USAF Boeing X-37B Helps Ensure Leadership in Space Technology

The US Air Force will launch the fourth unmanned mission of its dedicated space plane,the Boeing X-37B,on a United Launch Alliance Atlas V rocket from Cape Canaveral Air Force Station on 20 May 2015.The mission,known as OTV-4,or Orbital Test Vehicle-4,will be focused on the testing of experimental payloads,says Randy Walden,director of the USAF Rapid Capabilities Office.The RCO will test an experimental propulsion system developed by the Air Force Research Laboratory and Space and Missile Systems Center,among other experiments.A NASA advanced materials investigation is also on the docket.No other experiments have been disclosed.
We're very pleased with the experiments lined up for our fourth OTV mission,Mr.Walden said.We'll continue to evaluate improvements to the space vehicle's performance,but we're honoured to host these collaborative experiments that will help advance space technology.*
The Air Force has two of the vehicles,which are 8.8 meters/29 ft. long.One of the OTVs flew missions 1 and 3;the other flew mission 3.The last mission,OTV-3,lasted nearly two years at 674 days in orbit,landing on 14 October 2014.OTV-1 launched in April 2010 and lasted 225 days;OTV-2 blasted off in March 2011 and lasted 469 days.The duration of the OTV-4 mission wasn't released.*
The X-37B began as a NASA project in 1999,but was transferred to the USAF in 2004.The spacecraft was based on the aerodynamic design of the space shuttle.Indeed,it was originally intended to be launched from the shuttle's cargo bay,but was converted to an independent launch format when that was deemed too costly.Originating in Boeing's Phantom Works,it became a classified project of the Defense Advanced Research Projects Agency and part of the Department of Defense's independent space policy after the 1986 explosion of the space shuttle Challenger.The program is concerned with risk reduction,experimentation and operational concept development for reusable space technologies in support of long-term developmental space objectives.*
The X-37B has been landing at Vandenburg Air Force Base,California,with Edwards Air Force Base,California as an alternate site.By the end of 2014,the OTVs were to be housed in the former space shuttle hangars at Kennedy Space Center,OPF-1 and OPF-2,following the hangars' renovation.The spacecraft is the world's smallest orbital space plane,one-fourth the size of the space shuttle.It is powered by one Aerojet Rocketdyne human-rated AR2-3 engine.Flying an orbit of the same altitude as reconnaissance satellites and the International Space Station at 410 kilometers/255 miles,it is a crucial exponent of the Air Force's space doctrine that space is vitally important to everything it does,be it secure communications;intelligence,search and rescue;missile warning;weather prediction;or precision navigation and timing,all of which rely on space,a domain that is increasingly contested.*
One of the main experiments on OTV-4 will test the Hall effect thruster in support of the Advanced High Frequency Communications Satellite program.The AEHF satellites are nuclear-hardened and cost one billion dollars each.They are designed to ensure the continuity of military communications in the most drastic wartime scenarios.Three AEHFs have been deployed,with three more planned.
The Hall effect thruster experiment involves collection of telemetry from the thruster operating in the space environment,as well as measurement of the thrust imported on the vehicle.The data will be used to validate and improve Hall thruster and environmental modeling capabilities,which will enhance the ability to extrapolate ground test results to actual in-orbit performance,the Air Force said.A more efficient on-orbit thruster capability is highly significant.Less fuel burn lowers the cost to put a satellite in orbit,as well as enhances a spacecraft's operational flexibility,survivability and longevity.
The Hall thruster is a 4.5 kilowatt unit that uses electricity and xenon to produce thrust for maneuvering satellites.It produces whisper-like thrust by ionising and accelerating xenon gas.Xenon fuel weighs just a fraction of conventional hydrazine fuel,but takes longer to utilise.It is an electric propulsion system that needs very long periods of time to harness for orbital maneuvering.That may explain why the OTV-3 mission lasted almost two years.*
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