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Boeing ALASA design
The ALASA launch system under development by Boeing for DARPA will use a uniquely-designed rocket launched from an unmodified F-15E. (credit: Boeing)

Air launch, big and small

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For decades, the concept of air launch has captivated many aerospace engineers, government agencies, and companies. In theory, the case for air launch looks compelling. Using an aircraft as, in effect, a reusable first stage reduces the size of the rocket required to place a payload into orbit versus a conventional ground-launched system. An air launch system also reduces the ground infrastructure needed to support a launch—no pad, no gantry, etc.—and potentially allows any airport with a sufficiently long runway to serve as a spaceport.

“If I’m going to hit a million-dollar-per-flight target, I’ve got to do things in such a fundamentally different way that I change the cost equation for all the stuff in a space launch that has nothing to do with the rocket,” said Clapp.

In practice, though, air launch has failed to gain traction. The most successful air launch system developed to date, Orbital Sciences Corporation’s Pegasus, has flown 42 times in 24 years—an average of less than two launches a year—and a lack of business in recent years has threatened the vehicle with retirement. (After a launch a year ago for NASA, the vehicle’s manifest was empty until it received a contract in April from NASA to launch eight small meteorological satellites in 2016.) Pegasus was too small for most satellites, government or commercial, and even with the rise in interest in small satellites in recent years, most non-government spacecraft developers considered the rocket too expensive.

Despite Pegasus’s limited success, and the failure of many other air launch proposals to take off (figuratively or literally), there’s been a resurgence of interest in air launch systems in recent years by companies and government agencies. Most of these systems are focused on the smallsat market, seeking to provide dedicated launch options that are more affordable than what’s available from Pegasus or other, ground-launched vehicles.

Virgin Galactic, for example, formally announced nearly two years ago plans to develop an air launch system, called LauncherOne, to place satellites weighing up to a couple hundred kilograms into orbit for $10 million or less. Rumors of Google’s interest in investing in Virgin Galactic, as reported by British broadcaster Sky News earlier this month and Parabolic Arc last month, are most likely associated with Google’s interest in new options for launching smallsats for its planned remote sensing and communications satellite constellations (see “The commercial remote sensing boom”, The Space Review, June 16, 2014) rather than Virgin’s suborbital space tourism plans.

The small end of air launch

Smaller than LauncherOne, though, is a project funded by DARPA called the Airborne Launch Assist Space Access (ALASA) program. The goal of ALASA, started in late 2011, is to develop an air launch system that can place a 45-kilogram (100-pound) payload into orbit for less than $1 million per mission.

Achieving that cost goal led DARPA to focus on what the real cost drivers of launch operations are. “If I’m going to hit a million-dollar-per-flight target, I’ve got to do things in such a fundamentally different way that I change the cost equation for all the stuff in a space launch that has nothing to do with the rocket,” said Mitchell Burnside Clapp, the DARPA ALASA program manager, in a talk last month at the International Space Development Conference (ISDC) in Los Angeles.

That meant looking beyond the launch vehicle itself to the overall concept of operations for air launch systems, and what drives their costs. Clapp said there were several lessons learned from Pegasus, which had its origins in another DARPA program a quarter century ago. “Probably the biggest one is don’t have a dedicated launch aircraft,” he said. Peagsus launches from a customized L-1011 that is used solely for those missions. “Avoid using an aircraft that is specialized for the launch assist application.”

DARPA is applying those lessons learned with ALASA. In March, the agency awarded a $30.6-million contract to Boeing to develop the ALASA system, using a rocket that would launch from an unmodified F-15E aircraft. Clapp said in his ISDC talk that the two other competitors also planned to use existing aircraft: Lockheed Martin proposed using the F-22, while Virgin Galactic planned to use the WhiteKnightTwo aircraft it had already developed for its SpaceShipTwo suborbital vehicle and its own air-launch concept, LauncherOne.

The Boeing ALASA concept intends to use F-15 aircraft that require no modifications. The rocket, for example, will use the same communications protocols as weapons systems typically mounted on that aircraft. “ALSA is not a weapon, but it does talk the same language as weapons speak,” Clapp said. “There are no software changes needed for the F-15. That is a huge advantage.”

