeper missile hardware—was confirmed at 11:31 p.m. The Minotaur/LADEE combo then “coasted,” with the deactivation of the FTS and activation of the Tracking and Data Relay Satellite (TDRS) transmitter, ahead of the ignition of the Star-48V-powered fourth stage at 11:34 p.m.
Within minutes, tracking passed from the Bermuda ground station to the geosynchronous-orbiting TDRS network of NASA communications and relay satellites. The fourth stage separated at 11:41 p.m. and the fifth stage—propelled by the Star-37FM motor—ignited at 11:44 p.m., spinning LADEE up to 60 revolutions per minute for stabilization and insertion into Lunar Transfer Orbit (LTO). By this point, as reported by NASASpaceflight.com, the Minotaur V/LADEE combo had reached an altitude well in excess of 125 miles and were traveling at an estimated 6.5 miles per second. Following the burnout of the fifth stage, a “Yo-Yo” system despun the payload, ahead of LADEE’s separation, which was confirmed by NASA at 11:50 p.m. By now, the spacecraft had reached an altitude of about 380 miles. Initial communications checks and, as described by Spaceflight101, the separation event was monitored through TDRS, and initial LADEE communications acquisition occurred through the Hartebeesthoek ground station in South Africa.
At present, the spacecraft resides in a highly-elliptical Earth orbit, with an apogee of about 50 Earth-radii, and will be gradually maneuvered to lunar distance through a series of three propellant-saving “phasing loops” over the next three weeks. On Thursday, 12 September, LADEE should complete the first (or “A1”) loop, after which the spacecraft will ignite its main engine to increase its velocity and modify its apogee. The next stage will be the eight-day-long A2 loop, after which the final ten-day A3 loop will create an apogee condition of slightly greater than lunar distance. Coupled with propulsive maneuvering burns, this will enable the Moon’s gravity to capture LADEE.
“All of LADEE’s mission events, except the lunar gravitational capture, are made using the propulsion system to maneuver the spacecraft,” explained NASA’s 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 thus 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, 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.
The spacecraft’s arrival, on about 6 October, is expected to herald a period of several months spent studying the thin atmosphere and dust environment of our closest celestial neighbor in unrivaled depth. 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, while 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 last night’s launch was the 24th total mission by a member of the Minotaur rocket family—which first flew in the 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—the LADEE flight was the first by the uprated Minotaur V. The new vehicle has been described by Orbital Sciences as “a five-stage evolutionary version of the Minotaur IV,” which has completed five flights between April 2010 and September 2011, staged from Vandenberg and from Kodiak Island, Alaska.
All five of the Minotaur V’s stages are 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.”