Chair Force Engineer

Monday, May 25, 2009

Hubble Disposal Revisited

With the crew of shuttle Atlantis having completed the last servicing mission on the venerable space telescope, I've revisited the question of what happens to the large Hubble spacecraft when its mission finally ends in a few years. A piece of space debris the size of post-shutdown Hubble poses an increased risk to people on earth during an uncontrolled re-entry.

The original Hubble disposal plan called for a shuttle mission to retrieve it and send it back to earth. But the winding down of the shuttle program ensured that Hubble would out-last the spacecraft that delivered her to orbit in 1990. Besides, the risk to astronauts in order to deliver Hubble to a museum on earth really can't be justified for most people.

Back when Sean O'Keefe supported a robotic servicing mission to Hubble, the addition of a deorbit stage was considered. At least a deorbit motor would permit Hubble to control its re-entry and minimize the risk to people on the ground. The deorbit motor was also considered for the current mission before being dropped. Instead, the STS-125 astronauts added the Soft Capture Mechanism, which should allow future spacecraft to pay Hubble a visit. A deorbit stage could also be launched, although it would require some form of terminal propulsion and gudance to safely dock with Hubble.

It's always possible that a future Orion spacecraft could dock with Hubble, re-boost it, and perform maintenance. But Orion is ill-suited for the task at hand. It has no payload bay for delivering spare parts to Hubble, and there's no arm to reposition spacewalking astronauts who would repair Hubble.

The long-term Hubble situation reminds me much of the fate of Skylab. While the first American space station was boosted into a higher orbit in hopes that it would still be around when the Space Shuttle first flew, it ended up re-entering and breaking apart over the Australian outback two years before the first Space Shuttle mission. Hopefully NASA will have an executable plan to safely deorbit Hubble at the end of it's life, unlike Skylab. And if anybody's holding out hope for Orion giving Hubble another reprieve, I think they'll be sorely mistaken.

Tuesday, May 19, 2009

Amateurs talk rocket tactics, professionals talk rocket logistics

The DIRECT rebuttal to NASA’s analysis of their concept includes some very telling observations of NASA’s mentality in creating and defending the existing infrastructure. Perhaps the most telling NASA observation comes on slide 64:

-More detail on Launch Infrastructure than on vehicle design.

--This is a design that is sized by infrastructure as they note in their paper.

--However to date Launch Infrastructure is not on the critical path of Ares-V or Ares-I

To which DIRECT responds by saying:

-The fact that the infrastructure is not being considered by Ares is one of the reasons why that architecture costs as much as it does.

--Cost of all supporting systems, not just infrastructure must be one of the many factors considered as part of the critical path.

All I can say in response is “Wow.” Are we to believe that ESAS was designed with little or no consideration of what the supporting infrastructure would cost? It would certainly explain why we’re stuck with the unaffordable Ares I and Ares V.

Further NASA statements such as “Ares I + Ares V uses 15 SRB segments, while two Jupiter 232’s use 16 segments” also reveal an incredibly simplistic approach to cost estimation. Such simple methods might be appropriate for pre-algebra students. Professional cost estimators ought to know better. That's why cost estimation is so difficult; there may literally be thousands of dependent and independent variables that make up the true cost of the system over its lifetime. Saving a few million in rocket hardware may have bigger reprocussions with development dollars, standing army costs, and infrastructure costs. It’s best summed up on Slide 26, where Jupiter’s higher launch costs (measured in tens of millions per launch) are offset by the savings of billions in development costs.

The DIRECT rebuttal also points out a problem the EELV advocates have encountered. In estimating upper stage masses, NASA has become excessively reliant on software tools like INTROS, which give fairly high estimates for upper stage dry masses. When INTROS cannot match the values for real, flight-proven hardware (like the EELV upper stages,) it might be time to revise the INTROS code. If nothing else, NASA’s impartial estimators should defer to the real values of flight hardware when the numbers conflict with the computer estimates.

All-in-all, DIRECT appears to be a more affordable architecture for a shuttle-derived lunar transportation system. I say this as somebody who earned a BS in Aerospace Engineering and actually did some serious study of solid-rocket internal ballistics during senior design class, giving me a first-order feel for how lengthy a new SRB development program will be for ATK and NASA.

With that being said, DIRECT still faces an uphill battle against “the unknown unknowns.” How well will the Centaur balloon-tank structure scale up to the larger diameter of the Jupiter rockets? What new guidance and rendezvous techniques and docking systems are required to mate the Earth Departure Stage to the Altair-Orion stack once on-orbit? What other previously-unknown problems, such as SRB heating of the core engines, will affect DIRECT once development begins?

