U.S. space experts focus on reusable launch systems for small satellites

Sept. 1, 2004
The business of orbital satellites continues to grow, and the biggest growth in demand is coming from the smallest payloads.

The business of orbital satellites continues to grow, and the biggest growth in demand is coming from the smallest payloads. This is despite international public attention that focuses again on manned space. China has entered the small manned flight club, with the announced goal of going to the moon, while the new U.S. initiative is for a manned mission to Mars.

DARPA officials hope the Responsive Access, Small Cargo, Affordable Lainch (RASCAL) will be the foundation for a new generation of reuseable launch systems.
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Current commercial expendable launch vehicles, such as the Boeing Delta, European Ariane, international Sea Launch and Chinese Long March, are devoted primarily to heavy satellites, with smaller packages "piggy-backing" on some launches.

Such an arrangement is expensive and must be booked far in advance. Such microsatellites primarily low-Earth orbit (LEO), from 100 to 150 pounds, fit the needs of many science programs, as well as communications or reconnaissance satellites military commanders may need to launch quickly over specific areas of operation.

The Defense Advanced Research Projects Agency (DARPA) in Arlington, Va., is about midway through the second phase of a program called Responsive Access, Small Cargo, Affordable Launch (RASCAL), which they hope will build the foundation for a new generation of largely reusable launch systems to meet that need.

New concept

RASCAL is an advanced-technology-demonstration (ATD) program to create a system comprising a reusable airplane-like first stage and an expendable rocket second stage. It would be able to take off from any conventional airfield and fly to a designated waypoint until the launch window opens. At that moment, it would engage a Mass Injection Pre-Compressor Cooled (MIPCC) turbojet propulsion system and head up into a ballistic arc at speeds exceeding Mach 3.

At about 100,000 feet altitude, the second stage described as a spinner, similar to sounding rocket, with a head-end module to steer it into orbit would drop from the aircraft's cargo bay and continue upward to around 200,000 feet. Then the two-stage rocket would ignite, boosting to the edge of the atmosphere, where the first stage separates and falls into the ocean. The second stage ignites and lifts the payload and head-end module into an elliptical orbit. That stage then de-orbits and burns up on reentry.

Program officials say the throwaway elements are necessary to meet RASCAL's tight budget, but if it evolves into an actual production system, pushing the aircraft element to faster speeds could eliminate the first half of the second stage rocket. Even then, however, it would remain a hybrid air-and-space system, with a final expendable boost element to complete the trip to orbit. The key to making it a truly low-cost launch system lies in maximizing the capabilities of the air segment while reducing the cost of the space segment.

While the space component is getting the payload to its desired orbit, the MIPCC-powered vehicle (MPV) first stage would be completing its arc back into the atmosphere, relighting its standard engines at about 20,000 to 30,000 feet and returning to a conventional aircraft landing.

RASCAL program manager Dr. Preston Carter says the demand for an affordable launch capability for microsats is growing even as launch opportunities for such payloads is shrinking.

"This is not a case of 'if you build it, they will come'; they've already come, but nobody has built the launch system yet," he says. "DARPA believes small launches are a key technology and when available to meet the current requirement, demand will continue to increase.

Automation technology

RASCAL leverages advancements in autonomous range safety, first-stage guidance and predictive vehicle health diagnosis, management, and reporting to lower the recurring costs of space launch. RASCAL is attempting to show space-launch operations can be as adaptable and responsive as those of aircraft.

Space Launch Corp. in Irvine, Calif., is in charge of the 18-month RASCAL Phase II, the design stage, which includes development of MIPCC. If all goes well, Phase III will initiate construction and launch/relaunch of two payloads within 24 hours by 2006.

"Short term, we're trying to point the way with an ATD to reusable launch- vehicle technology that allows responsive and affordable launch. MIPCC is very much an enabling technology for that," Carter says. "Longer term, MIPCC has broad-based applicability for affordable, rapid access to space. Everything is going well; we're achieving our performance and technology and cost goals.

"The target is to make the launch price equivalent to $10,000 per kilogram (about $4,500/pound). which is a fairly common nominal launch-services price at large scale. At small scale, which is what the RASCAL system would be considered, we would be many times cheaper. So we're trying to achieve the economy of scale of a large system, which does not offer launch on demand. DARPA believes this will contribute greatly to the military need for rapid access to space, both tactical and strategic, and we hope to demonstrate that to the services."

The specific technical objectives for RASCAL include:

  • mission turnaround within 24 hours of payload arrival;
  • delivery of a 165-pound payload into a 310-mile sun-synchronous orbit;
  • recurring launch costs for the RASCAL operating system of $750,000 per launch for that weight payload; and
  • the ability to operate from an 8200-foot runway with minimal peculiar support equipment and independent of test ranges for telemetry and tracking support.

The MPV has a wingspan of about 80 feet and is about 105 feet long, with a gross takeoff weight around 110,000 pounds, roughly the size of an SR-71 Blackbird reconnaissance jet but 30,000 pounds lighter. The system includes a 16,000-pound expendable rocket vehicle (ERV), about 30,000 pounds of propellant for the MPV (jet propellant, water, and liquid oxygen) and a 165-pound payload (with about 1000-feet-per-second on-orbit delta V propellant).

"The lowest cost now for a dedicated ride is Pegasus, which runs around $20 million for a bigger payload," notes George Whittinghill, Space Launch's chief technology officer. "If you want to get something smaller up cheaper, you can buy a piggyback ride from several providers. The disadvantage there is you go where and when the primary vehicle wants to put you. That usually runs around $250,000 for about a 50-pound payload."

