Commercial space flight shows reignited interest in the Air Launch system
Virgin Galactic unveiled their new air launch system – called LauncherOne – this week, classing it as a “revolution” in space access for small satellites. However, the concept of carrying one’s rocket to a high altitude, prior to “dropping” the vehicle and lighting its engine, isn’t new, yet appears to be gaining renewed interest – with LauncherOne announced just half a year after another air-launcher, Stratolaunch, was revealed to the public.
Playing on the fundamental advantages air launching, such a concept offers a way of avoiding the earliest part of a launch vehicle’s flight regime, where a rocket suffers significant performance degradation.
A presentation into the concept (available on L2 – LINK) notes that by the time the Space Shuttle had reached the conditions of an air launch system, it had already burned 25 percent of its propellent, yet it had only added 0.16 percent to its required kinetic energy.
This provides the example of the problem normal launch vehicles have to struggle with when leaving the ground, fighting against Earth’s gravity for the most part, in addition to atmospheric drag losses. The main losses are incurred during the first 10 km of ascent.
“Gravity loss: At launch, ~80 percent of the rocket thrust is simply counteracting gravity rather than accelerating the vehicle,” the presentation noted by way of facts and figures.
“Aerodynamic drag / engine pressure losses. Thick atmosphere at sea level inhibits acceleration. Rocket engines exhaust must “push” air out of the way (~25 percent degradation at sea level). No initial kinetic energy. Vehicle is fixed on the pad.”
“Air-launching of rockets destined for orbit can have definite advantages over ground launch, if done properly. It avoids expending the energy required by ground-launched boosters to “chug” through the densest part of the atmosphere. Enables responsive and versatile launch capabilities (azimuth and inclination) from a given operations site.”
However, this is not a new concept.
The most famous Air Launcher is Orbital’s Pegasus, which has flown 41 times – 31 times as the Pegasus XL, most recently in action in June, when it launched NASA’s NuSTAR spacecraft into orbit.
Developed by Orbital Sciences Corporation in the late 1980s, Pegasus is a three-stage air-launched all-solid expendable launch system.
Dropped from a B-52, Pegasus made its first flight in April 1990, successfully delivering the SECS and Pegsat satellites into orbit. Four successful missions followed from the campaigns using the B-52.
The stretched and more powerful Pegasus-XL first flew in June 1994, its maiden flight was intended to orbit the STEP-1 spacecraft, however it failed to achieve orbit.
The XL’s second flight – - the ninth Pegasus mission overall – carrying STEP-3, also failed. However in March 1996 the Pegasus-XL successfully placed REX-2 into orbit. In addition to stretched first and second stages, the Pegasus-XL introduced redesigned tail fins, allowing it to be launched from an L-1011 aircraft instead of a B-52. The revised fins were incorporated into the original Pegasus as the Pegasus-Hybrid, or Pegasus-H, which made four flights between 1995 and 2000.
The aircraft used to launch Pegasus-XL rockets is a Lockheed L-1011-1 TriStar named ‘Stargazer’. The first launch from Stargazer was the maiden flight of the Pegasus-XL. The first successful launch from the aircraft came in April 1995, when a Pegasus-H was used to orbit Orbview-1, and two Orbcomm satellites.
Pegasus has enjoyed a largely successful life since, racking up 38 successful missions, including the last 27 in succession.
The launch of NuSTAR was the thirty-fifth from Stargazer, and the fourth from Kwajalein. In addition, twenty launches have been made with Stargazer flying from Vandenberg Air Force Base in California, six from the Wallops Flight Facility in Virginia, three from Cape Canaveral Air Force Station in Florida, and one from Gran Canaria Airport in the Canary Islands.
The mission campaign involves Stargazer flying to the designated drop zone, prior to the rocket being dropped from the aircraft. Five seconds later, its first stage is ignited and the vehicle pitched up to begin its ascent to orbit.
(L2 Link to full onboard cam video of a Pegasus launch)
The first stage of the Pegasus-XL is an ATK Orion-50SXL, which burns hydroxyl-terminated polybutadiene (HTPB) solid propellant, and also houses the wings and tail fins used to control the vehicle during atmospheric flight.
For the NuSTAR mission, the first stage burned for approximately 71 seconds, before separating fifteen seconds after burnout. 92.05 seconds into powered flight, the second stage, an Orion-50XL, ignited. Like the first stage, the second stage burns HTPB, and it fired for 72.75 seconds.
During the second stage burn, 128.3 seconds after launch, the payload fairing separated from around the NuSTAR satellite. When the second stage burned out, the mission entered a coast phase lasting approximately six minutes, 21 seconds.
During this coast phase, the second stage separated, with third stage ignition coming at the end, nine minutes and six seconds into the mission.
The third stage of the Pegasus-XL is an Orion-38, which also burns HTPB. It burned for sixty-eight seconds, inserting itself and NuSTAR into low Earth orbit, with powered flight ending ten minutes and 14 seconds after the mission began. The Pegasus placed NuSTAR into a circular orbit at an altitude of 600 kilometres, with six degrees of inclination.