At this point, a swap of Ares for DIRECT will result in little net gain from a schedule or technical risk perspective. While Ares proponents might argue that the last four years have seen the design mature, Ares is still years away from flying significant flightworthy hardware. The maturity of Ares today is comparable to where DIRECT’s predecessor, National Launch System (aka New Launch System) was in 1991. The only potential crew launcher with any maturity is Delta IV Heavy. If SpaceX is lucky, Falcon IX will have a successful flight before the Augustine Commission completes its report.

Monday, May 18, 2009

The Heat is On

If you want some interesting technical reading, do yourself a favor and check out the DIRECT Launcher rebuttal to NASA's review of their concept. I'll go into depth about the review tomorrow, but the most exciting (or shocking, depending on your point of view) development comes on Slide 112 of the presentation:

DIRECT has come to the conclusion that the ablative nozzle of the RS-68A/B will not be sufficiently robust for a cluster application in such close proximity to the exhaust from a pair of SRB’s, and a regeneratively cooled nozzle is necessary to survive this extreme base heating environment.

The takeaway: RS-68 isn't going to cut it for DIRECT or for Ares V without some MAJOR modifications. The DIRECT team believes that a regen nozzle is necessary, and they're advocating the Space Shuttle Main Engine as a replacement. NASA is conducting a trade study between SSME and a regenerative RS-68 for Ares V. This is consistent with reports from earlier this year that SSME was back in the trade space.

We've been down this road before. During the days of ESAS, before the "Ares" name was official, there was Cargo Launch Vehicle (CaLV.) Much like the Jupiter 232 of DIRECT, it used Shuttle-derived tankage and an upper stage. It also used five SSME's on the core. Over the next year, the RS-68 replaced SSME because it would be too expensive to throw away five SSME's per flight. The consequence was a wider, all-new core with more propellant to compensate for the lower specific impulse of the less-efficient RS-68.

NASA faces the choice of switching back to SSME, or trying to create a regen RS-68. Both choices are fraught with many unknowns. How easy will it be to restart SSME production? Can any incremental changes to the SSME result in cost savings? After all, Wayne Hale has said that if the shuttle program continued past 2010, the next upgrade might have been a channel-wall nozzle to replace the thousands of welded coolant tubes in the current SSME nozzle. But a regen nozzle for RS-68 won't be trivial, and it will add to Ares V schedule and development costs. And if NASA is going to pay for a regen nozzle on RS-68, it should also reconsider the expansion ratio of the new nozzle to ensure an optimal balance between thrust level and specific impulse.

When I look at the design problem created by SRB heating of the core engines, I wonder whether "SSME vs. RS-68 Regen" is a false choice. For starters, could an ablative RS-68 be viable if the outer nozzle was thicker and absorbed more heat? For that matter, could RS-68 work if its position on the booster changed? Remember that on the shuttle, the main engines aren't mounted between the two SRB's. A similar arrangment could work on Ares V if the six engines were mounted in two separate pods. If the base of Ares looked like a clock with SRB's mounted at three and nine, one engine pod would mount at twelve and the second pod would attach at six.

Just when it might have seemed like the design of Ares V was set in stone, it's all open for debate again. Perhaps the sixty days of ESAS studies weren't enough to thoroughly review all of the underlying assumptions behind the study. At least the DIRECT guys deserve credit for laying all of their assumptions out in the open. Let's hope that NASA gets it right this time around.

Tuesday, May 05, 2009

My Military Acquisition Rant

After a recent chat with a friend who is working on the F-22 program, I've decided that it's time for me to unleash my rant about the biggest problems I've observed with the way that the Pentagon and Congress deal with military acquisition. I make my case from the perspective that I hope we'll get smarter about the way we spend defense dollars, getting a good value for the taxpayer and ensuring that our fighting forces get the weapon systems that they need.

I think the poster-children for all the problems with military acquisition are the Seawolf-class and Virginia-class submarine programs. The Seawolf-class was designed during the 80's as a class of subs that could autonomously track and destroy Soviet ballistic missile subs. When the Soviet Union fell, the Seawolf-class was seen as a relic, and dropped after only three boats were authorized. But there was a problem; namely, how do you replace all the aging Los Angeles-class subs in the US Navy fleet? Rather than building more Seawolf-class boats, the Navy authorized the Virginia-class submarines. In comparison, the Virginia-class was smaller and slower than the Seawolf-class, with fewer torpedo tubes. After a lengthy and costly development program, the Virginia class proved to be only marginally cheaper per boat than the Seawolf-class.

