Minotaur IV debuts from the Cape with ORS-5 launch

by William Graham

Orbital ATK’s Minotaur rocket made its first launch from Cape Canaveral Friday, delivering the experimental space surveillance ORS-5 satellite to orbit. The Minotaur IV vehicle lifted off deep into a four-hour window with a T-0 of 02:04 Eastern (06:04 UTC) from Launch Complex-46 (LC-46).

Minotaur Launch:

The launch marked the first time that Orbital ATK – or its predecessor Orbital Sciences Corporation – has conducted a vertical launch from Cape Canaveral, although the company has previously deployed its air-launched Pegasus rocket from the runways of both the Cape Canaveral Air Force Station and the Shuttle Landing Facility at the nearby Kennedy Space Center.

The launch delivered the 140-kilogram (310-pound) ORS-5 satellite into a 600-kilometre (373-mile, 324-nautical-mile) orbit above Earth’s equator. Also known as SensorSat, the ORS-5 spacecraft will be used for a mission termed space situational awareness (SSA) or space surveillance – monitoring other satellites in orbit.

From its equatorial orbit, ORS-5 will use an optical imaging system to watch satellites in geostationary orbit high above it: detecting activity such as spacecraft being relocated, identifying debris and providing early warning of possible collisions.

The geostationary belt is home to a large number of spacecraft, including most of the world’s communications satellites, as the orbit allows a spacecraft to remain in the same position relative to the Earth’s surface indefinitely. From its lower vantage point, ORS-5 will orbit the Earth approximately once every seventy minutes, scanning the entire geostationary belt as it does so.

The ORS-5 satellite was built by the Lincoln Laboratory at the Massachusetts Institute of Technology, while the mission is a partnership between the US Department of Defense’s Operationally Responsive Space (ORS) office and the US Air Force.

The spacecraft is expected to serve two purposes: demonstrating technology and mitigating risks for future space surveillance platforms, while providing interim monitoring of geostationary satellites until these platforms can be made operational.

ORS-5 follows on from the Space-Based Space Surveillance (SBSS) satellite, or USA-216, which was deployed by a Minotaur IV in September 2010. Launched into a near-polar sun-synchronous orbit from Vandenberg Air Force Base, SBSS is approaching the end of its seven-year design life. A dedicated replacement mission is still at least four years away.

A 23.6-million-dollar contract to deliver SensorSat into orbit via a Minotaur IV rocket was awarded to Orbital ATK in 2015. Orbital’s Minotaur product line consists of rockets adapted from decommissioned intercontinental ballistic missiles (ICBMs).

The series included two separate families of missile-derived rockets, with the smaller Minotaur I and II based on the Minuteman II missile – while the larger Minotaur IV and V, as well as the unflown Minotaur III and VI designs, are based on the Peacekeeper missile.

As they use former military hardware, Minotaur rockets are only permitted to be used for US Government missions. Since 2014, Orbital ATK has also marketed its commercial ground-launched rocket, which was formerly named Taurus, as the Minotaur-C. It is expected to make its first flight under this guise, which also includes upgraded avionics, in mid-October.

The launch used a modified five-stage version of the Minotaur IV rocket. A standard Minotaur IV consists of the first three stages of a Peacekeeper missile, topped with an Orion-38 solid rocket motor as a fourth stage to insert the rocket’s payload into orbit.

The launch added an extra Orion-38 as a fifth stage, used to change the inclination of the vehicle’s trajectory, allowing it to deploy ORS-5 into an equatorial orbit. In this configuration, Minotaur IV uses only solid propellant.

Despite Cape Canaveral’s long history, no all-solid rocket had ever reached orbit from Florida’s Space Coast, except for the air-launched Pegasus. The only previous orbital launch attempt from the Cape to use a ground-launched rocket with only solid propulsion was made in November 1961.

A Blue Scout II rocket lifted off from Launch Complex 18B in an attempt to place NASA’s Mercury Network Test Vehicle (MNTV), also known as Mercury-Scout, into low Earth orbit. Intended to test NASA’s network of tracking stations and ships ahead of manned Mercury missions, MNTV was lost when the rocket went out of control shortly after launch, and was destroyed by range safety after less than a minute of flight.

The ORS-5 launch marked the first time a Minotaur vehicle has flown from Cape Canaveral, which was selected over Minotaur’s regular East coast launch site – the Mid-Atlantic Regional Spaceport (MARS) on Wallops Island, Virginia – due to the zero-inclination orbit to which the payload needs to be delivered. As Wallops Island is further North than Cape Canaveral, a greater maneuver would be required to reach the desired orbit.

To facilitate the launch, Orbital ATK reactivated the Cape Canaveral Air Force Station’s long-dormant Space Launch Complex 46 (SLC-46). Located at the Cape’s most easterly point, SLC-46 is one of Cape Canaveral’s youngest launch complexes, but has not supported a launch for over eighteen years.

