The US Air Force’s X-37B spaceplane began its fourth mission Wednesday, lifting off atop United Launch Alliance’s Atlas V rocket to begin a classified mission for Air Force Space Command. The Atlas departed from Cape Canaveral Air Force Station at 11:05 Eastern, the opening opportunity provided by two short launch windows on Wednesday.
Atlas V AFSPC-5 Mission:
Wednesday’s mission, designated Air Force Space Command 5 (AFSPC-5), is the fourth X-37B mission and is presumed to be the second trip into space for the second X-37B vehicle.
Also known as Orbital Test Vehicle 4 (OTV-4), the mission is believed to be demonstrating technology for future programs. One of the experiments aboard the spacecraft which has been publicised by the US Air Force consists of a Hall effect thruster for the AEHF series of communications satellites, allowing performance-enhancing modifications to be tested before they are introduced on operational missions.
The X-37 is also carrying NASA’s Materials Exposure and Technology Innovation in Space, or METIS, payload; building on research conducted aboard the International Space Station, METIS will expose an array of material samples to the space environment before returning them to Earth for study.
Developed by Boeing, the X-37B is an evolution of NASA’s proposed X-37A that was designed to be deployed from the Space Shuttle to conduct robotic satellite repair and research missions before returning to Earth independently.
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The X-37A underwent a series of glide tests in 2006, however the program was subsequently cancelled. The US Air Force and Defense Advanced Research Projects Agency (DARPA) opted to continue development as a military program, with the first launch coming in April 2010 atop an Atlas V.
That first mission, OTV-1 or USA-212, lasted over seven months, ending with the successful recovery of the spacecraft via a runway landing at Vandenberg Air Force Base in California. Vandenberg has been the landing site for all X-37B missions to date and it is likely that AFSPC-5 will also touch down there once it reaches its conclusion.
Boeing constructed two X-37B vehicles, with the second taking flight in March 2011 and remaining in orbit for over a year before landing in June 2012. The third and most recent mission, marking the second flight of the first vehicle, began in December 2012 and concluded in October 2014 after almost two years in space.
In addition to deploying the X-37B, Wednesday’s launch also carried the UltraSAT payload consisting of ten small satellites for NASA, the US military and educational institutions.
Mounted on an Aft Bulkhead Carrier (ABC) attached to the rocket’s upper stage, UltraSAT is a Naval Postgraduate School CubeSat Launcher (NPSCuL) equipped with eight Poly-Pico Orbital Deployers (PPODs).
The third NPSCuL to launch, UltraSAT follows the OutSAT mission that launched with NROL-36 in 2012 and the GemSAT mission that flew with NROL-39 in 2013.
The LightSail-A satellite, a three-unit CubeSat which will be operated by The Planetary Society, is a prototype solar sail. The primary objective of the LightSail-A mission is to demonstrate deployment of the spacecraft’s sail, with a later mission – LightSail-B – intended to demonstrate the use of the sail when it launches in 2016.
The LightSail missions build on technology developed for 2005’s Cosmos 1 solar sail experiment which was lost in a launch failure of Russia’s Volna rocket.
The launch of LightSail-A has been sponsored by NASA under its Educational Launch of Nanosatellites (ELaNa) program, with the flight designation ELaNa XI. The remainder of the payloads were sponsored by the National Reconnaissance Office.
The AeroCube-8 mission, consisting of two 1.5-unit CubeSats built by The Aerospace Corporation, will test the use of carbon nanotubes in spacecraft construction and radiation protection and investigate electric propulsion technologies. Also known as IMPACT, the two satellites are identical and will be deployed together from a single PPOD.
The US Naval Academy’s Ballistically Reinforced Communication Satellite Propulsion Test Unit, or BRICSat-P, is a 1.5-unit satellite which will be used to demonstrate the use of plasma thrusters for attitude control and orbital manoeuvring. It will share a PPOD with ParkinsonSat-A (PSAT-A), also developed by the US Naval Academy, which carries a communications experiment.
Equipped with a bidirectional transponder, the satellite will collect and relay data from buoys and remote stations in support of the Ocean Data Telemetry Microsatellite Lint (ODTML) as well as acting as a relay for amateur operators.
A further payload was carried for the Naval Academy is the USS Langley, or Unix Space Server Langley. A three-unit CubeSat, Langley is intended to demonstrate the use of off-the-shelf components to operate a Linux-based web server in space. This will be connected to the internet via the satellite’s ground stations.
The Globalstar Experiment and Risk Reduction Satellite 2 (GEARRS-2) is a three-unit CubeSat intended to demonstrate whether the Globalstar satellite constellation can be used to relay commands and telemetry for a small satellite mission. It follows on from the GEARRSAT spacecraft deployed from the International Space Station in March after its launch aboard a Cygnus spacecraft last September.
Three Optical CubeSats, or OptiCubes, were also carried for the California Polytechnic University (CalPoly) to serve as tracking and calibration targets for studying small satellites and debris in orbit.
United Launch Alliance was contracted to launch the AFSPC-5 mission, using an Atlas V carrier rocket. The Atlas used for Wednesday’s launch had the tail number AV-054, and flew in the 501 configuration.
