Chair Force Engineer

Saturday, April 14, 2007

Two EDS, no waiting

There's been some discussion on the NASA Spaceflight Forums about the best architecture for the DIRECT/Jupiter I launcher to launch a moon mission. I think that the number of missions has been limited by some people's insistence on a single Earth Departure Stage.

Remember that back in Apollo, there were several engine burns that had to take place after the CSM + LM stack was in earth orbit. The S-IVB fired again for Trans-Lunar Injection. The SM engine fired once for Lunar Orbit Insertion. The LM descent engine fired to de-orbit the LM and land. The LM ascent engine fired once to get the astronauts back into lunar orbit. The SM engine fired a second time, for Trans Earth Injection.

Some things are different in NASA's "Apollo on Steriods." The EDS is used much like the S-IVB, but the LSAM descent engine steals the LOI burn from the SM. Otherwise, the analogues are still performing the same burns that they did in Apollo.

My thought is that it will be more cost-effective to employ two EDS in a lunar architecture, while using a smaller LSAM descent stage. My logic is that the EDS will already be in production, and its tankage will be simple and cheap to fabricate. The LSAM descent stage will be more expensive, consisting of multiple propellant tanks which are designed to operate in 1/6 G.

My "two EDS" architecture doesn't employ any techniques that NASA would deem risky, like waiting until lunar orbit to perform the first rendezvous between Orion and LSAM. Orion will dock with LSAM as currently planned; the only difference is that Orion will have an EDS attached to its aft end in order to perform the LOI burn.

When looking at the "DIRECT launcher" proposal, I'm struck that, despite using two rockets of similar or equal lift capacity, the two payloads for most of the architectures are very different in mass. One rocket will launch the Orion CSM, while the other launches the EDS and the LSAM. In my mind, it makes more sense to off-load the mass of the LOI propellant from the LSAM, and then give the Orion CSM a second, partly-fueled EDS that will be used for the LOI burn.

In the current architecture for DIRECT-II (use of stock RS-68's instead of improved versions that only exist on paper,) the 3x RS-68 first stage and the baseline EDS can put 101.9 tonnes into the chosen assembly orbit. Assuming that one launch of DIRECT is used solely for the ~25 tonne Orion CSM, that's only 126.9 metric tonnes in the assembly orbit. This is probably less payload than the ill-conceived "1.5 launch" strategy using "Scotty Rocket" and "Zubrin Rocket" (Ares I & Ares V.)

NASA will probably fault DIRECT-II because it won't be possible for a single DIRECT/Jupiter rocket to launch their baseline LSAM and EDS masses in one throw. I propose that NASA should baseline a lighter LSAM and take off the LOI-burn requirement. That way, the two payloads in the DIRECT-II architecture will be a lot closer in terms of mass, and the architecture can make best use of the 203.8 tonne capability that two DIRECT/Jupiter boosters could place in an assembly orbit.

I realize that the architecture I propose has some drawbacks. The EDS tankage will undoubtedly be heavier than the LSAM tankage it will be replacing, although the specific impulse of the engines will be similar. Also, because the EDS launched with Orion will carry a small fraction of its total propellant load due to the needs of the LOI burn, it will be a pretty inefficient use of the EDS mass. It also introduces an additional two engines (2x J-2X on the EDS) into the lunar architecture, which causes the loss-of-mission probability to go up slightly. Finally, the higher inert mass of the partly-fueled LOI EDS will increase the amount of propellant that the TLI EDS must burn.

My solution to the inefficiency of the EDS is to design a "stumpy" EDS that will be correctly sized for the LOI burn. Alternatives would be the use of off-the-shelf Centaur or Delta IV upper stages in place of the "stumpy" EDS. Studies will have to demonstrate that a replacement stage would be capable of performing the mission in a cost-effective way.

In short, DIRECT Launcher is probably the best way to run a government-driven lunar exploration program in these times of constrined budgets. At the same time, NASA is looking for any way to invalidate DIRECT, and they will likely exploit inefficiencies in the architectures for DIRECT missions to the moon. I propose an architecture that makes better use of the tremendous capability that DIRECT can give us. The two-EDS architecture forces NASA to revise its LSAM baseline, which is something the agency is loathe to do. Then again, it's best to change the LSAM at this stage in the game before any proposals have been submitted, rather than wait until later when Congress has killed off the Ares V as "too expensive" and the moon has already been lost.