“That’s kind of a big deal,” Clapp said of the ALASA rocket, which uses a high-performance monopropellant. “In general, it’s a dramatic simplification of the complexity of a rocket vehicle.”

That means that ALASA doesn’t need a dedicated aircraft: any F-15 could serve as a launch platform without modification, and then go back to flying other missions. “You can use that aircraft and have it provide services to you at its marginal cost,” he said. “You’re buying one more sortie out of several hundred per year rather than an airplane that becomes a big white elephant.”

Another approach that DARPA is taking to better understand, and lower, the cost of operations sounds counterintuitive at first: the development a second, smaller launch system. The Small Air Launch Vehicle to Orbit, or SALVO, will also fly off an F-15. The rocket, a two-stage system using liquid oxygen (LOX) and RP-1 propellants, is being developed by Ventions, a small San Francisco-based launch technology company.

SALVO will demonstrate some new technologies, Clapp said, such as battery-powered pumps for the rocket’s engines. However, he said SALVO’s main purpose is to be an operational pathfinder for how the larger ALASA system will operate.

“It’s meant to be an icebreaker,” he said, giving the overall program experience with range approvals and other processes. “It makes sure everyone is comfortable so that when ALASA itself flies it will all be familiar to the people doing the work.”

In its role as an operations pathfinder, SALVO will fly six to nine months before the first ALASA launch. In his ISDC talk, Clapp said integrated rocket stage testing of SALVO was planned for August, and captive carry flights would begin in November. The first of up to three SALVO missions is planned for the spring of 2015. The rocket will be able to place a 3U CubeSat into orbit, a small fraction of ALASA’s payload. (SALVO will also be smaller than another small air launch system under development, GOLauncher 2 by Generation Orbit, which plans to have a payload capacity similar to ALASA.)

While SALVO is an operational testbed for ALASA, it will use different launch technologies. Boeing plans to take a unique approach with the ALASA launch vehicle that is also intended to lower complexity and thus costs. The rocket will be powered by a monopropellant: a combination of nitrous oxide and acetelyene, mixed together in the same propellant tank and “slightly chilled” below room temperature, Clapp said. That propellant choice offers simplicity as well as a specific impluse “not far off” from LOX and RP-1. “That’s kind of a big deal,” he said. “In general, it’s a dramatic simplification of the complexity of a rocket vehicle.”

The rocket’s design is also unusual, mounting four engines just below the payload on the vehicle. The engines are used for the first and second stages of the rocket, with propellant tanks below the engines dropping away when exhausted. This approach avoids the expense and complexity of separate sets of engines for the first two stages.

Current plans call for the first ALASA launch in late 2015, with a total of 12 ALASA launches planned through mid-2016. Those flights will all use F-15s based at Eglin Air Force Base in northwestern Florida, with the launches themselves taking place over the Atlantic Ocean off Florida’s east coast. “At that point, I’m hopeful we’ll transition to an actual operational customer,” Clapp said, although who that customer would be and how they would use it remain unclear.

Thunderbolt design
Orbital Sciences Corporation is developing the Thunderbolt rocket for use in Stratolaunch Systems’ air launch concept. (credit: Orbital Sciences Corp.)

The large end of air launch

ALASA, SALVO, and commercial systems like GOLauncher and LauncherOne are focused on the small end of the launch market: trying to offer the right combination of inexpensive and dedicated launch services for smallsats that today either have to spend a lot more for a dedicated launch or settle with a secondary payload opportunity on another customer’s launch.

One issue is whether, even with the growing interest in smallsats, there’s sufficient demand for these air launch systems. “Finding an abundant array of worthwhile 100-pound payloads is actually kind of hard,” Clapp acknowledged in his ISDC speech, although he said he expected that to change over the next few years as growing capabilities of smallsats enabled new missions.

The name “Thunderbolt”, Beames said, comes from “a childhood spaceship kind of thing that he [Allen] had named as a kid.”

An exception to this approach is by Stratolaunch Systems. In late 2011, it announced plans to develop the largest air launch system ever, capable of placing payloads in excess of 6,000 kilograms into low Earth orbit (see “Stratolaunch: SpaceShipThree or Space Goose?”, The Space Review, December 19, 2011). The Stratolaunch concept would require the development of a customized aircraft that will be the world’s largest (as measured by wingspan), and a new launch vehicle.

