Chair Force Engineer

Tuesday, May 24, 2011

Building a Better BUFF

Perhaps no airplane personifies the US Air Force like the B-52 Stratofortress. The mighty bomber, powered by eight engines, immediately became one of the most fearsome combat aircraft ever built when it first flew in 1952. Over the next ten years, 744 "BUFFs" were built. They have seved with distinction ever since as a symbol of the Cold War, in addition to their heavy use over Vietnam, Iraq, Kosovo & Afghanistan.

By the late 60's, defense planners saw the end of the road for the B-52, fearing that it would be unable to penetrate Soviet defenses. The B-1 was designed as a faster replacement with a heavier payload, designed for low-altitude penetration underneath the Soviet radars. A series of delays, mostly political, ensured that the B-1 would not go into service until 1986. By that time, even the B-1 had become vulnerable to the most advanced radars, and the B-2 Stealth Bomber was necessary.

Yet the B-52 still found a way to soldier on. A solid airframe with room for newer avionics was adapted to carry more sophisticated weapons that could strike from a safe distance. This was demonstrated to great effect when B-52G bombers launched cruise missles on the first night of Operation Desert Storm in January 1991. By the time of the September 11 attacks, B-52's had been equipped with satellite-guided JDAM bombs. For the first time, the Cold Warrior was able to drop small munitions on the front lines to support US and allied ground forces.

The military news & commentary site StrategyPage makes the interesting observation that the B-52 is the cheapest of the heavy bombers for performing airstrikes over Afghanistan. But one has to ask what can ever replace the BUFF once the airframes (the youngest are nearly 50 years old!) finally wear out. The Air Force will need a long-range aircraft, simple to maintain (i.e., no need for stealth or supersonic performance) with cavernous bomb bays to store large amounts of ordinance.

During the 1980's, Boeing actually responded to this need by proposing a modified 747 jumbo jet. The plane would be capable of carrying at least 70 cruise missiles internally. A decade later, Boeing studied a modified B-52 with its eight TF-33 engines replaced by four RB211 engines from old 757 airliners. The Air Force controversially shot the proposal down, arguing that the cost of installing the new engines didn't outweigh the reduced fuel & maintenance costs over the life of the B-52. (The open question was how long the Air Force intended to keep the B-52.)

While the Air Force continues to study the Next Generation Bomber and look towards stealthy flying wings that can fly without a human pilot, a modified long-range airliner (Boeing's 777 and 787, nd Airbus's A340 come to mind) would also be a prudent course of action. Today's airliners would probably be limited to carrying weapons internally, with little ground clearnace to carry them on underwing pylons. But they would have the range and endurance to loiter over their targets for half a day or more, and put bombs on targets of opportunity that arise. In future counter-insurgency wars similar to Afghanistan, speed and stealth are worthless in undefended airspace. A soldier in the field wants his air support planes to have persistence and precision in patrolling an area and dropping weapons on the enemy. The B-52 has been perfect for this mission, and a modified airliner may be the most economical way to keep this capability after the BUFF flies into the sunset.

Tuesday, May 17, 2011

Give Me Liberty, or Give Me The Shaft!

The idea of using a large solid rocket for the first stage of a human-rated crew launcher presents a lot of technical problems, so I was not surprised when NASA stopped development of the Ares I rocket. Supporters of Project Constellation were saddened at the time, but Ares I surprisingly isn't dead. Its principal contractor, ATK, is keeping "The Shaft" alive as a privately-funded venture (without even the benefit of NASA CCDEV money) called "Liberty." The true believers in Ares I now have a chance to put their money where their mouth is and bring the design to life.

I'm embarassed to say that I've been catching up on a lot of the NewSpace developments just now after several months away from the space industry, so the Liberty launcher took me by surprise. Undoubtedly, some of the Ares I vibration issues still need to be addressed in the form of an upper-stage isolation system, the parachute-mounted dampers, or the active d-strut system. Crew survivability in the event that the first stage explodes (either due to design defects or destruction by range safety) will still be almost nil. But other Ares I problems seem to have a solution in the new Liberty configuration.

One of the longest-lead items in "The Shaft's" schedule was J-2X, an all-new upper stage engine with similar performance to the old Apollo J-2. The teaming of ATK with EADS-Astrium gets around this problem thanks to the Vulcain 2 engine. Originally used on the Ariane 5 first stage, the Vulcain engines have been remarkable engines very similar to the J-2 in terms of performance. They were a natural choice to replace the J-2X; after all, Volvo Aero produced the innovative nozzles for both engines. The remaining challenge is whether the Vulcain engines can be adapted to ignite on the second stage, far away from the required ground support equipment they've relied on during the Ariane days. Presumably Astrium will be replacing Boeing as prime contractor for the Liberty's first stage as well.

My biggest questions about Liberty deal with the infrastructure to support the vehicle. Apparently ATK is going to leverage the shuttle infrastructure as much as possible, using the aging Mobile Launch Pads & Crawlers. Presumably the Liberty would be assembled in the Vehicle Assembly Building and launch from LC-39. The inherent contradiction is that these facilities were never designed for minimizing the amount of labor during the launch processing phase of the mission. If Liberty has any commercial prospects, the facilities may become an achilles heel in the face of strong competition from SpaceX, the Boeing-ULA team & others.

Admittedly, I've never been a big fan of Ares I. Perhaps it's a Challenger-inspired phobia of solid rockets, but Ares I always seemed like it would take too long to develop, cost too much to fly, and pose too much of a safety risk to the astronauts who flew onboard. But ATK now has the chance to prove me wrong. At least they will have to rely on their own money to make it work, instead of keeping "business as usual" going solely at the taxpayers' expense.