The facility was built at Launch Complex 46 (LC-46) in the 1980s to support testing of the US Navy’s Trident II submarine-launched ballistic missile (SLBM). Trident II was the last missile to be tested at Cape Canaveral, making nineteen development launches from LC-46 between January 1987 and January 1989. Subsequent Trident launches were made from submarines.

In the 1990s, SLC-46 became the focus of Florida’s effort to establish a commercial spaceport. Under the Spaceport Florida initiative, a new launch pedestal and tower were constructed at the pad to support small rockets using mostly solid propulsion.

Lockheed Martin used the launch complex for two flights of its Athena rocket, the first in January 1998 with NASA’s Lunar Prospector spacecraft aboard an Athena II. The second orbital launch from the complex occurred a year later, with an Athena I delivering ROCSAT-1 – later named Formosat-1 – to orbit for the Republic of China’s National Space Programme Office (NSPO).

Complex 46 is still managed by Space Florida, the successor to the Spaceport Florida Authority, as part of a commercial Cape Canaveral Spaceport.

Friday’s mission was the third orbital launch from SLC-46, and the twenty-second from the complex overall. It was the sixth flight, and fourth orbital launch, of the Minotaur IV, which has previously flown from Vandenberg Air Force Base in California and the Kodiak Launch Complex in Alaska.

Minotaur IV makes use of SR-118, SR-119 and SR-120 stages which were respectively developed by Thiokol, Aerojet and Hercules Incorporated for the LGM-118 Peacekeeper missile. First flown in 1983, the Peacekeeper was deployed from 1986 to 2005, with a peak deployment of fifty missiles. Peacekeeper was retired in 2005 under the terms of the START-II disarmament treaty.

The Minotaur launch began with ignition of the rocket’s SR-118 first stage at the zero mark in the countdown. Climbing rapidly away from Florida’s Space Coast, the Minotaur passed through the area of maximum dynamic pressure, or Max-Q, thirty-six seconds after liftoff at an altitude of 10 kilometers (6 miles, 5 nautical miles). Shortly afterwards, the rocket’s velocity reached Mach 1 and the rocket went transonic.

The first stage burned for fifty-six seconds before separating. The second stage – an SR-119 – ignited and burned for fifty-seven seconds, separating about eleven seconds after burnout. The third stage, an SR-120, ignited at staging to begin its seventy-three second burn. Nineteen seconds after the third stage ignites, with the rocket at an altitude of 130 kilometers (81 miles, 71 nautical miles), Minotaur’s payload fairing separated from the nose of the rocket.

After third stage burnout, the launch entered a coast phase as the vehicle ascends towards the apogee, or highest point, of its trajectory. Ten minutes and twenty-seven seconds into the coast, the spent third stage was jettisoned, with the fourth stage igniting eleven seconds later at thirteen minutes, 55 seconds mission elapsed time. The Orion-38 fourth stage burned for a minute and seven seconds, injecting ORS-5 into an initial parking orbit.

While in this orbit, three CubeSats separated from the rocket. One of these spacecraft is a three-unit CubeSat which will be operated by the Defense Advanced Research Projects Agency (DARPA), while the identity and operator of the other two satellites has not been disclosed. The three satellites deployed 120, 150 and 180 seconds after the end of the fourth stage burn.

In order to perform the plane change maneuver necessary to reach equatorial orbit, the fifth stage burn occurred as Minotaur crosses the equator. Following a ten-minute, six-second coast the rocket’s fourth and fifth stages separated, with fifth stage ignition coming eleven seconds later. The fifth stage burn, the last phase of powered flight, lasted sixty-nine seconds. Two minutes later, the ORS-5 satellite was released into orbit to begin its mission.

The target orbit for the launch was a near-circular equatorial low Earth orbit, 600 kilometers (373 miles, 324 nautical miles) in altitude with zero degrees inclination. About five minutes after spacecraft separation the guidance and control assembly, attached to the rocket’ fifth stage, vented any remaining gas for its reaction control system (RCS).

Minotaur’s mission was complete thirty-six minutes and 48 seconds after liftoff.

The launch was the first flight of a Minotaur IV since September 2011, although the closely-related Minotaur V was used in 2013 to deploy NASA’s Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft. It is unclear when Minotaur IV will next fly, however the Minuteman-derived Minotaur I is scheduled to launch a satellite for the National Reconnaissance Office next year, while Minotaur-C – formerly Taurus – will deploy six satellites for SkyBox Imaging in October.

The SkyBox launch is one of two which Orbital ATK plan to conduct between now and the end of 2017 – the other being November’s OA-8 resupply mission to the International Space Station, using a Cygnus spacecraft boosted by an Antares rocket.

(Images via Orbital ATK).

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