Another case-in-point is the F-22 fighter program. I will be the first to admit that it would have been wise to cancel the F-22 back in 1992 when the Soviet Union dissolved. But that didn't happen, and the F-22 development program slogged on, logging its first flight in 1997 and Initial Operational Capability by late 2005. Now it appears that F-22 production will soon end at 187 airframes. While the F-22 is undoubtedly an expensive plane, much of that can be attributed to its protracted and expensive development. Now that the development costs have been sunk, the marginal cost of each F-22 is a steal compared to what the F-35 will cost early in its production run. By comparison, the F-22 is faster, stealthier, and more maneuverable than the F-35. Even the F-35's touted advantages in attack capabilities are largely moot, because the F-22 can also carry two Joint Direct Attack Munitions internally. The F-35's only advantage is the novel lift fan which allows the Marine Corps' variant to land vertically.

The F-35 Joint Strike Fighter is another example of a program that has pressed on in spite of its questionable value to the taxpayers. It's supposed to replace the Air Force F-16 and A-10, Navy F/A-18 (and the A-6 long-range strike plane, which has been retired for the last 12 years,) and Marine Corps AV-8 Harrier. But is it really necessary to build an all-new fighter possessing "an affordable degree of stealth"? Stealth is overrated after the enemy's air defenses have been wiped out, and it constrains how much ordinance you can carry. The F-16 and F/A-18 are still very capable airplanes, and will remain on-top with avionics upgrades and integration of the newest weapon systems. Even the venerable A-10 is becoming less relevant, with F-15E Strike Eagles performing much of the close air support work in Iraq and Afghanistan. While the Harrier brings some very unique capabilities to the battlefield with its ability to operate from short airstrips and amphibious assault ships, it's worth asking whether the costs of Harrier acquisition and operations were superior compared to using Marine AH-1 Cobra attack choppers to meet the mission requirements.

So the F-22 production will soon end, while troubled programs like Global Hawk are kept on life support. Global Hawk is five years behind schedule, while the Predator series of tactical unmanned aerial vehicles continues pressing on at a remarkable pace. Originally used for recon in the Balkans, the baseline Predator has become a vital weapon for taking out high-value terrorists in Afghanistan and Pakistan. The bigger Predator-B was re-christened as the "Reaper," and it's living up to its name in dishing out laser-guided death to Jihad Joe. The new Predator-C introduces stealth and higher speeds to the successful Predator formula. While Global Hawk is more of a strategic intelligence asset than the tactical Predator, its myriad delays have motivated the defense department to find interim solutions that get results.

The big lesson for Congress and the military acquisition bureaucracy is that major development programs may take a decade or more and will require billions of dollars. They should never be undertaken lightly. And once we commit to them, we have a duty to see them through to production and build as many weapon systems from that program as we can to meet our mission requirements. It is a complete waste of taxpayer dollars and a dangerous disservice to our fighting men and women if we go back to the drawing board every time that we balk at the unit cost of a major weapon system.

Saturday, May 02, 2009

Orion Takes a Backseat to Nobody

NASA recently announced that the Orion Spacecraft will be initially limited to a crew of four, even for ISS missions. This is another step backwards from the ESAS Study which called for a crew of six on ISS missions and four on lunar missions.

There is a very clear reason why ESAS had a requirement for six crew to the ISS on Orion. The ISS has a crew of six, and it makes sense for Orion to deliver a full crew compliment to ISS and return them to earth. The alternative, in the post-shuttle era, is to send two Soyuz capsules (or one Dragon, if SpaceX ever sees COTS-D funding.) Apparently NASA is counting on one Orion and one Soyuz being docked at ISS at all times. If the station had to be evacuated in an emergency, NASA will have to hope that both capsules work properly to get the full crew compliment home.

Officially, NASA is justifying the smaller crew because it will eliminate the need for two different seat configurations in Orion. Development costs and mass savings have nothing to do with it. Yet this argument is pretty weak when considering that Apollo supported three crew for lunar missions and five crew in the Skylab Rescue configuration. The difference between 1973 and today is that NASA was willing to seat its astronauts in two rows during the Apollo era. Orion is significantly bigger than Apollo, in part because NASA is unwilling to have astronauts sitting in two rows during a hard landing. Only time and testing will validate this safety fear.

With the growing likelihood that ISS will see a life extension to 2020 or beyond, it doesn't make a lot of sense to take seats out of Orion and prevent it from serving as an ISS lifeboat.