Chair Force Engineer

Saturday, November 29, 2008

The Incredible Shrinking Orion

The NASA transition team is asking the agency to look at several options in order to craft the Obama Administration's space exploration policy. To wit, these options include:
1. Acceleration of Ares & Orion
2. Cancellation of Ares I while retaining Ares V
3. Shrinking Orion to fit on an Atlas V or Delta IV
4. Shrinking Orion to fit on a foreign launcher (H-2A or Ariane 5)
5. Accelerate COTS-D (SpaceX Dragon, perhaps other vehicles)

Before discussing any of these options, it's worth asking the question of how big Orion needs to be in the first place. While the ESAS report cited 22.5 tonnes and a diameter of 5.5 meters (later reduced to 5 meters,) there is no discussion of exactly how much volume a crew needs for a lunar mission, and the diameter seems to be an arbitrary number with zero justification. My preference is to look at historical examples (chiefly, Apollo,) and use that to determine the requirements for the next manned spacecraft.

The Apollo capsule had a diameter of 3.9 meters and afforded a 3-man crew an adequate amount of room for a two-week lunar voyage. That same volume was adequate to deliver a crew of five or six on a shorter trip to Skylab (as studied during the Skylab rescue planning and the shuttle escape study.) For earth-orbit missions, Apollo weighed as little as 14.7 tonnes. For lunar missions, the additional consumables and propellant brought that weight to 30 tonnes. Apollo also required nearly seven years to move from contract award to first manned flight.

In ESAS, NASA dismissed the stock Atlas and Delta on the grounds of crew safety during mission aborts. While those fears were shown to be spurious during the Atlas man-rating study performed by Lockheed Martin, the performance of both rockets leaves much to be desired. NASA should budget no less than 30 tonnes for Orion. While the new spacecraft won't need propellant to perform a lunar-orbit insertion burn, and it trades the mass of fuel cells for lighter solar arrays, the capsule will need to be heavier to accomodate a larger crew, and the spacecraft will have to carry more consumables.

If Orion shrinks to the point where it can fly on an existing launcher, the lunar goal will be deferred or cancelled entirely. Perhaps a two-man Orion would be light enough to launch on an EELV and still be capable of a lunar journey, at the expense of higher crew workload and diminished science return from a lunar sortie.

Most disturbingly, if Orion is limited to earth-orbit missions, it destroys the rationale for Dragon and COTS-D. What incentive will NASA have to buy commercial launches for ISS if Orion does the job? While Bob Bigelow's space hotel plans might give SpaceX some incentive, the real near-term prize is COTS-D. The chicken-and-egg dilemma here is that a COTS-type vehicle must be ready before the Bigelow space hotel can go into operation.

Getting back to the meat of the post, I wanted to take a quick look at the four scenarios being examined by the Obama transition team:

1. Acceleration would be difficult to achieve with the existing Ares and Orion vehicles. It may have to come at the expense of testing, which is rarely a sound strategy (except in the case of all-up testing in Apollo.) Based on the 2006 contract award for Orion and a seven-year development time, we can't expect the capsule to be ready for manned flight any sooner than early 2013. That figure is optimistic, assuming that Orion is at a similar level of completion to where Apollo was in early 1964. An infusion of added cash into Ares and Orion will probably not accelerate the schedule; rather, they will serve to prevent the schedule from slipping further to the right as unanticipated problems rear their ugly heads.

2. This is my favored option, when paired with #5. Ares I will take too long to develop and has no real chance of closing the gap. Ares V and Orion can be kept going as a jobs-retention program. Perhaps NASA can adopt a two-Ares V mission profile, avoiding the tight mass margins currently encountered by the current architecture.

3. Again, I think there's nothing to be gained by stripping Orion down to the point where it can no longer perform a practical, safe lunar mission. The EELV option should be a non-starter.

4. The foreign launchers option is an interesting one, even though it suffers the same flaws as the Atlas/Delta option. It's interesting to note that Ariane 5 was designed with a manned spacecraft (the Hermes spaceplane) in mind. Even if the foreign boosters had the performance required to lift Orion in its current form, I think that "not invented here" and jobs-retention issues will scuttle the idea.

5. As many NewSpacers have pointed out before, the most cost-effective use of manned spaceflight dollars would be cancelling Ares I and using the savings to fund the unfunded COTS-D program. If I were advising the president-elect, this is exactly the advice I'd give him. An accelerated Dragon program gives America the best shot to have a manned spacecraft flying by 2012 or 2013.

I'd also recommend keeping Orion, Altair and Ares V going at a slower schedule and a lower spending profile until "the gap" was closed. At that point, a decision could be made on whether to proceed with manned lunar missions. NASA could retain "Apollo on Steroids" using two Ares V's per mission, or an "Apollo Redux" which would perform a more limited mission with a single Ares V launch.