The launch was the fifty-fourth of an Atlas V overall and the sixth of the 501 configuration; consisting of a single Common Core Booster (CCB) with no solid rocket motors, a single-engine Centaur upper stage and a five-metre payload fairing. The 501’s five previous flights have carried three earlier X-37B missions and two Topaz radar imaging satellites for the National Reconnaissance Office.
The Atlas V was originally developed by Lockheed Martin as an evolution of and replacement for its Atlas II rocket; with a greater payload capacity to meet the requirements of the US Air Force’s Evolved Expendable Launch Vehicle (EELV) program.
Selected along with Boeing’s Delta IV for development, the Atlas first flew in 2002 carrying Eutelsat’s Hot Bird 6 communications satellite to orbit. Operations of the rocket were transferred to United Launch Alliance in December 2006, along with Boeing’s Delta vehicles.
Atlas V launches occur from two launch pads; Cape Canaveral’s Space Launch Complex 41 and Vandenberg Air Force Base’s Space Launch Complex 3E. Wednesday’s launch took place from SLC-41, which was originally built for the Titan IIIC rocket in the mid-1960s.
In the 1970s the pad was adapted for the Titan IIIE which sported a Centaur third stage, and served as the starting point for the Viking missions to Mars, the Voyager missions to the Outer Planets, and the Helios Solar research probes.
Later used by the Titan IV, the final Titan launch from SLC-41 occurred in April 1999 with an unsuccessful attempt to place a Defense Support Program missile detection spacecraft into geosynchronous orbit.
Following that launch the pad was levelled to make way for the Atlas V’s clean-pad approach, with a Vertical Integration Facility being erected nearby to replace the Titan Integrate-Transfer-Launch complex that had served both Complex 41 and the nearby Complex 40 during the Titan era. SLC-41 was first used by the Atlas V for its 2002 maiden flight.
Wednesday’s launch began with the ignition of AV-054’s RD-180 engine at the T-2.7 second mark in the countdown. The engine built up to full thrust, achieving launch readiness at the zero point in the countdown. Liftoff occurred about a tenth of a second later, with the thrust generated by the RD-180 exceeding the weight of the vehicle.
The RD-180 engine is manufactured by Russia’s NPO Energomash and is derived from the RD-170 series of engines developed originally for the Zenit and Energia family of rockets. A twin-chamber engine, it burns RP-1 propellant in liquid oxygen to provide thrust to the Atlas during the early stages of its mission.
The first stage, or Common Core Booster, has a single RD-180 engine and can also support up to five Aerojet AJ-60A solid rocket motors – although none of these were used for Wednesday’s flight.
Around 18.3 seconds after launch, the Atlas executed a pitch and yaw manoeuvre to attain the correct attitude for its journey to orbit, flying on an azimuth of 61 degrees.
The rocket passed through the area of maximum dynamic pressure, or Max-Q, seventy and a half seconds later at the T+88.8 second mark, experiencing peak aerodynamic forces as it accelerated through the atmosphere.
Three minutes and 38.4 seconds after lifting off, AV-054 jettisoned the payload fairing which encapsulated the X-37B for its ascent through the atmosphere.
Although the X-37 is designed to function in the atmosphere – and was at one point scheduled for launch atop a Delta II rocket without a fairing – engineers determined it would be too difficult to predict the aerodynamic properties of the unencapsulated spaceplane.
First stage powered flight ended with Booster Engine Cutoff, or BECO, at the four-minute, 23.5-second point in the mission. Six seconds later the spent first stage was separated with the Centaur beginning its prestart sequence.
The first ignition of the Centaur’s RL10C-1 engine came ten seconds after staging.
Mission events after second stage ignition have not been publicised, however the Centaur is likely to make a single burn of around fourteen minutes to reach Low Earth orbit, followed by separation of the X-37.
The Centaur will then make at least one further burn to achieve a more inclined orbit for CubeSat separation, before a final deorbit burn will cause the Centaur to reenter the atmosphere over the South Indian Ocean.
Orbital parameters for the X-37 have not been made public, however the launch azimuth suggests an inclination of approximately 39 degrees and apogee and perigee altitudes of 300 to 400 kilometres (186 to 249 miles, 162 to 216 nautical miles) would be consistent with previous flights.
A much more highly-inclined orbit has been given in documentation for some of the secondary payloads, suggesting that the Centaur will be called upon to make a significant manoeuvre – although one well within its capability once it has shed the mass of the X-37.
ULA declared mission success via a release later in the day on Wednesday.
AeroCube-8’s stated target orbit is 350 by 700 kilometres (189 by 435 miles; 217 by 378 nautical miles) at 57 degrees, while the orbit of LightSail-A is given with a perigee of 389 kilometres (242 miles or 210 nautical miles) – again with an apogee of 700 kilometres – and inclination of 58 degrees.
Wednesday’s launch was the twenty-sixth orbital launch attempt of 2015, including February’s uncatalogued Vega launch. The Atlas launch follows two back-to-back launch failures involving Russia’s Soyuz 2-1a and Proton-M rockets with the last successful launch having been SpaceX’s TurkmenÄlem launch on 27 April.
The AFSPC-5 mission was the fifth launch of the year for United Launch Alliance, and the third for the Atlas V. ULA’s next launch is scheduled for 14 July, with another Atlas V carrying the GPS IIF-10 satellite into orbit. This will be followed a week later by a Delta IV launch with the WGS-7 communications satellite for the US Air Force.
(Images via ULA and USAF).