Chair Force Engineer

Wednesday, July 29, 2009

Abort, retry... fail?

In response to my earlier post about man-rating the side-mount shuttle-derived rocket, NASA is dead-serious about putting humans on its side-mount heavy-lift launcher. Thanks to NASA Watch, we can now take a look at the agency's analysis of the side-mount abort situation. An initial study of the problem reveals no show-stoppers. As the days go by, side-mount is looking like a better alternative to Ares (assuming we are forced to accept a NASA-designed, NASA-operated launcher.)

At the same time, analysis of Ares aborts by the Air Force's 45th Space Wing at Cape Canaveral has led many engineers to believe this is a show-stopping issue for Ares I. I’m not ready to throw in the towel on Ares without more detailed analysis of the abort problem, but it's a vivid illustration of why solid rocket boosters pose such a challenge for manned launches.

Most Ares critics are focusing on a catastrophic failure of the Ares SRB which would immolate the Orion spacecraft in a cloud of burning fragments. Solid rocket boosters rarely blow up, but they create spectacular explosions and tragic results when they do. Two Titans suffered SRB explosions in recent memory: one in 1986 and another in 1993. The explosion of Brazil's VLS-1 solid rocket on the launchpad in 2003 killed 21 people and dealt the Brazilian space program a major setback.

The Challenger disaster was not the result of a catastrophic failure, but a similar O-ring burnthrough would still give Ares I’s guidance system fits as it struggles to keep the vehicle on course while being torqued by the hot blowtorch escaping from the failed joint. The most likely scenario for the Ares abort system would be escaping the cloud of hot fragments created if the range safety office had to destroy an off-course Ares. Range safety would probably have the luxury of a few seconds between the time when the capsule’s escape motors fire before sending the destruct command to the booster. Depending on how powerful the abort motor was and how much time they allowed, it’s possible for the Ares escape system to get the capsule high enough and downrange far enough to avoid the hot shrapnel that would doom the crew. Then again, this requirement would already add to the massive rocket which would allow Orion to out-run a thrusting Ares.

Much could be learned from the Challenger disaster in terms of how long range safety could wait before triggering the destruct sequence, and how big the debris cloud would become during the period of time Orion would be passing through its abort and descent sequence. Range safety waited what seemed like a long amount of time between the main vehicle breakup and the ground-commanded destruction of the SRB’s. I can't say if the crew module was subjected to an extreme thermal environment before slamming into the ocean. But this may be irrelevant, since the SRB's were quite some distance removed from the crew module before the SRB's were destroyed.

Taken together, all of the challenges going into the design of the Ares abort system demonstrate the compound problems created by the solid rocket first stage. The escape systems on Mercury, Apollo and Soyuz were far less challenging to design and test. They anticipated a shutdown of the liquid-fuel engines on the booster before the escape rocket fired. On a solid rocket, the only premature shutdowns are the ones caused by catastrophic failure. If there’s a need to abort, the astronauts had better hope their escape rocket can get them out of there in a hurry.

Thursday, July 16, 2009

From the Earth to the Moolah

For everybody contemplating the 40th anniversary of the Apollo 11 landings, I recommend heartily this retrospective by Ronald Bailey. In a world where "No Bucks" means "No Buck Rogers," Project Apollo was a grandiose feat, but one that could not be justified with sustained funding levels. "Flags and footprints" served the important geopolitical goal of demonstrating that a free society could be technologically superior to a totalitarian one. Once that goal was met, neither scientific curiosity nor heroic adventure could justify the expenses of further human lunar missions.

As a simple math equation, the Moon represents a goal to which the nation sinks its funds. Out of the moon come tangible and intangible benefits like scientific discovery, inspiration, and consumer spinoffs of space-related technologies. But even when taken together, these benefits of lunar exploration are hard-pressed to qualify as a return on investment on the funds that are spent on human lunar missions.

The answer to a sustained human lunar program is a capitalist approach in which profit is the primary motivation. Perhaps tourism or Helium-3 mining will motivate humans to return to the moon to stay. NASA may have paved the way, but firms like SpaceX and United Launch Alliance will be there to stay. We may not see the financial motivations for lunar exploration develop in my lifetime (and I stand a good chance of making it past 2040.) But all good things happen when the time is right, and when society is mature enough to handle their consequences.

There will always exist the cold warriors whose motivations behind Project Constellation mirror those of the Apollo cold warriors in racing the Soviets. This time the specter of Communist China is the new boogeyman. In spite of a methodically-paced human spaceflight plan and the lack of lunar hardware development, many people see imminent lunar ambitions behind China's current manned space efforts. Perhaps China will land a human on the moon during my lifetime. But any Chinese lunar effort that fails to learn Apollo's lessons is doomed to the same fate. If the Chinese Politboro no longer sees an overriding political goal in lunar exploration, they'll quickly view a human lunar program as a money pit from which they'll inevitably flee.

Saturday, July 11, 2009

You aren't going to stick people on that thing, are you?

During the Augustine Commission hearings, the side-mount, shuttle-derived vehicle has emerged as a surprising dark horse. Compared to Ares and even DIRECT, a side-mount can be developed quicker and cheaper than its shuttle-flavored competitors. It also does the most complete job of preserving more of the STS workforce within the first few years after the orbiters retire.

The most startling aspect of the side-mount SDV presentation is the option to mount a crew capsule and escape system. Because the crew capsule would be located laterally to the external tank, most observers feel it would not be a great improvement over the shuttle when it comes to launch aborts. Precise guidance and thrust-vectoring would be required in the escape system to pull the capsule away from the ET, even if the abort was triggered while the ET was structurally intact. In a Challenger-like situation where the ET rapidly disintegrates, there may be little or no chance of protecting the capsule from ET-produced shrapnel.

Another abort scenario worth considering is the shuttle's Return to Launch Site maneuver. The shuttle stack would flip end-over-end and fire the engines in the opposite direction to cancel out the forward velocity and head home. The orbiter would then separate and glide in for a landing. On a side-mount crew launcher, the capsule doesn't have the same cross-range as the shuttle orbiter. Hopefully the escape tower would be able to pull it away from the stack and set it down somewhere in the Atlantic ocean for recovery. The bigger question is the point at which the escape tower is going to be jettisoned for a side-mount crew launcher. Will the service module engine have the thrust and steering necessary to pull free from the ET during late-boost aborts?

The side-mount SDV has been given extensive study since the days before the first shuttle launch, and it remains a valid approach for transporting large unmanned payloads to space. But is it suitable as a crew launcher? It's probably no less safe than the existing shuttle, but it would still give me a high pucker-factor if I was an astronaut. The cynic in me suspects that NASA doesn't take the side-mount crew launcher seriously, but is pitching it as a means of undermining the rationale for EELV or DIRECT. After all, DIRECT may be a more difficult and expensive development than a side-mount SDV, but it's much more suitable for manned aborts during all phases of flight.

The approach I favored during the early days of Project Constellation was a Delta IV crew launcher and side-mount SDV for unmanned cargo. It's the cheapest crew launcher paired with the cheapest heavy lifter design. I would not be surprised if the Augustine Commission seriously considers this combination.