Saturday, November 22, 2008

Air Launch Revisited

The Selenian Boondocks blog has, since its inception, been one of the best sources for discussion of space transport ideas on the internet. Some of the ideas have been downright inventive, while others have only been shot down after much serious discussion. Nevertheless, it represents the kind of thinking we need to truly solve the problems of making space access routine and affordable. While already a great blog under the meticulous care of Jon Goff and Ken Murphy, Selenian Boondocks just got even better with the addition of John Hare to the team. Hopefully he will dispel the notion of a “Hare-brained” scheme as a bad thing. (Pardon the pun.)

My eye was recently caught by a discussion of an optimized carrier aircraft to serve as the first stage for a reusable launch vehicle. During Jon Goff’s previous air-launch discussions, I came out in favor of using unmodified military cargo planes for air-launching small vehicles with scissor-wings. While I still favor this idea based on tight development budgets, discussion of an optimized mothership has merit if somebody is willing to pay for one.

It should be noted that the most successful mothership in recent memory, the Lockheed Tristar operated by Orbital Sciences, was chosen because it was cheap to obtain second-hand, and because it had fairly tall landing gear which allowed for adequate ground clearance. While the option exists for captive-carry on top of the mothership, it has fallen out of favor because of incidents like the D-21 collision with its Blackbird mothership. While the idea worked for the Enterprise glide testing, it’s probably a much different story if the separation involves igniting a rocket.

John Hare’s idea for a “
flying wing” mothership does have some historical basis. One of the Northrop-Grumman concepts for Space Launch Initiative, released in 2002, used a six-engined flying wing as its first stage. A large winged rocket would provide most of the delta-V from subsonic cruise to orbit, and the crew would ride in a small lifting body. The biggest problem with the design is the amount of money required to develop it. The second biggest problem is whether the large winged rocket could accelerate from Mach 0.8 to orbital velocity, especially when burdened with the structural requirements of its own wings and landing gear. Problem three is how you’d get the winged rocket back to base after it’s expended all of its propellants.

One of the big assumptions here is that the mothership need only carry the vehicle to a speed around Mach 0.8. In fact,
Boeing twice patented a two-stage system with a supersonic mothership. The 1982 iteration used eight turbojets, while the 1993 version used six. Both designs made use of a Space Shuttle Main Engine for acceleration during climb, prior to staging. The mothership would be nearly 200 feet long. The problem is that multiple studies have shown that subsonic launch is a pretty efficient solution. The challenges of supersonic flight erode the benefits of a higher separation speed. Supersonic launch doesn’t break even with subsonic launch until hitting mach 3 or higher. The Boeing idea isn’t bad if your goal is to ignite a scramjet, but it seems like engineering and budgetary overkill for the space launch problem. The primary benefit of the Boeing patents was their addition to the lore of mythical craft like Aurora and Blackstar.

The challenge of a custom air-launch system is the need to develop both the rocket and the mothership aircraft. Systems that have utilized existing aircraft for motherships have been able to spare themselves the development of one element of the system. But the inverse paradigm has not been attempted: use of a newly-designed mothership aircraft to boost the performance of an existing rocket. Structurally, this may not be feasible due to the changes to bending and other loads encountered by the change to air launch. At the same time, it has been studied before (such as the Crossbow concept) and is worthy of further consideration. Even though the payload boost may be small, it reduces the facilities costs and the weather-related delays that have accompanied traditional ground-launched rockets. Air-launch makes space launches more flexible in terms of launch azimuths, launch sites, and reduced launch delays. The concept's advantages should draw the interest of the Defense Department as a solution to the problems of Operationally-Responsive Space.

Tuesday, November 11, 2008

The Shuttle Legacy

When Project Apollo was shut down, the most tragic aspect of it was all of the useful technologies that were lost as tooling was destroyed and experts were reassigned to other programs. The mighty F-1 engine was relegated to museums, ceding the kerosene-engine market to the Russians. The demise of the J-2 engine has led to an expensive development program for the new J-2X that will be used on the Ares launchers. Even the exact formulation and processes for creating the Apollo capsule's ablative heat shield were lost to time, complicating the effort to develop the Orion heat shield.

As the Space Shuttle winds down, it appears that the same mistake is not being repeated, at least not on the same scale. In taking stock of the program's technical accomplishments, many of them are being preserved or leveraged for the Ares and Orion systems. Of the ones being discarded, they have served as lessons for ways that a reusable launch vehicle should not be built.

When NASA transitioned from Saturn to Shuttle, significant propulsion elements had to be re-developed. While Space Shuttle Main Engine owes a lot to the J-2 program, it is a much bigger engine with higher specific impulse and thrust, a more complex staged combustion cycle, and built-in reusability. The solid rockets were a massive undertaking in many ways, eclipsing any solid rocket with flight history up to that point in time.