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Tuesday, April 10, 2007

Solid Support?

In announcing its memorandum of understanding with United Launch Alliance, SpaceDev revealed that it's willing to fly as many as three solid rocket boosters on the Atlas V that could possibly take the Dream Chaser spacecraft to orbit.

SpaceDev is not the first firm to advocate the use of an Atlas V with solid rocket boosters for manned spaceflight. TeamVision also proposed an Atlas V with four SRB's as a booster for the Orion spacecraft, eliminating the need for an expensive Ares I development program.

Lockheed Martin seemed to have ruled out the use of SRB's when conducting its man-rated Atlas V study. The reasoning was that NASA's specs for safety factors in human spaceflight were exceeded when the additional thrust and impulse of the SRB's was accounted for. Lockheed Martin concluded that only the single-core Atlas V's were suited for manned spaceflight.

The SpaceDev vehicle gets around the NASA safety regulations because it's developed and operated by a private entity. It remains to be seen whether the FAA will hold an orbital space tourism firm to the same standards as NASA.

At the same time, the NASA safety factors should be open to debate. As the TeamVision report argues, the safety factors on an Atlas V 551 were sufficient for an expensive, unmanned spacecraft like New Horizons. Is there any reason why a manned spacecraft with a robust abort system couldn't fly on the same launch vehicle? I suspect that the Redstone, Atlas and Titan II rockets would not have met NASA's current safety standards, either. Yet they worked well when they were employed in a total of sixteen manned spaceflights.

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Monday, April 09, 2007

Hell's Pass Hospital

The recent scandal regarding shoddy conditions on the Walter Reed campus came as a shock to many Americans. For people who are on active duty service with the US Armed Forces, the surprise was very muted. Even the military acts very cynically towards the military health care system and the Veterans' Administration.

Illustration of that point came for me today when getting my vaccination record updated. They say that I need a blood test to look for the Chicken Pox antibody. I was able to document that I had Chicken Pox as an adolescent, but they gave me some bullshit excuse about "all personnel born after 1980 have to have this test, regardless of documented history." Apparently there was something magical about all babies born after 1980, as they all need blood tests despite having contracted Chicken Pox back in the days when Ninja Turtles ruled the airwaves (waitaminit... the Ninja Turtles still rule the field of children's entertainment...)

So I go to the lab where an airman is supposed to draw my blood. He sticks me in the right arm and nothing flows. "I forgot to tell you to keep your arm straight," he says in apology. Then he sticks me in the left arm, and the bleeding stops almost as soon as it begins. So I got stuck twice by an airman who couldn't successfully take a routine blood sample.

I think the military health care system is best summed up by something my program manager once said:
My brother is one of these people who believes in socialized medicine. I told him, 'You've had to deal with the Air Force medical system for your entire adult life. Isn't that enough to scare you away?'

Thursday, April 05, 2007

Spaceplanes of Gossamer Wings?

About a month ago, beloved space-pundit Jeff Bell predicted disastrous safety problems for upcoming space tourist craft like SpaceShipTwo and Rocketplane XP. I will be the first to admit that rocket powered aircraft traveling into the exosphere will almost certainly be more dangerous than conventional aircraft. That being said, I also think that Jeff Bell overestimates the dangers of suborbital spaceplanes.

Most of the problems noted in Dr. Bell's analysis of the data show that engine problems accounted for a vast majority of catastrophic rocketplane incidents. Four of these were attributed to the use of ullmer leather, incompatible with liquid oxygen. The second X-15 had an in-flight engine failure, and the third X-15 had an engine explode on the ground. While this is a problem inherent in all rocketplane projects, it must be noted that the X-15 program was conducted at a time when large liquid rockets, especially complex ones like the XLR-99, were in their infancy. As time has progressed, rocket engines have become more reliable. Spaceplane engines need not be any different.

It should also be noted that all of the projects cited by Dr. Bell were research programs that "pushed the leading edge" of flight research. The X-15A-2 suffered structural damage during a high-speed run, the X-2 was lost due to inertial coupling, and the third X-15A spun out of control during re-entry. Flights of commercial spaceplanes will avoid these problems by flying well within the type's flight envelope instead of shooting for extreme speeds and maneuvers that are the norm in a flight research program. I especially think highly of SpaceShipTwo's "feather" maneuver, which takes much of the risk out of reentry.