Although the company unveiled its plans in a high-profile press conference that featured Paul Allen (who is funding its development), Burt Rutan, and others, the company has remained relatively quiet since then. The last press release the company published was in early June of last year, based on its website. That release announced that Orbital Sciences was taking over development of the launch vehicle after SpaceX, Stratolaunch’s original partner, dropped out (see “Egolauncher”, The Space Review, December 3, 2012).

In the last month, though, there have been a few bits of information released by Stratolaunch Systems, and those working with the company. At the very least, we now know what to call the launch system it’s working on other than “Stratolauncher.”

On May 19, Aerojet Rocketdyne announced it won a contract from Stratolaunch Systems to provide RL10 engines that will power the upper stage of the company’s rocket. (The lower two stages will use solid-propellant motors supplied by ATK.) The contract covers six RL10C-1 liquid-hydrogen/liquid-oxygen engines, covering three launches, with an option for additional six engines.

The release also provided a new name for Stratolaunch’s launch system. “The design concept for The Eagles Launch System involves the launch of an unmanned rocket dubbed Thunderbolt, carrying a commercial or government payload from beneath the fuselage of a giant carrier aircraft,” the Aerojet Rocketdyne release stated. Neither “Eagles Launch System” nor “Thunderbolt” had been previously used in public by the company (and, in fact, are not used on the company’s web site, as of late June.)

In a presentation at the 30th Space Symposium in Colorado Springs on May 22, Chuck Beames, president of Vulcan Aerospace Corporation, also used the “Thunderbolt” name to describe the launch vehicle. (Vulcan is Paul Allen’s holding company funding the system’s development.) The name, he said, comes from “a childhood spaceship kind of thing that he [Allen] had named as a kid.”

Neither the Aerojet release nor Beames offered a name for the other major element of the Eagles Launch System, the giant carrier aircraft. However, a fact sheet by Orbital Sciences, posted on its website recently with little fanfare, does give a name to that airplane: “Roc.”

In his Space Symposium talk, Beames said work on what is now known as the Eagles Launch System is going well. “It’s making great progress,” he said of Roc, currently being built at Stratolaunch Systems’ hangar at Mojave Air and Space Port. “I would say it’s about fifty percent done in terms of building the aircraft, so it’s really looking like a 385-foot-wingspan aircraft.”

Beames said the Thunderbolt launch vehicle would comply with EELV Standard Interface Specification for payloads. A chart he showed listed the vehicle’s payload capacity as 13,500 pounds (6,120 kilograms) to a 220-nautical-mile (407-kilometer) orbit at an inclination of 28.5 degrees, and noted it would have a payload fairing five meters in diameter. That would make the vehicle similar, or even slightly better, in performance to Orbital’s own Antares rocket.

Although flight tests of Roc are slated to begin in 2016, the first Thunderbolt launch won’t be until 2018. “We’re still on track for a first launch in 2018,” Beames said. “I can assure you that folks are working very, very hard both in Mojave and at Orbital Science to make progress on this project.”

Allen’s long-term vision, said Beames, “is to make this for human spaceflight, to make this a man-rated capability.”

While other air launch systems focus on smallsats, Stratolaunch hopes to launch larger satellites with the Eagles Launch System. “The target, as some folks now, is what we call in our community the ‘Delta II-class,’ the medium-class, payloads,” he said, referring to the workhorse launch vehicle that is gradually being phased out by United Launch Alliance: a launch early Tuesday of a NASA climate satellite is one of the last few missions slated for that vehicle.

However, Beames suggested that Paul Allen was looking at using Eagles for more than just satellite launches. “His vision, his ambition, his endeavor, his aspiration—that’s actually the term he likes to use—is to make this for human spaceflight, to make this a man-rated capability.”

“I remind him,” Beames added, “that it’ll be important to generate a little revenue along the way because manned space is very expensive, so we have this interim step of where we’re going to work hard to try and generate revenue through space launch.”

Generating revenue—and, ultimately, profits—from air launch systems has been a major obstacle for past efforts. While many may focus on unique rocket and aircraft concepts these systems propose, the issue of revenues and costs may be the critical challenge if air launch is ever to truly take off.