The next launch of a Pegasus is expected in January 2013, when another Pegasus-XL will launch from Vandenberg, carrying the IRIS satellite; the next scheduled Explorer mission.
Funded as a Paul G. Allen project under the banner of Stratolaunch, designer Burt Rutan is developing an air-launch system for payloads in the 10,000 lbm class into Low Earth Orbit (LEO).
The system will be able to launch from several possible operational sites and eventually aims to provide crewed services.
Per the December, 2011 announcement in Seattle, the Stratolaunch air-launch system is made up of four primary elements: a carrier aircraft – a super large derivative of SpaceShipTwo’s carrier plane (WhiteKnightTwo), a multi-stage booster – namely a Falcon 4 or 5, a mating and integration system, and an orbital payload.
Stratolaunch’s carrier aircraft, built by Scaled Composites, weighs more than 1.2 million pounds and has a wingspan of 385 feet. Using six 747 engines, the carrier aircraft will be the largest aircraft ever constructed.
At approximately 120 feet long, the booster is designed to loft the payload into LEO. After release of the booster from the aircraft at approximately 30,000 feet, the first stage engines ignite and the spacecraft begins its journey into space.
After the first stage burn and a short coast period, the second stage ignites and the orbital payload proceeds to its planned mission.
Eventually, the company hopes to move to crewed launches, involving SpaceX’s Dragon spacecraft.
Also utilizing SpaceShipTwo’s carrier plane “WhiteKnightTwo” – Virgin Galactic announced their air-launched rocket, specifically designed to deliver small satellites into orbit.
With contracts already signed for payloads to be delivered by the system – and what the company claims are several dozen other interested parties – LauncherOne will be a two-stage vehicle capable of carrying up to 500 pounds (225 kilograms) to orbit for prices below $10 million.
The rocket will be launched to the wide range of possible launch locations tailored to individual mission requirements and weather conditions. Missions are scheduled to begin in 2016.
“Virgin Galactic continues to innovate space access, and LauncherOne is a key step in its successful commercialization,” said Mohamed Badawy Al-Husseiny, CEO of aabar Investments PJS.
“This development promises to redefine the small satellite market and to promote new research and education opportunities. aabar is proud to be partnering in this exciting journey by continuing to support Virgin Galactic and its initiatives.”
Virgin Galactic are still waiting to carry out the powered qualification flight of their SpaceShipTwo (SS2) passenger vehicle, set to launch celebrities and rich people on a short suborbital joyride. The company current holds deposits from 529 customers, allowing them to buy the honor of being called an “astronaut”, simply due to the altitude of their flight.
“Virgin Galactic’s goal is to revolutionize the way we get to space. I’m immensely proud of what we have already achieved as we draw near to regular suborbital flights on SpaceShipTwo,” added Virgin boss Sir Richard Branson.
“Now, LauncherOne is bringing the price of satellite launch into the realm of affordability for innovators everywhere, from start-ups and schools to established companies and national space agencies. It will be a critical new tool for the global research community, enabling us all to learn about our home planet more quickly and affordably.”
One idea that did not make it past the conceptual stage was the ALTO/Crossbow, a system that was not restricted to just space launch requirements, in turn providing it with a wide-ranging marketplace.
At the center of the concept was a common aircraft carrier vehicle that contains aero control surfaces, propulsion, fuel, control systems, avionics, and landing gear – but no payload.
The potential payloads for Crossbow – as outlined in an expansive presentation available on L2 (LINK) – would be carried in standardized pods for specific missions, ranging from passengers, to cargo, and through to space launch vehicles – namely the Delta IV.
For campaigns with the Delta IV, the payload would be mated to the launch vehicle, the mated duo would then be readied for launch, again – in the cited example – from the Shuttle Landing Facility (SLF) at the Kennedy Space Center (KSC).
Because the pair would be taking off from the SLF, as opposed to the Delta IV launching vertically from Cape Canaveral, multiple launch azimuths and inclinations would be available, noted the associated presentation.
Once over the designated launch area, the Delta IV would ignite its first stage, whilst still attached to the crossbow – unlike the profile to be used by Stratolaunch or another example seen via Orbital’s Pegasus launch scenario.
For Crossbow, the pair would begin to pitch upwards to high-gamma angle using rocket thrust and aircraft flight surfaces. Using this technique would provide the Delta IV with the optimum assist at separation from the Crossbow.
Sporting a number of potential roles, the presentation adds that a wide variety of pods could be developed to meet various mission requirements.
Sadly, as mentioned earlier, the Crossbow system is no longer an active project. However, its findings provide a technical and insightful overview into the advantages of not only carrying your launch vehicle into the air prior to launch, but also the numerous applications such a system could unlock.
That advantage will live on with the remainder of Pegasus’ operational lifetime, the Stratolaunch system and Virgin’s LauncherOne.
(Images via L2 content, Orbital, Virgin Galactic, Stratolaunch)