Dr. Bell mentions the grounding of three X-1 series aircraft due to fatigue in the tankage. This is a problem that cannot be dismissed, but it's not a show-stopper either. Propellant tanks have to be designed to withstand a certain number of pressurization cycles, and they have to be inspected thoroughly between flights. Fortunately, our ability to inspect for microcracks in these tanks is much better today than it was in the 1950's.

I share Dr. Bell's concern with the SpaceShipTwo propulsion system. I studied hybrids for a lengthy period in college. In my mind, the supposed safety benefits never seemed that great, and they never seemed to outweigh their poor performance when compared with liquid systems (or even all-solid rockets, which usually have better specific impulse than N2O-HTPB hybrids.)

Noticeably absent from Jeff Bell's data is any mention of the Douglas D-558-II Skyrocket. This research aircraft flew 313 times using three airframes. None of the aircraft were lost during the highly-successful program. The program even racked up a remarkable aviation achievement: the first Mach 2 flight in history was achieved by Scott Crossfield in the D-558-II on November 20, 1953.

Of the 313 flights, three different propulsion schemes were employed: turbojet-only, turbojet + rocket, and rocket-only with launch from a B-29 mothership. Admittedly, the turbojet-only flights should be tossed out of this safety record, because they're no different from conventional aircraft. Nonetheless, the Skyrocket demonstrated that there's nothing inherently unsafe about mounting a rocket engine with a winged airframe.

As space tourism reaches the suborbital frontier, rocket-powered aircraft will lead the way. Flying in such craft will undoubtedly carry risks, but safe practices and smart engineering can bring risks down to acceptable levels. The passengers of such spaceplanes should go into their adventures with full awareness of those risks, and a belief that their space experience will outweigh any potential hazards.

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Monday, April 02, 2007

Marathon Woman

Astronaut Sunita Williams is running the Boston Marathon, at least in an honorary way, from the International Space Station. Due to her extreme (220 miles above the earth!) circumstances, she'll have to participate by running on the station's treadmill for 26.2 miles.

The differences between the space marathon and the real Boston Marathon are worth commenting on. Aside from the fact that the ISS is not Boston (unless the Boondock Saints buy a trip on a Soyuz,) the running environments are very different. An astronaut doesn't have to contend with wind, hills, insects, rain, temperature fluctuations, or other runners; the experience is somewhat mundane in comparison to the real thing. It's probably easier on the body, because the feet aren't impacting the treadmill with the same force that would be necessary to run under one G.

There are several drawbacks to running in space. For a 26.2 mile run, I'm certain that it will become very monotonous, very quickly. Hopefully the astronauts have TV screens to watch while on the treadmill, but all runners look forward to seeing new and interesting locales when they run. Another important factor is the deterioration of the body that occurs while in a microgravity environment. While the astronauts stay physically active, will that be enough to allow an astronaut to run the equivalent of a marathon in space?

Another good question is how long it will take Sunita Williams to get back in marathon shape upon her return to earth. While science has much to learn about the physiological effects of long-term microgravity on the human body, we've seen enough to learn that prolonged weightlessness is pretty bad for people. Muscles atrophy and bones decalcify. While many symptoms of weightlessness reverse themselves when astronauts return to earth, some do not. My guess is that Sunita Williams will eventually run the Boston Marathon again while on earth, but it may be years before it happens again.

Perhaps NASA should commit itself to artificial gravity solutions immediately. An artifical gravity, manned spacecraft would be a worthy experiment to conduct in earth orbit. It would certainly achieve a good deal of risk reduction before we send humans to Mars or the asteroids in an artifical-gravity ship.

The first space marathon appears to be a stunt more than anything else, but it poses important questions about the physical effects of weightlessness that will have to be overcome if humans are to live in space for years at a time. The extreme physical exertion required to run a marathon, even in the sterilized environment of a space station, will give the physiologists a lot to study. The recovery of an astronaut, to the point where he or she can run a terrestrial marathon again, will also be a fascinating venue of research.