Some elements of the propulsion system will remain relevant for the Ares generation. The shuttle solid rocket boosters will be leveraged for the boosters on the Ares rockets. While the new boosters are a leap beyond the current SRB, it's not as far of a leap as the original SRB was when compared to its predecessors. Additionally, the shuttle's maneuvering engines are being re-used for Orion. This may be the only element of the shuttle system that is reused with no changes.

For other shuttle developments, they will best serve as lessons learned in the development of equivalent systems. Perhaps the shuttle's most remarkable achievement was its main engines. Nevertheless, the SSME's taught us a lot of the ways not to design an engine for producibility or reliability. The high chamber pressure and staged combustion cycle ensured high performance, but required lots of ground support equipment. Thousands of tiny welded tubes in the nozzle and chamber for cooling? It was state of the art for the 70's, but channel-wall cooling is the preferred method nowadays. The RS-68 benefited from the lessons of SSME, sacrificing specific impulse in favor of producibility. Its gas-generator cycle, lower chamber pressure, and channel-wall chamber with ablative nozzle make for a much cheaper engine. Its only drawbacks when compared to SSME are specific impulse (which can be increased with a redesigned injector and regen-cooled nozzle) and lack of reusability. In fact, a channel-wall nozzle was planned as a shuttle upgrade until the program's 2010 retirement was announced.

At the same time, a lot of the shuttle's pioneering achievements in the field of re-usability are being discarded as dead-ends which taught us how not to build a reusable launcher. Case in point is the shuttle's thermal protection system. While the blankets will likely find use on the cooler surfaces of a future reusable launcher, the other heat shield materials will likely be dismissed. The ceramic tiles still are remarkable, but they form a complex system that is difficult to maintain. Reinforced carbon-carbon had incredible abilities to stand up to high temperatures on the shuttle's nose cap and leading edges, but they were too brittle to reliably ensure safe reentry. A future reusable launcher will likely be a "fluffier" design along the lines of X-33, which can get by using a robust, metallic thermal protection system.

Overall, NASA and the industry are taking a wiser approach to the end of the shuttle program than was taken at the end of Apollo. Many critical technologies are being reused, albeit in expendable rockets. The clear succession from Shuttle to Ares is mainly in the field of propulsion, where breakthroughs during the shuttle's development have reduced the risk for Ares. The enduring challenge from the shuttle program is to learn the correct lessons from the reusability concepts that proved so difficult to implement on the operational shuttle.

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Thursday, November 06, 2008

Reports of The Stick's Death Are Greatly Exaggerated

The speculation of Rocketman notwithstanding, I don't think that the recent election will have much effect on the development of the Ares I launch vehicle and Orion Spacecraft. Anybody who claims otherwise is broadcasting wishful thinking to the rest of the world.

There are many reasons why I believe that Ares I will continue to plod along. Most prominently, it's a jobs-retention vehicle. The political impacts of shutting down the shuttle facilities and laying off the workforce will make any politician think twice. The political ramifications of Ares cancellation would be felt prominently in Florida, Louisiana and California. While President-Elect Obama was able to win without the support of Louisiana or Florida's Brevard County (home to Kennedy Space Center,) I still doubt that many politicians want to tell thousands of people that they're getting laid off.

While shuttle program extension is talked about, particularly by the GAO, there's no compelling reason for adding any more missions to the current manifest (aside from the possibility of an Alpha Magnetic Sprectrometer mission, STS-134.) I do accept the possibility that unexpected delays will extend the current manifest to 2011 or even 2012. But the shuttle's lack of lifeboat capabilities ensures that it will not fill the gap.

At this point, we have no idea who the new administrator will be, or what his or her whims are. For all we know, the President-Elect might convince Michael Griffin to stay aboard. Much more will be known once the NASA Administrator situation shakes out.

The biggest threat to Ares I comes not from the next president or next administrator, but from Elon Musk and his outstanding team at SpaceX who are working on the Falcon IX rocket and Dragon spacecraft. The American public will be justifiably angry if a private firm like SpaceX can launch a manned, orbital spaceflight on a shorter schedule and smaller budget than NASA received for Ares-Orion. The shock of such an event might be able to overcome Congressional resistance to changing the NASA status-quo. It really doesn't matter to the public or Congress if Orion is a more able spacecraft capable of lunar flight. The spiral-development model should have taken this into account and worked on closing the gap first, worrying about the moon later.

While Ares V, Altair, and lunar hardware are a distant future whose continued funding is verymuch in doubt, it's clear that Orion and Ares I have significant momentum heading into the next administration. At this point, only a Dragon can break The Stick.