Takeoff from anywhere

"RASCAL also can put a payload anywhere in orbit because we can take off from anywhere and fly to anywhere before letting the rocket go," Whittinghill adds. "That gives us tremendous flexibility. DARPA also requires RASCAL to have a 24-hour mission turnaround. So if you have a payload, you must be able to launch within 24 hours of the previous launch. That also requires a one-hour scramble capability once called with a new mission. The only thing comparable to that is a tactical fighter wing and that's what they want."

While a 165-pound satellite is tiny compared to most current platforms in orbit, Whittinghill says it would cover a lot of communications and imaging payloads, by far the largest commercial and military markets that currently have a hard time finding a ride into space. Many traditional NASA space science payloads also would fit. With a payload area roughly 10 feet long by 4 feet in diameter, he adds, RASCAL can accommodate a lot of low-density payloads.

"It gives a disproportionately large payload volume for the throw weight," Whittinghill says. "Space access should not be as hard as it is, but it does take the government to push a system like this to really get things going. It is difficult to make a commercial business case without changing the way things are done and coming up with a radically new way. There is a commercial as well as DOD market, although the DOD missions will prime the pump in terms of putting the capability in place."

The all-composite MPV first stage, powered by four F100-class engines, is the largest aircraft ever built by RASCAL team member Scaled Composites in Mojave, Calif. A one-tenth-scale model is being used in a trisonic wind tunnel to verify computational fluid dynamics (predictions of lift and drag).

"We are trying to design it to be as much like an aircraft as possible. The only systems not aircraft-like are an attitude-control system that keeps it pointed in the right attitude when it leaves the atmosphere and a thermal protection system, which will require periodic maintenance," Whittinghill says. "It will be similar to what goes on the shuttle SRBs (solid rocket boosters). We estimate every tenth flight it will need a full check and probably some refurbishment. The thermal protection system is a spray, not a tile. If we had carbon-carbon leading edges which are expensive we wouldn't have to worry about it."

Man in the loop

Although DARPA has envisioned an unmanned aircraft for an operational system, Space Launch is designing RASCAL's MPV for a crew of one or possibly two, Whittinghill says, because "nothing beats a man in the loop to flush out how an aircraft behaves".

Space Launch also is responsible for developing the hybrid motor for the rocket's first stage and doing subscale motor test firing to verify the performance of the hydrogen peroxide and rubberized aluminum propellant they have selected.

"We chose that because it is ignited close to the airplane at altitude and a hybrid cannot explode, so it is the safest propulsion system there is," Whittinghill explains. "We are looking at alternate fuels that might give ultimate performance at less cost."

The solid-rocket second stage is being built by ATK (Alliant Techsystems in Brigham City, Utah, which is also looking for new designs to meet DARPA's requirements. They also plan to test-fire a motor using a new propellant mixture in August.

RASCAL's other component contractors include:

  • ATK's GASL Division in Ronkonkoma, N.Y., for the MIPCC;
  • Athena Technologies in Manassas, Va., for the flight-control system; and
  • Automated Controlled Environments Inc. (ACEi) in Valencia, Calif., for avionics.

Despite all the other firsts involved with RASCAL, Whittinghill describes MIPCC as "probably the most exciting technology." Sitting in front of the turbofan engine, the MIPCC provides increased thrust, higher Mach speeds and extended altitude. Water and liquid oxygen are injected just upstream of the turbofan and downstream of the inlet, increasing the mass flow into the engine while lowering the incoming temperature to facilitate enhanced thrust and speed. That also keeps the oxygen balance at proper levels for extreme-high-altitude operations using a standard F-100 engine, such as those powering F-15 and F-16 jet fighters.

With MIPCC boosting those parameters, the aircraft stage does not require a rocket, significantly lowering costs. The expendable second-stage rocket also was designed to be as inexpensive as possible, so it will not have thrust vector controls.

"We also have inlets on the front side, which also are a push in the state of the art because they have to function at subsonic conditions at sea level, during aircraft takeoff, as well as at Mach 3 and 100,000 feet," Whittinghill says. "Inlets normally are not designed to cover such a wide range of use.

"At the end of Phase 2, we will have taken as much technological risk out of the program as possible, so as soon as DARPA exercises Phase 3, we will be ready to cut tooling for the skins of the airplane."

If the program succeeds in making a one-day-turn-around double launch by mid-2006, DARPA's role will end.

DARPA's end game

"We hopefully would transition it to the Air Force, NASA, National Reconnaissance Office — organizations like that," Carter says. "Starting in 2007, they would be able to launch payloads with the capability left over from our program, but if the Air Force decided to build on the RASCAL effort, that would be an acquisitions program.

"With well over 90 percent of the system reusable, in terms of value, our intent is to have a launch, including the purchase of expendables, at less than $750,000."

Equally important, Carter adds, is the potential to scale the technology to vehicles larger and smaller than RASCAL.

Whittinghill says while the future of the launch technologies is open to speculation, the RASCAL design is being driven by an operational scenario that envisions the MPV component would fly at least 100 missions in five years.

"Our costs are designed to accommodate that kind of flight rate," he says. "I don't know what the minimum number of vehicles would be if the Air Force picked it up. More than likely, that could be three vehicles on each coast. But there are many mission models you could devise. And if it turned out to be a very popular concept, there is no reason there couldn't be many times more than that. If we are successful, we will be doing space missions at the cost of a cruise missile launch, which will open things up considerably. And that is very exciting."

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